The electronic configuration of gadolinium (atomic number 64) is:

Options

A. [Xe] `4f^(3) 5d^(5) 6s^(2)`
B. `[Xe] 4f^(7) 5d^(2) 6s^(1)`
C. [Xe] `4f^(7) 5d^(1) 6s^(2)`
D. [Xe] `4f^(8) 5d^(6) 6s^(2)`

Answer

C

Explanation

The electric configuration of La (Z = 57) is [Xe] `5d^(1) 6s^(2)`. Therefore, further addition of electrons occurs in the lower energy 4f-orbital till it is exactly half-filled at Eu (Z = 63). Thus, the electrons configuration of Eu is [Xe] `4f^(7) 6s^(2)`. Thereafter, addition of next electron does not occur in the more stable exactly half-filled `4f^(7)` shell but occurs in the little higher energy 5d-orbital. Thus, the electronic configuration of Gd (Z = 64) is [Xe] `4f^(7) 5d^(1) 6s^(2)`.