Fluoride is what? Properties of fluorine

Fluorine is a chemical element (symbol F, atomic number 9), a non-metal that belongs to the halogen group. This is the most active and electronegative substance. At normal temperature and pressure, the fluorine molecule is a poisonous gas of pale yellow color with the formula F ₂ . Like other halogens, molecular fluoride is very dangerous and, when in contact with the skin, causes severe chemical burns.

Using

Fluorine and its compounds are widely used, including for the production of pharmaceuticals, agrochemicals, fuels and lubricants and textiles. Hydrofluoric acid is used for etching glass, and plasma from fluorine is used for the production of semiconductor and other materials. Low concentrations of F ions in toothpaste and drinking water can help prevent dental caries, while higher concentrations are part of some insecticides. Many common anesthetics are derivatives of hydrofluorocarbons. Isotope ¹⁸ F is a source of positrons for obtaining medical images by positron emission tomography, and uranium hexafluoride is used to separate uranium isotopes and to obtain enriched uranium for nuclear power plants.

History of the discovery

Minerals containing fluorine compounds were known many years before the release of this chemical element. For example, a mineral fluorspar (or fluorite), consisting of calcium fluoride, was described in 1530 by George Agricola. He noticed that it can be used as a flux - a substance that helps lower the melting point of metal or ore and helps to clean the desired metal. Therefore fluorine the name its Latin name received from the word fluere ("leak").

In 1670, the glassblower Heinrich Schwanhard found that the glass was etched under the influence of calcium fluoride (fluorspar) treated with acid. Karl Scheele and many later researchers, including Humphry Davy, Joseph-Louis Gay-Lussac, Antoine Lavoisier, Louis Tenar, were experimenting 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, because of its excessive reactivity for many years could not be identified. It is not only difficult to separate from compounds, but it immediately reacts with 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 "martyrs of fluoride".

Opening and production

Finally, in 1886, the French chemist Henri Moissan succeeded in isolating fluorine by electrolysis of a mixture of molten potassium fluorides and hydrofluoric acid. For this he was awarded the Nobel Prize in 1906 in the field of chemistry. Its electrolytic approach continues to be used today for the industrial production of this chemical element.

The first large-scale production of fluoride began during the Second World War. It was required for one of the stages of the creation of the 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 the 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 in the upper part of group 17 (the 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 elemental form and has such an affinity with most materials, including silicon, that it can not be cooked or stored in glass containers. In humid air, it reacts with water, forming an equally dangerous hydrofluoric acid.

Fluorine, reacting with hydrogen, explodes even at low temperatures and in the dark. It reacts violently with water, forming hydrofluoric acid and gaseous oxygen. Various materials, including finely divided metals and glass, burn in a stream of fluorine gas with a bright flame. 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 fluoride, methods of its safe processing and transportation have become available today. The element can be stored in containers made of steel or a monel (nickel-rich alloy), since fluorides are formed 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. Compounds of fluorine 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. However, the fluorine isotopic composition includes only one of them, ¹⁹ F, which contains 10 neutrons, since only it is stable. The radioactive isotope ¹⁸ F 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 dramatically reduces the incidence of caries - according to the National Research Council of the National Academy of Sciences. On the other hand, excessive accumulation of fluoride can lead to fluorosis, which manifests itself in the mottle of the teeth. This effect is usually observed in areas where the content of this chemical element in drinking water exceeds the concentration of 10 ppm.

Elemental fluoride and fluoride salts are toxic and should be treated with great care. Contact with skin or eyes should be carefully avoided. Reaction with the skin produces hydrofluoric acid, which quickly penetrates through the tissues and reacts with calcium in the bones, damaging them forever.

Fluoride in the environment

The annual world production of fluorite mineral is about 4 million tons, and the total capacity of the explored deposits is within 120 million tons. The main mining areas for this mineral are Mexico, China and Western Europe.

In nature, fluoride is found in the earth's crust, where it can be found in rocks, coal and clay. Fluorides fall into the air with wind erosion of soils. Fluorine is the 13th most common chemical element in the earth's crust - its content is 950 ppm. In soils, its average concentration is about 330 ppm. Hydrogen fluoride can be released into the air as a result of combustion processes in industry. Fluorides that are in the air eventually fall to the ground or into 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 this chemical element is present as salt fog and organic chlorine compounds. In urban conditions, 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 them with hydrogen atoms, thereby creating a lot of new substances. Highly reactive halogen forms compounds with noble gases. In 1962, Neil Bartlett synthesized xenon hexafluoroplatinate (XePtF6). Fluorides of krypton and radon were also obtained. Another compound is argon fluoride, which is stable only at extremely low temperatures.

Industrial Applications

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 for etching glass in lamps and other products.

Along with some of its compounds, fluoride is an important component of the production of pharmaceuticals, agrochemicals, fuel and lubricants and textiles. The chemical element is necessary for the production of halogenated alkanes (halons), which, in turn, are widely used in air conditioning and cooling systems. Later, such use of chlorofluorocarbons was prohibited, as 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 that cause a greenhouse effect. Without fluorine, it is not possible to produce low -friction plastics , such as Teflon. Many anesthetics (for example, sevoflurane, desflurane and isoflurane) are derivatives of hydrofluorocarbons. Sodium hexafluoroaluminuminate (cryolite) is used in the electrolysis of aluminum.

Fluorine compounds, including NaF, are used in toothpaste to prevent caries. These substances are added to municipal water supply systems for water fluoridation, but due to health effects, this practice is controversial. At higher concentrations, NaF is used as an insecticide, especially for controlling cockroaches.

In the past, fluorides were used to reduce 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 fluorine

The basic characteristics of the chemical element are as follows:

• The atomic weight is 18,9984032 g / mol.
• Electronic configuration 1s ² 2s ² 2p ⁵ _.
• Degree of oxidation -1.
• The density is 1.7 g / l.
• Melting point 53.53 K.
• The boiling point is 85.03 K.
• The specific heat is 31.34 J / (K · mol).