text: When a disturbance from a thermal equilibrium situation occurs, the populations of the electrons in the conduction band and valence band change. If the disturbance is not too great or not changing too quickly, the bands each relax to a state of quasi thermal equilibrium. Because the relaxation time for electrons within the conduction band is much lower than across the band gap, we can consider that the electrons are in thermal equilibrium in the conduction band. This is also applicable for electrons in the valence band (often understood in terms of holes). We can define a quasi Fermi level and quasi temperature due to thermal equilibrium of electrons in conduction band, and quasi Fermi level and quasi temperature for the valence band similarly.

text: When a disturbance from a thermal equilibrium situation occurs, the populations of the electrons in the conduction band and valence band change. If the disturbance is not too great or not changing too quickly, the bands each relax to a state of quasi thermal equilibrium. Because the

entity_name: Relaxation (physics)

text: relaxation time

text: for electrons within the

entity_name: Valence and conduction bands

text: conduction band

text: is much lower than across the

entity_name: Band gap

text: band gap

text: , we can consider that the electrons are in thermal equilibrium in the conduction band. This is also applicable for electrons in the

text: valence band

text: (often understood in terms of

entity_name: Electron hole

text: hole

text: s). We can define a quasi Fermi level and quasi temperature due to thermal equilibrium of electrons in conduction band, and quasi Fermi level and quasi temperature for the valence band similarly.

text: The solid adopts the fluorite structure. In the vapour phase the SrF molecule is non-linear with an F-Sr-F angle  of approximately  120°. This is an exception to VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarization of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with  the Sr-F bonds.

text: The solid adopts the

entity_name: Calcium fluoride

text: fluorite

text: structure. In the vapour phase the SrF molecule is non-linear with an F-Sr-F angle  of approximately  120°. This is an exception to

entity_name: VSEPR theory

text: VSEPR theory

text: which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarization of the electron core of the strontium atom creates an approximately tetrahedral distribution of charge that interacts with  the Sr-F bonds.

text: Hot electrons can be created when a high-energy photon of electromagnetic radiation (such as light) strikes a semiconductor.  The energy from the photon can be transferred to an electron, exciting the electron out of the valence band, and forming an electron-hole pair.  If the electron receives enough energy to leave the valence band, and to surpass the conduction band, it becomes a hot electron.  Such electrons are characterized by high effective temperatures.  Because of the high effective temperatures, hot electrons are very mobile, and likely to leave the semiconductor and travel into other surrounding materials.

text: where V is the number of valence electrons of the neutral atom in isolation (in its ground state); N is the number of non-bonding valence electrons on this atom in the molecule; and B is the total number of electrons shared in bonds with other atoms in the molecule.

text: where V is the number of

entity_name: Valence electron

text: valence electron

text: s of the neutral atom in isolation (in its ground state); N is the number of non-bonding valence electrons on this atom in the molecule; and B is the total number of electrons shared in bonds with other atoms in the molecule.

method: UvABottomUpChangeOrder

method: UNH-tfidf-stem

method: UNH-tfidf-ptsim

method: UNH-tfidf-lem

text: The solid adopts the fluorite structure and at high pressure the PbCl structure. In the vapor phase the BaF molecule is non-linear with an F-Ba-F angle of approximately 108°. This is an exception to VSEPR theory which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarisation of the electron core of the barium atom creates an approximately tetrahedral distribution of charge that interacts with the Ba-F bonds.

text: The solid adopts the

text: fluorite

text: structure and at high pressure the

entity_name: Lead(II) chloride

text: PbCl

text: structure. In the vapor phase the BaF molecule is non-linear with an F-Ba-F angle of approximately 108°. This is an exception to

text: VSEPR theory

text: which would predict a linear structure. Ab initio calculations have been cited to propose that contributions from d orbitals in the shell below the valence shell are responsible. Another proposal is that polarisation of the electron core of the barium atom creates an approximately tetrahedral distribution of charge that interacts with the Ba-F bonds.

text: If a DLC material is close enough to ta-C on plots of bonding ratios and hydrogen content it can be an insulator with a high value of resistivity. Perhaps more interesting is that if prepared in the "medium" cobblestone version such as shown in the above figure, electricity is passed through it by a mechanism of hopping conductivity. In this type of conduction of electricity the electrons move by quantum mechanical tunneling between pockets of conductive material isolated in an insulator. The result is that such a process makes the material something like a semiconductor. Further research on electrical properties is needed to explicate such conductivity in ta-C in order to determine its practical value. However, a different electrical property of emissivity has been shown to occur at unique levels for ta-C. Such high values allow for electrons to be emitted from ta-C coated electrodes into vacuum or into other solids with application of modest levels of applied voltage. This has supported important advances in medical technology.

text: If a DLC material is close enough to ta-C on plots of bonding ratios and hydrogen content it can be an

entity_name: Insulator (electricity)

text: insulator

text: with a high value of resistivity. Perhaps more interesting is that if prepared in the "medium" cobblestone version such as shown in the above figure, electricity is passed through it by a mechanism of hopping

entity_name: Electrical resistivity and conductivity

text: conductivity

text: . In this type of conduction of electricity the electrons move by

entity_name: Quantum tunnelling

text: quantum mechanical tunneling

text: between pockets of conductive material isolated in an insulator. The result is that such a process makes the material something like a

entity_name: Semiconductor

text: semiconductor

text: . Further research on electrical properties is needed to explicate such conductivity in ta-C in order to determine its practical value. However, a different electrical property of

entity_name: Field electron emission

text: emissivity

text: has been shown to occur at unique levels for ta-C. Such high values allow for electrons to be emitted from ta-C coated electrodes into vacuum or into other solids with application of modest levels of applied voltage. This has supported important advances in medical technology.

text: There are two recognized types of charge carriers in semiconductors. One is electrons, which carry a negative electric charge. In addition, it is convenient to treat the traveling vacancies in the valence band electron population (holes) as the second type of charge carrier, which carry a positive charge equal in magnitude to that of an electron.

text: There are two recognized types of charge carriers in

text: semiconductor

text: s. One is

entity_name: Electron

text: electron

text: s, which carry a negative

entity_name: Electric charge

text: electric charge

text: . In addition, it is convenient to treat the traveling vacancies in the

text: valence band

text: electron population (

text: holes

text: ) as the second type of charge carrier, which carry a positive charge equal in magnitude to that of an electron.

text: The individual bond valences in turn are calculated from the observed bond lengths.

text: John Pople first introduced the Pople Diagram during the Symposium on Atomic and Molecular Quantum Theory held on Sanibel Island, Florida, in January 1965. He called it a "hyperbola of quantum chemistry", which illustrates the inverse relationship between the sophistication of a calculational method and the number of electrons in a molecule that can be studied by that method.  Alternative (reverse) arrangement of the vertical axis or interchange of the two axes are also possible.

text: In 2008, the festival operated a third location in Shoreditch, London, known as Hox to Dot. This leg catered for the more electronic extreme of the indie music spectrum, hosting DJs and turntablists. For this reason, there was no real crossover between artists at the London leg with either Nottingham or Bristol. Additionally, Hox to Dot operated on a Thursday (as opposed to a two-day, weekend festival).

text: In 2008, the festival operated a third location in

entity_name: Shoreditch

text: Shoreditch

text: , London, known as Hox to Dot. This leg catered for the more

entity_name: Electronic music

text: electronic

text: extreme of the

entity_name: Independent music

text: indie music

text: spectrum, hosting DJs and

entity_name: Turntablism

text: turntablists

text: . For this reason, there was no real crossover between artists at the London leg with either Nottingham or Bristol. Additionally, Hox to Dot operated on a Thursday (as opposed to a two-day, weekend festival).

text: The outermost electron shell is often referred to as the "valence shell" and (to a first approximation) determines the chemical properties. It should be remembered that the similarities in the chemical properties were remarked on more than a century before the idea of electron configuration. It is not clear how far Madelung's rule explains (rather than simply describes) the periodic table, although some properties (such as the common +2 oxidation state in the first row of the transition metals) would obviously be different with a different order of orbital filling.

text: The outermost electron shell is often referred to as the "valence shell" and (to a first approximation) determines the chemical properties. It should be remembered that the similarities in the chemical properties were remarked on more than a century before the idea of electron configuration. It is not clear how far Madelung's rule explains (rather than simply describes) the periodic table, although some properties (such as the common +2

entity_name: Oxidation state

text: oxidation state

text: in the first row of the transition metals) would obviously be different with a different order of orbital filling.

text: In the early 20th century, the American chemist Gilbert N. Lewis began to use dots in lecture, while teaching undergraduates at Harvard, to represent the electrons around atoms.  His students favored these drawings, which stimulated him in this direction.  From these lectures, Lewis noted that elements with a certain number of electrons seemed to have a special stability.  This phenomenon was pointed out by the German chemist Richard Abegg in 1904, to which Lewis referred to as "Abegg's law of valence" (now generally known as Abegg's rule).  To Lewis it appeared that once a core of eight electrons has formed around a nucleus, the layer is filled, and a new layer is started.  Lewis also noted that various ions with eight electrons also seemed to have a special stability. On these views, he proposed the rule of eight or octet rule: Ions or atoms with a filled layer of eight electrons have a special stability.

text: In the early 20th century, the American chemist

entity_name: Gilbert N. Lewis

text: Gilbert N. Lewis

text: began to use dots in lecture, while teaching undergraduates at

entity_name: Harvard University

text: Harvard

text: , to represent the electrons around atoms.  His students favored these drawings, which stimulated him in this direction.  From these lectures, Lewis noted that elements with a certain number of electrons seemed to have a special stability.  This phenomenon was pointed out by the German chemist

entity_name: Richard Abegg

text: Richard Abegg

text: in 1904, to which Lewis referred to as "Abegg's law of valence" (now generally known as

entity_name: Abegg's rule

text: Abegg's rule

text: ).  To Lewis it appeared that once a core of eight electrons has formed around a nucleus, the layer is filled, and a new layer is started.  Lewis also noted that various

entity_name: Ion

text: ion

text: s with eight electrons also seemed to have a special stability. On these views, he proposed the rule of eight or

entity_name: Octet rule

text: octet rule

text: : Ions or atoms with a filled layer of eight electrons have a special stability.

method: UNH-qee

text: A major application of Walsh diagrams is to explain the regularity in structure observed for related molecules having identical numbers of valence electrons (i.e. why HO and HS look similar), and to account for how molecules alter their geometries as their number of electrons or spin state changes.  Additionally, Walsh diagrams can be used to predict distortions of molecular geometry from knowledge of how the LUMO (Lowest Unoccupied Molecular Orbital) affects the HOMO (Highest Occupied Molecular Orbital) when the molecule experiences geometrical perturbation.

text: A major application of Walsh diagrams is to explain the regularity in structure observed for related molecules having identical numbers of

text: valence electrons

text: (i.e. why HO and HS look similar), and to account for how molecules alter their geometries as their number of electrons or

entity_name: Spin quantum number

text: spin state

text: changes.  Additionally, Walsh diagrams can be used to predict distortions of molecular geometry from knowledge of how the

entity_name: HOMO/LUMO

text: LUMO

text: (Lowest Unoccupied Molecular Orbital) affects the

text: HOMO

text: (Highest Occupied Molecular Orbital) when the molecule experiences geometrical perturbation.

text: Due to the role of the π-electron system in determining the electronic properties of graphene, doping in carbon nanotubes differs from that of bulk crystalline semiconductors from the same group of the periodic table (e.g. silicon).  Graphitic substitution of carbon atoms in the nanotube wall by boron or nitrogen dopants leads to p-type and n-type behavior, respectively, as would be expected in silicon.  However, some non-substitutional (intercalated or adsorbed) dopants introduced into a carbon nanotube, such as alkali metals as well as electron-rich metallocenes, result in n-type conduction because they donate electrons to the π-electron system of the nanotube.  By contrast, π-electron acceptors such as FeCl or electron-deficient metallocenes function as p-type dopants since they draw π-electrons away from the top of the valence band.

text: Due to the role of the π-electron system in determining the

entity_name: Graphene

entity_section: Electronic

text: electronic properties of graphene

text: , doping in carbon nanotubes differs from that of bulk crystalline semiconductors from the same group of the periodic table (e.g. silicon).  Graphitic substitution of carbon atoms in the nanotube wall by boron or nitrogen dopants leads to p-type and n-type behavior, respectively, as would be expected in silicon.  However, some non-substitutional (intercalated or adsorbed) dopants introduced into a carbon nanotube, such as alkali metals as well as electron-rich metallocenes, result in n-type conduction because they donate electrons to the π-electron system of the nanotube.  By contrast, π-electron acceptors such as FeCl or electron-deficient metallocenes function as p-type dopants since they draw π-electrons away from the top of the valence band.

text: Along with Daphne Oram, Fred was enthusiastically promoting electronic music to the British public via demonstrations and lectures to amateur tape recording clubs up and down the country. In 1961 his book Electronic Music and Musique Concrete was published – one of the earliest in the world to tackle the subject and provide practical information and circuit diagrams. Two years later he became chief editor of ATR and began issuing 7” records made available through the magazine. Castle and sister label Contrast issued a range of sound effects discs recorded by Fred, including 3 disks of electronic music. Some of these tracks were later issued by library label Studio G on the Electronic Age album.

text: Along with

entity_name: Daphne Oram

text: Daphne Oram

text: , Fred was enthusiastically promoting electronic music to the British public via demonstrations and lectures to amateur tape recording clubs up and down the country. In 1961 his book Electronic Music and Musique Concrete was published – one of the earliest in the world to tackle the subject and provide practical information and circuit diagrams. Two years later he became chief editor of ATR and began issuing 7” records made available through the magazine. Castle and sister label Contrast issued a range of sound effects discs recorded by Fred, including 3 disks of electronic music. Some of these tracks were later issued by library label Studio G on the Electronic Age album.

text: It is common in many theoretical studies to use the extended Hückel molecular orbitals  as a preliminary step to determining the molecular orbitals by a more sophisticated method such as the CNDO/2 method and ab initio quantum chemistry methods. Since the extended Hückel basis set is fixed, the monoparticle calculated wavefunctions must be projected to the basis set where the accurate calculation is to be done. One usually does this by adjusting the orbitals in the new basis to the old ones by least squares method.As only valence electron wavefunctions are found by this method, one must fill the core electron functions by orthonormalizing the rest of the basis set with the calculated orbitals and then selecting the ones with less energy. This leads to the determination of more accurate structures and electronic properties, or in the case of ab initio methods, to somewhat faster convergence.

text: It is common in many theoretical studies to use the extended Hückel molecular orbitals  as a preliminary step to determining the molecular orbitals by a more sophisticated method such as the

text: method and

entity_name: Ab initio quantum chemistry methods

text: ab initio quantum chemistry methods

text: . Since the extended Hückel basis set is fixed, the monoparticle calculated wavefunctions must be projected to the basis set where the accurate calculation is to be done. One usually does this by adjusting the orbitals in the new basis to the old ones by least squares method.As only valence electron wavefunctions are found by this method, one must fill the core electron functions by orthonormalizing the rest of the basis set with the calculated orbitals and then selecting the ones with less energy. This leads to the determination of more accurate structures and electronic properties, or in the case of ab initio methods, to somewhat faster convergence.

method: Bert-DRMMTKS

text: The nature of the process can be depicted as follows: Consider a cluster with two subunits, A and B. Suppose an inner-valence electron is removed from subunit A. If the resulting (ionized) state is higher in energy than the double ionization threshold of subunit A then an intraatomic (intramolecular) process (autoionization, in the case of core ionization Auger decay) sets in. Even though the excitation is energetically not higher than the double ionization threshold of subunit A itself, it may be higher than the double ionization threshold of the cluster which is lowered due to charge separation. If this is the case, an interatomic (intermolecular) process sets in which is called ICD. During the ICD the excess energy of subunit A is used to remove (due to electronic correlation) an outer-valence electron from subunit B. As a result, a doubly ionized cluster is formed with a single positive charge on A and B. Thus, charge separation in the final state is a fingerprint of ICD. As a consequence of the charge separation the cluster typically breaks apart via Coulomb explosion.

text: The nature of the process can be depicted as follows: Consider a cluster with two subunits, A and B. Suppose an inner-

entity_name: Electron shell

text: valence

text: electron

text: is removed from subunit A. If the resulting (ionized)

entity_name: Quantum state

text: state

text: is higher in energy than the double

entity_name: Ionization

text: ionization threshold

text: of subunit A then an intraatomic (intramolecular) process (

entity_name: Autoionization

text: autoionization

text: , in the case of core ionization

entity_name: Auger effect

text: Auger decay

text: ) sets in. Even though the excitation is energetically not higher than the double ionization threshold of subunit A itself, it may be higher than the double ionization threshold of the cluster which is lowered due to

text: charge

text: separation. If this is the case, an interatomic (intermolecular) process sets in which is called ICD. During the ICD the excess energy of subunit A is used to remove (due to

entity_name: Electronic correlation

text: electronic correlation

text: ) an outer-valence electron from subunit B. As a result, a doubly ionized cluster is formed with a single positive charge on A and B. Thus, charge separation in the final state is a fingerprint of ICD. As a consequence of the charge separation the cluster typically breaks apart via

entity_name: Coulomb explosion

text: Coulomb explosion

text: American physical chemist Gilbert N. Lewis laid the foundation of valence bond theory; he was instrumental in developing a bonding theory based on the number of electrons in the outermost "valence" shell of the atom. In 1902, while Lewis was trying to explain valence to his students, he depicted atoms as constructed of a concentric series of cubes with electrons at each corner. This "cubic atom" explained the eight groups in the periodic table and represented his idea that chemical bonds are formed by electron transference to give each atom a complete set of eight outer electrons (an "octet").

text: American physical chemist

text: Gilbert N. Lewis

text: laid the foundation of

entity_name: Valence bond theory

text: valence bond theory

text: ; he was instrumental in developing a bonding theory based on the number of electrons in the outermost "valence" shell of the atom. In 1902, while Lewis was trying to explain valence to his students, he depicted atoms as constructed of a concentric series of cubes with electrons at each corner. This "cubic atom" explained the eight groups in the periodic table and represented his idea that chemical bonds are formed by electron transference to give each atom a complete set of eight outer electrons (an "octet").

text: In his publications, Walsh showed through multiple examples that the geometry adopted by a molecule in its ground state primarily depends on the number of its valence electrons. He himself acknowledged that this general concept was not novel, but explained that the new data available to him allowed the previous generalizations to be expanded upon and honed.  He also noted that Mulliken had previously attempted to construct a correlation diagram for the possible orbitals of a polyatomic molecule in two different nuclear configurations, and had even tried to use this diagram to explain shapes and spectra of molecules in their ground and excited states.   However, Mulliken was unable to explain the reasons for the rises and falls of certain curves with increases in angle, thus Walsh claimed "his diagram was either empirical or based upon unpublished computations."

text: In his publications, Walsh showed through multiple examples that the geometry adopted by a molecule in its ground state primarily depends on the number of its valence electrons. He himself acknowledged that this general concept was not novel, but explained that the new data available to him allowed the previous generalizations to be expanded upon and honed.  He also noted that Mulliken had previously attempted to construct a correlation diagram for the possible orbitals of a polyatomic molecule in two different nuclear configurations, and had even tried to use this diagram to explain shapes and

entity_name: Spectrum

text: spectra

text: of molecules in their ground and excited states.   However, Mulliken was unable to explain the reasons for the rises and falls of certain curves with increases in angle, thus Walsh claimed "his diagram was either empirical or based upon unpublished computations."

text: In order to make contact with reality, then, the formulae would have to be rewritten in terms of measurable, renormalized quantities.  The charge of the electron, say, would be defined in terms of a quantity measured at a specific kinematic renormalization point or subtraction point (which will generally have a characteristic energy, called the renormalization scale or simply the energy scale).  The parts of the Lagrangian left over, involving the remaining portions of the bare quantities, could then be reinterpreted as counterterms, involved in divergent diagrams exactly canceling out the troublesome divergences for other diagrams.

text: In order to make contact with reality, then, the formulae would have to be rewritten in terms of measurable, renormalized quantities.  The charge of the electron, say, would be defined in terms of a quantity measured at a specific

entity_name: Kinematics

text: kinematic

text: renormalization point or subtraction point (which will generally have a characteristic energy, called the renormalization scale or simply the

entity_name: Length scale

text: energy scale

text: ).  The parts of the Lagrangian left over, involving the remaining portions of the bare quantities, could then be reinterpreted as

entity_name: Renormalization

text: counterterm

text: s, involved in divergent diagrams exactly canceling out the troublesome divergences for other diagrams.

text: Maurice Valency was educated in New York City, getting a Bachelor of Arts degree in 1923 at City College, and at Columbia University getting a Bachelor of Laws degree in 1927 (Valency was a member of the New York bar), and a Ph.D. in 1938.  In 1936 he married the artist Janet Cornell; they remained married for 60 years until Valency's death in New York City at the age of 93.

text: Maurice Valency was educated in New York City, getting a

entity_name: Bachelor of Arts

text: Bachelor of Arts

text: degree in 1923 at

entity_name: City College of New York

text: City College

text: , and at

entity_name: Columbia University

text: Columbia University

text: getting a

text: Bachelor of Laws

text: degree in 1927 (Valency was a member of the New York bar), and a Ph.D. in 1938.  In 1936 he married the artist Janet Cornell; they remained married for 60 years until Valency's death in New York City at the age of 93.

text: Jellium is the simplest model of interacting electrons. It is employed in the calculation of properties of metals, where the core electrons and the nuclei are modeled as the uniform positive background and the valence electrons are treated with full rigor. Semi-infinite jellium slabs are used to investigate surface properties such as work function and surface effects such as adsorption; near surfaces the electronic density varies in an oscillatory manner, decaying to a constant value in the bulk.

text: Jellium is the simplest model of interacting electrons. It is employed in the calculation of properties of metals, where the

text: core electron

text: s and the nuclei are modeled as the uniform positive background and the

text: valence electron

text: s are treated with full rigor. Semi-infinite jellium slabs are used to investigate surface properties such as

text: work function

text: and surface effects such as

text: adsorption

text: ; near surfaces the electronic density varies in an oscillatory manner, decaying to a constant value in the bulk.

text: The electrons in the outermost occupied shell (or shells) determine the chemical properties of the atom; it is called the valence shell.

text: Near the surface of a semi-conducting metal oxide the valence and conduction bands are of higher energy, causing the upward bending of the band energy as shown in the band energy diagram, such that promotion of an electron from the valence band to the conduction band by light of energy greater than the band gap results in migration of the electron towards the bulk of the solid or to a counter electrode, while the hole left in the valence band moves towards the surface. The increased concentration of holes near the surface facilitates electron transfer to the solid, such as the example shown in the figure of the oxidation of redox couple D-/D. In the absence of any mechanism to remove electrons from the bulk of the solid irradiation continues to excite electrons to the conduction band producing holes in the valence band. This leads to the reduction of the upward bending of the band energies near the surface, and the subsequent increase in excited electron availability for reduction reactions.

text: Near the surface of a semi-conducting metal oxide the valence and conduction bands are of higher energy, causing the upward bending of the band energy as shown in the band energy diagram, such that promotion of an electron from the valence band to the conduction band by light of energy greater than the band gap results in migration of the electron towards the bulk of the solid or to a counter electrode, while the hole left in the valence band moves towards the surface. The increased concentration of holes near the surface facilitates electron transfer to the solid, such as the example shown in the figure of the oxidation of redox couple D-/D. In the absence of any mechanism to remove electrons from the bulk of the solid irradiation continues to excite electrons to the conduction band producing holes in the valence band. This leads to the reduction of the upward

text: bending of the band energies

text: near the surface, and the subsequent increase in excited electron availability for reduction reactions.

text: Similar to an electron in an inner shell, a valence electron has the ability to absorb or release energy in the form of a photon. An energy gain can trigger an electron to move (jump) to an outer shell; this is known as atomic excitation. Or the electron can even break free from its associated atom's valence shell; this is ionization to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.

text: Similar to an electron in an inner shell, a valence electron has the ability to absorb or release energy in the form of a

text: photon

text: . An energy gain can trigger an electron to move (jump) to an outer shell; this is known as

text: atomic excitation

text: . Or the electron can even break free from its associated atom's valence shell; this is

text: ionization

text: to form a positive ion. When an electron loses energy (thereby causing a photon to be emitted), then it can move to an inner shell which is not fully occupied.

text: The number of electrons in an electrically neutral atom increases with the atomic number. The electrons in the outermost shell, or valence electrons, tend to be responsible for an element's chemical behavior. Elements that contain the same number of valence electrons can be grouped together and display similar chemical properties.

text: The number of electrons in an electrically neutral atom increases with the

text: atomic number

text: . The electrons in the outermost shell, or

text: valence electron

text: s, tend to be responsible for an element's chemical behavior. Elements that contain the same number of valence electrons can be grouped together and display similar chemical properties.

text: The two classes of carbenes are singlet and triplet carbenes. Singlet carbenes are spin-paired.  In the language of valence bond theory, the molecule adopts an sp hybrid structure. Triplet carbenes have two unpaired electrons.  Most carbenes have a nonlinear triplet ground state, except for those with nitrogen, oxygen, or sulfur atoms, and halides directly bonded to the divalent carbon.

text: The two classes of carbenes are

text: singlet

text: and

text: triplet

text: carbenes. Singlet carbenes are spin-paired.  In the language of

text: valence bond theory

text: , the molecule adopts an sp

text: hybrid structure

text: . Triplet carbenes have two unpaired electrons.  Most carbenes have a nonlinear triplet ground state, except for those with nitrogen, oxygen, or sulfur atoms, and halides directly bonded to the divalent carbon.

text: The table below shows the monomeric hydride for each element, which is closest to, but not surpassing its heuristic valence. A heuristic valence is the valence of an element that strictly obeys the octet, duodectet, and other valence rules. Elements may be prevented from reaching their heuristic valence for various electronic discrepancies. In chromium's case, stearic hindrance ensures that both the octahedral and trigonal prismatic molecular geometries for  are metastable, with a very low energy barrier for conversion to a Kubas complex.

text: The table below shows the monomeric hydride for each element, which is closest to, but not surpassing its heuristic valence. A heuristic valence is the valence of an element that strictly obeys the octet, duodectet, and other valence rules. Elements may be prevented from reaching their heuristic valence for various electronic discrepancies. In chromium's case, stearic hindrance ensures that both the octahedral and trigonal prismatic molecular geometries for  are metastable, with a very low energy barrier for conversion to a

text: Kubas complex

text: In solid-state physics, the valence band and conduction band are the bands closest to the Fermi level and thus determine the electrical conductivity of the solid. The valence band is the highest range of electron energies in which electrons are normally present at absolute zero temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the electronic band structure of a material, the valence band is located below the Fermi level, while the conduction band is located above it. This distinction is meaningless in metals as the highest band is partially filled, taking on the properties of both the valence and conduction bands.

text: In

text: solid-state physics

text: , the valence band and conduction band are the

text: bands

text: closest to the

text: Fermi level

text: and thus determine the

text: electrical conductivity

text: of the solid. The valence band is the highest range of

text: electron

text: energies

text: in which electrons are normally present at

text: absolute zero

text: temperature, while the conduction band is the lowest range of vacant electronic states. On a graph of the

text: electronic band structure

text: of a material, the valence band is located below the Fermi level, while the conduction band is located above it. This distinction is meaningless in metals as the highest band is partially filled, taking on the properties of both the valence and conduction bands.

text: The valence band has two types of charge carriers: light holes: m/m° = 0.051  and heavy holes: m/m° = 0.2.The electrical and optical properties of the valence band are dominated by the heavy holes, because the density of these states is much greater than that for light holes. This is also reflected in the mobility of holes at 295 K, which is a factor of 40 lower than that for electrons.

text: 2) Because of their tendency either to gain the missing valence electrons (thereby forming a negative ion), or to share valence electrons (thereby forming a covalent bond).

text: Recombination can occur by direct encounter with a majority carrier, annihilating both carriers, or through a recombination-generation center, a defect that alternately traps holes and electrons, assisting recombination. The minority carriers have a limited lifetime, and this lifetime in turn limits how far they can diffuse from the majority carrier side into the minority carrier side, the so-called diffusion length. In the LED recombination of electrons and holes is accompanied by emission of light of a wavelength related to the energy gap between valence and conduction bands, so the diode converts a portion of the forward current into light.

text: Recombination can occur by direct encounter with a majority carrier, annihilating both carriers, or through a

text: recombination-generation center

text: , a defect that alternately traps holes and electrons, assisting recombination. The minority carriers have a limited

text: lifetime

text: , and this lifetime in turn limits how far they can diffuse from the majority carrier side into the minority carrier side, the so-called

entity_section: Example solution in one dimension: diffusion length

text: diffusion length

text: . In the

text: LED

text: recombination of electrons and holes is accompanied by emission of light of a wavelength related to the energy gap between valence and conduction bands, so the diode converts a portion of the forward current into light.

text: In molecules such as methane, , the eight valence electrons are found in four MOs that are spread out over all five atoms. However, it is possible to transform the MOs into four localized sp orbitals. Linus Pauling, in 1931, hybridized the carbon 2s and 2p orbitals so that they pointed directly at the hydrogen 1s basis functions and featured maximal overlap. However, the delocalized MO description is more appropriate for predicting ionization energies and the positions of spectral absorption bands. When methane is ionized, a single electron is taken from the valence MOs, which can come from the s bonding or the triply degenerate p bonding levels, yielding two ionization energies. In comparison, the explanation in VB theory is more complicated. When one electron is removed from an sp orbital, resonance is invoked between four valence bond structures, each of which has a single one-electron bond and three two-electron bonds. Triply degenerate T and A ionized states (CH) are produced from different linear combinations of these four structures. The difference in energy between the ionized and ground state gives the two ionization energies.

text: In molecules such as

text: methane

text: , , the eight valence electrons are found in four MOs that are spread out over all five atoms. However, it is possible to transform the MOs into four localized sp orbitals. Linus Pauling, in 1931, hybridized the carbon 2s and 2p orbitals so that they pointed directly at the

text: hydrogen

text: 1s basis functions and featured maximal overlap. However, the delocalized MO description is more appropriate for predicting

text: ionization energies

text: and the positions of spectral

text: absorption band

text: s. When methane is ionized, a single electron is taken from the valence MOs, which can come from the s bonding or the triply degenerate p bonding levels, yielding two ionization energies. In comparison, the explanation in VB theory is more complicated. When one electron is removed from an sp orbital,

text: resonance

text: is invoked between four valence bond structures, each of which has a single one-electron bond and three two-electron bonds. Triply degenerate T and A ionized states (CH) are produced from different linear combinations of these four structures. The difference in energy between the ionized and ground state gives the two ionization energies.

text: In the periodic table, moscovium is a member of group 15, the pnictogens, below nitrogen, phosphorus, arsenic, antimony, and bismuth. Every previous pnictogen has five electrons in its valence shell, forming a valence electron configuration of nsnp. In moscovium's case, the trend should be continued and the valence electron configuration is predicted to be 7s7p; therefore, moscovium will behave similarly to its lighter congeners in many respects. However, notable differences are likely to arise; a largely contributing effect is the spin–orbit (SO) interaction—the mutual interaction between the electrons' motion and spin. It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the speed of light. In relation to moscovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p7p. These effects cause moscovium's chemistry to be somewhat different from that of its lighter congeners.

text: In the

text: periodic table

text: , moscovium is a member of group 15, the pnictogens, below

text: nitrogen

text: phosphorus

text: arsenic

text: antimony

text: , and bismuth. Every previous pnictogen has five electrons in its valence shell, forming a

text: valence electron

text: configuration of nsnp. In moscovium's case, the trend should be continued and the valence electron configuration is predicted to be 7s7p; therefore, moscovium will behave similarly to its lighter

text: congeners

text: in many respects. However, notable differences are likely to arise; a largely contributing effect is the

text: spin–orbit (SO) interaction

text: —the mutual interaction between the electrons' motion and

text: spin

text: . It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the

text: speed of light

text: . In relation to moscovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the

text: inert pair effect

text: , and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (

text: azimuthal

text: quantum number

text: l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p7p. These effects cause moscovium's chemistry to be somewhat different from that of its lighter

text: congeners

text: The Zener diode's operation depends on the heavy doping of its p-n junction. The depletion region formed in the diode is very thin (<1 µm) and the electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V, allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material.

text: The Zener diode's operation depends on the heavy

text: doping

text: of its

text: p-n junction

text: . The depletion region formed in the diode is very thin (<1 µm) and the electric field is consequently very high (about 500 kV/m) even for a small reverse bias voltage of about 5 V, allowing

text: electron

text: s to

text: tunnel

text: from the valence band of the p-type material to the conduction band of the n-type material.

text: The economic development of Valence can also count on a wealthy producer territory of food processing, hi-tech with the presence of large groups of electronics or aerospace, many innovative SMEs and a university centre of importance of film and knowledge with the presence of major animation studios internationally recognised for the quality of their productions.

text: For elements in the main groups of the periodic table, the valence can vary between 1 and 7.

text: For elements in the

text: main groups

text: of the

text: periodic table

text: , the valence can vary between 1 and 7.

text: The Madelung rule predicts that the typical electronic structure of transition metal atoms can be written as [Inert gas]ns(n-1)d where the inner d orbital is predicted to be filled after the valence-shell s orbital. This rule is however only approximate - it only holds for some of the transition elements, and only then in their neutral ground state.

text: The

text: Madelung

text: rule predicts that the typical

text: electronic structure

text: of transition metal atoms can be written as [Inert gas]ns(n-1)d where the inner d orbital is predicted to be filled after the

text: valence-shell

text: s orbital. This rule is however only approximate - it only holds for some of the transition elements, and only then in their neutral ground state.

text: The total number of electrons represented in a Lewis structure is equal to the sum of the numbers of valence electrons on each individual atom. Non-valence electrons are not represented in Lewis structures.

text: The total number of electrons represented in a Lewis structure is equal to the sum of the numbers of

text: valence electron

text: s on each individual atom. Non-valence electrons are not represented in Lewis structures.

text: Each diagram has an entry point and an end point. The diagram describes possible paths between these two points by going through other nonterminals and terminals. Terminals are represented by round boxes while nonterminals are represented by square boxes.

text: By doping pure silicon with Group V elements such as phosphorus, extra valence electrons are added that become unbonded from individual atoms and allow the compound to be an electrically conductive n-type semiconductor. Doping with Group III elements, which are missing the fourth valence electron, creates "broken bonds" (holes) in the silicon lattice that are free to move. The result is an electrically conductive p-type semiconductor. In this context, a Group V element is said to behave as an electron donor, and a group III element as an acceptor. This is a key concept in the physics of a diode.

text: By doping pure silicon with

text: Group V

text: elements such as phosphorus, extra

text: valence electrons

text: are added that become unbonded from individual atoms and allow the compound to be an electrically conductive

text: n-type semiconductor

text: . Doping with

text: Group III

text: elements, which are missing the fourth valence electron, creates "broken bonds" (holes) in the silicon lattice that are free to move. The result is an electrically conductive

text: p-type semiconductor

text: . In this context, a

text: Group V

text: element is said to behave as an electron donor, and a

text: group III

text: element as an acceptor. This is a key concept in the physics of a

text: diode

text: When the material is placed in the sun, photons from the sunlight can be absorbed in the p-type side of the semiconductor, causing electrons in the valence band to be promoted in energy to the conduction band. This process is known as photoexcitation. As the name implies, electrons in the conduction band are free to move about the semiconductor. When a load is placed across the cell as a whole, these electrons will flow from the p-type side into the n-type side, lose energy while moving through the external circuit, and then go back into the p-type material where they can re-combine with the valence-band holes they left behind. In this way, sunlight creates an electric current.

text: When the material is placed in the sun,

text: photon

text: s from the sunlight can be absorbed in the p-type side of the semiconductor, causing electrons in the

text: valence band

text: to be promoted in energy to the

text: conduction band

text: . This process is known as

text: photoexcitation

text: . As the name implies, electrons in the conduction band are free to move about the semiconductor. When a load is placed across the cell as a whole, these electrons will flow from the p-type side into the n-type side, lose energy while moving through the external circuit, and then go back into the p-type material where they can re-combine with the valence-band holes they left behind. In this way, sunlight creates an electric current.

text: It adopts the  same Chinese lantern structure as related acetate dimers such as rhodium(II) acetate, copper(II) acetate, and chromium(II) acetate.  Each Mo(II) center in Mo(OCCH) has four d valence electrons. These eight d-electrons form one σ, two π bonds, and one δ bond, creating a bonding electron configuration of σπδ. Each of these bonds are formed by the overlapping of pairs of d orbitals. The four acetate groups bridge the two metal centers.  The Mo-O bond between each Mo(II) center and O atom from acetate has a distance of 2.119 Å, and the Mo-Mo distance between the two metal centers is 2.0934 Å.

text: It adopts the  same

text: Chinese lantern structure

text: as related acetate dimers such as

text: rhodium(II) acetate

text: copper(II) acetate

text: , and

text: chromium(II) acetate

text: .  Each Mo(II) center in Mo(OCCH) has four d

text: valence electrons

text: . These eight d-electrons form one

text: σ

text: , two

text: π bonds

text: , and one

text: δ bond

text: , creating a bonding

text: electron configuration

text: of σπδ. Each of these bonds are formed by the overlapping of pairs of d orbitals. The four acetate groups bridge the two metal centers.  The Mo-O bond between each Mo(II) center and O atom from acetate has a

text: distance

text: of 2.119 Å, and the Mo-Mo distance between the two metal centers is 2.0934 Å.

text: denote, respectively, the pseudo wave-function and the true (all-electron) wave-function. The index n in the true wave-functions denotes the valence level. The distance beyond which the true and the pseudo wave-functions are equal,

text: denote, respectively, the pseudo wave-function and the true (all-electron) wave-function. The index n in the true wave-functions denotes the

text: valence

text: level. The distance beyond which the true and the pseudo wave-functions are equal,

text: In molecular orbital theory, bond order is also defined as half the difference between the number of bonding electrons and the number of antibonding electrons as per the equation below. This often but not always yields the same result. Bond order is also an index of bond strength and is also used extensively in valence bond theory.

text: In

text: molecular orbital theory

text: , bond order is also defined as half the difference between the number of

text: bonding electron

text: s and the number of

text: antibonding electron

text: s as per the equation below. This often but not always yields the same result. Bond order is also an index of

text: bond strength

text: and is also used extensively in

text: valence bond theory

text: In chemistry, a valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair. The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements: For a main group element, a valence electron can exist only in the outermost electron shell. In a transition metal, a valence electron can also be in an inner shell.

text: In

text: chemistry

text: , a valence electron is an

text: electron

text: that is associated with an

text: atom

text: , and that can participate in the formation of a

text: chemical bond

text: ; in a single

text: covalent bond

text: , both atoms in the bond contribute one valence electron in order to form a

text: shared pair

text: . The presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements: For a

text: main group element

text: , a valence electron can exist only in the outermost

text: electron shell

text: . In a

text: transition metal

text: , a valence electron can also be in an inner shell.

text: In the periodic table, livermorium is a member of group 16, the chalcogens, in the periodic table, below oxygen, sulfur, selenium, tellurium, and polonium. Every previous chalcogen has six electrons in its valence shell, forming a valence electron configuration of nsnp. In livermorium's case, the trend should be continued and the valence electron configuration is predicted to be 7s7p; therefore, livermorium will have some similarities to its lighter congeners. Differences are likely to arise; a large contributing effect is the spin–orbit (SO) interaction—the mutual interaction between the electrons' motion and spin. It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the speed of light. In relation to livermorium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively: the 7p subshell acts as a second inert pair, though not as inert as the 7s electrons, while the 7p subshell can easily participate in chemistry. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p7p.

text: In the

text: periodic table

text: , livermorium is a member of group 16, the chalcogens, in the

text: periodic table

text: , below

text: oxygen

text: sulfur

text: selenium

text: tellurium

text: , and polonium. Every previous chalcogen has six electrons in its valence shell, forming a

text: valence electron

text: configuration of nsnp. In livermorium's case, the trend should be continued and the valence electron configuration is predicted to be 7s7p; therefore, livermorium will have some similarities to its lighter

text: congeners

text: . Differences are likely to arise; a large contributing effect is the

text: spin–orbit (SO) interaction

text: spin

text: speed of light

text: . In relation to livermorium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the

text: inert pair effect

text: azimuthal

text: quantum number

text: l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively: the 7p subshell acts as a second inert pair, though not as inert as the 7s electrons, while the 7p subshell can easily participate in chemistry. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p7p.

text: In quantum dot solar cells, the excited electron in the conduction band interacts with the hole it leaves behind in the valence band, and this composite uncharged object is known as an exciton. The carrier multiplication effect in a dot can be understood as creating multiple excitons, and is called multiple exciton generation (MEG). MEG may considerably increase the energy conversion efficiency of nanocrystal based solar cells, though extracting the energy may be difficult because of the short lifetimes of the multiexcitons.

text: In

text: quantum dot solar cell

text: s, the excited electron in the conduction band interacts with the hole it leaves behind in the valence band, and this composite uncharged object is known as an

text: exciton

text: . The carrier multiplication effect in a dot can be understood as creating multiple excitons, and is called multiple exciton generation (MEG). MEG may considerably increase the

text: energy conversion

text: efficiency of

text: nanocrystal

text: based

text: solar cells

text: , though extracting the energy may be difficult because of the short lifetimes of the multiexcitons.

text: The example in the figure shows the Fermi level in the bulk material beyond the range of the applied field as lying close to the valence band edge. This position for the occupancy level is arranged by introducing impurities into the semiconductor. In this case the impurities are so-called acceptors which soak up electrons from the valence band becoming negatively charged, immobile ions embedded in the semiconductor material. The removed electrons are drawn from the valence band levels, leaving vacancies or holes in the valence band. Charge neutrality prevails in the field-free region because a negative acceptor ion  creates a positive deficiency in the host material: a hole is the absence of an electron, it behaves like a positive charge. Where no field is present, neutrality is achieved because the negative acceptor ions exactly balance the positive holes.

text: A Grotrian diagram, or term diagram, shows the allowed electronic transitions between the energy levels of atoms.  They can be used for one-electron and multi-electron atoms.  They take into account the specific selection rules related to changes in angular momentum of the electron. The diagrams are named after Walter Grotrian, who introduced them in his 1928 book Graphische Darstellung der Spektren von Atomen und Ionen mit ein, zwei und drei Valenzelektronen ("Graphical representation of the spectra of atoms and ions with one, two and three valence electrons").

text: A Grotrian diagram, or term diagram, shows the allowed

text: electronic transition

text: s between the

text: energy level

text: s of atoms.  They can be used for one-electron and multi-electron atoms.  They take into account the specific

text: selection rules

text: related to changes in

text: angular momentum

text: of the electron. The diagrams are named after

text: Walter Grotrian

text: , who introduced them in his 1928 book Graphische Darstellung der Spektren von Atomen und Ionen mit ein, zwei und drei Valenzelektronen ("Graphical representation of the spectra of atoms and ions with one, two and three valence electrons").

text: In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom and is sometimes called a non-bonding pair. Lone pairs are found in the outermost electron shell of atoms. They can be identified by using a Lewis structure. Electron pairs are therefore considered lone pairs if two electrons are paired but are not used in chemical bonding. Thus, the number of lone pair electrons plus the number of bonding electrons equals the total number of valence electrons around an atom.

text: In

text: chemistry

text: , a lone pair refers to a pair of

text: valence electrons

text: that are not shared with another atom and is sometimes called a non-bonding pair. Lone pairs are found in the outermost

text: electron shell

text: of atoms. They can be identified by using a

text: Lewis structure

text: . Electron pairs are therefore considered lone pairs if two electrons are paired but are not used in

text: chemical bonding

text: . Thus, the number of lone pair electrons plus the number of

text: bonding electron

text: s equals the total number of valence electrons around an atom.

text: Nocera's early work on two-electron bonds and multielectron exited states is considered to have established new paradigms in excited-state chemistry. The idea behind two-electron mixed-valency is that single-electron mixed-valence compounds and two-electron mixed-valence compounds may be analogous: single-electron mixed-valence compounds may react in one-electron steps, while two-electron mixed-valence compounds may react in two-electron steps. Further, a two-electron bond can be predicted to give rise to four multielectronic states. Nocera and his lab have extensively studied the excited states of metal complexes and clusters. Two Photon Excitation Spectrum of a Twisted Quadruple Bond Metal−Metal Complex completed the description of the four requisite states for the prototypical quadruple bond of a transition metal complex.

text: The arrangement of the d-orbitals on the central atom (as determined by the 'strength' of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes. It turns out that valence electrons occupying orbitals with significant 3 d-orbital character absorb in the 400–800 nm region of the spectrum (UV–visible range). The absorption of light (what we perceive as the color) by these electrons (that is, excitation of electrons from one orbital to another orbital under influence of light) can be correlated to the ground state of the metal complex, which reflects the bonding properties of the ligands. The relative change in (relative) energy of the d-orbitals as a function of the field-strength of the ligands is described in Tanabe–Sugano diagrams.

text: The arrangement of the d-orbitals on the central atom (as determined by the 'strength' of the ligand), has a strong effect on virtually all the properties of the resulting complexes. E.g., the energy differences in the d-orbitals has a strong effect in the optical absorption spectra of metal complexes. It turns out that valence electrons occupying orbitals with significant 3 d-orbital character absorb in the 400–800 nm region of the spectrum (UV–visible range). The absorption of light (what we perceive as the

text: color

text: ) by these electrons (that is, excitation of electrons from one orbital to another orbital under influence of light) can be correlated to the

text: ground state

text: of the metal complex, which reflects the bonding properties of the ligands. The relative change in (relative) energy of the d-orbitals as a function of the field-strength of the ligands is described in

text: Tanabe–Sugano diagram

text: s.

text: A modern version of the periodic table is constructed by Valery Tsimmerman, named the ADOMAH periodic table (2006). Its structure is based on the four quantum numbers of the electron configuration, hence it has a four-dimensional base.

