UPSC Combined Geo-Scientist, Mains · 2024 · Mains Paper I

Q11(c)(i). Why HfO₂ is denser than ZrO₂

5 marks
Topic: Chemistry of d- and f-block elements
Answered

Question

(i) Explain why isostructural HfO₂ and ZrO₂ have densities of 9.68 g cm⁻³ and 5.73 g cm⁻³ respectively.

Answer in brief

Lanthanoid contraction makes Hf⁴⁺ and Zr⁴⁺ similar in size, so their isostructural oxides have similar cell volumes; HfO₂ has a much greater formula mass.

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Topic notes: transition elements: 3d, 4d and 5d compared, atomic radii and the lanthanide contraction, oxidation states and oxidising power, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coverslanthanoid contractionHfO2 ZrO2 densityzirconium hafnium similarity4d 5d comparison

All parts of Question 11

11(a) Calcium in powdered milk10 marks
11(b) High oxidation states in the first d series10 marks
11(c)(i) Why HfO₂ is denser than ZrO₂5 marks
11(c)(ii) Coordination numbers of first-row metals5 marks