An Integrated Approach to the Lewis Model, Valence Bond Theory, and Molecular Orbital Theory

An appropriate understanding of covalent bonding is not only essential for general chemistry, but also for future studies in chemistry and chemical research. In general, formation of a covalent bond is described using three different theories: the Lewis model, valence bond (VB) theory, and molecular orbital (MO) theory. While the Lewis model is intuitive and generally well received by students, the VB and MO theories are relatively difficult and often dropped from many general chemistry curricula. Teaching and learning can be improved by using a different model from the traditional method. This article presents an integrated approach to the Lewis, VB, and MO theories that unifies them to proper electronic interactions with the aid of the Pauli principle. Bonding in H2, F2, and HF has been demonstrated effectively using this approach, showing it is a quicker way of learning covalent bonding. A new model for formation of simple molecular orbitals in these molecules in terms of superposition of spin-opposite electrons (bonding MO) and Pauli repulsion between two spin-parallel electrons (antibonding MO) has been developed. The model is supported by the related total wavefunctions that contain both spatial (orbital) and spin components.