Question

Atomic radii of two of lanthanides is considerably higher than other lanthanides

Answer 1

Answer:

Atomic radii of two of the lanthanides ,La (Lanthanum) and Ce (Cerium) , is considerably higher than other lanthanides. In the lanthanide series with increasing atomic number ,there is a progressive decrease in the size from Lanthanum to Lutetium .

This happens due to lanthanide contraction. Lanthanide contraction occurs because in these elements the added electron enters the deep seated  (n-2)f orbitals whose shielding effect is very poor as a result effective nuclear charge becomes very high , the enhanced nuclear charge leads to contraction in size of atoms or ions with increase in atomic number.