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Classification of Elements and Periodicity in Properties — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistryClassification of Elements and Periodicity in Properties1 Mark
MCQ
The electronic configuration of gadolinium (Atomic number 64)
  • A
    $\big[\text{Xe}\big]\ 4\text{f}^3\ 5\text{d}^5\ 6\text{s}^2 $
  • B
    $\big[\text{Xe}\big]\ 4\text{f}^7\ 5\text{d}^2\ 6\text{s}^1$
  • C
    $\big[\text{Xe}\big]\ 4\text{f}^7\ 5\text{d}^1\ 6\text{s}^2$
  • D
    $\big[\text{Xe}\big]\ 4\text{f}^8\ 5\text{d}^6\ 6\text{s}^2$
✓

Answer

  1. $\big[\text{Xe}\big]\ 4\text{f}^7\ 5\text{d}^1\ 6\text{s}^2$

Explanation:

The electronic configuration of La (Z = 57) is [Xe] 5dl 6s2. Therefore, further addition of electrons occurs in the lower energy 4f-orbital till it is exactly half-filled at Eu (Z = 63) Thus, the electronic configuration of Eu is [Xe] 4f7 6s2. Thereafter, addition of next electron does not occur in the more stable exactly half-filled 4f7 shell but occurs in the little higher energy 5d-orbital. Thus, the electronic configuration of Gd (Z = 64) is $\big[\text{Xe}\big]\ 4\text{f}^7\ 5\text{d}^1\ 6\text{s}^2$

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