The main assumptions of srystal field theory are as follows .
(i) The transition metal ion is surrounded by the ligands with lone pairs of electrons and the complex is a combination of central ion surrounded by other ions or molecules or dipoles ,e.g ligands .
(ii) all types of ligands are regarded as point charges in case of anions and as dipoles in case of neutral molecules .
(iii) The interactions between the meatl ion the negative ends of anion ( or ion dipoles ) is purely electrostatic ,i.e the bond between the metal and ligand is considered to be 100 % ionic .
(iv) The ligands surrounding the meta ion produces electrical fieeld and this electrical field influences the energies field and this electrical field influences the energies of the orbitals of central metal ion , particularly d - orbitals .
(v) In the case of free metal ion ,all five d-orbitals have the same energy .Orbitals having the same energies are called degenerate orbitals .
The five degenerate d- orbitals of the metal ion split into different sets of orbital having different energies in the presence of electrical field of ligands .This is called crystal field splitting .
The number of ligands and their arrangement (geometry ) around the central mtal ion will have different around the central metal ion will have different effect on the relative energies of the five d - orbitals .
Splitting of d - orbitals under the effect of an octahedral crystal field
The degeneracy of the d - orbitals has been removed due to ligand - metal electron repulsions in the octahedral complex to yield three orbitals of lower energy `t_(2g)` set and two orbitals of higher energy `e_(g)` .This splitting of the degenerate levels due to the presence of ligands in a definite geometry is termed as crystal field splitting .
