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The bond valence method or mean method (or bond valence sum) (not to be mistaken for the valence bond theory in quantum chemistry) is a popular method in coordination chemistry to estimate the oxidation states of atoms. It is derived from the bond valence model, which is a simple yet robust model for validating chemical structures with ...
The rule defines boranes to have four types of bonds besides the terminal B-H bonds: [2] The structures assigned to the letters s, t, y, and x. Where: B-H-B bonds are 3c-2e bonds, taking up three orbitals and two valence electrons. B-B-B bonds are 3c-2e bonds, taking up three orbitals and two valence electrons.
the latter being the equations to be solved, and the former the equation for the evaluation of the energy. (Note that we have made use of e − T e T = 1 {\displaystyle e^{-T}e^{T}=1} , the identity operator, and also assume that orbitals are orthogonal, though this does not necessarily have to be true, e.g., valence bond orbitals can be used ...
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.
A valence bond structure resembles a Lewis structure, but when a molecule cannot be fully represented by a single Lewis structure, multiple 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.
This is more than the naive π-bond order of (for a total bond order of ) that one might guess when simply considering the Kekulé structures and the usual definition of bond order in valence bond theory. The Hückel definition of bond order attempts to quantify any additional stabilization that the system enjoys resulting from delocalization.
For typical ionic solids, the cations are smaller than the anions, and each cation is surrounded by coordinated anions which form a polyhedron.The sum of the ionic radii determines the cation-anion distance, while the cation-anion radius ratio + / (or /) determines the coordination number (C.N.) of the cation, as well as the shape of the coordinated polyhedron of anions.
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. [1] The term ab initio was first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene.