extent. Further, it is important to note that in the formation of multiple bonds between two atoms of a molecule, pi bond(s) is formed in addition to a sigma bond. . Hybridisation In order to explain the characteristic geometrical shapes of polyatomic molecules like CH , NH and H O etc., Pauling introduced the concept of hybridisation.
According to him the atomic orbitals combine to form new set of equivalent orbitals known as hybrid orbitals . Unlike pure orbitals, the hybrid orbitals are used in bond formation. The phenomenon is known as hybridisation which can be defined as the process of intermixing of the orbitals of slightly different energies so as to redistribute their energies, resulting in the formation of new set of orbitals of equivalent energies and shape. For example when one s and three p -orbitals of carbon hybridise, there is the formation of four new sp hybrid orbitals.
Salient features of hybridisation: The main features of hybridisation are as under : . The number of hybrid orbitals is equal to the number of the atomic orbitals that get hybridised. . The hybridised orbitals are always equivalent in energy and shape.
. The hybrid orbitals are more effective in forming stable bonds than the pure atomic orbitals. . These hybrid orbitals are directed in space in some preferred direction to have minimum repulsion between electron pairs and thus a stable arrangement.
Therefore, the type of hybridisation indicates the geometry of the molecules. Important conditions for hybridisation (i) The orbitals present in the valence shell of the atom are hybridised. (ii) The orbitals undergoing hybridisation should have almost equal energy. (iii) Promotion of electron is not essential condition prior to hybridisation.
(iv) It is not necessary that only half filled orbitals participate in hybridisation. In some cases, even filled orbitals of valence shell take part in hybridisation. . .
Types of Hybridisation There are various types of hybridisation involving s , p and d orbitals. The different types of hybridisation are as under: (I) sp hybridisation: This type of hybridisation involves the mixing