Determine the exact number of completely unpaired electrons present in the ground state valence shel — d and f Block Elements Chemistry Question

💡 Solution & Explanation

The neutral Europium atom ($Z=63$) has an anomalous ground-state configuration of $[Xe] 4f^7 6s^2$ to maximize the stability of a half-filled subshell. Upon ionizing to $Eu^{2+}$, the two $6s$ electrons are removed. The remaining core is strictly $[Xe] 4f^7$. According to Hund's rule, the 7 electrons occupy the seven $f$ -orbitals singly, resulting in exactly $7$ unpaired electrons.