Consider the first ionization enthalpies of the third-period elements , and . Which of the following — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

The general trend is an increase in $IE_1$ across a period due to increasing $Z_{eff}$. However, $Mg$ ($3s^2$) has a fully filled, stable $s$ -subshell, making it harder to remove an electron compared to $Al$ ($3s^2 3p^1$), where the $3p$ electron is further out and easier to remove. Therefore, $Mg > Al$. The overall order is $Na < Al < Mg < Si$, which satisfies the pattern $Na < Mg > Al < Si$.