Properties Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with most organic and inorganic substances. Finely divided metals, glass, ceramics, carbon, and even water burn in fluorine with a bright flame. Until World War II, there was no commercial production of elemental fluorine. The nuclear bomb project and nuclear energy applications, however, made it necessary to produce large quantities.
Hydrofluoric acid etches the glass of light bulbs, etc.
Fluorochlorohydrocarbons are extensively used in air conditioning and refrigeration. Elemental fluorine has been studied as a rocket propellant as it has an exceptionally high specific impulse value. One hypothesis says that fluorine can be substituted for hydrogen wherever it occurs in organic compounds, which could lead to an astronomical number of new fluorine compounds. Compounds of fluorine with rare gases have now been confirmed in fluorides of xenon, radon, and krypton. Handling Elemental fluorine and the fluoride ion are highly toxic.