Crystal Field Theory

The Crystal Field Theory in now much more wiedly accepted than the valance bond theory. It assumes that

1. Attraction between the central metal and the ligands in a complex is purely electrostatic
2. The transition metal which forms the central atom in the complex is regarded as a positive ion of charge equal to the oxidation state.
3. Central metal atom is surrounded by negative ligands or neutral molecules which have a lone pair of electrons.
4. The electrons on the central metal aer under repulsive forces from those on the ligans , thus the electrons occupy the d orbital furthest away from the direction of approach of ligands.
5. There is no interaction between metal ornitals and ligand orbitals.
6. The d orbitals on the metal all have same energy in the free atom. However, when a complex is formed the ligands destroy the degeneracy of these orbitals, i.e the orbitals now have different energies. 
7. The approach of ligands split the d orbitals in two different energy state

                              a.       eg set of orbitals
                              b.       t2g set of orbitals