Fluorine was discovered by Karl Scheele in 1771, recognized as a halogen in 1825, and included in Mendeleev's periodic table of 1869. Fluorine is so active that it existed only in compounds and all efforts to isolate the element failed.  Because of its high corrosiveness/toxticity, early fluorine chemists died from fluorine poisoning and the element was dubbed "Tiger of Chemistry." Fluorine, from Latin "fleure" meaning to flow, is the 13th most abundant element in the earth's crust and the most reactive of all elements--it even forms compounds with noble gases.

Henri Moissan (1852-1907)
In 1886, French chemist Henri Moissan attempted to isolate fluorine. Since platinum was one of the few substances that might resist fluorine, Moissan constructed equipment from this metal platinum and lowered the temperature (-50°C) to reduce fluorine's activity. Then he passed an electric current through a solution of potassium fluoride in hydrofluoric acid and achieved his goal--fluorine was finally isolated.  In the electrolysis figure shown below, fluoride ions are oxidized at the positive electrode (anode) producing fluorine gas. Moissan made a full study of the properties of fluorine and its reactions with other elements.  Shortly after receiving the 1906 Nobel prize in chemistry, Moissan suddenly died (fluorine poisoning?).



Because the fluoride ion (F-1) makes teeth resistant to decay, it is added to drinking water in the form of sodium fluoride (NaF) and to toothpaste as SnF2. Highly reactive hydrogen fluoride (HF) is used to frost glass light bulbs.

Fluorine, almost as small as hydrogen, forms a very strong bond with carbon and fluorocarbon compounds are highly stable. In 1930, Thomas Midgley Jr. prepared Freon-12 (CF2Cl2).  Because Freon is easily liquefied as well as odorless/nontoxic/nonflammable, it is used universally in home refrigerators and air conditioners.  First hailed as a miracle of modern science, Freon propellant in spray cans has caused problems.  Evidence is beginning to mount that Freons lost to the atmosphere are depleting the ozone layer.

Polytetrafluoroethylene is a polymer (large molecule) having the repeat structure (CF2CF2)n.  Called teflon, it is used as a film to prevent sticking to frying pans (see useless information).

In 1962, a compound was prepared from platinum, fluorine and xenon--the first time an inert gas made into a compound.  Because numerous compounds have been prepared (XeF2, XeF4, XeF6, XeOF4), the inert gases were renamed noble gases.

Sulfur hexafluoride (SF6) has a high molecular weight (164) and is a virtually inert gas at room temperature. Because of its high molecular weight (164), it is used in the insulation of high voltage switch gear, window panes (insulation for heat/sound), high performance tires (prevents pressure loss), and sports shoes (impact absorption).

Astronomers keep adding to the list of molecules found in interstellar space. In 1996, the European Space Agency discovered trace amounts of hydrogen fluoride in a  giant cloud of interstellar gas near the galactic center. This is the first time a molecule containing fluorine has ever been discovered in interstellar space.
 

Fluorescence
Fluorescence is the emission of visible light from a substance under the stimulation of radiation at a shorter wavelength.  British scientist Sir George Stokes (1852) named the phenomenon after the strongly fluorescent mineral fluorite--known for its glassy luster and variety of colors, CaF2 is the main source of fluorite. Stokes discovered fluorescence can be induced in certain substances by stimulation with ultraviolet light. He formulated Stokes's law: the wavelength of the emitted light is always greater than the emitted radiation (fluorite typically emits green, violet, yellow, brown, and blue). The fluorescence in fluorite has been attributed to the presence of organic inclusions and unbonded fluorine. The fluorescence microscope (shown below) has photographed emitted light patterns of bacteria and DNA.

                                                                        DNA                        DNA                   Bacteria

For the phenomenon known as phosphorescence (below), light continues to be emitted after the external light source has been turned off.