This area chart shows element density across the periodic table. The variation spans four orders of magnitude, from hydrogen gas to osmium metal.

Osmium and iridium are the densest elements at ~22.6 g/cm³, packed tightly by relativistic contraction of their electron clouds. Density generally increases down groups but is modified by atomic radius expansion. Alkali metals are surprisingly light - lithium floats on water. This property determines applications from aircraft (aluminum, titanium) to radiation shielding (lead, tungsten).