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NEET CHEMISTRYStructure of AtomMedium

Question

The electronic configurations of Eu (Atomic no. 63), Gd (Atomic no. 64) and Tb (Atomic no. 65) are:

A

[Xe] 4f⁶ 5d¹ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s²

B

[Xe] 4f⁶ 5d¹ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁸ 5d¹ 6s²

C

[Xe] 4f⁷ 6s², [Xe] 4f⁷ 5d¹ 6s² and [Xe] 4f⁹ 6s²

D

[Xe] 4f⁷ 6s², [Xe] 4f⁸ 6s² and [Xe] 4f⁸ 5d¹ 6s²

Step-by-Step Solution

The electronic configurations follow the Aufbau principle with exceptions driven by the stability of half-filled (f7f^7) and fully-filled (f14f^{14}) subshells.

  1. Europium (Eu, Z=63): [Xe] 4f76s24f^7 6s^2. The 4f4f orbital is exactly half-filled, providing extra stability.
  2. Gadolinium (Gd, Z=64): [Xe] 4f75d16s24f^7 5d^1 6s^2. To maintain the stable half-filled 4f74f^7 configuration, the incoming electron enters the 5d5d orbital instead of pairing in the 4f4f orbital.
  3. Terbium (Tb, Z=65): [Xe] 4f96s24f^9 6s^2. The electron from the 5d5d orbital (seen in Gd) moves to the 4f4f orbital along with the new electron, resulting in 4f94f^9.

Exam Context & Concepts Covered

This question aligns with the NEET CHEMISTRY syllabus, specifically targeting concepts from Structure of Atom. Mastering this topic is crucial for scoring well in the upcoming medical entrance examinations. Solving conceptually related problems will help you understand the nuances of these concepts and improve your problem-solving speed.

CHEMISTRYStructure of Atomelectronicconfigurationsatomicatomicatomic

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