a) Which of the following oxidation state is common for lanthanids? (Say – 2015) i) +2 ii) +3 iii) +4 iv) +5 b)

Question

a) Which of the following oxidation state is common for lanthanids?

i) +2

ii) +3

iii) +4

iv) +5

b) Drawthe structures of chromate and dichromate ions.

c) Zirconium (Zr) belongs to ‘4d’ and Hafnium (Hf) belongs to ‘5d’ transition series. It is difficult to separate them. Explain.

Answer 1

a) ii) +3

c) It is a consequence of lanthanoid contraction, a cumulative effect of the contraction of atomic radii of the lanthanoid series caused by the imperfect shielding of one electron by another in the 4f sub-shell.