Question

The electronic configuration of gadolinium (Atomic No. 64) is:

• A. $\left[Xe\right]4f^{3}5d^{5}6s^2$
• B. $\left[Xe\right]4f^{6}5d^{2}6d^2$
• C. $\left[Xe\right]4f^{8}5d^{9}6s^2$
• D. $\left[Xe\right]4f^{7}5d^{1}6s^2$

Answer 1

Answer: (D)

$\left[Xe\right]4f^{7}5d^{1}6s^2$

The electronic configuration of $La(Z=57)$ is $\left[Xe\right]5d^{1}6s^2$. Therefore, further addition of electrons occurs in a lower energy 4f-orbital till it is exactly half filled at $Eu(Z=63)$. Thus,the electronic configuration of Eu is $\left[Xe\right]4f^{7}6s^2$. Therefore, addition of next electron doesn't occur in a more stable exactly half-filled $4f^7$ shell but occur in a little higher energy 5d-orbital. Thus, the electronic configuration of $Gd(Z=64)$ is $\left[Xe\right]4f^{7}5d^{1}6s^2$.