The lanthanoid contraction is caused by imperfect shielding of one 4f electron by another, similar to the shielding observed in an ordinary transition series. However, the shielding effectiveness of 4f electrons is less than that of d electrons, leading to a regular decrease in the size of the entire 4f orbitals.
What is the cause of the lanthanoid contraction, and how is it similar to the shielding observed in an ordinary transition series?
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The lanthanoid contraction is caused by imperfect shielding of one 4f electron by another, similar to the shielding observed in an ordinary transition series. However, the shielding effectiveness of 4f electrons is less than that of d electrons. As the nuclear charge increases along the series, there is a fairly regular decrease in the size of the entire 4f orbitals. This decrease in metallic radius, coupled with an increase in atomic mass, leads to a general increase in the density of these elements. The lanthanoid contraction compensates for the expected increase in atomic size with increasing atomic number.