Which Metal Is the Lightest?

Lithium (Li, atomic number 3) is the lightest metal and the least dense solid element, with a density of 0.534 g/cm3 — about half the density of water (1.0 g/cm3). It is so light it floats on water, though it also reacts vigorously with water (producing lithium hydroxide and hydrogen gas). Lithium is a soft, silver-white alkali metal that can be cut with a knife. Despite being the lightest metal, it has become one of the most strategically important materials on Earth due to its central role in rechargeable lithium-ion batteries powering everything from smartphones to electric vehicles. Global lithium demand has surged, with major reserves in Australia, Chile (Salar de Atacama), Argentina, and Bolivia. Lithium also has important medical applications: lithium salts have been used since the 1940s to treat bipolar disorder, and it remains one of the most effective mood-stabilising medications.