Fluorine is a yellowish, poisonous, highly corrosive gas. It is the most chemically active nonmetallic element and is the most electronegative of all the elements. Fluorine is a member of group VIIa of the periodic table . It readily displaces the other halogens from their salts.
Fluorine reacts with most inorganic and organic compounds.
With hydrogen it forms hydrogen fluoride gas, whose water solution is called hydrofluoric acid. Because of its extreme reactivity, fluorine does not occur uncombined in nature. Fluorine gas is produced commercially by electrolysis of a solution of hydrogen fluoride containing potassium hydrogen fluoride. Cryolite and apatite are other important natural compounds. Although there was no commercial production of fluorine before World War II, the use of the gas in a process for refining uranium ores prompted its manufacture.