Sir Humphry Davy, the English scientist, is undoubtedly the dominant figure in the history of the alkali metals. In 1807, he discovered both sodium and potassium by the then-new method of electrolysis, and after lithium had been discovered by the Swedish chemist, Johann August Arfvedson, in 1817, Davy was the first to isolate a sample of the pure metal.
Both rubidium and caesium were discovered by the German scientists, Robert Wilhelm von Bunsen and Gustav Robert Kirchhoff; caesium in 1860, rubidium in 1861. They were the first elements to be discovered spectroscopically, a method invented by the two scientists in 1859, and the names of the elements derive from the colour of their dominant spectral lines: rubidium derives from {Irubidus}, the Latin for red; and caesium from {Icaesius}, the Latin for blue. Rubidium was discovered in a sample of lepidolite, a mineral particularly rich in alkali metals: it contains both potassium and lithium, and, in small quantities, caesium.
Francium, a radioactive element, was discovered in 1939 by Marguerite Perey, and named in honour of her home country.
