Boiling point of carbon. Features of the structure of the carbon atom. Carbon and its main inorganic compounds

Carbon (from Latin: carbo "coal") is a chemical element with the symbol C and atomic number 6. Four electrons are available to form covalent chemical bonds. The substance is non-metallic and tetravalent. Three isotopes of carbon occur naturally, 12C and 13C are stable, and 14C is a decaying radioactive isotope with a half-life of about 5,730 years. Carbon is one of the few elements known since ancient times. Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass, after hydrogen, helium and oxygen. The abundance of carbon, its unique diversity organic compounds and him unusual ability form polymers at temperatures typically found on Earth, allowing this element to serve as a common element to all known life forms. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen. Carbon atoms can bond in different ways, called allotropes of carbon. The most well-known allotropes are graphite, diamond and amorphous carbon. The physical properties of carbon vary widely depending on the allotropic form. For example, graphite is opaque and black, while diamond is very transparent. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν", meaning "to write"), while diamond is the hardest material known in nature. Graphite is good electrical conductor, and diamond has low electrical conductivity. Under normal conditions, diamond, carbon nanotubes and graphene have the highest thermal conductivity of any known material. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically stable and require high temperatures to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, and +2 in carboxyl complexes of carbon monoxide and a transition metal. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant amounts come from organic deposits of coal, peat, petroleum and methane clathrates. Carbon forms a huge number of compounds, more than any other element, with almost ten million compounds described to date, and yet this number is only a fraction of the number of compounds theoretically possible under standard conditions. For this reason, carbon is often referred to as the "king of the elements".

Characteristics

Allotropes of carbon include graphite, one of the softest substances known, and diamond, the hardest natural substance. Carbon readily bonds with other small atoms, including other carbon atoms, and is capable of forming numerous stable covalent bonds with suitable multivalent atoms. Carbon is known to form almost ten million different compounds, the vast majority of all chemical compounds. Carbon also has the most high point sublimation among all elements. At atmospheric pressure, it has no melting point since its triple point is 10.8 ± 0.2 MPa and 4600 ± 300 K (~4330 °C or 7820 °F), so it sublimes at about 3900 K. Graphite is much more reactive than diamond under standard conditions, despite being more thermodynamically stable, since its delocalized pi system is much more vulnerable to attack. For example, graphite can be oxidized with hot concentrated nitric acid under standard conditions to mellitic acid C6(CO2H)6, which retains the hexagonal units of graphite while destroying the larger structure. Carbon sublimes in a carbon arc whose temperature is about 5,800 K (5,530 °C, 9,980 °F). Thus, regardless of its allotropic form, carbon remains solid at temperatures higher than the highest melting points such as tungsten or rhenium. Although carbon is thermodynamically prone to oxidation, it is more resistant to oxidation than elements such as iron and copper, which are weaker reducing agents at room temperature. Carbon is the sixth element with a ground state electronic configuration of 1s22s22p2, of which the outer four electrons are valence electrons. Its first four ionization energies are 1086.5, 2352.6, 4620.5 and 6222.7 kJ/mol, much higher than the heavier group 14 elements. Carbon's electronegativity is 2.5, significantly higher than the heavier ones elements of group 14 (1.8-1.9), but is close to most neighboring non-metals, as well as some transition metals of the second and third row. Covalent radii of carbon are generally taken to be 77.2 pm (C-C), 66.7 pm (C=C), and 60.3 pm (C≡C), although these can vary depending on the coordination number and what is bonded to carbon. In general, the covalent radius decreases as the coordination number decreases and the bond order increases. Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy released by the Sun and other stars. Although carbon forms an extraordinary variety of compounds, most forms of carbon are relatively unreactive under normal conditions. At standard temperatures and pressures, carbon can withstand all but the strongest oxidizing agents. It does not react with sulfuric acid, hydrochloric acid, chlorine or alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon oxides and removes oxygen from metal oxides, leaving the elemental metal. This exothermic reaction is used in the iron and steel industry to smelt iron and control the carbon content of steel:

Fe3O4 + 4 C (s) → 3 Fe (s) + 4 CO (g)

with sulfur to form carbon disulfide and with steam in the coal-gas reaction:

C(s) + H2O(g) → CO(g) + H2(g)

Carbon combines with certain metals at high temperatures to form metal carbides, such as cementite from iron carbide in steel and tungsten carbide, widely used as an abrasive and to make hard points for cutting tools. The system of carbon allotropes covers a number of extremes:

Some forms of graphite are used for thermal insulation (such as fire barriers and heat shields), but some other forms are good thermal conductors. Diamond is the most famous natural heat conductor. Graphite is opaque. Diamond is very transparent. Graphite crystallizes in the hexagonal system. Diamond crystallizes in the cubic system. Amorphous carbon is completely isotropic. Carbon nanotubes are one of the most famous anisotropic materials.

Allotropes of carbon

Atomic carbon is a very short-lived species and therefore carbon is stabilized in various polyatomic structures with different molecular configurations called allotropes. The three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Previously considered exotic, fullerenes are now commonly synthesized and used in research; these include buckyballs, carbon nanotubes, carbon nanodots and nanofibers. Several other exotic allotropes have also been discovered, such as lonsaletite, glassy carbon, nanofaum carbon, and linear acetylene carbon (carbyne). As of 2009, graphene is considered the strongest material ever tested. The process of separating it from graphite will require some further technological development before it becomes economical for industrial processes. If successful, graphene could be used in the construction of space elevators. It can also be used to safely store hydrogen for use in hydrogen-based engines in cars. The amorphous form is a collection of carbon atoms in a non-crystalline, irregular, glassy state rather than contained in a crystalline macrostructure. It is present in powder form and is the main component of substances such as charcoal, lamp soot (soot) and activated carbon. At normal pressures, carbon has the form of graphite, in which each atom is trigonally bonded by three other atoms in a plane consisting of fused hexagonal rings, as in aromatic hydrocarbons. The resulting network is two-dimensional, and the resulting flat sheets are folded and loosely connected through weak van der Waals forces. This gives graphite its softness and cleavage properties (sheets easily slide past each other). Due to the delocalization of one of the outer electrons of each atom to form a π cloud, graphite conducts electricity, but only in the plane of each covalently bonded sheet. This results in lower electrical conductivity for carbon than for most metals. Delocalization also explains the energetic stability of graphite over diamond at room temperature. At very high pressures, carbon forms a more compact allotrope, diamond, having almost twice the density of graphite. Here, each atom is tetrahedrally connected to four others, forming a three-dimensional network of wrinkled six-membered rings of atoms. Diamond has the same cubic structure as silicon and germanium, and due to the strength of its carbon-carbon bonds, it is the hardest natural substance, as measured by scratch resistance. Contrary to popular belief that "diamonds are forever", they are thermodynamically unstable under normal conditions and turn into graphite. Due to the high activation energy barrier, the transition to the graphite form is so slow at normal temperatures that it is undetectable. Under certain conditions, carbon crystallizes as lonsalite, a hexagonal crystal lattice with all atoms covalently bonded and properties similar to those of diamond. Fullerenes are a synthetic crystalline formation with a graphite-like structure, but instead of hexagons, fullerenes are composed of pentagons (or even heptagons) of carbon atoms. Missing (or extra) atoms deform the sheets into spheres, ellipses, or cylinders. The properties of fullerenes (divided into buckyballs, bakitubes and nanobads) have not yet been fully analyzed and represent an intensive area of ​​nanomaterials research. The names "fullerene" and "buckyball" are associated with the name of Richard Buckminster Fuller, the popularizer of geodesic domes, which resemble the structure of fullerenes. Buckyballs are fairly large molecules formed entirely from carbon bonds in a trigonal manner, forming spheroids (the most famous and simplest is the football-shaped buckynysterfellerene C60). Carbon nanotubes are structurally similar to buckyballs, except that each atom is trigonally bonded in a curved sheet that forms a hollow cylinder. Nanoballs were first introduced in 2007 and are hybrid materials (buckyballs are covalently bonded to the outer wall of a nanotube) that combine the properties of both in one structure. Of the other allotropes discovered, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a cluster assembly of low-density carbon atoms stretched together into a loose three-dimensional network in which the atoms are trigonally linked in six- and seven-membered rings. It is among the lightest solids with a density of about 2 kg/m3. Likewise, glassy carbon contains a high proportion of closed porosity, but unlike regular graphite, the graphite layers are not stacked like pages in a book, but are more randomly arranged. Linear acetylene carbon has the chemical structure - (C:::C)n-. Carbon in this modification is linear with sp orbital hybridization and is a polymer with alternating single and triple bonds. This carbyne is of significant interest for nanotechnology because its Young's modulus is forty times greater than that of the hardest material, diamond. In 2015, a team from the University of North Carolina announced the development of another allotrope, which they called Q-carbon, created by a high-energy, low-duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, fluorescence, and have a hardness superior to diamonds.

