Lithium, with the symbol Li and an atomic number of 3, is a pure element which, under standard conditions, is the lightest known metal. It has a density of 0.534 gram per cubic meter, making it the least dense solid element.
Lithium is almost half as dense as water; thus, a piece of this metal would float on water if it were not so reactive. It is also less dense than any liquid element, aside from helium and hydrogen, being only two-thirds as heavy as liquid nitrogen.
This metal belongs to the alkali metal group of chemical elements. It is soft, silver-white, flammable and highly reactive.