Is Covalent Bonding a One-Electron Phenomenon? Analysis of a Simple Potential Model of Molecular Structure

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

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Abstract Volume 15 (2010) pp 42-54

Is Covalent Bonding a One-Electron Phenomenon? Analysis of a Simple Potential Model of Molecular Structure

George B Bacskay,*^,† William Eek^‡and Sture Nordholm^‡

^†School of Chemistry, University of Sydney, N.S.W. 2006, Australia, ^‡Department of Chemistry, Göteborg University, SE-412 96 Göteborg, Sweden, * Corresponding author, E-mail: bacskay@chem.usyd.edu.au
Received April 22, 2009. Accepted July 1, 2009.

Published: 16 January 2010

Abstract. The aim of this work is to show that covalent bonding is essentially a one-electron quantum mechanical phenomenon. A correct understanding of the mechanism of covalent bonding in H₂⁺ is therefore vital for the understanding and description of bonding in the more complex many-electron molecules. In addition to a standard molecular orbital treatment of H₂⁺, in this work the molecule is also modeled simply as an electron in a square well potential as well as a molecule with Gaussian potential terms. These studies provide strong evidence that covalent bonding is a quantum mechanical phenomenon and a direct consequence of electron delocalization. For the study of more complex systems with comparable ease, a simple one-electron model is proposed where a given molecule is modeled as a superposition of screened atomic potentials, which can reproduce the appropriate atomic orbitals and their energies in a semi-quantitative manner. Application of this approach to the homonuclear diatomics H₂ to F₂ predict the existence of stable covalently bonded molecules with bond lengths which are in reasonable agreement with experiment. Comparisons are also made with the results of Hartree-Fock and density functional calculations in establishing support for the view that covalent bonding is indeed a one-electron phenomenon and should therefore be taught as such.

Key Words: In the Classroom; physical chemistry

(*) Corresponding author. (E-mail: bacskay@chem.usyd.edu.au)

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