Prevalence

Carbon is the fourth most abundant chemical element in the universe by mass, after hydrogen, helium and oxygen. Carbon is abundant in the Sun, stars, comets and the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. Microscopic diamonds can also form under intense pressure and high temperature in areas of meteorite impact. In 2014, NASA announced an updated database to track polycyclic aromatic hydrocarbons (PAHs) in the Universe. More than 20% of the carbon in the universe can be associated with PAHs, complex compounds of carbon and hydrogen without oxygen. These compounds feature in the global PAH hypothesis, where they are hypothesized to play a role in abiogenesis and the formation of life. PAHs appear to have been formed "a couple of billion years" after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets. The Earth's crust as a whole is estimated to contain 730 ppm of carbon, with 2,000 ppm contained in the core and 120 ppm in the combined mantle and crust. Since the mass of the earth is 5.9 72 × 1024 kg, this would mean 4360 million gigatons of carbon. This is much more than the amount of carbon in the oceans or atmosphere (below). Combined with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatons of carbon) and dissolved in all bodies of water (approximately 36,000 gigatons of carbon). There are about 1,900 gigatons of carbon in the biosphere. Hydrocarbons (such as coal, oil and natural gas) also contain carbon. Coal "reserves" (not "resources") are about 900 gigatons with perhaps 18,000 Gt of resources. Oil reserves amount to about 150 gigatons. Proven sources of natural gas are about 175,1012 cubic meters (containing about 105 gigatons of carbon), but studies estimate another 900,1012 cubic meters from “unconventional” deposits such as shale gas, amounting to about 540 gigatons of carbon. Carbon has also been found in methane hydrates in polar regions and under the seas. According to various estimates, the amount of this carbon is 500, 2500 Gt, or 3000 Gt. In the past, the amount of hydrocarbons was greater. According to one source, between 1751 and 2008, about 347 gigatons of carbon were released into the atmosphere as carbon dioxide into the atmosphere from burning fossil fuels. Another source adds the amount added to the atmosphere since 1750 to 879 Gt, and the total amount in the atmosphere, sea and land (e.g. peat bogs) is almost 2000 Gt. Carbon is integral part(12% by mass) of very large masses of carbonate rocks (limestone, dolomite, marble, etc.). Coal contains very high amounts of carbon (anthracite contains 92-98% carbon) and is the largest commercial source of mineral carbon, accounting for 4,000 gigatons or 80% of fossil fuels. As for individual allotropes of carbon, graphite is found in large quantities in the United States (mainly New York and Texas), Russia, Mexico, Greenland and India. Natural diamonds are found in rock kimberlite contained in ancient volcanic “necks” or “chimneys”. Most diamond deposits are found in Africa, especially South Africa, Namibia, Botswana, Republic of Congo and Sierra Leone. Diamond deposits have also been found in Arkansas, Canada, the Russian Arctic, Brazil, and Northern and Western Australia. Diamonds are also now being recovered from the ocean floor off the Cape of Good Hope. Diamonds occur naturally, but now produce about 30% of all industrial diamonds used in the United States. Carbon-14 is formed in the upper troposphere and stratosphere at altitudes of 9-15 km in a reaction that is deposited by cosmic rays. Thermal neutrons are produced and collide with nitrogen-14 nuclei to form carbon-14 and a proton. Thus, 1.2 × 1010% of atmospheric carbon dioxide contains carbon-14. Carbon-rich asteroids are relatively dominant in the outer parts of the asteroid belt in our solar system. These asteroids have not yet been directly examined by scientists. Asteroids could be used in hypothetical space-based coal mining, which may be possible in the future but is currently technologically impossible.

Carbon isotopes

Carbon isotopes are atomic nuclei that contain six protons plus a number of neutrons (2 to 16). Carbon has two stable, naturally occurring isotopes. The isotope carbon-12 (12C) forms 98.93% of carbon on Earth, and carbon-13 (13C) forms the remaining 1.07%. The concentration of 12C increases further in biological materials because biochemical reactions discriminate against 13C. In 1961, the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope carbon-12 as the basis for atomic weights. Carbon identification in nuclear magnetic resonance (NMR) experiments is carried out with the isotope 13C. Carbon-14 (14C) is a naturally occurring radioisotope created in the upper atmosphere (lower stratosphere and upper troposphere) by the interaction of nitrogen with cosmic rays. It is found in trace amounts on Earth in amounts up to 1 part per trillion (0.0000000001%), mainly in the atmosphere and surface sediments, particularly peat and other organic materials. This isotope decays during β-emission of 0.158 MeV. Due to its relatively short half-life of 5,730 years, 14C is virtually absent from ancient rocks. In the atmosphere and in living organisms, the amount of 14C is almost constant, but decreases in organisms after death. This principle is used in radiocarbon dating, invented in 1949, which has been widely used to date carbonaceous materials up to 40,000 years old. There are 15 known isotopes of carbon and the shortest-lived is 8C, which decays through proton emission and alpha decay and has a half-life of 1.98739 x 10-21 s. Exotic 19C exhibits a nuclear halo, meaning its radius is significantly larger than would be expected if the core were a sphere of constant density.

Education in the Stars

The formation of a carbon atomic nucleus requires a nearly simultaneous triple collision of alpha particles (helium nuclei) within the core of a giant or supergiant star, which is known as the triple alpha process, since the products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium -8 respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei. This occurs under conditions of temperatures greater than 100 megacalvin and helium concentrations, which are unacceptable in the rapid expansion and cooling of the early Universe, and therefore no significant amounts of carbon were created during the Big Bang. According to modern theory physical cosmology, carbon is formed inside stars in the horizontal branch by the collision and transformation of three helium nuclei. When these stars die as supernovae, the carbon is dispersed into space as dust. This dust becomes the building material for the formation of second or third generation star systems with accreted planets. solar system is one of those carbon-rich star systems that allows life as we know it to exist. The CNO cycle is an additional fusion mechanism that drives stars where carbon acts as a catalyst. Rotational transitions of various isotopic forms of carbon monoxide (such as 12CO, 13CO and 18CO) are detected in the submillimeter wavelength range and are used in the study of newly forming stars in molecular clouds.

Carbon cycle

Under terrestrial conditions, the conversion of one element to another is a very rare phenomenon. Therefore, the amount of carbon on Earth is effectively constant. Thus, in processes that use carbon, it must be obtained from somewhere and utilized somewhere else. Carbon pathways in environment form the carbon cycle. For example, photosynthetic plants extract carbon dioxide from the atmosphere (or seawater) and build it into biomass, as in the Calvin cycle, the process of carbon fixation. Some of this biomass is eaten by animals, while some of the carbon is exhaled by animals as carbon dioxide. The carbon cycle is much more complex than this short cycle; for example, some carbon dioxide dissolves in the oceans; if bacteria don't consume it, dead plant or animal matter can become oil or coal, which releases carbon when burned.

Carbon compounds

Carbon can form very long chains of interlocking carbon-carbon bonds, a property called chain formation. Carbon-carbon bonds are stable. Thanks to catanation (chain formation), carbon forms countless compounds. Evaluation of unique compounds shows that more of them contain carbon. A similar statement can be made for hydrogen because most organic compounds also contain hydrogen. The simplest form of an organic molecule is a hydrocarbon, a large family of organic molecules that consist of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains, and functional groups influence the properties of organic molecules. Carbon occurs in all forms known organic life and is the basis organic chemistry. When combined with hydrogen, carbon forms various hydrocarbons that are important to industry as refrigerants, lubricants, solvents, chemical feedstocks for plastics and petroleum products, and as fossil fuels. When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds, including sugars, lignans, chitins, alcohols, fats and aromatics. esters, carotenoids and terpenes. With nitrogen, carbon forms alkaloids, and with the addition of sulfur it also forms antibiotics, amino acids and rubber products. With the addition of phosphorus to these other elements, it forms DNA and RNA, the carriers of the chemical code of life, and adenosine triphosphate (ATP), the most important energy transport molecule in all living cells.

