Fluorine is a chemical element (symbol F, atomic number 9), non-metal, which belongs to the group of halogens. It is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is a pale yellow poisonous gas with the formula F2. Like other halides, molecular fluorine is very dangerous and causes severe chemical burns on contact with the skin.
Use
Fluorine and its compounds are widely used, including for the production of pharmaceuticals, agrochemicals, fuels and lubricants and textiles. Hydrofluoric acid is used to etch glass, while fluorine plasma is used to produce semiconductors and other materials. Low concentrations of F ions in toothpaste and drinking water may help prevent dental caries, while higher concentrations are found in some insecticides. Many general anesthetics are hydrofluorocarbon derivatives. The isotope 18F is a source of positrons for obtaining medicalpositron emission tomography imaging, and uranium hexafluoride is used to separate uranium isotopes and produce enriched uranium for nuclear power plants.
Discovery history
Minerals containing fluorine compounds were known many years before the isolation of this chemical element. For example, the mineral fluorspar (or fluorite), consisting of calcium fluoride, was described in 1530 by George Agricola. He noticed that it could be used as a flux, a substance that helps lower the melting point of a metal or ore and helps purify the desired metal. Therefore, fluorine got its Latin name from the word fluere (“flow”).
In 1670, glass blower Heinrich Schwanhard discovered that glass was etched by the action of calcium fluoride (fluorspar) treated with acid. Carl Scheele and many later researchers, including Humphry Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Thénard, experimented with hydrofluoric acid (HF), which was easily obtained by treating CaF with concentrated sulfuric acid.
In the end, it became clear that HF contained a previously unknown element. However, due to its excessive reactivity, this substance could not be isolated for many years. It is not only difficult to separate from compounds, but it immediately reacts with their other components. The isolation of elemental fluorine from hydrofluoric acid is extremely dangerous, and early attempts blinded and killed several scientists. These people became known as the martyrsfluorine.”
Discovery and production
Finally, in 1886, the French chemist Henri Moissan managed to isolate fluorine by electrolysis of a mixture of molten potassium fluorides and hydrofluoric acid. For this he was awarded the 1906 Nobel Prize in Chemistry. His electrolytic approach continues to be used today for the industrial production of this chemical element.
The first large-scale production of fluorine began during World War II. It was required for one of the stages of creating an atomic bomb as part of the Manhattan Project. Fluorine was used to produce uranium hexafluoride (UF6), which in turn was used to separate the two isotopes 235U andfrom each other 238U. Today, gaseous UF6 is needed to produce enriched uranium for nuclear power.
The most important properties of fluorine
In the periodic table, the element is at the top of group 17 (formerly group 7A), which is called halogen. Other halogens include chlorine, bromine, iodine and astatine. In addition, F is in the second period between oxygen and neon.
Pure fluorine is a corrosive gas (chemical formula F2) with a characteristic pungent odor that is found at a concentration of 20 nl per liter of volume. As the most reactive and electronegative of all elements, it easily forms compounds with most of them. Fluorine is too reactive to exist in elemental form and has suchaffinity with most materials, including silicon, that it cannot be prepared or stored in glass containers. In humid air, it reacts with water to form the equally dangerous hydrofluoric acid.
Fluorine, interacting with hydrogen, explodes even at low temperatures and in the dark. It reacts violently with water to form hydrofluoric acid and oxygen gas. Various materials, including finely dispersed metals and glasses, burn with a bright flame in a jet of gaseous fluorine. In addition, this chemical element forms compounds with the noble gases krypton, xenon and radon. However, it does not react directly with nitrogen and oxygen.
Despite the extreme activity of fluorine, methods for its safe handling and transportation have now become available. The element can be stored in steel or monel (nickel-rich alloy) containers, as fluorides form on the surface of these materials, which prevent further reaction.
Fluorides are substances in which fluorine is present as a negatively charged ion (F-) in combination with some positively charged elements. Fluorine compounds with metals are among the most stable s alts. When dissolved in water, they are divided into ions. Other forms of fluorine are complexes, for example, [FeF4]-, and H2F +.
