"Through the nuclear charge of sulphur is more than that of phosphorus, yet the ionisation potential of phosphorus is relatively high"-why?

Explanation

`""_(15)P:1s^(2)2s^(2)2p^(6)3s^(2)3p_(x)^(1)3p_(y)^(1)3p_(2)^(1) and ""_(16):1s^(2)2s^(2)2p^(6)3s^(2)2p_(x)^(2)3p_(y)^(1)3p_(x)^(1)`
3p-orbital of the outermost shellof P-atom being half-filled, this electronic configuration is very stable, so, the removal of one 3p-electron to produce `P^(+)` ion requires sufficiently high amount of energy. on the other hand, the amount of energy required for removing one electron from partially filled 3p-orbital of S-atom to yield `S^(+)` ion is relatively less,sice the half-filled 3p-orbital of `S^(+)` assumes th extra stability due to loss the this electron. this accounts for the higher value of ionisation potential of phosphorus, relative to sulphur.