The atomic radii of Zirconium () and Hafnium () are almost identical. What is the fundamental quantum mechanical reason for this anomaly?

Question

The atomic radii of Zirconium ($Zr, Z=40$) and Hafnium ($Hf, Z=72$) are almost identical. What is the fundamental quantum mechanical reason for this anomaly?

Prashant Kotian · Accepted Answer

Correct answer: B. Lanthanide contraction (poor shielding by 4f electrons) causes a steady decrease in size from La to Lu, exactly cancelling the expected size increase down the group from Zr(4d) to Hf(5d).

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