Inorganic compounds

Typically, carbon-containing compounds that are associated with minerals or that do not contain hydrogen or fluorine are treated separately from classical organic compounds; this definition is not strict. Among them are simple carbon oxides. Most known oxide is carbon dioxide (CO2). This substance was once a major component of the paleoatmosphere, but today is a minor component of the Earth's atmosphere. When dissolved in water, this substance forms carbon dioxide (H2CO3), but, like most compounds with several monooxygens on one carbon, it is unstable. However, through this intermediate substance, resonant stabilized carbonate ions are formed. Some important minerals are carbonates, especially calcite. Carbon disulfide (CS2) is similar. Another common oxide is carbon monoxide (CO). It is formed during incomplete combustion and is a colorless, odorless gas. Each molecule contains a triple bond and is quite polar, which causes it to constantly bind to hemoglobin molecules, displacing oxygen, which has a lower binding affinity. Cyanide (CN-) has a similar structure but behaves like halide ions (pseudohalogen). For example, it can form the molecule cyanogen nitride (CN)2), similar to diatom halides. Other uncommon oxides are carbon suboxide (C3O2), unstable carbon monoxide (C2O), carbon trioxide (CO3), cyclopentane peptone (C5O5), cyclohexane hexone (C6O6), and mellitic anhydride (C12O9). With reactive metals such as tungsten, carbon forms either carbides (C4-) or acetylides (C2-2) to form alloys with high melting points. These anions are also associated with methane and acetylene, both of which are very weak acids. With an electronegativity of 2.5, carbon prefers to form covalent bonds. Several carbides are covalent lattices such as carborundum (SiC), which resembles diamond. However, even the most polar and saline carbides are not completely ionic compounds.

Organometallic compounds

Organometallic compounds, by definition, contain at least one carbon-metal bond. There is a wide range of such compounds; major classes include simple alkyl-metal compounds (eg, tetraethyl alide), η2-alkene compounds (eg, Zeise salt), and η3-allyl compounds (eg, allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands (eg ferrocene); and carbene complexes of transition metals. There are many metal carbonyls (eg tetracarbonylnickel); Some workers believe that the carbon monoxide ligand is a purely inorganic, rather than organometallic, compound. While carbon is thought to exclusively form four bonds, an interesting compound containing an octahedral hexacoordinate carbon atom has been reported. The cation of this compound is 2+. This phenomenon is explained by the aurophilicity of gold ligands. In 2016, hexamethylbenzene was confirmed to contain a carbon atom with six bonds rather than the usual four.

History and etymology

The English name carbon comes from the Latin carbo, meaning "coal" and "charcoal", hence the French word charbon, meaning "charcoal". In German, Dutch and Danish, the names for carbon are Kohlenstoff, koolstof and kulstof respectively, all literally meaning coal substance. Carbon was discovered in prehistoric times and was known in the forms of soot and charcoal in the earliest human civilizations. Diamonds were probably known as early as 2500 BC. in China, and carbon in the form of charcoal was made in Roman times by the same chemistry as today, by heating wood in a pyramid covered with clay to exclude air. In 1722, René Antoine Ferjo de Reamur demonstrated that iron was converted into steel through the absorption of a substance now known as carbon. In 1772, Antoine Lavoisier showed that diamonds are a form of carbon; when he burned samples of charcoal and diamond and discovered that neither produced any water, and that both substances released equal amounts of carbon dioxide per gram. In 1779, Karl Wilhelm Scheele showed that graphite, which was thought to be a form of lead, was instead identical to charcoal but with a small admixture of iron, and that it produced "air acid" (which is carbon dioxide) when oxidized with nitric acid. In 1786, French scientists Claude Louis Berthollet, Gaspard Monge, and C. A. Vandermonde confirmed that graphite was primarily carbon by oxidizing it in oxygen in much the same way as Lavoisier did with diamond. Some iron remained again, which French scientists believed was necessary for the structure of graphite. In their publication, they proposed the name carbone (Latin for carbonum) for the element in graphite that was released as a gas when graphite was burned. Antoine Lavoisier then listed carbon as an element in his 1789 textbook. A new allotrope of carbon, fullerene, which was discovered in 1985, includes nanostructured forms such as buckyballs and nanotubes. Their discoverers - Robert Curl, Harold Kroteau and Richard Smalley - received Nobel Prize in chemistry in 1996. The resulting renewed interest in new forms leads to the discovery of additional exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly amorphous.

Production

Graphite

Commercially viable natural graphite deposits occur in many parts of the world, but the most economically important sources are found in China, India, Brazil and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica and feldspars in schists, gneisses and metamorphosed sandstones and limestones as lenses or veins, sometimes several meters or more thick. The supply of graphite at Borrowdale, Cumberland, England, was initially of sufficient size and purity that until the 19th century pencils were made simply by sawing blocks of natural graphite into strips before gluing the strips into wood. Today, smaller deposits of graphite are produced by crushing the parent rock and floating the lighter graphite on water. There are three types of natural graphite - amorphous, flake or crystalline. Amorphous graphite is the lowest quality and is the most common. Unlike in science, in industry "amorphous" refers to a very small crystal size rather than a complete lack of crystalline structure. The word "amorphous" is used to describe products with a low amount of graphite and is the cheapest graphite. Large deposits of amorphous graphite are located in China, Europe, Mexico and the USA. Flat graphite is less common and of higher quality than amorphous; it appears as individual plates that crystallize in metamorphic rocks. The price of granular graphite can be four times higher than the price of amorphous graphite. Flake graphite good quality can be processed into expandable graphite for many applications such as fire retardants. Primary deposits of graphite are found in Austria, Brazil, Canada, China, Germany and Madagascar. Liquid or lump graphite is the rarest, most valuable and highest quality type of natural graphite. It is found in veins along intrusive contacts in hard pieces, and is only mined commercially in Sri Lanka. According to the USGS, global production of natural graphite in 2010 was 1.1 million tons, with China producing 800,000 tons, India 130,000 tons, Brazil 76,000 tons, North Korea 30,000 tons and Canada - 25,000 tons. No natural graphite was mined in the United States, but 118,000 tons of synthetic graphite were mined in 2009 with an estimated value of $998 million.

Diamond

The supply of diamonds is controlled by a limited number of businesses and is highly concentrated in a small number of locations around the world. Only a very small proportion of diamond ore consists of actual diamonds. The ore is crushed, during which care must be taken to prevent large diamonds from being destroyed in the process, and the particles are then sorted by density. Today, diamonds are mined into the diamond-rich fraction using X-ray fluorescence, after which the final sorting steps are carried out manually. Before distribution of use x-rays, separation was carried out using lubricating belts; It is known that diamonds were discovered only in alluvial deposits in southern India. It is known that diamonds are more likely to stick to the mass than other minerals in the ore. India was a leader in the production of diamonds from their discovery around the 9th century BC until the mid-18th century AD, but the commercial potential of these sources was exhausted by the end of the 18th century, and by then India had been overshadowed by Brazil, where the first diamonds were found in 1725. Diamond production of primary deposits (kimberlites and lamproites) began only in the 1870s, after the discovery of diamond deposits in South Africa. Diamond production has increased over time and a total of 4.5 billion carats have been accumulated since this date. About 20% of this amount has been produced in the last 5 years alone, and within the last ten years 9 new deposits have begun production, with another 4 waiting to be discovered soon. Most of these deposits are located in Canada, Zimbabwe, Angola and one in Russia. In the United States, diamonds have been discovered in Arkansas, Colorado and Montana. In 2004, the astonishing discovery of a microscopic diamond in the United States led to the release in January 2008 of a massive sampling of kimberlite pipes in a remote part of Montana. Today, most commercially viable diamond deposits are found in Russia, Botswana, Australia and Democratic Republic Congo. In 2005, Russia produced almost one-fifth of the world's diamond supply, according to the British Geological Survey. Australia's richest diamond pipe reached peak production levels of 42 metric tons (41 t; 46 short tons) per year in the 1990s. There are also commercial deposits, active production of which is carried out in the Northwest Territories of Canada, Siberia (mainly in Yakutia, for example, in the Mir Pipe and in the Udachnaya Pipe), in Brazil, as well as in Northern and Western Australia.

