[XxslbabesxX]

Can someone explain to me why Sulfur has a lower first ionization energy than Phosphorus?

Also do group differences make more of a difference than does period differences when it comes to things like electron affinity and ionization energy.

Thanks!

[Blueshawk]

It could be due the their electron affinity.

Electron Affinity of P is 71.7 kJ/mol

Electron Affinity of S is 200.4 kJ/mol

Therefore P has less ability or want to hold onto electrons, therefore the electrons are more easily removed and the energy potential is therefore greater.

[Mitch]

Your numbers seem to indicate the opposite. One should note that electron affinity = -(delta h)