Why do actinoids show a much wider range of oxidation states compared to lanthanoids?

Why do actinoids show a much wider range of oxidation states compared to lanthanoids? +

Correct Answer

Actinoids have 5f, 6d and 7s orbitals of comparable energies, so electrons from all three subshells can participate in bonding.

Detailed Explanation

Both lanthanoids and actinoids are f-block elements, but the energy arrangement of their orbitals is different. In actinoids, the 5f, 6d and 7s orbitals have relatively close energies. Therefore, different numbers of electrons can participate in chemical bonding.

5f ≈ 6d ≈ 7s

Because these orbitals have comparable energies, actinoids can lose or share electrons from more than one subshell. Consequently, actinoids exhibit oxidation states ranging from approximately +3 to +7, with the early actinoids showing the widest variation.

Why Are Lanthanoids Different?

In lanthanoids, the 4f orbitals are more deeply buried and are relatively less available for bonding. The common oxidation state is therefore:

Ln → +3

Some lanthanoids can show +2 or +4 states, but these are generally associated with extra stability of particular electronic configurations. Thus, lanthanoids have a much narrower range of oxidation states than actinoids.

Actinoid Trend

The early actinoids show particularly large variations:

Th(+4), Pa(+5), U(+3,+4,+5,+6), Np(+3 to +7), Pu(+3 to +7)

The highest oxidation states are more accessible in the early actinoids because the 5f electrons are comparatively available for bonding. As we move toward the later actinoids, the 5f electrons become more strongly bound and the +3 state becomes increasingly important.

JEE Level Quick Trick

Actinoids → 5f, 6d & 7s energies are close → more electrons participate → many oxidation states.

Lanthanoids → 4f is buried → mainly +3 oxidation state.

30 Related MCQs with Solutions

1. Actinoids show a wider range of oxidation states mainly because:

A. 5f, 6d and 7s orbitals have comparable energies

B. 4f orbitals are very stable

C. They have no f-electrons

D. They are all gases

Answer: A

2. The most common oxidation state of lanthanoids is:

A. +1

B. +2

C. +3

D. +7

Answer: C. +3

3. Which subshell is involved in actinoid chemistry?

A. 3d

B. 4f

C. 5f

D. 6p

Answer: C. 5f

4. Which orbitals have comparable energies in actinoids?

A. 2s and 2p

B. 3d and 4s

C. 5f, 6d and 7s

D. 4f and 6p only

Answer: C

5. Which element commonly exhibits +6 oxidation state?

A. Uranium

B. Lanthanum

C. Cerium only

D. Lutetium

Answer: A. Uranium

6. Uranium can exhibit which oxidation state?

A. +2 only

B. +3 only

C. +6

D. −3 only

Answer: C. +6

7. The 5f orbitals in early actinoids are:

A. Completely inaccessible

B. Relatively available for bonding

C. Always empty

D. Identical to 4f orbitals

Answer: B

8. Which series generally shows more variable oxidation states?

A. Lanthanoids

B. Actinoids

C. Alkali metals

D. Noble gases

Answer: B. Actinoids

9. The +3 oxidation state is especially important for:

A. Lanthanoids

B. Halogens

C. Noble gases

D. Alkali metals only

Answer: A. Lanthanoids

10. Which orbitals are more deeply buried in lanthanoids?

A. 4f orbitals

B. 5f orbitals

C. 6d orbitals

D. 7s orbitals

Answer: A. 4f orbitals

11. Which actinoid can show oxidation states up to +7?

A. Neptunium

B. Lanthanum

C. Lutetium

D. Gadolinium

Answer: A. Neptunium

12. Which is a typical oxidation state of uranium?

A. +6

B. −6

C. +1 only

D. −2 only

Answer: A. +6

13. The wider oxidation-state range of actinoids is associated with:

A. Greater energy separation of 5f and 6d

B. Small energy difference among 5f, 6d and 7s

C. Absence of 7s electrons

D. Completely filled 5f subshell

Answer: B

14. Which f-block series has 5f filling?

A. Lanthanoids

B. Actinoids

C. Both

D. Neither

Answer: B. Actinoids

15. Lanthanoids mainly show +3 because:

A. 4f electrons are relatively less available for bonding

B. They have no valence electrons

C. They are noble gases

D. Their nuclear charge is zero

Answer: A

16. Which oxidation state is characteristic of many actinoids?

A. +3

B. −7

C. +8 only

D. −5 only

Answer: A. +3

17. Besides +3, actinoids commonly exhibit:

A. +4, +5 and +6

B. −1 only

C. +1 only

D. No other states

Answer: A

18. Which element is known for several oxidation states including +3 to +7?

A. Np

B. La

C. Lu

D. Ce only

Answer: A. Np

19. The 5f electrons of early actinoids are more available than:

A. Lanthanoid 4f electrons

B. Hydrogen electrons

C. Helium electrons

D. Oxygen 2p electrons

Answer: A

20. Which statement is correct?

A. Actinoids show only +3

B. Actinoids show a wide range of oxidation states

C. Lanthanoids show +7 predominantly

D. Both series show exactly the same states

Answer: B

21. The ability of actinoids to use 5f electrons in bonding leads to:

A. Variable oxidation states

B. Constant +1 state

C. Zero oxidation state only

D. Complete chemical inactivity

Answer: A

22. Which orbital is more diffuse and available for bonding in early actinoids compared with 4f?

A. 5f

B. 4f

C. 2s

D. 1s

Answer: A. 5f

23. Which actinoid commonly shows +5 oxidation state?

A. Protactinium

B. Lanthanum

C. Lutetium

D. Ytterbium

Answer: A. Protactinium

24. The higher oxidation states of actinoids are especially common in:

A. Early actinoids

B. Only the last actinoid

C. Noble gases

D. Alkali metals

Answer: A. Early actinoids

25. Towards the later actinoids, which oxidation state becomes increasingly important?

A. +3

B. +7 only

C. −3

D. +8

Answer: A. +3

26. The energy difference between 5f and 6d orbitals in actinoids is:

A. Relatively small

B. Extremely large

C. Infinite

D. Zero for every actinoid

Answer: A

27. Which pair correctly represents the f-block series and their principal differentiating subshell?

A. Lanthanoids—4f; Actinoids—5f

B. Lanthanoids—5f; Actinoids—4f

C. Both—3d

D. Both—5d

Answer: A

28. Which statement best explains the difference between lanthanoids and actinoids?

A. 5f electrons participate more readily in bonding than 4f electrons

B. 4f electrons are more reactive than 5f electrons

C. Actinoids have no f-electrons

D. Lanthanoids have no valence electrons

Answer: A

29. Which sequence correctly represents the general oxidation-state range of actinoids?

A. Mainly +3 with several higher states possible

B. Only −3

C. Only +1

D. Only +8

Answer: A

30. The most important reason for the wider oxidation-state range of actinoids is:

A. Comparable energies of 5f, 6d and 7s orbitals

B. Complete shielding of 5f electrons

C. Absence of d orbitals

D. Very low nuclear charge

Answer: A

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