text: A modern version of the periodic table is constructed by Valery Tsimmerman, named the ADOMAH periodic table (2006). Its structure is based on the four

text: quantum numbers

text: of the electron configuration, hence it has a four-dimensional base.

text: The chemical structure of a molecule is intimately related to its properties and reactivity. Valence bond theory proposes that molecular structures are due to covalent bonds between the atoms and that each bond consists of two overlapping and typically hybridised atomic orbitals. Traditionally, p-block elements in molecules are assumed to hybridise strictly as sp, where n is either 1, 2, or 3. In addition, the hybrid orbitals are all assumed to be equivalent (i.e. the  sp orbitals have the same p character). Results from this approach are usually good, but they can be improved upon by allowing isovalent hybridization, in which the hybridised orbitals may have noninteger and unequal p character. Bent's rule provides a qualitative estimate as to how these hybridised orbitals should be constructed. Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative.  By removing the assumption that all hybrid orbitals are equivalent sp orbitals, better predictions and explanations of properties such as molecular geometry and bond strength can be obtained.

text: The

text: chemical structure

text: of a

text: molecule

text: is intimately related to its properties and reactivity.

text: Valence bond theory

text: proposes that molecular structures are due to

text: covalent bond

text: s between the

text: atom

text: s and that each bond consists of two overlapping and typically

text: hybridised

text: atomic orbital

text: s. Traditionally,

text: p-block

text: elements in molecules are assumed to

text: hybridise

text: strictly as sp, where n is either 1, 2, or 3. In addition, the hybrid orbitals are all assumed to be equivalent (i.e. the  sp orbitals have the same p character). Results from this approach are usually good, but they can be improved upon by allowing

text: isovalent hybridization

text: , in which the hybridised orbitals may have noninteger and unequal p character. Bent's rule provides a qualitative estimate as to how these hybridised orbitals should be constructed. Bent's rule is that in a molecule, a central atom bonded to multiple groups will hybridise so that orbitals with more s character are directed towards electropositive groups, while orbitals with more p character will be directed towards groups that are more electronegative.  By removing the assumption that all hybrid orbitals are equivalent sp orbitals, better predictions and explanations of properties such as

text: molecular geometry

text: and bond strength can be obtained.

text: Valence TGV railway station, on the Lyon-Marseilles LGV Méditerranée line, is located  north-east of the city centre. Prior to its opening in 2001, the high speed TGV trains stopped in Valence-Ville railway station. Trains reached Paris in 2 hours 36 minutes. At the opening of the TGV station, a service of fifty TGVs per day was planned with eight of these TGVs continuing to serve Valence-Ville. Valence TGV station rail connections regularly connect to 35 cities, including Paris, Marseille, Lyon, Toulouse, Lille, Nice, Montpellier, Nantes, Le Havre, Reims, Avignon, Besançon, Strasbourg, Dijon and Brussels. In 2003, 60 daily TGVs served the station, with 1.8 million passengers. In 2008, the station was served by 58 daily TGVs, carrying 2.2 million passengers.

text: Valence TGV

text: railway station, on the Lyon-Marseilles

text: LGV Méditerranée

text: line, is located  north-east of the city centre. Prior to its opening in 2001, the high speed

text: TGV

text: trains stopped in Valence-Ville railway station. Trains reached Paris in 2 hours 36 minutes. At the opening of the TGV station, a service of fifty TGVs per day was planned with eight of these TGVs continuing to serve Valence-Ville. Valence TGV station rail connections regularly connect to 35 cities, including

text: Paris

text: Marseille

text: Lyon

text: Toulouse

text: Lille

text: Nice

text: Montpellier

text: Nantes

text: Le Havre

text: Reims

text: Avignon

text: Besançon

text: Strasbourg

text: Dijon

text: and

text: Brussels

text: . In 2003, 60 daily TGVs served the station, with 1.8 million passengers. In 2008, the station was served by 58 daily TGVs, carrying 2.2 million passengers.

text: The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as polyethylenes, the valence electrons are bound in sp hybridized covalent bonds. Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in conjugated materials, the situation is completely different. Conducting polymers have backbones of contiguous sp hybridized carbon centers. One valence electron on each center resides in a p orbital, which is orthogonal to the other three sigma-bonds. All the p orbitals combine with each other to a molecule wide delocalized set of orbitals. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the conjugated p-orbitals form a one-dimensional electronic band, and the electrons within this band become mobile when it is partially emptied. The band structures of conductive polymers can easily be calculated with a tight binding model. In principle, these same materials can be doped by reduction, which adds electrons to an otherwise unfilled band. In practice, most organic conductors are doped oxidatively to give p-type materials. The redox doping of organic conductors is analogous to the doping of silicon semiconductors, whereby a small fraction silicon atoms are replaced by electron-rich, e.g., phosphorus, or electron-poor, e.g., boron, atoms to create n-type and p-type semiconductors, respectively.

text: The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as

text: polyethylene

text: s, the valence electrons are bound in sp hybridized

text: covalent bond

text: s. Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in

text: conjugated

text: materials, the situation is completely different. Conducting polymers have backbones of contiguous sp hybridized carbon centers. One valence electron on each center resides in a p orbital, which is orthogonal to the other three sigma-bonds. All the p orbitals combine with each other to a molecule wide delocalized set of orbitals. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the

text: conjugated p-orbitals

text: form a one-dimensional

text: electronic band

text: , and the electrons within this band become mobile when it is partially emptied. The band structures of conductive polymers can easily be calculated with a

text: tight binding model

text: . In principle, these same materials can be doped by reduction, which adds electrons to an otherwise unfilled band. In practice, most organic conductors are doped oxidatively to give p-type materials. The redox doping of organic conductors is analogous to the doping of silicon semiconductors, whereby a small fraction silicon atoms are replaced by electron-rich, e.g.,

text: phosphorus

text: , or electron-poor, e.g.,

text: boron

text: , atoms to create

text: n-type

text: and

text: p-type semiconductor

text: s, respectively.

text: In traditional hybridisation theory, the hybrid orbitals are all equivalent. Namely the atomic s and p orbital(s) are combined to give four  (s+ p)}} orbitals, three  (s+ p)}} orbitals, or two  (s+ p)}} orbitals. These combinations are chosen to satisfy two conditions. First, the total amount of s and p orbital contributions must be equivalent before and after hybridisation. Second, the hybrid orbitals must be orthogonal to each other. If two hybrid orbitals were not orthogonal, by definition they would have nonzero orbital overlap. Electrons in those orbitals would interact and if one of those orbitals were involved in a covalent bond, the other orbital would also have a nonzero interaction with that bond, violating the two electron per bond tenet of valence bond theory.

text: In traditional hybridisation theory, the hybrid orbitals are all equivalent. Namely the atomic s and p orbital(s) are combined to give four  (s+ p)}} orbitals, three  (s+ p)}} orbitals, or two  (s+ p)}} orbitals. These combinations are chosen to satisfy two conditions. First, the total amount of s and p orbital contributions must be equivalent before and after hybridisation. Second, the hybrid orbitals must be

text: orthogonal

text: to each other. If two hybrid orbitals were not orthogonal, by definition they would have nonzero orbital overlap. Electrons in those orbitals would interact and if one of those orbitals were involved in a covalent bond, the other orbital would also have a nonzero interaction with that bond, violating the two electron per bond tenet of valence bond theory.

text: The lyrics of the song are composed of two of Robert Calvert's science fiction poems, the first verse being "The Starfarer's Despatch", which he had recited at shows whilst being the "resident poet" in the band in 1971, and the second being "The Clone's Poem". Both of these poems were published amongst a collection of his poetry issued as Centigrade 232, published by Quasar in 1978.  Throughout the song is a rhythmic electronic pulse.  This repeated sound is the Morse Code for SOS (dot-dot-dot,dash-dash-dash,dot-dot-dot).

text: The lyrics of the song are composed of two of

text: Robert Calvert

text: 's science fiction poems, the first verse being "The Starfarer's Despatch", which he had recited at shows whilst being the "resident poet" in the band in 1971, and the second being "The Clone's Poem". Both of these poems were published amongst a collection of his poetry issued as

text: Centigrade 232

text: , published by Quasar in 1978.  Throughout the song is a rhythmic electronic pulse.  This repeated sound is the Morse Code for SOS (dot-dot-dot,dash-dash-dash,dot-dot-dot).

text: The d electron count is a chemistry formalism used to describe the electron configuration of the valence electrons of a transition metal center in a coordination complex.  The d electron count is an effective way to understand the geometry and reactivity of transition metal complexes. The formalism has been incorporated into the two major models used to describe coordination complexes; crystal field theory and ligand field theory, which is a more advanced version based on molecular orbital theory.

text: The d electron count is a

text: chemistry

text: formalism used to describe the

text: electron configuration

text: of the

text: valence electron

text: s of a

text: transition metal

text: center in a

text: coordination complex

text: .  The d electron count is an effective way to understand the geometry and reactivity of transition metal complexes. The formalism has been incorporated into the two major models used to describe coordination complexes;

text: crystal field theory

text: and

text: ligand field theory

text: , which is a more advanced version based on

text: molecular orbital theory

text: Titanium(III) phosphide (TiP) is an inorganic chemical compound of titanium and phosphorus. Normally encountered as a grey powder, it is  a metallic conductor with a high melting point.  It is not attacked by common acids  or water. Its physical properties stand in contrast to the group 1 and group 2 phosphides that contain the P anion (such as NaP), which are not metallic and are readily hydrolysed. Titanium phosphide is classified as a "metal-rich phosphide", where extra valence electrons from the metal are delocalised.

text: Titanium(III) phosphide (TiP) is an inorganic chemical compound of

text: titanium

text: and

text: phosphorus

text: . Normally encountered as a grey powder, it is  a metallic conductor with a high melting point.  It is not attacked by common acids  or water. Its physical properties stand in contrast to the group 1 and group 2 phosphides that contain the P anion (such as

text: NaP

text: ), which are not metallic and are readily hydrolysed. Titanium phosphide is classified as a "metal-rich phosphide", where extra valence electrons from the metal are delocalised.

text: SuperDot was the electronic system used by the New York Stock Exchange to route market orders and limit orders from investors or their agents to a specialist located on the floor of the exchange. SuperDot was the upgraded form of the previous electronic system used to route orders, known as the Designated Order Turnaround (DOT) system. Since 1976, most of the orders in NYSE had been transmitting electronically to specialists screens over the DOT or via the upgraded SuperDot. In 2009, SuperDOT was replaced by the new NYSE Super Display Book system (SDBK) for processing orders. In 2012, Display Book was replaced by Universal Trading Platform (UTP).

text: SuperDot was the electronic system used by the

text: New York Stock Exchange

text: to route

text: market order

text: s and

text: limit order

text: s from

text: investors

text: or their

text: agents

text: to a

text: specialist

text: located on the floor of the exchange. SuperDot was the upgraded form of the previous electronic system used to route orders, known as the Designated Order Turnaround (DOT) system. Since 1976, most of the orders in NYSE had been transmitting electronically to specialists screens over the DOT or via the upgraded SuperDot. In 2009, SuperDOT was replaced by the new NYSE

text: Super Display Book system

text: (SDBK) for processing orders. In 2012, Display Book was replaced by

text: Universal Trading Platform

text: (UTP).

text: Methylaluminoxane (MAO) was discovered at the University of Hamburg in 1977. This substance is made by partial hydrolysis of trimethylaluminum and consists mainly of units of [Al4O3Me6]. The molecular weight of (MAO) can vary between 1200-1600 (g/mol) depending on how many units of  [Al4O3Me6] are present. (MAO) was found to drastically enhance the activity of polymerization, nearly 10,000 times that of previously discovered compounds. This compound, Methylaluminoxane, plays a major role in catalysis with metallocenes. The structure of (MAO) consists of aluminum and oxygen atoms arranged alternately, as well as free valence electrons that are saturated by methyl substitutes.

text: There is no electron repulsion in a d complex, and the single electron resides in the t orbital ground state. A d octahedral metal complex, such as [Ti(HO)], shows a single absorption band in a UV-vis experiment. The term symbol for d is D, which splits into the T and E states. The t orbital set holds the single electron and has a T state energy of -4Dq. When that electron is promoted to an e orbital, it is excited to  the E state energy, +6Dq. This is in accordance with the single absorption band in a UV-vis experiment. The prominent shoulder in this absorption band is due to a Jahn-Teller distortion which removes the degeneracy of the two E states. However, since these two transitions overlap in a UV-vis spectrum, this transition from T to E does not require a Tanabe–Sugano diagram.

text: There is no electron repulsion in a d complex, and the single electron resides in the t orbital ground state. A d octahedral metal complex, such as [Ti(HO)], shows a single absorption band in a UV-vis experiment. The term symbol for d is D, which splits into the T and E states. The t orbital set holds the single electron and has a T state energy of -4Dq. When that electron is promoted to an e orbital, it is excited to  the E state energy, +6Dq. This is in accordance with the single absorption band in a UV-vis experiment. The prominent shoulder in this absorption band is due to a

text: Jahn-Teller distortion

text: which removes the degeneracy of the two E states. However, since these two transitions overlap in a UV-vis spectrum, this transition from T to E does not require a Tanabe–Sugano diagram.

text: Valency refers to the number of participants that a verb takes. In Wayana, the subject of an intransitive sentence (S) is distinguished from subject of a transitive sentence (A) and the object of a transitive sentence (O). The valency on a verb stem can be decreased or increased by using certain affixes. Valence can be decreased by only one affix – the detransitivizing prefix – but can be increased by four different suffixes. Causational morphemes (such as the Wayana –po) are not considered as valence-increasing, since the participants they introduce are optional.

text: Valency

text: refers to the number of participants that a verb takes. In Wayana, the subject of an

text: intransitive

text: sentence (S) is distinguished from subject of a

text: transitive

text: sentence (A) and the object of a transitive sentence (O). The valency on a

text: verb stem

text: can be decreased or increased by using certain affixes. Valence can be decreased by only one affix – the detransitivizing prefix – but can be increased by four different suffixes. Causational morphemes (such as the Wayana –po) are not considered as valence-increasing, since the participants they introduce are optional.

text: The idea of covalent bonding can be traced several years before 1919 to Gilbert N. Lewis, who in 1916 described the sharing of electron pairs between atoms. He introduced the Lewis notation or electron dot notation or Lewis dot structure, in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as double bonds and triple bonds. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines.

text: The idea of covalent bonding can be traced several years before 1919 to

text: Gilbert N. Lewis

text: , who in 1916 described the sharing of electron pairs between atoms. He introduced the

text: Lewis notation

text: or electron dot notation or Lewis dot structure, in which valence electrons (those in the outer shell) are represented as dots around the atomic symbols. Pairs of electrons located between atoms represent covalent bonds. Multiple pairs represent multiple bonds, such as

text: double bond

text: s and

text: triple bond

text: s. An alternative form of representation, not shown here, has bond-forming electron pairs represented as solid lines.

text: The area was rural into the 18th century but was dominated by manorial estates dating from the mediaeval period. Some of these were demolished for market gardening with the expansion of the city. In the 1920s, the manors of Parsloes and Valence were acquired for the Becontree housing estate; remnants of the manors still exist as parks. Valence House now houses the Valence House Museum. Over the 19th century, industrialisation moved into the area; the borough remains the most industrialised in London. The growth in population necessitated urban expansion. The area became important as a place for social reform. With the expansion came a need for public parks as amenities. In the 1890s Barking town centre became planned out with Barking Park being established in 1898. The Becontree estate was created between 1919 and 1935 as a public housing for returning soldiers and to relieve overcrowding in the centre of London, covering the last of the borough's rural area. The estate accommodated a population over 167,000 and also included Valence and Parsloes parks, Mayesbrook Park, Castle Green and Goresbrook Sports Ground.

text: The area was rural into the 18th century but was dominated by manorial estates dating from the mediaeval period. Some of these were demolished for market gardening with the expansion of the city. In the 1920s, the manors of Parsloes and Valence were acquired for the

text: Becontree

text: housing estate; remnants of the manors still exist as parks. Valence House now houses the

text: Valence House Museum

text: . Over the 19th century, industrialisation moved into the area; the borough remains the most industrialised in London. The growth in population necessitated urban expansion. The area became important as a place for social reform. With the expansion came a need for public parks as amenities. In the 1890s

text: Barking

text: town centre became planned out with

text: Barking Park

text: being established in 1898. The Becontree estate was created between 1919 and 1935 as a public housing for returning soldiers and to relieve overcrowding in the centre of

text: London

text: , covering the last of the borough's rural area. The estate accommodated a population over 167,000 and also included Valence and Parsloes parks, Mayesbrook Park, Castle Green and

text: Goresbrook

text: Sports Ground.

text: Muonic helium is created by substituting a muon for one of the electrons in helium-4.  The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded like an isotope of helium whose nucleus consists of two neutrons, two protons and a muon, with a single electron outside.  Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1 amu. Chemically, muonic helium, possessing an unpaired valence electron, can bond with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

text: Muonic

text: helium

text: is created by substituting a muon for one of the electrons in helium-4.  The muon orbits much closer to the nucleus, so muonic helium can therefore be regarded like an isotope of helium whose nucleus consists of two neutrons, two protons and a muon, with a single electron outside.  Colloquially, it could be called "helium 4.1", since the mass of the muon is slightly greater than 0.1

text: amu

text: . Chemically, muonic helium, possessing an unpaired

text: valence electron

text: , can

text: bond

text: with other atoms, and behaves more like a hydrogen atom than an inert helium atom.

text: Early alumni of this company included Ed Esber who would later run Ashton-Tate, Bill Coleman who would found BEA Systems, Mitch Kapor founder of Lotus Software and the Electronic Frontier Foundation, Rich Melmon who would co-found Electronic Arts, Bruce Wallace author of Asteroids in Space, and Brad Templeton who would found early dot-com company ClariNet and was the director of the Electronic Frontier Foundation from 2000 to 2010.

text: Early alumni of this company included

text: Ed Esber

text: who would later run

text: Ashton-Tate

text: , Bill Coleman who would found

text: BEA Systems

text: Mitch Kapor

text: founder of

text: Lotus Software

text: and the

text: Electronic Frontier Foundation

text: , Rich Melmon who would co-found

text: Electronic Arts

text: , Bruce Wallace author of

text: Asteroids in Space

text: , and

text: Brad Templeton

text: who would found early

text: dot-com company

text: ClariNet

text: and was the director of the

text: Electronic Frontier Foundation

text: from 2000 to 2010.

text: Studies using XPS indicate that all of the copper atoms have an oxidation state of +1. This contradicts a formulation based on the crystal structure and obeying the octet rule that is found in many textbooks (e.g.) describing CuS as containing both Cu and Cu i.e. (Cu)Cu(S)S. An alternative formulation as (Cu)(S)(S) was proposed and supported by calculations.The formulation should not be interpreted as containing radical anion, but rather that there is a delocalized valence "hole".Electron paramagnetic resonance studies on the precipitation of Cu(II) salts indicates that the reduction of Cu(II) to Cu(I) occurs in solution.

text: Studies using

text: XPS

text: indicate that all of the copper atoms have an oxidation state of +1. This contradicts a formulation based on the crystal structure and obeying the

text: octet rule

text: that is found in many textbooks (e.g.) describing CuS as containing both Cu and Cu i.e. (Cu)Cu(S)S. An alternative formulation as (Cu)(S)(S) was proposed and supported by calculations.The formulation should not be interpreted as containing radical anion, but rather that there is a delocalized valence "hole".

text: Electron paramagnetic resonance

text: studies on the precipitation of Cu(II) salts indicates that the reduction of Cu(II) to Cu(I) occurs in solution.

text: Valence only describes connectivity; it does not describe the geometry of molecular compounds, or what are now known to be ionic compounds or giant covalent structures. A line between atoms does not represent a pair of electrons as it does in Lewis diagrams.

text: Valence only describes connectivity; it does not describe the geometry of molecular compounds, or what are now known to be ionic compounds or giant covalent structures. A line between atoms does not represent a pair of electrons as it does in

text: Lewis diagrams

text: The climate is semi-continental with Mediterranean influences. The Gotheron weather station of Saint-Marcel-lès-Valence, located  from the centre of Valence, recorded an average temperature of 12.3 °C and  of precipitation over the period from 1966 to 2004. The annual sunshine in Valence is 2,500 hours/year (average 1970–1994). However, there are large variations from one year to another, depending on the dominant influence (in turn Mediterranean and semi-continental). During the period from 1994 to 2004, the following years were remarkable: Lack of sunshine in 1996 (1,712 hours), low precipitation () and high temperatures in 1997, significant rainfall in 1999 () and in 2002 (). There was significant sunshine (approx. 2,500 hours) from 1999 to 2002, accompanied by higher than average temperatures. Frost in April 2003 which affected peach production, followed by a summer heatwave in 2003, with exceptional sunshine for the year (2,781 hours), and a rainfall deficit in 2004 ().

text: The climate is semi-continental with

text: Mediterranean

text: influences. The Gotheron weather station of

text: Saint-Marcel-lès-Valence

text: , located  from the centre of Valence, recorded an average temperature of 12.3 °C and  of precipitation over the period from 1966 to 2004. The annual sunshine in Valence is 2,500 hours/year (average 1970–1994). However, there are large variations from one year to another, depending on the dominant influence (in turn Mediterranean and semi-continental). During the period from 1994 to 2004, the following years were remarkable: Lack of sunshine in 1996 (1,712 hours), low precipitation () and high temperatures in 1997, significant rainfall in 1999 () and in 2002 (). There was significant sunshine (approx. 2,500 hours) from 1999 to 2002, accompanied by higher than average temperatures. Frost in April 2003 which affected peach production, followed by a summer heatwave in 2003, with exceptional sunshine for the year (2,781 hours), and a rainfall deficit in 2004 ().

text: The formal charge of an atom is computed as the difference between the number of valence electrons that a neutral atom would have and the number of electrons that belong to it in the Lewis structure. Electrons in covalent bonds are split equally between the atoms involved in the bond. The total of the formal charges on an ion should be equal to the charge on the ion, and the total of the formal charges on a neutral molecule should be equal to zero.

text: Luminescence in a semiconductor results when an electron in the conduction band recombines with a hole in the valence band. The excess energy of this transition can be emitted in form of a photon. The energy (color) of the photon, and the probability that a photon and not a phonon will be emitted, depends on the material, its purity, and the presence of defects. However, first the electron has to be excited from the valence band into the conduction band. In cathodoluminescence, this occurs as the result of an impinging high energy electron beam onto a semiconductor. However, these primary electrons carry far too much energy to directly excite electrons. Instead, the inelastic scattering of the primary electrons in the crystal leads to the emission of secondary electrons, Auger electrons and X-rays, which in turn can scatter as well. Such a cascade of scattering events leads to up to 10 secondary electrons per incident electron. These secondary electrons can excite valence electrons into the conduction band when they have a kinetic energy about three times the band gap energy of the material

text: Luminescence

text: in a semiconductor results when an

text: electron

text: in the

text: conduction band

text: recombines with a

text: hole

text: in the valence band. The excess energy of this transition can be emitted in form of a

text: photon

text: . The energy (color) of the photon, and the probability that a photon and not a

text: phonon

text: will be emitted, depends on the material, its purity, and the presence of defects. However, first the electron has to be excited from the

text: valence band

text: into the

text: conduction band

text: . In cathodoluminescence, this occurs as the result of an impinging high energy electron beam onto a

text: semiconductor

text: . However, these primary electrons carry far too much energy to directly excite electrons. Instead, the inelastic scattering of the primary electrons in the crystal leads to the emission of

text: secondary electrons

text: Auger electrons

text: and

text: X-rays

text: , which in turn can scatter as well. Such a cascade of scattering events leads to up to 10 secondary electrons per incident electron. These secondary electrons can excite valence electrons into the conduction band when they have a kinetic energy about three times the

text: band gap

text: energy of the material

text: In chemistry, a single bond is a chemical bond between two atoms involving two valence electrons. That is, the atoms share one pair of electrons where the bond forms. Therefore, a single bond is a type of covalent bond. When shared, each of the two electrons involved is no longer in the sole possession of the orbital in which it originated. Rather, both of the two electrons spend time in either of the orbitals which overlap in the bonding process. As a Lewis structure, a single bond is denoted as AːA or A-A, for which A represents an element (Moore, Stanitski, and Jurs 329). In the first rendition, each dot represents a shared electron, and in the second rendition, the bar represents both of the electrons shared in the single bond.

text: In

text: chemistry

text: , a single bond is a

text: chemical bond

text: between two

text: atom

text: s involving two

text: valence electron

text: s. That is, the atoms share one pair of

text: electron

text: s where the bond forms. Therefore, a single bond is a type of

text: covalent bond

text: . When shared, each of the two electrons involved is no longer in the sole possession of the

text: orbital

text: in which it originated. Rather, both of the two electrons spend time in either of the orbitals which overlap in the bonding process. As a

text: Lewis structure

text: , a single bond is denoted as AːA or A-A, for which A represents an element (Moore, Stanitski, and Jurs 329). In the first rendition, each dot represents a shared electron, and in the second rendition, the bar represents both of the electrons shared in the single bond.

text: After postulating a direct correlation between electron concentration and crystal structure in beta-phase alloys, Hume-Rothery analyzed the trends in melting points, compressibilities and bond lengths as a function of group number in the periodic table in order to establish a system of valencies of the transition elements in the metallic state. This treatment thus emphasized the increasing bond strength as a function of group number. The operation of directional forces were emphasized in one article on the relation between bond hybrids and the metallic structures. The resulting correlation between electronic and crystalline structures is summarized by a single parameter, the weight of the d-electrons per hybridized metallic orbital. The "d-weight" calculates out to 0.5, 0.7 and 0.9 for the fcc, hcp and bcc structures respectively. The relationship between d-electrons and crystal structure thus becomes apparent.

text: After postulating a direct correlation between electron concentration and crystal structure in beta-phase alloys,

text: Hume-Rothery

text: analyzed the trends in melting points, compressibilities and bond lengths as a function of group number in the periodic table in order to establish a system of valencies of the transition elements in the metallic state. This treatment thus emphasized the increasing bond strength as a function of group number. The operation of directional forces were emphasized in one article on the relation between bond hybrids and the metallic structures. The resulting correlation between electronic and crystalline structures is summarized by a single parameter, the weight of the d-electrons per hybridized metallic orbital. The "d-weight" calculates out to 0.5, 0.7 and 0.9 for the fcc, hcp and bcc structures respectively. The relationship between d-electrons and crystal structure thus becomes apparent.

text: The binding energy of an electron, or the energy needed to remove the electron from the atom, is a function of the electrostatic interaction between the negatively charged electrons and the positively charged nucleus. In Iron, atomic number 26, for instance, the nucleus contains 26 protons. The electrons that are closest to the nucleus will 'see' nearly all of them. However, electrons further away are screened from the nucleus by other electrons in between, and feel less electrostatic interaction as a result. The 1s electron of Iron (the closest one to the nucleus) sees an effective atomic number (number of protons) of 25. The reason why it is not 26 is because some of the electrons in the atom end up repelling the others, giving a net lower electrostatic interaction with the nucleus. One way of envisioning this effect is to imagine the 1s electron sitting on one side of the 26 protons in the nucleus, with another electron sitting on the other side; each electron will feel less than the attractive force of 26 protons because the other electron contributes a repelling force. The 4s electrons in Iron, which are furthest from the nucleus, feel an effective atomic number of only 5.43 because of the 25 electrons in between it and the nucleus screening the charge.

text: The

text: binding energy

text: of an electron, or the energy needed to remove the electron from the atom, is a function of the

text: electrostatic

text: interaction between the negatively charged electrons and the positively charged nucleus. In

text: Iron

text: , atomic number 26, for instance, the nucleus contains 26 protons. The electrons that are closest to the nucleus will 'see' nearly all of them. However, electrons further away are screened from the nucleus by other electrons in between, and feel less electrostatic interaction as a result. The

text: 1s electron

text: of Iron (the closest one to the nucleus) sees an effective atomic number (number of protons) of 25. The reason why it is not 26 is because some of the electrons in the atom end up repelling the others, giving a net lower electrostatic interaction with the nucleus. One way of envisioning this effect is to imagine the 1s electron sitting on one side of the 26 protons in the nucleus, with another electron sitting on the other side; each electron will feel less than the attractive force of 26 protons because the other electron contributes a repelling force. The 4s electrons in Iron, which are furthest from the nucleus, feel an effective atomic number of only 5.43 because of the 25 electrons in between it and the nucleus screening the charge.

text: Field electron emission (also known as field emission (FE) and electron field emission) is emission of electrons induced by an electrostatic field. The most common context is field emission from a solid surface into vacuum. However, field emission can take place from solid or liquid surfaces, into vacuum, air, a fluid, or any non-conducting or weakly conducting dielectric. The field-induced promotion of electrons from the valence to conduction band of semiconductors (the Zener effect) can also be regarded as a form of field emission. The terminology is historical because related phenomena of surface photoeffect, thermionic emission (or Richardson–Dushman effect) and "cold electronic emission", i.e. the emission of electrons in strong static (or quasi-static) electric fields, were discovered and studied independently from the 1880s to 1930s. When field emission is used without qualifiers it typically means "cold emission".

text: Field electron emission (also known as field emission (FE) and electron field emission) is emission of

text: electron

text: s induced by an electrostatic field. The most common context is field emission from a solid surface into vacuum. However, field emission can take place from solid or liquid surfaces, into vacuum, air, a fluid, or any non-conducting or weakly conducting dielectric. The field-induced promotion of electrons from the valence to conduction band of semiconductors (the

text: Zener effect

text: ) can also be regarded as a form of field emission. The terminology is historical because related phenomena of surface photoeffect,

text: thermionic emission

text: (or

text: Richardson–Dushman effect

text: ) and "cold electronic emission", i.e. the emission of electrons in strong static (or quasi-static) electric fields, were discovered and studied independently from the 1880s to 1930s. When field emission is used without qualifiers it typically means "cold emission".

text: The actinide series derives its name from the group 3 element actinium.  All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence.

text: The actinide series derives its name from the

text: group 3 element

text: actinium.  All but one of the actinides are

text: f-block

text: elements, corresponding to the filling of the 5f

text: electron shell

text: ; lawrencium, a

text: d-block

text: element, is also generally considered an actinide. In comparison with the

text: lanthanides

text: , also mostly

text: f-block

text: elements, the actinides show much more variable

text: valence

text: Oganesson is a member of group 18, the zero-valence elements. The members of this group are usually inert to most common chemical reactions (for example, combustion) because the outer valence shell is completely filled with eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. It is thought that similarly, oganesson has a closed outer valence shell in which its valence electrons are arranged in a 7s7p configuration.

text: Oganesson is a member of group 18, the zero-

text: valence

text: elements. The members of this group are usually inert to most common chemical reactions (for example, combustion) because the outer

text: valence shell

text: is completely filled with

text: eight electrons

text: . This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. It is thought that similarly, oganesson has a

text: closed

text: outer valence shell in which its

text: valence electron

text: s are arranged in a 7s7p

text: configuration

text: s electron. Instead, a valence electron for a transition metal is defined as an electron that resides outside a noble-gas core. For example, manganese (Mn) has configuration 1s 2s 2p 3s 3p 4s 3d; this is abbreviated to [Ar] 4s 3d, where [Ar] denotes a core configuration identical to that of the noble gas argon. In this atom, a 3d electron has energy similar to that of a 4s electron, and much higher than that of a 3s or 3p electron. In effect, there are possibly seven valence electrons (4s 3d) outside the argon-like core; this is consistent with the chemical fact that manganese can have an oxidation state as high as +7 (in the permanganate ion: ).

text: s electron. Instead, a valence electron for a transition metal is defined as an electron that resides outside a noble-gas core. For example,

text: manganese

text: (Mn) has configuration 1s 2s 2p 3s 3p 4s 3d; this is abbreviated to [Ar] 4s 3d, where [Ar] denotes a core configuration identical to that of the noble gas

text: argon

text: . In this atom, a 3d electron has energy similar to that of a 4s electron, and much higher than that of a 3s or 3p electron. In effect, there are possibly seven valence electrons (4s 3d) outside the argon-like core; this is consistent with the chemical fact that manganese can have an

text: oxidation state

text: as high as +7 (in the

text: permanganate

text: ion: ).

text: In a covalent bond, one or more pairs of valence electrons are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a molecule. Atoms will share valence electrons in such a way as to create a noble gas electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium, which has two electrons in its outer shell.

text: In a covalent bond, one or more pairs of

text: valence electron

text: s are shared by two atoms: the resulting electrically neutral group of bonded atoms is termed a

text: molecule

text: . Atoms will share valence electrons in such a way as to create a

text: noble gas

text: electron configuration (eight electrons in their outermost shell) for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the

text: octet rule

text: . However, some elements like

text: hydrogen

text: and

text: lithium

text: need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas

text: helium

text: , which has two electrons in its outer shell.

text: A carbon atom has four electrons in its outermost valence shell. So, it needs four more electrons to complete its octet. A carbon atom completes its octet only by sharing its valence electrons with other atoms. As a result, a carbon atom forms four covalent bonds by sharing valence electrons with other atoms. This is known as tetravalency of carbon ("tetra" means four). These four valences of carbon are directed towards four corners of a tetrahedron, and inclined to each other atomic an angle of a 109° 28´.

text: The periodic table may also be divided into several numbered rectangular 'blocks'. The elements belonging to a given block have this common feature: their highest-energy electrons all belong to the same -state (but the  associated with that -state depends upon the period). For instance, the leftmost two columns constitute the 's-block'. The outermost electrons of Li and Be respectively belong to the 2s subshell, and those of Na and Mg to the 3s subshell.

text: The periodic table may also be divided into several numbered rectangular '

text: blocks

text: '. The elements belonging to a given block have this common feature: their highest-energy electrons all belong to the same -state (but the  associated with that -state depends upon the period). For instance, the leftmost two columns constitute the 's-block'. The outermost electrons of

text: Li

text: and

text: Be

text: respectively belong to the 2s subshell, and those of

text: and

text: Mg

text: to the 3s subshell.

text: In compounds with multiple ring systems which are interconnected, this is no longer accurate, so alternating single and double bonds are used. In compounds such as chlorophyll and phenol, some diagrams show a dotted or dashed line to represent the de-localization of areas where the electron density is higher next to the single bonds. Conjugated systems can sometimes represent regions where electromagnetic radiation is absorbed at different wavelengths resulting in compounds appearing coloured. In polymers, these areas are known as chromophores.

text: In compounds with multiple ring systems which are interconnected, this is no longer accurate, so alternating single and double bonds are used. In compounds such as chlorophyll and phenol, some diagrams show a dotted or dashed line to represent the de-localization of areas where the electron density is higher next to the single bonds. Conjugated systems can sometimes represent regions where

text: electromagnetic radiation

text: is absorbed at different wavelengths resulting in compounds appearing coloured. In

text: polymer

text: s, these areas are known as chromophores.

text: Before Werner, chemists defined the valence of an element as the number of its bonds without distinguishing different types of bond. However, in complexes such as [Co(NH)]Cl for example, Werner considered that the Co-Cl bonds correspond to a "primary" valence of 3 at long distance, while the Co-NH bonds which correspond to a "secondary" or weaker valence of 6 at shorter distance. This secondary valence of 6 he referred to as the coordination number which he defined as the number of molecules (here of NH) directly linked to the central metal atom. In other complexes he found coordination numbers of 4 or 8.

text: Before Werner, chemists defined the

text: valence

text: of an element as the number of its bonds without distinguishing different types of bond. However, in complexes such as [Co(NH)]Cl for example, Werner considered that the Co-Cl bonds correspond to a "primary" valence of 3 at long distance, while the Co-NH bonds which correspond to a "secondary" or weaker valence of 6 at shorter distance. This secondary valence of 6 he referred to as the

text: coordination number

text: which he defined as the number of molecules (here of NH) directly linked to the central metal atom. In other complexes he found coordination numbers of 4 or 8.

text: Modern valence bond theory now complements molecular orbital theory, which does not adhere to the valence bond idea that electron pairs are localized between two specific atoms in a molecule but that they are distributed in sets of molecular orbitals which can extend over the entire molecule. Molecular orbital theory can predict magnetic and ionization properties in a straightforward manner, while valence bond theory gives similar results but is more complicated. Modern valence bond theory views aromatic properties of molecules as due to spin coupling of the π orbitals. This is essentially still the old idea of resonance between Kekulé and Dewar structures. In contrast, molecular orbital theory views aromaticity as delocalization of the π-electrons. Valence bond treatments are restricted to relatively small molecules, largely due to the lack of orthogonality between valence bond orbitals and between valence bond structures, while molecular orbitals are orthogonal. On the other hand, valence bond theory provides a much more accurate picture of the reorganization of electronic charge that takes place when bonds are broken and formed during the course of a chemical reaction. In particular, valence bond theory correctly predicts the dissociation of homonuclear diatomic molecules into separate atoms, while simple molecular orbital theory predicts dissociation into a mixture of atoms and ions. For example the molecular orbital function for dihydrogen is an equal mixture of the covalent and ionic valence bond structures and so predicts incorrectly that the molecule would dissociate into an equal mixture of hydrogen atoms and hydrogen positive and negative ions.

text: Modern valence bond theory

text: now complements

text: molecular orbital

text: theory, which does not adhere to the valence bond idea that electron pairs are localized between two specific atoms in a molecule but that they are distributed in sets of

text: molecular orbital

text: s which can extend over the entire molecule. Molecular orbital theory can predict

text: magnetic

text: and ionization properties in a straightforward manner, while valence bond theory gives similar results but is more complicated. Modern valence bond theory views

text: aromatic

text: properties of molecules as due to

text: spin coupling

text: of the

text: π orbitals

text: . This is essentially still the old idea of resonance between

text: Kekulé

text: and

text: Dewar

text: structures. In contrast, molecular orbital theory views aromaticity as delocalization of the π-electrons. Valence bond treatments are restricted to relatively small molecules, largely due to the lack of orthogonality between valence bond orbitals and between valence bond structures, while molecular orbitals are orthogonal. On the other hand, valence bond theory provides a much more accurate picture of the reorganization of electronic charge that takes place when bonds are broken and formed during the course of a chemical reaction. In particular, valence bond theory correctly predicts the dissociation of homonuclear diatomic molecules into separate atoms, while simple molecular orbital theory predicts dissociation into a mixture of atoms and ions. For example the molecular orbital function for

text: dihydrogen

text: is an equal mixture of the covalent and ionic valence bond structures and so predicts incorrectly that the molecule would dissociate into an equal mixture of hydrogen atoms and hydrogen positive and negative ions.

text: Cerium is the second element of the lanthanide series. In the periodic table, it appears between the lanthanides lanthanum to its left and praseodymium to its right, and above the actinide thorium. It is a ductile metal with a hardness similar to that of silver. Its 58 electrons are arranged in the configuration [Xe]4f5d6s, of which the four outer electrons are valence electrons. Immediately after lanthanum, the 4f orbitals suddenly contract and are lowered in energy to the point that they participate readily in chemical reactions; however, this effect is not yet strong enough at cerium and thus the 5d subshell is still occupied. Most lanthanides can only use three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an exception because of the stability of the empty f-shell in Ce and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until neodymium to allow the removal of the fourth valence electron.

text: Cerium is the second element of the

text: lanthanide

text: series. In the periodic table, it appears between the lanthanides

text: lanthanum

text: to its left and

text: praseodymium

text: to its right, and above the

text: actinide

text: thorium

text: . It is a

text: ductile

text: metal with a hardness similar to that of

text: silver

text: . Its 58 electrons are arranged in the

text: configuration

text: [Xe]4f5d6s, of which the four outer electrons are

text: valence electron

text: s. Immediately after lanthanum, the 4f

text: orbitals

text: suddenly contract and are lowered in energy to the point that they participate readily in chemical reactions; however, this effect is not yet strong enough at cerium and thus the 5d

text: subshell

text: is still occupied. Most lanthanides can only use three electrons as valence electrons, as afterwards the remaining 4f electrons are too strongly bound: cerium is an exception because of the stability of the empty f-shell in Ce and the fact that it comes very early in the lanthanide series, where the nuclear charge is still low enough until

text: neodymium

text: to allow the removal of the fourth valence electron.

text: In the 1970s, electronic components such as resistors, capacitors, transistors and even integrated circuits were common enough that interesting projects could be constructed at home with simple tools. The Radio Shack stores sold books that featured projects that could be constructed using the components that were being sold in their stores. In 1972 Mims wrote two hobbyist project books for Radio Shack.His books could be understood by hobbyists and were illustrated with hand-drawn schematics diagrams and hand-lettered text. This style proved popular and Radio Shack commissioned 36 books between 1972 and 2003. By the 1990s, components became smaller and it was difficult to assemble electronics projects with low-cost hand-tools. The interest in electronic kits and experiments declined, and in 2003 Radio Shack scaled back their project books and components. (Four compilations of Mims Engineers Notebooks are still available at Radio Shack today.)

text: In the 1970s, electronic components such as resistors, capacitors, transistors and even integrated circuits were common enough that interesting projects could be constructed at home with simple tools. The

text: Radio Shack

text: stores sold books that featured projects that could be constructed using the components that were being sold in their stores. In 1972 Mims wrote two hobbyist project books for Radio Shack.His books could be understood by hobbyists and were illustrated with hand-drawn schematics diagrams and hand-lettered text. This style proved popular and Radio Shack commissioned 36 books between 1972 and 2003. By the 1990s, components became smaller and it was difficult to assemble electronics projects with low-cost hand-tools. The interest in electronic kits and experiments declined, and in 2003 Radio Shack scaled back their project books and components. (Four compilations of Mims Engineers Notebooks are still available at Radio Shack today.)

text: The mechanical clock was abandoned in December 1981 in favour of a computerised clock - except in Wales, which retained the mechanical clock until 1985, making it the last BBC1 mechanical clock. A rebranding happened the same year.It was the longest running clock of 1974 and 1985 in Wales and was the last region to adopt the computerised clock and preserved the polo dot. Following BBC2's rebrand to the electronic striped 2 ident, technicians started working on an electronic clock to accompany the new look, and following its completion it was this that replaced the mechanical version. The new clock featured a single uniform line thickness all the way round, except at 12, 3, 6 and 9 where the lines were doubled. The polo mint centre was also removed in favour of a central dot.

text: The mechanical clock was abandoned in December 1981 in favour of a computerised clock - except in Wales, which retained the mechanical clock until 1985, making it the last BBC1 mechanical clock. A rebranding happened the same year.It was the longest running clock of 1974 and 1985 in Wales and was the last region to adopt the computerised clock and preserved the polo dot. Following

text: 's rebrand to the

text: electronic striped 2 ident

text: , technicians started working on an electronic clock to accompany the new look, and following its completion it was this that replaced the mechanical version. The new clock featured a single uniform line thickness all the way round, except at 12, 3, 6 and 9 where the lines were doubled. The polo mint centre was also removed in favour of a central dot.

text: Because the number of valence electrons which actually participate in chemical reactions is difficult to predict, the concept of the valence electron is less useful for a transition metal than for a main group element; the d electron count is an alternative tool for understanding the chemistry of a transition metal.

text: Because the number of valence electrons which actually participate in chemical reactions is difficult to predict, the concept of the valence electron is less useful for a transition metal than for a main group element; the

text: d electron count

text: is an alternative tool for understanding the chemistry of a transition metal.

text: The diagrams provide an effective way to organize and visualize the various terms in the perturbation series, and they naturally account for  the flow of electrons and photons during the scattering process. External lines in the diagrams represent incoming and outgoing particles, internal lines are connected with virtual particles and vertices with interactions. Each of these graphical elements is associated with mathematical expressions that contribute to the amplitude of the respective process. The diagrams are part of Feynman's very efficient and elegant algorithm for computing the probability of scattering processes.

text: The diagrams provide an effective way to organize and visualize the various terms in the perturbation series, and they naturally account for  the flow of electrons and photons during the scattering process. External lines in the diagrams represent incoming and outgoing particles, internal lines are connected with

text: virtual particles

text: and vertices with interactions. Each of these graphical elements is associated with mathematical expressions that contribute to the amplitude of the respective process. The diagrams are part of Feynman's very efficient and elegant algorithm for computing the probability of scattering processes.

text: At first the periodic system did not raise interest among chemists. However, with the discovery of the predicted elements, notably gallium in 1875, scandium in 1879, and germanium in 1886, it began to win wide acceptance. The subsequent proof of many of his predictions within his lifetime brought fame to Mendeleev as the founder of the periodic law. This organization surpassed earlier attempts at classification by Alexandre-Émile Béguyer de Chancourtois, who published the telluric helix, an early, three-dimensional version of the periodic table of the elements in 1862, John Newlands, who proposed the law of octaves (a precursor to the periodic law) in 1864, and Lothar Meyer, who developed an early version of the periodic table with 28 elements organized by valence in 1864. Mendeleev's table did not include any of the noble gases, however, which had not yet been discovered. Gradually the periodic law and table became the framework for a great part of chemical theory. By the time Mendeleev died in 1907, he enjoyed international recognition and had received distinctions and awards from many countries.

text: At first the periodic system did not raise interest among chemists. However, with the discovery of the predicted elements, notably gallium in 1875, scandium in 1879, and germanium in 1886, it began to win wide acceptance. The subsequent proof of many of his predictions within his lifetime brought fame to Mendeleev as the founder of the periodic law. This organization surpassed earlier attempts at classification by

text: Alexandre-Émile Béguyer de Chancourtois

text: , who published the telluric helix, an early, three-dimensional version of the periodic table of the elements in 1862,

text: John Newlands

text: , who proposed the law of octaves (a precursor to the periodic law) in 1864, and

text: Lothar Meyer

text: , who developed an early version of the periodic table with 28 elements organized by

text: valence

text: in 1864. Mendeleev's table did not include any of the

text: noble gas

text: es, however, which had not yet been discovered. Gradually the periodic law and table became the framework for a great part of chemical theory. By the time Mendeleev died in 1907, he enjoyed international recognition and had received distinctions and awards from many countries.

text: Most metal carbonyls have 18 valence electrons, and Fe(CO) fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands.  Reflecting its symmetrical structure and charge neutrality, Fe(CO) is volatile; it is one of the most frequently encountered liquid metal complexes.

