The first ionization enthalpy `(Delta_(1)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_(1)H` value 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.