Question

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

Answer 1

It will be closer to 575 kJ mol^-1 . The value for Al should be lower than that of Mg due to effective shielding of 3p electrons from the nucleus of 3s-electrons.