Question

How do lanthanoid contraction affect the following property of the elements placed after lanthanoids?

Basicity of oxides.

Answer 1

1. Lanthanoid contraction causes a decrease in the size of lanthanoid cations as the atomic number increases.
2. Smaller cations have higher polarising power.
3. Increased polarising power reduces the ionic character of oxides and hydroxides.
4. As a result, the basic strength of oxides decreases with increasing atomic number.
5. For example, La(OH)₃ is more basic, while Lu(OH)₃ is the least basic.

Thus, lanthanoid contraction leads to a regular decrease in the basicity of oxides of elements following lanthanoids due to increased cation polarization and reduced ionic character.