THE NATURE OF THE CHEMICAL BOND
Marco Antonio Chaer Nascimento
Instituto de Química da UFRJ
Cidade Universitária, CT Bloco A sala 412
Rio de Janeiro, RJ 21949-900 Brazil
[email protected]
ABSTRACT
In this paper we briefly review the basic requirements that must be satisfied by any
wave function representing many-electron systems. Next, we examine the conditions
under which the classical concepts of molecular structure, chemical structure and
chemical bond can be translated into a quantum-mechanical language. Essential to this
aim is the utilization of an independent particle model (IPM) for a many-electron
system. In spite of the great popularity of the Hartree-Fock (HF) model only ValenceBond (VB) type wave functions with optimized, singly occupied and non necessarily
orthogonal atomic-like orbitals, can provide a quantum-mechanical translation of the
classical concepts of chemical structure and chemical bond, although the HF model can
still be useful for translating the concept of molecular structure. Finally, a quantumdynamical-type of analysis allows us to conclude that, from the quantum mechanical
point of view, the chemical bond is a consequence of interference effects. This type of
analysis allow us to considerable enlarge the concept of chemical bond. From the
energetic point of view, the interference effect responsible for the bond formation
manifests itself as a reduction of the kinetic energy of the electrons as the bond is
formed.