Fluorine is a chemical element (symbol F, atomic number 9), non-metal, which belongs to the group of halogens. This is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is a pale yellow poisonous gas with the formula F 2 . Like other halogens, molecular fluoride is very dangerous and causes severe chemical burns when in contact with the skin.
Using
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, and fluorine plasma is used to produce semiconductor and other materials. Low concentrations of F ions in toothpaste and drinking water can help prevent tooth decay, while higher concentrations are found in some insecticides. Many common anesthetics are derivatives of fluorocarbons. The 18 F isotope is a positron source for medical imaging using positron emission tomography, and uranium hexafluoride is used to separate uranium isotopes and produce enriched uranium for nuclear power plants.
Discovery story
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 noted that it can be used as a flux, a substance that helps lower the melting point of a metal or ore and helps to clean the desired metal. Therefore, the name fluorine received its Latin name from the word fluere ("flow").
In 1670, glassblower Heinrich Schwanhard discovered that glass was etched by calcium fluoride (fluorspar) treated with acid. Karl Scheele and many later researchers, including Humphrey Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Tenard, experimented with hydrofluoric acid (HF), which was easy to obtain by treating CaF with concentrated sulfuric acid.
In the end, it became clear that HF contains a previously unknown element. This substance, however, could not be isolated for many years due to its excessive reactivity. It is not only difficult to separate from the 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 "martyrs of fluoride."
Discovery and Production
Finally, in 1886, the French chemist Henri Moissan was able 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 the Second World War. It was required for one of the stages of creating an atomic bomb in the framework of the Manhattan project. Fluorine was used to produce uranium hexafluoride (UF 6 ), which, in turn, was used to separate two isotopes 235 U and 238 U from each other. Today, gaseous UF 6 is needed to produce enriched uranium for nuclear power.
The most important properties of fluoride
In the periodic table, the element is located in the upper part of group 17 (former 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 F 2 ) with a characteristic pungent odor, which is detected 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 elementary form and has such an affinity for most materials, including silicon, that it cannot be prepared or stored in glass containers. In humid air, it reacts with water, forming no less dangerous hydrofluoric acid.
Fluorine, interacting with hydrogen, explodes even at low temperature and in the dark. It reacts violently with water, forming hydrofluoric acid and gaseous oxygen. Various materials, including finely divided metals and glasses, burn in a bright flame in a stream of gaseous fluorine. In addition, this chemical element forms compounds with 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 become available today. The element can be stored in containers made of steel or monel (nickel-rich alloy), since fluorides are formed on the surface of these materials, which prevent further reaction.
Fluorides are substances in which fluoride is present as a negatively charged ion (F - ) in combination with some positively charged elements. Fluorine compounds with metals are one of the most stable salts. When dissolved in water, they are divided into ions. Other forms of fluorine are complexes, for example, [FeF 4 ] - , and H 2 F + .
Isotopes
There are many isotopes of this halogen, ranging from 14 F to 31 F. But the fluorine isotopic composition includes only one of them, 19 F, which contains 10 neutrons, since only it is stable. The 18 F radioactive isotope is a valuable source of positrons.
Biological impact
Fluoride 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 US National Academy of Sciences. On the other hand, excessive accumulation of fluoride can lead to fluorosis, which manifests itself in mottling of the teeth. This effect is usually observed in areas where the content of a given chemical element in drinking water exceeds a concentration of 10 ppm.
Elementary fluoride and fluoride salts 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 tissues and reacts with calcium in the bones, damaging them permanently.
Fluoride in the environment
The annual global production of fluorite mineral is about 4 million tons, and the total capacity of explored deposits is in the range of 120 million tons. The main areas of production of this mineral are Mexico, China and Western Europe.
In nature, fluorine is found in the earth's crust, where it can be found in rocks, coal and clay. Fluorides fall into the air during wind erosion of soils. Fluorine is the 13th most abundant chemical element in the earth's crust - its content is 950 ppm. In soils, its average concentration is approximately 330 ppm. Hydrogen fluoride can be released into the air as a result of combustion processes in industry. The fluorides that are in the air eventually fall to the ground or to the water. When fluorine forms a bond with very small particles, it can remain in the air for a long period of time.
In the atmosphere, 0.6 billionths of a given chemical element is present in the form of salt fog and organic chlorine compounds. In urban environments, the concentration reaches 50 parts per billion.
Connections
Fluoride is a chemical element that forms a wide range of organic and inorganic compounds. Chemists can replace them with hydrogen atoms, 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 fluoride, stable only at extremely low temperatures.
Industrial application
In the atomic and molecular state, fluorine is used for plasma etching in the production of semiconductors, flat 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 lubricants and textiles. A chemical element is needed to produce halogenated alkanes (halons), which, in turn, have been widely used in air conditioning and cooling systems. Later, this use of chlorofluorocarbons was banned, since they contribute to the destruction of the ozone layer in the upper atmosphere.
Sulfur hexafluoride is an extremely inert, non-toxic gas related to substances causing a greenhouse effect. Without fluoride, plastics with a low coefficient of friction, such as Teflon, cannot be produced. Many anesthetics (e.g., sevoflurane, desflurane and isoflurane) are derivatives of fluorocarbons. Sodium hexafluoroaluminate (cryolite) is used in the electrolysis of aluminum.
Fluoride compounds, including NaF, are used in toothpastes to prevent tooth decay. These substances are added to municipal water supply systems for fluoridation of water, but this practice is considered controversial due to human health effects. At higher concentrations, NaF is used as an insecticide, especially for cockroach control.
In the past, fluorides have been used to lower the melting point of metals and ores and increase their fluidity. Fluorine is an important component of the production of uranium hexafluoride, which is used to separate its isotopes. 18 F, a radioactive isotope with a half-life of 110 minutes, emits positrons and is often used in medical positron emission tomography.
Physical properties of fluoride
The basic characteristics of a chemical element are as follows:
- Atomic mass of 18.9984032 g / mol.
- Electronic configuration 1s 2 2s 2 2p 5 .
- The oxidation state is -1.
- Density 1.7 g / l.
- Melting point 53.53 K.
- Boiling point 85.03 K.
- The heat capacity is 31.34 J / (K mol).