Question

The main reason for larger number of oxidation states exhibited by the actinides than the corresponding lanthanides, is :

• A. lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
• B. larger atomic size of actinides than the lanthanides
• C. more energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
• D. greater reactive nature of the actinides than the lanthanides

Answer 1

The Correct Option is A

The question is about the reason for the larger number of oxidation states exhibited by actinides compared to lanthanides. To understand this, let's examine the electronic configurations and the behavior of f-block elements, specifically actinides and lanthanides.

Actinides: The actinide series encompasses elements with atomic numbers 89 (actinium) to 103 (lawrencium). Their electrons are progressively filled in the 5f orbitals.

Lanthanides: The lanthanide series includes elements from atomic number 57 (lanthanum) to 71 (lutetium), with electrons filling the 4f orbitals.

The primary factor for the difference in oxidation states between these two series lies in the energy difference between their respective outer orbitals:

• 5f orbitals in actinides: These orbitals are not as well shielded by the outer electrons as the 4f orbitals. This results in lesser energy differences between the 5f and 6d orbitals.
• 4f orbitals in lanthanides: These have a larger energy difference when compared to 5d orbitals, primarily due to better shielding and lower penetrability.

Conclusion: The primary reason for the greater number of oxidation states in actinides compared to lanthanides is the lesser energy difference between the 5f and 6d orbitals than between the 4f and 5d orbitals. This allows electrons in actinides to participate more readily in bonding, leading to variable oxidation states.

Correct Answer: lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals