Carbon chemical formula. What is carbon? Description, properties and formula of carbon

One of the most amazing elements that can form a huge variety of compounds of organic and inorganic nature is carbon. This is an element so unusual in its properties that even Mendeleev predicted a great future for it, talking about features that have not yet been disclosed.

Later this was practically confirmed. It became known that he is the main biogenic element of our planet, which is part of absolutely all living things. In addition, it is capable of existing in such forms that are radically different in all parameters, but at the same time they consist only of carbon atoms.

In general, this structure has many features, and it is with them that we will try to figure it out in the course of the article.

Carbon: formula and position in the system of elements

In the periodic table, the element carbon is located in group IV (according to a new sample in 14), the main subgroup. Its ordinal number is 6, and its atomic weight is 12.011. The designation of an element by the sign C indicates its name in Latin - carboneum. There are several different forms in which carbon exists. Therefore, its formula is different and depends on the specific modification.

However, there is, of course, a specific designation for writing reaction equations. In general, when we talk about a substance in its pure form, the molecular formula of carbon C is accepted, without indexing.

Item discovery history

By itself, this element has been known since antiquity. After all, one of the most important minerals in nature is coal. Therefore, for the ancient Greeks, Romans and other peoples, it was not a secret.

Besides this variety, diamonds and graphite were also used. For a long time, there were many confusing situations with the latter, since often without analyzing the composition, such compounds were taken as graphite:

• silver lead;
• iron carbide;
• molybdenum sulfide.

They were all painted black and therefore were considered graphite. Later, this misunderstanding was clarified, and this form of carbon became itself.

Since 1725, diamonds have acquired great commercial importance, and in 1970 the technology of obtaining them artificially was mastered. Since 1779, thanks to the work of Karl Scheele, the chemical properties that carbon exhibits have been studied. This was the beginning of a number of important discoveries in the field of this element and became the basis for clarifying all of its unique features.

Carbon isotopes and distribution in nature

Despite the fact that the element under consideration is one of the most important biogenic elements, its total content in the mass of the earth's crust is 0.15%. This is due to the fact that it undergoes constant circulation, the natural cycle in nature.

In general, you can name several compounds of a mineral nature, which include carbon. These are such natural breeds as:

• dolomites and limestones;
• anthracite;
• oil shale;
• natural gas;
• coal;
• oil;
• brown coal;
• peat;
• bitumen.

In addition, one should not forget about living things, which are simply a storehouse of carbon compounds. After all, they form proteins, fats, carbohydrates, nucleic acids, which means the most vital structural molecules. In general, on recalculation of dry body mass, out of 70 kg, 15 falls on a pure element. And so it is with every person, not to mention animals, plants and other creatures.

If we consider both water, that is, the hydrosphere as a whole and the atmosphere, then there is a carbon-oxygen mixture, expressed by the formula CO 2. Dioxide or carbon dioxide is one of the main gases that make up air. It is in this form that the mass fraction of carbon is 0.046%. Even more dissolved carbon dioxide in the waters of the oceans.

The atomic mass of carbon as an element is 12.011. It is known that this value is calculated as the arithmetic mean between the atomic weights of all isotopic varieties existing in nature, taking into account their prevalence (in percentage). This also happens with the substance in question. There are three main isotopes that carbon is found in. It:

• 12 С - its mass fraction in the overwhelming majority is 98.93%;
• 13 C - 1.07%;
• 14 С - radioactive, half-life 5700 years, stable beta-emitter.

In the practice of determining the geochronological age of samples, the 14 C radioactive isotope is widely used, which is an indicator due to its long decay period.

Allotropic element modifications

Carbon is an element that, as a simple substance, exists in several forms. That is, it is capable of forming the largest number of allotropic modifications known to date.

1. Crystalline variations - exist in the form of strong structures with regular atomic lattices. This group includes such varieties as:

• diamonds;
• fullerenes;
• graphites;
• carbines;
• lonsdaleites;
• and tubes.

They all differ in lattice, in the sites of which there is a carbon atom. Hence the completely unique, dissimilar properties, both physical and chemical.

2. Amorphous forms - they are formed by a carbon atom, which is part of some natural compounds. That is, these are not pure varieties, but with impurities of other elements in small quantities. This group includes:

• Activated carbon;
• stone and wood;
• soot;
• carbon nanofoam;
• anthracite;
• glassy carbon;
• technical type of substance.

They are also united by the structural features of the crystal lattice, which explain and manifest properties.

3. Compounds of carbon in the form of clusters. Such a structure, in which the atoms are closed in a special hollow conformation from the inside, filled with water or the nuclei of other elements. Examples:

• carbon nanocones;
• astralenes;
• dicarbon.

Physical properties of amorphous carbon

Due to the wide variety of allotropic modifications, it is difficult to isolate any general physical properties for carbon. It's easier to talk about a specific form. For example, amorphous carbon has the following characteristics.

1. All forms are based on fine-crystalline varieties of graphite.
2. High heat capacity.
3. Good conductive properties.
4. The density of carbon is about 2 g / cm 3.
5. When heated above 1600 0 С, a transition to graphite forms occurs.

Carbon black and stone varieties are widely used for technical purposes. They are not a manifestation of pure carbon modification, but they contain very large amounts of it.

Crystalline carbon

There are several options in which carbon is a substance that forms regular crystals of various types, where atoms are connected in series. As a result, the following modifications are formed.

1. - cubic, in which four tetrahedrons are connected. As a result, all covalent chemical bonds of each atom are maximally saturated and strong. This explains the physical properties: the density of carbon is 3300 kg / m 3. High hardness, low heat capacity, lack of electrical conductivity - all this is the result of the structure of the crystal lattice. There are technically produced diamonds. Formed during the transition of graphite to the next modification under the influence of high temperature and a certain pressure. In general, it is as high as the strength - about 3500 0 С.
2. Graphite. The atoms are located similarly to the structure of the previous substance, however, only three bonds are saturated, and the fourth becomes longer and less durable, it connects the "layers" of the hexagonal rings of the lattice. As a result, it turns out that graphite is a soft, greasy black substance. It has good electrical conductivity and has a high melting point - 3525 0 С. It is capable of sublimation - sublimation from a solid to a gaseous state, bypassing the liquid state (at a temperature of 3700 0 С). The density of carbon is 2.26 g / cm 3, which is much lower than that of diamond. This explains their different properties. Due to the layered structure of the crystal lattice, it is possible to use graphite for the manufacture of lead pencils. When passed over the paper, the flakes flake off and leave a black trail on the paper.
3. Fullerenes. They were discovered only in the 80s of the last century. They are modifications in which the carbons are combined into a special convex closed structure with a void in the center. Moreover, the shape of the crystal is a polyhedron, of the correct organization. The number of atoms is even. The most famous form of fullerene is C 60. Samples of a similar substance were found during research:

• meteorites;
• bottom sediments;
• foilgurites;
• shungites;
• outer space, where they were contained in the form of gases.

All types of crystalline carbon are of great practical importance, since they have a number of properties useful in technology.

Chemical activity

Molecular carbon exhibits low reactivity due to its stable configuration. It is possible to force it to enter into reactions only by imparting additional energy to the atom and forcing the electrons of the external level to evaporate. At this moment, the valency becomes equal to 4. Therefore, in compounds it has an oxidation state of + 2, + 4, - 4.

Almost all reactions with simple substances, both metals and non-metals, proceed under the influence of high temperatures. The element in question can be both an oxidizing agent and a reducing agent. However, the latter properties are especially pronounced in him, it is on this that his use in metallurgical and other industries is based.

In general, the ability to enter into chemical interaction depends on three factors:

• dispersion of carbon;
• allotropic modification;
• reaction temperature.

Thus, in some cases, there is an interaction with the following substances:

• non-metals (hydrogen, oxygen);
• metals (aluminum, iron, calcium and others);
• metal oxides and their salts.

Does not react with acids and alkalis, very rarely with halogens. The most important of the properties of carbon is the ability to form long chains among themselves. They can close in a cycle, form ramifications. This is how the formation of organic compounds occurs, which today number in the millions. The basis of these compounds are two elements - carbon, hydrogen. Also, the composition may include other atoms: oxygen, nitrogen, sulfur, halogens, phosphorus, metals and others.

Basic compounds and their characteristics

There are many different compounds that contain carbon. The formula of the most famous of them is CO 2 - carbon dioxide. However, in addition to this oxide, there is also CO - monoxide or carbon monoxide, as well as C 3 O 2 under-oxide.

Among the salts that contain this element, the most common are calcium and magnesium carbonates. So, calcium carbonate has several synonyms in the name, since it occurs in nature in the form:

• chalk;
• marble;
• limestone;
• dolomite.

The importance of carbonates of alkaline earth metals is manifested in the fact that they are active participants in the formation of stalactites and stalagmites, as well as groundwater.

Carbonic acid is another compound that forms carbon. Its formula is H 2 CO 3. However, in its usual form, it is extremely unstable and immediately decomposes in solution into carbon dioxide and water. Therefore, only its salts are known, and not she herself, as a solution.

