Molecular Orbital Theory (MOT) : Molecular Orbital Theory (MOT) was developed by F. Hund and R.S Mulliken in 1932. Main postulates of this theory are :
1. Atomic orbitals of comparable energy and proper symmetry combine together to form molecular orbitals.
2. The movement of electrons in a molecular orbital is influenced by all the nuclei of combining atoms. (Molecular orbital is polycentric in nature)
3. The number of molecular orbitals formed is equal to the number of combining atomic orbitals. When two atomic orbitals (AO’s) combine together two molecular orbitals (MO’s) are formed. One molecular orbital possesses higher energy than corresponding atomic orbitals and is called anti bonding molecular orbital (ABMO) and the other has lower energy and is called bonding molecular orbitals (BMO).
4. In molecules, electrons are present in molecular orbitals. The electron filling is in accordance with Pauli’s exclusion principle, Aufbau principle and Hund’s rule.
Bond order = (10 – 5)/2 = 5/2 = 2.5
The bond order decreases in the order is :
As we know that stability is directly proportional to bond order.
Hence, increasing order of stability is :
