Theories of Bonding
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There is another convention in the labeling of molecular orbitals that we need to be aware of. This concerns the parity of the orbital.
The procedure for working out a molecular orbital of a general diatomic molecule is quite simple. We construct molecular orbitals using the available orbitals on the atoms.
Molecular orbital theory does not consider the electrons in a bond to be localised between two nuclei. Rather it considers them to occupy a molecular orbital. This orbital, the region of space in which the electron is most likely to be found, covers the whole molecule, and the atoms that make up the molecule are bound together by the electrons that move around them.
The fundamental aspects of valence bond theory as outlined on the previous page are that superposition of wavefunctions leads to a low energy bonding wavefunction in which the probability of finding the electrons in the internuclear region has been substantially increased.
There are two main approaches to the description of bonding in molecules, valence bond (VB) theory and molecular orbital (MO) theory.