Isotopes
There are many isotopes of this halogen, ranging from 14F to 31F. But the isotopic composition of fluorine includes only one of them,19F, which contains 10 neutrons, since it is the only one that is stable. The radioactive isotope 18F is a valuable source of positrons.
Biological impact
Fluorine in the body is mainly found in bones and teeth in the form of ions. Fluoridation of drinking water at a concentration of less than one part per million significantly reduces the incidence of caries - according to the National Research Council of the National Academy of Sciences of the United States. On the other hand, excessive accumulation of fluoride can lead to fluorosis, which manifests itself in mottled teeth. This effect is usually observed in areas where the content of this chemical element in drinking water exceeds a concentration of 10 ppm.
Elemental fluorine and fluoride s alts are toxic and should be handled with great care. Contact with skin or eyes should be carefully avoided. The reaction with the skin produces hydrofluoric acid, which quickly penetrates the tissues and reacts with the calcium in the bones, permanently damaging them.
Environmental fluorine
The annual world production of the mineral fluorite is about 4 million tons, and the total capacity of explored deposits is within 120 million tons. The main mining areas for this mineral are Mexico, China and Western Europe.
Fluorine occurs naturally in the earth's crust, where it can be found in rocks, coal and clay. Fluorides are released into the air by wind erosion of soils. Fluorine is the 13th most abundant chemical element in the earth's crust - its contentequals 950 ppm. In soils, its average concentration is about 330 ppm. Hydrogen fluoride can be released into the air as a result of industrial combustion processes. Fluorides that are in the air end up falling onto the ground or into the water. When fluorine forms a bond with very small particles, it can remain in the air for long periods of time.
In the atmosphere, 0.6 billionths of this chemical element is present in the form of s alt fog and organic chlorine compounds. In urban areas, the concentration reaches 50 parts per billion.
Connections
Fluorine is a chemical element that forms a wide range of organic and inorganic compounds. Chemists can replace hydrogen atoms with it, thereby creating many new substances. Highly reactive halogen forms compounds with noble gases. In 1962, Neil Bartlett synthesized xenon hexafluoroplatinate (XePtF6). Krypton and radon fluorides have also been obtained. Another compound is argon fluorohydride, which is stable only at extremely low temperatures.
Industrial applications
In its atomic and molecular state, fluorine is used for plasma etching in the production of semiconductors, flat panel displays, and microelectromechanical systems. Hydrofluoric acid is used to etch glass in lamps and other products.
Along with some of its compounds, fluorine is an important component in the production of pharmaceuticals, agrochemicals, fuels and lubricantsmaterials and textiles. The chemical element is needed to produce halogenated alkanes (halons), which, in turn, were widely used in air conditioning and refrigeration systems. Later, such use of chlorofluorocarbons was banned because they contribute to the destruction of the ozone layer in the upper atmosphere.
Sulfur hexafluoride is an extremely inert, non-toxic gas that is classified as a greenhouse gas. Without fluorine, the production of low friction plastics such as Teflon is not possible. Many anesthetics (eg sevoflurane, desflurane and isoflurane) are CFC derivatives. Sodium hexafluoroaluminate (cryolite) is used in aluminum electrolysis.
Fluoride compounds, including NaF, are used in toothpastes to prevent tooth decay. These substances are added to municipal water supplies to provide water fluoridation, however the practice is considered controversial due to the impact on human he alth. At higher concentrations, NaF is used as an insecticide, especially for cockroach control.
In the past, fluorides were used to lower the melting point of metals and ores and increase their fluidity. Fluorine is an important component in the production of uranium hexafluoride, which is used to separate its isotopes. 18F, a radioactive isotope with a half-life of 110 minutes, emits positrons and is often used in medical positron emission tomography.
Physical properties of fluorine
Basic characteristicschemical element as follows:
- Atomic mass 18.9984032 g/mol.
- Electronic configuration 1s22s22p5.
- Oxidation state -1.
- Density 1.7 g/L.
- Melting point 53.53 K.
- Boiling Point 85.03 K.
- Heat capacity 31.34 J/(K mol).
