The first ionization enthalpies of Na , Mg and Si are respectively 496,737 and 786 KJ mol ⁻¹ . What would be the first ionization enthalpy of Al in KJ mol ⁻¹ ?

Step-by-step solution

Na , Mg , Al and Si lie in the same period (3^ rd . period) and therefore the effective nuclear charge increases as Na < Mg < Al < Si because of which their ionization enthalpy (first) is also supposed to increase in this manner. However, the configuration of Al is 1 s^2 2 s^2 2 p^6 3 s^2 3 p^1 in which the loss of one 3 p - electron results in a stable, fully-filled configuration. This stable configuration is not as stable as that of Na ⁺ which is 1 s^2 2 s^2 2 p^6 and therefore the first ionization energy of Al w