Lanthanoids Vs Actinoids
Actinoids show a much wider range of oxidation states than lanthanoids; what is the main reason for this greater variability?
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About This Question
- Subject
- chemistry
- Chapter
- d- and f-block elements
- Topic
- lanthanoids vs actinoids
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
Actinoid 5f, 6d, and 7s orbitals have comparable energies allowing more electrons to bond
The contrast in oxidation-state variability between the two inner transition series stems from differences in orbital energies. In the actinoids, the 5f, 6d, and 7s orbitals lie close in energy, so a larger number of electrons can become involved in bonding, giving rise to a wide range of oxidation states such as +3 up to +6 or higher, as seen in uranium and plutonium. In the lanthanoids, the 4f orbitals are buried deep within the atom and are well shielded, so they participate little in bonding, and the lanthanoids are largely restricted to the +3 state. The option that actinoid 5f orbitals are more shielded is the opposite of the truth, since they are less shielded and more available. The option that actinoids have no f-electrons is false. The option that lanthanoids are radioactive does not explain oxidation-state range. This comparison is a standard NCERT f-block topic. Examiners frequently test whether a student can connect lanthanoids with the underlying principle rather than merely recalling an isolated fact. Plausibility check: uranium's well-known +3, +4, +5, and +6 states versus the dominant +3 state of lanthanoids confirm the greater orbital availability in actinoids.
This medium difficulty chemistry question is from the chapter d- and f-block elements, covering the topic of lanthanoids vs actinoids. It appeared in the 2025 exam.
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