The density of an element will depend upon
Naturally, gases will have low density and their density is directly proportional to molecular or atomic mass. There are few liquid elements, so the main point of this trend is the solid elements, most of which are metals. Review the trends in atomic radius if you need before proceeding.
As the atomic or metallic radius decreases, the density increases. As the mass of the nucleus increases, the density increases.
Since radius and mass both increase down a group in the periodic table, the relative rates of change determine density. The mass increases relatively more than does the radius; density generally increases down a group in the periodic table.
A 3-D Histogram using the periodic table to show density.
