The lanthanide contraction explains which of the following...

The lanthanide contraction explains which of the following periodic trends? (a) The atomic radii of the transitionmetals first decrease and then increase when moving horizontally across each period. (b) When forming ions the period 4 transition metals lose their 4$s$ electrons before their 3$d$ electrons. (c) The radii of the period 5 transition metals $(\mathrm{Y}-\mathrm{Cd})$ are very similar to the radii of the period 6 transition metals $(\mathrm{Lu}-\mathrm{Hg}).$

The lanthanide contraction explains which of the following periodic trends? (a) The atomic radii of the
transitionmetals first decrease and then increase when moving horizontally across each period. (b) When forming ions the period 4 transition metals lose their 4$s$ electrons before their 3$d$ electrons. (c) The radii of the period 5 transition metals $(\mathrm{Y}-\mathrm{Cd})$ are very similar to the radii of the period 6 transition metals $(\mathrm{Lu}-\mathrm{Hg}).$

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Key Concepts

Lanthanide Contraction

This concept refers to the gradual decrease in the size of the lanthanide ions as the atomic number increases, even though one would expect an increase due to the addition of more electrons. The contraction occurs because the 4f electrons do not shield the increasing nuclear charge effectively, resulting in a stronger pull on the outer electrons and a smaller ionic radius.

Periodic Trends in Atomic Radii

Periodic trends in atomic radii describe consistent changes in atomic size across periods and down groups in the periodic table, which are influenced by factors like effective nuclear charge and electron shielding. In the context of the lanthanide contraction, this trend explains why some transition metals, particularly those in period 5 and period 6, have very similar atomic radii despite differences in their position on the periodic table.

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