Ionic terms in valence states

The theory of the resonance valence state for covalent bonding (Craig & Thirunamachandran 1968) is extended to valence states for partial ionic bonding. A separation of ligands and central atom in molecules AX n into A + and X n -1 X - is considered and compared with the separation into A and X n within both the perfect-pairing and resonance methods. Application of the theory is illustrated in examples from first- and second-row elements. The symmetries of atomic terms appearing in valence states, and the energies of representative examples, are listed.