Applications

Carbon is essential for all known living systems. Without it, the existence of life as we know it is impossible. The main economic use of carbon, other than food and wood, is for hydrocarbons, primarily fossil fuels methane gas and crude oil. Crude oil is processed by oil refineries to produce gasoline, kerosene and other products. Cellulose is a natural carbon-containing polymer produced by plants in the form of wood, cotton, flax and hemp. Cellulose is used primarily to maintain the structure of plants. Commercially valuable animal-derived carbon polymers include wool, cashmere, and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain. The raw materials for many of these synthetics come from crude oil. The uses of carbon and its compounds are extremely diverse. Carbon can form alloys with iron, the most common of which is carbon steel. Graphite combines with clays to form the “lead” used in pencils used for writing and drawing. It is also used as a lubricant and pigment, as a molding material in glass making, in electrodes for dry cell batteries and electroplating and electroforming, in brushes for electric motors, and as a neutron moderator in nuclear reactors. Coal is used as a material for making art, as a barbecue grill, for smelting iron, and has many other uses. Wood, coal and oil are used as fuel for energy production and heating. High quality diamonds are used in jewelry making, and industrial diamonds are used for drilling, cutting, and polishing metal and stone working tools. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolyzing synthetic polyester fibers, is used to reinforce plastics to form advanced, lightweight composite materials. Carbon fiber is made by pyrolyzing extruded and stretched strands of polyacrylonitrile (PAN) and other organic substances. The crystal structure and mechanical properties of the fiber depend on the type source material and subsequent processing. Carbon fibers made from PAN have a structure that resembles narrow strands of graphite, but heat treatment can rearrange the structure into a continuous sheet. As a result, the fibers have a higher specific tensile strength than steel. Carbon black is used as a black pigment in printing inks, oil paint and artists' watercolors, carbon paper, automotive finishing, inks and laser printers. Carbon black is also used as a filler in rubber products such as tires and in plastic compounds. Activated carbon is used as an absorbent and adsorbent in filter media in applications as varied as gas masks, water purification and kitchen hoods, as well as in medicine to absorb toxins, poisons or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore into iron (smelting). Hardening of steel is achieved by heating finished steel components in carbon powder. Silicon, tungsten, boron and titanium carbides are among the hardest materials and are used as abrasives for cutting and grinding. Carbon compounds make up the majority of materials used in clothing, such as natural and synthetic textiles and leather, as well as almost all interior surfaces in environments other than glass, stone and metal.

Diamonds

The diamond industry is divided into two categories, one of which is high quality diamonds (gems) and the other is industrial grade diamonds. Although there is a large trade in both types of diamonds, the two markets operate very differently. Unlike precious metals such as gold or platinum, gemstone diamonds are not traded as a commodity: diamonds are sold at a significant premium and the resale market for diamonds is not very active. Industrial diamonds are valued primarily for their hardness and thermal conductivity, with the gemological qualities of clarity and color being largely irrelevant. About 80% of mined diamonds (equal to approximately 100 million carats or 20 tons per year) are unusable and are used in industry (diamond scrap). Synthetic diamonds, invented in the 1950s, found industrial applications almost immediately; 3 billion carats (600 tons) produced annually synthetic diamonds. The dominant industrial uses of diamond are cutting, drilling, grinding and polishing. Most of these applications do not require large diamonds; in fact, most gem quality diamonds, with the exception of small size diamonds, can be used industrially. Diamonds are inserted into drill bits or saw blades or ground into powder for use in grinding and polishing. Specialized applications include laboratory use as storage for high pressure experiments, high performance bearings, and limited use in specialty windows. Thanks to advances in synthetic diamond production, new applications are becoming feasible. Much attention has been paid to the possible use of diamond as a semiconductor suitable for microchips and, because of its exceptional thermal conductivity, as a heat sink in electronics.

CARBON, C (a. carbon; n. Kohlenstoff; f. carbone; i. carbono), - chemical element of group IV periodic table Mendeleev, atomic number 6, atomic mass 12.041. Natural carbon consists of a mixture of 2 stable isotopes: 12 C (98.892%) and 13 C (1.108%). There are also 6 radioactive isotopes of carbon, of which the most important is the 14 C isotope with a half-life of 5.73.10 3 years (this isotope is constantly formed in small quantities in the upper layers of the atmosphere as a result of irradiation of 14 N nuclei by neutrons from cosmic radiation).

Carbon has been known since ancient times. Wood was used to recover metals from ores, and diamond was used as a... The recognition of carbon as a chemical element is associated with the name of the French chemist A. Lavoisier (1789).

Carbon modifications and properties

There are 4 known crystalline modifications of carbon: graphite, diamond, carbyne and lonsdaleite, which differ greatly in their properties. Carbyne is an artificially produced variety of carbon, which is a finely crystalline black powder, the crystal structure of which is characterized by the presence of long chains of carbon atoms located parallel to each other. Density 3230-3300 kg/m3, heat capacity 11.52 J/mol.K. Lonsdaleite is found in meteorites and obtained artificially; its structure and physical properties have not been fully established. Carbon is also characterized by a state with a disordered structure - the so-called. amorphous carbon (soot, coke, charcoal). The physical properties of “amorphous” carbon largely depend on the dispersion of particles and the presence of impurities.

Chemical properties of carbon

In compounds, carbon has oxidation states +4 (the most common), +2 and +3. Under normal conditions, carbon is chemically inert; at high temperatures it combines with many elements, exhibiting strong restorative properties. The chemical activity of carbon decreases in the series “amorphous” carbon, graphite, diamond; interaction with atmospheric oxygen in these types of carbon occurs respectively at temperatures of 300-500°C, 600-700°C and 850-1000°C with the formation of carbon dioxide (CO 2) and carbon monoxide (CO). Dioxide dissolves in water to form carbonic acid. All forms of carbon are resistant to alkalis and acids. Carbon practically does not interact with halogens (except for graphite, which reacts with F2 above 900°C), so its halides are obtained indirectly. Among nitrogen-containing compounds, hydrogen cyanide HCN ( hydrocyanic acid) and its many derivatives. At temperatures above 1000°C, carbon reacts with many metals, forming carbides. All forms of carbon are insoluble in common inorganic and organic solvents.

The most important property of carbon is the ability of its atoms to form strong chemical bonds among themselves, as well as between themselves and other elements. The ability of carbon to form 4 equivalent valence bonds with other carbon atoms allows the construction of carbon skeletons of different types (linear, branched, cyclic); It is these properties that explain the exclusive role of carbon in the structure of all organic compounds and, in particular, all living organisms.

Carbon in nature

The average carbon content in the earth's crust is 2.3.10% (by mass); Moreover, the bulk of carbon is concentrated in sedimentary rocks (1%), while in other rocks there are significantly lower and approximately equal (1-3.10%) concentrations of this element. Carbon accumulates in the upper part, where its presence is associated mainly with living matter (18%), wood (50%), coal (80%), oil (85%), anthracite (96%), as well as dolomites and limestones. Over 100 carbon minerals are known, of which the most common are calcium, magnesium and iron carbonates (calcite CaCO 3, dolomite (Ca, Mg)CO 3 and siderite FeCO 3). The accumulation of carbon in the earth's crust is often associated with the accumulation of other elements that are sorbed by organic matter and precipitated after its burial at the bottom of reservoirs in the form of insoluble compounds. Large quantities of CO 2 dioxide are released into the atmosphere from the Earth during volcanic activity and during the combustion of organic fuels. From the atmosphere, CO 2 is absorbed by plants during the process of photosynthesis and dissolves in sea water, thereby forming the most important links in the overall carbon cycle on Earth. Important role carbon also plays in space; On the Sun, carbon ranks 4th in abundance after hydrogen, helium and oxygen, participating in nuclear processes.

Application and Use

The most important national economic importance of carbon is determined by the fact that about 90% of all primary sources of energy consumed by humans come from fossil fuels. There is a tendency to use oil not as fuel, but as a raw material for various chemical industries. A smaller, but nevertheless very significant role in national economy plays carbon, mined in the form of carbonates (metallurgy, construction, chemical production), diamonds (jewelry, technology) and graphite (nuclear technology, heat-resistant crucibles, pencils, some types of lubricants, etc.). By specific activity The 14 C isotope in remains of biogenic origin determines their age (radiocarbon dating method). 14 C is widely used as a radioactive tracer. The most common isotope 12 C is important - one twelfth of the mass of an atom of this isotope is taken as a unit of atomic mass of chemical elements.

The content of the article

CARBON, C (carboneum), a non-metallic chemical element of group IVA (C, Si, Ge, Sn, Pb) of the periodic table of elements. It is found in nature in the form of diamond crystals (Fig. 1), graphite or fullerene and other forms and is part of organic (coal, oil, animal and plant organisms, etc.) and inorganic substances(limestone, baking soda, etc.).

Carbon is widespread, but its content in the earth's crust is only 0.19%.

Carbon is widely used in the form of simple substances. In addition to precious diamonds, which are the subject of jewelry, great importance have industrial diamonds - for the manufacture of grinding and cutting tools.

