Among the representative elements belonging to the 3rd period of the modern periodic table (from to — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

The expected $IE_1$ trend across the 3rd period is $Na < Mg < Al < Si < P < S < Cl < Ar$. However, due to the stability of $Mg$'s filled $3s^2$ subshell compared to $Al$'s $3p^1$, $Mg > Al$. The actual trend is $Na < Al < Mg < Si < S < P < Cl < Ar$. The elements with higher $IE_1$ than $Al$ are $Mg, Si, S, P, Cl,$ and $Ar$. The total number is 6.