A generalized formalism of the quantum theory of valence and bonding

General definitions of valence, degree of bonding between pairs of atoms, and atomic anisotropy and reactivity are given. They can be applied to closed- or open-shell molecular wave functions (in the semiempirical, quasi or full ab initio SCF levels), as well as to GVB ones. The properties and usefulness of the definitions are discussed as well as their relation to former empirical notions. Examples of their application are also reported.