Q. Limitations of Hybrid orbitals?

• It gives no idea whether a particular metal ion would prefer to have any particular geometry say, an octahedral or tetrahedral with a given ligand.
• Even if we know that a complex formed is four coordinated we cannot decide whether it would be tetrahedral or square planar. It is only after measuring the magnetic moment that we can decide the correct geometry. For example in the case of two parallel compounds, [Ni(CN)₄]^2- and [Ni(Cl)₄]²the former is a square planar compound the other is tetrahedral. This example leads to the next weakness.
• The important role ligands play in deciding the geometry of the resultant complex is not taken into account by this theory.
• It gives only an approximate magnetic moment value which in some cases may differ considerably.
• Besides magnetic property, it does not throw any light on other physico-chemical Properties of complexes like-spectral, stability, reactivity etc.

Thus we see the need for a more comprehensive theory which could explain the observed properties and if possible, predict the formation of new compounds. Even if such a theory may not be all comprehensive, it should at least be able to recognise the factors responsible for the typical properties of complexes. Crystal field theory is such an attempt and in the next sub-section we shall deal with this new theory.