The elements Osmium () and Iridium () possess the highest known mass densities of all elements. What primarily accounts for the dramatic doubling of density from the 4d series to the 5d series?

Question

The elements Osmium ($Os$) and Iridium ($Ir$) possess the highest known mass densities of all elements. What primarily accounts for the dramatic doubling of density from the 4d series to the 5d series?

Prashant Kotian · Accepted Answer

Correct answer: B. Density is mass/volume. Because of the Lanthanoid Contraction, elements in the 5d series occupy almost the exact same volume as those in the 4d series. Since their atomic mass is roughly double, their densities are exceedingly high.

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