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A Model for the Chemical Bond
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Abstract
A simple model of the chemical bond is developed on the basis of an elementary MO theory requiring solution of at most a 2 × 2 Hückel secular equation including overlap. The fundamental quantities are the atomic integrals α1 and α2 giving the energies of the isolated atoms or ions, and the bond integral b which depends on the overlap S between the interacting AOs. For homonuclear diatomics, the interaction is first order in b, and the bond is formed as long as the number of electrons in bonding MOs is greater than the number of electrons in antibonding MOs. When the number of bonding electrons equals the number of antibonding electrons Pauli repulsion occurs, provided overlap between the interacting AOs is explicitly considered. Model bond energies with |β| « 60 kcal mol–1 and |βπ| « 55 kcal mol–1 reproduce experimental atomization energy results for σ- and π-electrons of most first-row homonuclear diatomics with an average error not exceeding 10%. Bond stereochemistry is introduced in terms of bond energy maximization. Symmetry arguments are used to reduce consideration of CH4 to a set of 2 × 2 secular equations, whose best energy corresponds to the tetrahedral arrangement of four straight CH bonds, explaining in a natural way the formation of four equivalent sp3 hybrids on carbon. Next, electron distribution in a two-electron bond is considered, and atomic, overlap, gross atomic, and formal charges are introduced to explain the origin of molecular electric moments.
Keywords (Audience):
Upper-Division UndergraduateKeywords (Domain):
Inorganic ChemistryKeywords (Feature):
Research: Science and EducationKeywords (Subject):
Covalent BondingCiting Articles
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This article has been cited by 3 ACS Journal articles (3 most recent appear below).
Orbital Exponent Optimization in Elementary VB Calculations of the Chemical Bond in the Ground State of Simple Molecular Systems
Valerio MagnascoJournal of Chemical Education2008 85 (12), 1686Orbital Exponent Optimization in Elementary VB Calculations of the Chemical Bond in the Ground State of Simple Molecular Systems
Valerio MagnascoJournal of Chemical Education2008 85 (12), 1686Orbital exponent optimization in the elementary ab-initio VB calculation of the ground states of H2+, H2, He2+, He2 gives a fair description of the exchange-overlap component of the interatomic interaction that is important in the bond region. Correct ...
On the Relative Merits of Non-Orthogonal and Orthogonal Valence Bond Methods Illustrated on the Hydrogen Molecule
Jean-Paul Malrieu , Celestino Angeli and Renzo CimiragliaJournal of Chemical Education2008 85 (1), 150On the Relative Merits of Non-Orthogonal and Orthogonal Valence Bond Methods Illustrated on the Hydrogen Molecule
Jean-Paul Malrieu , Celestino Angeli and Renzo CimiragliaJournal of Chemical Education2008 85 (1), 150Valence bond (VB) is one of the cornerstone theories of quantum chemistry. Even if in practical applications the molecular orbital (MO) approach has obtained more attention, some basic chemical concepts (such as the nature of the chemical bond and the ...
A Model for the Chemical Bond; J. Chem. Educ. 2004, 81, 427-435
Valerio MagnascoJournal of Chemical Education2005 82 (9), 1311A Model for the Chemical Bond; J. Chem. Educ. 2004, 81, 427-435
Valerio MagnascoJournal of Chemical Education2005 82 (9), 1311Corrections to "A Model for the Chemical Bond," J. Chem. Educ. 2004, 81, 427-435.
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- Received: August 03, 2009
ACS
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