The molecule of PCl3 it is made up of phosphorus and chlorine molecules However, the hybridization basically occurs within the central atom which is phosphorus. Also, the electronic structure in the ground state of phosphorus will be 1s2, 2s2, 2p6, 3s2, 3p2. The valence shell in phosphorus is 5. During the excited stated one of the s electrons moves to an empty d orbital resulting in the change in electronic configuration. In excited the electronic configuration will change to 1s2, 2s2, 2p6, 3s2, 3px1, 3py1, 3pz1. Now, three unpaired electrons will be used to form bonds with 3 chlorine atoms. During the formation of the bond, four orbitals (3s2, 3px1, 3py1, 3pz1) will hybridize to form 4 equivalent sp3 hybrid orbitals. One of the hybrid orbitals will contain one lone pair of electrons.