Molecular Orbital Theory

This theory was proposed by F.Hund and R.S.Mulliken in 1932 and the basic features of this theory are given below-

Electrons of the molecule are present in various molecular orbital just like the electrons of an atom are present in atomic orbitals.
Molecular orbitals are formed by mixing of atomic orbitals of comparable energies and proper symmetry.
An electron in an atomic orbital is influenced by only one nucleus and thus it is monocentric while in a molecular orbital it is influenced by two or more nuclei of the molecule and thus it is polycentric.
The total number of molecular orbitals are equal to the number of combining atomic orbitals.
Bonding molecular orbital has lower energy and greater satability than the corresponding antibonding molecular orbitals.
Molecular orbitals are also filled by electron in accordance with Aufbau principle obeying Pauli's exclusion principle and Hund's rule of maximum multiplicity.
Each electron movin in a molecular orbital has a spin od +1/2 and −1/2.