1. In the PCl5 molecule, the central atom phosphorous is covalently bonded to five chlorine atoms. Here the atomic orbitals of phosphorous undergoes sp3d2 hybridisation which involves its one 3s orbital, three 3p orbitals and one vacant 3d orbital (dz2)
2. The ground state electronic configuration of phosphorous is [Ne] 3s23px23py13pz1
3. One of the paired electrons in the 3s orbital of phosphorous is promoted to one of its vacant 3d orbital (dz2) in the excited state.
4. The 3pz orbitals of the five chlorine atoms linearly overlap along the axis with the five sp3d hybridised orbitals of phosphorous to form the five P – CI bonds as follows.