Density: definition in chemistry
Density: The mass of a substance per unit of volume, calculated as density = mass ÷ volume.
Density is usually given in grams per cubic centimeter (g/cm³) for solids and liquids and in grams per liter for gases. A material less dense than a liquid floats in it, which is why ice (0.92 g/cm³) floats on water (1.00 g/cm³). Because each pure substance has a characteristic density at a given temperature, measuring density helps identify materials and check their purity.
Examples
- Water — about 1.00 g/cm³
- Aluminum — 2.70 g/cm³, light enough for aircraft
- Gold — 19.3 g/cm³, much denser than lead (11.3 g/cm³)
- Osmium — about 22.6 g/cm³, the densest element
On the periodic table
Density generally increases down a group, and the densest elements, osmium and iridium, sit in the middle of period 6, while lithium is the least dense metal.