text: Most metal carbonyls have

text: 18 valence electrons

text: , and Fe(CO) fits this pattern with 8 valence electrons on Fe and five pairs of electrons provided by the CO ligands.  Reflecting its symmetrical structure and charge neutrality, Fe(CO) is

text: volatile

text: ; it is one of the most frequently encountered liquid metal complexes.

text: Semiconductors and dopant atoms are defined by the column of the periodic table in which they fall.  The column definition of the semiconductor determines how many valence electrons its atoms have and whether dopant atoms act as the semiconductor's donors or acceptors.

text: Semiconductors and dopant atoms are defined by the column of the

text: periodic table

text: in which they fall.  The column definition of the semiconductor determines how many valence electrons its atoms have and whether dopant atoms act as the semiconductor's donors or acceptors.

text: A semiconductor has an electrical conductivity that is intermediate between that of a metal and that of a nonmetal; a semiconductor also differs from a metal in that a semiconductor's conductivity increases with temperature. The typical elemental semiconductors are silicon and germanium, each atom of which has four valence electrons. The properties of semiconductors are best explained using band theory, as a consequence of a small energy gap between a valence band (which contains the valence electrons at absolute zero) and a conduction band (to which valence electrons are excited by thermal energy).

text: A

text: semiconductor

text: has an electrical conductivity that is intermediate between that of a metal and that of a nonmetal; a semiconductor also differs from a metal in that a semiconductor's conductivity increases with

text: temperature

text: . The typical elemental semiconductors are

text: silicon

text: and

text: germanium

text: , each atom of which has four valence electrons. The properties of semiconductors are best explained using

text: band theory

text: , as a consequence of a small energy gap between a

text: valence band

text: (which contains the valence electrons at absolute zero) and a

text: conduction band

text: (to which valence electrons are excited by thermal energy).

text: The lower oxidation state in each of the elements in question has 2 valence electrons in s - orbitals. On the face of it, a simple explanation could be that the valence electrons in an s orbital are more tightly bound and are of lower energy than electrons in p orbitals and therefore less likely to be involved in bonding. Unfortunately this explanation does not stand up. If the total ionization potentials (IP) (see below) of the 2 electrons in s orbitals (the 2nd + 3rd ionization potentials), are examined it can be seen that they increase in the sequence:

text: The lower oxidation state in each of the elements in question has 2 valence electrons in s - orbitals. On the face of it, a simple explanation could be that the valence electrons in an s orbital are more tightly bound and are of lower energy than electrons in p orbitals and therefore less likely to be involved in bonding. Unfortunately this explanation does not stand up. If the total

text: ionization potential

text: s (IP) (see below) of the 2 electrons in s orbitals (the 2nd + 3rd

text: ionization potential

text: s), are examined it can be seen that they increase in the sequence:

text: Hole conduction in a valence band can be explained by the following analogy. Imagine a row of people seated in an auditorium, where there are no spare chairs. Someone in the middle of the row wants to leave, so he jumps over the back of the seat into an empty row, and walks out. The empty row is analogous to the conduction band, and the person walking out is analogous to a free electron.

text: Hole conduction in a

text: valence band

text: can be explained by the following analogy. Imagine a row of people seated in an auditorium, where there are no spare chairs. Someone in the middle of the row wants to leave, so he jumps over the back of the seat into an empty row, and walks out. The empty row is analogous to the

text: conduction band

text: , and the person walking out is analogous to a free electron.

text: The chemical elements are often displayed in a periodic table that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the noble gases.

text: The

text: chemical element

text: s are often displayed in a

text: periodic table

text: that is laid out to display recurring chemical properties, and elements with the same number of valence electrons form a group that is aligned in the same column of the table. (The horizontal rows correspond to the filling of a quantum shell of electrons.) The elements at the far right of the table have their outer shell completely filled with electrons, which results in chemically inert elements known as the

text: noble gas

text: es.

text: A non-bonding orbital, also known as non-bonding molecular orbital (NBMO), is a molecular orbital whose occupation by electrons neither increases nor decreases the bond order between the involved atoms.  Non-bonding orbitals are often designated by the letter n in molecular orbital diagrams and electron transition notations.  Non-bonding orbitals are the equivalent in molecular orbital theory of the lone pairs in Lewis structures.  The energy level of a non-bonding orbital is typically in between the lower energy of a valence shell bonding orbital and the higher energy of a corresponding antibonding orbital.  As such, a non-bonding orbital with electrons would commonly be a HOMO (highest occupied molecular orbital).

text: A non-bonding orbital, also known as non-bonding molecular orbital (NBMO), is a

text: molecular orbital

text: whose occupation by electrons neither increases nor decreases the

text: bond order

text: between the involved

text: atom

text: s.  Non-bonding orbitals are often designated by the letter n in

text: molecular orbital diagram

text: s and

text: electron transition

text: notations.  Non-bonding orbitals are the equivalent in

text: molecular orbital theory

text: of the

text: lone pair

text: s in

text: Lewis structure

text: s.  The

text: energy level

text: of a non-bonding orbital is typically in between the lower energy of a

text: valence shell

text: bonding orbital

text: and the higher energy of a corresponding

text: antibonding orbital

text: .  As such, a non-bonding orbital with electrons would commonly be a HOMO (

text: highest occupied molecular orbital

text: The number of electrons in an atom's outermost valence shell governs its bonding behavior. Therefore, elements whose atoms can have the same number of valence electrons are grouped together in the periodic table of the elements. As a general rule, a main group element (except hydrogen or helium) tends to react to form a closed shell, corresponding to the electron configuration sp. This tendency is called the octet rule, because each bonded atom has eight valence electrons including shared electrons.

text: The number of electrons in an atom's outermost valence shell governs its

text: bonding

text: behavior. Therefore, elements whose atoms can have the same number of valence electrons are grouped together in the

text: periodic table

text: of the elements. As a general rule, a

text: main group element

text: (except hydrogen or helium) tends to react to form a

text: closed shell

text: , corresponding to the

text: electron configuration

text: sp. This tendency is called the

text: octet rule

text: , because each bonded atom has eight valence electrons including shared electrons.

text: The maximum oxidation state in the first row transition metals is equal to the number of valence electrons from titanium (+4) up to manganese (+7), but decreases in the later elements. In the second row the maximum occurs with ruthenium (+8), and in the third row, the maximum occurs with iridium (+9). In compounds such as  and  the elements achieve a stable octet by forming four covalent bonds.

text: The maximum oxidation state in the first row transition metals is equal to the number of valence electrons from

text: titanium

text: (+4) up to

text: manganese

text: (+7), but decreases in the later elements. In the second row the maximum occurs with

text: ruthenium

text: (+8), and in the third row, the maximum occurs with

text: iridium

text: (+9). In compounds such as  and  the elements achieve a stable

text: octet

text: by forming four

text: covalent

text: bonds.

text: 5f6d7s. This differs from the configuration expected by the Aufbau principle in that one electron is in the 6d subshell instead of being as expected in the 5f subshell. This is because of the similarity of the electron energies of the 5f, 6d, and 7s subshells. In forming compounds and ions, all the valence electrons may be lost, leaving behind an inert core of inner electrons with the electron configuration of the noble gas radon; more commonly, only some of the valence electrons will be lost. The electron configuration for the tripositive ion Np is [Rn] 5f, with the outermost 7s and 6d electrons lost first: this is exactly analogous to neptunium's lanthanide homolog promethium, and conforms to the trend set by the other actinides with their [Rn] 5f electron configurations in the tripositive state. The first ionization potential of neptunium was measured to be at most (6.19 ± 0.12) eV in 1974, based on the assumption that the 7s electrons would ionize before 5f and 6d; more recent measurements have refined this to 6.2657 eV.

text: 5f6d7s. This differs from the configuration expected by the

text: Aufbau principle

text: in that one electron is in the 6d subshell instead of being as expected in the 5f subshell. This is because of the similarity of the electron energies of the 5f, 6d, and 7s subshells. In forming compounds and ions, all the valence electrons may be lost, leaving behind an inert core of inner electrons with the electron configuration of the

text: noble gas

text: radon; more commonly, only some of the valence electrons will be lost. The electron configuration for the tripositive ion Np is [Rn] 5f, with the outermost 7s and 6d electrons lost first: this is exactly analogous to neptunium's lanthanide homolog promethium, and conforms to the trend set by the other actinides with their [Rn] 5f electron configurations in the tripositive state. The first

text: ionization potential

text: of neptunium was measured to be at most (6.19 ± 0.12)

text: eV

text: in 1974, based on the assumption that the 7s electrons would ionize before 5f and 6d; more recent measurements have refined this to 6.2657 eV.

text: Gyratory System is a three-piece music band based in London. It is fronted by producer/trumpet player Andrew Blick. Blick was a session musician in the 1990s and previously a member of One More Grain. His trumpet-playing style, which involves the heavy use of electronic treatments, has been likened to 'Miles Davis circa On The Corner, Andy Diagram or Jon Hassell'. Another journalist has written: 'A British experimental legend, producer Andrew Blick’s three piece must be the UK’s only acid-fried, horn-led electronic marching band'.

text: Gyratory System is a three-piece music band based in

text: London

text: . It is fronted by producer/trumpet player

text: Andrew Blick

text: . Blick was a session musician in the 1990s and previously a member of

text: One More Grain

text: . His trumpet-playing style, which involves the heavy use of electronic treatments, has been likened to '

text: Miles Davis

text: circa

text: On The Corner

text: Andy Diagram

text: or

text: Jon Hassell

text: '. Another journalist has written: 'A British experimental legend, producer Andrew Blick’s three piece must be the UK’s only acid-fried, horn-led electronic marching band'.

text: A nonmetal atom tends to attract additional valence electrons to attain a full valence shell; this can be achieved in one of two ways: An atom can either share electrons with a neighboring atom (a covalent bond), or it can remove electrons from another atom (an ionic bond). The most reactive kind of nonmetal element is a halogen (e.g., fluorine (F) or chlorine (Cl)). Such an atom has the following electron configuration: sp; this requires only one additional valence electron to form a closed shell. To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion (e.g., F, Cl, etc.). To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair (e.g., in the molecule H–F, the line represents a shared pair of valence electrons, one from H and one from F).

text: A

text: nonmetal

text: atom tends to attract additional valence electrons to attain a full valence shell; this can be achieved in one of two ways: An atom can either share electrons with a neighboring atom (a

text: covalent bond

text: ), or it can remove electrons from another atom (an

text: ionic bond

text: ). The most reactive kind of nonmetal element is a

text: halogen

text: (e.g.,

text: fluorine

text: (F) or

text: chlorine

text: (Cl)). Such an atom has the following electron configuration: sp; this requires only one additional valence electron to form a closed shell. To form an ionic bond, a halogen atom can remove an electron from another atom in order to form an anion (e.g., F, Cl, etc.). To form a covalent bond, one electron from the halogen and one electron from another atom form a shared pair (e.g., in the molecule H–F, the line represents a shared pair of valence electrons, one from H and one from F).

text: Bruce and Valence had first met in combat the previous year at the Battle of Methven just outside Perth, where Bruce's lack of preparedness, and his somewhat conventional military tactics, had brought him to the edge of disaster.  His army virtually disintegrated under Valence's rapid onslaught, with many of Bruce's leading supporters falling captive.  What was left of his force was mauled for a second time soon after this by the Macdougalls of Lorn, allies of the English, at the Battle of Dalrigh. As an organised military force the army of Scotland ceased to exist, and the king took to the heather as a fugitive.

text: Bruce and Valence had first met in combat the previous year at the

text: Battle of Methven

text: just outside

text: Perth

text: , where Bruce's lack of preparedness, and his somewhat conventional military tactics, had brought him to the edge of disaster.  His army virtually disintegrated under Valence's rapid onslaught, with many of Bruce's leading supporters falling captive.  What was left of his force was mauled for a second time soon after this by the

text: Macdougalls

text: of

text: Lorn

text: , allies of the English, at the

text: Battle of Dalrigh

text: . As an organised military force the army of Scotland ceased to exist, and the king took to the heather as a fugitive.

text: Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of the hypothetical heavier alkali metals. Being the first period 8 element, the undiscovered element ununennium (element 119) is predicted to be the next alkali metal after francium and behave much like their lighter congeners; however, it is also predicted to differ from the lighter alkali metals in some properties. Its chemistry is predicted to be closer to that of potassium or rubidium instead of caesium or francium. This is unusual as periodic trends, ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium. This lowered reactivity is due to the relativistic stabilisation of ununennium's valence electron, increasing ununennium's first ionisation energy and decreasing the metallic and ionic radii; this effect is already seen for francium. This assumes that ununennium will behave chemically as an alkali metal, which, although likely, may not be true due to relativistic effects. The relativistic stabilisation of the 8s orbital also increases ununennium's electron affinity far beyond that of caesium and francium; indeed, ununennium is expected to have an electron affinity higher than all the alkali metals lighter than it. Relativistic effects also cause a very large drop in the polarisability of ununennium. On the other hand, ununennium is predicted to continue the trend of melting points decreasing going down the group, being expected to have a melting point between 0 °C and 30 °C.

text: Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of the hypothetical heavier alkali metals. Being the first

text: period 8 element

text: , the undiscovered element

text: ununennium

text: (element 119) is predicted to be the next alkali metal after francium and behave much like their lighter

text: congener

text: s; however, it is also predicted to differ from the lighter alkali metals in some properties. Its chemistry is predicted to be closer to that of potassium or rubidium instead of caesium or francium. This is unusual as

text: periodic trends

text: , ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium. This lowered

text: reactivity

text: is due to the relativistic stabilisation of ununennium's valence electron, increasing ununennium's first ionisation energy and decreasing the

text: metallic

text: and

text: ionic radii

text: ; this effect is already seen for francium. This assumes that ununennium will behave chemically as an alkali metal, which, although likely, may not be true due to relativistic effects. The relativistic stabilisation of the 8s orbital also increases ununennium's

text: electron affinity

text: far beyond that of caesium and francium; indeed, ununennium is expected to have an electron affinity higher than all the alkali metals lighter than it. Relativistic effects also cause a very large drop in the

text: polarisability

text: of ununennium. On the other hand, ununennium is predicted to continue the trend of melting points decreasing going down the group, being expected to have a melting point between 0 °C and 30 °C.

text: A lateral quantum dot is a type of quantum dot made by imposing a small area of decreased potential in the two-dimensional electron gas (2DEG) by means of electrical gates such that electrons or electron holes are confined in the 2DEG plane.  The particles are confined in one dimension laterally where they are free to move in the plane of the 2DEG.  Once the potential is applied, it is energetically favorable for a certain number of electrons (or holes) to remain confined in a certain area of the 2DEG causing the remaining two-dimensional freedom to be removed and the three dimensional confinement of the electrons or holes.  The 2DEG is confined between two semiconductor sheets such as InAs and GaAs.  The fabrication process for a lateral dot is very different from that for a self-assembled quantum dot.

text: A lateral quantum dot is a type of

text: quantum dot

text: made by imposing a small

text: area

text: of decreased

text: potential

text: in the

text: two-dimensional electron gas

text: ) by means of electrical gates such that

text: electrons

text: or

text: electron hole

text: s are confined in the

text: plane.  The particles are confined in one

text: dimension

text: laterally where they are free to move in the plane of the

text: .  Once the

text: potential

text: is applied, it is energetically favorable for a certain number of

text: electron

text: s (or holes) to remain confined in a certain area of the 2DEG causing the remaining two-dimensional freedom to be removed and the three

text: dimensional

text: confinement

text: of the

text: electron

text: s or holes.  The 2DEG is confined between two

text: semiconductor

text: sheets such as

text: InAs

text: and

text: GaAs

text: .  The

text: fabrication

text: process for a lateral dot is very different from that for a self-assembled

text: quantum dot

text: However, if an electron in the valence band acquires enough energy to reach the conduction band, it can flow freely among the nearly empty conduction band energy states. Furthermore, it will also leave behind an electron hole that can flow as current exactly like a physical charged particle. Carrier generation describes processes by which electrons gain energy and move from the valence band to the conduction band, producing two mobile carriers; while recombination describes processes by which a conduction band electron loses energy and re-occupies the energy state of an electron hole in the valence band.

text: The number of valence electrons of an element can be determined by the periodic table group (vertical column) in which the element is categorized. With the exception of groups 3–12 (the transition metals), the units digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column.

text: The number of valence electrons of an element can be determined by the

text: periodic table group

text: (vertical column) in which the element is categorized. With the exception of groups 3–12 (the

text: transition metal

text: s), the units digit of the group number identifies how many valence electrons are associated with a neutral atom of an element listed under that particular column.

text: The Rutherford model of the nuclear atom (1911) showed that the exterior of an atom is occupied by electrons, which suggests that electrons are responsible for the interaction of atoms and the formation of chemical bonds. In 1916, Gilbert N. Lewis explained valence and chemical bonding in terms of a tendency of (main-group) atoms to achieve a stable octet of 8 valence-shell electrons. According to Lewis, covalent bonding leads to octets by the sharing of electrons, and ionic bonding leads to octets by the transfer of electrons from one atom to the other. The term covalence is attributed to Irving Langmuir, who stated in 1919 that "the number of pairs of electrons which any given atom shares with the adjacent atoms is called the covalence of that atom". The prefix co- means "together", so that a co-valent bond means that the atoms share a valence. Subsequent to that, it is now more common to speak of covalent bonds rather than "valence", which has fallen out of use in higher-level work from the advances in the theory of chemical bonding, but it is still widely used in elementary studies, where it provides a heuristic introduction to the subject.

text: The

text: Rutherford model

text: of the nuclear atom (1911) showed that the exterior of an atom is occupied by

text: electron

text: s, which suggests that electrons are responsible for the interaction of atoms and the formation of chemical bonds. In 1916,

text: Gilbert N. Lewis

text: explained valence and chemical bonding in terms of a tendency of (main-group) atoms to achieve a

text: stable octet

text: of 8 valence-shell electrons. According to Lewis,

text: covalent bond

text: ing leads to octets by the sharing of electrons, and

text: ionic bonding

text: leads to octets by the transfer of electrons from one atom to the other. The term covalence is attributed to

text: Irving Langmuir

text: , who stated in 1919 that "the number of pairs of

text: electron

text: s which any given atom shares with the adjacent atoms is called the covalence of that atom". The prefix co- means "together", so that a co-valent bond means that the atoms share a valence. Subsequent to that, it is now more common to speak of

text: covalent bond

text: s rather than "valence", which has fallen out of use in higher-level work from the advances in the theory of chemical bonding, but it is still widely used in elementary studies, where it provides a

text: heuristic

text: introduction to the subject.

text: Iodine is the fourth halogen, being a member of group 17 in the periodic table, below fluorine, chlorine, and bromine; it is the heaviest stable member of its group. (The scarce and fugitive fifth halogen, the radioactive astatine, is not well-studied due to its expense and inaccessibility in large quantities, but appears to show various unusual properties due to relativistic effects.) Iodine has an electron configuration of [Kr]4d5s5p, with the seven electrons in the fifth and outermost shell being its valence electrons. Like the other halogens, it is one electron short of a full octet and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell, although in keeping with periodic trends, it is the weakest oxidising agent among the stable halogens: it has the lowest electronegativity among them, just 2.66 on the Pauling scale (compare fluorine, chlorine, and bromine at 3.98, 3.16, and 2.96 respectively; astatine continues the trend with an electronegativity of 2.2). Elemental iodine hence forms diatomic molecules with chemical formula I, where two iodine atoms share a pair of electrons in order to each achieve a stable octet for themselves; at high temperatures, these diatomic molecules reversibly dissociate a pair of iodine atoms. Similarly, the iodide anion, I, is the strongest reducing agent among the stable halogens, being the most easily oxidised back to diatomic I. (Astatine goes further, being indeed unstable as At and readily oxidised to At or At, although the existence of At is not settled.)

text: Iodine is the fourth

text: halogen

text: , being a member of group 17 in the periodic table, below

text: fluorine

text: chlorine

text: , and

text: bromine

text: ; it is the heaviest stable member of its group. (The scarce and fugitive fifth halogen, the radioactive

text: astatine

text: , is not well-studied due to its expense and inaccessibility in large quantities, but appears to show various unusual properties due to

text: relativistic effects

text: .) Iodine has an electron configuration of [Kr]4d5s5p, with the seven electrons in the fifth and outermost shell being its

text: valence electron

text: s. Like the other halogens, it is one electron short of a full octet and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell, although in keeping with

text: periodic trend

text: s, it is the weakest oxidising agent among the stable halogens: it has the lowest

text: electronegativity

text: among them, just 2.66 on the Pauling scale (compare fluorine, chlorine, and bromine at 3.98, 3.16, and 2.96 respectively; astatine continues the trend with an electronegativity of 2.2). Elemental iodine hence forms

text: diatomic molecule

text: s with chemical formula I, where two iodine atoms share a pair of electrons in order to each achieve a stable octet for themselves; at high temperatures, these diatomic molecules reversibly dissociate a pair of iodine atoms. Similarly, the iodide anion, I, is the strongest reducing agent among the stable halogens, being the most easily oxidised back to diatomic I. (Astatine goes further, being indeed unstable as At and readily oxidised to At or At, although the existence of At is not settled.)

text: The methyl group carbon atom has six valence electrons from its bonds to the hydrogen atoms because carbon is more electronegative than hydrogen. Also, one electron is gained from its bond with the other carbon atom because the electron pair in the C−C bond is split equally. It therefore has a total of seven electrons, whereas a neutral carbon atom would have four valence electrons because carbon is in group 14 of the periodic table. The difference, 4 − 7 = −3, is the oxidation state of that carbon atom.  That is, if it is assumed that all the bonds were 100% ionic (which in fact they are not), the carbon would be described as .

text: The

text: methyl

text: group carbon atom has six valence electrons from its bonds to the hydrogen atoms because carbon is more electronegative than hydrogen. Also, one electron is gained from its bond with the other carbon atom because the electron pair in the

text: C−C bond

text: is split equally. It therefore has a total of seven electrons, whereas a neutral carbon atom would have four valence electrons because carbon is in

text: group 14

text: of the periodic table. The difference, 4 − 7 = −3, is the oxidation state of that carbon atom.  That is, if it is assumed that all the bonds were 100% ionic (which in fact they are not), the carbon would be described as .

text: Classical Isosteres are molecules or ions with the same number of atoms and/or the same number of valence electrons. The definition was later revised to include compounds with similarly reactive electron shells. For example, Hydrogen ion and Fluoride are classical isosteres because they both have relatively small nuclei and their outer valence shells are full (or empty in Hydrogen's case) when ionized (0 in Hydrogen, 1s + 2p = p in Fluoride).

text: Classical Isosteres are

text: molecules

text: or

text: ions

text: with the same number of

text: atom

text: s and/or the same number of

text: valence electrons

text: . The definition was later revised to include compounds with similarly reactive

text: electron shells

text: . For example, Hydrogen ion and Fluoride are classical isosteres because they both have relatively small nuclei and their outer

text: valence shells

text: are full (or empty in Hydrogen's case) when ionized (0 in Hydrogen, 1s + 2p = p in Fluoride).

text: Each molybdenum has local octahedral symmetry and two chlorides bridge between the molybdenum centers. A similar structure is also found for the pentachlorides of W, Nb and Ta. In the gas phase and partly in solution, the dimers partially dissociates to give a monomeric pentahalide. The monomer is paramagnetic, with one unpaired electron per Mo center, reflecting the fact that the formal oxidation state is +5, leaving one valence electron on the metal center.

text: Each molybdenum has local octahedral symmetry and two chlorides

text: bridge

text: between the molybdenum centers. A similar structure is also found for the pentachlorides of W, Nb and Ta. In the gas phase and partly in solution, the

text: dimer

text: s partially dissociates to give a monomeric pentahalide. The monomer is paramagnetic, with one unpaired electron per Mo center, reflecting the fact that the formal oxidation state is +5, leaving one valence electron on the metal center.

text: In the notation of the periodic table, the main shells of electrons are labeled:

text: is the particle density of the valence electrons.

text: is the

text: particle density

text: of the valence electrons.

text: In Lewis formulas, electrons are paired between atoms to form covalent bonds. Each single bond is made by two valence electrons, localized between the two bonded atoms. Each double bond has two additional localized π electrons, while each triple bond has four additional π electrons (two pairs) between the bonded atoms.

text: In Lewis formulas, electrons are paired between atoms to form

text: covalent bond

text: s. Each single bond is made by two

text: valence electron

text: s, localized between the two bonded atoms. Each

text: double bond

text: has two additional localized

text: π electron

text: s, while each

text: triple bond

text: has four additional π electrons (two pairs) between the bonded atoms.

text: In solids, the ability of electrons to act as charge carriers depends on the availability of vacant electronic states. This allows the electrons to increase their energy (i.e., accelerate) when an electric field is applied. This condition is only satisfied in the conduction band, since the valence band is full in non-metals.

text: In solids, the ability of electrons to act as

text: charge carrier

text: s depends on the availability of vacant electronic states. This allows the electrons to increase their energy (i.e.,

text: accelerate

text: ) when an

text: electric field

text: is applied. This condition is only satisfied in the conduction band, since the valence band is full in non-metals.

text: A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical bonding in molecules in terms of molecular orbital theory in general and the linear combination of atomic orbitals (LCAO) molecular orbital method in particular.   A fundamental principle of these theories is that as atoms bond to form molecules, a certain number of atomic orbitals combine to form the same number of molecular orbitals, although the electrons involved may be redistributed among the orbitals.  This tool is very well suited for simple diatomic molecules such as dihydrogen, dioxygen, and carbon monoxide but becomes more complex when discussing even comparatively simple polyatomic molecules, such as methane.  MO diagrams can explain why some molecules exist and others do not. They can also predict bond strength, as well as the electronic transitions that can take place.

text: A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining

text: chemical bonding

text: in

text: molecule

text: s in terms of

text: molecular orbital theory

text: in general and the

text: linear combination of atomic orbitals

text: (LCAO) molecular orbital method in particular.   A fundamental principle of these theories is that as atoms bond to form molecules, a certain number of

text: atomic orbital

text: s combine to form the same number of

text: molecular orbital

text: s, although the

text: electron

text: s involved may be redistributed among the orbitals.  This tool is very well suited for simple

text: diatomic molecule

text: s such as

text: dihydrogen

text: dioxygen

text: , and

text: carbon monoxide

text: but becomes more complex when discussing even comparatively simple polyatomic molecules, such as

text: methane

text: .  MO diagrams can explain why some molecules exist and others do not. They can also predict bond strength, as well as the

text: electronic transition

text: s that can take place.

text: In hydrogen, or any other atom in group 1A of the periodic table (those with only one valence electron), the force on the electron is just as large as the electromagnetic attraction from the nucleus. However, when more electrons are involved, each electron (in the n-shell) experiences not only the electromagnetic attraction from the positive nucleus, but also repulsion forces from other electrons in shells from 1 to n. This causes the net force on electrons in outer shells to be significantly smaller in magnitude; therefore, these electrons are not as strongly bonded to the nucleus as electrons closer to the nucleus. This phenomenon is often referred to as the orbital penetration effect. The shielding theory also contributes to the explanation of why valence-shell electrons are more easily removed from the atom.

text: In hydrogen, or any other atom in group 1A of the periodic table (those with only one valence electron), the force on the electron is just as large as the electromagnetic attraction from the nucleus. However, when more electrons are involved, each electron (in the n-

text: shell

text: ) experiences not only the electromagnetic attraction from the positive nucleus, but also repulsion forces from other electrons in shells from 1 to n. This causes the net force on electrons in outer shells to be significantly smaller in magnitude; therefore, these electrons are not as strongly bonded to the nucleus as electrons closer to the nucleus. This phenomenon is often referred to as the orbital penetration effect. The shielding theory also contributes to the explanation of why

text: valence-shell

text: electrons are more easily removed from the atom.

text: Covalent bonding includes many kinds of interactions, including σ-bonding, π-bonding, metal-to-metal bonding, agostic interactions, bent bonds, and three-center two-electron bonds. The term covalent bond dates from 1939. The prefix co- means jointly, associated in action, partnered to a lesser degree,  etc.; thus a "co-valent bond", in essence, means that the atoms share "valence", such as is discussed in valence bond theory.

text: Covalent bonding includes many kinds of interactions, including

text: σ-bonding

text: π-bonding

text: metal-to-metal bonding

text: agostic interaction

text: s,

text: bent bond

text: s, and

text: three-center two-electron bond

text: s. The term covalent bond dates from 1939. The prefix co- means jointly, associated in action, partnered to a lesser degree,  etc.; thus a "co-valent bond", in essence, means that the atoms share "

text: valence

text: ", such as is discussed in

text: valence bond theory

text: At the start of programmes, Le Mouv' initially had an eclectic format, mixing pop, rock and electronic dance music mixed with practical information for its young audience. By 1998 the media regulator CSA attributed 21 new FM frequencies to the network in small to medium-sized towns (such as Angers, Poitiers, Valence).

text: At the start of programmes, Le Mouv' initially had an eclectic format, mixing

text: pop

text: rock

text: and

text: electronic dance

text: music mixed with practical information for its young audience. By 1998 the media regulator

text: CSA

text: attributed 21 new FM frequencies to the network in small to medium-sized towns (such as

text: Angers

text: Poitiers

text: Valence

text: Silver halides are used in photographic film and photographic paper, including graphic art film and paper, where silver halide crystals in gelatin are coated on to a film base, glass or paper substrate. The gelatin is a vital part of the emulsion as the protective colloid of appropriate physical and chemical properties. Gelatin may also contain trace elements (such as sulfur) which increase the light sensitivity of the emulsion, although modern practice uses gelatin without such components. When absorbed by an AgX crystal, photons cause electrons to be promoted to a conduction band (de-localized electron orbital with higher energy than a valence band) which can be attracted by a sensitivity speck, which is a shallow electron trap, which may be a crystalline defect or a cluster of silver sulfide, gold, other trace elements (dopant), or combination thereof, and then combined with an interstitial silver ion to form silver metal speck.

text: Silver halides are used in

text: photographic film

text: and

text: photographic paper

text: , including graphic art film and paper, where silver halide

text: crystals

text: in

text: gelatin

text: are coated on to a

text: film base

text: , glass or paper

text: substrate

text: . The gelatin is a vital part of the emulsion as the protective colloid of appropriate physical and chemical properties. Gelatin may also contain trace elements (such as

text: sulfur

text: ) which increase the light sensitivity of the

text: emulsion

text: , although modern practice uses gelatin without such components. When absorbed by an AgX crystal,

text: photon

text: s cause electrons to be promoted to a

text: conduction band

text: (de-localized

text: electron orbital

text: with higher energy than a

text: valence band

text: ) which can be attracted by a

text: sensitivity speck

text: , which is a shallow electron trap, which may be a crystalline defect or a cluster of

text: silver sulfide

text: , gold, other trace elements (

text: dopant

text: ), or combination thereof, and then combined with an interstitial silver ion to form silver metal speck.

text: Neptunium has five ionic oxidation states ranging from +3 to +7 when forming chemical compounds, which can be simultaneously observed in solutions. It is the heaviest actinide that can lose all its valence electrons in a stable compound. The most stable state in solution is +5, but the valence +4 is preferred in solid neptunium compounds. Neptunium metal is very reactive. Ions of neptunium are prone to hydrolysis and formation of coordination compounds.

text: Neptunium has five ionic

text: oxidation state

text: s ranging from +3 to +7 when forming chemical compounds, which can be simultaneously observed in solutions. It is the heaviest actinide that can lose all its valence electrons in a stable compound. The most stable state in solution is +5, but the valence +4 is preferred in solid neptunium compounds. Neptunium metal is very reactive. Ions of neptunium are prone to hydrolysis and formation of

text: coordination compound

text: s.

text: The electron pairs (or groups if double, triple... bonds are present) are assumed to lie on the surface of a sphere centered on the central atom and tend to occupy positions that minimize their mutual repulsions by maximizing the distance between them. The number of electron pairs (or groups), therefore, determines the overall geometry that they will adopt. For example, when there are two electron pairs surrounding the central atom, their mutual repulsion is minimal when they lie at opposite poles of the sphere. Therefore, the central atom is predicted to adopt a linear geometry. If there are 3 electron pairs surrounding the central atom, their repulsion is minimized by placing them at the vertices of an equilateral triangle centered on the atom. Therefore, the predicted geometry is trigonal. Likewise, for 4 electron pairs, the optimal arrangement is tetrahedral.

text: The electron pairs (or groups if double, triple... bonds are present) are assumed to lie on the surface of a sphere centered on the central atom and tend to occupy positions that minimize their mutual repulsions by maximizing the distance between them. The number of electron pairs (or groups), therefore, determines the overall geometry that they will adopt. For example, when there are two electron pairs surrounding the central atom, their mutual repulsion is minimal when they lie at opposite poles of the sphere. Therefore, the central atom is predicted to adopt a linear geometry. If there are 3 electron pairs surrounding the central atom, their repulsion is minimized by placing them at the vertices of an equilateral triangle centered on the atom. Therefore, the predicted geometry is

text: trigonal

text: . Likewise, for 4 electron pairs, the optimal arrangement is

text: tetrahedral

text: Example: The quantum numbers used to refer to the outermost valence electrons of the Carbon (C) atom, which are located in the 2p atomic orbital, are; n = 2 (2nd electron shell),  = 1 (p orbital subshell), m = 1, 0 or −1, m = ½ (parallel spins).

text: Example: The quantum numbers used to refer to the outermost

text: valence

text: electron

text: s of the

text: Carbon

text: (C)

text: atom

text: , which are located in the 2p

text: atomic orbital

text: , are; n = 2 (2nd electron shell),  = 1 (p orbital

text: subshell

text: ), m = 1, 0 or −1, m = ½ (parallel spins).

text: The two most useful properties of the metal are corrosion resistance and the highest strength-to-density ratio of any metallic element. In its unalloyed condition, titanium is as strong as some steels, but less dense. There are two allotropic forms and five naturally occurring isotopes of this element, Ti through Ti, with Ti being the most abundant (73.8%). Although they have the same number of valence electrons and are in the same group in the periodic table, titanium and zirconium differ in many chemical and physical properties.

text: The two most useful properties of the metal are corrosion resistance and the highest strength-to-density ratio of any metallic element. In its unalloyed condition, titanium is as strong as some

text: steel

text: s, but less dense. There are two

text: allotropic

text: forms and five naturally occurring

text: isotope

text: s of this element, Ti through Ti, with Ti being the most

text: abundant

text: (73.8%). Although they have the same number of

text: valence electrons

text: and are in the same

text: group

text: in the

text: periodic table

text: , titanium and

text: zirconium

text: differ in many chemical and physical properties.

text: Radon is a member of the zero-valence elements that are called noble gases. It is inert to most common chemical reactions, such as combustion, because the outer valence shell contains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. 1037 kJ/mol is required to extract one electron from its shells (also known as the first ionization energy). In accordance with periodic trends, radon has a lower electronegativity than the element one period before it, xenon, and is therefore more reactive.  Early studies concluded that the stability of radon hydrate should be of the same order as that of the hydrates of chlorine () or sulfur dioxide (), and significantly higher than the stability of the hydrate of hydrogen sulfide ().

text: Radon is a member of the zero-

text: valence

text: elements that are called noble gases. It is

text: inert

text: to most common chemical reactions, such as combustion, because the outer

text: valence shell

text: contains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. 1037 kJ/mol is required to extract one electron from its shells (also known as the

text: first ionization energy

text: ). In accordance with

text: periodic trends

text: , radon has a lower

text: electronegativity

text: than the element one period before it,

text: xenon

text: , and is therefore more reactive.  Early studies concluded that the stability of radon

text: hydrate

text: should be of the same order as that of the hydrates of

text: chlorine

text: () or

text: sulfur dioxide

text: (), and significantly higher than the stability of the hydrate of

text: hydrogen sulfide

text: For a main group element, the number of valence electrons that it may have depends on the electron configuration in a simple way. However, for a transition metal, the relationship is more complex.

text: For a

text: main group element

text: , the number of valence electrons that it may have depends on the

text: electron configuration

text: in a simple way. However, for a

text: transition metal

text: , the relationship is more complex.

text: Thus, when a material is illuminated, individual photons of light can make the valence electrons of an atom transition to a higher electronic energy level. The photon is destroyed in the process and the absorbed radiant energy is transformed to electric potential energy. Several things can happen then to the absorbed energy: it may be re-emitted by the electron as radiant energy (in this case the overall effect is in fact a scattering of light), dissipated to the rest of the material (i.e. transformed into heat), or the electron can be freed from the atom (as in the photoelectric and Compton effects).

text: Thus, when a material is illuminated, individual photons of light can make the

text: valence electrons

text: of an atom transition to a higher electronic

text: energy level

text: . The photon is destroyed in the process and the absorbed radiant energy is transformed to electric potential energy. Several things can happen then to the absorbed energy: it may be re-emitted by the electron as

text: radiant energy

text: (in this case the overall effect is in fact a scattering of light), dissipated to the rest of the material (i.e. transformed into

text: heat

text: ), or the electron can be freed from the atom (as in the

text: photoelectric

text: and

text: Compton

text: effects).

text: Square planar geometry can also be achieved by the removal of a pair of ligands from the z-axis of an octahedron, leaving four ligands in the xy plane. For transition metal compounds, the crystal field splitting diagram for square planar geometry can thus be derived from the octahedral diagram. The removal of the two ligands stabilizes the d level, leaving the d level as the most destabilized. Consequently, the d remains unoccupied in complexes of metals with the d configuration. These compounds typically have 16 valence electrons (eight from ligands, eight from the metal).

text: Square planar geometry can also be achieved by the removal of a pair of

text: ligands

text: from the z-axis of an

text: octahedron

text: , leaving four ligands in the xy plane. For transition metal compounds, the

text: crystal field

text: splitting diagram for square planar geometry can thus be derived from the octahedral diagram. The removal of the two ligands stabilizes the d level, leaving the d level as the most destabilized. Consequently, the d remains unoccupied in complexes of metals with the d configuration. These compounds typically have

text: 16 valence electrons

text: (eight from ligands, eight from the metal).

text: Chlorine is the second halogen, being a nonmetal in group 17 of the periodic table. Its properties are thus similar to fluorine, bromine, and iodine, and are largely intermediate between those of the first two. Chlorine has the electron configuration [Ne]3s3p, with the seven electrons in the third and outermost shell acting as its valence electrons. Like all halogens, it is thus one electron short of a full octet, and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell. Corresponding to periodic trends, it is intermediate in electronegativity between fluorine and bromine (F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66), and is less reactive than fluorine and more reactive than bromine. It is also a weaker oxidising agent than fluorine, but a stronger one than bromine. Conversely, the chloride ion is a weaker reducing agent than bromide, but a stronger one than fluoride. It is intermediate in atomic radius between fluorine and bromine, and this leads to many of its atomic properties similarly continuing the trend from iodine to bromine upward, such as first ionisation energy, electron affinity, enthalpy of dissociation of the X molecule (X = Cl, Br, I), ionic radius, and X–X bond length. (Fluorine is anomalous due to its small size.)

text: Chlorine is the second

text: halogen

text: , being a

text: nonmetal

text: in group 17 of the periodic table. Its properties are thus similar to

text: fluorine

text: bromine

text: , and

text: iodine

text: , and are largely intermediate between those of the first two. Chlorine has the electron configuration [Ne]3s3p, with the seven electrons in the third and outermost shell acting as its

text: valence electron

text: s. Like all halogens, it is thus one electron short of a full octet, and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell. Corresponding to

text: periodic trend

text: s, it is intermediate in

text: electronegativity

text: between fluorine and bromine (F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66), and is less reactive than fluorine and more reactive than bromine. It is also a weaker oxidising agent than fluorine, but a stronger one than bromine. Conversely, the

text: chloride

text: ion is a weaker reducing agent than bromide, but a stronger one than fluoride. It is intermediate in

text: atomic radius

text: between fluorine and bromine, and this leads to many of its atomic properties similarly continuing the trend from iodine to bromine upward, such as first

text: ionisation energy

text: electron affinity

text: , enthalpy of dissociation of the X molecule (X = Cl, Br, I), ionic radius, and X–X bond length. (Fluorine is anomalous due to its small size.)

text: The relationship is the most important part of the cognitive schemata model. Partnership within a dyad has numerous labels. Within relationships (interpersonal relationships), we label our dyad partners as acquaintances, friends, colleagues, professional coworkers, personal friends, family members, fellow college students and college professors and, those people whose paths cross with ours simply as convenient contacts. Each dyad partner, whether initial or long-term may display a level of intimacy or immediacy based on a degree of appropriateness for the situation. Public forums are the stage in which positive or negative valence performs. As stated earlier, an unwanted look or a touch may heighten the degree of negative valence. In contrast, a look or an accepted touch may heighten the degree of positive valence and be the most desirable behavior for each of the dyad partners. Relationships are dependent upon both partners and their commitment to the dyad. Relationships therefore are fragile. Cognitive Valence Theory or CVT offers one explanation for this fragility. Negative valence received from any of the cognitive schemata can result in a negative relational outcome. Negative valence reduces the intimacy or immediacy strength within a relationship. Negative valence can also thwart healthy dyad growth by heightening the lack of love and care within the dyad. Positive valence acts in a 180 degree fashion as positive feeling promotes growth and strengthens the love and care within the dyad. With positive valence, there can still be risks, but the rewards may outweigh the costs.

text: The relationship is the most important part of the cognitive schemata model. Partnership within a dyad has numerous labels. Within relationships (

text: interpersonal relationships

text: Fig. 3 Energy diagram for Electron Transfer including inner and outer sphere reorganization and electronic coupling: The vertical axis is the free energy, and the horizontal axis is the "reaction coordinate" – a simplified axis representing the motion of all the atomic nuclei (inclusive solvent reorganization)

text: Folimage is a French animation studio, based in Bourg-lès-Valence, Drôme, France. It was founded in 1981 by Jacques-Rémy Girerd. The studio produces animation films for cinema and TV (short films, TV specials and series, feature films). In 1999, the company founded an animation school, La Poudrière, also in Valence. In 2009, Folimage and La Poudrière moved to  La Cartoucherie, a former munitions factory in Bourg-lès-Valence.

text: Folimage is a French animation studio, based in

text: Bourg-lès-Valence

text: Drôme

text: , France. It was founded in 1981 by Jacques-Rémy Girerd. The studio produces animation films for cinema and TV (short films, TV specials and series, feature films). In 1999, the company founded an animation school, La Poudrière, also in Valence. In 2009, Folimage and La Poudrière moved to  La Cartoucherie, a former munitions factory in

text: Bourg-lès-Valence

text: Once the vacuum levels are aligned it is possible to use the electron affinity and band gap values for each semiconductor to calculate the conduction band and valence band offsets. The electron affinity (usually given by the symbol

text: Once the vacuum levels are aligned it is possible to use the

text: electron affinity

text: and

text: band gap

text: values for each semiconductor to calculate the

text: conduction band

text: and

text: valence band

text: offsets. The electron affinity (usually given by the symbol

text: The nitrite ion has a symmetrical structure (C symmetry), with both N–O bonds having equal length. In valence bond theory, it is described as a resonance hybrid with equal contributions from two canonical forms that are mirror images of each other. In molecular orbital theory, there is a sigma bond between each oxygen atom and the nitrogen atom, and a delocalized pi bond made from the p orbitals on nitrogen and oxygen atoms which is perpendicular to the plane of the molecule. The negative charge of the ion is equally distributed on the two oxygen atoms. Both nitrogen and oxygen atoms carry a lone pair of electrons. Therefore, the nitrite ion is a Lewis base. Moreover, it can act as an ambidentate ligand towards a metal ion, donating a pair of electrons from either nitrogen or oxygen atoms.

text: The nitrite ion has a symmetrical structure (C

text: symmetry

text: ), with both N–O bonds having equal length. In

text: valence bond theory

text: , it is described as a

text: resonance hybrid

text: with equal contributions from two canonical forms that are mirror images of each other. In

text: molecular orbital theory

text: , there is a

text: sigma bond

text: between each oxygen atom and the nitrogen atom, and a delocalized

text: pi bond

text: made from the

text: p orbitals

text: on nitrogen and oxygen atoms which is perpendicular to the plane of the molecule. The negative charge of the ion is equally distributed on the two oxygen atoms. Both nitrogen and oxygen atoms carry a

text: lone pair

text: of electrons. Therefore, the nitrite ion is a

text: Lewis base

text: . Moreover, it can act as an

text: ambidentate ligand

text: towards a metal ion, donating a pair of electrons from either nitrogen or oxygen atoms.

text: When they are in a configuration belonging to metastable states np(n+1)s, (n = 5 for xenon), rare gases possess properties of polarizability and elastic scattering similar to those of alkali metals. The valence electron, s, of the excited rare gas has a bond energy close to that of the alkali metal that follows it in the periodic table. In older publications, this analogy that is applicable only for the heavier rare gases, is used to study the behavior of these gases with halogen donors. The alkali metals have good chemical affinity for halogen and should have affinity for excited rare gases. Experimentally the collision cross section of metastable states of rare gases with the halogens is similar to that of alkali metals with halogens. Thus, an excited xenon has an electronic structure close to that of cesium, so that it can react with a chlorine donor in order to form .

text: When they are in a configuration belonging to metastable states np(n+1)s, (n = 5 for xenon), rare gases possess properties of

text: polarizability

text: and elastic scattering similar to those of

text: alkali metals

text: . The valence electron, s, of the excited rare gas has a

text: bond energy

text: close to that of the alkali metal that follows it in the

text: periodic table

text: . In older publications, this analogy that is applicable only for the heavier rare gases, is used to study the behavior of these gases with halogen donors. The alkali metals have good chemical affinity for halogen and should have affinity for excited rare gases. Experimentally the collision cross section of metastable states of rare gases with the halogens is similar to that of alkali metals with halogens. Thus, an excited xenon has an electronic structure close to that of

text: cesium

text: , so that it can react with a chlorine donor in order to form .

