What is Lanthanide contraction ? What is the cause and consequences of Lanthanide contraction ?

Explanation

Lanthanoid Contraction : In Lanthanoids there is a regular decrease in the size of atom with increasing atomic number. Lanthanoid contraction may be defined as the steady decrease in the size of Lanthanoid ion `(Ln^(3+))` with increase in atomic number.
Cause : As we move through the lanthanoids series, 4f electron are being added one at each step. The mutual shielding effect of 4f electron is very ļow and shape of orbital are much diffused. The nuclear charge however, increase by one at each step. hence with increase atomic number the effective nuclear charge experience by each 4f electron increases as a result the whole of 4f electron shell contract at each successive element, though the decrease is very small. This result in gradual decrease in size of lanthanoids with increase in atomic number.