What does carbon look like? Features of the structure of the carbon atom
Carbon (from Latin: carbo "coal") is chemical element with the symbol C and atomic number 6. For the formation of covalent chemical bonds, four electrons are available. 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 5730 years. Carbon is one of the few elements known since antiquity. Carbon is the 15th most abundant element in earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen. The abundance of carbon, the unique diversity of its organic compounds, and its unusual ability to form polymers at temperatures commonly found on Earth allow this element to serve as a common element for 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 bind in different ways, while being called allotropes of carbon. The best 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 a good electrical conductor, while diamond has a 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 transition metal. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant amounts come from organic deposits of coal, peat, oil and methane clathrates. Carbon forms great amount 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 theoretically possible compounds 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 to other small atoms, including other carbon atoms, and is capable of forming numerous stable covalent bonds with suitable multivalent atoms. It is known that carbon forms almost ten million different compounds, the vast majority of all chemical compounds. Carbon also has the highest sublimation point of any element. At atmospheric pressure, it has no melting point as its triple point is 10.8 ± 0.2 MPa and 4600 ± 300 K (~4330 °C or 7820 °F), so it sublimates at about 3900 K. Graphite is much more reactive than diamond under standard conditions despite being more thermodynamically stable as 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 C6(CO2H)6 mellitic acid, which retains the graphite's hexagonal units when the larger structure is destroyed. The carbon is sublimated in a carbon arc, which is about 5800 K (5,530 °C, 9,980 °F). Thus, regardless of its allotropic form, carbon remains solid at higher temperatures 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 the ground state electron configuration 1s22s22p2, of which the four outer 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. The electronegativity of carbon is 2.5, which is significantly higher than the heavier elements of group 14 (1.8-1.9), but is close to most neighboring non-metals, as well as to some transition metals of the second and third rows. The covalent radii of carbon are usually taken as 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 it is associated with. 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 forms 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 comparatively unreactive under normal conditions. At standard temperatures and pressures, carbon will withstand all but the strongest oxidizers. It does not react with sulfuric acid, hydrochloric acid, chlorine or alkalis. At elevated temperatures, carbon reacts with oxygen to form oxides of carbon and removes oxygen from metal oxides, leaving the elemental metal. This exothermic reaction is used in the steel industry to melt 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 some metals at high temperatures to form metal carbides, such as iron carbide cementite in steel and tungsten carbide, widely used as an abrasive and for making hard tips for cutting tools. The system of carbon allotropes covers a number of extremes:
Some types 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 best known natural thermal 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 among the best known anisotropic materials.
Allotropes of carbon
Atomic carbon is a very short-lived species and therefore carbon is stabilized in various polyatomic structures with various 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; they include buckyballs, carbon nanotubes, carbon nanodots, and nanofibers. Several other exotic allotropes have also been discovered, such as lonsaletite, glassy carbon, carbon nanofaum, and linear acetylenic carbon (carbine). 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 to build space elevators. It can also be used to safely store hydrogen for use in hydrogen-based vehicles in vehicles. The amorphous form is a set of carbon atoms in a non-crystalline, irregular, glassy state, and not 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 composed of fused hexagonal rings, as in aromatic hydrocarbons. The resulting network is two-dimensional and the resulting flat sheets are folded and freely connected through weak van der Waals forces. This gives graphite its softness and splitting properties (sheets slide easily over 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 a lower electrical conductivity for carbon than for most metals. Delocalization also explains the energy stability of graphite over diamond at room temperature. At very high pressures, carbon forms a more compact allotrope, diamond, which has 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 because of 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 energy activation barrier, the transition to the graphite form is so slow at normal temperature that it is not noticeable. Under certain conditions, carbon crystallizes as a lonsaleite, a hexagonal crystal lattice with all covalent bonded atoms 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. The missing (or extra) atoms deform the sheets into spheres, ellipses, or cylinders. The properties of fullerenes (divided into buckyballs, buckytubes, and nanobads) have not yet been fully analyzed and represent an intense area of nanomaterials research. The names "fullerene" and "buckyball" are associated with the name of Richard Buckminster Fuller, who popularized geodesic domes that resemble the structure of fullerenes. Buckyballs are rather large molecules formed entirely of carbon bonds trigonally, forming spheroids (the most famous and simplest is C60 baksinisterfellerene with the shape of a soccer ball). Carbon nanotubes are structurally similar to buckyballs, except that each atom is trigonally bonded in a curved sheet that forms a hollow cylinder. Nanobads 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 a single structure. Of the other allotropes discovered, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a clustered assembly of low-density carbon atoms strung together in 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. Similarly, 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 acetylenic carbon has the chemical structure - (C:::C) n-. The carbon in this modification is linear with sp orbital hybridization and is a polymer with alternating single and triple bonds. This carbine 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 at the University of North Carolina announced the development of another allotrope, which they called Q-carbon, created by a low-duration, high-energy laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, fluorescence, and has 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 at meteorite impact sites. In 2014, NASA announced an updated database for tracking 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 appear in the world PAH hypothesis, where they presumably play a role in abiogenesis and the formation of life. It looks like the PAHs were formed "a couple of billion years" after big bang, are widespread in the universe and associated with new stars and exoplanets. The hard shell of the earth is estimated to contain 730 ppm of carbon in total, with 2000 ppm in the core and 120 ppm in the combined mantle and crust. Since the mass of the earth is 5.9 x 72 x 1024 kg, this would mean 4360 million gigatonnes of carbon. This is much more than the amount of carbon in the oceans or the 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 1900 gigatons of carbon in the biosphere. Hydrocarbons (such as coal, oil, and natural gas) also contain carbon. Coal "reserves" (rather than "resources") are about 900 gigatons with perhaps 18,000 Gt of resources. Oil reserves are about 150 gigatons. Proven Sources natural gas are about 175,1012 cubic meters (containing about 105 gigatons of carbon), but studies estimate another 900,1012 cubic meters of "unconventional" deposits such as shale gas, which is about 540 gigatons of carbon. Carbon has also been found in methane hydrates in the 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 gigatonnes of carbon were released into the atmosphere as carbon dioxide into the atmosphere from the burning of fossil fuels. Another source adds the amount added to the atmosphere between 1750 to 879 Gt, and the total in the atmosphere, sea and land (such as peat bogs) is almost 2000 Gt. Carbon is a component (12% by mass) of very large masses of carbonate rocks (limestone, dolomite, marble, etc.). Coal contains a very high amount 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. In terms of individual carbon allotropes, 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 "pipes". Most diamond deposits are found in Africa, especially in South Africa, Namibia, Botswana, the Republic of the Congo and Sierra Leone. Diamond deposits have also been found in Arkansas, Canada, Russian Arctic, Brazil, and Northern and Western Australia. Now diamonds are also recovered from the ocean floor at the Cape of Good Hope. Diamonds occur naturally, but about 30% of all industrial diamonds used in the US are now produced. 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 that 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 explored by scientists. Asteroids could be used in hypothetical space-based coal mining, which may be possible in the future but is currently technologically impossible.
Isotopes of carbon
Isotopes of carbon are atomic nuclei that contain six protons plus a number of neutrons (from 2 to 16). Carbon has two stable naturally occurring isotopes. The isotope carbon-12 (12C) forms 98.93% of the carbon on Earth, and carbon-13 (13C) forms the remaining 1.07%. The concentration of 12C increases even more in biological materials because biochemical reactions discriminate against 13C. In 1961, the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotopic carbon-12 as the basis for atomic weights. Identification of carbon in experiments with nuclear magnetic resonance (NMR) is carried out with the 13C isotope. Carbon-14 (14C) is a natural 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 at up to 1 part per trillion (0.0000000001%), primarily in the atmosphere and surface sediments, particularly peat and other organic materials. This isotope decays during 0.158 MeV β-emission. Due to the relatively short half-life of 5730 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 age carbonaceous materials up to 40,000 years old. There are 15 known isotopes of carbon and the shortest lifetime of them is 8C, which decays by proton emission and alpha decay and has a half-life of 1.98739 × 10-21 s. Exotic 19C exhibits a nuclear halo, meaning that its radius is significantly larger than what would be expected if the nucleus were a sphere of constant density.
