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Question
Which of the following factors may be regarded as the main cause of lanthanide contraction?
Which of the following factors may be regarded as the main cause of lanthanide contraction?
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Solution
The correct option is D Poor shielding of one of 4-electrons by another in the subshell
In lanthanides, the additional electron enters 4f - subshell but not in the valence-shell namely sixth shell. The shielding effect of one electron in 4f-subshell by another in the same sub-shell (i.e. mutual shielding effect of 4f -electrons) is very little, being even smaller than that of d-electrons, because the shape of f-subshell is very much diffused.
The nuclear charge (i.e. atomic number), however, increases by unity at each step. Thus the nuclear charge increases at each step, while there is no comparable increase in the mutual shielding effect of 4f-electrons.
This results in that electrons in the outermost shell experience increasing nuclear attraction from the growing nucleus. Consequently, the atomic and ionic radii go on decreasing as we move from 57 La and 71 Lu.
In lanthanides, the additional electron enters 4f - subshell but not in the valence-shell namely sixth shell. The shielding effect of one electron in 4f-subshell by another in the same sub-shell (i.e. mutual shielding effect of 4f -electrons) is very little, being even smaller than that of d-electrons, because the shape of f-subshell is very much diffused.
The nuclear charge (i.e. atomic number), however, increases by unity at each step. Thus the nuclear charge increases at each step, while there is no comparable increase in the mutual shielding effect of 4f-electrons.
This results in that electrons in the outermost shell experience increasing nuclear attraction from the growing nucleus. Consequently, the atomic and ionic radii go on decreasing as we move from 57 La and 71 Lu.
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