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Screening Effect and Lanthanoid Contraction - (Concept)
The Lanthanide Contraction describes the atomic radius trend that the lanthanide series exhibit. The Lanthanide Contraction refers to the fact that the 5s and 5p orbitals penetrate the 4f sub-shell so the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease. This decrease in size continues throughout the series.
The Lanthanide Contraction is the result of a poor shielding effect of the 4f electrons. The shielding effect is described as the phenomenon by which the inner-shell electrons shield the outer-shell electrons so they are not affected by nuclear charge. So when the shielding is not as good, this would mean that the positively charged nucleus has a greater attraction to the electrons, thus decreasing the atomic radius as the atomic number increases. The s orbital has the greatest shielding while f has the least and p and d in between the two with p being greater than d.
The Lanthanide Contraction can be seen by comparing the elements with f electrons and those without f electrons in the d block elements. Pd and Pt are such elements. Pd has 4d electrons while Pt has 5d and 4f electrons. These 2 elements have roughly the same atomic radius. This is due to Lanthanide Contraction and shielding. While we would expect Pt to have a significantly larger radius because more electrons and protons are added, it does not because the 4f electrons are poor at shielding. When the shielding is not good there will be a greater nuclear charge, thus pulling the electrons in closer, resulting in a smaller than expected radius.
| Exam | Chapter |
| JEE MAIN | d - and f - BLOCK ELEMENTS |
Which of the following factors may be regarded as the main cause of lanthanide contraction?
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What are the consequences of Lanthanide Contraction?
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Given below are two statement : one is labelled as Assertion A and the other is labelled as Reason R:
Assertion A : Size of Bk3+ ion less than Np3+ion.
Reason R : The above is a consequence of the lanthanoid contraction.
In the light of the above statements, choose the correct answer from the options given below :
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Which of the following fact is/are true for variation of shielding effect in periodic table?
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Due to increase in screening or shielding of inner electrons, Zeff
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The correct order of ionic radii of ,
and
is
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The lanthanide contraction is responsible for the fact that
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Knowing that the chemistry of lanthanoids is dominated by its +3 oxidation state, which of the following statements is incorrect?
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In slater's rule the correct arrangement of electron are according to the extent of their screening.
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What is the shielding constant experienced by a 3d electron in the selenium atom?
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Electron present in the nth shell of an element is most effectively shielded by:
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Given below are two statements :
Statement (I) : In the Lanthanoids the formation $\mathrm{Ce}^{+4}$ is favoured by its noble gas configuration
Statement (II) : $\mathrm{Ce}^{+4}$ is a strong oxidant reverting to the common +3 state.
In the light of the above statements, choose the most appropriate answer from the options given below:
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The filling of 4f before 5d orbital results in a regular decrease in atomic radii called Lanthanoid contraction which essentially compensates for the expected increase in atomic size with increasing atomic number.
