sp2 hybridization

 sp² hybridization

In this hybridization there is involvement of one s and two p-orbitals in order to form three equivalent sp² hybridized orbitals. For example, in BCl₃ molecule, the ground state electronic configuration of central boron atom is 1s²2s²2p¹. In the excited state, one of the 2s electrons is promoted to vacant 2p orbitals as a result boron has three unpaired electrons. These three orbitals (one 2s and two 2p) hybridise to form three sp² hybrid orbitals. The three hybrid orbitals so formed are oriented in a trigonal planar arrangement and overlap with 2p orbitals of chlorine to form three B-Cl bonds. Therefore, in BCl₃ the geometry is trigonal planar with CIBCl bond of 120.