What orbital hybridisation?

Orbital hybridisation is a model used to explain covalent bonding in molecules. It involves the merging of orbitals that are on the same energy level to form new hybrid orbitals.

Orbital hybridisation most commonly occurs with the merging of the s and p orbitals. Though in the same energy level the s orbitals have a lower energy than the p orbitals, the hybrid orbitals have an energy between the s and p orbitals. An atom can be sp, sp² or sp³ hybridised depending if the s orbital was merged with one, two or three orbitals respectively. Thus the exponent on the p refers to the number of p orbitals that merged with the s orbital. These new hybrid orbitals can bond with other orbitals just like any other orbitals.