Chemical Bonding and Molecular Structure · Class 11
Hybridisation
What is hybridisation in chemistry? sp, sp², sp³, sp³d and sp³d² hybridisation with shapes, bond angles, and JEE/NEET examples.
Direct answer
Hybridisation is the mixing of atomic orbitals of similar energy on the same atom to form new hybrid orbitals of equal energy and definite geometry.
Why hybridisation is needed
Observed shapes of molecules (for example CH₄ tetrahedral, BF₃ trigonal planar) cannot be explained if carbon or boron uses pure s and p orbitals alone.
Hybridisation gives a simple model: atomic orbitals combine, then each hybrid orbital forms a σ bond (or holds a lone pair).
Common types (Class 11 / JEE / NEET)
sp — two orbitals; linear geometry; bond angle 180° (example: BeCl₂, acetylene C in C₂H₂).
sp² — three orbitals; trigonal planar; ~120° (example: BF₃, ethene C in C₂H₄).
sp³ — four orbitals; tetrahedral; ~109.5° (example: CH₄, NH₃, H₂O — lone pairs reduce the angle).
sp³d — five orbitals; trigonal bipyramidal; 90° and 120° (example: PCl₅).
sp³d² — six orbitals; octahedral; 90° (example: SF₆).
How to find hybridisation quickly
For many main-group molecules: count steric number = (number of σ bonds) + (number of lone pairs) on the central atom.
Steric number 2 → sp, 3 → sp², 4 → sp³, 5 → sp³d, 6 → sp³d².
π bonds do not change the hybridisation count of the central atom for this steric-number method (they use leftover p orbitals).
Formulae
Steric number = σ bonds + lone pairs (on central atom)
Maps to hybridisation type for many Class 11 molecules.