text: Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the alkaline earth metal barium and to the left of the lanthanide cerium. Lanthanum is often considered to be a group 3 element, along with its lighter congeners scandium and yttrium and its heavier congener, the radioactive actinium, although this classification is sometimes disputed. Similarly to scandium, yttrium, and actinium, the 57 electrons of a lanthanum atom are arranged in the configuration [Xe]5d6s, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s subshells to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas xenon. Some lanthanum(II) compounds are also known, but they are much less stable.

text: Lanthanum is the first element and prototype of the lanthanide series. In the periodic table, it appears to the right of the

text: alkaline earth metal

text: barium

text: and to the left of the lanthanide cerium. Lanthanum is often considered to be a

text: group 3 element

text: , along with its lighter

text: congeners

text: scandium

text: and

text: yttrium

text: and its heavier congener, the radioactive

text: actinium

text: , although this classification is sometimes disputed. Similarly to scandium, yttrium, and actinium, the 57 electrons of a lanthanum atom are arranged in the

text: configuration

text: [Xe]5d6s, with three valence electrons outside the noble gas core. In chemical reactions, lanthanum almost always gives up these three valence electrons from the 5d and 6s

text: subshells

text: to form the +3 oxidation state, achieving the stable configuration of the preceding noble gas

text: xenon

text: . Some lanthanum(II) compounds are also known, but they are much less stable.

text: Electron affinity generally increases across a period. This is caused by the filling of the valence shell of the atom; a group 17 atom releases more energy than a group 1 atom on gaining an electron because it obtains a filled valence shell and is therefore more stable.

text: Many of the symbols are drawn from existing character sets or ISO or other national and international standards. The Unicode Standard states that "The universe of symbols is rich and open-ended." This makes the issue of what symbols to encode and how symbols should be encoded more complicated than the issues surrounding writing systems. Unicode focuses on symbols that make sense in a one-dimensional plain-text context. For example, the typical two-dimensional arrangement of electronic diagram symbols justifies their exclusion. (Box-drawing characters are a partial exception, for legacy purposes, and a number of electronic diagram symbols are indeed encoded in Unicode's Miscellaneous Technical block.) For adequate treatment in plain text, symbols must also be displayable in a monochromatic setting. Even with these limitations monochromatic, one-dimensional and standards-based the domain of potential Unicode symbols is extensive. (However, emojis ideograms, graphic symbols that where admitted into Unicode, allow colors while the colors are not standardized.)

text: Many of the symbols are drawn from existing character sets or

entity_name: International Organization for Standardization

text: ISO

text: or other national and international standards. The Unicode Standard states that "The universe of symbols is rich and open-ended." This makes the issue of what symbols to encode and how symbols should be encoded more complicated than the issues surrounding writing systems. Unicode focuses on symbols that make sense in a one-dimensional plain-text context. For example, the typical two-dimensional arrangement of electronic diagram symbols justifies their exclusion. (

text: Box-drawing character

text: s are a partial exception, for legacy purposes, and a number of electronic diagram symbols are indeed encoded in Unicode's

text: Miscellaneous Technical

text: block.) For adequate treatment in plain text, symbols must also be displayable in a

text: monochromatic

text: setting. Even with these limitations monochromatic, one-dimensional and standards-based the domain of potential Unicode symbols is extensive. (However,

text: emoji

text: s

text: ideogram

text: s,

text: graphic

text: symbol

text: s that where admitted into Unicode, allow colors while the colors are not standardized.)

text: 10 June 2009 – Bourg-lès-Valence to Valence, 42.4 km (ITT)

text: 10 June 2009 –

text: Bourg-lès-Valence

text: to

text: Valence

text: , 42.4 km (

text: ITT

text: In contrast to the Fabre or Bechgaard salts universal phase diagrams for all the ET-based salts have only been proposed yet. For sure such a phase diagram wouldn’t only depend on temperature and pressure (i.e. bandwidth) but also on electronic correlations. In addition to the superconducting ground state these materials show charge-order, antiferromagnetism or remain metallic down to lowest temperatures. One compound is even predicted to be a spin liquid.

text: In contrast to the Fabre or Bechgaard salts universal

text: phase diagrams

text: for all the ET-based salts have only been proposed yet. For sure such a phase diagram wouldn’t only depend on temperature and pressure (i.e. bandwidth) but also on

text: electronic correlation

text: s. In addition to the superconducting ground state these materials show

text: charge-order

text: antiferromagnetism

text: or remain

text: metal

text: lic down to lowest temperatures. One compound is even predicted to be a

text: spin liquid

text: An extended set of diagrams and moves are used for describing 4-manifolds.A framed link in the 3-sphere encodes instructions for attaching 2-handles to the 4-ball.(The 3-dimensional boundary of this manifold is the 3-manifold interpretation of the link diagram mentioned above.)  1-handles are denoted by either (a) a pair of 3-balls (the attaching region of the 1-handle) or, more commonly, (b) unknotted circles with dots. The dot indicates that a neighborhood of a standard 2-disk with boundary the dotted circle is to be excised from the interior of the 4-ball.  Excising this 2-handle is equivalent to adding a 1-handle. 3-handles and 4-handles are usually not indicated in the diagram.

text: An extended set of diagrams and moves are used for describing

text: s.A framed link in the 3-sphere encodes instructions for attaching 2-handles to the 4-ball.(The 3-dimensional boundary of this manifold is the 3-manifold interpretation of the link diagram mentioned above.)  1-handles are denoted by either (a) a pair of 3-balls (the attaching region of the 1-handle) or, more commonly, (b) unknotted circles with dots. The dot indicates that a neighborhood of a standard 2-disk with boundary the dotted circle is to be excised from the interior of the 4-ball.  Excising this 2-handle is equivalent to adding a 1-handle. 3-handles and 4-handles are usually not indicated in the diagram.

text: Valence electrons are the electrons in the outermost electron shell of an isolated atom of an element. Sometimes, it is also regarded as the basis of Modern Periodic Table. In a period, the number of valence electrons increases (mostly for light metal/elements) as we move from left to right side. However, in a group this periodic trend is constant, that is the number of valence electrons remains the same.

text: Valence electrons

text: are the electrons in the outermost electron shell of an isolated atom of an

text: element

text: . Sometimes, it is also regarded as the basis of Modern

text: Periodic Table

text: . In a period, the number of valence electrons increases (mostly for

text: light metal

text: elements

text: ) as we move from left to right side. However, in a group this periodic trend is constant, that is the number of valence electrons remains the same.

text: The noble gases have full valence electron shells. Valence electrons are the outermost electrons of an atom and are normally the only electrons that participate in chemical bonding. Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons. However, heavier noble gases such as radon are held less firmly together by electromagnetic force than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases.

text: The noble gases have full valence

text: electron shells

text: Valence electron

text: s are the outermost

text: electron

text: s of an atom and are normally the only electrons that participate in

text: chemical bond

text: ing. Atoms with full valence electron shells are extremely stable and therefore do not tend to form chemical bonds and have little tendency to gain or lose electrons. However, heavier noble gases such as radon are held less firmly together by

text: electromagnetic force

text: than lighter noble gases such as helium, making it easier to remove outer electrons from heavy noble gases.

text: Donor impurity atoms have more valence electrons than the atoms they replace in the intrinsic semiconductor lattice.  Donor impurities "donate" their extra valence electrons to a semiconductor's conduction band, providing excess electrons to the intrinsic semiconductor.  Excess electrons increase the electron carrier concentration (n) of the semiconductor, making it n-type.

text: Donor impurity atoms have more

text: valence electron

text: s than the atoms they replace in the intrinsic semiconductor lattice.  Donor impurities "donate" their extra valence electrons to a semiconductor's conduction band, providing excess electrons to the intrinsic semiconductor.  Excess electrons increase the electron carrier concentration (n) of the semiconductor, making it n-type.

text: In the bond valence model, the valence of an atom, V, is defined as the number of electrons the atom uses for bonding.  This is equal to the number of electrons in its valence shell if all the valence shell electrons are used for bonding.  If they are not, the remainder will form non-bonding electron pairs, usually known as lone pairs.

text: The diagram shows a schematic representation of an NPN transistor connected to two voltage sources.  To make the transistor conduct appreciable current (on the order of 1 mA) from C to E, V must be above a minimum value sometimes referred to as the cut-in voltage. The cut-in voltage is usually about 650 mV for silicon BJTs at room temperature but can be different depending on the type of transistor and its biasing. This applied voltage causes the lower P-N junction to 'turn on', allowing a flow of electrons from the emitter into the base. In active mode, the electric field existing between base and collector (caused by V) will cause the majority of these electrons to cross the upper P-N junction into the collector to form the collector current I. The remainder of the electrons recombine with holes, the majority carriers in the base, making a current through the base connection to form the base current, I. As shown in the diagram, the emitter current, I, is the total transistor current, which is the sum of the other terminal currents, (i.e., I = I + I).

text: The diagram shows a schematic representation of an NPN transistor connected to two voltage sources.  To make the transistor conduct appreciable current (on the order of 1 mA) from C to E, V must be above a minimum value sometimes referred to as the cut-in voltage. The cut-in voltage is usually about 650 mV for silicon BJTs at

text: room temperature

text: but can be different depending on the type of transistor and its

text: biasing

text: . This applied voltage causes the lower P-N junction to 'turn on', allowing a flow of electrons from the emitter into the base. In active mode, the electric field existing between base and collector (caused by V) will cause the majority of these electrons to cross the upper P-N junction into the collector to form the collector current I. The remainder of the electrons recombine with holes, the majority carriers in the base, making a current through the base connection to form the base current, I. As shown in the diagram, the emitter current, I, is the total transistor current, which is the sum of the other terminal currents, (i.e., I = I + I).

text: In semiconductor detectors, ionizing radiation is measured by the number of charge carriers set free in the detector material which is arranged between two electrodes, by the radiation. Ionizing radiation produces free electrons and holes. The number of electron-hole pairs is proportional to the energy of the radiation to the semiconductor.  As a result, a number of electrons are transferred from the valence band to the conduction band, and an equal number of holes are created in the valence band.  Under the influence of an electric field, electrons and holes travel to the electrodes, where they result in a pulse that can be measured in an outer circuit, as described by the Shockley-Ramo theorem. The holes travel in the opposite direction and can also be measured. As the amount of energy required to create an electron-hole pair is known, and is independent of the energy of the incident radiation, measuring the number of electron-hole pairs allows the intensity of the incident radiation to be determined.

text: In semiconductor detectors, ionizing radiation is measured by the number of

text: charge carrier

text: s set free in the detector material which is arranged between two

text: electrode

text: s, by the radiation. Ionizing radiation produces free

text: electron

text: s and

text: holes

text: . The number of electron-hole pairs is proportional to the energy of the radiation to the semiconductor.  As a result, a number of electrons are transferred from the

text: valence band

text: to the

text: conduction band

text: , and an equal number of holes are created in the valence band.  Under the influence of an

text: electric field

text: , electrons and holes travel to the electrodes, where they result in a pulse that can be measured in an outer

text: circuit

text: , as described by the

text: Shockley-Ramo theorem

text: . The holes travel in the opposite direction and can also be measured. As the amount of energy required to create an electron-hole pair is known, and is independent of the energy of the incident radiation, measuring the number of electron-hole pairs allows the intensity of the incident radiation to be determined.

text: Valence electrons are also responsible for the electrical conductivity of an element; as a result, an element may be classified as a metal, a nonmetal, or a semiconductor (or metalloid).

text: Valence electrons are also responsible for the

text: electrical conductivity

text: of an element; as a result, an element may be classified as a

text: metal

text: , a

text: nonmetal

text: , or a

text: semiconductor

text: (or

text: metalloid

text: Figure 2 shows a simplified diagram of a quantum-dot cell. If the cell is charged with two electrons, each free to tunnel to any site in the cell, these electrons will try to occupy the furthest possible site with respect to each other due to mutual electrostatic repulsion. Therefore, two distinguishable cell states exist. Figure 3 shows the two possible minimum energy states of a quantum-dot cell. The state of a cell is called its polarization, denoted as P. Although arbitrarily chosen, using cell polarization P = -1 to represent logic “0” and P = +1 to represent logic “1” has become standard practice.

text: Figure 2 shows a simplified diagram of a quantum-dot cell. If the cell is charged with two electrons, each free to tunnel to any site in the cell, these electrons will try to occupy the furthest possible site with respect to each other due to mutual

text: electrostatic repulsion

text: . Therefore, two distinguishable cell states exist. Figure 3 shows the two possible minimum

text: energy states

text: of a quantum-dot cell. The state of a cell is called its

text: polarization

text: , denoted as P. Although arbitrarily chosen, using cell polarization P = -1 to represent

text: logic

text: “0” and P = +1 to represent logic “1” has become standard practice.

text: Instead of analyzing the movement of an empty state in the valence band as the movement of many separate electrons, a single equivalent imaginary particle called a "hole" is considered. In an applied electric field, the electrons move in one direction, corresponding to the hole moving in the other. If a hole associates itself with a neutral atom, that atom loses an electron and becomes positive. Therefore, the hole is taken to have positive charge of +e, precisely the opposite of the electron charge.

text: Instead of analyzing the movement of an empty state in the valence band as the movement of many separate electrons, a single equivalent imaginary particle called a "hole" is considered. In an applied

text: electric field

text: , the electrons move in one direction, corresponding to the hole moving in the other. If a hole associates itself with a neutral atom, that atom loses an electron and becomes positive. Therefore, the hole is taken to have positive

text: charge

text: of +e, precisely the opposite of the electron charge.

text: In solid-state physics, a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in electron volts) between the top of the valence band and the bottom of the conduction band in insulators and semiconductors.  It is the energy required to promote a valence electron bound to an atom to become a conduction electron, which is free to move within the crystal lattice and serve as a charge carrier to conduct electric current.  It is closely related to the HOMO/LUMO gap in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow (see carrier generation and recombination). Therefore, the band gap is a major factor determining the electrical conductivity of a solid. Substances with large band gaps are generally insulators, those with smaller band gaps are semiconductors, while conductors either have very small band gaps or none, because the valence and conduction bands overlap.

text: In

text: solid-state physics

text: , a band gap, also called an energy gap or bandgap, is an energy range in a

text: solid

text: where no

text: electron

text: states can exist. In graphs of the

text: electronic band structure

text: of solids, the band gap generally refers to the energy difference (in

text: electron volt

text: s) between the top of the

text: valence band

text: and the bottom of the

text: conduction band

text: in

text: insulators

text: and

text: semiconductor

text: s.  It is the energy required to promote a

text: valence electron

text: bound to an atom to become a

text: conduction electron

text: , which is free to move within the crystal lattice and serve as a charge carrier to conduct

text: electric current

text: .  It is closely related to the

text: HOMO/LUMO gap

text: in chemistry. If the valence band is completely full and the conduction band is completely empty, then electrons cannot move in the solid; however, if some electrons transfer from the valence to the conduction band, then current can flow (see

text: carrier generation and recombination

text: ). Therefore, the band gap is a major factor determining the

text: electrical conductivity

text: of a solid. Substances with large band gaps are generally

text: insulators

text: , those with smaller band gaps are

text: semiconductor

text: s, while

text: conductors

text: either have very small band gaps or none, because the valence and conduction bands overlap.

text: The most widespread application of electron configurations is in the rationalization of chemical properties, in both inorganic and organic chemistry. In effect, electron configurations, along with some simplified form of molecular orbital theory, have become the modern equivalent of the valence concept, describing the number and type of chemical bonds that an atom can be expected to form.

text: The most widespread application of electron configurations is in the rationalization of chemical properties, in both inorganic and organic chemistry. In effect, electron configurations, along with some simplified form of

text: molecular orbital theory

text: , have become the modern equivalent of the

text: valence

text: concept, describing the number and type of chemical bonds that an atom can be expected to form.

text: Several physical properties of CMPs can be attributed to their extended conjugation or microporosity. Much like conductive metals, conjugated polymers exhibit electronic bands.  The electrons of the conjugated system occupy the valence band and removal of electrons from this band or addition of electrons to the higher energy conductive band can lead to conductivity.  Conjugated materials can in many cases  absorb visible light because of their delocalized π-system.  These properties have led to applications in organic electronics and organic photonics.  CMPs exhibit a high level of tunability with respect to surface area and pore size.  Monomers can be designed with longer rigid moieties to increase surface area.  The series of CMP-1,4 to CMP-5 shows a dramatic increase in surface area from 500 m/g to 1000 m/g.  The increase in surface area can drastically improve their ability to be filled with various organic and inorganic compounds for different applications.  The increased surface area can also improve gas sorption capabilities.

text: Several physical properties of CMPs can be attributed to their extended conjugation or microporosity. Much like conductive metals, conjugated polymers exhibit

text: electronic bands

text: .  The electrons of the conjugated system occupy the

text: valence band

text: and removal of electrons from this band or addition of electrons to the higher energy

text: conductive band

text: can lead to conductivity.  Conjugated materials can in many cases  absorb visible light because of their delocalized π-system.  These properties have led to applications in

text: organic electronics

text: and

text: organic photonics

text: .  CMPs exhibit a high level of tunability with respect to surface area and pore size.  Monomers can be designed with longer rigid moieties to increase surface area.  The series of CMP-1,4 to CMP-5 shows a dramatic increase in surface area from 500 m/g to 1000 m/g.  The increase in surface area can drastically improve their ability to be filled with various organic and inorganic compounds for different applications.  The increased surface area can also improve gas sorption capabilities.

text: CO, ,  and  are isoelectronic because each has two nuclei and 10 valence electrons, with each atom considered to have 5 of them (a lone-pair and a triple-bond). Isoelectronicity does not relate to formal charge on the atoms in a structure: these all have the same configuration even though carbon monoxide has formal charges that are balanced (:C≡O:) whereas dinitrogen has each atom neutral (:NN:) and nitrosonium has an overall net charge.

text: CO

text: , ,  and  are isoelectronic because each has two nuclei and 10 valence electrons, with each atom considered to have 5 of them (a lone-pair and a triple-bond). Isoelectronicity does not relate to

text: formal charge

text: on the atoms in a structure: these all have the same configuration even though carbon monoxide has formal charges that are balanced (:C≡O:) whereas dinitrogen has each atom neutral (:NN:) and nitrosonium has an overall net charge.

text: An atom with a closed shell of valence electrons (corresponding to an electron configuration sp) tends to be chemically inert. Atoms with one or two more valence electrons than are needed for a "closed" shell are highly reactive due to following reasons.

text: An atom with a

text: closed shell

text: of valence electrons (corresponding to an

text: electron configuration

text: sp) tends to be

text: chemically inert

text: . Atoms with one or two more valence electrons than are needed for a "closed" shell are highly reactive due to following reasons.

text: The overall geometry is further refined by distinguishing between bonding and nonbonding electron pairs. The bonding electron pair shared in a sigma bond with an adjacent atom lies further from the central atom than a nonbonding (lone) pair of that atom, which is held close to its positively charged nucleus. VSEPR theory therefore views repulsion by the lone pair to be greater than the repulsion by a bonding pair. As such, when a molecule has 2 interactions with different degrees of repulsion, VSEPR theory predicts the structure where lone pairs occupy positions that allow them to experience less repulsion. Lone pair–lone pair (lp–lp) repulsions are considered stronger than lone pair–bonding pair (lp–bp) repulsions, which in turn are considered stronger than bonding pair–bonding pair (bp–bp) repulsions, distinctions that then guide decisions about overall geometry when 2 or more non-equivalent positions are possible. For instance, when 5 valence electron pairs surround a central atom, they adopt a trigonal bipyramidal molecular geometry with two collinear axial positions and three equatorial positions. An electron pair in an axial position has three close equatorial neighbors only 90° away and a fourth much farther at 180°, while an equatorial electron pair has only two adjacent pairs at 90° and two at 120°. The repulsion from the close neighbors at 90° is more important, so that the axial positions experience more repulsion than the equatorial positions; hence, when there are lone pairs, they tend to occupy equatorial positions as shown in the diagrams of the next section for steric number five.

text: The overall geometry is further refined by distinguishing between bonding and nonbonding electron pairs. The bonding electron pair shared in a

text: sigma bond

text: with an adjacent atom lies further from the central atom than a nonbonding (lone) pair of that atom, which is held close to its positively charged nucleus. VSEPR theory therefore views repulsion by the lone pair to be greater than the repulsion by a bonding pair. As such, when a molecule has 2 interactions with different degrees of repulsion, VSEPR theory predicts the structure where lone pairs occupy positions that allow them to experience less repulsion. Lone pair–lone pair (lp–lp) repulsions are considered stronger than lone pair–bonding pair (lp–bp) repulsions, which in turn are considered stronger than bonding pair–bonding pair (bp–bp) repulsions, distinctions that then guide decisions about overall geometry when 2 or more non-equivalent positions are possible. For instance, when 5 valence electron pairs surround a central atom, they adopt a

text: trigonal bipyramidal molecular geometry

text: with two collinear axial positions and three equatorial positions. An electron pair in an axial position has three close equatorial neighbors only 90° away and a fourth much farther at 180°, while an equatorial electron pair has only two adjacent pairs at 90° and two at 120°. The repulsion from the close neighbors at 90° is more important, so that the axial positions experience more repulsion than the equatorial positions; hence, when there are lone pairs, they tend to occupy equatorial positions as shown in the diagrams of the next section for steric number five.

text: The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode oxidize, i.e. they give up both their valence electrons to become positively charged ions. As the zinc ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. When the cell is connected in an external electrical circuit, the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an electric current.

text: The chemical process which produces electricity in a Leclanché cell begins when zinc atoms on the surface of the anode

text: oxidize

text: , i.e. they give up both their valence electrons to become positively charged

text: ions

text: . As the zinc ions move away from the anode, leaving their electrons on its surface, the anode becomes more negatively charged than the cathode. When the cell is connected in an external

text: electrical circuit

text: , the excess electrons on the zinc anode flow through the circuit to the carbon rod, the movement of electrons forming an

text: electric current

text: Chemical structure refers to both molecular geometry and electronic structure. The structure can be represented by a variety of diagrams called structural formulas. Lewis structures use a dot notation to represent the valence electrons for an atom; these are the electrons that determine the role of the atom in chemical reactions. Bonds between atoms can be represented by lines with one line for each pair of electrons that is shared. In a simplified version of such a diagram, called a skeletal formula, only carbon-carbon bonds and functional groups are shown.

text: Chemical structure refers to both molecular geometry and electronic structure. The structure can be represented by a variety of diagrams called

text: structural formula

text: s.

text: Lewis structure

text: s use a dot notation to represent the

text: valence electron

text: s for an atom; these are the electrons that determine the role of the atom in chemical reactions. Bonds between atoms can be represented by lines with one line for each pair of electrons that is shared. In a simplified version of such a diagram, called a

text: skeletal formula

text: , only carbon-carbon bonds and functional groups are shown.

text: In organic chemistry, when a molecule with a planar ring obeys Hückel's rule, where the number of π electrons fit the formula 4n + 2 (where n is an integer), it attains extra stability and symmetry. In benzene, the prototypical aromatic compound, there are 6 π bonding electrons (n = 1, 4n + 2 = 6). These occupy three delocalized π molecular orbitals (molecular orbital theory) or form conjugate π bonds in two resonance structures that linearly combine (valence bond theory), creating a regular hexagon exhibiting a greater stabilization than the hypothetical 1,3,5-cyclohexatriene.

text: In

text: organic chemistry

text: , when a molecule with a planar ring obeys

text: Hückel's rule

text: , where the number of

text: π electrons

text: fit the formula 4n + 2 (where n is an integer), it attains extra stability and symmetry. In

text: benzene

text: , the prototypical aromatic compound, there are 6 π bonding electrons (n = 1, 4n + 2 = 6). These occupy three delocalized π molecular orbitals (

text: molecular orbital theory

text: ) or form conjugate π bonds in two resonance structures that linearly combine (

text: valence bond theory

text: ), creating a regular hexagon exhibiting a greater stabilization than the hypothetical 1,3,5-cyclohexatriene.

text: X-ray diffraction confirms that all six carbon-carbon bonds in benzene are the same length, 140 pm (1.40 Å) – intermediate between the bond lengths of single (154 pm) and double (134 pm) carbon-carbon bonds.  This is consistent with delocalization of the electrons from the double bonds in Kekulé's structures equally between each of the six carbon atoms which form a planar ring.  The molecular orbital theory description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond theory description involves a superposition of resonance structures.  This electronic structure provides benzene with unusual stability and contributes to the molecular and chemical properties which are now known as aromaticity.  To accurately reflect the nature of the bonding as having neither single nor double bonds, but rather something in between, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms, similar to the structure first illustrated by Thiele.

text: X-ray diffraction

text: confirms that all six carbon-carbon bonds in benzene are the same length, 140

text: pm

text: Å

text: ) – intermediate between the

text: bond length

text: s of single (154 pm) and double (134 pm) carbon-carbon bonds.  This is consistent with

text: delocalization

text: of the electrons from the double bonds in Kekulé's structures equally between each of the six carbon atoms which form a planar ring.  The

text: molecular orbital theory

text: description involves the formation of three delocalized

text: π orbitals

text: spanning all six carbon atoms, while the

text: valence bond theory

text: description involves a superposition of resonance structures.  This electronic structure provides benzene with unusual stability and contributes to the molecular and chemical properties which are now known as

text: aromaticity

text: .  To accurately reflect the nature of the bonding as having neither single nor double bonds, but rather something in between, benzene is often depicted with a circle inside a hexagonal arrangement of carbon atoms, similar to the structure first illustrated by Thiele.

text: A. Louis Allred and Eugene G. Rochow considered that electronegativity should be related to the charge experienced by an electron on the "surface" of an atom: The higher the charge per unit area of atomic surface the greater the tendency of that atom to attract electrons. The effective nuclear charge, Z, experienced by valence electrons can be estimated using Slater's rules, while the surface area of an atom in a molecule can be taken to be proportional to the square of the covalent radius, r. When r is expressed in picometres,

text: A. Louis Allred and

text: Eugene G. Rochow

text: considered that electronegativity should be related to the charge experienced by an electron on the "surface" of an atom: The higher the charge per unit area of atomic surface the greater the tendency of that atom to attract electrons. The

text: effective nuclear charge

text: , Z, experienced by

text: valence electron

text: s can be estimated using

text: Slater's rules

text: , while the surface area of an atom in a molecule can be taken to be proportional to the square of the

text: covalent radius

text: , r. When r is expressed in

text: picometre

text: s,

text: The "periodic" nature of the filling of orbitals, as well as emergence of the s, p, d and f "blocks", is more obvious if this order of filling is given in matrix form, with increasing principal quantum numbers starting the new rows ("periods") in the matrix. Then, each subshell (composed of the first two quantum numbers) is repeated as many times as required for each pair of electrons it may contain. The result is a compressed periodic table, with each entry representing two successive elements:

text: When placed in the sun, photons of the sunlight can excite electrons on the p-type side of the semiconductor, a process known as photoexcitation. In silicon, sunlight can provide enough energy to push an electron out of the lower-energy valence band into the higher-energy conduction band. As the name implies, electrons in the conduction band are free to move about the silicon. When a load is placed across the cell as a whole, these electrons will flow out of the p-type side into the n-type side, lose energy while moving through the external circuit, and then flow back into the p-type material where they can once again re-combine with the valence-band hole they left behind. In this way, sunlight creates an electric current.

text: When placed in the sun,

text: photon

text: s of the sunlight can excite electrons on the p-type side of the semiconductor, a process known as

text: photoexcitation

text: . In silicon, sunlight can provide enough energy to push an electron out of the lower-energy

text: valence band

text: into the higher-energy

text: conduction band

text: . As the name implies, electrons in the conduction band are free to move about the silicon. When a load is placed across the cell as a whole, these electrons will flow out of the p-type side into the n-type side, lose energy while moving through the external circuit, and then flow back into the p-type material where they can once again re-combine with the valence-band hole they left behind. In this way, sunlight creates an electric current.

text: In the context of atomic orbitals, an open shell is a valence shell which is not completely filled with electrons or that has not given all of its valence electrons through chemical bonds with other atoms or molecules during a chemical reaction.  Atoms generally reach a noble gas configuration in a molecule.  The noble gases (He, Ne, Ar, Kr, Xe, Rn) are less reactive and have configurations 1s (He),1s2s2p (Ne), 1s2s2p3s3p (Ar), etc.

text: In the context of

text: atomic orbital

text: s, an open shell is a

text: valence shell

text: which is not completely filled with

text: electron

text: s or that has not given all of its valence electrons through

text: chemical bond

text: s with other

text: atom

text: s or

text: molecule

text: s during a chemical reaction.  Atoms generally reach a

text: noble gas

text: configuration in a molecule.  The noble gases (

text: He

text: Ne

text: Ar

text: Kr

text: Xe

text: Rn

text: ) are less reactive and have configurations 1s (He),1s2s2p (Ne), 1s2s2p3s3p (Ar), etc.

text: However other models describe the bonding using only s and p orbitals in agreement with the octet rule. A valence bond description of PF uses resonance between different PF F structures, so that each F is bonded by a covalent bond in four structures and an ionic bond in one structure. Each resonance structure has eight valence electrons on P. A molecular orbital theory description considers the highest occupied molecular orbital to be a non-bonding orbital localized on the five fluorine atoms, in addition to four occupied bonding orbitals, so again there are only eight valence electrons on the phosphorus. The validity of the octet rule for hypervalent molecules is further supported by ab initio molecular orbital calculations, which show that the contribution of d functions to the bonding orbitals is small.

text: However other models describe the bonding using only s and p orbitals in agreement with the octet rule. A

text: valence bond

text: description of PF uses

text: resonance

text: between different PF F structures, so that each F is bonded by a covalent bond in four structures and an ionic bond in one structure. Each resonance structure has eight valence electrons on P. A

text: molecular orbital theory

text: description considers the

text: highest occupied molecular orbital

text: to be a non-bonding orbital localized on the five fluorine atoms, in addition to four occupied bonding orbitals, so again there are only eight valence electrons on the phosphorus. The validity of the octet rule for hypervalent molecules is further supported by

text: ab initio molecular orbital calculations

text: , which show that the contribution of d functions to the bonding orbitals is small.

text: The farther right in each transition metal series, the lower the energy of an electron in a d subshell and the less such an electron has the properties of a valence electron. Thus, although a nickel atom has, in principle, ten valence electrons (4s 3d), its oxidation state never exceeds four. For zinc, the 3d subshell is complete and behaves similarly to core electrons.

text: The farther right in each transition metal series, the lower the energy of an electron in a d subshell and the less such an electron has the properties of a valence electron. Thus, although a

text: nickel

text: atom has, in principle, ten valence electrons (4s 3d), its oxidation state never exceeds four. For

text: zinc

text: , the 3d subshell is complete and behaves similarly to core electrons.

text: As such, the electrical conductivity of a solid depends on its capability to flow electrons from the valence to the conduction band. Hence, in the case of a semimetal with an overlap region, the electrical conductivity is high. If there is a small band gap (E), then the flow of electrons from valence to conduction band is possible only if an external energy (thermal, etc.) is supplied; these groups with small E are called semiconductors. If the E is sufficiently high, then the flow of electrons from valence to conduction band becomes negligible under normal conditions; these groups are called insulators.

text: As such, the

text: electrical conductivity

text: of a solid depends on its capability to flow electrons from the valence to the conduction band. Hence, in the case of a semimetal with an overlap region, the electrical conductivity is high. If there is a small band gap (E), then the flow of electrons from valence to conduction band is possible only if an external energy (thermal, etc.) is supplied; these groups with small E are called

text: semiconductors

text: . If the E is sufficiently high, then the flow of electrons from valence to conduction band becomes negligible under normal conditions; these groups are called

text: insulators

text: The valence of a bond, S, is defined as the number of electron pairs forming the bond.  In general this is not an integral number.  Since each of the terminal atoms contributes equal numbers of electrons to the bond, the bond valence is also equal to the number of valence electrons that each atom contributes.  Further, since within each atom, the negatively charged valence shell is linked to the positively charged core by an electrostatic flux that is equal to the charge on the valence shell, it follows that the bond valence is also equal to the electrostatic flux that links the core to the electrons forming the bond.  The bond valence is thus equal to three different quantities: the number of electrons each atom contributes to the bond, the number of electron pairs that form the bond, and the electrostatic flux linking each core to the bonding electron pair.

text: Not all binary alloys have eutectic points because the valence electrons of the component species are not always compatible, in any mixing ratio, to form a new type of joint crystal lattice. For example, in the silver-gold system the melt temperature (liquidus) and freeze temperature (solidus) "meet at the pure element endpoints of the atomic ratio axis while slightly separating in the mixture region of this axis".

text: Not all

text: binary alloy

text: s have eutectic points because the

text: valence electron

text: s of the component species are not always compatible, in any mixing ratio, to form a new type of joint crystal lattice. For example, in the silver-gold system the melt temperature (

text: liquidus

text: ) and freeze temperature (

text: solidus

text: ) "meet at the pure element endpoints of the atomic ratio axis while slightly separating in the mixture region of this axis".

text: In molecular orbital theory, the main alternative to valence bond theory, the equivalent of the symmetry-adapted linear combination role of resonance is the linear combination of atomic orbitals. In MO theory, the molecular orbitals (MOs) are approximated as sums of all the atomic orbitals (AOs) on all the atoms; there are as many MOs as AOs. Each AO has a weighting coefficient c that indicates the AO's contribution to a particular MO. For example, in benzene, the MO model gives us 6 π MOs which are combinations of the 2p AOs on each of the 6 C atoms. Thus, each π MO is delocalized over the whole benzene molecule and any electron occupying an MO will be delocalized over the whole molecule. This MO interpretation has inspired the picture of the benzene ring as a hexagon with a circle inside. When describing benzene, the VB concept of localized sigma 'bonds' and the MO concept of 'delocalized' π electrons are frequently combined in elementary chemistry courses.

text: In

text: molecular orbital theory

text: , the main alternative to

text: valence bond theory

text: , the equivalent of the symmetry-adapted linear combination role of resonance is the

text: linear combination of atomic orbitals

text: . In MO theory, the molecular orbitals (MOs) are approximated as sums of all the atomic orbitals (AOs) on all the atoms; there are as many MOs as AOs. Each AO has a weighting coefficient c that indicates the AO's contribution to a particular MO. For example, in benzene, the MO model gives us 6 π MOs which are combinations of the 2p AOs on each of the 6 C atoms. Thus, each π MO is delocalized over the whole benzene molecule and any electron occupying an MO will be delocalized over the whole molecule. This MO interpretation has inspired the picture of the benzene ring as a hexagon with a circle inside. When describing benzene, the VB concept of localized sigma 'bonds' and the MO concept of 'delocalized' π electrons are frequently combined in elementary chemistry courses.

text: The valence electrons can be counted using a Lewis electron dot diagram as  shown at the right for carbon dioxide. The electrons shared by the two atoms in a covalent bond are counted twice, once for each atom. In carbon dioxide each oxygen shares four electrons with the central carbon, two (shown in red) from the oxygen itself and two (shown in black) from the carbon. All four of these electrons are counted in both the carbon octet and the oxygen octet.

text: The valence electrons can be counted using a

text: Lewis electron dot diagram

text: as  shown at the right for carbon dioxide. The electrons shared by the two atoms in a

text: covalent bond

text: are counted twice, once for each atom. In carbon dioxide each oxygen shares four electrons with the central carbon, two (shown in red) from the oxygen itself and two (shown in black) from the carbon. All four of these electrons are counted in both the carbon octet and the oxygen octet.

text: By considering the propagation of the negative energy modes of the electron field backward in time, Ernst Stueckelberg reached a pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q. This allowed him to rewrite perturbation theory precisely in the form of diagrams. Richard Feynman later gave an independent systematic derivation of these diagrams from a particle formalism, and they are now called Feynman diagrams. Each line of a diagram represents a particle propagating either backward or forward in time. This technique is the most widespread method of computing amplitudes in quantum field theory today.

text: By considering the propagation of the negative energy modes of the electron field backward in time,

text: Ernst Stueckelberg

text: reached a pictorial understanding of the fact that the particle and antiparticle have equal mass m and spin J but opposite charges q. This allowed him to rewrite

text: perturbation theory

text: precisely in the form of diagrams.

text: Richard Feynman

text: later gave an independent systematic derivation of these diagrams from a particle formalism, and they are now called

text: Feynman diagram

text: s. Each line of a diagram represents a particle propagating either backward or forward in time. This technique is the most widespread method of computing amplitudes in quantum field theory today.

text: The "oxidation state" of an atom in a molecule gives the number of valence electrons it has gained or lost. In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an electronegative atom).

text: The "

text: oxidation

text: state" of an atom in a molecule gives the number of valence electrons it has gained or lost. In contrast to the valency number, the oxidation state can be positive (for an electropositive atom) or negative (for an

text: electronegative

text: atom).

text: Within each group of nonmetals, reactivity decreases with each lower rows of the table (from a light element to a heavy element) in the periodic table, because the valence electrons are at progressively higher energies and thus progressively less tightly bound. In fact, oxygen (the lightest element in group 16) is the most reactive nonmetal after fluorine, even though it is not a halogen, because the valence shell of a halogen is at a higher principal quantum number.

text: Since force = mass × acceleration, a negative-effective-mass electron near the top of the valence band would move the opposite direction as a positive-effective-mass electron near the bottom of the conduction band, in response to a given electric or magnetic force. Therefore, a hole moves this way as well.

text: Inorganic chemistry has greatly benefited from qualitative theories.  Such theories are easier to learn as they require little background in quantum theory.  Within main group compounds, VSEPR theory powerfully predicts, or at least rationalizes, the structures of main group compounds, such as an explanation for why NH is pyramidal whereas ClF is T-shaped.  For the transition metals, crystal field theory allows one to understand the magnetism of many simple complexes, such as why [Fe(CN)] has only one unpaired electron, whereas [Fe(HO)] has five.  A particularly  powerful qualitative approach to assessing the structure and reactivity begins with classifying molecules according to electron counting, focusing on the numbers of valence electrons, usually at the central atom in a molecule.

text: Inorganic chemistry has greatly benefited from qualitative theories.  Such theories are easier to learn as they require little background in quantum theory.  Within main group compounds,

text: VSEPR

text: theory powerfully predicts, or at least rationalizes, the

text: structures

text: of main group compounds, such as an explanation for why NH is pyramidal whereas ClF is T-shaped.  For the transition metals,

text: crystal field theory

text: allows one to understand the magnetism of many simple complexes, such as why

text: [Fe(CN)]

text: has only one unpaired electron, whereas [Fe(HO)] has five.  A particularly  powerful qualitative approach to assessing the structure and reactivity begins with classifying molecules according to

text: electron counting

text: , focusing on the numbers of

text: valence electron

text: s, usually at the central atom in a molecule.

text: A chemical bond can be a covalent bond, an ionic bond, a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, valence bond theory, the Valence Shell Electron Pair Repulsion model (VSEPR), and the concept of oxidation number can be used to explain molecular structure and composition.

text: A chemical bond can be a

text: covalent bond

text: , an

text: ionic bond

text: , a

text: hydrogen bond

text: or just because of

text: Van der Waals force

text: . Each of these kinds of bonds is ascribed to some potential. These potentials create the

text: interaction

text: s which hold atoms together in

text: molecule

text: s or

text: crystal

text: s. In many simple compounds,

text: valence bond theory

text: , the Valence Shell Electron Pair Repulsion model (

text: VSEPR

text: ), and the concept of

text: oxidation number

text: can be used to explain molecular structure and composition.

text: With one more valence electron than diamagnetic TiCl, VCl is a paramagnetic liquid.  It is one of only a few paramagnetic compounds that is liquid at room temperature.

text: With one more valence electron than diamagnetic

text: TiCl

text: , VCl is a paramagnetic liquid.  It is one of only a few paramagnetic compounds that is liquid at room temperature.

text: Being the second period 8 element, unbinilium is predicted to be an alkaline earth metal, below beryllium, magnesium, calcium, strontium, barium, and radium. Each of these elements has two valence electrons in the outermost s-orbital (valence electron configuration ns), which is easily lost in chemical reactions to form the +2 oxidation state: thus the alkaline earth metals are rather reactive elements, with the exception of beryllium due to its small size. Unbinilium is predicted to continue the trend and have a valence electron configuration of 8s. It is therefore expected to behave much like its lighter congeners; however, it is also predicted to differ from the lighter alkaline earth metals in some properties.

text: Being the second

text: period 8 element

text: , unbinilium is predicted to be an alkaline earth metal, below

text: beryllium

text: magnesium

text: calcium

text: strontium

text: barium

text: , and

text: radium

text: . Each of these elements has two

text: valence electron

text: s in the outermost s-orbital (valence electron configuration ns), which is easily lost in chemical reactions to form the +2

text: oxidation state

text: : thus the alkaline earth metals are rather

text: reactive

text: elements, with the exception of beryllium due to its small size. Unbinilium is predicted to continue the trend and have a valence electron configuration of 8s. It is therefore expected to behave much like its lighter

text: congener

text: s; however, it is also predicted to differ from the lighter alkaline earth metals in some properties.

text: A thorium atom has 90 electrons, of which four are valence electrons. Three atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, and 7s. Despite thorium's position in the f-block of the periodic table, it has an anomalous [Rn]6d7s electron configuration in the ground state, as the 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides: thorium's 6d subshells are lower in energy than its 5f subshells, because its 5f subshells are not well-shielded by the filled 6s and 6p subshells and are destabilised. Such unusual behaviour is due to relativistic effects, which are increasingly stronger near the bottom of the periodic table, specifically the relativistic spin–orbit interaction. The closeness in energy levels of the 5f, 6d, and 7s energy levels of thorium result in thorium almost always losing all four of its valence electrons and hence occurring in its highest possible oxidation state of +4. This behaviour is quite distinct from that of its lanthanide congener cerium, for whom +4 is the highest possible state but +3 also plays an important role and is more stable. Therefore, thorium is much more similar to the transition metals zirconium and hafnium than to its true lanthanide congener cerium in its properties such as ionisation energies and redox potentials, and hence also in its chemistry.

text: A thorium atom has 90 electrons, of which four are

text: valence electron

text: s. Three

text: atomic orbital

text: s are theoretically available for the valence electrons to occupy: 5f, 6d, and 7s. Despite thorium's position in the

text: f-block

text: of the periodic table, it has an anomalous [Rn]6d7s electron configuration in the ground state, as the 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides: thorium's 6d subshells are lower in energy than its 5f subshells, because its 5f subshells are not well-shielded by the filled 6s and 6p subshells and are destabilised. Such unusual behaviour is due to

text: relativistic effects

text: , which are increasingly stronger near the bottom of the periodic table, specifically the relativistic

text: spin–orbit interaction

text: . The closeness in energy levels of the 5f, 6d, and 7s energy levels of thorium result in thorium almost always losing all four of its valence electrons and hence occurring in its highest possible oxidation state of +4. This behaviour is quite distinct from that of its lanthanide congener cerium, for whom +4 is the highest possible state but +3 also plays an important role and is more stable. Therefore, thorium is much more similar to the

text: transition metal

text: s zirconium and hafnium than to its true lanthanide congener cerium in its properties such as ionisation energies and redox potentials, and hence also in its chemistry.

text: Transition metal complexes often have spectacular colors caused by electronic transitions by the absorption of light. For this reason they are often applied as pigments. Most transitions that are related to colored metal complexes are either d–d transitions or charge transfer bands.  In a d–d transition, an electron in a d orbital on the metal is excited by a photon to another d orbital of higher energy.  A charge transfer band entails promotion of an electron from a metal-based orbital into an empty ligand-based orbital (Metal-to-Ligand Charge Transfer or MLCT).  The converse also occurs: excitation of an electron in a ligand-based orbital into an empty metal-based orbital (Ligand to Metal Charge Transfer or LMCT).  These phenomena can be observed with the aid of electronic spectroscopy; also known as UV-Vis. For simple compounds with high symmetry, the d–d transitions can be assigned using Tanabe–Sugano diagrams.  These assignments are gaining increased support with computational chemistry.

text: Transition metal complexes often have spectacular colors caused by electronic transitions by the absorption of light. For this reason they are often applied as

text: pigments

text: . Most transitions that are related to colored metal complexes are either d–d transitions or charge transfer bands.  In a d–d transition, an electron in a d orbital on the metal is excited by a photon to another d orbital of higher energy.  A charge transfer band entails promotion of an electron from a metal-based orbital into an empty ligand-based orbital (

text: Metal-to-Ligand Charge Transfer

text: or MLCT).  The converse also occurs: excitation of an electron in a ligand-based orbital into an empty metal-based orbital (

text: Ligand to Metal Charge Transfer

text: or LMCT).  These phenomena can be observed with the aid of electronic spectroscopy; also known as

text: UV-Vis

text: . For simple compounds with high symmetry, the d–d transitions can be assigned using

text: Tanabe–Sugano diagram

text: s.  These assignments are gaining increased support with

text: computational chemistry

text: Although group 12 lies in the d-block of the modern 18-column periodic table, the d electrons of zinc, cadmium, and (almost always) mercury behave as core electrons and do not take part in bonding. This behavior is similar to that of the main-group elements, but is in stark contrast to that of the neighboring group 11 elements (copper, silver, and gold), which also have filled d-subshells in their ground-state electron configuration but behave chemically as transition metals. For example, the bonding in chromium(II) sulfide (CrS) involves mainly the 3d electrons; that in iron(II) sulfide (FeS) involves both the 3d and 4s electrons; but that of zinc sulfide (ZnS) involves only the 4s electrons and the 3d electrons behave as core electrons. Indeed, useful comparison can be made between their properties and the first two members of group 2, beryllium and magnesium, and in earlier short-form periodic table layouts, this relationship is illustrated more clearly. For instance, zinc and cadmium are similar to beryllium and magnesium in their atomic radii, ionic radii, electronegativities, and also in the structure of their binary compounds and their ability to form complex ions with many nitrogen and oxygen ligands, such as complex hydrides and amines. However, beryllium and magnesium are small atoms, unlike the heavier alkaline earth metals and like the group 12 elements (which have a greater nuclear charge but the same number of valence electrons), and the periodic trends down group 2 from beryllium to radium (similar to that of the alkali metals) are not as smooth when going down from beryllium to mercury (which is more similar to that of the p-block main groups) due to the d-block and lanthanide contractions. It is also the d-block and lanthanide contractions that give mercury many of its distinctive properties.