Charcoal and other amorphous forms of carbon are used for decolorization, purification, gas adsorption, and in areas of technology where adsorbents with a developed surface are required. Carbides, compounds of carbon with metals, as well as with boron and silicon (for example, Al 4 C 3, SiC, B 4 C) are characterized by high hardness and are used for the manufacture of abrasive and cutting tools. Carbon is part of steels and alloys in the elemental state and in the form of carbides. Saturation of the surface of steel castings with carbon at high temperatures (cementation) significantly increases surface hardness and wear resistance. see also ALLOYS.

There are many different forms of graphite in nature; some are obtained artificially; There are amorphous forms (for example, coke and charcoal). Soot, bone char, lamp black, and acetylene black are formed when hydrocarbons are burned in the absence of oxygen. So-called white carbon obtained by sublimation of pyrolytic graphite under reduced pressure - these are tiny transparent crystals of graphite leaves with pointed edges.

Historical reference.

Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that graphite can be used to mark other materials, and the name “graphite” itself, which comes from the Greek word meaning “to write”, was proposed by A. Werner in 1789. However, the history of graphite is complicated; substances with similar external physical properties were often mistaken for it , such as molybdenite (molybdenum sulfide), at one time considered graphite. Other names for graphite include “black lead,” “iron carbide,” and “silver lead.” In 1779, K. Scheele established that graphite can be oxidized with air to form carbon dioxide.

Diamonds first found use in India, and in Brazil gems became commercially important in 1725; deposits in South Africa were discovered in 1867. In the 20th century. The main diamond producers are South Africa, Zaire, Botswana, Namibia, Angola, Sierra Leone, Tanzania and Russia. Man-made diamonds, the technology of which was created in 1970, are produced for industrial purposes.

Allotropy.

If the structural units of a substance (atoms for monoatomic elements or molecules for polyatomic elements and compounds) are able to combine with each other in more than one crystalline form, this phenomenon is called allotropy. Carbon has three allotropic modifications: diamond, graphite and fullerene. In diamond, each carbon atom has 4 tetrahedrally arranged neighbors, forming a cubic structure (Fig. 1, A). This structure corresponds to the maximum covalency of the bond, and all 4 electrons of each carbon atom form high-strength C–C bonds, i.e. There are no conduction electrons in the structure. Therefore, diamond is characterized by its lack of conductivity, low thermal conductivity, and high hardness; it is the hardest known substance (Fig. 2). Breaking the C–C bond (bond length 1.54 Å, hence covalent radius 1.54/2 = 0.77 Å) in a tetrahedral structure requires large amounts of energy, so diamond, along with exceptional hardness, is characterized by a high melting point (3550 °C).

Another allotropic form of carbon is graphite, which has very different properties from diamond. Graphite is a soft black substance made of easily exfoliated crystals, characterized by good electrical conductivity (electrical resistance 0.0014 Ohm cm). Therefore, graphite is used in arc lamps and furnaces (Fig. 3), in which it is necessary to create high temperatures. High purity graphite is used in nuclear reactors as a neutron moderator. Its melting point at high blood pressure equal to 3527° C. At normal pressure, graphite sublimates (transfers from solid state into gas) at 3780° C.

Structure of graphite (Fig. 1, b) is a system of fused hexagonal rings with a bond length of 1.42 Å (much shorter than in diamond), but each carbon atom has three (rather than four, as in diamond) covalent bonds with three neighbors, and the fourth bond ( 3.4 Å) is too long for a covalent bond and weakly binds parallel graphite layers to each other. It is the fourth electron of carbon that determines the thermal and electrical conductivity of graphite - this longer and less strong bond forms the less compactness of graphite, which is reflected in its lower hardness compared to diamond (graphite density 2.26 g/cm 3, diamond - 3.51 g /cm 3). For the same reason, graphite is slippery to the touch and easily separates flakes of the substance, which is why it is used to make lubricant and pencil leads. The lead-like sheen of the lead is mainly due to the presence of graphite.

Carbon fibers have high strength and can be used to make rayon or other high carbon yarns.

At high pressure and temperature in the presence of a catalyst such as iron, graphite can transform into diamond. This process has been implemented for industrial production artificial diamonds. Diamond crystals grow on the surface of the catalyst. The graphite-diamond equilibrium exists at 15,000 atm and 300 K or at 4000 atm and 1500 K. Artificial diamonds can also be obtained from hydrocarbons.

Amorphous forms of carbon that do not form crystals include charcoal, obtained by heating wood without access to air, lamp and gas soot, formed during low-temperature combustion of hydrocarbons with a lack of air and condensing on a cold surface, bone char - an admixture to calcium phosphate in the process of bone destruction fabrics, as well as coal (a natural substance with impurities) and coke, a dry residue obtained from the coking of fuels by the method of dry distillation of coal or petroleum residues (bituminous coals), i.e. heating without air access. Coke is used for smelting cast iron and in ferrous and non-ferrous metallurgy. During coking, gaseous products are also formed - coke oven gas (H 2, CH 4, CO, etc.) and chemical products, which are raw materials for the production of gasoline, paints, fertilizers, medicines, plastics, etc. A diagram of the main apparatus for coke production - a coke oven - is shown in Fig. 3.

Various types of coal and soot have a developed surface and are therefore used as adsorbents for purifying gas and liquids, and also as catalysts. Special methods are used to obtain various forms of carbon chemical technology. Artificial graphite is produced by calcining anthracite or petroleum coke between carbon electrodes at 2260 ° C (Acheson process) and is used in the production of lubricants and electrodes, in particular for the electrolytic production of metals.

Structure of the carbon atom.

The nucleus of the most stable carbon isotope, mass 12 (98.9% abundance), has 6 protons and 6 neutrons (12 nucleons), arranged in three quartets, each containing 2 protons and two neutrons, similar to the helium nucleus. Another stable isotope of carbon is 13 C (about 1.1%), and in trace quantities there exists in nature an unstable isotope 14 C with a half-life of 5730 years, which has b- radiation. All three isotopes participate in the normal carbon cycle of living matter in the form of CO 2 . After the death of a living organism, carbon consumption stops and C-containing objects can be dated by measuring the level of 14 C radioactivity. Decrease b-14 CO 2 radiation is proportional to the time elapsed since death. In 1960, W. Libby was awarded the Nobel Prize for research with radioactive carbon.

In the ground state, 6 electrons of carbon form electron configuration 1 s 2 2s 2 2p x 1 2p y 1 2p z 0 . Four electrons of the second level are valence, which corresponds to the position of carbon in group IVA of the periodic table ( cm. PERIODIC SYSTEM OF ELEMENTS). Since large energy is required to remove an electron from an atom in the gas phase (approx. 1070 kJ/mol), carbon does not form ionic bonds with other elements, since this would require the removal of an electron to form a positive ion. Having an electronegativity of 2.5, carbon does not exhibit strong electron affinity and, accordingly, is not an active electron acceptor. Therefore, it is not prone to form a particle with a negative charge. But some carbon compounds exist with a partially ionic nature of the bond, for example carbides. In compounds, carbon exhibits an oxidation state of 4. In order for four electrons to participate in the formation of bonds, pairing 2 is necessary s-electrons and the jump of one of these electrons by 2 p z-orbital; in this case, 4 tetrahedral bonds are formed with an angle between them of 109°. In compounds, carbon's valence electrons are only partially withdrawn from it, so carbon forms strong covalent bonds between neighboring C–C atoms using a shared electron pair. The breaking energy of such a bond is 335 kJ/mol, whereas for the Si–Si bond it is only 210 kJ/mol, so long –Si–Si– chains are unstable. The covalent nature of the bond is preserved even in compounds of highly reactive halogens with carbon, CF 4 and CCl 4. Carbon atoms are capable of donating more than one electron from each carbon atom to form a bond; This is how double C=C and triple CєC bonds are formed. Other elements also form bonds between their atoms, but only carbon is capable of forming long chains. Therefore, for carbon, thousands of compounds are known, called hydrocarbons, in which the carbon is bonded to hydrogen and other carbon atoms to form long chains or ring structures. Cm. ORGANIC CHEMISTRY.

In these compounds, it is possible to replace hydrogen with other atoms, most often with oxygen, nitrogen and halogens to form a variety of organic compounds. Fluorocarbons are important among them - hydrocarbons in which hydrogen is replaced by fluorine. Such compounds are extremely inert, and they are used as plastic and lubricants (fluorocarbons, i.e. hydrocarbons in which all hydrogen atoms are replaced by fluorine atoms) and as low-temperature refrigerants (chlorofluorocarbons, or freons).

