Question

Actinoids show larger number of oxidation states :

• A. because they are radioactive in nature
• B. because they have large atomic numbers
• C. because they have large atomic masses
• D. due to comparable energies of 5f, 6d and 7s orbitals

Hint:

Lanthanoids primarily show a +3 oxidation state because the energy gap between 4f and 5d is larger.
Actinoids are much more complex due to the energy proximity of 5f, 6d, and 7s.
The maximum oxidation state increases towards the middle of the actinoid series and then decreases.

Answer 1

The Correct Option is D

Concept:

• Oxidation states in elements are determined by the number of electrons available in the valence shells for bonding.

• In f-block elements, electrons from the (n-2)f, (n-1)d, and ns subshells can potentially participate in bond formation.

• The diversity of oxidation states depends on the energy gap between these participating subshells.
Step 1: Analyzing the electronic configuration and energy levels
Actinoids are elements in which the 5f subshell is being filled.
The general electronic configuration involves the 5f, 6d, and 7s orbitals.
Unlike Lanthanoids, where the energy gap between 4f and 5d is relatively large, the energy gap between 5f, 6d, and 7s orbitals in actinoids is very small.

Step 2: Relating orbital energy to oxidation states
Because the 5f, 6d, and 7s orbitals have comparable (very similar) energies, electrons can be removed from all these levels with relatively similar amounts of energy.
This allows actinoids to utilize a larger number of electrons for bonding compared to lanthanoids.

Step 3: Conclusion
This results in a wide range of oxidation states, typically from +3 up to +7 for some elements like Neptunium and Plutonium.
The fundamental reason is the comparable energies of the 5f, 6d, and 7s orbitals.