Question

State the salient features of Molecular Orbital Theory (MOT).

Answer 1

Hint : Molecular Orbital theory is helpful to explain certain characteristics of a molecule like their relative bond strengths, paramagnetic and diamagnetic properties. Molecular orbitals are defined as , when two or more atomic orbitals overlap to form new orbitals after losing their identity , these new orbitals are called Molecular Orbitals.

Complete Step By Step Answer:
Molecular Orbital Theory was developed by F.Hund and R.S. Mulliken in $ 1932\; $ . Salient features of Molecular Orbital Theory is:
The electrons in the molecules that are present in various molecular orbitals are filled just like the atomic orbitals. When two atomic orbitals combine they form a molecular orbital. Imagine two eggs opened in a put then put in a frying pan, this represents somewhat like a molecular orbital. From this we can also conclude that the electron in the molecular orbital is influenced by two or more nuclei depending upon the number of atoms in the molecules, thus molecular orbitals are polycentric.
For a molecular orbital to form an atomic orbital of comparable energies and proper symmetry should combine together. For example $ 1\;s $ can only combine with $ 1\;s $ orbital not with $ 2\;s $ orbital as the energies and symmetry of these orbital are not same or comparable.
When two atomic orbitals combine, they form bonding and an- bonding molecular orbitals.
The bonding orbitals have lower energy. As we’ve learned that any atom or molecule having lower energy corresponds to higher stability. Therefore bonding molecular orbitals are highly stable than the antibonding orbitals.
The bonding molecular orbitals are represented by $ \sigma ,\pi ,\partial $ whereas the corresponding anti-bonding orbitals are represented by $ {\sigma ^*},{\pi ^*},{\partial ^*} $ .
In terms of probability distribution, a molecular orbital gives the electron probability distribution around a group of nuclei just like the atomic orbital around a single nucleus.
The filling of molecular orbitals takes place in accordance with Aufbau’s principle, Pauli’s exclusion principle and Hund’s rule of maximum multiplicity.

Note :
Aufbau’s principle states that Molecular orbitals (MO) are filled in order of their increasing energies.
Pauli’s exclusion principle – MO can have maximum two electrons with opposite spin.
Hund’s rule of maximum multiplicity- pairing of electrons does not take place until each of them has got one electron each.