lithium

Soft, ductile, silver-white, metallic element, atomic number 3, relative atomic mass 6.941. It is one of the alkali metals (being found at the top of Group 1 of the periodic table). It has a very low density (far less than most woods), and floats on water (relative density 0.57); it is the lightest of all metals. Although in the reactivity series it is the least reactive of the alkali metals, it reacts readily with water and the oxygen in air, and so has to be kept under oil. Lithium is used to harden alloys, and in batteries; its compounds are used in medicine to treat manic depression.

Lithium was named in 1818 by Swedish chemist Jöns Berzelius, having been discovered the previous year by his student Johan A Arfwedson. Berzelius named it after ‘stone’ because it is found in most igneous rocks and many mineral springs.

In March 2001, a scientific study concluded that long-term use of lithium salts for manic depression leads to kidney disease. Other potential side effects include tremors, drowsiness, and diarrhoea. However, lithium needs to be taken over a long period to be effective.