Question

Which of the following property does not show resemblance between lanthanides and actinides?

• A. Complex formation tendency
• B. Reducing property
• C. +3 ionic radius trends
• D. Stable oxidation state is +3

Answer 1

Answer: (A)

Complex formation tendency

Answer 2

The question asks to identify the property that does not show resemblance between lanthanides and actinides. Let's analyze each option:

A. Complex formation tendency:

• Lanthanides: Have a relatively low tendency to form complexes. This is because their 4f electrons are well-shielded by the outer 5s, 5p, and 6s electrons, making them less available for bonding.
• Actinides: Have a much greater tendency to form complexes compared to lanthanides. This is due to several reasons:
  • The 5f electrons are less effectively shielded than 4f electrons, making them more exposed and available for bonding.
  • Actinides exhibit a wider range of oxidation states, including higher ones (+4, +5, +6, +7), which leads to higher charge density and smaller ionic radii, favoring complex formation.
  • They can also utilize 6d orbitals for bonding.
• Conclusion: The complex formation tendency is significantly different (low for lanthanides vs. high for actinides). Therefore, this property does not show resemblance.

B. Reducing property:

• Lanthanides: Are generally good reducing agents, tending to lose electrons to achieve the stable +3 oxidation state.
• Actinides: Are also strong reducing agents, often stronger than lanthanides.
• Conclusion: Both series exhibit reducing properties. While the strength might differ, the fundamental property of being reducing agents is a resemblance.

C. +3 ionic radius trends:

• Lanthanides: Exhibit "lanthanide contraction," a steady decrease in ionic radii for their +3 ions as the atomic number increases across the series. This is due to the poor shielding of 4f electrons.
• Actinides: Exhibit "actinide contraction," a similar steady decrease in ionic radii for their +3 ions as the atomic number increases across the series. This is due to the poor shielding of 5f electrons.
• Conclusion: Both series show a similar trend of decreasing ionic radii for their +3 ions. This is a clear resemblance.

D. Stable oxidation state is +3:

• Lanthanides: The +3 oxidation state is the most characteristic, common, and stable oxidation state for almost all lanthanides.
• Actinides: The +3 oxidation state is also a stable oxidation state for actinides, and it becomes the most stable for the heavier actinides. However, unlike lanthanides, actinides (especially the lighter ones like U, Np, Pu) exhibit a wider range of stable oxidation states (+4, +5, +6, +7) due to the comparable energies of 5f, 6d, and 7s orbitals.
• Conclusion: While +3 is a stable oxidation state for both, the predominance and range of stable oxidation states are significantly different. Lanthanides are almost exclusively +3, whereas actinides show a wide variety of stable oxidation states. Thus, the statement "Stable oxidation state is +3" as a defining or predominant characteristic does not show a complete resemblance. However, if interpreted as "the property that +3 is a stable oxidation state exists in both", it would be a resemblance. Given the options, the tendency for complex formation (Option A) is a more direct and unambiguous non-resemblance because their abilities are on opposite ends of the spectrum (low vs. high). The wide range of oxidation states in actinides, implying that +3 is not the only or predominant stable state for all members, also points to a non-resemblance in the nature of the +3 stability.

Comparing A and D:

The question asks what does not show resemblance.

• For complex formation (A), the tendency itself is very different (low vs. high). This is a clear difference.
• For stable oxidation state +3 (D), while +3 is stable in both, the range of stable oxidation states is a key difference. Lanthanides are almost exclusively +3, while actinides show a wide range. So, if the property is "the characteristic stable oxidation state is +3", it does not resemble.

In most textbooks, the greater complexing ability of actinides compared to lanthanides is highlighted as a significant difference. Similarly, the wider range of oxidation states for actinides is a major point of distinction.

However, the phrasing "Stable oxidation state is +3" is technically true for both. The extent of stability or the exclusivity of this state is what differs. The "complex formation tendency" is a direct comparison of their ability, which is distinctly different (low vs. high). This is a more direct "non-resemblance".

Let's consider the most prominent difference. The ability to form complexes is much higher for actinides. So, the tendency is different.

Final check:

A. Complex formation tendency: Low (Ln) vs High (An) -> Non-resemblance.

B. Reducing property: Good (Ln) vs Stronger (An) -> Resemblance (both are reducing agents).

C. +3 ionic radius trends: Contraction (Ln) vs Contraction (An) -> Resemblance.

D. Stable oxidation state is +3: Yes (Ln) vs Yes (An, but also other states) -> This is a tricky one. If it implies only +3 or predominantly +3, then it's a non-resemblance for actinides. If it means +3 is a stable state, then it's a resemblance. However, the range of oxidation states is a fundamental difference.

Given the options, the difference in complex formation tendency is very clear and often cited as a distinct difference. The wider range of oxidation states in actinides is also a major difference. If we interpret "Stable oxidation state is +3" as implying that this is the sole or predominant stable state, then it does not resemble. But if we interpret it as +3 is a stable state, then it does.

However, the tendency to form complexes is unequivocally different.