Lanthanide Contraction Effect
Lanthanide contraction chiefly causes which pair of 4d/5d elements to have similar radii?
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About This Question
- Subject
- chemistry
- Chapter
- classification of elements and periodicity in properties
- Topic
- lanthanide contraction effect
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Zr and Hf
- Lanthanide Contraction: The steady decrease in atomic and ionic radii along the Lanthanide series (Z=58 to 71).
- Reason: Poor shielding by 4f electrons. The nuclear charge increases by 14 units, but 4f electrons do not block it effectively.
- Impact on 5d elements: Elements following the Lanthanides (like Hf,Ta,W) have an unexpectedly small radius.
- Observation: This effectively cancels out the normal size increase expected when moving from 4d shells (period 5) to 5d shells (period 6).
- Pairs: Zirconium (Zr, radius 1.60 Å) and Hafnium (Hf, radius 1.59 Å) end up with nearly identical atomic radii.
This medium difficulty chemistry question is from the chapter classification of elements and periodicity in properties, covering the topic of lanthanide contraction effect. It appeared in the 2025 exam.
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