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प्रश्न
The chemistry of the actinoid elements is not so smooth as that of the Lanthanoids. Justify this statement by giving some examples from the oxidation state of these elements.
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उत्तर १
The oxidation states of lanthanoids are +2, +3, and +4. Of these, +3 is the most common state. The limited number of oxidation states is due to the large energy differences among the 4f, 5d, and 6s suborbitals. In contrast, actinoids exhibit multiple oxidation states, including +2, +3, +4, +5, +6, and +7, although their most common state is +3. This is because there is a small energy difference between the 5f, 6d, and 7s sub-orbitals.
उत्तर २
- The actinoids are radioactive elements, with the older members exhibiting relatively long half-lives, while the latest members have half-lives ranging from one day to three minutes, with lawrencium (Z = 103) having the shortest. The latter members could only be prepared in nanogram quantities. These facts complicate their study.
- The greater range of oxidation states is due to the comparable energies of the 5f, 6d, and 7s levels. The actinoids usually exhibit a +3 oxidation state. The elements in the first half of the series frequently have higher oxidation states.
- For example, the maximum oxidation state increases from +4 in Th to +5, +6 and +7, respectively, in Pa, U and Np, but decreases in succeeding elements.
- The actinoids, such as lanthanoids, exhibit a greater number of compounds in the +3 oxidation state compared to the +4 state. However, +3 and +4 ions exhibit a tendency to undergo hydrolysis. The distribution of oxidation states among the actinoids is markedly irregular and varies significantly between the earlier and later elements. It is inadequate to evaluate their chemistry solely on the basis of oxidation states.
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संबंधित प्रश्न
What are lanthanoids?
Name the members of the lanthanoid series which exhibit +4 oxidation state and those which exhibit +2 oxidation state. Try to correlate this type of behavior with the electronic configurations of these elements.
Explain, why lanthanum (Z = 57) forms La3+ ion, while cerium (Z = 58) forms Ce4+ ion?
Account for the following:
Zn, Cd and Hg are soft metals.
Explain the cause of Lanthanoids contraction.
Which trivalent ion has the maximum size in the Lanthanoid series, i.e., Lanthanum ion (La3+) to Luteium ion (Lu3+)?
(at. no. of Lanthanum = 57 and Lutetium = 71)
Name an element of lanthanoid series which is well knwon to shown +4 oxidation state. Is it a strong oxidising agent or reducing agent?
What is lanthanoid contraction?
The f-block elements are known as ____________.
Gadolinium belongs to 4f series. It’s atomic number is 64. Which of the following is the correct electronic configuration of gadolinium?
Although +3 is the characteristic oxidation state for lanthanoids but cerium also shows +4 oxidation state because:
(i) it has variable ionisation enthalpy
(ii) it has a tendency to attain noble gas configuration
(iii) it has a tendency to attain f 0 configuration
(iv) it resembles Pb4+
Although Zr belongs to 4d and Hf belongs to 5d transition series but it is quite difficult to separate them. Why?
Match the compounds/elements given in Column I with uses given in Column II.
| Column I (Compound/element) | Column II (Use) | |
| (i) | Lanthanoid oxide | (a) Production of iron alloy |
| (ii) | Lanthanoid | (b) Television screen |
| (iii) | Misch metal | (c) Petroleum cracking |
| (iv) | Magnesium based alloy is constituent of | (d) Lanthanoid metal + iron |
| (v) | Mixed oxides of lanthanoids are employed | (e) Bullets |
| (f) In X-ray screen |
On the basis of Lanthanoid contraction, explain the following:
Stability of the complexes of lanthanoids.
How would you account for the following:
There is a greater range of oxidation states among the actinoids than among the lanthanides.
Write any two consequences of Lanthanoid Contraction.
Mischmetal is an alloy consisting mainly of ______.
Write a note on lanthanoids.
Name an important alloy which contains some of the lanthanoid metals.
