Molecular Charge Distributions and Chemical Binding. II. First-Row Diatomic Hydrides, AH

Abstract

An interpretation of the binding in the first-row diatomic hydrides AH is presented, based upon the molecular charge distribution and the forces which it exerts on the nuclei. The density distributions are discussed in relation to ``molecular'' size and the partitioning of the total charge between different spatial regions. Density difference maps are employed to compare the molecular charge distribution with that of the separated atomic charge densities and the charge density of the corresponding united atom. The molecular-orbital charge densities are classified as binding, nonbinding, or antibinding with respect to the forces which they exert on the nuclei. The orbital forces provide a quantitative assessment of the relative binding abilities of the orbital charge densities; for a given molecule, or through the complete series of molecules. On the basis of the total charge distributions, the density difference distributions and the forces exerted on the nuclei, the bonding in LiH is classified as ionic, that in BH→HF as covalent. The binding in BeH is found to be transitional between the limiting classifications of ionic and covalent.