The first ionization enthalpy `(Delta_(t)H)` values of the third period elements, `Na, Mg` and `Si` are respectively 496, 737 and `786 kJ mol^(-1)`. Predict whether the first `Delta_(t)H` valye for Al will be more close to 575 or `760 kJ mol^(-1)`? Justify your answer.

Explanation

It will be more close to 575 `kJ "mol"^(-1)`. The value for Al should be lower than that of Mg because of effective shielding of 3p electrons from the nucleus by 3s-electrons.