Hybridization

NEED FOR CONCEPT OF HYBRIDIZATION

Structures of simple molecules like H₂, F₂ and HF etc can be readily explained by the electron pair theory. But the formation of the compound of Beryllium, Boron & carbon cannot be that easily explained on the basis of same theory.

The electronic configuration of Be, b & c are

        ₄Be = 1s², 2s²

        ₅B = 1s², 2s² 2p_x¹

        ₆C = 1s², 2s² 2p_x¹2p_y¹

    On the basis of electron pair theory, Beryllium should be zero valent and behave like noble gas since it has no unpaired electron, boron with one unpaired electron (2P_x^l) should be monovalent and carbon with two unpaired electrons (2p_x¹, 2p_y¹) should be divalent. But Be forms compounds like BeH₂, BeF₂
in which it is bivalent, B forms compounds
like
BF₃, BCl₃ in which it is trivalent and C forms compounds like CH₄, CCl₄, in which it is tetravalent. Thus, it is not possible to explain the valencies of the elements like Be, B and C, on the basis of the number of unpaired electrons in the ground state of their atoms. Hence, in order to explain the bi, tri and tetravalency of Be, B and C respectively and to explain the observed geometry of their molecules, a new concept, called Hybridization is introduced by Pauling. This concept, though hypothetical is extremely useful.

CONCEPT

    "Hybridization may be defined as the phenomenon of mixing up of orbitals of an atom of nearly equal energy, giving rise to entirely new orbitals equal in number to the mixing orbitals & having same energies & identical shapes". The new set of orbitals so formed is known as Hybrid Orbitals. In order to minimize the repulsion among hybrid orbitals these rearrange themselves in space in definite orientation.