Question

What are the causes of lanthanide contraction?

Answer 1

As we move along the lanthanoid series, there is a decrease in atomic and ionic radii. This steady decrease in the atomic and ionic radii is called lanthanoid contraction.
Causes of lanthanide contraction
As we move from one element to another the nuclear charge increases by one unit and one electron is added. The new electrons are added to the same inner 4f subshell. Thus, the 4f electrons shield each other from the nuclear charge poorly owing to their diffused nature. With the increasing atomic number and nuclear charge, the effective nuclear charge experienced by each 4f electrons Increases. As a result, the whole 4f electron shell contracts at each successive element.