The electronic configurations of Europium (, ) and Gadolinium (, ) display significant half-filled s — d and f Block Elements Chemistry Question
Question
The electronic configurations of Europium ($Eu$, $Z=63$) and Gadolinium ($Gd$, $Z=64$) display significant half-filled stability anomalies. Which of the following statements regarding their ground-state configurations are correct?
Answer: A,B
💡 Solution & Explanation
Europium ($Z=63$) simply fills the $f$ -subshell to exactly half capacity, yielding $[Xe] 4f^7 6s^2$. Gadolinium ($Z=64$) must add one more electron. To maintain the incredible stability of the half-filled $4f^7$ core, the newly added electron enters the $5d$ orbital instead, making $Gd$ $[Xe] 4f^7 5d^1 6s^2$.
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