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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.
A key choice that must be made is how many atoms to explicitly include in one's calculation. In Big-O notation, calculations general scale as O(N3) where N is the number of combined ions and valence electrons. [2] For structure calculations, it is generally desirable to choose the smallest number of ions that can represent the structure.
Similar to a core electron, a valence electron has the ability to absorb or release energy in the form of a photon. An energy gain can trigger the 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 shell; this is ionization to form a positive ion. When an ...
Since metals can display multiple oxidation numbers, the exact definition of how many "valence electrons" an element should have in elemental form is somewhat arbitrary, but the following table lists the free electron densities given in Ashcroft and Mermin, which were calculated using the formula above based on reasonable assumptions about ...
Valence bond (VB) computer programs for modern valence bond calculations:-CRUNCH, by Gordon A. Gallup and his group. [1] GAMESS (UK), includes calculation of VB wave functions by the TURTLE code, due to J.H. van Lenthe. [2] GAMESS (US), has links to interface VB2000, and XMVB.
The valence electrons (here 3s 2 3p 3) are written explicitly for all atoms. Electron configurations of elements beyond hassium (element 108) have never been measured; predictions are used below. As an approximate rule, electron configurations are given by the Aufbau principle and the Madelung rule.
In the more general case of metals having more valence electrons, is the radius of a sphere whose volume is equal to the volume per a free electron. [2] This parameter is used frequently in condensed matter physics to describe the density of a system.
In the extended Hückel method, only valence electrons are considered; the core electron energies and functions are supposed to be more or less constant between atoms of the same type. The method uses a series of parametrized energies calculated from atomic ionization potentials or theoretical methods to fill the diagonal of the Fock matrix.