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प्रश्न
What are chemical twins? Write ‘two’ examples.
उत्तर
Chemical twins are those in which the properties of some elements are same. Atomic size of Zr and Hf , Nb and Ta are similar. This is due to Lanthanide contraction.
Example - Zr and Hf ; Nb and Ta
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संबंधित प्रश्न
What are lanthanoids?
Which among the following pairs of elements is 'not' an example of chemical twins?
Account for the following :
Zr and Hf have almost similar atomic radii.
What are the different oxidation states exhibited by the lanthanoids?
Compare the chemistry of actinoids with that of the lanthanoids with special reference to oxidation state.
Compare the chemistry of actinoids with that of the lanthanoids with special reference to chemical reactivity.
Write the electronic configurations of the elements with the atomic numbers 61, 91, 101 and 109.
What is lanthanoid contraction?
Explain effects of lanthanoid contraction
What are the consequences of lanthanoid contraction?
Explain the cause of lanthanoid contraction?
What is 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 lanthanoid contraction? Write the.............
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+
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 |
Match the property given in Column I with the element given in Column II.
| Column I (Property) | Column II (Element) | |
| (i) | Lanthanoid which shows +4 oxidation state |
(a) Pm |
| (ii) | Lanthanoid which can show +2 oxidation state |
(b) Ce |
| (iii) | Radioactive lanthanoid | (c) Lu |
| (iv) | Lanthanoid which has 4f7 electronic configuration in +3 oxidation state |
(d) Eu |
| (v) | Lanthanoid which has 4f14 electronic configuration in +3 oxidation state |
(e) Gd |
| (f) Dy |
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.
The titanium (Z = 22) compound that does not exist is:-
Which one of the lanthanoids given below is the most stable in divalent form?
State a reason for the following:
La(OH)3 is more basic than Lu(OH)3.
Assertion: There is a continuous increase in size among Lanthanoids with an increase in atomic number.
Reason: Lanthanoids do not show Lanthanoid contraction.
Name an important alloy which contains some of the lanthanoid metals.
