Question

Write a note on lanthanoid contraction.

Answer 1

In lanthanoid series with increasing atomic number, there is a progressive decrease in the atomic as well as ionic radii. This regular decrease is known as lanthanoide contraction. This is due to the poor shielding of f orbitals, which are unable to counter balance the effect of increasing nulcear charge with the net result of contraction in the size of atoms. From ${}_{57}La$ to ${}_{58}Ce$, there is a sudden contraction in atomic radius from $187$ Pm to $183$ Pm but the further decrease upto the last $4f$ element, ${}_{71}Lu$ is comparitively low.