Carbon halides - are obtained mainly indirectly, since direct syntheses take place only at very high temperatures and with a low product yield. One of the most common is CCL 4 - carbon tetrachloride. Poisonous compound that can cause poisoning if inhaled. Obtained by reactions of radical photochemical substitution in methane.

Metal carbides are carbon compounds in which it exhibits oxidation state 4. It is also possible that there are combinations with boron and silicon. The main property of some metal carbides (aluminum, tungsten, titanium, niobium, tantalum, hafnium) is high strength and excellent electrical conductivity. Boron carbide B 4 C is one of the hardest substances after diamond (9.5 according to Mohs). These compounds are used in engineering, as well as in the chemical industry, as sources of hydrocarbons (calcium carbide with water leads to the formation of acetylene and calcium hydroxide).

Many metal alloys are made using carbon, thereby significantly increasing their quality and technical characteristics (steel is an alloy of iron with carbon).

Numerous organic carbon compounds deserve special attention, in which it is a fundamental element capable of combining with the same atoms in long chains of various structures. These include:

• alkanes;
• alkenes;
• arenas;
• proteins;
• carbohydrates;
• nucleic acids;
• alcohols;
• carboxylic acids and many other classes of substances.

Application of carbon

The importance of carbon compounds and its allotropic modifications in human life is very great. We can name a few of the most global industries to make it clear that this is indeed the case.

1. This element forms all types of organic fuel, from which a person receives energy.
2. The metallurgical industry uses carbon as a powerful reducing agent for the production of metals from their compounds. Carbonates are also widely used here.
3. The construction and chemical industries consume a huge amount of carbon compounds to synthesize new substances and obtain the necessary products.

You can also name such sectors of the economy as:

• nuclear industry;
• jewelry making;
• technical equipment (lubricants, heat-resistant crucibles, pencils, etc.);
• determination of the geological age of rocks - a radioactive indicator 14 С;
• carbon is an excellent adsorbent, which allows it to be used for making filters.

The cycle in nature

The mass of carbon found in nature is included in a constant cycle, which occurs cyclically every second around the globe. Thus, the atmospheric source of carbon, CO 2, is absorbed by plants and released by all living things in the process of respiration. Once in the atmosphere, it is absorbed again, and so the cycle does not stop. In this case, the dying off of organic residues leads to the release of carbon and its accumulation in the ground, from where it is then again absorbed by living organisms and excreted into the atmosphere in the form of gas.

Carbon(lat. Carboneum), C, chemical element of group IV of Mendeleev's periodic system, atomic number 6, atomic mass 12.011. There are two known stable isotopes: 12 C (98.892%) and 13 C (1.108%). The most important of the radioactive isotopes is 14 C with a half-life (T ½ = 5.6 · 10 3 years). Small amounts of 14 C (about 2 · 10 -10% by mass) are constantly formed in the upper atmosphere under the action of cosmic radiation neutrons on the nitrogen isotope 14 N. Their age is determined by the specific activity of the 14 C isotope in the residues of biogenic origin. 14 C is widely used as an isotope indicator.

Historical reference. Carbon has been known since ancient times. Charcoal was used to recover metals from ores, diamond - as a precious stone. Much later, graphite began to be used for the manufacture of crucibles and pencils.

In 1778, K. Scheele, heating graphite with saltpeter, discovered that in this case, as when heating coal with saltpeter, carbon dioxide was released. The chemical composition of diamond was established as a result of the experiments of A. Lavoisier (1772) on the study of diamond combustion in air and the research of S. Tennant (1797), who proved that equal amounts of diamond and coal give equal amounts of carbon dioxide during oxidation. Carbon was recognized as a chemical element in 1789 by Lavoisier. The Latin name sagboneum Carbon received from carbo - coal.

Distribution of carbon in nature. The average carbon content in the earth's crust is 2.3 10 -2% by mass (1 10 -2 in ultrabasic, 1 10 -2 - in basic, 2 acidic rocks). Carbon accumulates in the upper part of the earth's crust (biosphere): in living matter 18% Carbon, wood 50%, coal 80%, oil 85%, anthracite 96%. A significant part of the carbon of the lithosphere is concentrated in limestones and dolomites.

The number of own minerals of Carbon - 112; extremely large number of organic compounds of Carbon - hydrocarbons and their derivatives.

The accumulation of carbon in the earth's crust is associated with the accumulation of many other elements sorbed by organic matter and precipitated in the form of insoluble carbonates, etc. CO 2 and carbonic acid play a large geochemical role in the earth's crust. A huge amount of CO 2 is released during volcanism - in the history of the Earth, it was the main source of carbon for the biosphere.

Compared to the average content in the earth's crust, mankind extracts carbon from the bowels of the earth in exceptionally large quantities (coal, oil, natural gas), since these fossils are the main source of energy.

