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प्रश्न
What is Lanthanoid contraction?
उत्तर
1) Definition of Lanthanoid Contraction: The Lanthanoid contraction may be defined as gradual
(or small) the decrease in atomic and ionic radii of lanthanoids with the increase in atomic number.
2) In Lanthanides, after Lanthanum (`""_57La`), the electrons are added to anti-penultimate shell i.e. 4f orbital.
3) There are 14 Lanthanoides from `""_58Ce` to `""_57Lu`
4) For each electron, one proton is also added to the nucleus of the atom of the element. Hence from `""_58Ce`to `""_71Lu` as atomic number increases, nuclear charge increases, therefore nuclear attraction increases.
5) Due to this as atomic number increases, atomic volume or radius decreases as observed with all the elements along the period.
6) But in case of Lanthanoids, this decreases in atomic volume or radius is very slow or comparatively small. This is explained in terms of Lanthanoid contraction
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संबंधित प्रश्न
Define lanthanoid contraction.
What are lanthanoids?
Which among the following pairs of elements is 'not' an example of chemical twins?
Compare the chemistry of actinoids with that of lanthanoids with special reference to electronic configuration.
Explain, why lanthanum (Z = 57) forms La3+ ion, while cerium (Z = 58) forms Ce4+ ion?
What are the consequences of lanthanoid contraction?
Explain the cause of Lanthanoids contraction.
Answer the followiiig questions:
Which trivalent ion has maximum size in the Lanthanoid series i.e. Lanthanum ion (La3+) to Luteium ion (Lu3+)?
(at. no. of Lanthanum = 57 and Lutetium = 71)
What is meant by Lanthanide contraction? Write the general electronic configuration of inner transition elements.
What is the action of the following on lanthanoids?
a. water
b. Sulphur, heat
c. nitrogen, heat
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 +3 oxidation states is the characteristic oxidation state of lanthanoids but cerium shows +4 oxidation state also. 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 |
Match the statements given in Column I with the oxidation states given in Column II.
| Column I | Column II | |
| (i) | Oxidation state of Mn in MnO2 is | (a) + 2 |
| (ii) | Most stable oxidation state of Mn is | (b) + 3 |
| (iii) | Most stable oxidation state of | (c) + 4 |
| Mn in oxides is | (d) + 5 | |
| (iv) | Characteristic oxidation state of lanthanoids is | (e) + 7 |
On the basis of Lanthanoid contraction, explain the following:
Trends in the stability of oxo salts of lanthanoids from \[\ce{La}\] to \[\ce{Lu}\].
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.
Zr (Z = 40) and Hf (Z = 72) have similar atomic and ionic radii because of ______.
Mischmetal is an alloy consisting mainly of ______.
State a reason for the following:
La(OH)3 is more basic than Lu(OH)3.
Trivalent Lanthanoid ions such as La3+ (Z = 57) and Lu3+ (Z = 71) do not show any colour in their solution. Give a reason.
Assertion: There is a continuous increase in size among Lanthanoids with an increase in atomic number.
Reason: Lanthanoids do not show Lanthanoid contraction.
Mention alloy uses.
