Hybridization is the phenomenon of intermixing of orbitals of slightly different energies so as to redistribute their energies and to give new set of orbitals of equivalent energy and shape. The atomic orbitals taking part in hybridisation are called hybrid orbitals. These hybrid orbitals have minimum repulsion between their electron pairs and thus are more stable. Only orbitals of almost similar energies and belonging to same atom or ion undergo hybridization. The number of hybrid orbitals produced is equal to the number of pure orbitals mixed during hybridization. The type of hybridisation indicates the geometry of the molecules. Only atomic orbitals participate in hybridisation. Electron’s present in them do not take part.
(a) sp hybridisation : This type of hybridisation involves the mixing of one s and one p orbital resulting in the formation of two equivalent sp hybrid orbitals. Each sp hybrid orbital has 50% s-character and 50% p-character. Such a molecule in which the central atom is sp-hybridised and linked directly to two other central atoms possesses linear geometry.
This type of hybridisation is also known as diagonal hybridisation. The bond angle is 180°.
(b) sp2 hybridisation : In this hybridisation, there is involvement of one s and two p-orbitals in order to form three equivalent sp2 hybridised orbitals. The three hybrid orbitals so formed are oriented in a plane at maximum distance to form an angle of 120° between the hybrid orbitals. The hybrid orbitals are oriented in a trigonal planar arrangement
(c) sp3 hybridisation : In this type of hybridisation, there is mixing of one s-orbital and three p-orbitals of the valence shell to form four sp3 hybrid orbital of equivalent energies and shape. There is 25% s-character and 75% p-character in each sp3 hybrid orbital. This hybridisation has tetrahedral geometry.