Which is the valency of phosphorus 3,5 / how can we learn valency

which is the valency of phosphorus 3,5 / how can we learn valency

Phosphorous shows both the valencies 3 and 5.

Electronic configuration of Phosphorous

P: 1s 2s2 2p63s2 3p3

Phosphorous with valency 3:

With three unpaired electrons in three p orbitals, phosphorous shows valency 3, like in case of compound PCl3.

Phosphorous with valency 5:

In case of PCl5, one of 3s electron gets promoted to 3d orbital as follows:

P: 1s2 2s2 2p6 3s1 3p33d1

Thus, phosphorous atom undergoes sp3d hybridisation to form five equivalent sp3d orbitals each containing one unpaired electron.