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प्रश्न
What is lanthanoid contraction?
What do you understand by lanthanoid contraction?
What is lanthanoid contraction? Explain.
What is meant by lanthanide contraction?
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उत्तर १
The lanthanide series of elements is defined as a gradual reduction in atom size, known as lanthanoid contraction. This reduction occurs due to insufficient shielding of additional electrons in the 4f subshell by filled 5s and 5p orbitals. As a result, the effective nuclear charge increases, resulting in smaller atomic sizes.
उत्तर २
- The size of the atoms and ions has been found to routinely decrease as one moves from cerium to lutetium. In the case of tripositive ions, this size reduction is more consistent.
- The nuclear charge rises with atomic number when one transitions from Ce to Lu, and the inner 4f-orbital gains the differentiating electron.
- The shielding of one 4f-electron by another from growing nuclear charge is imperfect due to the irregular geometries of 4f-orbitals.
- As a result, each 4f-electron experiences an increasing effective nuclear charge as the atomic number rises. As each electron in the 4f-subshell is added, the size is somewhat decreased.
- As a result, the size steadily contracts as the effective nuclear charge steadily rises with each additional electron in the 4f-subshell.
- Lanthanoid contraction refers to the cumulative effect of successive contractions on all lanthanoids.
- The total contraction in atomic radius in going from Ce to Lu is about 15 pm.
- Atomic radii show a tendency to decrease in size; however, the pattern is irregular.
Notes
Students can refer to the provided solutions based on their preferred marks.
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संबंधित प्रश्न
What are chemical twins? Write ‘two’ examples.
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 the lanthanoids with special reference to chemical reactivity.
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.
Write the different oxidation states of iron
Explain, why lanthanum (Z = 57) forms La3+ ion, while cerium (Z = 58) forms Ce4+ ion?
What are the consequences of lanthanoid contraction?
Account for the following:
Zn, Cd and Hg are soft metals.
Explain the cause of Lanthanoids contraction.
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? Write the.............
What is the action of the following on lanthanoids?
a. water
b. Sulphur, heat
c. nitrogen, heat
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?
General electronic configuration of actinoids is `(n-2)f^(1-14)(n - 1)d^(0-2)ns^2`.Which of the following actinoids have one electron in 6d orbital?
(i) U (Atomic no. 92)
(ii) Np (Atomic no.93)
(iii) Pu (Atomic no. 94)
(iv) Am (Atomic no. 95)
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 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:
Nature of bonding in \[\ce{La2O3}\] and \[\ce{Lu2O3}\] .
On the basis of Lanthanoid contraction, explain the following:
Stability of the complexes of lanthanoids.
On the basis of Lanthanoid contraction, explain the following:
Trends in acidic character of lanthanoid oxides.
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:-
In lanthanoid the last electron enters (n - 2)f subshell where n is equal to ______.
Zr (Z = 40) and Hf (Z = 72) have similar atomic and ionic radii because of ______.
Mischmetal is an alloy consisting mainly of ______.
Cerium (Z = S8) is an important member of lanthanoids. Which of the following statements about cerium is incorrect?
Write a note on lanthanoids.
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. Mention its uses.
The pair of lanthanoid ions which are diamagnetic is:
