Molecular orbital theory rests on the notion that atomic orbitals
are combined to form
molecular orbitals. Because electron density from each
atom is spread out over the span of the
entire molecule, the electrons are lowered in energy. This accounts for the
stabilization that occurs during bonding. The amount of the stabilization
depends on the amount of
overlap between
atomic orbitals and the difference in energy between them. Atomic orbitals
that overlap effectively
produce stable molecular orbitals. One condition for overlap is that
the overlapping atomic
orbitals must be of similar energies.
The bonding in homonuclear and heteronuclear diatomic molecules will be
discussed to show how
molecular orbital theory works. Due to the complexities of describing the
molecular orbitals in
polynuclear molecules, we will introduce the notion of bonding through
hybridized atomic
orbitals to account for the bonding in such systems.
Molecular orbital theory can give us information about both ionic and
covalent molecules
and naturally predicts which molecules will be ionic and which will be
covalent. It is a powerful
and complex tool available to chemists for predicting the properties of
molecules. In this SparkNote,
only a brief introduction to molecular orbital theory will be given. The
interested reader should
consult the further reading section accompanying this document to gain
access to more detailed
treatments.
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