Can we talk about ionic bonds in molecules? Yes, just as we do for covalent bonds†

Abstract

A claim that ionic bonds exist only in ionic solids is critically analyzed by focusing on the controversial LiH molecule, classified as covalent by non-orthogonal valence bond supporters, polar-covalent by molecular orbital advocates, and ionic by real-space proponents. Using orbital invariant techniques we show that LiH can be regarded ionic in the same manner as dihydrogen covalent.