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Question
Explain the cause of Lanthanoids contraction.
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Solution
- In the Lanthanoid series with increasing atomic number, the atomic and ionic radii decrease from one element to another but a decrease is very small.
- An increase in nuclear charge in a period increases the force of attraction towards the outer electrons. Hence
atomic size or radius decreases. - Filling of the electrons in the inner shells increases the atomic size as inner electrons repel outer electrons. The shielding effect of electrons decreases in the order s > p > d > f
- The new electrons are added to the same inner 4f orbital. Hence, Lanthanoid contraction is due to
- Poor shielding effect of the 4f electrons
- Increase in nuclear charge.
- Non-introduction of new outer shells.
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