ja5b12434_si_001.pdf (686.02 kB)
Distinguishing Bonds
journal contribution
posted on 2016-02-24, 00:00 authored by Martin Rahm, Roald HoffmannThe
energy change per electron in a chemical or physical transformation,
ΔE/n, may be expressed as
Δχ̅ + Δ(VNN +
ω)/n, where Δχ̅ is the average
electron binding energy, a generalized electronegativity, ΔVNN is the change in nuclear repulsions, and
Δω is the change in multielectron interactions in the
process considered. The last term can be obtained by the difference
from experimental or theoretical estimates of the first terms. Previously
obtained consequences of this energy partitioning are extended here
to a different analysis of bonding in a great variety of diatomics,
including more or less polar ones. Arguments are presented for associating
the average change in electron binding energy with covalence, and
the change in multielectron interactions with electron transfer, either
to, out, or within a molecule. A new descriptor Q, essentially the scaled difference between the Δχ̅
and Δ(VNN + ω)/n terms, when plotted versus the bond energy, separates nicely a wide
variety of bonding types, covalent, covalent but more correlated,
polar and increasingly ionic, metallogenic, electrostatic, charge-shift
bonds, and dispersion interactions. Also, Q itself shows a set of
interesting relations with the correlation energy of a bond.