In the Group 13 elements, the first ionization energy drops abruptly from Aluminium to Gallium. This — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

The presence of 10 inner 3d electrons in Gallium provides very poor shielding. This increases the effective nuclear charge ($Z_{eff}$) pulling the valence electrons tighter, making $IE_1$ of Ga slightly higher than expected (often $Ga > Al$).