Question

Which of the following lanthanoid has the outer electronic configuration \(4f^7 6s^2\) in its ground state

• A. Neodymium
• B. Gadolinium
• C. Europium
• D. Promethium
• E. Samarium

Hint:

Gadolinium (Gd, Z=64) also has a half-filled f-orbital, but its configuration is \(4f^7 5d^1 6s^2\).

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
The general electronic configuration of lanthanoids is \([Xe] 4f^{1-14} 5d^{0-1} 6s^2\). Exceptions occur for atoms with half-filled or fully-filled f-orbitals.

Step 2: Detailed Explanation:
Europium (Eu) has atomic number 63. Its expected configuration is \([Xe] 4f^6 5d^0 6s^2\). However, to achieve the extra stability of a half-filled f-orbital (f\(^7\)), one electron is promoted, resulting in the configuration \([Xe] 4f^7 6s^2\). This is similar to the chromium exception.

Step 3: Final Answer:
Europium (Eu) has the outer electronic configuration \(4f^7 6s^2\).