Education in the stars
Formation atomic nucleus carbon requires an almost simultaneous triple collision of alpha particles (helium nuclei) inside 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 at temperatures over 100 megacalvins and helium concentrations, which is unacceptable under conditions of rapid expansion and cooling. 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 a horizontal branch by the collision and transformation of three helium nuclei. When these stars die in a supernova, the carbon is scattered into space as dust. This dust becomes the constituent material for the formation of second or third generation star systems with accreted planets. solar system is one such star system with an abundance of carbon, allowing the existence of life as we know it. 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 (for example, 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 disposed of elsewhere. Carbon's pathways environment form a carbon cycle. For example, photosynthetic plants extract carbon dioxide from the atmosphere (or sea water) 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 is dissolved in the oceans; if bacteria do not absorb 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. Through katanation (formation of chains), carbon forms an innumerable number of 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 the hydrocarbon, a large family of organic molecules that are made up of hydrogen atoms bonded to a chain of carbon atoms. Chain length, side chains, and functional groups affect the properties of organic molecules. Carbon is found in every form of known organic life and is the basis of organic chemistry. When combined with hydrogen, carbon forms various hydrocarbons that are important to industry as refrigerants, lubricants, solvents, as chemical feedstocks for the production of 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 aromatic 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 oxides of carbon. The best known oxide is carbon dioxide (CO2). Once a major constituent of the paleoatmosphere, this matter is today a minor constituent of the Earth's atmosphere. When dissolved in water, this substance forms carbonic acid (H2CO3), but, like most compounds with several single-bonded oxygens on one carbon, it is unstable. However, resonant stabilized carbonate ions are formed through this intermediate. Some important minerals are carbonates, especially calcites. 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 fairly polar, which results in it constantly binding to hemoglobin molecules, displacing oxygen, which has a lower binding affinity. Cyanide (CN-) has a similar structure but behaves like a halide ion (pseudohalogen). For example, it can form a cyanogen nitride (CN) 2 molecule similar to diatom halides. Other unusual oxides are carbon suboxide (C3O2), unstable carbon monoxide (C2O), carbon trioxide (CO3), cyclopentane peptone (C5O5), cyclohexanehexone (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. At 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 salt-like carbides are not fully 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 elide), η2-alkene compounds (eg Zeise salt) and η3-allylic compounds (eg allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands (eg ferrocene); and carbene complexes of transition metals. There are many metal carbonyls (for example, nickel tetracarbonyl); some workers believe that the carbon monoxide ligand is a purely inorganic, not organometallic, compound. While carbon is thought to exclusively form four bonds, an interesting compound has been reported containing an octahedral hexacoordinate carbon atom. 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 (carbon) comes from the Latin carbo, meaning "charcoal" and "charcoal", hence the French word charbon, which means "charcoal". The German, Dutch, and Danish names for carbon are Kohlenstoff, koolstof, and kulstof, respectively, all literally meaning a 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 known probably as early as 2500 BC. in China, and carbon in the form of charcoal was made in Roman times by the same chemistry as it is today, by heating wood in a clay-covered pyramid to exclude air. In 1722, René Antoine Ferhot de Réamour demonstrated that iron is converted into steel through the absorption of some 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 found that neither produced any water, and that both substances released an equal amount of carbon dioxide per gram. In 1779, Carl Wilhelm Scheele showed that graphite, thought to be a form of lead, was instead identical to charcoal but with a small amount 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 essentially carbon, by oxidizing it in oxygen in much the same way that Lavoisier did with diamond. Some iron remained again, which, according to French scientists, was necessary for the structure of graphite. In their publication, they proposed the name carbone (Latin for carbonum) for an element in graphite that was released as a gas when the 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 Kroto and Richard Smalley - received the 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 most economically important sources located in China, India, Brazil and North Korea. Graphite deposits are metamorphic in origin, found in association with quartz, mica, and feldspars in shales, gneisses, and metamorphosed sandstones and limestones in the form of lenses or veins, sometimes several meters or more thick. Graphite stocks at Borrowdale, Cumberland, England were at the beginning of sufficient size and purity that until the 19th century pencils were made simply by sawing blocks of natural graphite into strips before pasting the strips into wood. Today, smaller graphite deposits are obtained 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 of the lowest quality and is the most common. In contrast to 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 refer to products with a low amount of graphite and is the cheapest graphite. Large deposits of amorphous graphite are found in China, Europe, Mexico and the USA. Planar graphite is less common and of higher quality than amorphous; it looks like separate plates that crystallize in metamorphic rocks. The price of granular graphite can be four times the price of amorphous. Good quality flake graphite can be processed into expandable graphite for many applications such as flame retardants. Primary graphite deposits 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 lumps and is only commercially mined 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 was mined in 2009 at an estimated cost of $998 million.
Diamond
The supply of diamonds is controlled by a limited number of businesses and is also highly concentrated in a small number of locations around the world. Only a very small proportion of diamond ore is made up of real diamonds. The ore is crushed, during which care must be taken to prevent the destruction of large diamonds in this process, and then the particles are sorted by density. Today, diamonds are mined in the diamond-rich fraction using X-ray fluorescence, after which the final sorting steps are performed manually. Prior to the spread of the use of X-rays, the separation was carried out using lubricating tapes; it is known that diamonds have only been found 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 the leader in the production of diamonds from their discovery around the 9th century BC until the middle of the 18th century AD, but the commercial potential of these sources was exhausted by the end of the 18th century, by which time India was swamped 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, with only 4.5 billion carats accumulated since that date. About 20% of this amount has been mined in the last 5 years alone, and over the past ten years, 9 new deposits have started production, and 4 more are 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, a startling discovery of a microscopic diamond in the United States led to the release in January 2008 of a mass sampling of kimberlite pipes in a remote part of Montana. Today, the majority of commercially viable diamond deposits are in Russia, Botswana, Australia and Democratic Republic Congo. In 2005, Russia produced nearly one-fifth of the world's diamond supply, according to the British Geological Survey. In Australia, the richest diamonded pipe reached peak production levels of 42 metric tons (41 tons, 46 short tons) per year in the 1990s. There are also commercial deposits, which are actively mined in the Northwest Territories of Canada, Siberia (mainly in Yakutia, for example, in the Mir Pipe and the Udachnaya Pipe), in Brazil, as well as in Northern and Western Australia.
Applications
Carbon is essential for all known living systems. Without it, life as we know it cannot exist. The main economic uses of carbon other than food and wood are hydrocarbons, primarily fossil fuels methane gas and crude oil. Crude oil is processed by refineries to produce gasoline, kerosene and other products. Cellulose is a naturally occurring carbon-containing polymer produced by plants in the form of wood, cotton, flax and hemp. Cellulose is mainly used to maintain the structure of plants. Commercially valuable animal-based carbon polymers include wool, cashmere, and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms incorporated at regular intervals into the polymer backbone. The raw material for many of these synthetics comes from crude oil. The use of carbon and its compounds is 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 manufacture, in electrodes for dry batteries and electroplating and electroforming, in brushes for electric motors, and as a neutron moderator in nuclear reactors. Charcoal is used as a material for making art, as a barbecue grill, for smelting iron, and for many other uses. Wood, coal and oil are used as fuel for energy production and for heating. Diamonds High Quality are used in jewelry making, while industrial diamonds are used for drilling, cutting and polishing metal and stone working tools. Plastics are made from fossil hydrocarbons, and carbon fiber, made from the pyrolysis of synthetic polyester fibers, is used to reinforce plastics into advanced, lightweight composite materials. Carbon fiber is made by pyrolyzing extruded and stretched filaments of polyacrylonitrile (PAN) and other organic materials. The crystal structure and mechanical properties of the fiber depend on the type of starting material and subsequent processing. Carbon fibers made from PAN have a structure resembling narrow filaments of graphite, but heat treatment can reorder 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, artists' oil paint and watercolors, carbon paper, automotive trim, 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 diverse as gas masks, water treatment, and cooker hoods, and 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 in iron (smelting). Solidification 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 cutting and grinding abrasives. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all interior surfaces in environments other than glass, stone, and metal.
diamonds
The diamond industry is divided into two categories, one is high quality diamonds (gems) and the other is industrial grade diamonds. While there is a lot of trading in both types of diamonds, the two markets operate quite differently. Unlike precious metals such as gold or platinum, gemstone diamonds are not traded as a commodity: there is a substantial markup on the sale of diamonds and the resale market for diamonds is not very active. Industrial diamonds are valued mainly for their hardness and thermal conductivity, while the gemological qualities of clarity and color are largely irrelevant. About 80% of mined diamonds (equal to about 100 million carats or 20 tons per year) are unusable and are used in industry (diamond scrap). Synthetic diamonds, invented in the 1950s, were found almost immediately industrial applications; 3 billion carats (600 tons) of synthetic diamonds are produced annually. The dominant industrial use of diamond is 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-sized diamonds, can be used in industry. Diamonds are inserted into drill tips or saw blades, or ground into a powder for use in grinding and polishing. Specialized applications include use in laboratories as storage for experiments high pressure, high performance bearings and limited use in specialized boxes. Thanks to advances in the production of synthetic diamonds, new applications are becoming feasible. Much attention has been given 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, С, chemical element of group IV periodic system, atomic weight 12.00, serial number 6. Until recently, carbon was considered to have no isotopes; only recently has the existence of the C 13 isotope been discovered with the help of particularly sensitive methods. Carbon is one of the most important elements in terms of abundance, abundance and diversity of its compounds, biological significance(as an organogen), by the vastness of the technical use of carbon itself and its compounds (as a raw material and as a source of energy for industrial and domestic needs), and finally, by its role in the development of chemical science. Carbon in the free state reveals a pronounced phenomenon of allotropy, which has been known for more than a century and a half, but still not fully understood, both because of the extreme difficulty in obtaining carbon in a chemically pure form, and because most of the constants of allotropic modifications of carbon vary greatly depending on morphological features of their structure, due to the method and conditions of obtaining.