The carbon cycle is of great geochemical importance.

Carbon is also widespread in space; on the Sun it ranks 4th after hydrogen, helium and oxygen.

Physical properties of Carbon. Several crystalline modifications of Carbon are known: graphite, diamond, carbyne, lonsdaleite, and others. Graphite is gray-black, opaque, oily to the touch, scaly, very soft mass with a metallic sheen. Built from crystals of a hexagonal structure: a = 2.462 Å, c = 6.701 Å. At room temperature and normal pressure (0.1 MN / m 2, or 1 kgf / cm 2), graphite is thermodynamically stable. Diamond is a very hard, crystalline substance. Crystals have a face-centered cubic lattice: a = 3.560 Å. At room temperature and normal pressure, diamond is metastable. A noticeable transformation of diamond into graphite is observed at temperatures above 1400 ° C in a vacuum or in an inert atmosphere. At atmospheric pressure and a temperature of about 3700 ° C, graphite sublimes. Liquid Carbon can be obtained at pressures above 10.5 MN / m 2 (105 kgf / cm 2) 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 does not represent an independent modification; its structure is based on the structure of fine-crystalline graphite. Heating some varieties of "amorphous" carbon above 1500-1600 ° C without access to air causes their transformation into graphite. The physical properties of "amorphous" carbon are highly dependent on the particle size and the presence of impurities. The density, heat capacity, thermal conductivity and electrical conductivity of "amorphous" carbon are always higher than graphite. Carbyne is obtained artificially. It is a fine-crystalline black powder (density 1.9-2 g / cm 3). Built from long chains of C atoms stacked parallel to each other. Lonsdaleite is found in meteorites and artificially obtained.

Chemical properties of Carbon. The configuration of the outer electron shell of a Carbon atom is 2s 2 2p 2. Carbon is characterized by the formation of four covalent bonds due to the excitation of the outer electron shell to the 2sp 3 state. Therefore, Carbon is equally capable of both attracting and donating electrons. The chemical bond can be carried out due to sp 3 -, sp 2 - and sp-hybrid orbitals, which correspond to coordination numbers 4, 3 and 2. The number of valence electrons of carbon and the number of valence orbitals are the same; this is one of the reasons for the stability of the bond between carbon atoms.

The unique ability of carbon atoms to combine with each other to form strong and long chains and cycles has led to the emergence of a huge number of various carbon compounds studied by organic chemistry.

In compounds, Carbon exhibits oxidation states of -4; +2; +4. Atomic radius 0.77 Å, covalent radii 0.77 Å, 0.67 Å, ​​0.60 Å, respectively, in single, double and triple bonds; ionic radius of C 4 - 2.60 Å, C 4+ 0.20 Å. Under normal conditions, carbon is chemically inert; at high temperatures, it combines with many elements, exhibiting strong reducing properties. Chemical activity decreases in the following order: "amorphous" Carbon, graphite, diamond; interaction with atmospheric oxygen (combustion) occurs, respectively, at temperatures above 300-500 ° C, 600-700 ° C and 850-1000 ° C with the formation of carbon monoxide (IV) CO 2 and carbon monoxide (II) CO.

CO 2 dissolves in water to form carbonic acid. In 1906 O. Diels received carbon undeoxide С 3 О 2. All forms of Carbon are resistant to alkalis and acids and are slowly oxidized only by very strong oxidants (chromium mixture, a mixture of concentrated HNO 3 and KClO 3, and others). "Amorphous" Carbon reacts with fluorine at room temperature, graphite and diamond when heated. Direct connection of Carbon with chlorine occurs in an electric arc; carbon does not react with bromine and iodine; therefore, numerous carbon halides are synthesized indirectly. Of the oxyhalides of the general formula COX 2 (where X is halogen), chloroxide COCl (phosgene) is best known. Hydrogen does not interact with diamond; reacts with graphite and "amorphous" carbon at high temperatures in the presence of catalysts (Ni, Pt): at 600-1000 ° C, mainly methane CH 4 is formed, at 1500-2000 ° C - acetylene C 2 H 2; other hydrocarbons may also be present in the products, for example, ethane C 2 H 6, benzene C 6 H 6. The interaction of sulfur with "amorphous" carbon and graphite begins at 700-800 ° C, with diamond at 900-1000 ° C; in all cases, carbon disulfide CS 2 is formed. Other carbon compounds containing sulfur (thioxide CS, thionedoxide C 3 S 2, sulfur dioxide COS and thiophosgene CSCl 2) are obtained indirectly. When CS 2 interacts with metal sulfides, thiocarbonates, salts of weak thiocarbonic acid, are formed. The interaction of carbon with nitrogen to produce cyanogen (CN) 2 occurs when an electric discharge is passed between carbon electrodes in a nitrogen atmosphere. Among the nitrogen-containing compounds of Carbon, hydrogen cyanide HCN (Hydrocyanic acid) and its numerous derivatives: cyanides, halocyanines, nitriles and others are of great practical importance. At temperatures above 1000 ° C, Carbon interacts with many metals, giving carbides. When heated, all forms of Carbon reduce metal oxides to form free metals (Zn, Cd, Cu, Pb and others) or carbides (CaC 2, Mo 2 C, WC, TaC and others). Carbon reacts at temperatures above 600-800 ° C with water vapor and carbon dioxide (Gasification of fuels). A distinctive feature of graphite is the ability, at moderate heating up to 300-400 ° C, to interact with alkali metals and halides with the formation of inclusion compounds of the type C 8 Me, C 24 Me, C 8 X (where X is halogen, Me is metal). Known compounds of inclusion of graphite with HNO 3, H 2 SO 4, FeCl 3 and others (for example, graphite bisulfate C 24 SO 4 H 2). All forms of Carbon are insoluble in common inorganic and organic solvents, but dissolve in some molten metals (e.g. Fe, Ni, Co).

The national economic significance of Carbon is determined by the fact that over 90% of all primary sources of energy consumed in the world are fossil fuels, the leading role of which will remain in the coming decades, despite the intensive development of nuclear energy. Only about 10% of the extracted fuel is used as raw material for basic organic synthesis and petrochemical synthesis, for the production of plastics and others.

Carbon in the body. Carbon is the most important biogenic element that forms the basis of life on Earth, a structural unit of a huge number of organic compounds participating in the construction of organisms and ensuring their vital activity (biopolymers, as well as numerous low molecular weight biologically active substances - vitamins, hormones, mediators, and others). A significant part of the energy necessary for organisms is formed in cells due to the oxidation of carbon. The emergence of life on Earth is considered in modern science as a complex process of the evolution of carbonaceous compounds.

The unique role of Carbon in living nature is due to its properties, which in the aggregate do not have any other element of the periodic system. Strong chemical bonds are formed between carbon atoms, as well as between carbon and other elements, which, however, can be broken under relatively mild physiological conditions (these bonds can be single, double and triple). The ability of Carbon to form 4 equivalent valence bonds with other carbon atoms makes it possible to build carbon skeletons of various types - linear, branched, cyclic. It is significant that only three elements - C, O and H - account for 98% of the total mass of living organisms. This achieves a certain cost-effectiveness in living nature: with an almost unlimited structural diversity of carbon compounds, a small number of types of chemical bonds can significantly reduce the amount of enzymes required for the breakdown and synthesis of organic substances. The structural features of the carbon atom underlie various types of isomerism of organic compounds (the ability for optical isomerism turned out to be decisive in the biochemical evolution of amino acids, carbohydrates, and some alkaloids).

According to the generally accepted hypothesis of A.I. Oparin, the first organic compounds on Earth were of abiogenic origin. The sources of carbon were methane (CH 4) and hydrogen cyanide (HCN) contained in the primary atmosphere of the Earth. With the emergence of life, the only source of inorganic carbon, due to which all organic matter of the biosphere is formed, is carbon monoxide (IV) (CO 2), which is in the atmosphere, and also dissolved in natural waters in the form of HCO 3. The most powerful mechanism of assimilation (assimilation) of carbon (in the form of CO 2) - photosynthesis - is carried out everywhere by green plants (about 100 billion tons of CO 2 are assimilated annually). On Earth, there is an evolutionarily more ancient way of assimilating CO 2 by chemosynthesis; in this case, chemosynthetic microorganisms use not the radiant energy of the sun, but the energy of oxidation of inorganic compounds. Most animals consume carbon in their diet in the form of ready-made organic compounds. Depending on the method of assimilation of organic compounds, it is customary to distinguish between autotrophic organisms and heterotrophic organisms. The use of microorganisms for the biosynthesis of protein and other nutrients, using petroleum hydrocarbons as the only source of carbon, is one of the most important modern scientific and technical problems.

The carbon content in living organisms calculated on dry matter is 34.5-40% in aquatic plants and animals, 45.4-46.5% in terrestrial plants and animals and 54% in bacteria. In the process of life of organisms, mainly due to tissue respiration, oxidative decomposition of organic compounds occurs with the release of CO 2 into the external environment. Carbon is also released in more complex metabolic end products. After the death of animals and plants, part of the Carbon is again converted into CO 2 as a result of putrefaction processes carried out by microorganisms. Thus, the carbon cycle occurs in nature. A significant part of Carbon is mineralized and forms deposits of fossil Carbon: coal, oil, limestone and others. In addition to the main function - a source of Carbon - СО 2, dissolved in natural waters and in biological fluids, participates in maintaining the acidity of the environment optimal for life processes. In the composition of CaCO 3, Carbon forms the outer skeleton of many invertebrates (for example, shells of mollusks), and is also found in corals, eggshells of birds and others. further, in the process of biological evolution, they turned into strong antimetabolites of metabolism.

In addition to stable isotopes of Carbon, radioactive 14 C is widespread in nature (it contains about 0.1 μcurie in the human body). Many major advances in the study of metabolism and the cycle of carbon in nature are associated with the use of carbon isotopes in biological and medical research. So, using a radiocarbon label, the possibility of fixing Н 14 СО 3 by plants and animal tissues was proved, the sequence of photosynthesis reactions was established, the exchange of amino acids was studied, the pathways of biosynthesis of many biologically active compounds were traced. The use of 14 С contributed to the success of molecular biology in the study mechanisms of protein biosynthesis and transmission of hereditary information. Determination of the specific activity of 14 C in carbon-containing organic residues makes it possible to judge their age, which is used in paleontology and archeology.

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

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

Modifications and properties of carbon

There are 4 known crystalline modifications of carbon: graphite, diamond, carbyne and lonsdaleite, which differ greatly in their properties. Carbyne is an artificially obtained type of carbon, which is a fine-crystalline black powder, the crystal structure of which is characterized by the presence of long chains of carbon atoms located parallel to each other. Density 3230-3300 kg / m 3, heat capacity 11.52 J / mol.K. Lonsdaleite found in meteorites and artificially obtained; its structure and physical properties have not been definitively established. Carbon is also characterized by a state with a disordered structure - the so-called. amorphous carbon (soot, coke, charcoal). The physical properties of "amorphous" carbon to a large extent depend on the particle size and on the presence of impurities.

Chemical properties of carbon

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

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

Carbon in nature

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

Application and use

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

Carbon (from Latin: carbo "coal") is a chemical element with the symbol C and atomic number 6. Four electrons are available to form covalent chemical bonds. The substance is non-metallic and tetravalent. Three isotopes of carbon occur naturally, 12C and 13C are stable, and 14C is a radioactive isotope that decays 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 the 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 variety 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 weight (about 18.5%) after oxygen. Carbon atoms can bond in different ways, called carbon allotropes. The most famous 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 low electrical conductivity. Under normal conditions, diamond, carbon nanotubes and graphene have the highest thermal conductivity of any known material. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form. They are chemically stable and require high temperatures to react even with oxygen. The most common oxidation state of carbon in inorganic compounds is +4, and +2 in carboxyl complexes of carbon monoxide and a transition metal. The largest sources of inorganic carbon are limestone, dolomite and carbon dioxide, but significant amounts come from organic deposits of coal, peat, oil and methanate clathrates. Carbon forms a huge number of compounds, more than any other element, with nearly 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."

Specifications

Allotropes of carbon include graphite, one of the softest substances known, and diamond, the hardest natural substance. Carbon binds readily 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 nearly 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, since its triple point is 10.8 ± 0.2 MPa and 4600 ± 300 K (~ 4330 ° C or 7 820 ° F), so it sublimes at about 3900 K. Graphite is much more reactive than diamond under standard conditions, despite being more thermodynamically stable, since its delocalized pi system is much more vulnerable to attack. For example, graphite can be oxidized with hot concentrated nitric acid under standard conditions to C6 (CO2H) 6 mellitic acid, which retains the hexagonal units of graphite while breaking down the larger structure. Carbon sublimes in a carbon arc at a temperature of 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 thermodynamically prone to oxidation, carbon 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 electronic configuration of the ground state 1s22s22p2, of which 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 that of the heavier elements of group 14. The electronegativity of carbon is 2.5, which is significantly higher than that of 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 row. Carbon covalent radii are generally accepted as 77.2 pm (CC), 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 with decreasing coordination number and increasing bond order. Carbon compounds form the basis of all known life on Earth, and the carbon-nitrogen cycle provides some of the energy released by the Sun and other stars. Although carbon forms an extraordinary variety of compounds, most forms of carbon are relatively unreactive under normal conditions. At standard temperatures and pressures, carbon will withstand all but the most powerful oxidants. It does not react with sulfuric acid, hydrochloric acid, chlorine or alkalis. At elevated temperatures, carbon reacts with oxygen to form carbon oxides and removes oxygen from the metal oxides, leaving an elemental metal. This exothermic reaction is used in the iron and steel industry to smelt iron and control the carbon content of steel:

Fe3О4 + 4 C (s) → 3 Fe (s) + 4 CO (g)

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

C (s) + H2O (g) → CO (g) + H2 (g)

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

Some types of graphite are used for thermal insulation (for example, firewalls and heat shields), but some other forms are good thermal conductors. Diamond is the most famous natural heat conductor. Graphite is opaque. The diamond is very transparent. Graphite crystallizes in a hexagonal system. Diamond crystallizes in a 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 different molecular configurations called allotropes. Three relatively well-known allotropes of carbon are amorphous carbon, graphite, and diamond. Previously considered exotic, fullerenes are now commonly synthesized and used in research; these include buckyballs, carbon nanotubes, carbon nanodots, and nanofibers. Several other exotic allotropes have also been discovered, such as lonsaletite, glassy carbon, carbon nanofaum, and linear acetylene carbon (carbyne). As of 2009, graphene is considered the most powerful material ever tested. The process of separating it from graphite will require some further technological development before it becomes economical for industrial processes. If successful, graphene could be used in the construction of space elevators. It can also be used to safely store hydrogen for use in hydrogen-based engines in automobiles. An 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 constituent of substances such as charcoal, lamp soot (soot) and activated carbon. At normal pressures, carbon is in 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 loosely connected through weak van der Waals forces. This gives the graphite its softness and splitting properties (the sheets slide easily one after the 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 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 is almost twice as dense as 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 in the world, as measured by its 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 barrier to activation, the transition to the graphite form is so slow at normal temperatures that it is invisible. Under certain conditions, carbon crystallizes as lonsaleite, a hexagonal crystal lattice with all covalently 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 additional) atoms deform the sheets into spheres, ellipses, or cylinders. The properties of fullerenes (divided into buckyballs, bakitubas, and nanobads) have not yet been fully analyzed and represent an intensive area of ​​research in nanomaterials. The names "fullerene" and "buckyball" are associated with the name of Richard Buckminster Fuller, popularizer of geodesic domes that resemble the structure of fullerenes. Buckyballs are fairly large molecules formed entirely from carbon bonds trigonally to form spheroids (the most famous and simplest is Baxinisterfellerene C60 with the shape of a soccer ball). Carbon nanotubes are structurally similar to buckyballs, except that each atom is bonded trigonally 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 one structure. Of the other allotropes found, carbon nanofoam is a ferromagnetic allotrope discovered in 1997. It consists of a cluster 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 one of the lightest solids with a density of about 2 kg / m3. Likewise, vitreous carbon contains a high proportion of closed porosity, but unlike conventional graphite, the graphite layers are not stacked like pages in a book, but are more randomly arranged. Linear acetylene carbon has a 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 carbyne is of considerable interest for nanotechnology, since 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 high-energy, low-duration laser pulse on amorphous carbon dust. Q-carbon is reported to exhibit ferromagnetism, fluorescence and hardness superior to diamonds.

Prevalence

Carbon is the fourth most abundant chemical element in the Universe by mass after hydrogen, helium and oxygen. Carbon is abundant in the sun, stars, comets, and the atmospheres of most planets. Some meteorites contain microscopic diamonds that were formed when the solar system was still a protoplanetary disk. Microscopic diamonds can also form under intense pressure and high temperature in areas of meteorite impact. In 2014, NASA announced an updated database 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 figure in the global PAH hypothesis, where they presumably play a role in abiogenesis and life formation. It appears that PAHs were formed “a couple of billion years” after the Big Bang, are widespread throughout the universe, and are associated with new stars and exoplanets. The earth's solid shell is estimated to contain 730 ppm of carbon overall, with 2,000 ppm in the core and 120 ppm in the combined mantle and crust. Since the mass of the earth is 5.9 72 × 1024 kg, this would mean 4360 million gigatons of carbon. This is much more than the amount of carbon in the oceans or the atmosphere (below). When combined with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 810 gigatons of carbon) and dissolves in all bodies of water (approximately 36,000 gigatons of carbon). The biosphere contains about 1,900 gigatons of carbon. Hydrocarbons (such as coal, oil, and natural gas) also contain carbon. Coal “reserves” (not “resources”) are around 900 gigatons with possibly 18,000 Gt of resources. Oil reserves are about 150 gigatons. Proven sources of natural gas are around 175 1012 cubic meters (containing about 105 gigatons of carbon), but studies have estimated 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 higher. According to one source, between 1751 and 2008, about 347 gigatons of carbon were released into the atmosphere as carbon dioxide into the atmosphere from the burning of fossil fuels. Another source adds the amount added to the atmosphere between 1750 and 879 Gt, and the total in the atmosphere, sea and land (eg peat bogs) is almost 2,000 Gt. Carbon is a constituent part (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 rocky kimberlite contained in ancient volcanic "necks" or "pipes." Most of the diamond deposits are located 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, the Russian Arctic, Brazil, and Northern and Western Australia. Now diamonds are also being recovered from the ocean floor off the Cape of Good Hope. Diamonds are found naturally, but about 30% of all industrial diamonds used in the United States are now produced. Carbon-14 is formed in the upper troposphere and stratosphere at altitudes of 9-15 km in a reaction that is precipitated by cosmic rays. Thermal neutrons are produced which collide with nitrogen-14 nuclei to form carbon-14 and a proton. Thus, 1.2 x 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 investigated by scientists. Asteroids can be used in hypothetical space-based coal mining, which may be possible in the future, but is currently technologically impossible.

