What is the correct sequence of the first ionisation enthalpy for the 3rd-period elements and ? — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

The general trend is an increase across the period ($Na < Si$). However, Magnesium has a stable $3s^2$ configuration, giving it a higher $IE_1$ than Aluminium ($3p^1$). Thus, the order is $Na < Al < Mg < Si$.