Which of the following factors may be regarded as the main cause of la...
Lanthanide contraction is due to poor shielding of one of 4f electron by another in the subshell.
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Which of the following factors may be regarded as the main cause of la...
Explanation:
The main cause of lanthanide contraction is the poor shielding of one 4f electron by another in the subshell.
The lanthanide series consists of elements with atomic numbers from 57 to 71, and they are characterized by the filling of the 4f subshell. As we move from left to right across the lanthanide series, there is an increase in the nuclear charge due to the addition of protons in the nucleus. This increase in nuclear charge results in a stronger attraction between the nucleus and the outermost electrons.
The lanthanide contraction refers to the decrease in atomic and ionic radii of the elements in the lanthanide series as we move from left to right. This decrease in size is primarily due to the poor shielding of one 4f electron by another in the subshell.
Shielding refers to the ability of inner electrons to reduce the effective nuclear charge felt by the outermost electrons. In the case of lanthanides, the 4f subshell is shielded by the 5s, 5p, and 5d subshells. However, the 4f electrons themselves do not shield each other effectively.
The 4f electrons are relatively ineffective at shielding each other because they are quite diffuse and have poor overlap with each other. As a result, the 4f electrons experience a relatively high effective nuclear charge from the nucleus, leading to a strong attraction and contraction of the electron cloud.
This poor shielding of one 4f electron by another in the subshell results in a higher effective nuclear charge experienced by the outermost electrons. As a result, the atomic and ionic radii of the lanthanide elements decrease as we move from left to right across the series.
Therefore, option D, which states that the poor shielding of one 4f electron by another in the subshell is the main cause of lanthanide contraction, is the correct answer.