Question

# Discuss the consequences of lanthanide contraction.

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Hint:
The lanthanide contraction is observed from La to Lu due to the increasing nuclear charge and due to the electrons entering the inner (n-2) f orbital.

- Effect on the basic strength of hydroxides: As the size of lanthanides decreases from La to Lu, their basic strength also decreases because of the decrease in the ions from$C{{e}^{3+}}\text{ }to\text{ }L{{u}^{3+}}$,the covalent character of the hydroxides increases and hence, the basic strength decreases. Thus, we can say that $Lu{{\left( OH \right)}_{3}}$is the least basic and $La{{\left( OH \right)}_{3}}$is more basic .
- Complex formation ability: lanthanides are having the smaller size but higher nuclear charge. This results in higher charge density and high nuclear charge, which will facilitate the acceptance of lone pairs of electrons from ligands. Therefore we can see that these has tendency to form coordinate complexes, this is found to increase from$L{{a}^{3+}}$to $L{{u}^{3+}}$.