Fluorine
In stars fluorine is rare compared to other light elements. In Earth's crust fluorine is the thirteenth most abundant element. Fluorine's most important mineral, fluorite, was first formally described in 1530, in the context of smelting. The mineral's name derives from the Latin verb fluo, which means "flow", because fluorite was added to metal ores to lower their melting points. Suggested as a chemical element in 1811, fluorine was named after the source mineral, but resisted many attempts to isolate the element. In 1886, French chemist Henri Moissan succeeded. His method of electrolysis remains the industrial production method for fluorine gas. The main use of elemental fluorine, uranium enrichment, was developed during the Manhattan Project.
Because of the difficulty in making elemental fluorine, most fluorine used in commerce is never converted to free fluorine. Instead, hydrofluoric acid is the key intermediate for the $16 billion per year global fluorochemical industry. The fluorides of low charged metals are ionic compounds (salts); those of high charged metals are volatile molecular compounds. The largest uses of inorganic fluorides are steel making and aluminium refining.
Organic fluorine compounds tend to have high chemical and thermal stability. The largest commercial use is in refrigerant gases (the many types of "Freons"). Although traditional chlorofluorocarbons are widely banned, the replacement gases still contain fluorine. Polytetrafluoroethylene (Teflon) is the most important fluoropolymer and is used in electrical insulation, chemical-resistant parts, stadium roofs, and cookware. A growing fraction of modern pharmaceuticals contain fluorine; Lipitor and Prozac are prominent examples. While a few plants and bacteria synthesize organofluorine poisons, fluorine has no metabolic role in mammals. The fluoride ion, when directly applied to teeth, reduces decay and for this reason is used in toothpaste and municipal water fluoridation.
Origin and occurrence
In the universe
From the perspective of cosmology, fluorine is relatively rare with 400 ppb in the universe. Within stars, any fluorine that is created is rapidly eliminated through nuclear fusion: either with hydrogen to form oxygen and helium, or with helium to make neon and hydrogen. The presence of fluorine at all—outside of temporary existence in stars is somewhat of a mystery because of the need to escape these fluorine-destroying reactions.
Three theoretical solutions to the mystery exist. In type II supernovae, atoms of neon are hit by neutrinos during the explosion and converted to fluorine. In Wolf-Rayet stars (blue stars over 40 times heavier than the Sun), a strong solar wind blows the fluorine out of the star before hydrogen or helium can destroy it. In asymptotic giant branch (a type of red giant) stars, fusion reactions occur in pulses and convection lifts fluorine out of the inner star. Only the red giant hypothesis has supporting evidence from observations.
In space, fluorine commonly combines with hydrogen to form hydrogen fluoride. (This compound has been suggested as a proxy to enable tracking reservoirs of hydrogen in the universe.) In addition to HF, monatomic fluorine has been observed in the interstellar medium. Fluorine cations have been seen in planetary nebulae and in stars, including our Sun.
On Earth
Fluorine is the thirteenth most common element in Earth's crust, comprising between 600 and 700 ppm of the crust by mass. Because of its reactivity, it is essentially only found in compounds. Three minerals exist that are industrially relevant sources: fluorite, fluorapatite, and cryolite.
Fluorite (CaF2), also called fluorspar or Blue John, is the main source of commercial fluorine. Fluorite is a colorful mineral associated with hydrothermal deposits. It is common and found worldwide. China supplies more than half of the world's demand; Mexico is the second-largest producer. The United States produced most of the world's fluorite in the early 20th century, but the last mine, in Illinois, shut down in 1995.
Fluorapatite (Ca5(PO4)3F) is mined along with other apatites for its phosphate content and is used mostly for production of fertilizers. Most of the Earth's fluorine is bound in this mineral, but because the percentage within the mineral is low (3.5%), the fluorine is discarded as waste. Only in the United States is there significant recovery. There the hexafluorosilicates produced as byproducts are used to supply municipal water fluoridation.
Cryolite (Na3AlF6) is the least abundant of the three, but is a concentrated source of fluorine. It was formerly used directly in aluminium production. However, the main commercial mine, on the west coast of Greenland, closed in 1987.Several other minerals, such as the gemstone topaz, contain fluoride. Fluoride is not significant in seawater or brines, unlike the other halides, because the alkaline earth fluorides precipitate out of water.
Organofluorines have been observed in volcanic eruptions and in geothermal springs. Their ultimate origin is said to vary from physical formation under geological conditions to initial biological production and deposition in sediments. However, the provenance is still being studied, as is the natural organofluorine distribution. They are not found in large quantites (compare also the number of known natural organofluorines, 30, to that of organochlorines, 2150), so they are not commercially important source of fluorine.
The possibility of small amounts of gaseous fluorine within crystals has been debated for many years. One form of fluorite, antozonite, has a smell suggestive of fluorine when crushed. The mineral also has a dark black color, perhaps from free calcium (not bonded to fluoride). In 2012, a study reported detection of trace quantities (0.04% by weight) of diatomic fluorine in antozonite. It was suggested that radiation from small amounts of uranium within the crystals had caused the free fluorine defects.
| Symbol | F | |
| Atomic Number | 9 | |
| Atomic Weight | 18.998403 | |
| Oxidation States | -1 | |
| Electronegativity, Pauling | 3.98 | |
| State at RT | Gas, Nonmetal | |
| Melting Point, K | 53.53 | |
| Boiling Point, K | 85.01 |
Interesting Facts about Fluorine
- Henri Moissan, who first isolated fluorine, also produced the world’s first artificial diamonds by applying huge pressures to charcoal.
- Fluorine is the most chemically reactive element. It reacts, often very vigorously, with all of the other elements except oxygen, helium, neon and krypton.
- Fluorine is the most electronegative element. This means that in molecules fluorine attracts electrons more powerfully than any other element can.
- Hydrofluoric acid, HF, dissolves glass. Its fluoride ions have a high affinity for calcium and can cause death by interfering with the body’s blood calcium metabolism when absorbed through the skin.
Appearance and Characteristics
Harmful effects:
Fluorine is highly toxic and corrosive.
Characteristics:
- Fluorine is the most reactive and the most electronegative of all the elements.
- Fluorine is a pale yellow, diatomic, highly corrosive, flammable gas, with a pungent odor. It is the lightest halogen.
- It reacts violently with water to produce oxygen and the extremely corrosive hydrofluoric acid.
Uses of Fluorine
- Fluorine and its compounds – mostly uranium hexafluoride – are used in processing nuclear fuel.
- Fluorochemicals, including many high-temperature plastics such as Teflon, are also made using fluorine.
- Compounds of fluorine, including sodium fluoride, are used in toothpaste and in drinking water to prevent dental cavities.
- Hydrofluoric acid can dissolve glass and is used to etch the glass in light bulbs and in other products.
- Chlorofluorocarbons (CFCs) were used in as refrigerants in air conditioning units and freezers but they have now been banned because they contribute to ozone depletion.
Fluorine gas, when it contacts other chemicals, results in flames.
Fluorine gas is so reactive that when it flows onto a brick, the brick ignites!
