Why is the second ionization enthalpy () of Potassium () massively greater than that of Copper (), e — Periodic Table and Periodicity Chemistry Question

💡 Solution & Explanation

$K$ loses its single $4s$ electron easily to form $K^+$, which possesses the extremely stable $[Ar]$ $3s^2 3p^6$ noble gas core. Removing a second electron from this core requires immense energy. $Cu$ loses its $4s$ electron to form $Cu^+$, which has a $[Ar]$ $3d^{10}$ pseudo-noble gas core. Removing a 3d electron requires less energy than breaking a true noble gas $3p^6$ core.