Question

The electronic configuration of gadolinium (at. no. = 64) is

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

Answer 1

Answer: (D)

The electronic configuration of $La(Z=57)$ is $[Xe]5d^{1}6s^2$. Therefore, further addition of electrons occurs in a lower energy $4f$ -orbital till it is exactly half filled at $\mathrm{Eu}(Z=63)$. Thus, the electronic configuration of Eu is $[Xe]4f^{7}6s^2.$ 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 $[Xe]4f^{7}5d^{1}6s^2$