Carbon forms two crystalline forms - diamond and graphite, and is also known in the amorphous state in the form of the so-called. amorphous coal. The individuality of the latter as a result of recent studies was disputed: coal was identified with graphite, considering both as morphological varieties of the same form - "black carbon", and the difference in their properties was explained by the physical structure and degree of dispersion of the substance. However, at the very recent times facts were obtained confirming the existence of coal as a special allotropic form (see below).
Natural sources and stocks of carbon. In terms of abundance in nature, carbon occupies 10th place among the elements, accounting for 0.013% of the atmosphere, 0.0025% of the hydrosphere and about 0.35% of the entire mass of the earth's crust. Most of the carbon is in the form of oxygen compounds: atmospheric air contains ~800 billion tons of carbon in the form of CO 2 dioxide; in the water of the oceans and seas - up to 50,000 billion tons of carbon in the form of CO 2, carbonic acid ions and bicarbonates; in rocks ax - insoluble carbonates (calcium, magnesium and other metals), and the share of one CaCO 3 accounts for ~160·10 6 billion tons of carbon. These colossal reserves, however, do not represent an energy value; much more valuable are combustible carbonaceous materials - fossil coals, peat, then oil, hydrocarbon gases and other natural bitumens. The stock of these substances in the earth's crust is also quite significant: the total mass of carbon in fossil coals reaches ~6000 billion tons, in oil ~10 billion tons, etc. In the free state, carbon is quite rare (diamond and part of the graphite substance). Fossil coals contain little or no free carbon: they consist of Ch. arr. from high-molecular (polycyclic) and very stable compounds of carbon with other elements (H, O, N, S) are still very little studied. Carbonaceous compounds of living nature (the biosphere of the globe), synthesized in plant and animal cells, are distinguished by an extraordinary variety of properties and composition quantities; the most common substances in the plant world - fiber and lignin - also play a role as energy resources.
Carbon maintains a constant distribution in nature due to the continuous cycle, the cycle of which is made up of the synthesis of complex organic substances in plant and animal cells and of the reverse disaggregation of these substances during their oxidative decay (combustion, decay, respiration), leading to the formation of CO 2 , which is reused plants for synthesis. The general scheme of this circulation can be. presented in the following form:
Getting carbon. Carbonaceous compounds of plant and animal origin are unstable at high temperatures and, when heated to at least 150-400 ° C without air, decompose, releasing water and volatile carbon compounds and leaving a solid non-volatile residue rich in carbon and commonly called coal. This pyrolytic process is called charring, or dry distillation, and is widely used in engineering. High-temperature pyrolysis of fossil coals, oil and peat (at a temperature of 450-1150°C) leads to the release of carbon in graphite form (coke, retort coal). The higher the charring temperature of the starting materials, the closer the resulting coal or coke is in composition to free carbon, and in properties to graphite.
Amorphous coal, which is formed at temperatures below 800 ° C, cannot be. we consider it as free carbon, because it contains significant amounts of chemically bound other elements, Ch. arr. hydrogen and oxygen. Of the technical products, activated carbon and soot are closest in properties to amorphous carbon. The purest coal can be. obtained by charring pure sugar or piperonal, special treatment of carbon black, etc. Artificial graphite obtained by electrothermal means is almost pure carbon in composition. Natural graphite is always contaminated with mineral impurities and also contains a certain amount of bound hydrogen (H) and oxygen (O); in a relatively pure state, it can be. received only after special treatments: mechanical enrichment, washing, treatment with oxidizing agents and calcination at high temperature until the complete removal of volatile substances. Carbon technology never deals with perfectly pure carbon; this applies not only to natural carbon raw materials, but also to the products of its enrichment, refining and thermal decomposition (pyrolysis). Below is the carbon content of some carbonaceous materials (in %):
Physical properties of carbon. Free carbon is almost completely infusible, non-volatile, and at ordinary temperature is insoluble in any of the known solvents. It dissolves only in certain molten metals, especially at temperatures approaching the boiling point of the latter: in iron (up to 5%), silver (up to 6%) | ruthenium (up to 4%), cobalt, nickel, gold and platinum. In the absence of oxygen, carbon is the most refractory material; the liquid state for pure carbon is unknown, and its transformation into vapor begins only at temperatures above 3000°C. Therefore, the determination of the properties of carbon was carried out exclusively for the solid state of aggregation. Of the modifications of carbon, diamond has the most constant physical properties; the properties of graphite in its various samples (even the purest ones) vary considerably; the properties of amorphous coal are even more variable. The most important physical constants of various modifications of carbon are compared in the table.
Diamond is a typical dielectric, while graphite and carbon have metallic electrical conductivity. In absolute value, their conductivity varies over a very wide range, but for coals it is always lower than for graphites; in graphites, it approaches the conductivity of real metals. The heat capacity of all modifications of carbon at a temperature of >1000°C tends to a constant value of 0.47. At temperatures below -180°C, the heat capacity of diamond becomes vanishingly small, and at -27°C it practically becomes equal to zero.
Chemical properties of carbon. When heated above 1000°C, both diamond and coal gradually transform into graphite, which therefore should be considered as the most stable (at high temperatures) monotropic form of carbon. The transformation of amorphous carbon into graphite apparently begins at about 800°C and ends at 1100°C (at this last point, coal loses its adsorption activity and ability to reactivate, and its electrical conductivity increases sharply, remaining almost constant in the future). Free carbon is characterized by inertness at ordinary temperatures and significant activity at high temperatures. Amorphous carbon is the most active chemically, while diamond is the most resistant. For example, fluorine reacts with coal at 15°C, with graphite only at 500°C, and with diamond at 700°C. When heated in air, porous coal begins to oxidize below 100°C, graphite at about 650°C, and diamond above 800°C. At a temperature of 300°C and above, coal combines with sulfur to form carbon disulfide CS 2 . At temperatures above 1800°C, carbon (coal) begins to interact with nitrogen, forming (in small amounts) cyanogen C 2 N 2 . The interaction of carbon with hydrogen begins at 1200°C, and in the temperature range of 1200-1500°C, only methane CH 4 is formed; above 1500 ° C - a mixture of methane, ethylene (C 2 H 4) and acetylene (C 2 H 2); at a temperature of about 3000°C almost exclusively acetylene is obtained. At the temperature of the electric arc, carbon enters into direct combination with metals, silicon and boron, forming the corresponding carbides. Direct or indirect ways m. b. compounds of carbon with all known elements were obtained, except for gases of the zero group. Carbon is a non-metallic element that exhibits some signs of amphotericity. The carbon atom has a diameter of 1.50 Ᾰ (1Ᾰ = 10 -8 cm) and contains external sphere 4 valence electrons, which are equally easily given away or supplemented to 8; therefore, the normal valency of carbon, both oxygen and hydrogen, is four. In the vast majority of its compounds, carbon is tetravalent; only a small number are known compounds of divalent carbon (carbon monoxide and its acetals, isonitriles, explosive acid and its salts) and trivalent (the so-called "free radical").
With oxygen, carbon forms two normal oxides: acidic carbon dioxide CO 2 and neutral carbon monoxide CO. In addition, there are a number carbon suboxides containing more than 1 atom C, having no technical significance; of these, the most famous is the underoxidation of the composition C 3 O 2 (a gas with a boiling point of +7 ° C and a melting point of -111 ° C). The first combustion product of carbon and its compounds is CO 2, which is formed according to the equation:
C + O 2 \u003d CO 2 +97600 cal.
