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 2pz 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: