The elements Osmium () and Iridium () have the highest known mass densities in the periodic table. What is the primary reason the 5d transition elements are exceptionally denser than their 4d counterp

Question

The elements Osmium ($Os$) and Iridium ($Ir$) have the highest known mass densities in the periodic table. What is the primary reason the 5d transition elements are exceptionally denser than their 4d counterparts?

Prashant Kotian · Accepted Answer

Correct answer: B. Density = Mass/Volume. Due to the Lanthanoid contraction, 5d elements have almost the exact same atomic volume as 4d elements. Since their atomic mass is roughly double, their density doubles as well.

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