explain the structure of PCl5

In PCl₅ molecule, P forms 5 bonds with 5 Cl atoms, therefore it has to unpair 5 electrons. Now, the electronic configuration of phosphorus can be written as:

P : 1s²2s²2p⁶3s²3p³.

So P unpairs its, 3s² electron and one of the 3s electron is promoted to the empty 3d orbital.

P : 1s²2s²3s¹3p³3d¹.

Thus, P atom undergoes sp³d hybridization and forms 5 equivalent sp³d orbitals, each contain an unpaired electron. These hybrid orbitals arrange themselves in a trigonal bipyramidal structure, and each hybrid orbital overlaps with the 2p_z orbital of Cl atom containing one electron, leading to formation of 5 P-Cl sigma bonds directed at the coreners of a regular trigonal bipyramidal structure. Thus, geometry of PCl₅ molecule can be shown as: