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

Explanation

Lanthanoid Contraction : In Lanthanoides there is a regular decrease in the size of atom and increasing atomic number. Lanthanoid contraction may be defined as the steady decrease in the size of Lanthnoid ion `(Li^(3+))` with incerase in atomic number.
Canse : As we move through the lanthnoids series, 4f electron are being added one at each step. The mutual shielding effect of 4f electron is very row and shape of orbital are much diffused. The nuclear charge however, increase by one at each step. hence 4f electron increase.