Question

Which lanthanide element has half-filled 4f orbitals in its +3 state?

• A. Terbium
• B. Gadolinium
• C. Cerium
• D. Lanthanum
• E. Lutetium

Hint:

In transition and lanthanide elements, half-filled and fully-filled d or f orbitals are especially stable due to exchange energy and symmetry considerations. This often leads to unusual electron configurations in their ionic states.

Answer 1

The Correct Option is B

Step 1: The lanthanides are the series of elements from \( {Ce} \) to \( {Lu} \) in the periodic table, and they involve filling the 4f orbitals. In the +3 oxidation state, these elements generally lose their 5s and 4d electrons, but the 4f electrons remain.
Step 2: In the case of gadolinium (\( {Gd} \)), the electronic configuration in the ground state is:
\[ {Gd (Z = 64):} \, [{Xe}] \, 4f^7 5s^2 5d^1. \]
When it loses three electrons to form the +3 state, the electron configuration becomes: \[ {Gd}^{3+}: [{Xe}] \, 4f^7. \] Thus, the 4f orbitals in gadolinium’s +3 state are half-filled (\( 4f^7 \)), which is a stable configuration due to the special stability of half-filled subshells.
Step 3: This half-filled configuration is a notable characteristic of gadolinium in its +3 oxidation state.
Thus, the correct answer is option (B).