Question

The electronic configuration of $Eu$ (Atomic $No. 63$), $Gd$ (Atomic $No. 64$) and $Tb$ (Atomic $No. 65$) are :

• A. $[ Xe ] 4 f ^{7} 6 s ^{2},[ Xe ] 4 f ^{8} 6 s ^{2}$ and $[ Xe ] 4 f ^{8} 5 d ^{1} 6 s ^{2}$
• B. $[ Xe ] 4 f ^{7} 5 d ^{1} 6 s ^{2},[ Xe ] 4 f ^{7} 5 d ^{1} 6 s ^{2}$ and $[ Xe ] 4 f ^{9} 6 s ^{2}$
• C. $[ Xe ] 4 f ^{6} 5 d ^{1} 6 s ^{2},[ Xe ] 4 f ^{7} 5 d ^{1} 6 s ^{2}$ and $[ Xe ] 4 f ^{8} 5 d ^{1} 6 s ^{2}$
• D. $[ Xe ] 4 f ^{7} 6 s ^{2},[ Xe ] 4 f ^{7} 5 d ^{1} 6 s ^{2}$ and $[ Xe ] 4 f ^{9} 6 s ^{2}$

Answer 1

Answer: (D)

The electronic configuration of $Eu$ (Atomic $No. 63$), $Gd$ (Atomic $No. 64$) and $Tb$ (Atomic $No. 65$) are :
$[ Xe ] 4 f ^{7} 6 s ^{2},[ Xe ] 4 f ^{7} 5 d ^{1} 6 s ^{2}$ and $[ Xe ] 4 f ^{9} 6 s ^{2}$ respectively.
$Gd$ possesses a single electron in the $5d$ subshell. In the case of other lanthanoids, the $5d$ orbital is empty.