Question

The electronic configurations of bivalent europium and trivalent cerium are :
(atomic number: $Xe = 54, Ce =58, Eu — 63$)

• A. $[Xe] 4f^7$ and $[Xe] 4f^1$
• B. $[Xe] 4f^7 \,6s^2$ and $[Xe] 4f^2\,6s^2$
• C. $[Xe] 4f^2$ and $[Xe] 4f^7$
• D. $[Xe] 4f^4$ and $[Xe] 4f^9$

Answer 1

Answer: (A)

$Eu_{63} \Rightarrow \, \left[Xe\right] 4 f^{7} 5 d^{\circ} 6s^{2}$
$Eu^{2\oplus} \Rightarrow \left[Xe\right]4f^{7}$
$Ce_{58} \Rightarrow \left[Xe\right]4 f^{1} 5d^{1} 6s^{2}$
$Ce^{3\oplus} \Rightarrow \, \left[Xe\right]4f^{1}$