Valence bond theory : The salient feature of this theory are-
- The central metal ion has a number of empty orbitals for accommodating electrons donated by the ligands. The number of empty orbitals is equal to the co-ordination number of the metal ion for the particular complex.
- The atomic orbitals (s, p or d) of a metal ion hybridize to form hybrid orbitals with definite directional properties. These hybrid orbitals now overlaps with the ligands orbitals to form strong chemical bonds.
- The d-orbitals involved in the hybridisation may be either inner (n-1)d or outer n-d orbitals.The complexes formed in the two ways are referred to as low spin or high spin complexes, respectively.
- Each ligand contains a lone pair of electrons.
- A covalent bond is formed by the overlapping of a vacant hybridised metal orbital and a filled orbital of a ligand. The bond is also sometime called as co-ordinate bond.
- If a complex contains an unpaired electrons, it is paramagnetic in nature, while if it does not contains unpaired electron, it is diamagnetic in nature.
- The number of unpaired electrons in the complex, points out the geometry of the complex as well as hybridisation of the central metal ion and vice-versa. In practice, the number of unpaired electrons in a complex as formed from magnetic moment measured from-
μ={n(n+2)}1/2
{ where n= no. of lone pair of electrons.}
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