The formation of CO during incomplete combustion of fuel is the result of a secondary reduction process; in this case, carbon itself serves as a reducing agent, which reacts with CO 2 at temperatures above 450 ° C according to the equation:
CO 2 + C \u003d 2CO -38800 cal;
this reaction is reversible; above 950°C, the conversion of CO 2 into CO becomes almost complete, which is carried out in gas-generating furnaces. The energetic reducing ability of carbon at high temperatures is also used in the production of water gas (H 2 O + C \u003d CO + H 2 -28380 cal) and in metallurgical processes - to obtain a free metal from its oxide. Allotropic forms of carbon are treated differently to the action of some oxidizing agents: for example, a mixture of KCIO 3 + HNO 3 does not affect diamond at all, amorphous coal is completely oxidized by it into CO 2, while graphite gives compounds of the aromatic series - graphitic acids with the empirical formula (C 2 OH) x and beyond mellitic acid C 6 (COOH) 6 . Compounds of carbon with hydrogen - hydrocarbons - are extremely numerous; most of the remaining organic compounds are genetically produced from them, which, in addition to carbon, most often include H, O, N, S and halides.
The exceptional variety of organic compounds, of which up to 2 million are known, is due to certain features of carbon as an element. 1) Carbon is characterized by the strength of a chemical bond with most other elements, both metallic and non-metallic, due to which it forms fairly stable compounds with both. Combining with other elements, carbon is very little inclined to form ions. Most organic compounds are of the homeopolar type and do not dissociate under normal conditions; the rupture of intramolecular bonds in them often requires the expenditure of a significant amount of energy. When judging the strength of bonds, one should, however, distinguish; a) absolute bond strength, measured by thermochemical means, and b) the ability of the bond to break under the action of various reagents; these two characteristics do not always coincide. 2) Carbon atoms bond with each other with exceptional ease (nonpolar), forming carbon chains, open or closed. The length of such chains appears to be unrestricted; thus, completely stable molecules with open chains of 64 carbon atoms are known. The elongation and complication of open chains does not affect the strength of the connection of their links with each other or with other elements. Among closed chains, 6- and 5-membered rings are most easily formed, although annular chains containing from 3 to 18 carbon atoms are known. The ability of carbon atoms to interconnect well explains the special properties of graphite and the mechanism of charring processes; it also makes clear the fact that carbon is unknown in the form of diatomic C 2 molecules, which might be expected by analogy with other light non-metallic elements (in vapor form, carbon consists of monatomic molecules). 3) Due to the non-polar nature of the bonds, many carbon compounds have chemical inertness not only external (slow response), but also internal (difficulty in intramolecular rearrangements). The presence of large "passive resistances" greatly complicates the spontaneous transformation of unstable forms into stable ones, often reducing the rate of such a transformation to zero. The result of this is the possibility of implementing a large number isomeric forms, almost equally stable at ordinary temperature.
Allotropy and the atomic structure of carbon. X-ray analysis made it possible to reliably establish the atomic structure of diamond and graphite. The same research method shed light on the question of the existence of a third allotropic modification carbon, which is essentially a question of the amorphism or crystallinity of coal: if coal is an amorphous formation, then it cannot be. identified neither with graphite nor with diamond, but should be considered as special shape carbon as an individual simple substance. In a diamond, carbon atoms are arranged in such a way that each atom lies in the center of a tetrahedron, the vertices of which are 4 adjacent atoms; each of the latter, in turn, is the center of another such tetrahedron; the distances between adjacent atoms are 1.54 Ᾰ (the edge of the elementary cube of the crystal lattice is 3.55 Ᾰ). This structure is the most compact; it corresponds to high hardness, density and chemical inertness of diamond (uniform distribution of valence forces). The mutual bonding of carbon atoms in the diamond lattice is the same as in the molecules of most fatty organic compounds (tetrahedral model of carbon). In graphite crystals, carbon atoms are arranged in dense layers spaced from one another by 3.35-3.41 Ᾰ; the direction of these layers coincides with the cleavage planes and slip planes during mechanical deformations. In the plane of each layer, the atoms form a grid with hexagonal cells (companies); the side of such a hexagon is 1.42-1.45 Ᾰ. In adjacent layers, the hexagons do not lie one under the other: their vertical coincidence is repeated only after 2 layers in the third. The three bonds of each carbon atom lie in the same plane, forming angles of 120°; The 4th bond is directed alternately in one direction or another from the plane to the atoms of neighboring layers. The distances between atoms in a layer are strictly constant, while the distance between individual layers can be changed by external influences: for example, when pressed under pressure up to 5000 atm, it decreases to 2.9 Ᾰ, and when graphite swells in concentrated HNO 3, it increases to 8 Ᾰ. In the plane of one layer, the carbon atoms are homeopolarly bonded (as in hydrocarbon chains), while the bonds between the atoms of adjacent layers are rather metallic in nature; this can be seen from the fact that the electrical conductivity of graphite crystals in the direction perpendicular to the layers is ~100 times higher than the conductivity in the direction of the layer. That. graphite has the properties of a metal in one direction and the properties of a non-metal in the other. The arrangement of carbon atoms in each layer of the graphite lattice is exactly the same as in the molecules of complex aromatic compounds. This configuration well explains the sharp anisotropy of graphite, the exceptionally developed cleavage, antifriction properties, and the formation of aromatic compounds during its oxidation. Amorphous modification of black carbon, apparently, exists as an independent form (O. Ruff). For her, the most likely is a foamy cellular structure, devoid of any regularity; the walls of such cells are formed by layers of active atoms carbon about 3 atoms thick. In practice, the active substance of coal usually lies under a shell of closely spaced inactive carbon atoms oriented graphite-like, and is permeated with inclusions of very small graphite crystallites. There is probably no definite point of coal → graphite transformation: between both modifications, a continuous transition occurs, during which the randomly crowded mass of C-atoms of amorphous coal is rearranged into the regular crystal lattice of graphite. Due to their random arrangement, carbon atoms in amorphous coal show a maximum of residual affinity, which (according to Langmuir's ideas about the identity of adsorption forces with valence forces) corresponds to the high adsorption and catalytic activity so characteristic of coal. Carbon atoms oriented in the crystal lattice spend all their affinity (in diamond) or most of it (in graphite) for mutual adhesion; this corresponds to a decrease in chemical activity and adsorption activity. For diamond, adsorption is possible only on the surface of a single crystal, while for graphite, residual valence can appear on both surfaces of each flat lattice (in the “gaps” between layers of atoms), which is confirmed by the fact that graphite can swell in liquids (HNO 3) and the mechanism of its oxidation to graphitic acid.
The technical significance of carbon. As for b. or m. of free carbon obtained during the processes of charring and coking, then its use in technology is based both on chemical (inertness, reducing ability) and on its physical properties (heat resistance, electrical conductivity, adsorption capacity). So, coke and charcoal, in addition to their partial direct utilization as flameless fuel, are used to produce gaseous fuel (generator gases); in the metallurgy of ferrous and non-ferrous metals - for the reduction of metal oxides (Fe, Cu, Zn, Ni, Cr, Mn, W, Mo, Sn, As, Sb, Bi); in chemical technology - as a reducing agent in the production of sulfides (Na, Ca, Ba) from sulfates, anhydrous chloride salts (Mg, Al), from metal oxides, in the production of soluble glass and phosphorus - as a raw material for the production of calcium carbide, carborundum and other carbides carbon disulfide, etc.; in construction business - as the heat-insulating material. Retort coal and coke serve as material for the electrodes of electric furnaces, electrolytic baths and galvanic cells, for the manufacture of arc coals, rheostats, collector brushes, melting crucibles, etc., and also as a packing in tower-type chemical equipment. Charcoal, in addition to the above applications, is used to obtain concentrated carbon monoxide, cyanide salts, for carburizing steel, is widely used as an adsorbent, as a catalyst for some synthetic reactions, and finally is part of black powder and other explosive and pyrotechnic compositions.
Analytical determination of carbon. Qualitatively, carbon is determined by charring a sample of a substance without access to air (which is far from suitable for all substances) or, which is much more reliable, by exhaustively oxidizing it, for example, by calcining it in a mixture with copper oxide, and the formation of CO 2 is proved by ordinary reactions. To quantify carbon, a sample of a substance is burned in an oxygen atmosphere; the resulting CO 2 is captured by the alkali solution and determined by weight or volume by conventional methods of quantitative analysis. This method is suitable for determining carbon not only in organic compounds and industrial coals, but also in metals.
