Relation between orbital binding energies and ionicities in alkali and alkaline earth flourides

The differences between the ionization potentials and binding energies for M^q+ (np⁶), F^?(1 s²), andF^?(2p⁶) orbital electrons, adjusted for the electrostatic self-potentials, in alkali and alkaline earth fluorides have been correlated with ionicites derived from the indices of refraction through optical dispersion theory of Phillips and van Vechten. The differences are linear in ionicities and are related to the covalent energies and the polarizabilities. The gap between the valence band and the Fermi level, determined with X-ray photoelectron spectroscopy, has been compared with the energy in the Phillips-van Vechten model. Whereas the former is a measure of the thermal activation energy for conduction, the latter is determined essentially by the valence electron density, the molar volume, and the polarizability.