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Questions
Define lanthanoid contraction.
What is lanthanoid contraction?
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Solution
In the lanthanoids, the electrons are filling the 4f-subshell. On moving from left to right, the nuclear charge increases, and this increase is expected to be compensated by the increase in the magnitude of the shielding effect by the 4f-electrons. However, the f-electrons have very poor shielding effects. With an increasing atomic number in the lanthanoid series, there is a progressive decrease in the atomic as well as ionic radii of trivalent ions from La3+ to Lu3+, and this is known as lanthanoid contraction.
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| Column I (Compound/element) | Column II (Use) | |
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| (ii) | Lanthanoid | (b) Television screen |
| (iii) | Misch metal | (c) Petroleum cracking |
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| Column I | Column II | |
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| Column I (Property) | Column II (Element) | |
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(d) Eu |
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(e) Gd |
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