Structure of a diamond (a) and graphite (b)
Carbon(Latin carboneum) - C, a chemical element of the IV group of the periodic system of Mendeleev, atomic number 6, atomic mass 12.011. It occurs in nature in the form of crystals of diamond, 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 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, adsorption of gases, 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 highly hard and are used to make abrasive and cutting tools. Carbon is present in steels and alloys in the elemental state and in the form of carbides. Saturation of the surface of steel castings with carbon at high temperature (carburizing) significantly increases the surface hardness and wear resistance.
History reference
Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that other material can be marked with graphite, and the very name "graphite", which comes from the Greek word meaning "to write", was proposed by A. Werner in 1789. However, the history of graphite is confused, often substances with similar external physical properties were mistaken for it. , such as molybdenite (molybdenum sulfide), at one time considered graphite. Among other names of graphite, "black lead", "iron carbide", "silver lead" are known.
In 1779, K. Scheele found that graphite can be oxidized with air to form carbon dioxide. For the first time, diamonds found use in India, and in Brazil, precious stones acquired commercial importance 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. Artificial diamonds, the technology of which was created in 1970, are produced for industrial purposes.
Properties
Four crystalline modifications of carbon are known:
- graphite,
- diamond,
- carbine,
- lonsdaleite.
Graphite- gray-black, opaque, greasy to the touch, scaly, very soft mass with a metallic sheen. At room temperature and normal pressure (0.1 MN/m2, or 1 kgf/cm2), graphite is thermodynamically stable.
Diamond- very solid, crystalline substance. Crystals have a cubic face-centered lattice. At room temperature and normal pressure, diamond is metastable. A noticeable transformation of diamond into graphite is observed at temperatures above 1400°C in vacuum or in an inert atmosphere. At atmospheric pressure and a temperature of about 3700 ° C, graphite sublimates.
Liquid carbon can be obtained at pressures above 10.5 MN/m2 (105 kgf/cm2) and temperatures above 3700°C. Solid carbon (coke, soot, charcoal) is also characterized by a state with a disordered structure - the so-called "amorphous" carbon, which is not an independent modification; its structure is based on the structure of fine-grained graphite. Heating some varieties of "amorphous" carbon above 1500-1600 ° C without air causes their transformation into graphite.
The physical properties of "amorphous" carbon depend very strongly on the dispersion of particles and the presence of impurities. Density, heat capacity, thermal conductivity and electrical conductivity of "amorphous" carbon is always higher than graphite.
Carbine obtained artificially. It is a finely crystalline powder of black color (density 1.9-2 g / cm 3). Built from long chains of atoms FROM laid parallel to each other.
Lonsdaleite found in meteorites and obtained artificially; its structure and properties have not been finally established.
Properties of carbon | ||
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atomic number | 6 | |
Atomic mass | 12,011 | |
Isotopes: | stable | 12, 13 |
unstable | 8, 9, 10, 11, 14, 15, 16, 17, 18, 19, 20, 21, 22 | |
Melting temperature | 3550°C | |
Boiling temperature | 4200°C | |
Density | 1.9-2.3 g / cm 3 (graphite) 3.5-3.53 g / cm 3 (diamond) |
|
Hardness (Mohs) | 1-2 | |
Content in the earth's crust (mass.) | 0,19% | |
Oxidation states | -4; +2; +4 |
Alloys
Steel
Coke is used in metallurgy as a reducing agent. Charcoal - in forges, to obtain gunpowder (75% KNO 3 + 13% C + 12% S), to absorb gases (adsorption), as well as in everyday life. Soot is used as a rubber filler, for the manufacture of black paints - printing ink and ink, as well as in dry galvanic cells. Glassy carbon is used for the manufacture of equipment for highly aggressive environments, as well as in aviation and astronautics.
Activated charcoal absorbs harmful substances from gases and liquids: they fill gas masks, purification systems, it is used in medicine for poisoning.
Carbon is the basis of all organic substances. Every living organism is to a large extent from carbon. Carbon is the basis of life. The source of carbon for living organisms is usually CO 2 from the atmosphere or water. As a result of photosynthesis, it enters biological food chains in which living things eat each other or the remains of each other and thereby extract carbon to build their own body. The biological cycle of carbon ends either with oxidation and return to the atmosphere, or with disposal in the form of coal or oil.
The use of the radioactive isotope 14 C contributed to the success molecular biology in the study of the mechanisms of protein biosynthesis and transmission hereditary information. Determination of the specific activity of 14 C in carbonaceous organic remains makes it possible to judge their age, which is used in paleontology and archeology.
Sources
Chemical elements and materials |
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Chemical elements | Nitrogen. Argon. Hydrogen. Helium. Iron . Calcium. Oxygen. Silicon. Magnesium. Manganese. |
Physical properties: carbon forms many allotropic modifications: diamond one of the hardest substances graphite, coal, soot.
A carbon atom has 6 electrons: 1s 2 2s 2 2p 2 . The last two electrons are located in separate p-orbitals and are unpaired. In principle, this pair could occupy one orbital, but in this case the interelectron repulsion strongly increases. For this reason, one of them takes 2p x, and the other, either 2p y , or 2p z-orbitals.
The difference between the energies of the s- and p-sublevels of the outer layer is small, therefore, the atom quite easily passes into an excited state, in which one of the two electrons from the 2s-orbital passes to a free one. 2r. A valence state arises having the configuration 1s 2 2s 1 2p x 1 2p y 1 2p z 1 . It is this state of the carbon atom that is characteristic of the diamond lattice - the tetrahedral spatial arrangement of hybrid orbitals, the same bond length and energy.
This phenomenon is known to be called sp 3 -hybridization, and the resulting functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three rr- and one s-s-bond. In addition to sp 3 hybridization, sp 2 and sp hybridization are also observed at the carbon atom . In the first case, there is a mutual overlap s- and two p-orbitals. Three equivalent sp 2 - hybrid orbitals are formed, located in the same plane at an angle of 120 ° to each other. The third orbital p is unchanged and directed perpendicular to the plane sp2.
In sp hybridization, the s and p orbitals overlap. An angle of 180° arises between the two equivalent hybrid orbitals formed, while the two p-orbitals of each of the atoms remain unchanged.
Allotropy of carbon. diamond and graphite
In a graphite crystal, carbon atoms are located in parallel planes, occupying the vertices of regular hexagons in them. Each of the carbon atoms is linked to three adjacent sp 2 hybrid bonds. Between parallel planes, the connection is carried out due to van der Waals forces. Free p-orbitals of each of the atoms are directed perpendicular to the planes of covalent bonds. Their overlap explains the additional π-bond between carbon atoms. So from the valence state in which carbon atoms are in a substance, the properties of this substance depend.
Chemical properties of carbon
The most characteristic oxidation states: +4, +2.
At low temperatures, carbon is inert, but when heated, its activity increases.
Carbon as a reducing agent:
- with oxygen
C 0 + O 2 - t ° \u003d CO 2 carbon dioxide
with a lack of oxygen - incomplete combustion:
2C 0 + O 2 - t° = 2C +2 O carbon monoxide
- with fluorine
C + 2F 2 = CF 4
- with steam
C 0 + H 2 O - 1200 ° \u003d C + 2 O + H 2 water gas
— with metal oxides. In this way metal is smelted from ore.
C 0 + 2CuO - t ° \u003d 2Cu + C +4 O 2
- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) \u003d C +4 O 2 + 2SO 2 + 2H 2 O
С 0 + 4HNO 3 (conc.) = С +4 O 2 + 4NO 2 + 2H 2 O
- forms carbon disulfide with sulfur:
C + 2S 2 \u003d CS 2.
Carbon as an oxidizing agent:
- forms carbides with some metals
4Al + 3C 0 \u003d Al 4 C 3
Ca + 2C 0 \u003d CaC 2 -4
- with hydrogen - methane (as well as a huge amount of organic compounds)
C 0 + 2H 2 \u003d CH 4
- with silicon, forms carborundum (at 2000 ° C in an electric furnace):
Finding carbon in nature
Free carbon occurs as diamond and graphite. In the form of compounds, carbon is found in minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 *CaCO 3; bicarbonates - Mg (HCO 3) 2 and Ca (HCO 3) 2, CO 2 is part of the air; carbon is the main component of natural organic compounds - gas, oil, coal, peat, is part of organic substances, proteins, fats, carbohydrates, amino acids that are part of living organisms.
Inorganic carbon compounds
Neither C 4+ nor C 4- ions are formed in any conventional chemical processes: there are covalent bonds of different polarity in carbon compounds.
Carbon monoxide (II) SO
Carbon monoxide; colorless, odorless, sparingly soluble in water, soluble in organic solvents, poisonous, bp = -192°C; t sq. = -205°C.