text: Although group 12 lies in the

text: d-block

text: of the modern 18-column periodic table, the d electrons of zinc, cadmium, and (almost always) mercury behave as core electrons and do not take part in bonding. This behavior is similar to that of the

text: main-group element

text: s, but is in stark contrast to that of the neighboring

text: group 11 element

text: s (

text: copper

text: silver

text: , and

text: gold

text: ), which also have filled d-subshells in their ground-state

text: electron configuration

text: but behave chemically as transition metals. For example, the bonding in

text: chromium(II) sulfide

text: (CrS) involves mainly the 3d electrons; that in

text: iron(II) sulfide

text: (FeS) involves both the 3d and 4s electrons; but that of

text: zinc sulfide

text: (ZnS) involves only the 4s electrons and the 3d electrons behave as core electrons. Indeed, useful comparison can be made between their properties and the first two members of

text: group 2

text: beryllium

text: and

text: magnesium

text: , and in earlier short-form periodic table layouts, this relationship is illustrated more clearly. For instance, zinc and cadmium are similar to beryllium and magnesium in their

text: atomic radii

text: ionic radii

text: electronegativities

text: , and also in the structure of their

text: binary compound

text: s and their ability to form complex ions with many

text: nitrogen

text: and

text: oxygen

text: ligand

text: s, such as complex

text: hydride

text: s and

text: amine

text: s. However, beryllium and magnesium are small atoms, unlike the heavier

text: alkaline earth metal

text: s and like the group 12 elements (which have a greater nuclear charge but the same number of

text: valence electron

text: s), and the

text: periodic trend

text: s down group 2 from beryllium to

text: radium

text: (similar to that of the

text: alkali metal

text: s) are not as smooth when going down from beryllium to mercury (which is more similar to that of the p-block main groups) due to the

text: d-block

text: and

text: lanthanide contraction

text: s. It is also the d-block and lanthanide contractions that give mercury many of its distinctive properties.

text: The scintillation process in inorganic materials is due to the electronic band structure found in the crystals. An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap). This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). In case of inorganic scintillators, the activator impurities are typically chosen so that the emitted light is in the visible range or near-UV where photomultipliers are effective. The holes associated with electrons in the conduction band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states, slowed down by reliance on the low-probability forbidden mechanism, again results in light emission (slow component).

text: The scintillation process in inorganic materials is due to the

text: electronic band structure

text: found in the

text: crystal

text: s. An incoming particle can excite an electron from the

text: valence band

text: to either the

text: conduction band

text: or the

text: exciton

text: band (located just below the conduction band and separated from the valence band by an

text: energy gap

text: ). This leaves an associated

text: hole

text: behind, in the valence band. Impurities create electronic levels in the

text: forbidden gap

text: . The excitons are loosely bound

text: electron-hole pair

text: s which wander through the

text: crystal lattice

text: until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). In case of inorganic

text: scintillator

text: s, the activator impurities are typically chosen so that the emitted light is in the visible range or

text: near-UV

text: where

text: photomultiplier

text: s are effective. The holes associated with electrons in the conduction band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain

text: metastable state

text: s not accessible to the excitons. The delayed de-excitation of those metastable impurity states, slowed down by reliance on the low-probability

text: forbidden mechanism

text: , again results in light emission (slow component).

text: In complexation reactions, several ligands react with a metal atom to form a coordination complex. This is achieved by providing lone pairs of the ligand into empty orbitals of the metal atom and forming dipolar bonds. The ligands are Lewis bases, they can be both ions and neutral molecules, such as carbon monoxide, ammonia or water. The number of ligands that react with a central metal atom can be found using the 18-electron rule, saying that the valence shells of a transition metal will collectively accommodate 18 electrons, whereas the symmetry of the resulting complex can be predicted with the crystal field theory and ligand field theory. Complexation reactions also include ligand exchange, in which one or more ligands are replaced by another, and redox processes which change the oxidation state of the central metal atom.

text: In complexation reactions, several

text: ligand

text: s react with a metal atom to form a

text: coordination complex

text: . This is achieved by providing

text: lone pair

text: s of the ligand into empty

text: orbital

text: s of the metal atom and forming

text: dipolar bond

text: s. The ligands are

text: Lewis base

text: s, they can be both ions and neutral molecules, such as carbon monoxide, ammonia or water. The number of ligands that react with a central metal atom can be found using the

text: 18-electron rule

text: , saying that the

text: valence shell

text: s of a

text: transition metal

text: will collectively accommodate 18

text: electron

text: s, whereas the symmetry of the resulting complex can be predicted with the

text: crystal field theory

text: and

text: ligand field theory

text: . Complexation reactions also include

text: ligand exchange

text: , in which one or more ligands are replaced by another, and redox processes which change the oxidation state of the central metal atom.

text: Coffins on Io is the seventh album by avant-garde band Kayo Dot, released on October 15, 2014 through experimental metal label The Flenser. It is a follow up to 2013's Hubardo. It's the first album from Kayo Dot to not be self-released since 2012's Gamma Knife. Coffins on Io marks a notable change in sound. It combines influences of Type O Negative, The Sisters of Mercy, Peter Gabriel, dark wave and other 80s electronic musicians. It combines aspects of electronic music, jazz fusion, post-punk, gothic rock and new wave.  It was produced by Toby Driver.

text: Coffins on Io is the seventh album by

text: avant-garde

text: band

text: Kayo Dot

text: , released on October 15, 2014 through

text: experimental metal

text: label

text: The Flenser

text: . It is a follow up to 2013's

text: Hubardo

text: . It's the first album from Kayo Dot to not be self-released since 2012's

text: Gamma Knife

text: . Coffins on Io marks a notable change in sound. It combines influences of

text: Type O Negative

text: The Sisters of Mercy

text: Peter Gabriel

text: dark wave

text: and other 80s electronic musicians. It combines aspects of

text: electronic music

text: jazz fusion

text: post-punk

text: gothic rock

text: and

text: new wave

text: .  It was produced by Toby Driver.

text: The form of the periodic table is closely related to the electron configuration of the atoms of the elements. For example, all the elements of group 2 have an electron configuration of [E] ns (where [E] is an inert gas configuration), and have notable similarities in their chemical properties. In general, the periodicity of the periodic table in terms of periodic table blocks is clearly due to the number of electrons (2, 6, 10, 14...) needed to fill s, p, d, and f subshells.

text: The form of the

text: periodic table

text: is closely related to the electron configuration of the atoms of the elements. For example, all the elements of

text: group 2

text: have an electron configuration of [E] ns (where [E] is an

text: inert gas

text: configuration), and have notable similarities in their chemical properties. In general, the periodicity of the periodic table in terms of

text: periodic table block

text: s is clearly due to the number of electrons (2, 6, 10, 14...) needed to fill s, p, d, and f subshells.

text: The VSEPR theory also predicts that substitution of a ligand at a central atom by a lone pair of valence electrons leaves the general form of the electron arrangement unchanged with the lone pair now occupying one position. For molecules with five pairs of valence electrons including both bonding pairs and lone pairs, the electron pairs are still arranged in a trigonal bipyramid but one or more equatorial positions is not attached to a ligand atom so that the molecular geometry (for the nuclei only) is different.

text: The minus sign arises because of the sense the current i has been defined in the diagram. With both currents defined going into the dots the sign of M will be positive (the equation would read with a plus sign instead).

text: Actinide chemistry (or actinoid chemistry) is one of the main branches of nuclear chemistry that investigates the processes and molecular systems of the actinides. The actinides chemistry derives its name from the group 3 element actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. The actinide series encompasses the 15 metallic chemical elements with atomic numbers from 89 to 103, actinium through lawrencium.

text: Actinide chemistry (or actinoid chemistry) is one of the main branches of

text: nuclear chemistry

text: that investigates the processes and molecular systems of the

text: actinide

text: s. The actinides chemistry derives its name from the

text: group 3 element

text: actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are

text: f-block

text: electron shell

text: ; lawrencium, a

text: d-block

text: lanthanide

text: s, also mostly

text: f-block

text: valence

text: . The actinide series encompasses the 15 metallic

text: chemical element

text: s with

text: atomic number

text: s from 89 to 103,

text: actinium

text: through

text: lawrencium

text: Bromine is the third halogen, being a nonmetal in group 17 of the periodic table. Its properties are thus similar to those of fluorine, chlorine, and iodine, and tend to be intermediate between those of the two neighbouring halogens, chlorine and iodine. Bromine has the electron configuration [Ar]3d4s4p, with the seven electrons in the fourth and outermost shell acting as its valence electrons. Like all halogens, it is thus one electron short of a full octet, and is hence a strong oxidising agent, reacting with many elements in order to complete its outer shell. Corresponding to periodic trends, it is intermediate in electronegativity between chlorine and iodine (F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66), and is less reactive than chlorine and more reactive than iodine. It is also a weaker oxidising agent than chlorine, but a stronger one than iodine. Conversely, the bromide ion is a weaker reducing agent than iodide, but a stronger one than chloride. These similarities led to chlorine, bromine, and iodine together being classified as one of the original triads of Johann Wolfgang Döbereiner, whose work foreshadowed the periodic law for chemical elements. It is intermediate in atomic radius between chlorine and iodine, and this leads to many of its atomic properties being similarly intermediate in value between chlorine and iodine, such as first ionisation energy, electron affinity, enthalpy of dissociation of the X molecule (X = Cl, Br, I), ionic radius, and X–X bond length. The volatility of bromine accentuates its very penetrating, choking, and unpleasant odour.

text: Bromine is the third

text: halogen

text: , being a

text: nonmetal

text: in group 17 of the periodic table. Its properties are thus similar to those of

text: fluorine

text: chlorine

text: , and

text: iodine

text: , and tend to be intermediate between those of the two neighbouring halogens, chlorine and iodine. Bromine has the electron configuration [Ar]3d4s4p, with the seven electrons in the fourth and outermost shell acting as its

text: valence electron

text: periodic trend

text: s, it is intermediate in

text: electronegativity

text: between chlorine and iodine (F: 3.98, Cl: 3.16, Br: 2.96, I: 2.66), and is less reactive than chlorine and more reactive than iodine. It is also a weaker oxidising agent than chlorine, but a stronger one than iodine. Conversely, the

text: bromide

text: ion is a weaker reducing agent than iodide, but a stronger one than chloride. These similarities led to chlorine, bromine, and iodine together being classified as one of the original triads of

text: Johann Wolfgang Döbereiner

text: , whose work foreshadowed the

text: periodic law

text: for chemical elements. It is intermediate in

text: atomic radius

text: between chlorine and iodine, and this leads to many of its atomic properties being similarly intermediate in value between chlorine and iodine, such as first

text: ionisation energy

text: electron affinity

text: , enthalpy of dissociation of the X molecule (X = Cl, Br, I), ionic radius, and X–X bond length. The volatility of bromine accentuates its very penetrating, choking, and unpleasant odour.

text: The 18-electron rule is a rule used primarily for predicting and rationalizing formulae for stable metal complexes, especially organometallic compounds. The rule is based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs.  This means that, the combination of these nine atomic orbitals with ligand orbitals creates nine molecular orbitals that are either metal-ligand bonding or non-bonding. When a metal complex has 18 valence electrons, it is said to have achieved the same electron configuration as the noble gas in the period. The rule and its exceptions are similar to the application of the octet rule to main group elements. The rule is not helpful for complexes of metals that are not transition metals, and interesting or useful transition metal complexes will violate the rule because of the consequences deviating from the rule bears on reactivity.  The rule was first proposed by American chemist Irving Langmuir in 1921.

text: The 18-electron rule is a rule used primarily for predicting and rationalizing formulae for stable metal complexes, especially

text: organometallic compounds

text: . The rule is based on the fact that the

text: valence shell

text: s of

text: transition metal

text: s consist of nine valence orbitals (one

text: s orbital

text: , three

text: p orbitals

text: and five

text: d orbitals

text: ), which collectively can accommodate 18

text: electron

text: s as either bonding or nonbonding electron pairs.  This means that, the combination of these nine

text: atomic orbitals

text: with

text: ligand

text: orbitals creates nine

text: molecular orbital

text: s that are either metal-ligand bonding or non-bonding. When a metal complex has 18 valence electrons, it is said to have achieved the same electron configuration as the

text: noble gas

text: in the period. The rule and its exceptions are similar to the application of the

text: octet rule

text: to main group elements. The rule is not helpful for complexes of metals that are not transition metals, and interesting or useful transition metal complexes will violate the rule because of the consequences deviating from the rule bears on reactivity.  The rule was first proposed by American chemist

text: Irving Langmuir

text: in 1921.

text: It is important not to over-interpret these diagrams. Nothing is implied about how a particle gets from one point to another. The diagrams do not imply that the particles are moving in straight or curved lines. They do not imply that the particles are moving with fixed speeds. The fact that the photon is often represented, by convention, by a wavy line and not a straight one does not imply that it is thought that it is more wavelike than is an electron. The images are just symbols to represent the actions above: photons and electrons do, somehow, move from point to point and electrons, somehow, emit and absorb photons. We do not know how these things happen, but the theory tells us about the probabilities of these things happening.

text: Certain molecules such as xenon difluoride and sulfur hexafluoride have higher co-ordination numbers than would be possible due to strictly covalent bonding according to the octet rule. This is explained by the three-center four-electron bond ("3c–4e") model which interprets the molecular wavefunction in terms of non-bonding highest occupied molecular orbitals in molecular orbital theory and ionic-covalent resonance in valence bond theory.

text: Certain molecules such as

text: xenon difluoride

text: and

text: sulfur hexafluoride

text: have higher co-ordination numbers than would be possible due to strictly covalent bonding according to the

text: octet rule

text: . This is explained by the

text: three-center four-electron bond

text: ("3c–4e") model which interprets the molecular wavefunction in terms of non-bonding

text: highest occupied molecular orbital

text: s in

text: molecular orbital theory

text: and ionic-covalent

text: resonance

text: in

text: valence bond theory

text: The charged carbon atom in a carbocation is a "sextet", i.e. it has only six electrons in its outer valence shell instead of the eight valence electrons that ensures maximum stability (octet rule). Therefore, carbocations are often reactive, seeking to fill the octet of valence electrons as well as regain a neutral charge. One could reasonably assume a carbocation to have sp hybridization with an empty sp orbital giving positive charge. However, the reactivity of a carbocation more closely resembles sp hybridization with a trigonal planar molecular geometry. An example is the methyl cation, .

text: The charged carbon atom in a carbocation is a "sextet", i.e. it has only six

text: electron

text: s in its outer

text: valence shell

text: instead of the eight valence electrons that ensures maximum stability (

text: octet rule

text: ). Therefore, carbocations are often reactive, seeking to fill the octet of valence electrons as well as regain a neutral

text: charge

text: . One could reasonably assume a carbocation to have sp hybridization with an empty sp orbital giving positive charge. However, the reactivity of a carbocation more closely resembles

text: sp hybridization

text: with a

text: trigonal planar

text: molecular geometry. An example is the methyl cation, .

text: A solid compound containing metals can also be an insulator if the valence electrons of the metal atoms are used to form ionic bonds. For example, although elemental sodium is a metal, solid sodium chloride is an insulator, because the valence electron of sodium is transferred to chlorine to form an ionic bond, and thus that electron cannot be moved easily.

text: A solid compound containing metals can also be an insulator if the valence electrons of the metal atoms are used to form

text: ionic bond

text: s. For example, although elemental

text: sodium

text: is a metal, solid

text: sodium chloride

text: is an insulator, because the valence electron of sodium is transferred to chlorine to form an ionic bond, and thus that electron cannot be moved easily.

text: Lewis structures (also known as Lewis dot diagrams, Lewis dot formulas, Lewis dot structures, and electron dot structures) are diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule. A Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. The Lewis structure was named after Gilbert N. Lewis, who introduced it in his 1916 article The Atom and the Molecule. Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.

text: Lewis structures (also known as Lewis dot diagrams, Lewis dot formulas, Lewis dot structures, and electron dot structures) are diagrams that show the

text: bonding

text: between

text: atom

text: s of a

text: molecule

text: and the

text: lone pairs

text: of

text: electron

text: s that may exist in the molecule. A Lewis structure can be drawn for any

text: covalent

text: ly bonded molecule, as well as

text: coordination compounds

text: . The Lewis structure was named after

text: Gilbert N. Lewis

text: , who introduced it in his 1916 article The Atom and the Molecule. Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent

text: shared pair

text: s in a chemical bond.

text: The number of electron pairs in the valence shell of a central atom is determined after drawing the Lewis structure of the molecule, and expanding it to show all bonding groups and lone pairs of electrons. In VSEPR theory, a double bond or triple bond are treated as a single bonding group. The sum of the number of atoms bonded to a central atom and the number of lone pairs formed by its nonbonding valence electrons is known as the central atom's steric number.

text: The number of electron pairs in the valence shell of a central atom is determined after drawing the

text: Lewis structure

text: of the molecule, and expanding it to show all bonding groups and

text: lone pair

text: s of electrons. In VSEPR theory, a

text: double bond

text: or

text: triple bond

text: are treated as a single bonding group. The sum of the number of atoms bonded to a central atom and the number of

text: lone pair

text: s formed by its nonbonding

text: valence electron

text: s is known as the central atom's

text: steric number

text: A thorium atom has 90 electrons, of which four are valence electrons. Four atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, 7s, and 7p. However, the 7p orbital is greatly destabilised and hence it is not occupied in the ground state of any thorium ion. Despite thorium's position in the f-block of the periodic table, it has an anomalous [Rn]6d7s electron configuration in the ground state, as the 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides. However, in metallic thorium, the [Rn]5f6d7s configuration is a low-lying excited state and hence the 5f orbitals contribute, existing in a rather broad energy band. In fact, the 5f subshells of the actinides have a larger spatial extent than the 4f orbitals of the lanthanides and thus actinide compounds have greater covalent character than the corresponding lanthanide compounds, leading to a more extensive coordination chemistry for the actinides than the lanthanides.

text: valence electron

text: s. Four

text: atomic orbital

text: s are theoretically available for the valence electrons to occupy: 5f, 6d, 7s, and 7p. However, the 7p orbital is greatly destabilised and hence it is not occupied in the ground state of any thorium ion. Despite thorium's position in the

text: f-block

text: of the periodic table, it has an anomalous [Rn]6d7s electron configuration in the ground state, as the 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides. However, in metallic thorium, the [Rn]5f6d7s configuration is a low-lying

text: excited state

text: and hence the 5f orbitals contribute, existing in a rather broad

text: energy band

text: . In fact, the 5f subshells of the actinides have a larger spatial extent than the 4f orbitals of the lanthanides and thus actinide compounds have greater covalent character than the corresponding lanthanide compounds, leading to a more extensive coordination chemistry for the actinides than the lanthanides.

text: A period 1 element is one of the chemical elements in the first row (or period) of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two: hydrogen and helium. This situation can be explained by modern theories of atomic structure. In a quantum mechanical description of atomic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements obey the duet rule in that they need two electrons to complete their valence shell. The maximum number of electrons that these elements can accommodate is two, both in the 1s orbital. Therefore, period 1 can have only two elements.

text: A period 1 element is one of the

text: chemical element

text: s in the first row (or

text: period

text: ) of the

text: periodic table of the chemical elements

text: . The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The first period contains fewer elements than any other row in the table, with only two:

text: hydrogen

text: and

text: helium

text: . This situation can be explained by modern theories of

text: atomic structure

text: . In a

text: quantum mechanical

text: description of

text: atom

text: ic structure, this period corresponds to the filling of the

text: orbital

text: . Period 1 elements obey the

text: duet rule

text: in that they need two

text: electron

text: s to complete their

text: valence shell

text: . The maximum number of electrons that these elements can accommodate is two, both in the 1s orbital. Therefore, period 1 can have only two elements.

text: The dispersion relation near the top of the valence band is E=ℏk/(2m) with negative effective mass. So electrons near the top of the valence band behave like they have negative mass. When a force pulls the electrons to the right, these electrons actually move left. This is solely due to the shape of the valence band, and is unrelated to whether the band is full or empty. If you could somehow empty out the valence band and just put one electron near the valence band maximum (an unstable situation), this electron would move the "wrong way" in response to forces.

text: The dispersion relation near the top of the valence band is E=ℏk/(2m) with negative effective mass. So electrons near the top of the valence band behave like they have

text: negative mass

text: . When a force pulls the electrons to the right, these electrons actually move left. This is solely due to the shape of the valence band, and is unrelated to whether the band is full or empty. If you could somehow empty out the valence band and just put one electron near the valence band maximum (an unstable situation), this electron would move the "wrong way" in response to forces.

text: Several different types of technology have been used for destination signs, from simple rigid placards held in place by a frame or clips, to rollsigns, to various types of computerized, electronically controlled signs, such as flip-dot, LCD or LED displays. All of these can still be found in use today, but most transit-vehicle destination signs now in use in North America and Europe are electronic signs. In the USA, the Americans with Disabilities Act of 1990 specifies certain design criteria for transit-vehicle destination signs, such as maximum and minimum character height-to-width ratio and contrast level, to ensure the signs are sufficiently readable to visually impaired persons.  In the 2010s, LED signs have replaced flip-dot signs as the most common type of destination sign in new buses and rail transit vehicles.

text: Several different types of technology have been used for destination signs, from simple rigid placards held in place by a frame or clips, to

text: rollsign

text: s, to various types of computerized,

text: electronically

text: controlled signs, such as

text: flip-dot

text: LCD

text: or

text: LED

text: displays. All of these can still be found in use today, but most transit-vehicle destination signs now in use in North America and Europe are electronic signs. In the USA, the

text: Americans with Disabilities Act of 1990

text: specifies certain design criteria for transit-vehicle destination signs, such as maximum and minimum character height-to-width ratio and contrast level, to ensure the signs are sufficiently readable to visually impaired persons.  In the 2010s, LED signs have replaced flip-dot signs as the most common type of destination sign in new buses and

text: rail transit

text: vehicles.

text: The second term corrects for the effect of adding the polarization functions. The third term corrects for the diffuse functions. The final term corrects for the larger basis set with the terms from steps 2, 3 and 4 preventing contributions from being counted twice. Two final corrections are made to this energy. The ZPVE is scaled by 0.8929. An empirical correction is then added to account for factors not considered above. This is called the higher level correction (HC) and is given by -0.00481 x (number of valence electrons) -0.00019 x (number of unpaired valence electrons). The two numbers are obtained calibrating the results against the experimental results for a set of molecules. The scaled ZPVE and the HLC are added to give the final energy. For some molecules containing one of the third row elements Ga–Xe, a further term is added to account for spin orbit coupling.

text: The second term corrects for the effect of adding the polarization functions. The third term corrects for the diffuse functions. The final term corrects for the larger basis set with the terms from steps 2, 3 and 4 preventing contributions from being counted twice. Two final corrections are made to this energy. The ZPVE is scaled by 0.8929. An empirical correction is then added to account for factors not considered above. This is called the higher level correction (HC) and is given by -0.00481 x (number of valence electrons) -0.00019 x (number of unpaired valence electrons). The two numbers are obtained calibrating the results against the experimental results for a set of molecules. The scaled ZPVE and the HLC are added to give the final energy. For some molecules containing one of the third row elements Ga–Xe, a further term is added to account for

text: spin orbit coupling

text: It is also important to consider the core electrons when speaking about the valence electrons.

text: is the density of holes in the bulk metal valence band. E is the lowest energy of the conduction band,E is the Fermi energy(electrochemical energy of the electrons), E is the highest energy of the valence band, N is the effective mass and mobility of an electron in the conduction band (constant), and N is the effective mass and mobility of a valence band hole (constant).

text: In 1907 he became chair of the Chemistry Department at the University of Illinois at Urbana-Champaign, a position he would hold until 1926. In the process, he helped it to become one of the leading departments of chemistry in the United States. Despite his earlier work in analytical chemistry, Noyes is perhaps best known as an organic chemist. He was the first to prove the structure of camphor definitively and studied rearrangements in camphor and related compounds. He also worked on "electronic theories of valence, and the valence and nature of nitrogen in nitrogen trichloride" as well as developing "methods for the determination of phosphorus, sulfur, and manganese in iron".

text: In 1907 he became

text: chair

text: of the Chemistry Department at the

entity_name: University of Illinois at Urbana–Champaign

text: University of Illinois at Urbana-Champaign

text: , a position he would hold until 1926. In the process, he helped it to become one of the leading departments of

text: chemistry

text: in the

text: United States

text: . Despite his earlier work in analytical chemistry, Noyes is perhaps best known as an organic chemist. He was the first to prove the structure of

text: camphor

text: definitively and studied rearrangements in camphor and related compounds. He also worked on "electronic theories of

text: valence

text: , and the valence and nature of

text: nitrogen

text: in

text: nitrogen trichloride

text: " as well as developing "methods for the determination of

text: phosphorus

text: sulfur

text: , and

text: manganese

text: in

text: iron

text: The differences in the chiral angle and the diameter cause the differences in the properties of the various carbon nanotubes. For example, it can be shown that an (n,m) carbon nanotube is metallic when n = m, has a small gap (i.e. semi-metallic) when n – m = 3i, where i is an integer, and is semiconducting when n – m ≠ 3i. This is due to the fact that the periodic boundary conditions for the one-dimensional carbon nanotubes permit only a few wave vectors to exist around the circumference of carbon nanotubes. Metallic conduction occurs when one of these wave vectors passes through the K-point of graphene’s 2D hexagonal Brillouin zone, where the valence and conduction bands are degenerate. For the semiconducting carbon nanotubes, there is a diameter dependency on bandgap. For example, according to a single-particle tight-binding description of the electronic structure,

text: The differences in the chiral angle and the diameter cause the differences in the properties of the various carbon nanotubes. For example, it can be shown that an (n,m) carbon nanotube is metallic when n = m, has a small gap (i.e. semi-metallic) when n – m = 3i, where i is an integer, and is semiconducting when n – m ≠ 3i. This is due to the fact that the periodic boundary conditions for the one-dimensional carbon nanotubes permit only a few wave vectors to exist around the circumference of carbon nanotubes. Metallic conduction occurs when one of these wave vectors passes through the K-point of graphene’s 2D hexagonal

text: Brillouin zone

text: , where the valence and conduction bands are degenerate. For the semiconducting carbon nanotubes, there is a diameter dependency on bandgap. For example, according to a single-particle tight-binding description of the electronic structure,

text: Graphite is an electric conductor, consequently, useful in such applications as arc lamp electrodes. It can conduct electricity due to the vast electron delocalization within the carbon layers (a phenomenon called aromaticity). These valence electrons are free to move, so are able to conduct electricity. However, the electricity is primarily conducted within the plane of the layers. The conductive properties of powdered graphite allows its use as pressure sensor in carbon microphones.

text: Graphite is an electric conductor, consequently, useful in such applications as

text: arc lamp

text: electrodes

text: . It can conduct electricity due to the vast

text: electron

text: delocalization

text: within the carbon layers (a phenomenon called

text: aromaticity

text: ). These valence electrons are free to move, so are able to conduct electricity. However, the electricity is primarily conducted within the plane of the layers. The conductive properties of powdered graphite allows its use as pressure sensor in

text: carbon microphone

text: s.

text: Diamonds containing boron as a substitutional impurity are termed type IIb. Only one percent of natural diamonds are of this type, and most are blue to grey. Boron is an acceptor in diamond: boron atoms have one less available electron than the carbon atoms; therefore, each boron atom substituting for a carbon atom creates an electron hole in the band gap that can accept an electron from the valence band. This allows red light absorption, and due to the small energy (0.37 eV) needed for the electron to leave the valence band, holes can be thermally released from the boron atoms to the valence band even at room temperatures. These holes can move in an electric field and render the diamond electrically conductive (i.e., a p-type semiconductor). Very few boron atoms are required for this to happen—a typical ratio is one boron atom per 1,000,000 carbon atoms.

text: Diamonds containing boron as a substitutional impurity are termed type IIb. Only one percent of natural diamonds are of this type, and most are blue to grey. Boron is an acceptor in diamond: boron atoms have one less available electron than the carbon atoms; therefore, each boron atom substituting for a carbon atom creates an

text: electron hole

text: in the band gap that can accept an electron from the

text: valence band

text: . This allows red light absorption, and due to the small energy (0.37 eV) needed for the electron to leave the valence band, holes can be thermally released from the boron atoms to the

text: valence band

text: even at room temperatures. These holes can move in an

text: electric field

text: and render the diamond

text: electrically conductive

text: (i.e., a

text: p-type semiconductor

text: ). Very few boron atoms are required for this to happen—a typical ratio is one boron atom per 1,000,000 carbon atoms.

text: There are a large number of different valence bond methods. Most use n valence bond orbitals for n electrons. If a single set of these orbitals is combined with all linear independent combinations of the spin functions, we have spin-coupled valence bond theory. The total wave function is optimized using the variational method by varying the coefficients of the basis functions in the valence bond orbitals and the coefficients of the different spin functions. In other cases only a sub-set of all possible spin functions is used. Many valence bond methods use several sets of the valence bond orbitals. Be warned that different authors use different names for these different valence bond methods.

text: There are a large number of different valence bond methods. Most use n valence bond orbitals for n electrons. If a single set of these orbitals is combined with all linear independent combinations of the

text: spin function

text: s, we have spin-coupled valence bond theory. The total

text: wave function

text: is optimized using the

text: variational method

text: by varying the coefficients of the

text: basis functions

text: in the valence bond orbitals and the coefficients of the different spin functions. In other cases only a sub-set of all possible spin functions is used. Many valence bond methods use several sets of the valence bond orbitals. Be warned that different authors use different names for these different valence bond methods.

text: When an electron meets with a hole, they recombine and these free carriers effectively vanish. The energy released can be either thermal, heating up the semiconductor (thermal recombination, one of the sources of waste heat in semiconductors), or released as photons (optical recombination, used in LEDs and semiconductor lasers). The recombination means an electron which has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes. The holes are the empty state created in the valence band when an electron gets excited after getting some energy to overpass the energy gap.

text: When an electron meets with a hole, they

text: recombine

text: and these free carriers effectively vanish. The energy released can be either thermal, heating up the semiconductor (thermal recombination, one of the sources of waste heat in semiconductors), or released as

text: photon

text: s (optical recombination, used in

text: LEDs

text: and

text: semiconductor laser

text: s). The recombination means an electron which has been excited from the valence band to the conduction band falls back to the empty state in the valence band, known as the holes. The holes are the empty state created in the valence band when an electron gets excited after getting some energy to overpass the energy gap.

text: Element 118 is the last element that has been claimed to have been synthesized. The next two elements, elements 119 and 120, should form an 8s series and be an alkali and alkaline earth metal respectively. The 8s electrons are expected to be relativistically stabilized, so that the trend towards higher reactivity down these groups will reverse direction and the elements will behave more like their period 5 homologs, rubidium and strontium. Nevertheless, the 7p orbital is still relativistically destabilized, potentially giving these elements larger ionic radii and perhaps even being able to participate chemically. In this region, the 8p electrons are also relativistically stabilized, resulting in a ground-state 8s8p valence electron configuration for element 121. Large changes are expected to occur in the subshell structure in going from element 120 to element 121: for example, the radius of the 5g orbitals should drop drastically, from 25 Bohr units in element 120 in the excited [Og]5g8s configuration to 0.8 Bohr units in element 121 in the excited [Og]5g7d8s configuration, in a phenomenon called "radial collapse" that occurs at element 125. Element 122 should add a further 7d electron to element 121's electron configuration. Elements 121 and 122 should be homologs of actinium and thorium, respectively.

text: Element 118 is the last element that has been claimed to have been synthesized. The next two elements,

text: elements 119

text: and

text: , should form an 8s series and be an

text: alkali

text: and

text: alkaline earth metal

text: respectively. The 8s electrons are expected to be relativistically stabilized, so that the trend towards higher reactivity down these groups will reverse direction and the elements will behave more like their period 5 homologs,

text: rubidium

text: and

text: strontium

text: . Nevertheless, the 7p orbital is still relativistically destabilized, potentially giving these elements larger ionic radii and perhaps even being able to participate chemically. In this region, the 8p electrons are also relativistically stabilized, resulting in a ground-state 8s8p valence electron configuration for element 121. Large changes are expected to occur in the subshell structure in going from element 120 to element 121: for example, the radius of the 5g orbitals should drop drastically, from 25

text: Bohr unit

text: s in element 120 in the excited [Og]5g8s configuration to 0.8 Bohr units in element 121 in the excited [Og]5g7d8s configuration, in a phenomenon called "radial collapse" that occurs at element 125. Element 122 should add a further 7d electron to element 121's electron configuration. Elements 121 and 122 should be homologs of

text: actinium

text: and

text: thorium

text: , respectively.

text: A thorium atom has 90 protons and therefore 90 electrons, of which four are valence electrons. Thorium metal is silvery and tarnishes black when exposed to air, forming the dioxide. Thorium is weakly radioactive: all its known isotopes are unstable. Thorium-232 (Th), which has 142 neutrons, is the most stable isotope of thorium and accounts for nearly all natural thorium, with six other natural isotopes occurring only as trace radioisotopes. Thorium has the longest half-life of all the significantly radioactive elements, 14.05 billion years, or about the age of the universe; it decays very slowly through alpha decay to radium-228 (Ra), starting a decay chain named the thorium series that ends at stable lead-208 (Pb). Thorium is estimated to be about three to four times more abundant than uranium in the Earth's crust, and is chiefly refined from monazite sands as a by-product of extracting rare earth metals.

text: A thorium atom has 90

text: proton

text: s and therefore 90

text: electron

text: s, of which four are

text: valence electron

text: s. Thorium metal is silvery and

text: tarnish

text: es black when exposed to air, forming the dioxide. Thorium is weakly radioactive: all its known

text: isotope

text: s are unstable. Thorium-232 (Th), which has 142

text: neutron

text: s, is the most stable isotope of thorium and accounts for nearly all natural thorium, with six other natural isotopes occurring only as

text: trace radioisotope

text: s. Thorium has the longest half-life of all the significantly radioactive elements, 14.05 billion years, or about the

text: age of the universe

text: ; it decays very slowly through

text: alpha decay

text: to

text: (Ra), starting a

text: decay chain

text: named the

text: thorium series

text: that ends at stable

text: lead

text: -208 (Pb). Thorium is estimated to be about three to four times more

text: abundant

text: than uranium in the Earth's crust, and is chiefly refined from

text: monazite

text: sands as a by-product of extracting

text: rare earth metal

text: s.

text: At room temperature radiation damage induced defects temporarily trap electrons and holes resulting from ionization, which are then emitted back to the conduction band or valence band in a time that is typically longer than the read-out time of the connected electronics. Consequently the measured signal is smaller than it should be. This leads to low signal to noise ratios that in turn can prevent the detection of the traversing particle.At cryogenic temperatures, however, once an electron or hole, resulting from ionization or from detector leakage current, is trapped in a local defect, it remains trapped for a long time due to the very low thermal energy of the lattice. This leads to a large fraction of 'traps' becoming filled and therefore inactive. Trapping of electrons and holes generated by particles traversing the detector is then prevented and little or no signal is lost. The understanding of this has been detailed in a number of papers.

text: At room temperature

text: radiation

text: damage induced defects temporarily trap

text: electron

text: s and

text: hole

text: s resulting from

text: ionization

text: , which are then emitted back to the

text: conduction band

text: or

text: valence band

text: in a time that is typically longer than the read-out time of the connected electronics. Consequently the measured signal is smaller than it should be. This leads to low

text: signal to noise ratio

text: s that in turn can prevent the detection of the traversing

text: particle

text: .At

text: cryogenic

text: temperature

text: s, however, once an

text: electron

text: or

text: hole

text: , resulting from

text: ionization

text: or from detector

text: leakage

text: current

text: , is trapped in a local defect, it remains trapped for a long time due to the very low

text: thermal energy

text: of the

text: lattice

text: . This leads to a large fraction of 'traps' becoming filled and therefore inactive. Trapping of

text: electron

text: s and

text: hole

text: s generated by

text: particle

text: s traversing the detector is then prevented and little or no signal is lost. The understanding of this has been detailed in a number of papers.

text: The list below gives the elements arranged by increasing atomic number and shows the number of electrons per shell. At a glance, one can see that subsets of the list show obvious patterns. In particular, the seven elements (in ) before a noble gas (group 18, in ) higher than helium have the number of electrons in the valence shell in arithmetic progression. (However, this pattern may break down in the seventh period due to relativistic effects.)

text: The list below gives the elements arranged by increasing atomic number and shows the number of electrons per shell. At a glance, one can see that subsets of the list show obvious patterns. In particular, the seven elements (in ) before a

text: noble gas

text: (group 18, in ) higher than helium have the number of electrons in the

text: valence shell

text: in

text: arithmetic progression

text: . (However, this pattern may break down in the

text: seventh period

text: due to

text: relativistic effects

text: The vertical axis of the band diagram represents the energy of an electron, which includes both kinetic and potential energy.The horizontal axis represents position, often not being drawn to scale. Note that the Heisenberg uncertainty principle prevents the band diagram from being drawn with a high positional resolution, since the band diagram shows energy bands (as resulting from a momentum-dependent band structure).

text: The vertical axis of the band diagram represents the energy of an electron, which includes both kinetic and potential energy.The horizontal axis represents position, often not being drawn to scale. Note that the

text: Heisenberg uncertainty principle

text: prevents the band diagram from being drawn with a high positional resolution, since the band diagram shows energy bands (as resulting from a momentum-dependent

text: band structure

text: The  orbitals that are involved in the transition metals are very significant because they influence such properties as magnetic character, variable oxidation states, formation of colored compounds etc. The valence  and  orbitals have very little contribution in this regard since they hardly change in the moving from left to the right in a transition series.In transition metals, there is a greater horizontal similarities in the properties of the elements in a period in comparison to the periods in which the d-orbitals are not involved. This is because in a transition series, the valence shell electronic configuration of the elements do not change. However, there are some group similarities as well.

text: In many cases, the interaction between the Lewis base and Lewis acid in a complex is indicated by an arrow indicating the Lewis base donating electrons toward the Lewis acid using the notation of a dative bond—for example, MeB←NH. Some sources indicate the Lewis base with a pair of dots (the explicit electrons being donated), which allows consistent representation of the transition from the base itself to the complex with the acid:

text: In many cases, the interaction between the Lewis base and Lewis acid in a complex is indicated by an arrow indicating the Lewis base donating electrons toward the Lewis acid using the notation of a

text: dative bond

text: —for example, MeB←NH. Some sources indicate the Lewis base with a pair of dots (the explicit electrons being donated), which allows consistent representation of the transition from the base itself to the complex with the acid:

text: Often, cases where complexes have more than 18 valence electrons are attributed to electrostatic forces – the metal attracts ligands to itself to try to counterbalance its positive charge, and the number of electrons it ends up with is unimportant.  In the case of the metallocenes, the chelating nature of the cyclopentadienyl ligand stabilizes its bonding to the metal. Somewhat satisfying are the two following observations: cobaltocene is a strong electron donor, readily forming the 18-electron cobaltocenium cation; and nickelocene tends to react with substrates to give 18-electron complexes, e.g. CpNiCl(PR) and free CpH.

text: The top of the diagram, point A, represents the electron collection end.  The bottom of the tether, point C, is the electron emission end.  Similarly,

text: On a graph of atom velocities (atoms moving rapidly to the right correspond with stationary dots far to the right, atoms moving rapidly to the left correspond with stationary dots far to the left), there is a narrow band on the left edge corresponding to the speed those atoms start absorbing photons from the left laser. Atoms in that band are the only ones that interact with the left laser. When a photon from the left laser slams into one of those atoms, it suddenly slows down an amount corresponding to the momentum of that photon (the dot would be redrawn some fixed "quantum" distance further to the right). If the atom releases the photon directly to the right, then the dot is redrawn that same distance to the left, putting it back in the narrow band of interaction. But usually the atom releases the photon in some other random direction, and the dot is redrawn that quantum distance in the opposite direction.

text: However, this is a simplification of the truth. The electrons that determine how an atom reacts chemically are those that travel farthest from the nucleus, that is, those with the highest energy. For the transition elements, the partially filled (n − 1) energy level is very close in energy to the n level and hence the  electrons in transition metals behave as valence electrons although they are not in the so-called valence shell.

text: However, this is a simplification of the truth. The electrons that determine how an atom reacts chemically are those that travel farthest from the nucleus, that is, those with the highest

text: energy

text: . For the

text: transition element

text: s, the partially filled (n − 1) energy level is very close in energy to the n level and hence the  electrons in transition metals behave as valence electrons although they are not in the so-called valence shell.

text: Molecular geometry is determined by the quantum mechanical behavior of the electrons. Using the valence bond approximation this can be understood by the type of bonds between the atoms that make up the molecule. When atoms interact to form a chemical bond, the atomic orbitals of each atom are said to combine in a process called orbital hybridisation.  The two most common types of bonds are sigma bonds (usually formed by hybrid orbitals) and pi bonds (formed by unhybridized p orbitals for atoms of main group elements).  The geometry can also be understood by molecular orbital theory where the electrons are delocalised.

text: Molecular geometry is determined by the

text: quantum mechanical

text: behavior of the electrons. Using the

text: valence bond approximation

text: this can be understood by the type of bonds between the atoms that make up the molecule. When atoms interact to form a

text: chemical bond

text: , the atomic orbitals of each atom are said to combine in a process called

text: orbital hybridisation

text: .  The two most common types of bonds are

text: sigma bond

text: s (usually formed by hybrid orbitals) and

text: pi bond

text: s (formed by unhybridized p orbitals for atoms of

text: main group element

text: s).  The geometry can also be understood by

text: molecular orbital theory

text: where the electrons are delocalised.

text: Crystalline solids cohesion is obtained by a metallic or chemical bond which is formed between the constituent atoms. Chemical bonds can be grouped into two types consisting of ionic and covalent. To form an ionic bond, either a valence or bonding electron separates from one atom and becomes attached to another atom to form oppositely charged ions. The bonding in the static position is when the ions occupy an equilibrium position where the resulting force between them is zero. When the ions are exerted in tension force, the inter-ionic spacing increases creating an electrostatic attractive force, while a repulsing force under compressive force between the atomic nuclei is dominant.

text: Crystalline solids cohesion is obtained by a metallic or chemical bond which is formed between the constituent atoms. Chemical bonds can be grouped into two types consisting of

text: ionic

text: and

text: covalent

text: . To form an ionic bond, either a

text: valence

text: or

text: bond

text: ing electron separates from one atom and becomes attached to another atom to form oppositely charged

text: ions

text: . The bonding in the static position is when the ions occupy an equilibrium position where the resulting force between them is zero. When the ions are exerted in

text: tension

text: force, the inter-ionic spacing increases creating an electrostatic attractive force, while a repulsing force under

text: compressive

text: force between the atomic nuclei is dominant.

text: S-block elements are unified by the fact that their valence electrons (outermost electrons) are in the s orbital. The s orbital is a single spherical cloud which can contain only one pair of electrons; hence, the s-block consists of only two columns in the periodic table. Elements in column 1, with a single s-orbital valence electron, are the most reactive of the block.  Elements in the second column have two s-orbital valence electrons, and, except for helium, are only slightly less reactive.

text: Sodium at standard temperature and pressure is a soft silvery metal that combines with oxygen in air and forms grayish white sodium oxide unless immersed in oil or inert gas, which are the conditions it is usually stored in. Sodium metal can be easily cut with a knife and is a good conductor of electricity and heat because it has only one electron in its valence shell, resulting in weak metallic bonding and free electrons, which carry energy. Due to having low atomic weight and large atomic radius, sodium is third-least dense of all elemental metals and is one of only three metals that can float on water, the other two being lithium and potassium. The melting (98 °C) and boiling (883 °C) points of sodium are lower than those of lithium but higher than those of the heavier alkali metals potassium, rubidium, and caesium, following periodic trends down the group. These properties change dramatically at elevated pressures: at 1.5 Mbar, the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent with a red color; and at 3 Mbar, sodium is a clear and transparent solid. All of these high-pressure allotropes are insulators and electrides.

text: Sodium at

entity_name: Standard conditions for temperature and pressure

text: standard temperature and pressure

text: is a soft silvery metal that combines with oxygen in air and forms grayish white

text: sodium oxide

text: unless immersed in oil or inert gas, which are the conditions it is usually stored in. Sodium metal can be easily cut with a knife and is a good conductor of electricity and heat because it has only one electron in its valence shell, resulting in weak

text: metallic bonding

text: and

text: free electron

text: s, which carry energy. Due to having low atomic weight and large atomic radius, sodium is third-least dense of all elemental metals and is one of only three metals that can float on water, the other two being lithium and potassium. The melting (98 °C) and boiling (883 °C) points of sodium are lower than those of lithium but higher than those of the heavier alkali metals potassium, rubidium, and caesium, following periodic trends down the group. These properties change dramatically at elevated pressures: at 1.5

text: Mbar

text: , the color changes from silvery metallic to black; at 1.9 Mbar the material becomes transparent with a red color; and at 3 Mbar, sodium is a clear and transparent solid. All of these high-pressure

text: allotrope

text: s are insulators and

text: electride

text: s.

text: The electron–hole pair is the fundamental unit of generation and recombination, corresponding to an electron transitioning between the valence band and the conduction band where generation of electron is a transition from the valence band to the conduction band and recombination leads to a reverse transition.

text: In chemistry, a tetravalence is the state of an atom with four electrons available for covalent chemical bonding in its valence (outermost electron shell). An example is methane (CH): the tetravalent carbon atom forms a covalent bond with four hydrogen atoms. The carbon atom is called tetravalent because it forms 4 covalent bonds.A carbon atom has a total of six electrons occupying the first two shells, i.e., the K-shell has two electrons and the L-shell has four electrons. This distribution indicates that in the outermost shell there are one completely filled 's' orbital and two half-filled 'p' orbitals, showing carbon to be a divalent atom. But in actuality, carbon displays tetravalency in the combined state. Therefore, a carbon atom has four valence electrons. It could gain four electrons to form the C anion or lose four electrons to form the C cation. Both these conditions would take carbon far away from achieving stability by the octet rule. To overcome this problem carbon undergoes bonding by sharing its valence electrons. This allows it to be covalently bonded to one, two, three or four carbon atoms or atoms of other elements or groups of atoms. Let us see how carbon forms the single, double and triple bonds in the following examples.

