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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 · 2024 · Paper I

Q5(e)(i). Lanthanide contraction

Question

Explain lanthanide contraction.

Answer in brief

Lanthanide contraction is the steady decrease in atomic and ionic size from La to Lu (La³⁺ 103 pm to Lu³⁺ 86 pm), caused by poor shielding of the growing nuclear charge by the 4f electrons.

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The full model answer

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

Coverslanthanide contraction4f shieldingeffective nuclear chargeionic radiuslanthanides

All parts of Question 5