CBSE Class 12 · 2011 · All India; also Foreign · d and f Block ElementsVery Short Answer

What is lanthanoid contraction?

Answer: The steady decrease in atomic and (trivalent) ionic radii from La to Lu, caused by the poor shielding of 4f electrons.

Solution

Lanthanoid contraction is the regular, steady decrease in the atomic and ionic (Ln

^{3 +}

) radii across the lanthanoid series from La to Lu as the atomic number increases.
It arises because the 4f electrons shield the growing nuclear charge very poorly, so each successive electron cloud is pulled in a little more.

CBSE Class 12 Board · 2011 · All India; also Foreign · Subjective

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