text: In

text: chemistry

text: , a tetravalence is the state of an

text: atom

text: with four

text: electron

text: s available for

text: covalent

text: chemical bond

text: ing in its

text: valence

text: (outermost

text: electron shell

text: ). An example is

text: methane

text: (CH): the tetravalent

text: carbon

text: atom forms a covalent bond with four

text: hydrogen atom

text: s. The carbon atom is called tetravalent because it forms 4 covalent bonds.A carbon atom has a total of six electrons occupying the first two shells, i.e., the K-shell has two electrons and the L-shell has four electrons. This distribution indicates that in the outermost shell there are one completely filled 's' orbital and two half-filled 'p' orbitals, showing carbon to be a

text: divalent atom

text: . But in actuality, carbon displays tetravalency in the combined state. Therefore, a carbon atom has four valence electrons. It could gain four electrons to form the C

text: anion

text: or lose four electrons to form the C

text: cation

text: . Both these conditions would take carbon far away from achieving stability by the

text: octet rule

text: . To overcome this problem carbon undergoes bonding by sharing its valence electrons. This allows it to be covalently bonded to one, two, three or four carbon atoms or atoms of other elements or groups of atoms. Let us see how carbon forms the single, double and triple bonds in the following examples.

text: Earphone –Earpiece –Earth's magnetic field –EDIF –EEPROM –Effective antenna gain contour –Effective boresight area –Effective data transfer rate –Effective Earth radius –Effective height –Effective input noise temperature –Effective isotropically radiated power –Effective monopole radiated power –Effective radiated power –Effective transmission rate –Efficiency factor –E-layer –Electric charge –Electric current –Electric field –Electric motor –Electric power transmission –Electric power –Electrical conduction –Electrical conductivity –Electrical connector –Electrical current –Electrical efficiency –Element –Electrical engineering –Electrical generator –Impedance –Insulation –Electrical length –Load –Electrical network –Circuit –Electrical resistance –Electrical room –Electrical signal –Electricity distribution –Electricity –Electrochemical cell –Electrochemistry –Electrode –Electrodynamics –Electrolytic capacitor –Electromagnetic environment –Electromagnetic induction –Electromagnetic interference control –Electromagnetic pulse –Electromagnetic radiation and health –Electromagnetic radiation –Electromagnetic spectrum –Electromagnetic survivability –Electromagnetism –Electrometer –Electron hole –Electron –Electronic amplifier –Electronic color code –Color code –Electronic data processing –Electronic deception –Electronic design automation –Electronic filter –Filter –Electronic imager –Electronic mixer –Electronic musical instrument –Electronic oscillator –Electronic power supply –Electronic switching system –Electronic tagging –Electronic test equipment –Electronic warfare support measures –Electronics –Electro-optic effect –Electro-optic modulator –Electro-optics –Electrostatic discharge –Electrostatics –Emergency Locator Transmitter –Emergency Position-Indicating Radio Beacon –Emitter coupled logic –End distortion –Endurability –Enhanced service –Entropy encoding –Equilibrium length –Equivalent impedance transforms -Equivalent noise resistance –Equivalent pulse code modulation noise –Error burst –Error ratio –Error-correcting code –E-skip –Examples of electrical phenomena –Extremely Low Frequency (ELF) –Eye pattern

text: Earphone

text: Earpiece

text: Earth's magnetic field

text: EDIF

text: EEPROM

text: Effective antenna gain contour

text: Effective boresight area

text: Effective data transfer rate

text: Effective Earth radius

text: Effective height

text: Effective input noise temperature

text: Effective isotropically radiated power

text: Effective monopole radiated power

text: Effective radiated power

text: Effective transmission rate

text: Efficiency factor

text: E-layer

text: Electric charge

text: Electric current

text: Electric field

text: Electric motor

text: Electric power transmission

text: Electric power

text: Electrical conduction

text: Electrical conductivity

text: Electrical connector

text: Electrical current

text: Electrical efficiency

text: Element

text: Electrical engineering

text: Electrical generator

text: Impedance

text: Insulation

text: Electrical length

text: Load

text: Electrical network

text: Circuit

text: Electrical resistance

text: Electrical room

text: Electrical signal

text: Electricity distribution

text: Electricity

text: Electrochemical cell

text: Electrochemistry

text: Electrode

text: Electrodynamics

text: Electrolytic capacitor

text: Electromagnetic environment

text: Electromagnetic induction

text: Electromagnetic interference control

text: Electromagnetic pulse

text: Electromagnetic radiation and health

text: Electromagnetic radiation

text: Electromagnetic spectrum

text: Electromagnetic survivability

text: Electromagnetism

text: Electrometer

text: Electron hole

text: Electron

text: Electronic amplifier

text: Electronic color code

text: Color code

text: Electronic data processing

text: Electronic deception

text: Electronic design automation

text: Electronic filter

text: Filter

text: Electronic imager

text: Electronic mixer

text: Electronic musical instrument

text: Electronic oscillator

text: Electronic power supply

text: Electronic switching system

text: Electronic tagging

text: Electronic test equipment

text: Electronic warfare support measures

text: Electronics

text: Electro-optic effect

text: Electro-optic modulator

text: Electro-optics

text: Electrostatic discharge

text: Electrostatics

entity_name: Emergency position-indicating radiobeacon station

text: Emergency Locator Transmitter

text: Emergency Position-Indicating Radio Beacon

text: Emitter coupled logic

text: End distortion

text: Endurability

text: Enhanced service

text: Entropy encoding

text: Equilibrium length

text: Equivalent impedance transforms

text: Equivalent noise resistance

text: Equivalent pulse code modulation noise

text: Error burst

text: Error ratio

text: Error-correcting code

text: E-skip

text: Examples of electrical phenomena

text: Extremely Low Frequency

text: (ELF) –

text: Eye pattern

text: is the dipole matrix element between the conduction and valence band and

text: is the

text: dipole

text: matrix element between the conduction and valence band and

text: The figure shows a band bending diagram for a p–n diode; that is, the band edges for the conduction band (upper line) and the valence band (lower line) are shown as a function of position on both sides of the junction between the p-type material (left side) and the n-type material (right side). When a p-type and an n-type region of the same semiconductor are brought together and the two diode contacts are short-circuited, the Fermi half-occupancy level (dashed horizontal straight line) is situated at a constant level. This level ensures that in the field-free bulk on both sides of the junction the hole and electron occupancies are correct. (So, for example, it is not necessary for an electron to leave the n-side and travel to the p-side through the short circuit to adjust the occupancies.)

text: The figure shows a band bending diagram for a p–n diode; that is, the band edges for the conduction band (upper line) and the valence band (lower line) are shown as a function of position on both sides of the junction between the p-type material (left side) and the n-type material (right side). When a p-type and an n-type region of the same semiconductor are brought together and the two diode contacts are short-circuited, the

text: Fermi half-occupancy level

text: (dashed horizontal straight line) is situated at a constant level. This level ensures that in the field-free bulk on both sides of the junction the hole and electron occupancies are correct. (So, for example, it is not necessary for an electron to leave the n-side and travel to the p-side through the short circuit to adjust the occupancies.)

text: In the late 19th century it was known that coordination compounds (formerly called “molecular compounds”) were formed by the combination of atoms or molecules in such a manner that the valencies of the atoms involved apparently became satisfied. In 1893, Alfred Werner showed that the number of atoms or groups associated with a central atom (the “coordination number”) is often 4 or 6; other coordination numbers up to a maximum of 8 were known, but less frequent. In 1904 Richard Abegg was one of the first to extend the concept of coordination number to a concept of valence in which he distinguished atoms as electron donors or acceptors, leading to positive and negative valence states that greatly resemble the modern concept of oxidation states. Abegg noted that the difference between the maximum positive and negative valences of an element under his model is frequently eight. Gilbert N. Lewis referred to this insight as Abegg's rule and used it to help formulate his cubical atom model and the "rule of eight", which began to distinguish between valence and valence electrons.  In 1919 Irving Langmuir refined these concepts further and renamed them the "cubical octet atom" and "octet theory".  The "octet theory" evolved into what is now known as the "octet rule".

text: In the late 19th century it was known that coordination compounds (formerly called “molecular compounds”) were formed by the combination of atoms or molecules in such a manner that the valencies of the atoms involved apparently became satisfied. In 1893,

text: Alfred Werner

text: showed that the number of atoms or groups associated with a central atom (the “

text: coordination number

text: ”) is often 4 or 6; other coordination numbers up to a maximum of 8 were known, but less frequent. In 1904

text: Richard Abegg

text: was one of the first to extend the concept of

text: coordination number

text: to a concept of

text: valence

text: in which he distinguished atoms as electron donors or acceptors, leading to positive and negative valence states that greatly resemble the modern concept of

text: oxidation states

text: . Abegg noted that the difference between the maximum positive and negative

text: valences

text: of an

text: element

text: under his model is frequently eight.

text: Gilbert N. Lewis

text: referred to this insight as

text: Abegg's rule

text: and used it to help formulate his

text: cubical atom

text: model and the "rule of eight", which began to distinguish between

text: valence

text: and

text: valence electron

text: s.  In 1919

text: Irving Langmuir

text: refined these concepts further and renamed them the "cubical octet atom" and "octet theory".  The "octet theory" evolved into what is now known as the "octet rule".

text: The valence shell is the outermost shell of an atom. It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons, that is, the electrons that determine how the atom behaves in chemical reactions. Just as atoms with complete valence shells (noble gases) are the most chemically non-reactive, those with only one electron in their valence shells (alkali metals) or just missing one electron from having a complete shell (halogens) are the most reactive.

text: The valence shell is the outermost shell of an

text: atom

text: . It is usually (and misleadingly) said that the electrons in this shell make up its

text: valence electrons

text: , that is, the electrons that determine how the atom behaves in chemical reactions. Just as atoms with complete valence shells (

text: noble gases

text: ) are the most chemically non-reactive, those with only one electron in their valence shells (

text: alkali metal

text: s) or just missing one electron from having a complete shell (

text: halogen

text: s) are the most reactive.

text: Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of atomic orbitals is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one valence electron in its outermost shell, so in ionized form it is commonly found with one lost electron, as . On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as . Caesium has the lowest measured ionization energy of all the elements and helium has the greatest. In general, the ionization energy of metals is much lower than the ionization energy of nonmetals, which is why, in general, metals will lose electrons to form positively charged ions and nonmetals will gain electrons to form negatively charged ions.

text: Each successive ionization energy is markedly greater than the last. Particularly great increases occur after any given block of

text: atomic orbital

text: s is exhausted of electrons. For this reason, ions tend to form in ways that leave them with full orbital blocks. For example, sodium has one

text: valence electron

text: in its outermost shell, so in ionized form it is commonly found with one lost electron, as . On the other side of the periodic table, chlorine has seven valence electrons, so in ionized form it is commonly found with one gained electron, as . Caesium has the lowest measured ionization energy of all the elements and helium has the greatest. In general, the ionization energy of

text: metals

text: is much lower than the ionization energy of

text: nonmetals

text: , which is why, in general, metals will lose electrons to form positively charged ions and nonmetals will gain electrons to form negatively charged ions.

text: When the hour goes by itself, it is preceded by the abbreviation "godz." (for hour);when it is accompanied by minutes, this introductory abbreviation is not needed.Minutes are traditionally superscribed to the hour and underlined, as in 17 (both in handwriting and in typewritten documents). This is by far the prevailing form in handwritten text, but very rare in electronic communication other than official documents, owing to the difficulty of producing it in most applications.According to Polish printed publishings norm, a dot is used to separate hours and minutes when not using superscription but popularity of electronic devices caused the dot to be often replaced with a colon (less official).

text: An example of a molecule with inequivalent atoms of the same element is the thiosulfate ion (), for which the algebraic sum rule yields the average value +2 for sulfur, where the two ionizing electrons are assigned to the terminal sulfur atom. However, the use of a Lewis structure and electron counting shows that the two sulfur atoms are different. The central sulfur is assigned only one valence electron from the S−S bond and no valence electrons from the S−O bonds, compared to six valence electrons for a free sulfur atom, so the oxidation state of the central sulfur is +5. The terminal sulfur atom is assigned the other electron from the S−S bond plus three lone pairs for a total of seven valence electrons, so its oxidation state is −1.

text: An example of a molecule with inequivalent atoms of the same element is the

text: thiosulfate

text: ion (), for which the algebraic sum rule yields the average value +2 for sulfur, where the two ionizing electrons are assigned to the terminal sulfur atom. However, the use of a Lewis structure and electron counting shows that the two sulfur atoms are different. The central sulfur is assigned only one valence electron from the S−S bond and no valence electrons from the S−O bonds, compared to six valence electrons for a free sulfur atom, so the oxidation state of the central sulfur is +5. The terminal sulfur atom is assigned the other electron from the S−S bond plus three lone pairs for a total of seven valence electrons, so its oxidation state is −1.

text: Every system has the tendency to acquire the state of stability or a state of minimum energy, and so chemical elements take part in chemical reactions to acquire a stable electronic configuration similar to that of its nearest noble gas. An example of this tendency is hydrogen'(H)s reaction with oxygen(O) to form water(HO). Hydrogen in ground state has the Valency 1 and on formation of water it acquires a stable valency of 2, similar to that of its nearest noble gas helium. Nevertheless, a lot of chemical elements especially transition elements can achieve stability with other configurations.

text: Every system has the tendency to acquire the state of stability or a state of minimum energy, and so

text: chemical elements

text: take part in

text: chemical reaction

text: s to acquire a stable electronic configuration similar to that of its nearest

text: noble gas

text: . An example of this tendency is

text: hydrogen

text: '(H)s reaction with

text: oxygen

text: (O) to form water(HO).

text: Hydrogen

text: in ground state has the

text: Valency

text: 1 and on formation of water it acquires a stable valency of 2, similar to that of its nearest

text: noble gas

text: helium

text: . Nevertheless, a lot of chemical elements especially transition elements can achieve stability with other configurations.

text: Tennessine is expected to be a member of group 17 in the periodic table, below the five halogens; fluorine, chlorine, bromine, iodine, and astatine, each of which has seven valence electrons with a configuration of . For tennessine, being in the seventh period (row) of the periodic table, continuing the trend would predict a valence electron configuration of , and it would therefore be expected to behave similarly to the halogens in many respects that relate to this electronic state. However, going down group 17, the metallicity of the elements increases; for example, iodine already exhibits a metallic luster in the solid state, and astatine is often classified as a metalloid due to its properties being quite far from those of the four previous halogens. As such, an extrapolation based on periodic trends would predict tennessine to be a rather volatile post-transition metal.

text: Tennessine is expected to be a member of group 17 in the periodic table, below the five halogens;

text: fluorine

text: chlorine

text: bromine

text: iodine

text: , and astatine, each of which has seven valence electrons with a configuration of . For tennessine, being in the seventh

text: period

text: (row) of the periodic table, continuing the trend would predict a valence electron configuration of , and it would therefore be expected to behave similarly to the halogens in many respects that relate to this electronic state. However, going down group 17, the metallicity of the elements increases; for example, iodine already exhibits a metallic luster in the solid state, and astatine is often classified as a

text: metalloid

text: due to its properties being quite far from those of the four previous halogens. As such, an extrapolation based on periodic trends would predict tennessine to be a rather volatile

text: post-transition metal

text: The energy gap of a quantum dot is the energy gap between its valence and conduction bands. This energy gap (E(r)) is equal to the band gap of the bulk material (E) plus the energy equation derived from particle-in-a-box, which gives the energy for electrons and holes. This can be seen in the following equation, where m and m are the effective masses of the electron and hole, r is radius of the dot, and h is Plank's constant:

text: The

text: energy gap

text: of a quantum dot is the energy gap between its

text: valence and conduction bands

text: . This energy gap (E(r)) is equal to the band gap of the bulk material (E) plus the energy equation derived from particle-in-a-box, which gives the energy for electrons and

text: holes

text: . This can be seen in the following equation, where m and m are the effective masses of the electron and hole, r is radius of the dot, and h is Plank's constant:

text: Every solid has its own characteristic energy-band structure. This variation in band structure is responsible for the wide range of electrical characteristics observed in various materials.In semiconductors and insulators, electrons are confined to a number of bands of energy, and forbidden from other regions. The term "band gap" refers to the energy difference between the top of the valence band and the bottom of the conduction band.  Electrons are able to jump from one band to another. However, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition. The required energy differs with different materials. Electrons can gain enough energy to jump to the conduction band by absorbing either a phonon (heat) or a photon (light).

text: Every solid has its own characteristic energy-band structure. This variation in band structure is responsible for the wide range of electrical characteristics observed in various materials.In semiconductors and insulators,

text: electron

text: s are confined to a number of

text: bands

text: of energy, and forbidden from other regions. The term "band gap" refers to the energy difference between the top of the valence band and the bottom of the conduction band.  Electrons are able to jump from one band to another. However, in order for an electron to jump from a valence band to a conduction band, it requires a specific minimum amount of energy for the transition. The required energy differs with different materials. Electrons can gain enough energy to jump to the conduction band by absorbing either a

text: phonon

text: (heat) or a

text: photon

text: (light).

text: According to this theory a covalent bond is formed between the two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron. A valence bond structure is similar to a Lewis structure, but where a single Lewis structure cannot be written, several valence bond structures are used. Each of these VB structures represents a specific Lewis structure. This combination of valence bond structures is the main point of resonance theory. Valence bond theory considers that the overlapping atomic orbitals of the participating atoms form a chemical bond. Because of the overlapping, it is most probable that electrons should be in the bond region. Valence bond theory views bonds as weakly coupled orbitals (small overlap). Valence bond theory is typically easier to employ in ground state molecules. The inner-shell orbitals and electrons remain essentially unchanged during the formation of bonds.

text: According to this theory a covalent bond is formed between the two atoms by the overlap of half filled valence atomic orbitals of each atom containing one unpaired electron. A valence bond structure is similar to a

text: Lewis structure

text: , but where a single Lewis structure cannot be written, several valence bond structures are used. Each of these VB structures represents a specific Lewis structure. This combination of valence bond structures is the main point of

text: resonance

text: theory. Valence bond theory considers that the overlapping

text: atomic orbitals

text: of the participating atoms form a

text: chemical bond

text: . Because of the overlapping, it is most

text: probable

text: that

text: electrons

text: should be in the bond region. Valence bond theory views bonds as weakly coupled orbitals (small overlap). Valence bond theory is typically easier to employ in

text: ground state

text: molecules. The

text: inner-shell

text: orbitals and electrons remain essentially unchanged during the formation of bonds.

text: Stimuli may be automatically evaluated in ways that affect behavior, an automatic evaluation. In a study conducted by Chen and Bargh, subjects were faster to pull a lever toward themselves (an approach tendency) when a word had a positive valence than a negative valence, and were similarly faster to push the lever away (an avoidance tendency) when the word had a negative valence compared to a positive valence. The "sequential evaluative priming paradigm"  refers to the related phenomenon of response times reducing when primed by stimuli with congruent valence. In an examination of the generality of the effects of this paradigm, Bargh, Chaiken, Govender and Pratto show that simply seeing or hearing mention of stimuli triggers automatically activated evaluations. This occurs even when the subject has not been asked to think about their evaluation of the stimulus beforehand. It was further shown that novel stimuli are automatically evaluated and produce the same effect as nonnovel stimuli: when positively valenced novel stimuli prime positively valenced targets, reaction time is faster.

text: A major complicating factor is that many decay processes involve multiple energy states, and thus multiple rate constants. Though non-linear least squared analysis can usually detect the different rate constants, determining the processes involved is often very difficult and requires the combination of multiple ultra-fast techniques. Even more complicating is the presence of inter-system crossing and other non-radiative processes in a molecule. A limiting factor of this technique is that it is limited to studying energy states that result in fluorescent decay. The technique can also be used to study relaxation of electrons from the conduction band to the valence band in semiconductors.

text: In reality, the distribution of electrons in the molecule lies somewhere between these two extremes.   The inadequacy of the simple Lewis structure view of molecules led to the development of the more generally applicable and accurate valence bond theory of Slater, Pauling, et al., and henceforth the molecular orbital theory developed by Mulliken and Hund.

text: In reality, the distribution of electrons in the molecule lies somewhere between these two extremes.   The inadequacy of the simple Lewis structure view of molecules led to the development of the more generally applicable and accurate

text: valence bond theory

text: of

text: Slater

text: Pauling

text: , et al., and henceforth the

text: molecular orbital theory

text: developed by

text: Mulliken

text: and

text: Hund

text: The atoms that bind together to make the molecules of any particular substance contain a number of electrons (given by the atomic number Z in the periodic chart). Recall that all light waves are electromagnetic in origin. Thus they are affected strongly when coming into contact with negatively charged electrons in matter. When photons (individual packets of light energy) come in contact with the valence electrons of atom, one of several things can and will occur:

text: The atoms that bind together to make the molecules of any particular substance contain a number of electrons (given by the

text: atomic number

text: Z in the

text: periodic chart

text: ). Recall that all light waves are electromagnetic in origin. Thus they are affected strongly when coming into contact with

text: negatively charged

text: electrons in matter. When

text: photons

text: (individual packets of light energy) come in contact with the

text: valence electrons

text: of atom, one of several things can and will occur:

text: Following several years of work and exhibitions, in 2012 the IVAM (Valency Institute of Modern Art) is host to what was up to then his most ambitious exhibition. The Valency institution selects some 50 works for exhibition which are representative of his career to date.

text: Following several years of work and exhibitions, in 2012 the

text: IVAM

text: (Valency Institute of Modern Art) is host to what was up to then his most ambitious exhibition. The Valency institution selects some 50 works for exhibition which are representative of his career to date.

text: E generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom; a Group 17 atom releases more energy than a Group 1 atom on gaining an electron because it obtains a filled valence shell and therefore is more stable.

text: E generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom; a

text: Group 17

text: atom releases more energy than a

text: Group 1

text: atom on gaining an electron because it obtains a filled

text: valence shell

text: and therefore is more stable.

text: Another factor that has a significant effect on the SFE of a material and is very interrelated with alloy content is the e/a ratio, or the ratio of valence electrons to atoms. Thornton showed this in 1962 by plotting the e/a ratio vs SFE for a few Cu based alloys. He found that the valence-electron to atom ratio is a good predictor of stacking fault energy, even when the alloying element is changed. This directly support to graphs to the right. Zinc is a heavier element and only has two valence electrons, whereas aluminum is lighter and has three valence electrons. Thus each weight percent of aluminum has a much greater impact on the SFE of the Cu-based alloy than does zinc.

text: Another factor that has a significant effect on the SFE of a material and is very interrelated with alloy content is the e/a ratio, or the ratio of valence electrons to atoms. Thornton showed this in 1962 by plotting the e/a ratio vs SFE for a few Cu based alloys. He found that the valence-electron to atom ratio is a good predictor of stacking fault energy, even when the alloying element is changed. This directly support to graphs to the right.

text: Zinc

text: is a heavier element and only has two valence electrons, whereas

text: aluminum

text: is lighter and has three valence electrons. Thus each weight percent of aluminum has a much greater impact on the SFE of the Cu-based alloy than does zinc.

text: This is made precise in the state correlation diagram below.  The ground state in the starting materials is the electronic state where π and π are both doubly populated – i.e. the state (SS)(AS).  As such, this state attempts to correlate with the electronic state in the product where both σ and σ are doubly populated – i.e. the state (SS)(AS).  However, this state is neither the ground state (SS)(SA) of cyclobutane, nor the first excited state ES-1'=(SS)(SA)(AS), where an electron is promoted from the HOMO to the LUMO.  So the ground state of the reactants attempts to correlate with a second excited state ES-2'=(SS)(AS).

text: To perform a pulsed EDMR experiment, the system is first initialised by placing it in a magnetic field. This orients the spins of the electrons occupying the donor and acceptor in the direction of the magnetic field. To study the donor, we apply a microwave pulse ("γ" in the diagram) at a resonant frequency of the donor. This flips the spin of the electron on the donor. The donor electron can then decay to the acceptor energy state (it was forbidden from doing that before it was flipped due to the Pauli exclusion principle) and from there to the valence band, where it recombines with a hole. With more recombination, there will be fewer conduction electrons in the conduction band and a corresponding increase in the resistance, which can be directly measured. Above-bandgap light is used throughout the experiment to ensure that there are lots of electrons in the conduction band.

text: To perform a pulsed EDMR experiment, the system is first initialised by placing it in a magnetic field. This orients the

text: spin

text: s of the

text: electron

text: s occupying the donor and acceptor in the direction of the

text: magnetic field

text: . To study the donor, we apply a

text: microwave

text: pulse ("γ" in the diagram) at a resonant frequency of the donor. This flips the spin of the electron on the donor. The donor electron can then decay to the acceptor energy state (it was forbidden from doing that before it was flipped due to the

text: Pauli exclusion principle

text: ) and from there to the valence band, where it

text: recombines

text: with a hole. With more recombination, there will be fewer conduction electrons in the

text: conduction band

text: and a corresponding increase in the resistance, which can be directly measured. Above-bandgap light is used throughout the experiment to ensure that there are lots of electrons in the conduction band.

text: A perfectly full band always has zero current. One way to think about this fact is that the electron states near the top of the band have negative effective mass, and those near the bottom of the band have positive effective mass, so the net motion is exactly zero. If an otherwise-almost-full valence band has a state without an electron in it, we say that this state is occupied by a hole. There is a mathematical shortcut for calculating the current due to every electron in the whole valence band: Start with zero current (the total if the band were full), and subtract the current due to the electrons that would be in each hole state if it wasn't a hole. Since subtracting the current caused by a negative charge in motion is the same as adding the current caused by a positive charge moving on the same path, the mathematical shortcut is to pretend that each hole state is carrying a positive charge, while ignoring every other electron state in the valence band.

text: Density functional theory seeks to solve for an approximate form of the electronic density of a system.  In general, atoms are split into ionic cores and valence electrons.  The ionic cores (nuclei plus non-bonding electrons) are assumed to be stable and are treated as a single object.  Each valence electron is treated separately.  Thus, for example, a Lithium atom is treated as two bodies – Li+ and e- – while oxygen is treated as three bodies, namely O and 2e.

text: Covalent bonds are better understood by valence bond theory or molecular orbital theory. The properties of the atoms involved can be understood using concepts such as oxidation number. The electron density within a bond is not assigned to individual atoms, but is instead delocalized between atoms. In valence bond theory, the two electrons on the two atoms are coupled together with the bond strength depending on the overlap between them. In molecular orbital theory, the linear combination of atomic orbitals (LCAO) helps describe the delocalized molecular orbital structures and energies based on the atomic orbitals of the atoms they came from. Unlike pure ionic bonds, covalent bonds may have directed anisotropic properties. These may have their own names, such as sigma bond and pi bond.

text: Covalent bonds are better understood by

text: valence bond theory

text: or

text: molecular orbital theory

text: . The properties of the atoms involved can be understood using concepts such as

text: oxidation number

text: . The electron density within a bond is not assigned to individual atoms, but is instead delocalized between atoms. In valence bond theory, the two electrons on the two atoms are coupled together with the bond strength depending on the overlap between them. In molecular orbital theory, the

text: linear combination of atomic orbitals

text: (LCAO) helps describe the delocalized molecular orbital structures and energies based on the atomic orbitals of the atoms they came from. Unlike pure ionic bonds, covalent bonds may have directed

text: anisotropic

text: properties. These may have their own names, such as

text: sigma bond

text: and

text: pi bond

text: Valence has two SNCF railway stations. Commissioned in 1865, the role of the Valence-Ville railway station has refocused on regional transport since the 2001 commissioning of the gare de Valence TGV, or simply Valence-TGV. It is the point of departure of the trains in the direction of Grenoble, Chambéry, Annecy and Geneva. Valence-Ville railway station was also the origin of the relationship which serves , , , , ,  and Briançon. The passenger building of Valence-Ville railway station has been in service in April 1866. It was designed by , architect of Napoleon III. The facade of the main body, in stone, is inspired by the Petit Trianon of Versailles. The main façade on the Rue du Pavilion Central has been registered as an historic monument since 11 October 1982.

text: Valence has two SNCF railway stations. Commissioned in 1865, the role of the

text: Valence-Ville

text: railway station has refocused on regional transport since the 2001 commissioning of the

text: gare de Valence TGV

text: , or simply Valence-TGV. It is the point of departure of the trains in the direction of

text: Grenoble

text: Chambéry

text: Annecy

text: and

text: Geneva

text: . Valence-Ville railway station was also the origin of the relationship which serves , , , , ,  and

text: Briançon

text: . The passenger building of Valence-Ville railway station has been in service in April 1866. It was designed by , architect of

text: Napoleon III

text: . The facade of the main body, in stone, is inspired by the

text: Petit Trianon

text: of

text: Versailles

text: . The main façade on the Rue du Pavilion Central has been registered as an

text: historic monument

text: since 11 October 1982.

text: At Illinois Arduengo examined more broadly the areas of organo-main group element chemistry, and molecules containing unusual valency. His first publications involving the chemistry of electron-deficient carbenes occurred during this period. This work with electron deficient carbenes led to the first structure determinations on a nitrile ylide and a carbonyl ylide. His later work with carbene chemistry would become his most recognized contribution to the field of chemistry (vide infra). During the Illinois years Arduengo had a close collaboration with his colleague J.C. Martin who was a physical-organic chemist also working on organo-main group element chemistry and hypervalency. Many of the technical discussions between Martin and Arduengo would take place over lunch (the choice of restaurants often influenced by the quality of the napkins for writing chemical structures). To facilitate discussions about unusual molecular structures and bonding for main-group element centers, Martin and Arduengo devised the N-X-L nomenclature system. The synthesis and characterization of the first compound with a planar T-shaped, 10-electron 3-coordinate bonding arrangement at a phosphorus atom, ADPO, was also accomplished by the Arduengo group at Illinois and paved the way for a range of novel main-group element chemistry (including the discovery of edge inversion) on his return to DuPont. The final Illinois research extended the newly discovered ADPO chemistry to the arsenic analog (ADAsO).

text: At

text: Illinois

text: Arduengo examined more broadly the areas of organo-

text: main group element

text: chemistry, and molecules containing unusual

text: valency

text: . His first publications involving the chemistry of

text: electron-deficient

text: carbene

text: s occurred during this period. This work with electron deficient carbenes led to the first structure determinations on a

text: nitrile ylide

text: and a carbonyl

text: ylide

text: . His later work with

text: carbene

text: chemistry would become his most recognized contribution to the field of chemistry (vide infra). During the Illinois years Arduengo had a close collaboration with his colleague

text: J.C. Martin

text: who was a physical-organic chemist also working on organo-

text: main group element

text: chemistry and hypervalency. Many of the technical discussions between Martin and Arduengo would take place over lunch (the choice of restaurants often influenced by the quality of the napkins for writing chemical structures). To facilitate discussions about unusual molecular structures and bonding for

text: main-group element

text: centers, Martin and Arduengo devised the

text: N-X-L nomenclature system

text: . The synthesis and characterization of the first compound with a planar T-shaped, 10-

text: electron

text: coordinate bonding

text: arrangement at a

text: phosphorus

text: atom, ADPO, was also accomplished by the Arduengo group at Illinois and paved the way for a range of novel

text: main-group element

text: chemistry (including the discovery of

text: edge inversion

text: ) on his return to

text: DuPont

text: . The final Illinois research extended the newly discovered ADPO chemistry to the arsenic analog (ADAsO).

text: Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orbital are likely to be found. The diagrams cannot, however, show the entire region where an electron can be found, since according to quantum mechanics there is a non-zero probability of finding the electron (almost) anywhere in space. Instead the diagrams are approximate representations of boundary or contour surfaces where the probability density  has a constant value, chosen so that there is a certain probability (for example 90%) of finding the electron within the contour. Although  as the square of an absolute value is everywhere non-negative, the sign of the wave function  is often indicated in each subregion of the orbital picture.

text: Simple pictures showing orbital shapes are intended to describe the angular forms of regions in space where the electrons occupying the orbital are likely to be found. The diagrams cannot, however, show the entire region where an electron can be found, since according to quantum mechanics there is a non-zero probability of finding the electron (almost) anywhere in space. Instead the diagrams are approximate representations of boundary or

text: contour surfaces

text: where the probability density  has a constant value, chosen so that there is a certain probability (for example 90%) of finding the electron within the contour. Although  as the square of an

text: absolute value

text: is everywhere non-negative, the sign of the

text: wave function

text: is often indicated in each subregion of the orbital picture.

text: |-| colspan="5" |In electronics a NOT gate is more commonly called an inverter. The circle on the symbol is called a bubble, and is used in logic diagrams to indicate a logic negation between the external logic state and the internal logic state (1 to 0 or vice versa). On a circuit diagram it must be accompanied by a statement asserting that the positive logic convention or negative logic convention is being used (high voltage level = 1 or high voltage level = 0, respectively). The wedge is used in circuit diagrams to directly indicate an active-low (high voltage level = 0) input or output without requiring a uniform convention throughout the circuit diagram. This is called Direct Polarity Indication. See IEEE Std 91/91A and IEC 60617-12. Both the bubble and the wedge can be used on distinctive-shape and rectangular-shape symbols on circuit diagrams, depending on the logic convention used. On pure logic diagrams, only the bubble is meaningful.|-| NAND|

text: |-| colspan="5" |In electronics a NOT gate is more commonly called an inverter. The circle on the symbol is called a bubble, and is used in logic diagrams to indicate a logic negation between the external logic state and the internal logic state (1 to 0 or vice versa). On a circuit diagram it must be accompanied by a statement asserting that the positive logic convention or negative logic convention is being used (high voltage level = 1 or high voltage level = 0, respectively). The wedge is used in circuit diagrams to directly indicate an active-low (high voltage level = 0) input or output without requiring a uniform convention throughout the circuit diagram. This is called Direct Polarity Indication. See IEEE Std 91/91A and IEC 60617-12. Both the bubble and the wedge can be used on distinctive-shape and

text: rectangular

text: -shape symbols on circuit diagrams, depending on the logic convention used. On pure logic diagrams, only the bubble is meaningful.|-|

text: NAND

text: The possibility of using unique properties of lanthanides in the nanotechnology is demonstrated. The origination of linear and nonlinear optical properties of lanthanide compounds with phthalocyanines, porphyrins, naphthalocyanines, and their analogs in solutions and condensed state and the prospects of obtaining novel materials on their basis are discussed. Based on the electronic structure and properties of lanthanides and their compounds, namely, optical and magnetic characteristics, electronic and ionic conductivity, and fluctuating valence, molecular engines are classified. High-speed storage engines or memory storage engines; photoconversion molecular engines based on Ln(II) and Ln(III); electrochemical molecular engines involving silicate and phosphate glasses; molecular engines whose operation is based on insulatorsemiconductor, semiconductor-metal, and metal-superconductor types of conductivity phase transitions; solid electrolyte molecular engines; and miniaturized molecular engines for medical analysis are distinguished. It is shown that thermodynamically stable nanoparticles of LnM composition can be formed by d elements of the second halves of the series, i.e., those arranged after M = Mn, Tc, and Re.

text: There is some conductivity in semiconductors, however. This is due to thermal excitation—some of the electrons get enough energy to jump the band gap in one go. Once they are in the conduction band, they can conduct electricity, as also can the hole they left behind in the valence band. The hole is an empty state that allows electrons in the valence band some degree of freedom.

text: There is some conductivity in semiconductors, however. This is due to thermal excitation—some of the electrons get enough energy to jump the band gap in one go. Once they are in the conduction band, they can conduct electricity, as also can the

text: hole

text: they left behind in the valence band. The hole is an empty state that allows electrons in the valence band some degree of freedom.

text: Within each group (each periodic table column) of metals, reactivity increases with each lower row of the table (from a light element to a heavier element), because a heavier element has more electron shells than a lighter element; a heavier element's valence electrons exist at higher principal quantum numbers (they are farther away from the nucleus of the atom, and are thus at higher potential energies, which means they are less tightly bound).

text: Within each group (each periodic table column) of metals, reactivity increases with each lower row of the table (from a light element to a heavier element), because a heavier element has more electron shells than a lighter element; a heavier element's valence electrons exist at higher

text: principal quantum number

text: s (they are farther away from the nucleus of the atom, and are thus at higher potential energies, which means they are less tightly bound).

text: A normal uncharged piece of matter has equal numbers of positive and negative electric charges in each part of it, located close together, so no part of it has a net electric charge.   The positive charges are the atoms' nuclei which are bound into the structure of matter and are not free to move.  The negative charges are the atoms' electrons.  In electrically conductive objects such as metals, some of the electrons are able to move freely about in the object.

text: A normal uncharged piece of matter has equal numbers of positive and negative

text: electric charge

text: s in each part of it, located close together, so no part of it has a net electric charge.   The positive charges are the

text: atom

text: s'

text: nuclei

text: which are bound into the structure of matter and are not free to move.  The negative charges are the atoms'

text: electron

text: s.  In

text: electrically conductive

text: objects such as metals, some of the electrons are able to move freely about in the object.

text: Cerium has a variable electronic structure. The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalised in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valency states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. It appears that the valence changes from about 3 to 4 when it is cooled or compressed.

text: Cerium has a variable

text: electronic structure

text: . The energy of the 4f electron is nearly the same as that of the outer 5d and 6s electrons that are delocalised in the metallic state, and only a small amount of energy is required to change the relative occupancy of these electronic levels. This gives rise to dual valency states. For example, a volume change of about 10% occurs when cerium is subjected to high pressures or low temperatures. It appears that the valence changes from about 3 to 4 when it is cooled or compressed.

text: Further evidence that the assignment of the so-called "valence hole" should be to the S units in these two formulae is the length of the S-S bonds, which are significantly shorter in CuS (0.207 nm) and CuS (0.203 nm) than in the "classical" disulfide Fe(S) (0.218 nm). This bond length difference has been ascribed to the higher bond order in (S-S) compared to (S-S) due to electrons being removed from a π* antibonding orbital. NMR studies on CuS show that there are two distinct species of copper atom, one with a more metallic nature than the other. and this apparent discrepancy with the X-ray photo-electron spectrum data simply highlights the problem that NMR has in assigning oxidation states in a mixed-valence compound. The issue of the valence of copper in sulfides (as well as selenides and tellurides) continues to be revisited in the literature. A good example is a 2009 study of the ternary compound CuCoS<ref>Electronic environments in carrollite, CuCo2S4, determined by soft X-ray photoelectron and absorption spectroscopy<br> Alan N. Buckleya, , William M. Skinnerb, Sarah L. Harmerb, Allan Pringc and Liang-Jen Fand

text: Further evidence that the assignment of the so-called "valence hole" should be to the S units in these two formulae is the length of the S-S bonds, which are significantly shorter in CuS (0.207 nm) and CuS (0.203 nm) than in the "classical" disulfide Fe(S) (0.218 nm). This bond length difference has been ascribed to the higher bond order in (S-S) compared to (S-S) due to electrons being removed from a π*

text: antibonding

text: orbital. NMR studies on CuS show that there are two distinct species of copper atom, one with a more metallic nature than the other. and this apparent discrepancy with the X-ray photo-electron spectrum data simply highlights the problem that NMR has in assigning oxidation states in a

text: mixed-valence

text: compound. The issue of the valence of copper in sulfides (as well as selenides and tellurides) continues to be revisited in the literature. A good example is a 2009 study of the ternary compound CuCoS<ref>Electronic environments in carrollite, CuCo2S4, determined by soft X-ray photoelectron and absorption spectroscopy<br> Alan N. Buckleya, , William M. Skinnerb, Sarah L. Harmerb, Allan Pringc and Liang-Jen Fand

text: A simpler method has been proposed for constructing Lewis structures, eliminating the need for electron counting: the atoms are drawn showing the valence electrons; bonds are then formed by pairing up valence electrons of the atoms involved in the bond-making process, and anions and cations are formed by adding or removing electrons to/from the appropriate atoms.

text: , is made for the valence band electrons. The corresponding electronic interband transition then becomes

text: In semiconductors and insulators the two bands are separated by a band gap, while in semimetals the bands overlap. A band gap is an energy range in a solid where no electron states can exist due to the quantization of energy. Electrical conductivity of non-metals is determined by the susceptibility of electrons to excitation from the valence band to the conduction band.

text: In semiconductors and insulators the two bands are separated by a

text: band gap

text: , while in

text: semimetals

text: the bands overlap. A band gap is an energy range in a solid where no electron states can exist due to the

text: quantization

text: of energy. Electrical conductivity of non-metals is determined by the susceptibility of electrons to excitation from the valence band to the conduction band.

text: A metal is an element with high electrical conductivity or malleability when in the solid state. In each row of the periodic table, the metals occur to the left of the nonmetals, and thus a metal has fewer possible valence electrons than a nonmetal. However, a valence electron of a metal atom has a small ionization energy, and in the solid state this valence electron is relatively free to leave one atom in order to associate with another nearby. Such a "free" electron can be moved under the influence of an electric field, and its motion constitutes an electric current; it is responsible for the electrical conductivity of the metal. Copper, aluminium, silver, and gold are examples of good conductors.

text: A

text: metal

text: is an element with high electrical conductivity or malleability when in the

text: solid

text: state. In each row of the

entity_name: Properties of metals, metalloids and nonmetals

text: periodic table

text: , the metals occur to the left of the nonmetals, and thus a metal has fewer possible valence electrons than a nonmetal. However, a valence electron of a metal atom has a small

text: ionization energy

text: , and in the solid state this valence electron is relatively free to leave one atom in order to associate with another nearby. Such a "free" electron can be moved under the influence of an

text: electric field

text: , and its motion constitutes an

text: electric current

text: ; it is responsible for the electrical conductivity of the metal.

text: Copper

text: aluminium

text: silver

text: , and

text: gold

text: are examples of good conductors.

text: Lewis's theory of chemical bonding continued to evolve and, in 1916, he published his seminal article "The Atom of the Molecule", which suggested that a chemical bond is a pair of electrons shared by two atoms. Lewis's model equated the classical chemical bond with the sharing of a pair of electrons between the two bonded atoms. Lewis introduced the  "electron dot diagrams" in this paper to symbolize the electronic structures of atoms and molecules. Now known as Lewis structures, they are discussed in virtually every introductory chemistry book.

text: Lewis's theory of chemical bonding continued to evolve and, in 1916, he published his seminal article "The Atom of the Molecule", which suggested that a chemical bond is a pair of electrons shared by two atoms. Lewis's model equated the classical

text: chemical bond

text: with the sharing of a pair of electrons between the two bonded atoms. Lewis introduced the  "electron dot diagrams" in this paper to symbolize the electronic structures of atoms and molecules. Now known as

text: Lewis structures

text: , they are discussed in virtually every introductory chemistry book.

text: As one progresses down a group on the periodic table, the ionization energy will likely decrease since the valence electrons are farther away from the nucleus and experience a weaker attraction to the nucleus's positive charge. There will be an increase of ionization energy from left to right of a given period and a decrease from top to bottom. As a rule, it requires far less energy to remove an outer-shell electron than an inner-shell electron. As a result, the ionization energies for a given element will increase steadily within a given shell, and when starting on the next shell down will show a drastic jump in ionization energy. Simply put, the lower the principal quantum number, the higher the ionization energy for the electrons within that shell. The exceptions are the elements in the boron and oxygen family, which require slightly less energy than the general trend.

text: As one progresses down a group on the periodic table, the ionization energy will likely decrease since the

text: valence electrons

text: are farther away from the nucleus and experience a weaker attraction to the nucleus's positive charge. There will be an increase of ionization energy from left to right of a given period and a decrease from top to bottom. As a rule, it requires far less energy to remove an outer-shell electron than an inner-shell electron. As a result, the ionization energies for a given element will increase steadily within a given shell, and when starting on the next shell down will show a drastic jump in ionization energy. Simply put, the lower the principal quantum number, the higher the ionization energy for the electrons within that shell. The exceptions are the elements in the boron and oxygen family, which require slightly less energy than the general trend.

text: Atoms that have an almost full or almost empty valence shells tend to be very reactive. Atoms that are strongly electronegative (as is the case with halogens) often only have one or two empty orbitals in their valence shell, and frequently bond with other molecules or gain electrons to form anions. Atoms that are weakly electronegative (such as alkali metals) have relatively few valence electrons that can easily be shared with atoms that are strongly electronegative. As a result, weakly electronegative atoms tend to distort their electrons cloud and form cations.

text: Atoms that have an almost full or almost empty

text: valence shell

text: s tend to be very

text: reactive

text: . Atoms that are strongly electronegative (as is the case with

text: halogens

text: ) often only have one or two empty orbitals in their valence shell, and frequently

text: bond

text: with other molecules or gain electrons to form

text: anions

text: . Atoms that are weakly electronegative (such as

text: alkali metals

text: ) have relatively few valence electrons that can easily be shared with atoms that are strongly electronegative. As a result, weakly electronegative atoms tend to distort their electrons cloud and form

text: cations

text: Isocyanic acid, HNCO, is produced when a cyanate salt is acidified. Although the electronic structure according to valence bond theory can be written as HN=C=O, as illustrated, the vibrational spectrum has a band at 2268.8 cm in the gas phase, which clearly requires the C≡N bond to be a triple bond. In valence bond theory the canonical form HN≡C-O is the major contributor to the resonance hybrid.The pure compound has a melting point of −86.8 °C and a boiling point of 23.5 °C, so it is volatile at ambient temperatures. In aqueous solution it is a weak acid.

text: Isocyanic acid

text: , HNCO, is produced when a cyanate salt is acidified. Although the electronic structure according to

text: valence bond theory

text: can be written as HN=C=O, as illustrated, the vibrational spectrum has a band at 2268.8 cm in the gas phase, which clearly requires the C≡N bond to be a triple bond. In valence bond theory the canonical form HN≡C-O is the major contributor to the

text: resonance hybrid

text: .The pure compound has a

text: melting point

text: of −86.8 °C and a

text: boiling point

text: of 23.5 °C, so it is volatile at ambient temperatures. In aqueous solution it is a

text: weak acid

text: A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode, all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over part or all of the molecule. These materials have conductivity levels ranging from insulators to conductors, and are therefore considered organic semiconductors. The highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors.

