Question

The first ionization enthalpies of Na, Mg, Al and Si are in the order.

• A. Na < Mg > Al < Si
• B. Na > Mg > Al > Si
• C. Na < Mg < Al < Si
• D. Na > Mg> Al < Si

Answer 1

Answer: (A)

Na < Mg > Al < Si

Answer 2

: As we move across the period, atomic size decreases hence, ionization enthalpy increases. But for Al $(3s^{2}3p^{1})$, electron has to be removed from outer 3p orbital ehereas in Mg$(3s^{2})$, electron has to be removed from stable fully filled 3s orbital. Thus, I.E. for Mg > Al. So, the correct order of first ionization enthalpies is:

Na < Mg > Al < Si.