Orbital hybridization is defined as the phenomenon of intermixing of atomic orbitals with slightly different energies and then of redistributing their energies to form new set of equivalent-energy orbitals in identical shapes.
For instance, the configuration of the valence electrons in carbon is a combination of s and p orbitals. Graphite is one example with an sp2 type, while diamond is of an sp3 form. Figure 2630a illustrates the hybridization process for diamond. During this process, the energy levels of the 2s are raised while the 2p levels are reduced so that the four sp3 orbitals have an identical energy, resulting in a more favourable lower energy system. In this case, these four valence electrons form σ bonds.
Figure 2630a. Schematic illustration of the process of hybridisation for carbon. Each carbon atom in diamond forms a series of sp3 hybridised atomic orbitals.
The schematic illustration in Figure 2630b shows the bonding levels for diamond in a different way. When the hybrid carbon atoms bond they form a series of four bonding and four antibonding orbitals. In a large diamond structure involving many carbon atoms, these energy levels form a continuous band structure represented by the valence and conduction bands.
Figure 2630b. Schematic illustration showing the progression of the electronic structure for an sp3 bonded system.
The significant features of hybridization are:
i) The hybrid orbital has electron density concentrated on one side on the nucleus, in other words, it has one lobe relatively larger than the other,
ii) The hybrid orbitals can form much stronger bonds as compared to the pure atomic orbitals because they can overlap to a greater degree,
iii) The hybridized orbitals in identical shapes have equivalent energies,
iv) The number of orbitals taking part in hybridization is equal to the number of hybrid orbitals,
v) The orbitals in hybridization must have only a small difference of energies,
vi) Hybridization can occur in both half-filled and completely filled orbitals.
Table 2630. Types of orbital hybridization.
|Type of hybridization
||Atomic orbitals taking part in hybridization
||ns + np
|| ns + npx + npy
||ns + npx + npy + npz
||ns + npx + npy + npz + ndz2
||(n - 1)dz2 + ns + npx + npy + npz
||ns + npx + npy + npz + ndx2-y2 + ndz2
||(n-1)dz2 + (n-1) dx2-y2 +
ns + npx + npy + npz
||(n-1) dx2-y2 + ns + npx + npy