The basic character of the lanthanoid hydroxides, , decreases progressively from to . What is the pr — d and f Block Elements Chemistry Question

💡 Solution & Explanation

Due to the lanthanoid contraction, the ionic radius of the $Ln^{3+}$ cations steadily decreases from $La^{3+}$ to $Lu^{3+}$. According to Fajan's rules, a smaller cation possesses a higher charge density (polarizing power), which increases the covalent character of the $Ln-OH$ bond. Increased covalency makes it harder to cleave the bond to release $OH^-$ ions in water, thus steadily decreasing the basic strength.