Receipt
1) In industry (in gas generators):
C + O 2 = CO 2
2) In the laboratory - thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):
HCOOH = H2O + CO
H 2 C 2 O 4 \u003d CO + CO 2 + H 2 O
Chemical properties
Under ordinary conditions, CO is inert; when heated - reducing agent; non-salt-forming oxide.
1) with oxygen
2C +2 O + O 2 \u003d 2C +4 O 2
2) with metal oxides
C +2 O + CuO \u003d Cu + C +4 O 2
3) with chlorine (in the light)
CO + Cl 2 - hn \u003d COCl 2 (phosgene)
4) reacts with alkali melts (under pressure)
CO + NaOH = HCOONa (sodium formate)
5) forms carbonyls with transition metals
Ni + 4CO - t° = Ni(CO) 4
Fe + 5CO - t° = Fe(CO) 5
Carbon monoxide (IV) CO2
Carbon dioxide, colorless, odorless, solubility in water - 0.9V CO 2 dissolves in 1V H 2 O (under normal conditions); heavier than air; t°pl.= -78.5°C (solid CO 2 is called "dry ice"); does not support combustion.
Receipt
- Thermal decomposition of salts of carbonic acid (carbonates). Limestone firing:
CaCO 3 - t ° \u003d CaO + CO 2
- The action of strong acids on carbonates and bicarbonates:
CaCO 3 + 2HCl \u003d CaCl 2 + H 2 O + CO 2
NaHCO 3 + HCl \u003d NaCl + H 2 O + CO 2
ChemicalpropertiesCO2
Acid oxide: reacts with basic oxides and bases to form carbonic acid salts
Na 2 O + CO 2 \u003d Na 2 CO 3
2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O
NaOH + CO 2 \u003d NaHCO 3
May exhibit oxidizing properties at elevated temperatures
C +4 O 2 + 2Mg - t ° \u003d 2Mg +2 O + C 0
Qualitative reaction
Turbidity of lime water:
Ca (OH) 2 + CO 2 \u003d CaCO 3 ¯ (white precipitate) + H 2 O
It disappears when CO 2 is passed through lime water for a long time, because. insoluble calcium carbonate is converted to soluble bicarbonate:
CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2
carbonic acid and itssalt
H2CO3 — Weak acid, exists only in aqueous solution:
CO 2 + H 2 O ↔ H 2 CO 3
Dual base:
H 2 CO 3 ↔ H + + HCO 3 - Acid salts - bicarbonates, bicarbonates
HCO 3 - ↔ H + + CO 3 2- Medium salts - carbonates
All properties of acids are characteristic.
Carbonates and bicarbonates can be converted into each other:
2NaHCO 3 - t ° \u003d Na 2 CO 3 + H 2 O + CO 2
Na 2 CO 3 + H 2 O + CO 2 \u003d 2NaHCO 3
Metal carbonates (except alkali metals) decarboxylate when heated to form an oxide:
CuCO 3 - t ° \u003d CuO + CO 2
Qualitative reaction- "boiling" under the action of a strong acid:
Na 2 CO 3 + 2HCl \u003d 2NaCl + H 2 O + CO 2
CO 3 2- + 2H + = H 2 O + CO 2
Carbides
calcium carbide:
CaO + 3 C = CaC 2 + CO
CaC 2 + 2 H 2 O \u003d Ca (OH) 2 + C 2 H 2.
Acetylene is released when zinc, cadmium, lanthanum and cerium carbides react with water:
2 LaC 2 + 6 H 2 O \u003d 2La (OH) 3 + 2 C 2 H 2 + H 2.
Be 2 C and Al 4 C 3 are decomposed by water to form methane:
Al 4 C 3 + 12 H 2 O \u003d 4 Al (OH) 3 \u003d 3 CH 4.
Titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum - as an abrasive and material for heaters) are used in technology.
cyanides
obtained by heating soda in an atmosphere of ammonia and carbon monoxide:
Na 2 CO 3 + 2 NH 3 + 3 CO \u003d 2 NaCN + 2 H 2 O + H 2 + 2 CO 2
Hydrocyanic acid HCN is an important chemical industry product widely used in organic synthesis. Its world production reaches 200 thousand tons per year. Electronic structure cyanide anion, similarly to carbon monoxide (II), such particles are called isoelectronic:
C = O:[:C = N:]-
Cyanides (0.1-0.2% aqueous solution) are used in gold mining:
2 Au + 4 KCN + H 2 O + 0.5 O 2 \u003d 2 K + 2 KOH.
When cyanide solutions are boiled with sulfur or when solids are fused, thiocyanates:
KCN + S = KSCN.
When cyanides of low-active metals are heated, cyanide is obtained: Hg (CN) 2 \u003d Hg + (CN) 2. cyanide solutions are oxidized to cyanates:
2KCN + O2 = 2KOCN.
Cyanic acid exists in two forms:
H-N=C=O; H-O-C = N:
In 1828, Friedrich Wöhler (1800-1882) obtained urea from ammonium cyanate: NH 4 OCN \u003d CO (NH 2) 2 by evaporating an aqueous solution.
This event is usually seen as the victory of synthetic chemistry over "vitalistic theory".
There is an isomer of cyanic acid - fulminic acid
H-O-N=C.
Its salts (mercury fulminate Hg(ONC) 2) are used in impact igniters.
Synthesis urea(carbamide):
CO 2 + 2 NH 3 \u003d CO (NH 2) 2 + H 2 O. At 130 0 C and 100 atm.
Urea is an amide of carbonic acid, there is also its "nitrogen analogue" - guanidine.
Carbonates
The most important organic compounds carbon - salts of carbonic acid (carbonates). H 2 CO 3 is a weak acid (K 1 \u003d 1.3 10 -4; K 2 \u003d 5 10 -11). Carbonate buffer supports carbon dioxide balance in the atmosphere. The oceans have a huge buffer capacity because they are an open system. The main buffer reaction is the equilibrium during the dissociation of carbonic acid:
H 2 CO 3 ↔ H + + HCO 3 -.
With a decrease in acidity, additional absorption of carbon dioxide from the atmosphere occurs with the formation of acid:
CO 2 + H 2 O ↔ H 2 CO 3.
With an increase in acidity, carbonate rocks (shells, chalk and limestone deposits in the ocean) dissolve; this compensates for the loss of hydrocarbonate ions:
H + + CO 3 2- ↔ HCO 3 -
CaCO 3 (tv.) ↔ Ca 2+ + CO 3 2-
Solid carbonates are converted into soluble hydrocarbons. It is this process of chemical dissolution of excess carbon dioxide that counteracts the "greenhouse effect" - global warming due to the absorption of Earth's thermal radiation by carbon dioxide. Approximately one third of the world's production of soda (sodium carbonate Na 2 CO 3) is used in the manufacture of glass.
MOU "Nikiforovskaya average comprehensive school№1"
Carbon and its main inorganic compounds
abstract
Completed by: student of class 9B
Sidorov Alexander
Teacher: Sakharova L.N.
Dmitrievka 2009
Introduction
Chapter I. All About Carbon
1.1. carbon in nature
1.2. Allotropic modifications of carbon
1.3. Chemical properties of carbon
1.4. Application of carbon
Chapter II. Inorganic carbon compounds
Conclusion
Literature
Introduction
Carbon (lat. Carboneum) C is a chemical element of Group IV of the Mendeleev periodic system: atomic number 6, atomic mass 12.011(1). Consider the structure of the carbon atom. There are four electrons in the outer energy level of the carbon atom. Let's graph it:
Carbon has been known since ancient times, and the name of the discoverer of this element is unknown.
At the end of the XVII century. Florentine scientists Averani and Targioni tried to fuse several small diamonds into one large one and heated them with the help of burning glass with the sun's rays. The diamonds disappeared after burning in the air. In 1772, the French chemist A. Lavoisier showed that CO 2 is formed during the combustion of diamond. Only in 1797, the English scientist S. Tennant proved the identity of the nature of graphite and coal. After burning equal amounts of coal and diamond, the volumes of carbon monoxide (IV) turned out to be the same.
The variety of carbon compounds, which is explained by the ability of its atoms to combine with each other and with atoms of other elements in various ways, determines the special position of carbon among other elements.
Chapter I . All about carbon
1.1. carbon in nature
Carbon is found in nature both in the free state and in the form of compounds.
Free carbon occurs as diamond, graphite, and carbine.
Diamonds are very rare. The largest known diamond - "Cullinan" was found in 1905 in South Africa, weighed 621.2 g and measured 10 × 6.5 × 5 cm. The Diamond Fund in Moscow holds one of the largest and most beautiful diamonds in world - "Orlov" (37.92 g).
