Virial Partitioning of Charge Distributions and Properties of Diatomic Hydrides; NaH ↔ HCl

Abstract

The virial partitioning method is applied to the ground states of the AH diatomic hydrides (A = Na, Mg, Al, Si, P, S, Cl) in their neutral and charged forms. This is a spatial partitioning of a molecular system, the partitioning surfaces, which in this instance divide each molecule into an (A) and an (H) fragment, being determined by the topographical features of the electronic charge distribution. The kinetic and potential energies of the virial fragments are well-defined quantities and in addition, satisfy the quantum mechanical virial relationship. Most important, virial fragments faithfully reflect the chemistry of the individual elemental components of molecular systems, the fragments and their properties remaining nearly constant or changing when in different systems, in accordance with chemical expectations.The populations of (H) in combination with (A) are used to order the first- and second-row elements (neutral and charged) in their abilities to abstract or donate charge relative to hydrogen. This ordering is of general interest as the population of (H) in AH changes little on passage to the general (most stable) polyatomic AHn. The virial equations are used to relate the kinetic energy of binding in AH to the changes in the potential energies and total energies of each fragment. One finds, in comparison of first- and second-row results, that the nature of the most important stabilizing interactions in the formation of AH change in a similar manner across the two rows of elements, but the change in the second-row set occurs two members to the right with respect to the first-row set.