Question

The Lanthanide contraction from Ce to Lu is

• A. 0.20 Å
• B. 0.10 Å
• C. 0.30 Å
• D. 0.25 Å

Hint:

The lanthanide contraction is a result of the filling of f-orbitals, leading to poor shielding and smaller atomic radii.

Answer 1

The Correct Option is D

The lanthanide contraction describes the gradual reduction in atomic and ionic sizes observed across the lanthanide series, from cerium (Ce) to lutetium (Lu). This occurs despite the increasing atomic number. Its understanding is vital as it impacts the chemical behavior of subsequent elements.

1. Understanding the Lanthanide Contraction:
   The lanthanide series includes 14 elements, numbered 57 (lanthanum, La) to 71 (lutetium, Lu). Moving across the series:
   • Increasing Nuclear Charge: Each element gains a proton, increasing the positive charge in the nucleus.
   • Electron Configuration: Electrons fill the 4f orbitals, which are ineffective at shielding the nucleus's increasing positive charge.
2. Effect of Poor Shielding by 4f Electrons:
   Due to the poor shielding of 4f electrons, the effective nuclear charge (\( Z_{\text{eff}} \)) felt by outer electrons rises more sharply compared to elements filling better-shielding orbitals (like 3d or 5f). This increased \( Z_{\text{eff}} \) draws electrons closer, shrinking atomic and ionic radii.
3. Quantifying the Lanthanide Contraction:
   The measured contraction across the series is about \( 0.10 \, \text{Å} \). This significantly affects the chemistry and properties of elements following the lanthanides, such as 5d transition metals.
4. Implications of Lanthanide Contraction:
   • Chemical Properties: This contraction influences ionic radii, affecting coordination numbers and complex stability.
   • Physical Properties: It causes similar ionic radii within groups, leading to comparable chemistry.
5. Conclusion:
   The lanthanide contraction from Ce to Lu involves a steady decrease in ionic radii, driven by increasing nuclear charge and weak shielding from 4f electrons. The contraction's magnitude is approximately \( 0.10 \, \text{Å} \).

In summary, the lanthanide contraction from Ce to Lu is \( \boxed{0.10 \, \text{Å}} \).