Question

Lanthanide contraction is due to an increase in:

• A. Shielding by 4f electrons
• B. Atomic number
• C. Effective nuclear charge
• D. Size of 4f orbitals

Answer 1

The correct option is C Effective nuclear charge

The shielding effect due to the f electrons is very low because of the diffused shape of their orbitals. With an increase in the atomic number, the effective nuclear charge $\left(Z_{eff}\right)$ experienced by the valence electrons increases along the period. This increase in $Z_{eff}$ causes the radii of atoms or ions to shrink as you go from La to Lu. This is what we call lanthanide contraction.