Question

Please give short answer ph3 is known but Ph5 not give a reasion

Answer 1

Electronic configuration of P(15)=1s²2s²2p63s²3p³

Hence,p orbital has 3 electron which is unpaired. So, 3 hydrogen goes to 3 unpaired electron of p orbital & becomes paired n form ph3.

But in case of ph5, 1 electron from s orbital excites to vacant d orbital of third shell n now total unpaired electron become 5 n 5H can paired with unpaired e of P but it can't form ph5 because the extent of overlapping of d orbital of phosphorous and 1s orbital of hydrogen is very less because the energy difference between them is too high for favourable bond formation so that the most of 1s orbitals of hydrogens interact with p orbitals so that we can form PH3 but PH5 doesnt exists as d-s orbital overlapping is less and so ph5 will dissociate into PH3 and H2.