The steady decrease in the size of lanthanoid ions (M3+) with the increase in atomic number is called lanthanoid contraction.
Consequences of lanthanoid contraction :
(i) Separation of lanthanoids is difficult due to lanthanoid contraction because due to this contraction their ionic radii is very small.
(ii) The basic strength of hydrofdes decreases from La(OH)3 to Lu(OH)3. Due to lanthanoid contraction, the size of M3+ ions decreases and there is increase in the covalent character in M - OH bond.
