The lanthanoid contraction refers to the overall decrease in atomic and ionic radii from lanthanum to lutetium. It is a unique feature in the chemistry of the lanthanoids and has far-reaching consequences, particularly in the third transition series.
What is the lanthanoid contraction, and how does it influence the atomic and ionic radii of the lanthanoids?
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The lanthanoid contraction is the phenomenon where there is a smaller-than-expected increase in atomic and ionic radii across the lanthanide series. Despite adding electrons to the 4f orbitals, the poor shielding ability of these inner electrons leads to an incomplete screening of the increasing nuclear charge. As a result, the effective nuclear charge felt by the outer electrons is higher, causing a contraction in size. This contraction is most pronounced in the ionic radii of the lanthanoid series, where consecutive elements exhibit similar sizes. The lanthanoid contraction highlights the unique electronic and size characteristics of the lanthanides.