The diamond got its name from the Greek. "adamas" - invincible, indestructible. The most significant diamond deposits are located in South Africa, Brazil, and Yakutia.
Large deposits of graphite are located in Germany, in Sri Lanka, in Siberia, in Altai.
The main carbon-bearing minerals are: magnesite MgCO 3, calcite (lime spar, limestone, marble, chalk) CaCO 3, dolomite CaMg (CO 3) 2, etc.
All fossil fuels - oil, gas, peat, hard and brown coal, shale - are built on a carbon basis. Close in composition to carbon are some fossil coals containing up to 99% C.
Carbon accounts for 0.1% of the earth's crust.
In the form of carbon monoxide (IV) CO 2 carbon is part of the atmosphere. A large amount of CO 2 is dissolved in the hydrosphere.
1.2. Allotropic modifications of carbon
Elemental carbon forms three allotropic modifications: diamond, graphite, carbine.
1. Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly. Carbon atoms in diamond are in a state of sp 3 hybridization. In the excited state, the valence electrons in the carbon atoms are depaired and four unpaired electrons are formed. When chemical bonds are formed, electron clouds acquire the same elongated shape and are located in space so that their axes are directed towards the vertices of the tetrahedron. When the tops of these clouds overlap with clouds of other carbon atoms, covalent bonds appear at an angle of 109°28", and an atomic crystal lattice is formed, which is characteristic of diamond.
Each carbon atom in a diamond is surrounded by four others located from it in directions from the center of the tetrahedra to the vertices. The distance between atoms in tetrahedra is 0.154 nm. The strength of all bonds is the same. Thus, the atoms in a diamond are "packed" very tightly. At 20°C, the density of diamond is 3.515 g/cm 3 . This explains its exceptional hardness. Diamond does not conduct well electricity.
In 1961, the Soviet Union began industrial production synthetic diamonds from graphite.
In the industrial synthesis of diamonds, pressures of thousands of MPa and temperatures from 1500 to 3000°C are used. The process is carried out in the presence of catalysts, which can be some metals, such as Ni. The bulk of the formed diamonds are small crystals and diamond dust.
Diamond, when heated without access to air above 1000 ° C, turns into graphite. At 1750°C, the transformation of diamond into graphite occurs rapidly.
Structure of a diamond
2. Graphite is a gray-black crystalline substance with a metallic sheen, greasy to the touch, inferior in hardness even to paper.
Carbon atoms in graphite crystals are in a state of sp 2 hybridization: each of them forms three covalent σ bonds with neighboring atoms. The angles between the bond directions are 120°. The result is a grid composed of regular hexagons. The distance between adjacent nuclei of carbon atoms within the layer is 0.142 nm. The fourth electron of the outer layer of each carbon atom in graphite occupies a p-orbital, which is not involved in hybridization.
Non-hybrid electron clouds of carbon atoms are oriented perpendicular to the plane of the layer, and overlapping with each other, form delocalized σ-bonds. Neighboring layers in a graphite crystal are located at a distance of 0.335 nm from each other and are weakly interconnected, mainly by van der Waals forces. Therefore, graphite has low mechanical strength and is easily split into flakes, which are very strong in themselves. The bond between the layers of carbon atoms in graphite is partially metallic. This explains the fact that graphite conducts electricity well, but still not as well as metals.
graphite structure
Physical properties in graphite differ greatly in directions - perpendicular and parallel to the layers of carbon atoms.
When heated without access to air, graphite does not undergo any changes up to 3700°C. At this temperature, it sublimates without melting.
Artificial graphite is obtained from the best grades of hard coal at 3000°C in electric furnaces without air access.
Graphite is thermodynamically stable over a wide range of temperatures and pressures, so it is accepted as the standard state of carbon. The density of graphite is 2.265 g/cm 3 .
3. Carbin - fine-grained black powder. In his crystal structure carbon atoms are connected by alternating single and triple bonds in linear chains:
−С≡С−С≡С−С≡С−
This substance was first obtained by V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin, Yu.P. Kudryavtsev in the early 1960s.
Subsequently, it was shown that carbyne can exist in different forms and contains both polyacetylene and polycumulene chains in which carbon atoms are linked double bonds:
C=C=C=C=C=C=
Later, carbine was found in nature - in meteorite matter.
Carbyne has semiconductor properties; under the action of light, its conductivity increases greatly. Due to the existence of different types of bonds and different ways of stacking chains of carbon atoms in the crystal lattice physical properties carbine can vary widely. When heated without access to air above 2000°C, carbine is stable; at temperatures of about 2300°C, its transition to graphite is observed.
Natural carbon consists of two isotopes (98.892%) and (1.108%). In addition, minor impurities of a radioactive isotope, which are obtained artificially, were found in the atmosphere.
Previously, it was believed that charcoal, soot and coke are close in composition to pure carbon and differ in properties from diamond and graphite, represent an independent allotropic modification of carbon (“amorphous carbon”). However, it was found that these substances consist of the smallest crystalline particles in which carbon atoms are connected in the same way as in graphite.
4. Coal - finely divided graphite. It is formed during the thermal decomposition of carbon-containing compounds without air access. Coals differ significantly in properties depending on the substance from which they are obtained and the method of production. They always contain impurities that affect their properties. The most important grades of coal are coke, charcoal, and soot.
Coke is obtained by heating coal in the absence of air.
Charcoal is formed when wood is heated in the absence of air.
Soot is a very fine graphite crystalline powder. It is formed during the combustion of hydrocarbons (natural gas, acetylene, turpentine, etc.) with limited air access.
Activated carbons are porous industrial adsorbents consisting mainly of carbon. Adsorption is the absorption by the surface of solids of gases and dissolved substances. Active carbons are obtained from solid fuels (peat, brown and hard coal, anthracite), wood and its products (charcoal, sawdust, paper production waste), leather industry waste, animal materials, such as bones. Coals, characterized by high mechanical strength, are produced from the shells of coconuts and other nuts, from the seeds of fruits. The structure of coals is represented by pores of all sizes, however, the adsorption capacity and adsorption rate are determined by the content of micropores per unit mass or volume of granules. In the production of active carbon, the raw material is first subjected to heat treatment without air access, as a result of which moisture and partially resins are removed from it. In this case, a large-pore structure of coal is formed. To obtain a microporous structure, activation is carried out either by oxidation with gas or steam, or by treatment with chemical reagents.
1.3. Chemical properties of carbon
At ordinary temperatures diamond, graphite, coal are chemically inert, but at high temperatures their activity increases. As follows from the structure of the main forms of carbon, coal reacts more easily than graphite and even more so diamond. Graphite is not only more reactive than diamond, but, reacting with certain substances, it can form products that diamond does not form.
1. As an oxidizing agent, carbon reacts with certain metals at high temperatures to form carbides:
ZS + 4Al \u003d Al 4 C 3 (aluminum carbide).
2. With hydrogen, coal and graphite form hydrocarbons. The simplest representative - methane CH 4 - can be obtained in the presence of a Ni catalyst at a high temperature (600-1000 ° C):
C + 2H 2 CH 4.
3. When interacting with oxygen, carbon exhibits reducing properties. With the complete combustion of carbon of any allotropic modification, carbon monoxide (IV) is formed:
C + O 2 \u003d CO 2.
Incomplete combustion produces carbon monoxide (II) CO:
C + O 2 \u003d 2CO.
Both reactions are exothermic.
4. The reducing properties of coal are especially pronounced when interacting with metal oxides (zinc, copper, lead, etc.), for example:
C + 2CuO \u003d CO 2 + 2Cu,
C + 2ZnO = CO 2 + 2Zn.
The most important process of metallurgy is based on these reactions - the smelting of metals from ores.
In other cases, for example, when interacting with calcium oxide, carbides are formed:
CaO + 3C \u003d CaC 2 + CO.
5. Coal is oxidized with hot concentrated sulfuric and nitric acids:
C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O,
ZS + 4HNO 3 \u003d ZSO 2 + 4NO + 2H 2 O.
All forms of carbon are resistant to alkalis!
1.4. Application of carbon
Diamonds are used for processing various hard materials, for cutting, grinding, drilling and engraving glass, for drilling rocks. Diamonds after grinding and cutting turn into diamonds used as jewelry.
Graphite is the most valuable material for modern industry. Graphite is used to make molds, melting crucibles and other refractory products. Due to its high chemical resistance, graphite is used for the manufacture of pipes and apparatus lined with graphite plates from the inside. Significant amounts of graphite are used in the electrical industry, for example, in the manufacture of electrodes. Graphite is used to make pencils and some paints, as a lubricant. Very pure graphite is used in nuclear reactors to moderate neutrons.