text: A typical OLED is composed of a layer of organic materials situated between two electrodes, the

text: anode

text: and

text: cathode

text: , all deposited on a

text: substrate

text: . The organic molecules are electrically conductive as a result of

text: delocalization

text: of

text: pi electrons

text: caused by

text: conjugation

text: over part or all of the molecule. These materials have conductivity levels ranging from insulators to conductors, and are therefore considered

text: organic semiconductor

text: s. The highest occupied and lowest unoccupied molecular orbitals (

text: HOMO and LUMO

text: ) of organic semiconductors are analogous to the

text: valence

text: and

text: conduction

text: bands of inorganic semiconductors.

text: Individual electrons can now be easily confined in ultra small (, ) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4 K) to about −258 °C (15 K). The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the effective mass tensor.

text: Individual electrons can now be easily confined in ultra small (, ) CMOS transistors operated at cryogenic temperature over a range of −269 °C (4

text: K

text: ) to about −258 °C (15

text: K

text: ). The electron wavefunction spreads in a semiconductor lattice and negligibly interacts with the valence band electrons, so it can be treated in the single particle formalism, by replacing its mass with the

text: effective mass tensor

text: In practice, the current density mainly comes out of a group of states close in energy to state F, most of which lie within the heavily shaded area in the energy-space diagram. Since, for a free-electron model, the contribution to the current density is directly proportional to the area in energy space (with the Sommerfeld supply density z as the constant of proportionality), it is useful to think of the ECD as drawn from electron states in an area of size d (measured in eV) in the energy-space diagram. That is, it is useful to think of the ECD as drawn from states in the heavily shaded area in Fig. 1. (This approximation gets slowly worse as temperature increases.)

text: In practice, the current density mainly comes out of a group of states close in energy to state F, most of which lie within the heavily shaded area in the energy-space diagram. Since, for a

text: free-electron model

text: , the contribution to the current density is directly proportional to the area in energy space (with the

text: Sommerfeld

text: supply density z as the constant of proportionality), it is useful to think of the ECD as drawn from electron states in an area of size d (measured in eV) in the energy-space diagram. That is, it is useful to think of the ECD as drawn from states in the heavily shaded area in Fig. 1. (This approximation gets slowly worse as temperature increases.)

text: Like the other alkali metals, lithium has a single valence electron that is easily given up to form a cation. Because of this, lithium is a good conductor of heat and electricity as well as a highly reactive element, though it is the least reactive of the alkali metals. Lithium's low reactivity is due to the proximity of its valence electron to its nucleus (the remaining two electrons are in the 1s orbital, much lower in energy, and do not participate in chemical bonds).

text: Like the other

text: alkali metal

text: s, lithium has a single

text: valence electron

text: that is easily given up to form a

text: cation

text: . Because of this, lithium is a good conductor of heat and electricity as well as a highly reactive element, though it is the least reactive of the alkali metals. Lithium's low reactivity is due to the proximity of its valence electron to its

text: nucleus

text: (the remaining

text: two electrons

text: are in the

text: 1s orbital

text: , much lower in energy, and do not participate in chemical bonds).

text: The many electron Schrödinger equation can be very much simplified if electrons are divided in two groups: valence electrons and inner core electrons. The electrons in the inner shells are strongly bound and do not play a significant role in the chemical binding of atoms; they also partially screen the nucleus, thus forming with the nucleus an almost inert core. Binding properties are almost completely due to the valence electrons, especially in metals and semiconductors.This separation suggests that inner electrons can be ignored in a large number of cases, thereby reducing the atom to an ionic core that interacts with the valence electrons. The use of an effective interaction, a pseudopotential, that approximates the potential felt by the valence electrons, was first proposed by Fermi in 1934 and Hellmann in 1935. In spite of the simplification pseudo-potentials introduce in calculations, they remained forgotten until the late 50's.

text: The many electron

text: Schrödinger equation

text: can be very much simplified if electrons are divided in two groups:

text: valence electrons

text: and inner core

text: electrons

text: . The electrons in the inner shells are strongly bound and do not play a significant role in the chemical binding of

text: atoms

text: ; they also partially

text: screen

text: the nucleus, thus forming with the

text: nucleus

text: an almost inert core. Binding properties are almost completely due to the valence electrons, especially in metals and semiconductors.This separation suggests that inner electrons can be ignored in a large number of cases, thereby reducing the atom to an ionic core that interacts with the valence electrons. The use of an effective interaction, a

text: pseudopotential

text: , that approximates the potential felt by the valence electrons, was first proposed by Fermi in 1934 and Hellmann in 1935. In spite of the simplification pseudo-potentials introduce in calculations, they remained forgotten until the late 50's.

text: The luminescent properties of quantum dots arise from exciton decay (recombination of electron hole pairs) which can proceed through a radiative or nonradiative pathway.  The radiative pathway involves electrons relaxing from the conduction band to the valence band by emitting photons with wavelengths corresponding to the semiconductor's bandgap. Nonradiative recombination can occur through energy release via phonon emission or Auger recombination. In this size regime, quantum confinement effects lead to a size dependent increasing bandgap with observable, quantized energy levels.  The quantized energy levels observed in quantum dots lead to electronic structures that are intermediate between single molecules which have a single HOMO-LUMO gap and bulk semiconductors which have continuous energy levels within bands

text: The luminescent properties of quantum dots arise from

text: exciton

text: decay (recombination of electron hole pairs) which can proceed through a radiative or nonradiative pathway.  The radiative pathway involves electrons relaxing from the conduction band to the valence band by emitting photons with wavelengths corresponding to the semiconductor's bandgap. Nonradiative recombination can occur through energy release via phonon emission or

text: Auger recombination

text: . In this size regime, quantum confinement effects lead to a size dependent increasing

text: bandgap

text: with observable, quantized energy levels.  The quantized energy levels observed in quantum dots lead to electronic structures that are intermediate between single molecules which have a single

text: HOMO

text: LUMO

text: gap and bulk semiconductors which have continuous energy levels within bands

text: Quantum mechanical models and simulations of quantum dots often involve the interaction of electrons with a pseudopotential or random matrix.

text: Quantum mechanical models and simulations of quantum dots often involve the interaction of electrons with a

text: pseudopotential

text: or

text: random matrix

text: AlO commonly exists as a gas, since the solid state is not stable at room temperature and is only stable between 1050 and 1600 °C.  Aluminium (I) Oxide is formed by heating Al and AlO in vacuo while in the presence of SiO and C, and only by condensing the products.  Information is not commonly available on this compound due to instability, complex high-temperature spectra, difficult detection, and identification.  In reduction, AlO is a major component of vapors of AlO.  There are also 12 valence electrons in AlO.  AlO molecules can be detected by mass spectrometry, infrared emission, and ultraviolet absorption and emission in the gas phase.  The molecule is linear at equilibrium in the ground state. In term of valence bond theory, these molecules can be described as adopting sp orbital hybridisation, featuring one sigma and two pi bonds. The corresponding ground state for the valence electrons is 1σ 1σ* 2σ 1π 1π*, where the 1σ and 1σ* orbitals cancel, and the 1π and 1π* partially cancel. The overall configuration yields a divalent triplet molecule, with one lone electron focused on the oxygen atom and the other focused equally between the aluminium atoms.

text: AlO commonly exists as a gas, since the solid state is not stable at room temperature and is only stable between 1050 and 1600 °C.  Aluminium (I) Oxide is formed by heating Al and AlO in vacuo while in the presence of SiO and C, and only by condensing the products.  Information is not commonly available on this compound due to instability, complex high-temperature spectra, difficult detection, and identification.  In reduction, AlO is a major component of vapors of AlO.  There are also 12 valence electrons in AlO.  AlO molecules can be detected by

text: mass spectrometry

text: infrared

text: emission, and

text: ultraviolet

text: absorption and emission in the gas phase.  The molecule is linear at equilibrium in the

text: ground state

text: . In term of valence bond theory, these molecules can be described as adopting sp

text: orbital hybridisation

text: , featuring one sigma and two pi bonds. The corresponding ground state for the valence electrons is 1σ 1σ* 2σ 1π 1π*, where the 1σ and 1σ* orbitals cancel, and the 1π and 1π* partially cancel. The overall configuration yields a divalent triplet molecule, with one lone electron focused on the oxygen atom and the other focused equally between the aluminium atoms.

text: The bonding in copper sulfides cannot be correctly described in terms of a simple oxidation state formalism because the Cu-S bonds are somewhat covalent rather than ionic in character, and have a high degree of delocalization resulting in complicated electronic band structures. Although many textbooks (e.g.) give the mixed valence formula (Cu)(Cu)(S)(S) for CuS, X-ray photoelectron spectroscopic data give strong evidence that, in terms of the simple oxidation state formalism, all the known copper sulfides should be considered as purely monovalent copper compounds, and more appropriate formulae would be (Cu)(S)(S) for CuS, and (Cu)(S) for CuS, respectively.

text: The bonding in copper sulfides cannot be correctly described in terms of a simple oxidation state formalism because the Cu-S bonds are somewhat

text: covalent

text: rather than

text: ionic

text: in character, and have a high degree of

text: delocalization

text: resulting in complicated

text: electronic band structure

text: s. Although many textbooks (e.g.) give the mixed valence formula (Cu)(Cu)(S)(S) for CuS, X-ray photoelectron spectroscopic data give strong evidence that, in terms of the simple oxidation state formalism, all the known copper sulfides should be considered as purely monovalent copper compounds, and more appropriate formulae would be (Cu)(S)(S) for CuS, and (Cu)(S) for CuS, respectively.

text: http://rdp.cme.msu.edu/ The Ribosomal Database Project (RDP) is a curated database that offers ribosome data along with related programs and services. The offerings include phylogenetically ordered alignments of ribosomal RNA (rRNA) sequences, derived phylogenetic trees, rRNA secondary structure diagrams and various software packages for handling, analyzing and displaying alignments and trees. The data are available via ftp and electronic mail. Certain analytic services are also provided by the electronic mail server.

text: The chemistry of element 120 is predicted to be closer to that of calcium or strontium instead of barium or radium. This is unusual as periodic trends would predict element 120 to be more reactive than barium and radium. This lowered reactivity is due to the expected energies of element 120's valence electrons, increasing element 120's ionization energy and decreasing the metallic and ionic radii.

text: The chemistry of element 120 is predicted to be closer to that of

text: calcium

text: or

text: strontium

text: instead of

text: barium

text: or

text: radium

text: . This is unusual as

text: periodic trends

text: would predict element 120 to be more reactive than barium and radium. This lowered

text: reactivity

text: is due to the expected energies of element 120's valence electrons, increasing element 120's

text: ionization energy

text: and decreasing the

text: metallic

text: and

text: ionic radii

text: The elements in group-3 have an ns(n-1)d configuration. The first transition series is present in the 4th period, and starts after Ca (Z=20) of group-2 with the configuration [Ar]4s, or scandium (Sc), the first element of group-3 with atomic number Z=21 and configuration [Ar]4s3d, depending on the definition used. As we move from left to right, electrons are added to the same d-sub-shell till it is complete. The element of group-11 in the first transition series is copper (Cu) with an untypical configuration [Ar]4s13d. Despite the filled d subshell in metallic copper it nevertheless forms a stable ion with an incomplete d subshell. Since the electrons added fill the  orbitals, the properties of the d-block elements are quite different from those of s and p block elements in which the filling occurs either in s or in p-orbitals of the valence shell.The electronic configuration of the individual elements present in all the d block series are given below:

text: The elements in group-3 have an ns(n-1)d configuration. The first transition series is present in the 4th period, and starts after Ca (Z=20) of group-2 with the configuration [Ar]4s, or

text: scandium

text: (Sc), the first element of group-3 with atomic number Z=21 and configuration [Ar]4s3d, depending on the definition used. As we move from left to right, electrons are added to the same d-sub-shell till it is complete. The element of group-11 in the first transition series is

text: copper

text: (Cu) with an untypical configuration [Ar]4s13d. Despite the filled d subshell in metallic copper it nevertheless forms a stable ion with an incomplete d subshell. Since the electrons added fill the  orbitals, the properties of the d-block elements are quite different from those of s and p block elements in which the filling occurs either in s or in p-orbitals of the valence shell.The electronic configuration of the individual elements present in all the d block series are given below:

text: For example, when silicon (Si), having four valence electrons, needs to be doped as an n-type semiconductor, elements from group V like phosphorus (P) or arsenic (As) can be used because they have five valence electrons. A dopant with five valence electrons is also called a pentavalent impurity. Other pentavalent dopants are antimony (Sb) and  bismuth (Bi).

text: For example, when

text: silicon

text: (Si), having four

text: valence electron

text: s, needs to be doped as an

text: n-type semiconductor

text: , elements from

text: group V

text: like

text: phosphorus

text: (P) or

text: arsenic

text: (As) can be used because they have five valence electrons. A dopant with five valence electrons is also called a pentavalent impurity. Other pentavalent dopants are

text: antimony

text: (Sb) and

text: bismuth

text: (Bi).

text: The scintillation process in inorganic materials is due to the electronic band structure found in crystals and is not molecular in nature as is the case with organic scintillators. An incoming particle can excite an electron from the valence band to either the conduction band or the exciton band (located just below the conduction band and separated from the valence band by an energy gap; see picture). This leaves an associated hole behind, in the valence band. Impurities create electronic levels in the forbidden gap. The excitons are loosely bound electron-hole pairs which wander through the crystal lattice until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). The activator impurities are typically chosen so that the emitted light is in the visible range or near-UV where photomultipliers are effective. The holes associated with electrons in the conduction band are independent from the latter. Those holes and electrons are captured successively by impurity centers exciting certain metastable states not accessible to the excitons. The delayed de-excitation of those metastable impurity states again results in scintillation light (slow component).

text: electronic band structure

text: found in

text: crystal

text: s and is not molecular in nature as is the case with organic scintillators. An incoming particle can excite an electron from the

text: valence band

text: to either the

text: conduction band

text: or the

text: exciton

text: energy gap

text: ; see picture). This leaves an associated

text: hole

text: forbidden gap

text: . The excitons are loosely bound

text: electron-hole pair

text: s which wander through the

text: crystal lattice

text: until they are captured as a whole by impurity centers. The latter then rapidly de-excite by emitting scintillation light (fast component). The

text: activator

text: impurities are typically chosen so that the emitted light is in the visible range or

text: near-UV

text: where

text: photomultiplier

text: metastable state

text: s not accessible to the excitons. The delayed de-excitation of those metastable impurity states again results in scintillation light (slow component).

text: A third major interest that originated during Lewis’ Harvard years was his valence theory. In 1902, while trying to explain the laws of valence to his students, Lewis conceived the idea that atoms were built up of a concentric series of cubes with electrons at each corner. This “cubic atom” explained the cycle of eight elements in the periodic table and was in accord with the widely accepted belief that chemical bonds were formed by transfer of electrons to give each atom a complete set of eight. This electrochemical theory of valence found its most elaborate expression in the work of Richard Abegg in 1904, but Lewis’ version of this theory was the only one to be embodied in a concrete atomic model. Again Lewis’ theory did not interest his Harvard mentors, who, like most American chemists of that time, had no taste for such speculation. Lewis did not publish his theory of the cubic atom, but in 1916 it became an important part of his theory of the shared electron pair bond.

text: and for electrons in valence band as

text: and for electrons in valence band as

text: Complexes with fewer than 18 valence electrons tend to show enhanced reactivity.  Thus, the 18-electron rule is often a recipe for non-reactivity in either a stoichiometric or a catalytic sense.

text: Complexes with fewer than 18 valence electrons tend to show enhanced reactivity.  Thus, the 18-electron rule is often a recipe for non-reactivity in either a

text: stoichiometric

text: or a

text: catalytic

text: sense.

text: Valence House is in Becontree Avenue. It is the only surviving of the five manor houses of Dagenham.Dating back to the 13th century it is sited in parkland and is partially surrounded by a moat. Valence House is the borough's local history museum, displaying an impressive collection of artifacts and archives that tell the story of the lives of the people of Barking and Dagenham. The collection also includes portraits, family papers and other mementoes of the Fanshawe family, who occupied Parsloes Manor, since demolished, from the sixteenth century.The Fanshawe collection is "one of the best collections of gentry portraits in the country and is of international importance," according to Valence House.Among members of the Fanshawe family was the diplomat Sir Richard Fanshawe, 1st Baronet, whose portrait is at Valence House. Nine successive members of the Fanshawe family served as Remembrancer to the Crown, following Henry Fanshawe's appointment to the position by Queen Elizabeth I in 1566. The appointment made possible the family's rise to prominence.

text: Valence House

text: is in Becontree Avenue. It is the only surviving of the five manor houses of Dagenham.Dating back to the 13th century it is sited in parkland and is partially surrounded by a moat. Valence House is the borough's local history museum, displaying an impressive collection of artifacts and archives that tell the story of the lives of the people of Barking and Dagenham. The collection also includes portraits, family papers and other mementoes of the Fanshawe family, who occupied

text: Parsloes Manor

text: , since demolished, from the sixteenth century.The Fanshawe collection is "one of the best collections of gentry portraits in the country and is of international importance," according to Valence House.Among members of the Fanshawe family was the diplomat

text: Sir Richard Fanshawe, 1st Baronet

text: , whose portrait is at Valence House. Nine successive members of the Fanshawe family served as

text: Remembrancer

text: to the Crown, following Henry Fanshawe's appointment to the position by

text: Queen Elizabeth I

text: in 1566. The appointment made possible the family's rise to prominence.

text: Flerovium is a member of group 14 in the periodic table, below carbon, silicon, germanium, tin, and lead. Every previous group 14 element has four electrons in its valence shell, forming a valence electron configuration of nsnp. In flerovium's case, the trend will be continued and the valence electron configuration is predicted to be 7s7p; flerovium will behave similarly to its lighter congeners in many respects. Differences are likely to arise; a largely contributing effect is the spin–orbit (SO) interaction—the mutual interaction between the electrons' motion and spin. It is especially strong for the superheavy elements, because their electrons move faster than in lighter atoms, at velocities comparable to the speed of light. In relation to flerovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p. These effects cause flerovium's chemistry to be somewhat different from that of its lighter neighbours.

text: Flerovium is a member of group 14 in the

text: periodic table

text: , below

text: carbon

text: silicon

text: germanium

text: tin

text: , and lead. Every previous group 14 element has four electrons in its valence shell, forming a

text: valence electron

text: configuration of nsnp. In flerovium's case, the trend will be continued and the valence electron configuration is predicted to be 7s7p; flerovium will behave similarly to its lighter

text: congeners

text: in many respects. Differences are likely to arise; a largely contributing effect is the

text: spin–orbit (SO) interaction

text: spin

text: . It is especially strong for the superheavy elements, because their electrons move faster than in lighter atoms, at velocities comparable to the

text: speed of light

text: . In relation to flerovium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the

text: inert pair effect

text: azimuthal

text: quantum number

text: l from 1 to  and  for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p. These effects cause flerovium's chemistry to be somewhat different from that of its lighter neighbours.

text: The uranyl ion is linear and symmetrical, with both U–O bond lengths of about 180 pm. The bond lengths are indicative of the presence of multiple bonding between the uranium and oxygen atoms. Since uranium(VI) has the electronic configuration [ radon ], the electrons used in forming the U-O bonds are supplied by the oxygen atoms. The electrons are donated into empty atomic orbitals on the uranium atom. The empty orbitals of lowest energy are 7s, 5f and 6d. In terms of valence bond theory the sigma bonds may be formed using d and f to construct sd, sf and df hybrid orbitals (the z-axis passes through the oxygen atoms). (d, d) and (f and f) may be used to form pi bonds. Since the pair of d or f orbitals used in bonding are doubly degenerate this equates to an overall bond order of three.

text: The uranyl ion is linear and symmetrical, with both U–O bond lengths of about 180 pm. The bond lengths are indicative of the presence of multiple bonding between the uranium and oxygen atoms. Since uranium(VI) has the

text: electronic configuration

text: radon

text: ], the electrons used in forming the U-O bonds are supplied by the oxygen atoms. The electrons are donated into empty

text: atomic orbitals

text: on the uranium atom. The empty orbitals of lowest energy are 7s, 5f and 6d. In terms of

text: valence bond theory

text: the

text: sigma bond

text: s may be formed using d and f to construct sd, sf and df

text: hybrid orbitals

text: (the z-axis passes through the oxygen atoms). (d, d) and (f and f) may be used to form

text: pi bond

text: s. Since the pair of d or f orbitals used in bonding are

text: doubly degenerate

text: this equates to an overall

text: bond order

text: of three.

text: Kaufman is noted for carrying out the first all-valence-electron, three-dimensional quantum-chemical calculations, and for research on the clinical effects of tranquilizers and narcotic drugs.

text: Especially in the area of organometallic chemistry, ligands are classified as L and X (or combinations of the two). The classification scheme – the "CBC Method" for Covalent Bond Classification – was popularized by M.L.H. Green and "is based on the notion that there are three basic types [of ligands]... represented by the symbols L, X, and Z, which correspond respectively to 2-electron, 1-electron and 0-electron neutral ligands." Another type of ligand worthy of consideration is the LX ligand which as expected from the used conventional representation will donate three electrons if NVE (Number of Valence Electrons) required. Example is alkoxy ligands( which is regularly known as X ligand too). L ligands are derived from charge-neutral precursors and are represented by amines, phosphines, CO, N, and alkenes. X ligands typically are derived from anionic precursors such as chloride but includes ligands where salts of anion do not really exist such as hydride and alkyl. Thus, the complex IrCl(CO)(PPh) is classified as an MXL complex, since CO and the two PPh ligands are classified as Ls. The oxidative addition of H2 to IrCl(CO)(PPh) gives an 18e MLX product, IrClH(CO)(PPh). EDTA is classified as an LX ligand, as it features four anions and two neutral donor sites. Cp is classified as an LX ligand.

text: Especially in the area of

text: organometallic chemistry

text: , ligands are classified as L and X (or combinations of the two). The classification scheme – the "CBC Method" for Covalent Bond Classification – was popularized by

text: M.L.H. Green

text: and "is based on the notion that there are three basic types [of ligands]... represented by the symbols L, X, and Z, which correspond respectively to 2-electron, 1-electron and 0-electron neutral ligands." Another type of ligand worthy of consideration is the LX ligand which as expected from the used conventional representation will donate three electrons if NVE (Number of Valence Electrons) required. Example is alkoxy ligands( which is regularly known as X ligand too). L ligands are derived from charge-neutral precursors and are represented by

text: amine

text: s,

text: phosphine

text: s,

text: CO

text: , N, and

text: alkene

text: s. X ligands typically are derived from anionic precursors such as chloride but includes ligands where salts of anion do not really exist such as hydride and alkyl. Thus, the complex

text: IrCl(CO)(PPh)

text: is classified as an MXL complex, since CO and the two PPh ligands are classified as Ls. The

text: oxidative addition

text: of H2 to IrCl(CO)(PPh) gives an 18e MLX product, IrClH(CO)(PPh).

text: EDTA

text: is classified as an LX ligand, as it features four anions and two neutral donor sites.

text: Cp

text: is classified as an LX ligand.

text: Consequently, some expect oganesson to have similar physical and chemical properties to other members of its group, most closely resembling the noble gas above it in the periodic table, radon.Following the periodic trend, oganesson would be expected to be slightly more reactive than radon. However, theoretical calculations have shown that it could be quite reactive, so that it probably cannot be considered a noble gas. In addition to being far more reactive than radon, oganesson may be even more reactive than elements flerovium and copernicium. The reason for the apparent enhancement of the chemical activity of oganesson relative to radon is an energetic destabilization and a radial expansion of the last occupied 7p-subshell. More precisely, considerable spin–orbit interactions between the 7p electrons and the inert 7s electrons effectively lead to a second valence shell closing at flerovium, and a significant decrease in stabilization of the closed shell of element 118. It has also been calculated that oganesson, unlike the other noble gases, binds an electron with release of energy—or in other words, it exhibits positive electron affinity, due to the relativistically stabilized 8s energy level.

text: Consequently, some expect oganesson to have similar physical and chemical properties to other members of its group, most closely resembling the noble gas above it in the periodic table,

text: radon

text: .Following the

text: periodic trend

text: , oganesson would be expected to be slightly more reactive than radon. However, theoretical calculations have shown that it could be quite reactive, so that it probably cannot be considered a noble gas. In addition to being far more reactive than radon, oganesson may be even more reactive than elements

text: flerovium

text: and

text: copernicium

text: . The reason for the apparent enhancement of the chemical activity of oganesson relative to radon is an energetic destabilization and a radial expansion of the last occupied 7p-

text: subshell

text: . More precisely, considerable

text: spin–orbit interaction

text: s between the 7p electrons and the inert 7s electrons effectively lead to a second valence shell closing at

text: flerovium

text: , and a significant decrease in stabilization of the closed shell of element 118. It has also been calculated that oganesson, unlike the other noble gases, binds an electron with release of energy—or in other words, it exhibits positive

text: electron affinity

text: , due to the relativistically stabilized 8s energy level.

text: Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds. The outermost electron shell of an atom in its uncombined state is known as the valence shell, and the electrons inthat shell are called valence electrons. The number of valence electrons determines the bondingbehavior with other atoms. Atoms tend to chemically react with each other in a manner that fills (or empties) their outer valence shells. For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound sodium chloride and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus, chemical bonding between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the organic compounds.

text: Valency is the combining power of an element. It is equal to number of hydrogen atoms that atom can combine or displace in forming compounds. The outermost electron shell of an atom in its uncombined state is known as the

text: valence shell

text: , and the electrons inthat shell are called

text: valence electron

text: s. The number of valence electrons determines the

text: bonding

text: behavior with other atoms. Atoms tend to

text: chemically react

text: with each other in a manner that fills (or empties) their outer valence shells. For example, a transfer of a single electron between atoms is a useful approximation for bonds that form between atoms with one-electron more than a filled shell, and others that are one-electron short of a full shell, such as occurs in the compound

text: sodium chloride

text: and other chemical ionic salts. However, many elements display multiple valences, or tendencies to share differing numbers of electrons in different compounds. Thus,

text: chemical bond

text: ing between these elements takes many forms of electron-sharing that are more than simple electron transfers. Examples include the element carbon and the

text: organic compounds

text: Additionally, the correlation diagram for any 4n electrocyclic reaction will resemble the diagram for the 4 electron cyclization of 1,3-butadiene, while the correlation diagram any 4n+2 electron electrocyclic reaction will resemble the correlation diagram for the 6 electron cyclization of 1,3,5-hexatriene.

text: Main-group elements in the third and later rows of the periodic table can form hypercoordinate or  hypervalent molecules in which the central main-group atom is bonded to more than four other atoms, such as phosphorus pentachloride, PCl, and sulfur hexafluoride, SF. For example in PCl, if it is supposed that there are five true covalent bonds in which five distinct electron pairs are shared, then the phosphorus would be surrounded by 10 valence electrons in violation of the octet rule. In the early days of quantum mechanics, Pauling proposed that third-row atoms can form five bonds by using one s, three p and one d orbitals, or six bonds by using one s, three p and two d orbitals. To form five bonds, the one s, three p and one d orbitals combine to form five spd hybrid orbitals which each share an electron pair with a halogen atom, for a total of 10 shared electrons, two more than the octet rule predicts. Similarly to form six bonds, the six spd hybrid orbitals form six bonds with 12 shared electrons. In this model the availability of empty d orbitals is used to explain the fact that third-row atoms such as phosphorus and sulfur can form more than four covalent bonds, whereas second-row atoms such as nitrogen and oxygen are strictly limited by the octet rule.

text: Main-group elements in the third and later rows of the periodic table can form hypercoordinate or

text: hypervalent molecule

text: s in which the central main-group atom is bonded to more than four other atoms, such as

text: phosphorus pentachloride

text: , PCl, and

text: sulfur hexafluoride

text: , SF. For example in PCl, if it is supposed that there are five true

text: covalent bond

text: s in which five distinct electron pairs are shared, then the phosphorus would be surrounded by 10 valence electrons in violation of the octet rule. In the early days of quantum mechanics,

text: Pauling

text: proposed that third-row atoms can form five bonds by using one s, three p and one d orbitals, or six bonds by using one s, three p and two d orbitals. To form five bonds, the one s, three p and one d orbitals combine to form five spd

text: hybrid orbital

text: s which each share an electron pair with a halogen atom, for a total of 10 shared electrons, two more than the octet rule predicts. Similarly to form six bonds, the six spd hybrid orbitals form six bonds with 12 shared electrons. In this model the availability of empty d orbitals is used to explain the fact that third-row atoms such as phosphorus and sulfur can form more than four covalent bonds, whereas second-row atoms such as nitrogen and oxygen are strictly limited by the octet rule.

text: Resonant interband tunneling diodes (RITDs) combine the structures and behaviors of both intraband resonant tunneling diodes (RTDs) and conventional interband tunneling diodes, in which electronic transitions occur between the energy levels in the quantum wells in the conduction band and that in the valence band. Like resonant tunneling diodes, resonant interband tunneling diodes can be realized in both the III-V and Si/SiGe materials systems.

text: Diborane adopts a D structure containing four terminal and two bridging hydrogen atoms. The model determined by molecular orbital theory indicates that the bonds between boron and the terminal hydrogen atoms are conventional 2-center, 2-electron covalent bonds. The bonding between the boron atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the terminal hydrogen atoms, each boron has one valence electron remaining for additional bonding. The bridging hydrogen atoms provide one electron each. Thus the BH ring is held together by four electrons, an example of 3-center 2-electron bonding. This type of bond is sometimes called a 'banana bond'. The lengths of the B-H bonds and the B-H bonds are 1.33 and 1.19 Å respectively, and this difference in the lengths of these bonds reflects the difference in their strengths, the B-H bonds being relatively weaker.  The weakness of the B-H vs B-H bonds is indicated by their vibrational signatures in the infrared spectrum, being ~2100 and 2500 cm, respectively. The structure is isoelectronic with CH, which would arise from the diprotonation of the planar molecule ethene. Diborane is one of many compounds with such unusual bonding.<ref>{{ cite journal | author = Laszlo, P. | title = A Diborane Story | journal= Angewandte Chemie International Edition | year = 2000  | volume = 39 | issue = 12 | pages = 2071–2072 | doi = 10.1002/1521-3773(20000616)39:12

text: Diborane adopts a D structure containing four terminal and two bridging hydrogen atoms. The model determined by

text: molecular orbital theory

text: indicates that the bonds between boron and the terminal hydrogen atoms are conventional 2-center, 2-electron

text: covalent bond

text: s. The bonding between the boron atoms and the bridging hydrogen atoms is, however, different from that in molecules such as hydrocarbons. Having used two electrons in bonding to the terminal hydrogen atoms, each boron has one

text: valence electron

text: remaining for additional bonding. The bridging hydrogen atoms provide one electron each. Thus the BH ring is held together by four electrons, an example of

text: 3-center 2-electron bonding

text: . This type of bond is sometimes called a 'banana bond'. The lengths of the B-H bonds and the B-H bonds are 1.33 and 1.19 Å respectively, and this difference in the lengths of these bonds reflects the difference in their strengths, the B-H bonds being relatively weaker.  The weakness of the B-H vs B-H bonds is indicated by their vibrational signatures in the

text: infrared spectrum

text: , being ~2100 and 2500 cm, respectively. The structure is

text: isoelectronic

text: with CH, which would arise from the diprotonation of the planar molecule

text: ethene

text: . Diborane is one of many compounds with such unusual bonding.<ref>{{ cite journal | author = Laszlo, P. | title = A Diborane Story | journal= Angewandte Chemie International Edition | year = 2000  | volume = 39 | issue = 12 | pages = 2071–2072 | doi = 10.1002/1521-3773(20000616)39:12

text: Hydrogen and chlorine were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one valence electron and can form only one bond with an atom that has an incomplete outer shell. Chlorine has seven valence electrons and can form only one bond with an atom that donates a valence electron to complete chlorine's outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating valence electrons.

text: Hydrogen

text: and

text: chlorine

text: were originally used as examples of univalent atoms, because of their nature to form only one single bond. Hydrogen has only one valence electron and can form only one bond with an atom that has an incomplete

text: outer shell

text: . Chlorine has seven valence electrons and can form only one bond with an atom that donates a valence electron to complete chlorine's outer shell. However, chlorine can also have oxidation states from +1 to +7 and can form more than one bond by donating valence electrons.

text: Nihonium is the first member of the 7p series of elements and the heaviest boron group element on the periodic table, below boron, aluminium, gallium, indium, and thallium. It is predicted to show many differences from its lighter homologues: a largely contributing effect is the spin–orbit (SO) interaction. It is especially strong for the superheavy elements, because their electrons move much faster than in lighter atoms, at velocities comparable to the speed of light. In relation to nihonium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the inert pair effect, and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called the subshell splitting. Computation chemists see the split as a change of the second (azimuthal) quantum number l from 1 to 1/2 and 3/2 for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p. These effects stabilize lower oxidation states: the first ionization energy of nihonium is expected to be 7.306 eV, the highest among the boron group elements. Hence, the most stable oxidation state of nihonium is predicted to be the +1 state, and nihonium is expected to be less reactive than thallium. Differences for other electron levels also exist. For example, the 6d electron levels (also split in halves, with four being 6d and six being 6d) are both raised, so that they are close in energy to the 7s ones. Thus, the 6d electron levels, being destabilized, should still be able to participate in chemical reactions in nihonium (as well as in the next 7p element, flerovium), thus making it behave in some ways like transition metals and allow higher oxidation states. Nihonium should hence also be able to show stable +3 and possibly also +5 oxidation states. However, the +3 state should still be less stable than the +1 state, following periodic trends. Nihonium should be the most electronegative among all the boron group elements: for example, in the compound NhTs, the negative charge is expected to be on the nihonium atom rather than the tennessine atom, the opposite of what would be expected from simple periodicity. The electron affinity of nihonium is calculated to be around 0.68 eV; in comparison, that of thallium is 0.4 eV. The high electron affinity and electronegativity of nihonium are due to it being only one electron short of the closed-shell valence electron configuration of flerovium (7s7p): this would make the −1 oxidation state of nihonium more stable than that of its lighter congener thallium. The standard electrode potential for the Nh/Nh couple is predicted to be −0.6 V.

text: Nihonium is the first member of the 7p series of elements and the heaviest

text: boron group

text: element on the periodic table, below

text: boron

text: aluminium

text: gallium

text: indium

text: , and

text: thallium

text: . It is predicted to show many differences from its lighter homologues: a largely contributing effect is the

text: spin–orbit (SO) interaction

text: . It is especially strong for the

text: superheavy element

text: s, because their electrons move much faster than in lighter atoms, at velocities comparable to the

text: speed of light

text: . In relation to nihonium atoms, it lowers the 7s and the 7p electron energy levels (stabilizing the corresponding electrons), but two of the 7p electron energy levels are stabilized more than the other four. The stabilization of the 7s electrons is called the

text: inert pair effect

text: , and the effect "tearing" the 7p subshell into the more stabilized and the less stabilized parts is called the subshell splitting. Computation chemists see the split as a change of the second (

text: azimuthal

text: quantum number

text: l from 1 to 1/2 and 3/2 for the more stabilized and less stabilized parts of the 7p subshell, respectively. For many theoretical purposes, the valence electron configuration may be represented to reflect the 7p subshell split as 7s7p. These effects stabilize lower oxidation states: the first ionization energy of nihonium is expected to be 7.306

text: eV

text: , the highest among the boron group elements. Hence, the most stable oxidation state of nihonium is predicted to be the +1 state, and nihonium is expected to be less reactive than thallium. Differences for other electron levels also exist. For example, the 6d electron levels (also split in halves, with four being 6d and six being 6d) are both raised, so that they are close in energy to the 7s ones. Thus, the 6d electron levels, being destabilized, should still be able to participate in chemical reactions in nihonium (as well as in the next 7p element,

text: flerovium

text: ), thus making it behave in some ways like

text: transition metal

text: s and allow higher oxidation states. Nihonium should hence also be able to show stable +3 and possibly also +5 oxidation states. However, the +3 state should still be less stable than the +1 state, following

text: periodic trends

text: . Nihonium should be the most

text: electronegative

text: among all the boron group elements: for example, in the compound Nh

text: Ts

text: , the negative charge is expected to be on the nihonium atom rather than the tennessine atom, the opposite of what would be expected from simple periodicity. The electron affinity of nihonium is calculated to be around 0.68 eV; in comparison, that of thallium is 0.4 eV. The high electron affinity and electronegativity of nihonium are due to it being only one electron short of the closed-shell valence electron configuration of

text: flerovium

text: (7s7p): this would make the −1 oxidation state of nihonium more stable than that of its lighter congener thallium. The

text: standard electrode potential

text: for the Nh/Nh couple is predicted to be −0.6 V.

text: The species MoCl feature Mo(II) (d) centers.  Six Mo(II) centers gives rise to a total of 24 valence electrons, or 2e/Mo-Mo vector.  More electron-deficient derivatives such as TaCl have fewer d-electrons.  For example, the naked cluster Ta, the core of TaCl would have 5(6) - 14 = 16 valence electrons.  Fewer d-electrons result in weakened M-M bonding and the extended Ta---Ta distances accommodate doubly bridging halides.

text: The species MoCl feature Mo(II) (d) centers.  Six Mo(II) centers gives rise to a total of 24 valence electrons, or 2e/Mo-Mo vector.  More electron-deficient derivatives such as TaCl have fewer d-electrons.  For example, the

text: naked cluster

text: Ta, the core of TaCl would have 5(6) - 14 = 16 valence electrons.  Fewer d-electrons result in weakened M-M bonding and the extended Ta---Ta distances accommodate doubly bridging halides.

text: In many ways the chemistry of group 2 elements (the alkaline earth metals) mimics that of group 12 elements because both groups have filled s shells for valence electrons. Thus, both groups have nominal valency 2 and oxidation state +2. All group 2 elements are electropositive towards carbon and electronegativity decreases down the row. At the same time the atomic radius increases resulting in increasingly ionic character, higher coordination numbers, and increased ligand reactivity.

text: In many ways the chemistry of group 2 elements (the

text: alkaline earth metals

text: ) mimics that of

text: group 12 element

text: s because both groups have filled

text: s shell

text: s for

text: valence electron

text: s. Thus, both groups have nominal

text: valency

text: 2 and

text: oxidation state

text: +2. All group 2 elements are electropositive towards carbon and

text: electronegativity

text: decreases down the row. At the same time the

text: atomic radius

text: increases resulting in increasingly ionic character, higher

text: coordination number

text: s, and increased ligand reactivity.

text: The bond valence model can be reduced to the traditional ionic model if certain conditions are satisfied.  These conditions require that atoms be divided into cations and anions in such a way that (a) the electronegativity of every anion is equal to, or greater than, the electronegativity of any of the cations, (b) that the structure is electroneutral when the ions carry charges equal to their valence, and (c) that all the bonds have a cation at one end and an anion at the other.  If these conditions are satisfied, as they are in many ionic and covalent compounds, the electrons forming a bond can all be formally assigned to the anion.  The anion thus acquires a formal negative charge and the cation a formal positive charge, which is the picture on which the ionic model is based.  The electrostatic flux that links the cation core to its bonding electrons now links the cation core to the anion.  In this picture, a cation and anion are bonded to each other if they are linked by electrostatic flux, with the flux being equal to the valence of the bond.  In a representative set of compounds Preiser et al. have confirmed that the electrostatic flux is the same as the bond valence determined from the bond lengths using Eq. 2.

text: Graphene is a zero-gap semiconductor, because its conduction and valence bands meet at the Dirac points. The Dirac points are six locations in momentum space, on the edge of the Brillouin zone, divided into two non-equivalent sets of three points. The two sets are labeled K and K'. The sets give graphene a valley degeneracy of . By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Four electronic properties separate it from other condensed matter systems.

text: Graphene is a zero-gap

text: semiconductor

text: , because its

text: conduction

text: and

text: valence bands

text: meet at the Dirac points. The Dirac points are six locations in

text: momentum space

text: , on the edge of the

text: Brillouin zone

text: , divided into two non-equivalent sets of three points. The two sets are labeled K and K'. The sets give graphene a valley degeneracy of . By contrast, for traditional semiconductors the primary point of interest is generally Γ, where momentum is zero. Four electronic properties separate it from other

text: condensed matter

text: systems.

text: Baro was born in Valence, Drôme, to a professor at the university of Valence. He studied at Tournon-sur-Rhône then at Valence, where he gained his law doctorate in 1615, and became secretary to Honoré d'Urfé, whom he had met when they attended the same collège in Tournon, he published Urfé's L'Astrée and wrote a fifth book for it himself (from his master's notes) in 1628. Coming to Paris, he attended on Madame de Chevreuse, sworn enemy of cardinal Richelieu, but even so the immense success of L'Astrée gained him entry to the Académie française in 1636. After being gentleman to Mademoiselle de Montpensier, he held two jobs towards the end of his life, that of procurer to the présidial de Valence and that of treasurer of France at Montpellier.  He died in Paris.

text: Baro was born in

text: Valence, Drôme

text: , to a professor at the

text: university of Valence

text: . He studied at

text: Tournon-sur-Rhône

text: then at Valence, where he gained his law doctorate in 1615, and became secretary to

text: Honoré d'Urfé

text: , whom he had met when they attended the same collège in

text: Tournon

text: , he published Urfé's

text: L'Astrée

text: and wrote a fifth book for it himself (from his master's notes) in 1628. Coming to Paris, he attended on

text: Madame de Chevreuse

text: , sworn enemy of

text: cardinal Richelieu

text: , but even so the immense success of L'Astrée gained him entry to the

text: Académie française

text: in 1636. After being gentleman to

entity_name: Marie de Bourbon, Duchess of Montpensier

text: Mademoiselle de Montpensier

text: , he held two jobs towards the end of his life, that of procurer to the présidial de Valence and that of treasurer of France at

text: Montpellier

text: .  He died in

text: Paris

text: For the La and Ac and the Lu and Lr periodic tables, the following two tables compare the idealized numbers of f electrons for period 6 and 7 elements in the f-block with their actual numbers of f electrons. There are 20 irregularities in the first table compared to 9 in the second.<br>

text: When counting electrons for each cluster, the number of valence electrons is enumerated. For each transition metal present, 10 electrons are subtracted from the total electron count. For example, in Rh(CO) the total number of electrons would be  =  = 26. Therefore, the cluster is a closo polyhedron because , with .

text: When counting electrons for each cluster, the number of

text: valence electrons

text: is enumerated. For each

text: transition metal

text: present, 10 electrons are subtracted from the total electron count. For example, in Rh(CO) the total number of electrons would be  =  = 26. Therefore, the cluster is a closo polyhedron because , with .

text: Warwick Electronics Inc. assigned Lester L. Kushner, an engineer with the Thomas Organ Company, and Brad Plunkett to write and submit the documentation for the wah-wah pedal patent. The patent application was submitted on February 24, 1967 which included technical diagrams of the pedal being connected to a four-stringed "guitar" (as noted from the "Description of the Preferred Embodiment"). Warwick Electronics Inc. was granted US patent 3530224 ("foot-controlled continuously variable preference circuit for musical instruments") on September 22, 1970.

text: Warwick Electronics Inc. assigned Lester L. Kushner, an engineer with the Thomas Organ Company, and Brad Plunkett to write and submit the documentation for the wah-wah pedal

text: patent

text: . The patent application was submitted on February 24, 1967 which included technical diagrams of the pedal being connected to a four-stringed "guitar" (as noted from the "Description of the Preferred Embodiment"). Warwick Electronics Inc. was granted US patent 3530224 ("foot-controlled continuously variable preference circuit for musical instruments") on September 22, 1970.

text: Perhaps the earliest examples of the importance of vibronic coupling were found during the 1930s. In 1934 Renner wrote about the vibronic coupling in an electronically excited Π-state in CO. Calculations of the lower excited levels of benzene by Sklar in 1937 (with the valence bond method) and later in 1938 by Goeppert-Mayer and Sklar (with the molecular orbital method) demonstrated a correspondence between the theoretical predictions and experimental results of the benzene spectrum. The benzene spectrum was the first qualitative computation of the efficiencies of various vibrations at inducing intensity absorption.

text: Perhaps the earliest examples of the importance of vibronic coupling were found during the 1930s. In 1934

text: Renner

text: wrote about the vibronic coupling in an electronically excited Π-state in CO. Calculations of the lower

text: excited levels

text: of

text: benzene

text: by Sklar in 1937 (with the valence bond method) and later in 1938 by

text: Goeppert-Mayer

text: and Sklar (with the

text: molecular orbital

text: method) demonstrated a correspondence between the theoretical predictions and experimental results of the benzene

text: spectrum

text: . The benzene spectrum was the first qualitative computation of the efficiencies of various vibrations at inducing intensity absorption.

text: In the diagram, the arrows representing current point in the direction of conventional current – the flow of electrons is in the opposite direction of the arrows because electrons carry negative electric charge. In active mode, the ratio of the collector current to the base current is called the DC current gain. This gain is usually 100 or more, but robust circuit designs do not depend on the exact value (for example see op-amp). The value of this gain for DC signals is referred to as

text: In the diagram, the arrows representing current point in the direction of

text: conventional current

text: – the flow of electrons is in the opposite direction of the arrows because electrons carry negative

text: electric charge

text: . In active mode, the ratio of the collector current to the base current is called the DC current gain. This gain is usually 100 or more, but robust circuit designs do not depend on the exact value (for example see

text: op-amp

text: ). The value of this gain for DC signals is referred to as

text: The second meaning of 'reactivity', that of whether or not a substance reacts, can be rationalised at the atomic and molecular level using older and simpler valence bond theory and also atomic and molecular orbital theory. Thermodynamically, a chemical reaction occurs because the products (taken as a group) are at a lower free energy than the reactants; the lower energy state is referred to as the 'more stable state'. Quantum chemistry provides the most in-depth and exact understanding of the reason this occurs. Generally, electrons exist in orbitals that are the result of solving the Schrödinger equation for specific situations.

