Hybridisation: The phenomenon of mixing of orbitals of the same atom with slight difference in energies so as
to redistribute their energies and give new orbitals of equivalent energy and shape. The new orbitals which get
formed are known as hybrid orbitals.
Conditions for hybridisation:
i) Only the orbitals belong to the same atom take part in the hybridisation.
ii) The orbitals that participate in hybridisation should have only small energy difference.
iii) Promotion of electron is not essential condition prior to hybridisation.
iv) It is not necessary that only the half-filled orbitals may participate in hybridisation. In some cases, even the
filled orbitals may participate in hybridisation.
Salient features of hybridisation:
i) Only the orbitals with small difference in energy take part in the hybridisation.
ii) Orbitals of a particular sub-shell cannot hybridise of their own since they have same energy.
iii) The number of hybrid orbitals formed is equal to the number of atomic orbitals taking part in hybridisation.
iv) Hybridisation never takes place in isolated atoms and it occurs only when the atom is to take part in bond
formation.
v) The hybridised orbitals are more effective in forming stable bonds than the pure atomic orbitals.
vi) The observed shape of a covalent molecule can be predicted from the type of the hybridisation involved.
Types of hybridisation: There are various types of hybridisation involving s, p and d orbitals. The different
types of hybridisation are as under:
1. sp hybridisation (linear): This type of hybridisation involves the mixing of one s and one p orbital resulting
in the formation of two equivalent sp hybrid orbitals. The suitable orbitals for sp hybridisation are s and pz
orbitals, if the hybrid orbitals are to lie along the z-axis.
Each sp hybrid orbitals 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.
e.g. C2H2 , BeF2
2. sp2 hybridisation (trigonal planar):
In this hybridisation there is involvement of one s and two p-orbitals in order to form three equivalent sp2
hybridised orbitals. The geometry is trigonal planar with bond angle of 1200.
e.g C2H2 , BH3
3. sp3 hybridisation (tetrahedral):
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. The four sp3 hybrid orbitals so formed are directed towards the four corners of the tetrahedron.
The angle between sp3 hybrid orbital is 109.5°.
e.g: CH4 , NH3 , H2O
4. sp3d hybridisation (trigonal bipyramidal): PF5
5. sp3d2 hybridisation (octahedral): SF6
6. sp3d3 hybridisation (pentagonal bipyramidal): IF7
Predicting Hybridisation and shapes of molecules and ions:
H = 1/2 [No. of valence electrons in the valence shell of atom
+ no. of monovalent atoms surrounding the atom − charge on cation + charge on anion]