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What is meant by lanthanoid contraction?
What is meant by lanthanoid contraction?
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Lanthanoid contraction affects size and properties of transition elements.
Updated On: Mar 2, 2026
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Solution and Explanation
Lanthanoid Contraction:
Lanthanoid contraction refers to the gradual decrease in the size of the lanthanide ions (from La³⁺ to Lu³⁺) with increasing atomic number as you move across the lanthanide series, from left to right. This phenomenon occurs due to the ineffective shielding of the increasing nuclear charge by the 4f-electrons.
Step 1: Explanation of Lanthanides
The lanthanides are a series of 15 elements in the periodic table with atomic numbers from 57 (La) to 71 (Lu). These elements fill their 4f orbitals as they progress across the series.
Step 2: Cause of Lanthanoid Contraction
- As the atomic number increases across the lanthanide series, the nuclear charge increases, meaning the number of protons in the nucleus increases. - Although electrons are added to the 4f orbitals, the shielding effect provided by the 4f-electrons is weak. This is because the 4f orbitals are poorly shielded from the increasing nuclear charge. - As a result, the outer electrons experience a stronger pull from the nucleus, causing the ionic size to decrease progressively.
Step 3: Consequences of Lanthanoid Contraction
- Lanthanoid contraction leads to several properties: 1. **Similar ionic sizes**: The ionic radii of the lanthanides are very similar, which makes it difficult to separate these elements. 2. **Similar chemical properties**: The elements show similar chemical behavior due to their similar sizes and effective nuclear charge. 3. **Effect on chemistry of subsequent periods**: The contraction also affects the elements in period 5 (actinoids) and the transition elements following the lanthanides, as the atomic size of elements like Zr (Zirconium) and Hf (Hafnium) are almost identical, leading to similar properties.
Conclusion:
Lanthanoid contraction is the progressive decrease in the size of the ions from La³⁺ to Lu³⁺ due to the weak shielding of the nuclear charge by the 4f-electrons, resulting in a stronger attraction of electrons towards the nucleus.
Lanthanoid contraction refers to the gradual decrease in the size of the lanthanide ions (from La³⁺ to Lu³⁺) with increasing atomic number as you move across the lanthanide series, from left to right. This phenomenon occurs due to the ineffective shielding of the increasing nuclear charge by the 4f-electrons.
Step 1: Explanation of Lanthanides
The lanthanides are a series of 15 elements in the periodic table with atomic numbers from 57 (La) to 71 (Lu). These elements fill their 4f orbitals as they progress across the series.
Step 2: Cause of Lanthanoid Contraction
- As the atomic number increases across the lanthanide series, the nuclear charge increases, meaning the number of protons in the nucleus increases. - Although electrons are added to the 4f orbitals, the shielding effect provided by the 4f-electrons is weak. This is because the 4f orbitals are poorly shielded from the increasing nuclear charge. - As a result, the outer electrons experience a stronger pull from the nucleus, causing the ionic size to decrease progressively.
Step 3: Consequences of Lanthanoid Contraction
- Lanthanoid contraction leads to several properties: 1. **Similar ionic sizes**: The ionic radii of the lanthanides are very similar, which makes it difficult to separate these elements. 2. **Similar chemical properties**: The elements show similar chemical behavior due to their similar sizes and effective nuclear charge. 3. **Effect on chemistry of subsequent periods**: The contraction also affects the elements in period 5 (actinoids) and the transition elements following the lanthanides, as the atomic size of elements like Zr (Zirconium) and Hf (Hafnium) are almost identical, leading to similar properties.
Conclusion:
Lanthanoid contraction is the progressive decrease in the size of the ions from La³⁺ to Lu³⁺ due to the weak shielding of the nuclear charge by the 4f-electrons, resulting in a stronger attraction of electrons towards the nucleus.
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