Question

The electronic configuration of gadolinium(Atomic No. 64) is:
(A) $[Xe]4{{f}^{3}}5{{d}^{5}}6{{s}^{2}}$
(B) $[Xe]4{{f}^{6}}5{{d}^{2}}6{{s}^{2}}$
(C) $[Xe]4{{f}^{8}}5{{d}^{9}}6{{s}^{2}}$
(D) $[Xe]4{{f}^{7}}5{{d}^{1}}6{{s}^{2}}$

Answer 1

Identify the position of the element Gadolinium in the periodic table. Write the electronic configuration such that electrons are filled in increasing order of energy of orbitals. The Aufbau principle can be used as it clearly states the order of energies of the orbitals making it easier to write electronic configuration.

Complete step by step solution:
Gadolinium is a chemical element having the symbol Gd and atomic number 64. Gadolinium is silvery-white in appearance once the oxidation layer is removed.
It is a rare earth metal. It lies in the 6th period of the periodic table under f block. It belongs to the class of compounds called lanthanides.
The common oxidation state shown by the element is +3 which is a characteristic feature of lanthanides. It has a standard atomic mass of 157.25 g.
We will now determine the electronic configuration of gadolinium in the ground state.
The electrons are filled in increasing order of energies of orbitals in accordance with the Aufbau principle.
The electronic configuration of the first lanthanide (La) is $[Xe]5{{d}^{1}}6{{s}^{2}}$. Upon further addition of electrons, we arrive at the element Gadolinium.
E.C = $[Xe]4{{f}^{7}}5{{d}^{1}}6{{s}^{2}}$

Therefore, the correct answer is option (D).

Note: It is important to know that the last electron of the gadolinium atom goes into the d orbital although the element belongs to the f block. This is because the 4f orbital has a stable half-filled configuration which cannot be disturbed easily. This is the reason the energy required to place the electron to 5d orbital is easier than placing it in the same stable 4f orbital. So, the above-ground state configuration obeys Aufbau principle and Hund's rule of maximum multiplicity.