The resonance valence state

An alternative definition of the atomic valence state is proposed. It is based upon a valence-bond wavefunction for molecules AX n , in which equivalence of the bonds is secured by allowing resonance among pairing schemes for ligand orbitals at X paired to natural s, p and d orbitals at A. The valence state of A is then either the lowest term of the valence configuration, for example, 7 F of sulphur in SF 6 , or is a linear combination of terms of highest multiplicity. The valence state energy is directly available from spectral term values in many important examples. The resonance valence state has a number of advantages, including easier availability of energies, over the usual perfect-pairing valence state, which is a linear combination of terms belonging to each of a number of different electron configurations. The two valence states are compared, and the resonance valence state analysed in several examples including AX 4 in T d , D 2d and S 4 symmetries.