Question

Why is actinoid contraction more as compared to lanthanoide contraction?

• A. The shielding effect of electrons present in 4f and 5f orbitals is equal
• B. The azimuthal quantum numbers of 4f and 5f are same
• C. Poor shielding is offered by 5f electrons compared to 4f electrons in actinoids.
• D. 4f orbitals are more diffused as compared to 5f orbitals

Hint:

5f electrons shield the nuclear charge poorly compared with 4f electrons.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept
Lanthanoid and actinoid contractions arise because the added electrons enter f orbitals, which shield the nuclear charge poorly.

Step 2: Compare 4f and 5f
5f orbitals are more diffuse and spread out than 4f orbitals.
Hence 5f electrons shield the increasing nuclear charge even less effectively.

Step 3: Conclusion
Poorer shielding means a stronger pull on the outer electrons and a larger decrease in size across the actinoids.

Final Answer:
Actinoid contraction is larger because 5f electrons shield poorly compared with 4f electrons. \[ \boxed{\text{(C) }\text{Poor shielding is offered by 5f electrons compared to 4f electrons in actinoids.}} \]