Second ionization potential of Li, Be and B is in the order : — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

Step 1: Write the electronic configurations of the monovalent cations (M^+): Li^+ (1s^2), Be^+ (1s^2 2s^1), B^+ (1s^2 2s^2). Step 2: Li^+ has a fully filled 1s^2 Helium-like noble gas configuration. Disruption of this shell requires an enormous amount of energy, making Li^+ have the highest second ionization potential. Step 3: Comparing Be^+ (2s^1) and B^+ (2s^2), the electron in B^+ is removed from a stable, fully-filled 2s subshell, which is harder than removing the single valence electron from Be^+. Thus, the correct order is Li > B > Be.