Question

Which trend is correct regarding ionic radius in the 4f-series (lanthanides)?

• A. Radius increases from La\(^{3+}\) to Lu\(^{3+}\)
• B. Radius remains same
• C. Radius decreases across the series
• D. No regular trend observed

Hint:

Remember "lanthanide contraction"—as you move from La\(^{3+}\) to Lu\(^{3+}\), the size of ions decreases due to ineffective shielding by 4f electrons.

Answer 1

The Correct Option is C

As electrons are added to the 4f orbitals across the lanthanide series (from La\(^{3+}\) to Lu\(^{3+}\)), their poor shielding effect results in an increased effective nuclear charge. This enhanced attraction draws electrons nearer to the nucleus, causing a progressive reduction in ionic radii, a phenomenon termed lanthanide contraction.