Q. The outer electronic configuration of Gd (At. No 64) is
A) $4f^{3}\ 5d^{5}6s^{2}$
B) $4f^{8}\ 5d^{0}6s^{2}$
C) $4f^{4}\ 5d^{4}6s^{2}$
D) $4f^{7}5d^{1}s^{2}$
Explanation
(d)
Gd(64)
$\lbrack Xe\rbrack_{54}$ $4f^{7}$
[table] ↑ | ↑ | ↑ | ↑ | ↑ | ↑ | ↑ [/table]
$\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ 5d^{1}$
[table] ↑ | | | | | | ⥮ [/table]
All the electrons of $4f$-orbital are unpaired, hence stable.
Thus, Gd(64) has EC as $\lbrack Xe\rbrack_{54}$ $4f^{7}\ \ 5d^{1}\ \ 6s^{2}$
Instead of $\lbrack Xe\rbrack_{54}\ 4f^{8}\ 6s^{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.