A linear polymer of carbon, carbine, is attracting the attention of scientists as a promising material for the manufacture of semiconductors that can operate at high temperatures and ultra-strong fibers.
Charcoal is used in the metallurgical industry, in blacksmithing.
Coke is used as a reducing agent in the smelting of metals from ores.
Soot is used as a filler for rubber to increase strength, so car tires are black. Soot is also used as a component of printing inks, ink, and shoe polish.
Activated carbons are used to purify, extract and separate various substances. Activated carbons are used as fillers for gas masks and as a sorbent agent in medicine.
Chapter II . Inorganic carbon compounds
Carbon forms two oxides - carbon monoxide (II) CO and carbon monoxide (IV) CO 2.
Carbon monoxide (II) CO is a colorless, odorless gas, slightly soluble in water. It is called carbon monoxide because it is very poisonous. Getting into the blood during breathing, it quickly combines with hemoglobin, forming a strong carboxyhemoglobin compound, thereby depriving hemoglobin of the ability to carry oxygen.
When inhaling air containing 0.1% CO, a person can suddenly lose consciousness and die. Carbon monoxide is formed during incomplete combustion of fuel, which is why premature closing of chimneys is so dangerous.
Carbon monoxide (II) is referred, as you already know, to non-salt-forming oxides, since, being a non-metal oxide, it must react with alkalis and basic oxides to form salt and water, but this is not observed.
2CO + O 2 \u003d 2CO 2.
Carbon monoxide (II) is able to take oxygen from metal oxides, i.e. recover metals from their oxides.
Fe 2 O 3 + ZSO \u003d 2Fe + ZSO 2.
It is this property of carbon monoxide (II) that is used in metallurgy for iron smelting.
Carbon monoxide (IV) CO 2 - commonly known as carbon dioxide - is a colorless, odorless gas. It is about one and a half times heavier than air. Under normal conditions, 1 volume of carbon dioxide dissolves in 1 volume of water.
At a pressure of about 60 atm, carbon dioxide turns into a colorless liquid. When liquid carbon dioxide evaporates, part of it turns into a solid snow-like mass, which is pressed in industry - this is the “dry ice” you know, which is used to store food. You already know that solid carbon dioxide has a molecular lattice and is capable of sublimation.
Carbon dioxide CO 2 is a typical acid oxide: Reacts with alkalis (eg causes cloudiness in lime water), basic oxides and water.
It does not burn and does not support combustion and therefore is used to extinguish fires. However, magnesium continues to burn in carbon dioxide to form oxide and release carbon as soot.
CO 2 + 2Mg \u003d 2MgO + C.
Carbon dioxide is obtained by acting on salts of carbonic acid - carbonates with solutions of hydrochloric, nitric and even acetic acids. In the laboratory, carbon dioxide is produced by the action of hydrochloric acid on chalk or marble.
CaCO 3 + 2HCl \u003d CaCl 2 + H 2 0 + C0 2.
In industry, carbon dioxide is produced by burning limestone:
CaCO 3 \u003d CaO + C0 2.
Carbon dioxide, in addition to the already mentioned field of application, is also used for the manufacture of fizzy drinks and for the production of soda.
When carbon monoxide (IV) is dissolved in water, carbonic acid H 2 CO 3 is formed, which is very unstable and easily decomposes into its original components - carbon dioxide and water.
As a dibasic acid, carbonic acid forms two series of salts: medium - carbonates, for example CaCO 3, and acidic - bicarbonates, for example Ca (HCO 3) 2. Of the carbonates, only potassium, sodium and ammonium salts are soluble in water. Acid salts are usually soluble in water.
With an excess of carbon dioxide in the presence of water, carbonates can turn into hydrocarbons. So, if carbon dioxide is passed through lime water, then it will first become cloudy due to the precipitation of water-insoluble calcium carbonate, however, with further passage of carbon dioxide, the cloudiness disappears as a result of the formation of soluble calcium bicarbonate:
CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2.
It is the presence of this salt that explains the temporary hardness of water. Why temporary? Because when heated, soluble calcium bicarbonate turns back into insoluble carbonate:
Ca (HCO 3) 2 \u003d CaCO 3 ↓ + H 2 0 + C0 2.
This reaction leads to the formation of scale on the walls of boilers, steam heating pipes and domestic kettles, and in nature, as a result of this reaction, bizarre stalactites hanging down are formed in caves, towards which stalagmites grow from below.
Other calcium and magnesium salts, in particular chlorides and sulfates, give the water permanent hardness. Boiling permanent water hardness cannot be eliminated. You have to use another carbonate - soda.
Na 2 CO 3, which precipitates these Ca 2+ ions, for example:
CaCl 2 + Na 2 CO 3 \u003d CaCO 3 ↓ + 2NaCl.
Soda can also be used to eliminate temporary hardness of water.
Carbonates and bicarbonates can be detected using acid solutions: when exposed to acids, a characteristic “boiling” is observed due to the released carbon dioxide.
This reaction is a qualitative reaction to carbonic acid salts.
Conclusion
All life on earth is based on carbon. Each molecule of a living organism is built on the basis of a carbon skeleton. Carbon atoms are constantly migrating from one part of the biosphere (the narrow shell of the Earth where life exists) to another. Using the example of the carbon cycle in nature, one can trace the dynamics of life on our planet in dynamics.
The main carbon reserves on Earth are in the form of carbon dioxide contained in the atmosphere and dissolved in the oceans, that is, carbon dioxide (CO 2). Consider first the carbon dioxide molecules in the atmosphere. Plants absorb these molecules, then in the process of photosynthesis the carbon atom is converted into a variety of organic compounds and thus included in the structure of plants. Following are several options:
1. Carbon can remain in plants until the plants die. Then their molecules will be eaten by decomposers (organisms that feed on dead organic matter and at the same time break it down to simple inorganic compounds), such as fungi and termites. Eventually the carbon will return to the atmosphere as CO 2 ;
2. Plants can be eaten by herbivores. In this case, carbon will either return to the atmosphere (during the respiration of animals and during their decomposition after death), or herbivores will be eaten by carnivores (and then carbon will again return to the atmosphere in the same ways);
3. Plants may die and end up underground. Then eventually they will turn into fossil fuels - for example, into coal.
In the case of dissolution of the original CO 2 molecule in sea water, several options are also possible:
Carbon dioxide can simply return to the atmosphere (this type of mutual gas exchange between the oceans and the atmosphere occurs all the time);
Carbon can enter the tissues of marine plants or animals. Then it will gradually accumulate in the form of sediments on the bottom of the oceans and eventually turn into limestone or again pass from the sediments into sea water.
Once carbon is incorporated into sediments or fossil fuels, it is removed from the atmosphere. Throughout the existence of the Earth, the carbon withdrawn in this way was replaced by carbon dioxide released into the atmosphere during volcanic eruptions and other geothermal processes. In modern conditions, emissions from human combustion of fossil fuels are also added to these natural factors. Due to the influence of CO 2 on the greenhouse effect, the study of the carbon cycle has become an important task for atmospheric scientists.
Integral part one of these searches is to determine the amount of CO 2 present in plant tissues (for example, in a newly planted forest) – scientists call this carbon sink. Because governments different countries are trying to reach an international agreement to limit CO 2 emissions, the issue of a balanced ratio of sinks and carbon emissions in individual states has become a major bone of contention for industrial countries. However, scientists doubt that the accumulation of carbon dioxide in the atmosphere can be stopped by forest plantations alone.
Carbon constantly circulates in the earth's biosphere along closed interconnected pathways. Currently to natural processes added to the effects of burning fossil fuels.
Literature:
1. Akhmetov N.S. Chemistry grade 9: textbook. for general education textbook establishments. - 2nd ed. – M.: Enlightenment, 1999. – 175 p.: ill.
2. Gabrielyan O.S. Chemistry grade 9: textbook. for general education textbook establishments. - 4th ed. - M.: Bustard, 2001. - 224 p.: ill.
3. Gabrielyan O.S. Chemistry grades 8-9: method. allowance. - 4th ed. – M.: Bustard, 2001. – 128 p.
4. Eroshin D.P., Shishkin E.A. Methods for solving problems in chemistry: textbook. allowance. – M.: Enlightenment, 1989. – 176 p.: ill.
5. Kremenchugskaya M. Chemistry: Schoolchildren's Handbook. – M.: Philol. Society "WORD": LLC "Publishing House AST", 2001. - 478 p.
6. Kritsman V.A. Reading book on inorganic chemistry. – M.: Enlightenment, 1986. – 273 p.