In the 1980s, US physicists discovered very interesting carbon compounds in which carbon atoms are connected into 5- or 6-gons, forming a C 60 molecule in the shape of a hollow ball with the perfect symmetry of a soccer ball. Since this design forms the basis of the “geodesic dome” invented by the American architect and engineer Buckminster Fuller, the new class of compounds was called “buckminsterfullerenes” or “fullerenes” (and also more briefly “phasyballs” or “buckyballs”). Fullerenes - the third modification of pure carbon (except for diamond and graphite), consisting of 60 or 70 (or even more) atoms - were obtained by the action laser radiation into tiny particles of carbon. Fullerenes are more complex shape consist of several hundred carbon atoms. The diameter of the C molecule is 60 ~ 1 nm. In the center of such a molecule there is enough space to accommodate a large uranium atom.

Standard atomic mass.

In 1961, the International Union of Pure and Applied Chemistry (IUPAC) and Physics adopted the mass of the carbon isotope 12 C as a unit of atomic mass, abolishing the previously existing oxygen scale of atomic masses. The atomic mass of carbon in this system is 12.011, as it is the average of the three naturally occurring isotopes of carbon, given their abundance in nature. Cm. ATOMIC MASS.

Chemical properties of carbon and some of its compounds.

Some physical and Chemical properties carbon are given in the article CHEMICAL ELEMENTS. The reactivity of carbon depends on its modification, temperature and dispersion. At low temperatures all forms of carbon are quite inert, but when heated they are oxidized by atmospheric oxygen, forming oxides:

Finely dispersed carbon in excess oxygen can explode when heated or from a spark. In addition to direct oxidation, there are more modern methods obtaining oxides.

Carbon suboxide

C 3 O 2 is formed by the dehydration of malonic acid over P 4 O 10:

C 3 O 2 has an unpleasant odor and is easily hydrolyzed, again forming malonic acid.

Carbon(II) monoxide CO is formed during the oxidation of any modification of carbon under conditions of lack of oxygen. The reaction is exothermic, 111.6 kJ/mol is released. Coke reacts with water at white heat temperature: C + H 2 O = CO + H 2 ; the resulting gas mixture is called “water gas” and is a gaseous fuel. CO is also formed during incomplete combustion of petroleum products; it is found in noticeable quantities in automobile exhausts; it is obtained during the thermal dissociation of formic acid:

The oxidation state of carbon in CO is +2, and since carbon is more stable in the oxidation state +4, CO is easily oxidized by oxygen to CO 2: CO + O 2 → CO 2, this reaction is highly exothermic (283 kJ/mol). CO is used in industry in a mixture with H2 and other flammable gases as a fuel or gaseous reducing agent. When heated to 500° C, CO forms C and CO 2 to a noticeable extent, but at 1000° C, equilibrium is established at low concentrations of CO 2. CO reacts with chlorine, forming phosgene - COCl 2, reactions with other halogens proceed similarly, in reaction with sulfur carbonyl sulfide COS is obtained, with metals (M) CO forms carbonyls of various compositions M(CO) x, which are complex compounds. Iron carbonyl is formed when blood hemoglobin reacts with CO, preventing the reaction of hemoglobin with oxygen, since iron carbonyl is a stronger compound. As a result, the function of hemoglobin as a carrier of oxygen to cells is blocked, which then die (and the brain cells are primarily affected). (Hence another name for CO – “carbon monoxide”). Already 1% (vol.) CO in the air is dangerous for humans if they are in such an atmosphere for more than 10 minutes. Some physical properties of CO are given in the table.

Carbon dioxide, or carbon monoxide (IV) CO 2 is formed by the combustion of elemental carbon in excess oxygen with the release of heat (395 kJ/mol). CO 2 (the trivial name is “carbon dioxide”) is also formed during the complete oxidation of CO, petroleum products, gasoline, oils and other organic compounds. When carbonates are dissolved in water, CO 2 is also released as a result of hydrolysis:

This reaction is often used in laboratory practice to produce CO 2 . This gas can also be obtained by calcination of metal bicarbonates:

during gas-phase interaction of superheated steam with CO:

when burning hydrocarbons and their oxygen derivatives, for example:

Similarly, food products are oxidized in a living organism, releasing heat and other types of energy. In this case, oxidation occurs under mild conditions through intermediate stages, but the end products are the same - CO 2 and H 2 O, as, for example, during the decomposition of sugars under the action of enzymes, in particular during the fermentation of glucose:

Large-scale production of carbon dioxide and metal oxides is carried out in industry by the thermal decomposition of carbonates:

CaO is used in large quantities in cement production technology. The thermal stability of carbonates and the heat consumption for their decomposition according to this scheme increase in the series CaCO 3 ( see also FIRE PREVENTION AND FIRE PROTECTION).

Electronic structure of carbon oxides.

The electronic structure of any carbon monoxide can be described by three equally probable schemes with different arrangements of electron pairs - three resonant forms:

All carbon oxides have a linear structure.

Carbonic acid.

When CO 2 reacts with water, carbonic acid H 2 CO 3 is formed. In a saturated solution of CO 2 (0.034 mol/l), only some of the molecules form H 2 CO 3, and most of the CO 2 is in the hydrated state CO 2 CHH 2 O.

Carbonates.

Carbonates are formed by the interaction of metal oxides with CO 2, for example, Na 2 O + CO 2 Na 2 CO 3.

With the exception of alkali metal carbonates, the rest are practically insoluble in water, and calcium carbonate is partially soluble in carbonic acid or a solution of CO 2 in water under pressure:

These processes occur in groundwater flowing through a limestone layer. In conditions low pressure and evaporation from groundwater containing Ca(HCO 3) 2, CaCO 3 is deposited. This is how stalactites and stalagmites grow in caves. The color of these interesting geological formations is explained by the presence of impurities in the waters of iron, copper, manganese and chromium ions. Carbon dioxide reacts with metal hydroxides and their solutions to form bicarbonates, for example:

CS 2 + 2Cl 2 ® CCl 4 + 2S

CCl 4 tetrachloride is a non-flammable substance, used as a solvent in dry cleaning processes, but it is not recommended to use it as a flame arrester, since at high temperatures toxic phosgene (a gaseous toxic substance) is formed. CCl 4 itself is also poisonous and, if inhaled in noticeable quantities, can cause liver poisoning. CCl 4 is also formed by the photochemical reaction between methane CH 4 and Cl 2; in this case, the formation of products of incomplete chlorination of methane - CHCl 3, CH 2 Cl 2 and CH 3 Cl - is possible. Reactions occur similarly with other halogens.

Reactions of graphite.

Graphite as a modification of carbon, characterized by large distances between the layers of hexagonal rings, enters into unusual reactions, for example, alkali metals, halogens and some salts (FeCl 3) penetrate between the layers, forming compounds such as KC 8, KC 16 (called interstitial, inclusion or clathrates). Strong oxidizing agents such as KClO 3 in an acidic environment (sulfuric or nitric acid) form substances with a large volume of the crystal lattice (up to 6 Å between layers), which is explained by the introduction of oxygen atoms and the formation of compounds on the surface of which, as a result of oxidation, carboxyl groups (–COOH) are formed ) – compounds such as oxidized graphite or mellitic (benzene hexacarboxylic) acid C 6 (COOH) 6. In these compounds, the C:O ratio can vary from 6:1 to 6:2.5.

Carbides.

Carbon forms various compounds called carbides with metals, boron and silicon. The most active metals (IA–IIIA subgroups) form salt-like carbides, for example Na 2 C 2, CaC 2, Mg 4 C 3, Al 4 C 3. In industry, calcium carbide is obtained from coke and limestone using the following reactions:

Carbides are non-electrically conductive, almost colorless, hydrolyze to form hydrocarbons, for example

CaC 2 + 2H 2 O = C 2 H 2 + Ca(OH) 2

The acetylene C 2 H 2 formed by the reaction serves as the starting material in the production of many organic substances. This process is interesting because it represents a transition from raw materials of inorganic nature to the synthesis of organic compounds. Carbides that form acetylene upon hydrolysis are called acetylenides. In silicon and boron carbides (SiC and B 4 C), the bond between the atoms is covalent. Transition metals (elements of B-subgroups) when heated with carbon also form carbides of variable composition in cracks on the metal surface; the bond in them is close to metallic. Some carbides of this type, for example WC, W 2 C, TiC and SiC, are distinguished by high hardness and refractoriness, and have good electrical conductivity. For example, NbC, TaC and HfC are the most refractory substances (mp = 4000–4200° C), diniobium carbide Nb 2 C is a superconductor at 9.18 K, TiC and W 2 C are close in hardness to diamond, and hardness B 4 C (structural analogue of diamond) is 9.5 on the Mohs scale ( cm. rice. 2). Inert carbides are formed if the radius of the transition metal

Nitrogen derivatives of carbon.

