Molecular Orbital Theory

Introduction :
Molecular orbital theory is a polycentric region in space, defined by its size and shape, associated with two or more atoms in a molecule and each has a capacity of two electrons with opposite spins. Thus, in a molecular orbital, electrons are revolving in the field of more than one nucleus. The molecular orbital to explain formation of chemical bond, relative bond strengths, paramagnetic or diamagnetic nature.

Feature of Molecular Orbital Theory:

• The main features of the Molecular Orbital Theory are:
• The atomic orbital of the combine atoms partly cover to form new orbital, called molecular orbital.
• As a result of this, the atomic orbitals lose their being identity.
• Thus in a Molecular Orbital Theory, electrons revolves in the field of more than one nucleus.
• The number of Molecular Orbital is produced is equal to the number of overlap atomic orbitals.
• Maximum capacity of a Molecular Orbital is two electrons with opposite spins.
• Only those atomic orbitals can come together to form Molecular Orbital Theory which has analogous energies as well as proper orientations.
• Molecular orbital theory obtained addition of wave functions of atoms involved,`Psi`(MO)=`Psi`_A + `Psi` _B   is called bonding molecular orbital.
• Molecular orbital theory obtained by subtraction of wave functions of atoms involved  `Psi`  ^*(MO)=`Psi`_A - `Psi`_B is called antibonding molecular orbital.
• Probability of bonding molecular orbital formation greater than that of antibonding molecular orbital formation.
• Molecular theory gives the electron probability distribution around a group of nuclei just gives the electron probability distribution around nucleus.
• The shape of the molecular orbital theory produced depends on the type of the combining atomic orbitals.
• Inner molecular orbital theories which do not take part in bond formation are called non-bonding molecular orbital theory.

 Conditions for the formation of molecular orbitals:

• Any two atomic on combination do not form molecular orbitals.

• In fact, there are certain limitations to the combination of atomic orbitals.

• The energies of combining atomic orbitals should of similar magnitude.

• Thus, a homonuclear diatomic molecule will not be formed. if 1s orbital of one atom overlaps with 2s-orbital of another atom.

• Combination of atomic orbitals takes place only, if overlapping takes place to a considerable extent, since greater the overlapping of atomic orbitals, the greater is the build-up of the charge between the nuclei.

• The combining atomic orbitals should have power over the same symmetry about the molecular axis.