Q. Illustrate Crystal Field Theory with s-orbitals?

Let us start with s-orbitals which are spherically symmetrical. Any effect due to mutual repulsions between the s-electrons and the negatively charged ligands will be equal in all the three directions. The net result of such an interaction would be to raise the total energy of the system - metal and ligand combined. In the case of p-orbitals, when they are completely filled as in a transition metal ion, once again the interaction will raise the total energy of the system.

The real differences arise in case of d-orbitals. They will all be raised in energy compared to free ion state. However, due to the differences in their orientation, all the five d-orbitals are not affected equally by the presence of ligands. Three orbitals, d_xy, d_yz, d_xz have their electron density concentrated between the three Cartesian axes whereas in the other two orbitals d_x2-_y2, d_z2 the electron density is concentrated along the axes as shown in Fig.

Thus, depending upon the position of the ligands the interaction between the d-electrons will not be uniform and the five d-orbital? Will  no more be equal in energy. When all the  orbitals are equal in energy we call them degenerate but when they are no more equal as in  case of complexes we say that the degeneracy of the orbitals has been removed due to the  presence of ligands. Crystal field theory accounts for the properties of complexes in terms of splitti.ng of the d-orbitals into different energy levels. We shall consider the complexes with three most common geometries namely octahedral, tetrahedral and square planar and see how the splitting of the orbitals takes place in each case.