text: The second meaning of 'reactivity', that of whether or not a substance reacts, can be rationalised at the atomic and molecular level using older and simpler valence bond theory and also atomic and molecular orbital theory. Thermodynamically, a

text: chemical reaction

text: occurs because the products (taken as a group) are at a lower

text: free energy

text: than the reactants; the lower energy state is referred to as the 'more stable state'.

text: Quantum chemistry

text: provides the most in-depth and exact understanding of the reason this occurs. Generally,

text: electron

text: s exist in

text: orbital

text: s that are the result of solving the

text: Schrödinger equation

text: for specific situations.

text: The most reactive kind of metallic element is an alkali metal of group 1 (e.g., sodium or potassium); this is because such an atom has only a single valence electron; during the formation of an ionic bond which provides the necessary ionization energy, this one valence electron is easily lost to form a positive ion (cation) with a closed shell (e.g., Na or K). An alkaline earth metal of Group 2 (e.g., magnesium) is somewhat less reactive, because each atom must lose two valence electrons to form a positive ion with a closed shell (e.g., Mg).

text: The most

text: reactive

text: kind of

text: metallic element

text: is an

text: alkali metal

text: of group 1 (e.g.,

text: sodium

text: or

text: potassium

text: ); this is because such an atom has only a single valence electron; during the formation of an

text: ionic bond

text: which provides the necessary

text: ionization energy

text: , this one valence electron is easily lost to form a positive

text: ion

text: (cation) with a closed shell (e.g., Na or K). An

text: alkaline earth metal

text: of Group 2 (e.g.,

text: magnesium

text: ) is somewhat less reactive, because each atom must lose two valence electrons to form a positive ion with a closed shell (e.g., Mg).

text: Core electrons are the electrons in an atom that are not valence electrons and therefore do not participate in bonding. The number of valence electrons of an element can be determined by the periodic table group of the element. With the exception of the transition metals in groups 3-12 and the Lanthanide and Actinide series, the number of valence electrons ranges from 0-8 electrons. All the non-valence electrons for an atom of that element are considered core electrons.Core electrons are tightly bound to the nucleus. Therefore, unlike valence electrons the core electrons play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence shell of electrons. In transition metals, the distinction between core and valence electrons is less distinct with electrons in the highest d-shell acting more like valence electrons than core electrons.

text: Core electrons are the electrons in an

text: atom

text: that are not

text: valence electron

text: s and therefore do not participate in bonding. The number of valence electrons of an element can be determined by the

text: periodic table group

text: of the element. With the exception of the

text: transition metal

text: s in groups 3-12 and the

text: Lanthanide

text: and

text: Actinide

text: series, the number of valence electrons ranges from 0-8 electrons. All the non-valence electrons for an atom of that element are considered core electrons.Core electrons are tightly bound to the nucleus. Therefore, unlike valence electrons the core electrons play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence shell of electrons. In transition metals, the distinction between core and valence electrons is less distinct with electrons in the highest

text: d-shell

text: acting more like valence electrons than core electrons.

text: <span id="CAS and old IUPAC">Two earlier group number systems exist: CAS (Chemical Abstracts Service) and old IUPAC. Both use numerals (Arabic or Roman) and letters A and B. Both systems agree on the numbers. The numbers indicate approximately the highest oxidation number of the elements in that group, and so indicate similar chemistry with other elements with the same numeral. The number proceeds in a linearly increasing fashion for the most part, once on the left of the table, and once on the right (see List of oxidation states of the elements), with some irregularities in the transition metals. However, the two systems use the letters differently. For example, potassium (K) has one valence electron. Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains two valence electrons.

text: <span id="CAS and old IUPAC">Two earlier group number systems exist: CAS (

text: Chemical Abstracts Service

text: ) and old IUPAC. Both use

text: numeral

text: s (

text: Arabic

text: or

text: Roman

text: ) and letters A and B. Both systems agree on the numbers. The numbers indicate approximately the highest oxidation number of the elements in that group, and so indicate similar chemistry with other elements with the same numeral. The number proceeds in a linearly increasing fashion for the most part, once on the left of the table, and once on the right (see

entity_name: List of oxidation states of the elements

text: List of oxidation states of the elements

text: ), with some irregularities in the transition metals. However, the two systems use the letters differently. For example, potassium (K) has one valence electron. Therefore, it is located in group 1. Calcium (Ca) is in group 2, for it contains two valence electrons.

text: Bismuth has characteristics which are uncommon in the majority of the metals. As with gallium, it expands when solidified, approximately 3.32%. Its electrical resistance is higher in the solid state than in the liquid (in a half proportion). The thermal conductivity is low, only bigger than the mercury one (just considering pure metals). It is fragile, highly diamagnetic (higher value of metals) with magnetic susceptibility of -1,68x10mks. Bismuth is used as catalyst in the production of plastics and cosmetics, as additives in steel alloys, aluminum and in electronics. It has a rhombohedral (Biα) structure, with an atomic radius of 1.54 Å, electronegativity of 1.83, and valence of +3 and +5.

text: Bismuth has characteristics which are uncommon in the majority of the metals. As with

text: gallium

text: , it expands when solidified, approximately 3.32%. Its electrical resistance is higher in the solid state than in the liquid (in a half proportion). The thermal conductivity is low, only bigger than the

text: mercury

text: one (just considering pure metals). It is fragile, highly diamagnetic (higher value of metals) with magnetic susceptibility of -1,68x10mks. Bismuth is used as

text: catalyst

text: in the production of

text: plastics

text: and cosmetics, as additives in

text: steel alloys

text: aluminum

text: and in

text: electronics

text: . It has a

text: rhombohedral

text: (Biα) structure, with an

text: atomic radius

text: of 1.54 Å,

text: electronegativity

text: of 1.83, and valence of +3 and +5.

text: Conducting polymers have backbones of contiguous sp hybridized carbon centers. One valence electron on each center resides in a p orbital, which is orthogonal to the other three sigma-bonds. The electrons in these delocalized orbitals have high mobility when the material is doped by oxidation, which removes some of these delocalized electrons. Thus the conjugated p-orbitals form a one-dimensional electronic band, and the electrons within this band become mobile when it is emptied partly.  Despite intensive research, the relationship between morphology, chain structure, and conductivity is poorly understood yet.

text: Conducting polymers have backbones of contiguous sp hybridized carbon centers. One valence electron on each center resides in a p orbital, which is orthogonal to the other three sigma-bonds. The electrons in these delocalized orbitals have high mobility when the material is doped by oxidation, which removes some of these delocalized electrons. Thus the

text: conjugated

text: p-orbitals form a one-dimensional

text: electronic band

text: , and the electrons within this band become mobile when it is emptied partly.  Despite intensive research, the relationship between morphology, chain structure, and conductivity is poorly understood yet.

text: Electronic commerce or e-commerce in Southeast Asia is the buying and selling of products and services over the internet in the countries of Southeast Asia. These practices reached southeast Asia during the dot-com mania in the 1990s. After the dot-com bust, native e-companies have seen promising and fast growth in their sector.

text: Electronic commerce or e-commerce in Southeast Asia is the buying and selling of products and services over the internet in

text: the countries of Southeast Asia

text: . These practices reached southeast Asia during the

text: dot-com mania

text: in the 1990s. After the dot-com bust, native e-companies have seen promising and fast growth in their sector.

text: Because of the diverse range of elements and the correspondingly diverse properties of the resulting derivatives, inorganic chemistry is closely associated with many methods of analysis.  Older methods tended to examine bulk properties such as the electrical conductivity of solutions, melting points, solubility, and acidity.  With the advent of quantum theory and the corresponding expansion of electronic apparatus, new tools have been introduced to probe the electronic properties of inorganic molecules and solids.  Often these measurements provide insights relevant to theoretical models.  For example, measurements on the photoelectron spectrum of methane demonstrated that describing the bonding by the two-center, two-electron bonds predicted  between the carbon and hydrogen using Valence Bond Theory is not appropriate for describing ionisation processes in a simple way. Such insights led to the popularization of molecular orbital theory as fully delocalised orbitals are a more appropriate simple description of electron removal and electron excitation.

text: Because of the diverse range of elements and the correspondingly diverse properties of the resulting derivatives, inorganic chemistry is closely associated with many methods of analysis.  Older methods tended to examine bulk properties such as the electrical conductivity of solutions,

text: melting point

text: s,

text: solubility

text: , and

text: acidity

text: .  With the advent of

text: quantum theory

text: and the corresponding expansion of electronic apparatus, new tools have been introduced to probe the electronic properties of inorganic molecules and solids.  Often these measurements provide insights relevant to theoretical models.  For example, measurements on the

text: photoelectron spectrum

text: of

text: methane

text: demonstrated that describing the bonding by the two-center, two-electron bonds predicted  between the carbon and hydrogen using

text: Valence Bond Theory

text: is not appropriate for describing ionisation processes in a simple way. Such insights led to the popularization of

text: molecular orbital theory

text: as fully delocalised orbitals are a more appropriate simple description of electron removal and electron excitation.

text: In 1964, he founded the theoretical chemistry division at Yale.  During his tenure at Yale, he developed the "Many Electron Theory of Atoms and Molecules" (1961), "Solvophobic Theory" (1964), "Network Theory" (1974), "Microthermodynamic surface tension"(1981), and "Valency Interaction Formula Theory" (1983). He developed a revolutionary method called "Sinanoğlu Made Simple" from his own mathematical theories and published in 1988. With the help of this research system, and using simple pictures and periodic table, chemists could predict the ways in which chemicals combine in the laboratory, and solve other complex problems of chemistry.  After 37 years on the Yale faculty, Sinanoğlu retired in 1997.  During his time at Yale, Sinanoğlu served as a frequent consultant to several Turkish universities and to the Scientific and Technological Research Council of Turkey (TÜBİTAK) as well as to the Japan Society for the Promotion of Science (JSPS). In 1962, the Board of Trustees of Middle East Technical University in Ankara dignified him with the title "consulting professor", for the first time and unique only for him.

text: In 1964, he founded the

text: theoretical chemistry

text: division at Yale.  During his tenure at Yale, he developed the "Many Electron Theory of Atoms and Molecules" (1961), "Solvophobic Theory" (1964), "Network Theory" (1974), "Microthermodynamic surface tension"(1981), and "Valency Interaction Formula Theory" (1983). He developed a revolutionary method called "Sinanoğlu Made Simple" from his own mathematical theories and published in 1988. With the help of this research system, and using simple pictures and

text: periodic table

text: , chemists could predict the ways in which chemicals combine in the laboratory, and solve other complex problems of chemistry.  After 37 years on the Yale faculty, Sinanoğlu retired in 1997.  During his time at Yale, Sinanoğlu served as a frequent consultant to several Turkish universities and to the

entity_name: Scientific and Technological Research Council of Turkey

text: Scientific and Technological Research Council of Turkey

text: (TÜBİTAK) as well as to the

entity_name: Japan Society for the Promotion of Science

text: Japan Society for the Promotion of Science

text: (JSPS). In 1962, the Board of Trustees of

text: Middle East Technical University

text: in Ankara dignified him with the title "consulting professor", for the first time and unique only for him.

text: Palladium belongs to group 10 in the periodic table, but the configuration in the outermost electron shells is atypical for group 10 (see also niobium (41), ruthenium (44), and rhodium (45)).  Fewer electron shells are filled than the elements directly preceding it (a phenomenon unique to palladium). The valence shell has eighteen electrons – ten more than the eight found in the valence shells of the noble gases from neon onward.

text: Palladium belongs to

text: group 10

text: in the periodic table, but the configuration in the outermost electron shells is atypical for group 10 (see also

text: niobium

text: ruthenium

text: (44), and

text: rhodium

text: (45)).  Fewer electron shells are filled than the elements directly preceding it (a phenomenon unique to palladium). The

text: valence shell

text: has eighteen electrons – ten more than the eight found in the valence shells of the

text: noble gas

text: es from

text: neon

text: onward.

text: Typically, in passive clauses, what is usually expressed by the object (or sometimes another argument) of the verb is now expressed by the subject, while what is usually expressed by the subject is either deleted, or is indicated by some adjunct of the clause. Thus, turning an active verb into a passive verb is a valence-decreasing process ("detransitivizing process"), because it turns transitive verbs into intransitive verbs. This is not always the case; for example in Japanese a passive-voice construction does not necessarily decrease valence.

text: Typically, in passive clauses, what is usually expressed by the

text: object

text: (or sometimes another

text: argument

text: ) of the verb is now expressed by the subject, while what is usually expressed by the subject is either deleted, or is indicated by some

text: adjunct

text: of the clause. Thus, turning an active verb into a passive verb is a

text: valence-decreasing

text: process ("detransitivizing process"), because it turns

text: transitive verb

text: s into

text: intransitive verb

text: s. This is not always the case; for example in

text: Japanese

text: a passive-voice construction does not necessarily decrease valence.

text: In semiconductor detectors, an electric field is applied to the detector volume. An electron in the semiconductor is fixed in its valence band in the crystal until a gamma ray interaction provides the electron enough energy to move to the conduction band.  Electrons in the conduction band can respond to the electric field in the detector, and therefore move to the positive contact that is creating the electrical field. The gap created by the moving electron is called a "hole," and is filled by an adjacent electron. This shuffling of holes effectively moves a positive charge to the negative contact. The arrival of the electron at the positive contact and the hole at the negative contact produces the electrical signal that is sent to the preamplifier, the MCA, and on through the system for analysis. The movement of electrons and holes in a solid-state detector is very similar to the movement of ions within the sensitive volume of gas-filled detectors such as ionization chambers.

text: In semiconductor detectors, an electric field is applied to the detector volume. An electron in the semiconductor is fixed in its

text: valence band

text: in the crystal until a gamma ray interaction provides the electron enough energy to move to the

text: conduction band

text: .  Electrons in the conduction band can respond to the electric field in the detector, and therefore move to the positive contact that is creating the electrical field. The gap created by the moving electron is called a "hole," and is filled by an adjacent electron. This shuffling of holes effectively moves a positive charge to the negative contact. The arrival of the electron at the positive contact and the hole at the negative contact produces the electrical signal that is sent to the preamplifier, the MCA, and on through the system for analysis. The movement of electrons and holes in a solid-state detector is very similar to the movement of ions within the sensitive volume of gas-filled detectors such as

text: ionization chamber

text: s.

text: Shri G.B. Meemasi was the first ITS to receive Padma Shri (1998) for his work in Electronic Switching in DOT. He was the founder Director of CDOT and father of RAX. Shri SM Agarwal(Secretary DOT) and Shri P.S. Saran(Member Services) were other subsequent recipients, from ITS.

text: Shri G.B. Meemasi was the first ITS to receive

text: Padma Shri

text: (1998) for his work in Electronic Switching in DOT. He was the founder Director of CDOT and father of RAX. Shri SM Agarwal(Secretary DOT) and Shri P.S. Saran(Member Services) were other subsequent recipients, from ITS.

text: Email has become one of the most widely used methods of communication within organizations and workplaces.  When discussing expectancy violationswith electronic e-mail, just as with other modes of communication, a distinctionmust be made between inadvertent violations of norms and purposeful violations,referred to as 'flaming'.  Flamingis defined as hostile and aggressive interactions via text-based CMC.  One form of expectancy violation in email is the length of time between the sending of the initial email and the receiver's reply. Communicator reward valence plays a large part in how expectancy violations are handled in email communications. Chronemic studies on email have shown that in organizations, responder status played a large part in how individuals reacted to various lapses in response to the previously sent email. Long pauses between responses for high-status responders produced positive expectancy violation valence and long pauses from low-status responders produced a negative expectancy violation valence. However, in the case of job interviews, long pauses between email for high-status candidates reflected negatively on their reviews. Expectations for email recipients to respond within a normative time limit illustrate the medium's capacity for expectancy violations to occur.

text: Email

text: has become one of the most widely used methods of communication within

text: organizations

text: and workplaces.  When discussing expectancy violationswith electronic e-mail, just as with other modes of communication, a distinctionmust be made between inadvertent violations of norms and purposeful violations,referred to as '

text: flaming

text: '.  Flamingis defined as hostile and aggressive interactions via text-based CMC.  One form of expectancy violation in email is the length of time between the sending of the initial email and the receiver's reply. Communicator reward valence plays a large part in how expectancy violations are handled in email communications.

text: Chronemic

text: studies on email have shown that in organizations, responder status played a large part in how individuals reacted to various lapses in response to the previously sent email. Long pauses between responses for high-status responders produced positive expectancy violation valence and long pauses from low-status responders produced a negative expectancy violation valence. However, in the case of

text: job interviews

text: , long pauses between email for high-status candidates reflected negatively on their reviews. Expectations for email recipients to respond within a normative time limit illustrate the medium's capacity for expectancy violations to occur.

text: The superactinide series is expected to contain elements 121 to 157. In the superactinide series, the 7d, 8p, 6f and 5g shells should all fill simultaneously: this creates very complicated situations, so much so that complete and accurate CCSD calculations have been done only for elements 121 and 122. The first superactinide, unbiunium (element 121), should be a congener of lanthanum and actinium and should have similar properties to them: its main oxidation state should be +3, although the closeness of the valence subshells' energy levels may permit higher oxidation states, just like in elements 119 and 120. Relativistic stabilization of the 8p subshell should result in a ground-state 8s8p valence electron configuration for element 121, in contrast to the ds configurations of lanthanum and actinium. Its first ionization energy is predicted to be 429.4 kJ/mol, which would be lower than those of all known elements except for the alkali metals potassium, rubidium, caesium, and francium: this value is even lower than that of the period 8 alkali metal ununennium (463.1 kJ/mol). Similarly, the next superactinide, unbibium (element 122), may be a congener of cerium and thorium, with a main oxidation state of +4, but would have a ground-state 7d8s8p valence electron configuration, unlike thorium's 6d7s configuration. Hence, its first ionization energy would be smaller than thorium's (Th: 6.54 eV; Ubb: 5.6 eV) because of the greater ease of ionizing unbibium's 8p electron than thorium's 7s electron.

text: The superactinide series is expected to contain elements 121 to 157. In the superactinide series, the 7d, 8p, 6f and 5g shells should all fill simultaneously: this creates very complicated situations, so much so that complete and accurate CCSD calculations have been done only for elements 121 and 122. The first superactinide, unbiunium (element 121), should be a

text: congener

text: of

text: lanthanum

text: and

text: actinium

text: and should have similar properties to them: its main oxidation state should be +3, although the closeness of the valence subshells' energy levels may permit higher oxidation states, just like in elements 119 and 120. Relativistic stabilization of the 8p subshell should result in a ground-state 8s8p valence electron configuration for element 121, in contrast to the ds configurations of lanthanum and actinium. Its first ionization energy is predicted to be 429.4 kJ/mol, which would be lower than those of all known elements except for the

text: alkali metals

text: potassium

text: rubidium

text: caesium

text: , and

text: francium

text: : this value is even lower than that of the period 8 alkali metal ununennium (463.1 kJ/mol). Similarly, the next superactinide, unbibium (element 122), may be a congener of

text: cerium

text: and

text: thorium

text: , with a main oxidation state of +4, but would have a ground-state 7d8s8p valence electron configuration, unlike thorium's 6d7s configuration. Hence, its first

text: ionization energy

text: would be smaller than thorium's (Th: 6.54

text: eV

text: ; Ubb: 5.6 eV) because of the greater ease of ionizing unbibium's 8p electron than thorium's 7s electron.

text: An important aspect of HEMTs is that the band discontinuities across the conduction and valence bands can be modified separately. This allows the type of carriers in and out of the device to be controlled. As HEMTs require electrons to be the main carriers, a graded doping can be applied in one of the materials making the conduction band discontinuity smaller, and keeping the valence band discontinuity the same. This diffusion of carriers leads to the accumulation of electrons along the boundary of the two regions inside the narrow band gap material. The accumulation of electrons leads to a very high current in these devices. The accumulated electrons are also known as 2DEG or two-dimensional electron gas.

text: An important aspect of HEMTs is that the band discontinuities across the conduction and valence bands can be modified separately. This allows the type of carriers in and out of the device to be controlled. As HEMTs require electrons to be the main carriers, a graded doping can be applied in one of the materials making the conduction band discontinuity smaller, and keeping the valence band discontinuity the same. This diffusion of carriers leads to the accumulation of electrons along the boundary of the two regions inside the narrow band gap material. The accumulation of electrons leads to a very high current in these devices. The accumulated electrons are also known as

text: or two-dimensional electron gas.

text: The molecule ClO has an odd number of valence electrons, and therefore, it is a paramagnetic radical. Its electronic structure has long baffled chemists because none of the possible Lewis structures is very satisfactory. In 1933, L. O. Brockway proposed a structure that involved a three-electron bond. Chemist Linus Pauling further developed this idea and arrived at two resonance structures involving a double bond on one side and a single bond plus three-electron bond on the other. In Pauling's view the latter combination should represent a bond that is slightly weaker than the double bond. In molecular orbital theory this idea is commonplace if the third electron is placed in an anti-bonding orbital. Later work has confirmed that the HOMO is indeed an incompletely-filled orbital.

text: The molecule ClO has an odd number of

text: valence electron

text: s, and therefore, it is a

text: paramagnetic

text: radical

text: . Its electronic structure has long baffled chemists because none of the possible

text: Lewis structure

text: s is very satisfactory. In 1933, L. O. Brockway proposed a structure that involved a

text: three-electron bond

text: . Chemist

text: Linus Pauling

text: further developed this idea and arrived at two

text: resonance structure

text: s involving a double bond on one side and a single bond plus three-electron bond on the other. In Pauling's view the latter combination should represent a bond that is slightly weaker than the double bond. In

text: molecular orbital theory

text: this idea is commonplace if the third electron is placed in an anti-bonding orbital. Later work has confirmed that the

text: HOMO

text: is indeed an incompletely-filled orbital.

text: Triple decker complexes are known to obey a 30 valence electron (VE) rule. If we subtract 6 pairs of non-bonding electrons from the two metal atoms, it becomes 9 pairs. For a triple decker complex with CH as the decks, m+n+o+p-q = 3+17+2+2-0=24. Subtracting the 15 pairs corresponding to C-C σ bonds, it becomes 9 pairs. Thus Jemmis rule merges with the 30VE rule for triple decker complexes. For example, consider (CMe)Ru. 15 C-CH groups provide 22.5 pairs. Each Ru provides one pair. Removal of one electron corresponding to the positive charge of the complex leads to a total of 22.5+2-0.5 = 24 pairs.

text: Although E varies greatly across the periodic table, some patterns emerge. Generally, nonmetals have more positive E than metals. Atoms whose anions are more stable than neutral atoms have a greater E. Chlorine most strongly attracts extra electrons; mercury most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.

text: Although E varies greatly across the periodic table, some patterns emerge. Generally,

text: nonmetals

text: have more positive E than

text: metal

text: s. Atoms whose anions are more stable than neutral atoms have a greater E.

text: Chlorine

text: most strongly attracts extra electrons;

text: mercury

text: most weakly attracts an extra electron. The electron affinities of the noble gases have not been conclusively measured, so they may or may not have slightly negative values.

text: Methane is a tetrahedral molecule with four equivalent C–H bonds. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H. The lowest energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements.

text: Methane is a

text: tetrahedral

text: molecule with four equivalent

text: C–H bond

text: s. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on

text: C

text: and

text: H

text: . The lowest energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements.

text: Organic compounds such as octane, which has 8 carbon atoms and 18 hydrogen atoms, cannot conduct electricity. Oils are hydrocarbons, since  carbon has the property of tetracovalency and forms covalent bonds with other elements such as hydrogen, since it does not lose or gain electrons, thus does not form ions. Covalent bonds are simply the sharing of electrons. Hence, there is no separation of ions when electricity is passed through it. So the liquid (oil or any organic compound) cannot conduct electricity.

text: In a crystal structure of  metallic solids, the free electron model (zero potential, φ = 0) for the behavior of valence electrons is used. However, in a periodic lattice (crystal), there is periodic crystal potential, so the electron Hamiltonian becomes

text: In a

text: crystal structure

text: of  metallic solids, the

text: free electron model

text: (zero potential, φ = 0) for the behavior of

text: valence electron

text: s is used. However, in a

text: periodic lattice (crystal)

text: , there is periodic crystal potential, so the electron Hamiltonian becomes

text: For partial filling at the top of the valence band, it is helpful to introduce the concept of an electron hole.Although the electrons in the valence band are always moving around, a completely full valence band is inert, not conducting any current.If an electron is taken out of the valence band, then the trajectory that the electron would normally have taken is now missing its charge.For the purposes of electric current, this combination of the full valence band, minus the electron, can be converted into a picture of a completely empty band containing a positively charged particle that moves in the same way as the electron.Combined with the negative effective mass of the electrons at the top of the valence band, we arrive at a picture of a positively charged particle that responds to electric and magnetic fields just as a normal positively charged particle would do in vacuum, again with some positive effective mass.This particle is called a hole, and the collection of holes in the valence band can again be understood in simple classical terms (as with the electrons in the conduction band).

text: For partial filling at the top of the valence band, it is helpful to introduce the concept of an

text: electron hole

text: For a main group element, a valence electron is defined as an electron that resides in the electronic shell of highest principal quantum number n. For example, the electronic configuration of phosphorus (P) is 1s 2s 2p 3s 3p so that there are 5 valence electrons (3s 3p), corresponding to a maximum valence for P of 5 as in the molecule PF; this configuration is normally abbreviated to [Ne] 3s 3p, where [Ne] signifies the core electrons whose configuration is identical to that of the noble gas neon.

text: For a main group element, a valence electron is defined as an electron that resides in the electronic shell of highest

text: principal quantum number

text: n. For example, the electronic configuration of phosphorus (P) is 1s 2s 2p 3s 3p so that there are 5 valence electrons (3s 3p), corresponding to a maximum valence for P of 5 as in the molecule PF; this configuration is normally abbreviated to [Ne] 3s 3p, where [Ne] signifies the core electrons whose configuration is identical to that of the

text: noble gas

text: neon.

text: The valence electrons of moscovium fall into three subshells: 7s (two electrons), 7p (two electrons), and 7p (one electron). The first two of these are relativistically stabilized and hence behave as inert pairs, while the last is relativistically destabilized and can easily participate in chemistry. (The 6d electrons are not destabilized enough to participate chemically, although this may still be possible in the two previous elements nihonium and flerovium.) Thus, the +1 oxidation state should be favored, like Tl, and consistent with this the first ionization potential of moscovium should be around 5.58 eV, continuing the trend towards lower ionization potentials down the pnictogens. Moscovium and nihonium both have one electron outside a quasi-closed shell configuration that can be delocalized in the metallic state: thus they should have similar melting and boiling points (both melting around 400 °C and boiling around 1100 °C) due to the strength of their metallic bonds being similar. Additionally, the predicted ionization potential, ionic radius (1.5 Å for Mc; 1.0 Å for Mc), and polarizability of Mc are expected to be more similar to Tl than its true congener Bi. Moscovium should be a dense metal due to its high atomic weight, with a density around 13.5 g/cm. The electron of the hydrogen-like moscovium atom (oxidized so that it only has one electron, Mc) is expected to move so fast that it has a mass 1.82 times that of a stationary electron, due to relativistic effects. For comparison, the figures for hydrogen-like bismuth and antimony are expected to be 1.25 and 1.077 respectively.

text: The valence electrons of moscovium fall into three subshells: 7s (two electrons), 7p (two electrons), and 7p (one electron). The first two of these are relativistically stabilized and hence behave as

text: inert pairs

text: , while the last is relativistically destabilized and can easily participate in chemistry. (The 6d electrons are not destabilized enough to participate chemically, although this may still be possible in the two previous elements nihonium and flerovium.) Thus, the +1

text: oxidation state

text: should be favored, like

text: Tl

text: , and consistent with this the first

text: ionization potential

text: of moscovium should be around 5.58

text: eV

text: , continuing the trend towards lower ionization potentials down the pnictogens. Moscovium and nihonium both have one electron outside a quasi-closed shell configuration that can be

text: delocalized

text: in the metallic state: thus they should have similar

text: melting

text: and

text: boiling point

text: s (both melting around 400 °C and boiling around 1100 °C) due to the strength of their

text: metallic bond

text: s being similar. Additionally, the predicted ionization potential,

text: ionic radius

text: Å

text: for Mc; 1.0 Å for Mc), and

text: polarizability

text: of Mc are expected to be more similar to Tl than its true congener

text: Bi

text: . Moscovium should be a dense metal due to its high

text: atomic weight

text: , with a density around 13.5 g/cm. The electron of the

text: hydrogen-like

text: moscovium atom (oxidized so that it only has one electron, Mc) is expected to move so fast that it has a mass 1.82 times that of a stationary electron, due to

text: relativistic effects

text: . For comparison, the figures for hydrogen-like bismuth and antimony are expected to be 1.25 and 1.077 respectively.

text: Lewis proposed that an atom forms enough covalent bonds to form a full (or closed) outer electron shell. In the methane diagram shown here, the carbon atom has a valence of four and is, therefore, surrounded by eight electrons (the octet rule), four from the carbon itself and four from the hydrogens bonded to it. Each hydrogen has a valence of one and is surrounded by two electrons (a duet rule) – its own one electron plus one from the carbon. The numbers of electrons correspond to full shells in the quantum theory of the atom; the outer shell of a carbon atom is the n = 2 shell, which can hold eight electrons, whereas the outer (and only) shell of a hydrogen atom is the n = 1 shell, which can hold only two.

text: Lewis proposed that an atom forms enough covalent bonds to form a full (or closed) outer electron shell. In the methane diagram shown here, the carbon atom has a valence of four and is, therefore, surrounded by eight electrons (the

text: octet rule

text: ), four from the carbon itself and four from the hydrogens bonded to it. Each hydrogen has a valence of one and is surrounded by two electrons (a duet rule) – its own one electron plus one from the carbon. The numbers of electrons correspond to full shells in the quantum theory of the atom; the outer shell of a carbon atom is the n = 2 shell, which can hold eight electrons, whereas the outer (and only) shell of a hydrogen atom is the n = 1 shell, which can hold only two.

text: The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are f-block elements, corresponding to the filling of the 5f electron shell; lawrencium, a d-block element, is also generally considered an actinide. In comparison with the lanthanides, also mostly f-block elements, the actinides show much more variable valence. They all have very large atomic and ionic radii and exhibit an unusually large range of physical properties. While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium through neptunium are much more similar to transition metals in their chemistry.

text: The actinide series derives its name from the first element in the series, actinium. The informal chemical symbol An is used in general discussions of actinide chemistry to refer to any actinide. All but one of the actinides are

text: f-block

text: electron shell

text: ; lawrencium, a

text: d-block

text: lanthanide

text: s, also mostly

text: f-block

text: valence

text: . They all have very large

text: atomic

text: and

text: ionic radii

text: and exhibit an unusually large range of physical properties. While actinium and the late actinides (from americium onwards) behave similarly to the lanthanides, the elements thorium through neptunium are much more similar to

text: transition metal

text: s in their chemistry.

text: On the periodic table, homologous elements share many electrochemical properties and appear in the same group (column) of the table. For example, all noble gases are colorless, monatomic gases with very low reactivity. These similarities are due to similar structure in their outer shells of valence electrons. Mendeleev used the prefix eka- for an unknown element below a known one in the same group.

text: On the

text: periodic table

text: , homologous elements share many

text: electrochemical

text: properties and appear in the same group (column) of the table. For example, all

text: noble gases

text: are colorless,

text: monatomic gas

text: es with very low reactivity. These similarities are due to similar structure in their

text: outer shells

text: of

text: valence electrons

text: Mendeleev

text: used the prefix

text: eka-

text: for an unknown element below a known one in the same group.

text: Boron is adjacent to carbon in the periodic table and has similar valence orbitals. Unlike carbon, boron cannot form a honeycomb hexagonal framework (like graphene) because of its electron deficiency.

text: Boron is adjacent to

text: carbon

text: in the

text: periodic table

text: and has similar

text: valence orbital

text: s. Unlike carbon, boron cannot form a

text: honeycomb

text: hexagonal framework (like graphene) because of its electron deficiency.

text: Two factors contribute to ReB's high hardness: a high density of valence electrons, and an abundance of short covalent bonds. Rhenium has one of the highest valence electron densities of any transition metal (476 electrons/nm, compare to 572 electrons/nm for osmium and 705 electrons/nm for diamond). The addition of boron requires only a 5% expansion of the rhenium lattice, because the small boron atoms fill the existing spaces between the rhenium atoms. Furthermore, the electronegativities of rhenium and boron are close enough (1.9 and 2.04 on the Pauling scale) that they form covalent bonds in which the electrons are shared almost equally.

text: Two factors contribute to ReB's high hardness: a high density of

text: valence electron

text: s, and an abundance of short

text: covalent bond

text: s. Rhenium has one of the highest valence electron densities of any transition metal (476 electrons/nm, compare to 572 electrons/nm for

text: osmium

text: and 705 electrons/nm for diamond). The addition of boron requires only a 5% expansion of the rhenium lattice, because the small boron atoms fill the existing spaces between the rhenium atoms. Furthermore, the

text: electronegativities

text: of rhenium and boron are close enough (1.9 and 2.04 on the

text: Pauling scale

text: ) that they form covalent bonds in which the electrons are shared almost equally.

text: Norbert Schwarz's work on categorization and mental construal led to the development of his inclusion/exclusion model that accounts for the emergence of contrast and Assimilation effects in social judgments. Contrast effects occur when exposure to valenced information influences judgments in a way that is incongruent with the valenced information. Assimilation effects occur when exposure to valenced information influences judgments in a way that is congruent with the valenced information. The key insight of the inclusion/exclusion model is that the evaluation of a target of judgment requires bringing to mind both the target itself, and a standard against which it is to be evaluated. Whether valenced information produces contrast or assimilation depends on whether it is included within the target (assimilation) or in the standard against which it is compared (contrast).

text: Norbert Schwarz's work on categorization and mental construal led to the development of his

text: inclusion/exclusion model

text: that accounts for the emergence of contrast and

text: Assimilation effect

text: s in social judgments. Contrast effects occur when exposure to valenced information influences judgments in a way that is incongruent with the valenced information. Assimilation effects occur when exposure to valenced information influences judgments in a way that is congruent with the valenced information. The key insight of the inclusion/exclusion model is that the evaluation of a target of judgment requires bringing to mind both the target itself, and a standard against which it is to be evaluated. Whether valenced information produces contrast or assimilation depends on whether it is included within the target (assimilation) or in the standard against which it is compared (contrast).

text: For elements with high atomic number , the effects of relativity become more pronounced, and especially so for s electrons, which move at relativistic velocities as they penetrate the screening electrons near the core of high- atoms. This relativistic increase in momentum for high speed electrons causes a corresponding decrease in wavelength and contraction of 6s orbitals relative to 5d orbitals (by comparison to corresponding s and d electrons in lighter elements in the same column of the periodic table); this results in 6s valence electrons becoming lowered in energy.

text: Verbs are often flexible with regard to valency. In non-valency marking languages such as English, a transitive verb can often drop its object and become intransitive; or an intransitive verb can take an object and become transitive. For example, in English the verb move has no grammatical object in he moves (though in this case, the subject itself may be an implied object, also expressible explicitly as in he moves himself); but in he moves the car, the subject and object are distinct and the verb has a different valency. Some verbs in English, however, have historically derived forms that show change of valency in some causative verbs, such as fall-fell-fallen:fell-felled-felled; rise-rose-risen:raise-raised-raised; cost-cost-cost:cost-costed-costed.

text: In chemistry, the valence or valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of  valence was developed in the second half of the 19th century and was successful in explaining the molecular structure of inorganic and organic compounds. The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the cubical atom (1902), Lewis structures (1916), valence bond theory (1927), molecular orbitals (1928), valence shell electron pair repulsion theory (1958), and all of the advanced methods of quantum chemistry.

text: In

text: chemistry

text: , the valence or valency of an

text: element

text: is a measure of its combining power with other atoms when it forms

text: chemical compound

text: s or

text: molecule

text: s. The concept of  valence was developed in the second half of the 19th century and was successful in explaining the molecular structure of inorganic and organic compounds. The quest for the underlying causes of valence led to the modern theories of chemical bonding, including the

text: cubical atom

text: Lewis structure

text: s (1916),

text: valence bond theory

text: molecular orbital

text: s (1928),

text: valence shell electron pair repulsion theory

text: (1958), and all of the advanced methods of

text: quantum chemistry

text: By controlling the charge or spin degree of freedom of carriers, as proposed by spintronics, novel devices have already been made. If there are different conduction/valence band extrema in the electronic band structure in k-space, the carrier can be confined in one of these valleys. This degree of freedom opens up a new field of physics: the controlling of carriers k-valley index, also called valleytronics.

text: By controlling the charge or spin degree of freedom of carriers, as proposed by

text: spintronics

text: , novel devices have already been made. If there are different conduction/valence band extrema in the electronic band structure in k-space, the carrier can be confined in one of these valleys. This degree of freedom opens up a new field of physics: the controlling of carriers k-valley index, also called

text: valleytronics

text: Being the first period 8 element, ununennium is predicted to be an alkali metal, below lithium, sodium, potassium, rubidium, caesium, and francium. Each of these elements has one valence electron in the outermost s-orbital (valence electron configuration ns), which is easily lost in chemical reactions to form the +1 oxidation state: thus the alkali metals are very reactive elements. Ununennium is predicted to continue the trend and have a valence electron configuration of 8s. It is therefore expected to behave much like its lighter congeners; however, it is also predicted to differ from the lighter alkali metals in some properties.

text: Being the first

text: period 8 element

text: , ununennium is predicted to be an alkali metal, below

text: lithium

text: sodium

text: potassium

text: rubidium

text: caesium

text: , and

text: francium

text: . Each of these elements has one

text: valence electron

text: in the outermost s-orbital (valence electron configuration ns), which is easily lost in chemical reactions to form the +1

text: oxidation state

text: : thus the alkali metals are very

text: reactive

text: elements. Ununennium is predicted to continue the trend and have a valence electron configuration of 8s. It is therefore expected to behave much like its lighter

text: congener

text: s; however, it is also predicted to differ from the lighter alkali metals in some properties.

text: The sixth meeting was held from December 20 to 22, 2010 at Grand Hotel, Taipei, Taiwan. SEF had 21 representatives, while ARATs had 20 representatives, both with notable people from the health industry.

text: The sixth meeting was held from December 20 to 22, 2010 at

text: Grand Hotel

text: Taipei

text: Taiwan

text: . SEF had 21 representatives, while ARATs had 20 representatives, both with notable people from the health industry.

text: South Carolina Highway 19 Truck (SC 19 Truck) provides routing west around downtown Aiken, via SC 118, for trucks; which are not allowed in the downtown area.

text: South Carolina Highway 19 Truck (SC 19 Truck) provides routing west around downtown Aiken, via

text: SC 118

text: , for trucks; which are not allowed in the downtown area.

text: Fady, in Malagasy culture, refers to a wide range of cultural prohibitions or taboos. People, places, actions or objects may be the subject of fady, which vary by region within Madagascar. The taboos are believed to be enforced by supernatural powers, and are particularly connected with Malagasy ancestor worship. Although some are held nationwide, others may be particular to regions, villages or even individual families. Fady are an integral part of Malagasy identity and play an important part in community and identity formation.

text: Fady, in

text: Malagasy culture

text: , refers to a wide range of cultural prohibitions or

text: taboo

text: s. People, places, actions or objects may be the subject of fady, which vary by region within

text: Madagascar

text: . The taboos are believed to be enforced by supernatural powers, and are particularly connected with Malagasy ancestor worship. Although some are held nationwide, others may be particular to regions, villages or even individual families. Fady are an integral part of Malagasy identity and play an important part in

text: community

text: and

text: identity formation

text: The Japanese electronic industry as a result has maintained its dominance in the market over the United States, and maintained its export strength in this field due to the high reputation of its electronics.

text: Although copernicium is the heaviest known group 12 element, there has been some theoretical work regarding possible heavier group 12 elements. Although a simple extrapolation of the periodic table would put element 162, unhexbium (Uhb), under copernicium, relativistic Dirac-Fock calculations predict that the next group 12 element after copernicium should actually be element 164, unhexquadium (Uhq), which is predicted to have an electron configuration of [Og] 5g 6f 7d 8s 8p. The 8s and 8p orbitals are predicted to be so strongly stabilized relativistically that they become core electrons and do not participate in chemical reactions, unlike the earlier group 12 elements where the s electrons behave as valence electrons. However, the 9s and 9p levels are expected to be readily available for hybridization and bonding, so that unhexquadium should still behave chemically like a normal transition metal. Calculations predict that the 7d electrons of unhexquadium should participate very readily in chemical reactions, so that unhexquadium should be able to show stable +6 and +4 oxidation states in addition to the normal +2 state in aqueous solutions with strong ligands. Unhexquadium should thus be able to form compounds like Uhq(CO), Uhq(PF) (both tetrahedral), and  (linear), which is very different behavior from that of lead, which unhexquadium would be a heavier homologue of if not for relativistic effects. Nevertheless, the divalent state would be the main one in aqueous solution, and unhexquadium(II) should behave more similarly to lead than unhexquadium(IV) and unhexquadium(VI).

text: Although copernicium is the heaviest known group 12 element, there has been some theoretical work regarding possible heavier group 12 elements. Although a simple extrapolation of the periodic table would put element 162, unhexbium (Uhb), under copernicium,

text: relativistic

text: Dirac-Fock calculations predict that the next group 12 element after copernicium should actually be element 164, unhexquadium (Uhq), which is predicted to have an electron configuration of [

text: Og

text: ] 5g 6f 7d 8s 8p. The 8s and 8p

text: orbital

text: s are predicted to be so strongly stabilized relativistically that they become core electrons and do not participate in chemical reactions, unlike the earlier group 12 elements where the s electrons behave as valence electrons. However, the 9s and 9p levels are expected to be readily available for

text: hybridization

text: and bonding, so that unhexquadium should still behave chemically like a normal transition metal. Calculations predict that the 7d electrons of unhexquadium should participate very readily in chemical reactions, so that unhexquadium should be able to show stable +6 and +4 oxidation states in addition to the normal +2 state in

text: aqueous solution

text: s with strong

text: ligand

text: s. Unhexquadium should thus be able to form compounds like Uhq(

text: CO

text: ), Uhq(

text: PF

text: ) (both

text: tetrahedral

text: ), and  (

text: linear

text: ), which is very different behavior from that of

text: lead

text: , which unhexquadium would be a heavier

text: homologue

text: of if not for relativistic effects. Nevertheless, the divalent state would be the main one in aqueous solution, and unhexquadium(II) should behave more similarly to lead than unhexquadium(IV) and unhexquadium(VI).

text: Sven Nilsson (8 March 1787 – 30 November 1883) was a Swedish zoologist and archaeologist.

text: Sven Nilsson (8 March 1787 – 30 November 1883) was a

text: Swedish

text: zoologist

text: and

text: archaeologist

text: Loreo borders the following municipalities: Adria, Cavarzere, Chioggia, Porto Viro, Rosolina, Taglio di Po.

text: Loreo borders the following municipalities:

text: Adria

text: Cavarzere

text: Chioggia

text: Porto Viro

text: Rosolina

text: Taglio di Po

text: Barkhimer became a Senior Vice President in NASCAR. During his career, he had also promoted boxing, car shows, roller derbies, and wrestling. He retired after his first wife died in 1976. He had promoted 3000 races in his career. Barkhimer and Burke sold out to Ken Clapp. After retiring, he traveled and wrote stories about the early years of racing.

text: Barkhimer became a Senior Vice President in NASCAR. During his career, he had also promoted

text: boxing

text: car show

text: s,

text: roller derbies

text: , and

text: wrestling

text: . He retired after his first wife died in 1976. He had promoted 3000 races in his career. Barkhimer and Burke sold out to

text: Ken Clapp

text: . After retiring, he traveled and wrote stories about the early years of racing.

text: Survivors of catastrophic injury may also have catastrophic facial injuries, such as fractured facial bones, particularly those from events associated with ice hockey, cycling, and snowmobiling.

text: A deoxyribonuclease (DNase, for short) is any enzyme that catalyzes the hydrolytic cleavage of phosphodiester linkages in the DNA backbone, thus degrading DNA.  Deoxyribonucleases are one type of nuclease, a generic term for enzymes capable of hydrolyzing phosphodiester bonds that link nucleotides.  A wide variety of deoxyribonucleases are known, which differ in their substrate specificities, chemical mechanisms, and biological functions.

text: A deoxyribonuclease (DNase, for short) is any

text: enzyme

text: that catalyzes the

text: hydrolytic cleavage

text: of

text: phosphodiester linkages

text: in the

text: DNA

text: backbone, thus degrading DNA.  Deoxyribonucleases are one type of

text: nuclease

text: , a generic term for enzymes capable of hydrolyzing phosphodiester bonds that link nucleotides.  A wide variety of deoxyribonucleases are known, which differ in their

text: substrate

text: specificities, chemical mechanisms, and biological functions.

text: The 2000 U.S. census counted 41,905 residents in the  Encino neighborhood — , among the lowest population densities for the city but average for the county. In 2008, the city estimated that the resident population had increased to 44,581.

text: The 2000 U.S. census counted 41,905 residents in the  Encino neighborhood — , among the lowest

text: population densities

text: for the city but average for the county. In 2008, the city estimated that the resident population had increased to 44,581.

text: Founded in 1989 as a research and development company by Lev Dawson  Valence has its headquarters in Austin, Texas, and facilities in Las Vegas, Nevada, Mallusk, Northern Ireland, and Suzhou, China. Valence is currently owned by Berg and Berg Enterprises.

text: Founded in 1989 as a research and development company by Lev Dawson  Valence has its headquarters in

text: Austin, Texas

text: , and facilities in

text: Las Vegas

text: Nevada

text: , Mallusk,

text: Northern Ireland

text: , and

text: Suzhou

text: China

text: . Valence is currently owned by Berg and Berg Enterprises.