This group includes urea NH 2 CONH 2 - a nitrogen fertilizer used in the form of a solution. Urea is obtained from NH 3 and CO 2 by heating under pressure:

Cyanogen (CN) 2 has many properties similar to halogens and is often called a pseudohalogen. Cyanide is obtained by mild oxidation of cyanide ion with oxygen, hydrogen peroxide or Cu 2+ ion: 2CN – ® (CN) 2 + 2e.

Cyanide ion, being an electron donor, easily forms complex compounds with transition metal ions. Like CO, cyanide ion is a poison, binding vital iron compounds in a living organism. Cyanide complex ions have general formula –0,5x, Where X– coordination number of the metal (complexing agent), empirically equal to twice the oxidation state of the metal ion. Examples of such complex ions are (the structure of some ions is given below) tetracyanonickelate(II) ion 2–, hexacyanoferrate(III) 3–, dicyanoargentate –:

Carbonyls.

Carbon monoxide is capable of reacting directly with many metals or metal ions, forming complex compounds called carbonyls, for example Ni(CO) 4, Fe(CO) 5, Fe 2 (CO) 9, 3, Mo(CO) 6, 2. The bonding in these compounds is similar to the bonding in the cyano complexes described above. Ni(CO) 4 is a volatile substance used to separate nickel from other metals. The deterioration of the structure of cast iron and steel in structures is often associated with the formation of carbonyls. Hydrogen can be part of carbonyls, forming carbonyl hydrides, such as H 2 Fe (CO) 4 and HCo (CO) 4, which exhibit acidic properties and react with alkali:

H 2 Fe(CO) 4 + NaOH → NaHFe(CO) 4 + H 2 O

Carbonyl halides are also known, for example Fe(CO)X 2, Fe(CO) 2 X 2, Co(CO)I 2, Pt(CO)Cl 2, where X is any halogen.

Hydrocarbons.

A huge number of carbon-hydrogen compounds are known

In this book, the word “carbon” appears quite often: in stories about green leaves and iron, about plastics and crystals, and in many others. Carbon - “giving birth coal” - is one of the most amazing chemical elements. Its history is the history of the emergence and development of life on Earth, because it is part of all living things on Earth.

What does carbon look like?

Let's do some experiments. Let's take sugar and heat it without air. It will first melt, turn brown, and then turn black and turn into coal, releasing water. If you now heat this coal in the presence of , it will burn without a residue and turn into . Therefore, sugar consisted of coal and water (sugar, by the way, is called a carbohydrate), and “sugar” coal is, apparently, pure carbon, because carbon dioxide is a compound of carbon with oxygen. This means carbon is a black, soft powder.

Let's take a gray soft graphite stone, well known to you thanks to pencils. If you heat it in oxygen, it will also burn without a residue, although a little slower than coal, and carbon dioxide will remain in the device where it burned. Does this mean that graphite is also pure carbon? Of course, but that's not all.

If a diamond, a transparent sparkling gemstone and the hardest of all minerals, is heated in oxygen in the same device, it too will burn, turning into carbon dioxide. If you heat a diamond without access to oxygen, it will turn into graphite, and at very high pressures and temperatures you can get a diamond from graphite.

So, coal, graphite and diamond are various shapes existence of the same element - carbon.

Even more amazing is the ability of carbon to “participate” in a huge number of different compounds (which is why the word “carbon” appears so often in this book).

The 104 elements of the periodic table form more than forty thousand studied compounds. And over a million compounds are already known, the basis of which is carbon!

The reason for this diversity is that carbon atoms can be connected to each other and to other atoms by strong bonds, forming complex ones in the form of chains, rings and other shapes. No element in the table except carbon is capable of this.

There is an infinite number of shapes that can be built from carbon atoms, and therefore an infinite number of possible compounds. It can be very simple substances, for example, the illuminating gas methane, in a molecule of which four atoms are bonded to one carbon atom, and are so complex that the structure of their molecules has not yet been established. Such substances include

In connection state carbon is part of the so-called organic substances, i.e., many substances found in the body of every plant and animal. It is found in the form of carbon dioxide in water and air, and in the form of carbon dioxide salts and organic residues in the soil and mass of the earth's crust. The variety of substances that make up the body of animals and plants is known to everyone. Wax and oil, turpentine and resin, cotton paper and white, cell tissue plants and muscle tissue of animals, tartaric acid and starch - all these and many other substances included in the tissues and juices of plants and animals are carbon compounds. The area of ​​carbon compounds is so large that it constitutes a special branch of chemistry, that is, the chemistry of carbon or, better, hydrocarbon compounds.”

These words from D.I. Mendeleev’s “Fundamentals of Chemistry” serve as a kind of extended epigraph to our story about the vital element - carbon. However, there is one thesis here, with which, from the point of view modern science one can argue about the substance, but more on that below.

There are probably enough fingers on your hands to count chemical elements, to which at least one was not dedicated scientific book. But an independent popular science book - not some brochure on 20 incomplete pages with a cover made of wrapping paper, but a completely solid volume of almost 500 pages - contains only one element - carbon.

In general, the literature on carbon is very rich. These are, firstly, all books and articles by organic chemists without exception; secondly, almost everything related to polymers; thirdly, countless publications related to fossil fuels; fourthly, a significant part of the biomedical literature...

Therefore, we will not try to embrace the immensity (after all, it is no coincidence that the authors of the popular book about element No. 6 called it “Inexhaustible”!, but we will focus only on the main thing of the main thing - we will try to see carbon from three points of view.

Carbon is one of the few elements"without clan, without tribe." The history of human interaction with this substance goes back to prehistoric times. The name of the discoverer of carbon is unknown, and it is also unknown which form of elemental carbon - diamond or graphite - was discovered first. Both happened too long ago. Only one thing can be said with certainty: before diamond and before graphite, a substance was discovered that just a few decades ago was considered the third, amorphous form of elemental carbon - coal. But in reality, charcoal, even charcoal, is not pure carbon. It contains hydrogen, oxygen, and traces of other elements. True, they can be removed, but even then the carbon in coal will not become an independent modification of elemental carbon. This was established only in the second quarter of our century. Structural analysis showed that amorphous carbon is essentially the same graphite. This means that it is not amorphous, but crystalline; only its crystals are very small and have more defects. After this, they began to believe that carbon on Earth exists only in two elementary forms - in the form of graphite and diamond.

Have you ever thought about the reasons for the sharp “watershed” of properties that occurs in the second short period of the periodic table along the line separating carbon from the next nitrogen? Nitrogen, oxygen, fluorine are gaseous under normal conditions. Carbon - in any form - solid. The melting point of nitrogen is minus 210.5°C, and carbon (in the form of graphite under pressure over 100 atm) is about plus 4000°C...

Dmitry Ivanovich Mendeleev was the first to suggest that this difference is explained by the polymeric structure of carbon molecules. He wrote: “If carbon formed a C 2 molecule, like O 2, it would be a gas.” And further: “The ability of coal atoms to connect with each other and form complex molecules is manifested in all carbon compounds. In no other element is this capacity for complexity developed to such an extent as in carbon. To this day there is no basis for determining the degree of polymerization of coal, graphite, or diamond molecules; one can only think that they contain Cn, where n is a large value.”

Carbon and its polymers

This assumption has been confirmed in our time. Both graphite and diamond are polymers consisting of the same carbon atoms.

According to the apt remark of Professor Yu.V. Khodakov, “if we proceed from the nature of the forces being overcome, the profession of a diamond cutter could be classified as a chemical profession.” Indeed, the lapidary has to overcome not the relatively weak forces of intermolecular interaction, but the forces chemical bond, which combine carbon atoms into a diamond molecule. Any diamond crystal, even a huge, six-hundred-gram Cullinan, is essentially one molecule, a molecule of a highly regular, almost perfectly structured three-dimensional polymer.

Graphite is a different matter. Here, polymer ordering extends only in two directions - along the plane, and not in space. In a piece of graphite, these planes form a fairly dense pack, the layers of which are connected to each other not by chemical forces, but by weaker forces of intermolecular interaction. This is why graphite exfoliates so easily - even from contact with paper. At the same time, it is very difficult to break a graphite plate in the transverse direction - there is a chemical bond that opposes it.

It is the features of the molecular structure that explain the huge difference in the properties of graphite and diamond. Graphite is an excellent conductor of heat and electricity, while diamond is an insulator. Graphite does not transmit light at all - diamond is transparent. No matter how diamond is oxidized, the oxidation product will only be CO 2 . And by oxidizing graphite, you can, if desired, obtain several intermediate products, in particular graphitic (variable composition) and mellitic C 6 (COOH) 6 acids. Oxygen seems to wedge itself between the layers of the graphite pack and oxidizes only some carbon atoms. In a diamond crystal weak points no, and therefore either complete oxidation or complete non-oxidation is possible - there is no third option...

