MOT postulates and types of molecular orbitals

Molecular Orbital Theory (MOT) is a theoretical model used to describe the behavior of electrons in molecules. It is based on the postulates that electrons in a molecule occupy molecular orbitals, which are formed by the combination of atomic orbitals.

The first postulate of MOT is the conservation of electron number, which states that the total number of electrons in a molecule is equal to the sum of the number of electrons in the constituent atoms.

The second postulate is the conservation of energy, which states that the total energy of the molecule is equal to the sum of the energies of the individual atomic orbitals.

There are two types of molecular orbitals: bonding molecular orbitals (BMOs) and antibonding molecular orbitals (ABMOs). BMOs are formed by the constructive interference of atomic orbitals, resulting in a lower energy and greater electron density between the nuclei. ABMOs, on the other hand, are formed by the destructive interference of atomic orbitals, resulting in a higher energy and a node between the nuclei.

The number and arrangement of BMOs and ABMOs depend on the number of atomic orbitals involved in the molecular orbital formation. For example, in a diatomic molecule, such as H2, there are two atomic orbitals (one from each hydrogen atom) that combine to form two molecular orbitals: a bonding molecular orbital and an antibonding molecular orbital.

In summary, MOT postulates that electrons in a molecule occupy molecular orbitals, which are formed by the combination of atomic orbitals. These molecular orbitals can be either bonding or antibonding, depending on the constructive or destructive interference of the atomic orbitals.