SP2 HYBRIDIZATION OF CARBON

In sp² hybridization, there is intermixing of one 2s and two of the 2p orbitals of carbon in the excited state to form three hybrid orbitals. These are oriented in trigonal planar geometry. Each sp² hybrid orbital is occupied by one electron. The remaining pure 2p orbital with one electron lies at right angle to the plane of hybrid orbitals.

 The sp² hybrid orbital form 3 σ-bonds in trigonal planar geometry. Thus the bond angles are about 120^o. The remaining pure 'p' orbital will form a π-bond. Thus carbon forms total four bonds i.e., three σ-bonds and one π-bond.
E.g. In ethylene molecule, C₂H₄, each carbon atom undergoes sp² hybridization. Each carbon forms 2 σ-bonds with hydrogens and one σ-bond with another carbon. The remaining pure 'p' orbitals on two carbons overlap sidewise to form a π-bond. Thus there is a double bond between two carbons.

Note that whenever carbon atom undergoes sp² hybridization, it forms 3 σ-bonds and 1 π-bond i.e., two single bonds and one double bond.