Question

The first ionisation potential of $Na$, $Mg$ and $Si$ are 496, 737, and 776 $kJmo{l}^{-1}$ respectively. The ionisation potential of $Al$ could be:

• A. $760kJmo{l}^{-1}$
• B. $575kJmo{l}^{-1}$
• C. $801kJmo{l}^{-1}$
• D. $419kJmo{l}^{-1}$

Answer 1

The correct option is B $575kJmo{l}^{-1}$

Ionisation potential increases when we move from left to right in a period. But the ionisation enthalpy of $Al$ is lower than that of $Mg$ as the $3p^1$ electron of $Al$ is easier to remove than to remove an electron from a fully-filled $3s$-orbital of $Mg$.