On the periodic table, lithium is the lightest solid element at standard room temperature.
Lithium has atomic number 3 and the symbol Li. It is the first alkali metal and the least dense solid element, with a density of about 0.534 grams per cubic centimeter. Its low density allows lithium metal to float on water, although it reacts with water rather than behaving like an inert floating object.
Lithium is used in rechargeable batteries, lightweight alloys, ceramics, glass, and some medicines. It was discovered in the mineral petalite by Johan August Arfwedson in 1817, and the name comes from the Greek word lithos, meaning stone. Hydrogen is lighter overall, but it is a gas at standard room temperature, so lithium is the lightest solid.