Question

Give Reasons:

What is the cause of Lanthanide Contraction?

Answer 1

Lanthanide contraction:

Lanthanide contraction is the steady decrease in atomic and ionic size of lanthanoids as their atomic number increases.

Causes of Lanthanide contraction:

• In f-block elements, the positive charge on the nucleus rises by one unit, and one additional electron enters the same $4\mathrm{f}$ subshell, as the atomic number increases.
• Electrons in the $4\mathrm{f}$ subshell poorly shield each another. Shielding is less in a $4\mathrm{f}$subshell than in a d subshell.
• As the nuclear charge increases, the valence shell is drawn closer to the nucleus. Hence, as a result contraction takes place.