Lanthanoid contraction is caused due to:

Options

A. Negligible screening effect of 'f' orbitals
B. Incresing nuclear charge
C. Decreasing nuclear charge
D. Decreasing screening effect

Answer

A

Explanation

As we proceed form one element to the next element in the lanthanide series, the nuclear charge (i.e. atomic number) increases by one unit and the addition of one electron occurs at the same time in 4f subshell. On account of the very diffused shapes of f orbitals, the 4f electrons shield each other quite poorly form the nuclear charge. Thus, the effect of nuclear charge increase is somewhat that the increased shilding effect. This brings the outermost shell nearer to the nucleus and hence the size of the atom (or ion) goes on decreasing as we move in the series. The sum of the succesive reductions is equal to the total lanthanide contraction.