So, there is a “spatial” polymer of elemental carbon, and there is a “planar” one. In principle, the existence of a “one-dimensional” - linear polymer of carbon has long been assumed, but it has not been found in nature.

Was not found for the time being. A few years after its synthesis, a linear polymer of carbon was found in a meteorite crater in Germany. And the first to obtain it were Soviet chemists V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin and Yu.P. Kudryavtsev. The linear polymer of carbon was called carbyne. Outwardly, it looks like a black fine-crystalline powder, has semiconducting properties, and under the influence of light, the electrical conductivity of carbyne greatly increases. Carbyne has discovered completely unexpected properties. It turned out, for example, that blood upon contact with it does not form clots - thrombi, so fiber coated with carbin began to be used in the manufacture of artificial blood vessels that are not rejected by the body.

According to the discoverers of carbyne, the most difficult thing for them was to determine by what bonds the carbon atoms were connected in a chain. It could have alternating single and triple bonds (-C = C-C=C -C=), or it could only have double bonds (=C=C=C=C=)... Or it could have both at the same time. Only a few years later Korshak and Sladkov managed to prove that there are no double bonds in carbyne. However, since the theory allowed the existence of a carbon linear polymer with only double bonds, an attempt was made to obtain this species - essentially a fourth modification of elemental carbon.

Carbon in minerals

This substance was obtained at the Institute of Organoelement Compounds of the USSR Academy of Sciences. The new linear polymer of carbon was called polycumulene. And now at least eight linear carbon polymers are known, differing from each other in the structure of the crystal lattice. In foreign literature they are all called carbines.

This element is always tetravalent, but since it is located right in the middle in the period, its oxidation state in different circumstances is sometimes +4, sometimes - 4. In reactions with non-metals it is electropositive, with metals - vice versa. Even in cases where the bond is not ionic, but covalent, carbon remains true to itself - its formal valence remains equal to four.

There are very few compounds in which carbon at least formally exhibits a valency other than four. Only one such compound is generally known - CO, carbon monoxide, in which carbon appears divalent. It seems exactly, because in reality there is more complex type communications. The carbon and oxygen atoms are connected by a 3-covalent polarized bond, and the structural formula of this compound is written as follows: O+=C."

In 1900, M. Gomberg obtained the organic compound triphenylmethyl (C 6 H 5) 3 C. It seemed that the carbon atom here was trivalent. But later it turned out that this time the unusual valence was purely formal. Triphenylmethyl and its analogues are free radicals, but unlike most radicals they are quite stable.

Historically, very few carbon compounds remained “under roof” inorganic chemistry. These are oxides of carbon, carbides - its compounds with metals, as well as boron and silicon, carbonates - salts of the weakest carbonic acid, carbon disulfide CS 2, cyanide compounds. We have to console ourselves with the fact that, as often happens (or has happened) in production, the shortcomings in the nomenclature are compensated for by the “shaft”. Indeed, the largest part of the carbon in the earth's crust is not contained in the organisms of plants and animals, not in coal, oil and all other organic matter taken together, but in only two inorganic compounds - limestone CaCO 3 and dolomite MgCa(CO 3) 2. Carbon is part of several dozen more minerals; just remember marble CaCO 3 (with additives), malachite Cu 2 (OH) 2 CO 3, zinc mineral Smithsonite ZnCO 3 ... There is carbon in both igneous rocks and crystalline schists.

Minerals containing carbides are very rare. As a rule, these are substances of especially deep origin; Therefore, scientists assume that in the nucleus globe there is carbon.

For the chemical industry, carbon and its inorganic compounds are of significant interest - often as raw materials, less often as construction materials.

Many chemical production equipment, such as heat exchangers, are made of graphite. And this is natural: graphite has great heat resistance and chemical resistance and at the same time conducts heat well. By the way, thanks to these same properties, graphite has become an important material for jet technology. The rudders are made of graphite and operate directly in the flame of the nozzle apparatus. It is almost impossible to ignite graphite in air (even in pure oxygen this is not easy), and to evaporate graphite, you need a temperature much higher than that developing even in a rocket engine. And, besides, at normal pressure, graphite, like granite, does not melt.

It is difficult to imagine modern electrochemical production without graphite. Graphite electrodes are used not only by electrometallurgists, but also by chemists. It is enough to remember that in electrolyzers used to produce caustic soda and chlorine, the anodes are graphite.

Carbon use

Many books have been written about the use of carbon compounds in the chemical industry. Calcium carbonate, limestone, serves as a raw material in the production of lime, cement, and calcium carbide. Another mineral, dolomite, is the “ancestor” of a large group of dolomite refractories. Sodium carbonate and bicarbonate - soda ash and baking soda. One of the main consumers of soda ash has been and remains the glass industry, which supplies about a third of the world's Na 2 CO 3 production.

And finally, a little about carbides. Usually, when they say carbide, they mean calcium carbide - a source of acetylene, and therefore, numerous products of organic synthesis. But calcium carbide, although the most famous, is far from the only very important and necessary substance in this group. Boron carbide B 4 C is an important nuclear material

technology, silicon carbide SiC or carborundum is the most important abrasive material. Carbides of many metals are characterized by high chemical resistance and exceptional hardness; Carborundum, for example, is only slightly inferior to diamond. Its hardness on the Mooca scale is 9.5-9.75 (diamond - 10). But carborundum is cheaper than diamond. It is produced in electric furnaces at a temperature of about 2000°C from a mixture of coke and quartz sand.

According to the famous Soviet scientist Academician I.L. Knunyants, organic chemistry can be considered as a kind of bridge thrown by science from inanimate nature to its highest form - life. And just a century and a half ago, the best chemists of that time themselves believed and taught their followers that organic chemistry is the science of substances formed with the participation and under the guidance of some strange “matter” - vital force. But this force was soon consigned to the dustbin of natural history. Syntheses of several organic substances - urea, acetic acid, fats, sugar-like substances - made it simply unnecessary.

Appeared classic definition K. Schorlemmer, which has not lost its meaning even 100 years later: “Organic chemistry is the chemistry of hydrocarbons and their derivatives, that is, products formed when hydrogen is replaced by other atoms or groups of atoms.”

So, organics is the chemistry of not even one element, but only one class of compounds of this element. But what a class! A class divided not only into groups and subgroups - into independent sciences. Biochemistry, the chemistry of synthetic polymers, the chemistry of biologically active and medicinal compounds emerged from organics, from organics...

Now millions of organic compounds (carbon compounds!) and about one hundred thousand compounds of all other elements combined are known.

It is common knowledge that life is built on carbon. But why exactly did carbon, the eleventh most abundant element on Earth, take on the most difficult task of being the basis of all life?

The answer to this question is ambiguous. First, “in no element is such a capacity for complexity developed to such an extent as in carbon.” Secondly, carbon is capable of combining with most elements, and in a wide variety of ways. Thirdly, the connection of carbon atoms with each other, as well as with the atoms of hydrogen, oxygen, nitrogen, sulfur, phosphorus and other elements that make up organic substances, can be destroyed under the influence of natural factors. Therefore, carbon continuously circulates in nature: from the atmosphere - into plants, from plants - into animal organisms, from living things - into dead ones,

from dead to alive...

The four valences of a carbon atom are like four hands. And if two such atoms unite, then there are already six “hands”. Or - four, if two electrons are spent on pair formation (double bond). Or - just two, if the bond, as in acetylene, is triple. But these connections (they are called unsaturated) are like a bomb in your pocket or a genie in a bottle. They are hidden for the time being, but at the right moment they break free to take their toll in a stormy, gambling game chemical interactions and transformations. A wide variety of structures are formed as a result of these “games” if carbon is involved in them. The editors of the Children's Encyclopedia calculated that from 20 carbon atoms and 42 hydrogen atoms, 366,319 different hydrocarbons, 366,319 substances of the composition C 20 H42, can be obtained. And if the “game” has not six dozen participants, but several thousand; if among them are representatives of not two “teams”, but, say, eight!

Where there is carbon, there is diversity. Where there is carbon, there is complexity. And the designs are very different in molecular architecture. Simple chains, as in butane CH 3 -CH 2 -CH 2 -CH 3 or polyethylene -CH 2 -CH 2 -CH 2 - CH 2 -, and branched structures, the simplest of which is isobutane.