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Chemistry · 2022 · 3 marks
CBSE 2022 · Region 3 · Set 2 · Q7
What is Lanthanoid contraction? What is the cause of Lanthanoid contraction? Write two consequences of Lanthanoid contraction.
What is Lanthanoid contraction ? What is the cause of Lanthanoid contraction ? Write two consequences of Lanthanoid contraction.
Marking-scheme solution
The filling of the 4f orbital before the 5d orbital resulting into regular decrease in atomic radii is called lanthanoid contraction.
Cause: This is due to poor screening effect of \(\displaystyle 4 f\)-orbitals.
Consequences:
(i) Similarity in the radii of the atoms of the elements of \(\displaystyle 2^{\text {nd }} / 4 \mathrm{~d}\) and \(\displaystyle 3^{\text {rd }} / 5 \mathrm{~d}\) transition series.
(ii) Difficulty in separation of Lanthanoids in pure state.
(iii) Similar physical and chemical properties.
(iv) Basic character of the lanthanoid hydroxides \(\displaystyle \mathrm{M}(\mathrm{OH})_{3}\) decreases with increase in atomic number.
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