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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2023 · Paper I

Q7(b). Configurations of Pr, Eu and Gd and the moments of their M³⁺ ions

Question

Write the ground-state electronic configurations of the following lanthanides: (i) ₅₉Pr (praseodymium); (ii) ₆₃Eu (europium); (iii) ₆₄Gd (gadolinium). Calculate the predicted effective magnetic moment (μS+L) for the metal ions in the +3 oxidation state in units of Bohr magneton.

Answer in brief

Pr [Xe]4f³6s², Eu [Xe]4f⁷6s², Gd [Xe]4f⁷5d¹6s²; μS+L: Pr³⁺ 6.16 BM, Eu³⁺ 7.75 BM, Gd³⁺ 7.94 BM.

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Topic notes: lanthanides and actinides (lanthanide contraction, magnetic moments, separation), with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverslanthanideselectronic configurationmagnetic momentRussell–Saunders couplingLandé g factorgadolinium

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