Carbon isotopes

Carbon isotopes are atomic nuclei that contain six protons plus a range of neutrons (2 to 16). Carbon has two stable naturally occurring isotopes. The isotope carbon-12 (12C) forms 98.93% of the earth's carbon, 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. The identification of carbon in nuclear magnetic resonance (NMR) experiments 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 in amounts of up to 1 part per trillion (0.0000000001%), mainly in the atmosphere and surface sediments, in particular peat and other organic materials. This isotope decays during β-emission of 0.158 MeV. Due to its relatively short half-life, 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 was widely used to determine the age of carbonaceous materials up to 40,000 years old. There are 15 known isotopes of carbon and the shortest of them has 8C, which decays due to the emission of protons and alpha decay and has a half-life of 1.98739 × 10-21 s. Exotic 19C exhibits a nuclear halo, which means its radius is significantly larger than would be expected if the core were a sphere of constant density.

Star education

The formation of an atomic carbon nucleus requires an almost simultaneous triple collision of alpha particles (helium nuclei) inside the core of a giant or supergiant star, which is known as a triple alpha process, since the products of further nuclear fusion of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium -8 respectively, both of which are very unstable and decay back into smaller nuclei almost instantaneously. This occurs under conditions of temperatures over 100 mega calvin and helium concentration, which is unacceptable under the conditions of the rapid expansion and cooling of the early Universe, and therefore significant amounts of carbon were not created during the Big Bang. According to the modern theory of physical cosmology, carbon is formed inside stars in a horizontal branch through the collision and transformation of three helium nuclei. When these stars die like a supernova, carbon is scattered into space in the form of dust. This dust becomes a constituent material for the formation of second or third generation stellar systems with accreted planets. The solar system is one such stellar system with an abundance of carbon, enabling 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 different isotopic forms of carbon monoxide (for example, 12CO, 13CO and 18CO) are found in the submillimeter wavelength range and are used in the study of newly formed stars in molecular clouds.

Carbon cycle

Under terrestrial conditions, the conversion of one element into another is a very rare phenomenon. Therefore, the amount of carbon on Earth is effectively constant. Thus, in processes that use carbon, it must come from somewhere and be disposed of elsewhere. The pathways of carbon in the environment form the carbon cycle. For example, photosynthetic plants extract carbon dioxide from the atmosphere (or seawater) and build it into biomass, as in the Calvin cycle, the process of carbon fixation. Some of this biomass is eaten by animals, while some of the carbon is exhaled by animals as carbon dioxide. The carbon cycle is much more complex than this short cycle; for example, some carbon dioxide dissolves in the oceans; if bacteria 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 interconnected carbon-carbon bonds, a property called chain formation. Carbon-carbon bonds are stable. Through catanation (chain formation), carbon forms countless compounds. Evaluation of unique compounds shows that more of them contain carbon. A similar statement can be made for hydrogen because most organic compounds also contain hydrogen. The simplest form of an organic molecule is a hydrocarbon - a large family of organic molecules that 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 all forms 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 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

Usually carbon-containing compounds that are bound to minerals or that do not contain hydrogen or fluorine are treated separately from classical organic compounds; this definition is not strict. Among them are simple carbon oxides. The best known oxide is carbon dioxide (CO2). Once this substance was the main component of the paleoatmosphere, but today it is a minor component of the Earth's atmosphere. When dissolved in water, this substance forms carbon dioxide (H2CO3), but, like most compounds with several singly connected oxygen 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 by incomplete combustion and is a colorless, odorless gas. Each molecule contains a triple bond and is fairly polar, which causes it to constantly bind to hemoglobin molecules, displacing oxygen, which has a lower binding affinity. Cyanide (CN-) has a similar structure but behaves like 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), cyclopentanepeptone (C5O5), cyclohexanexone (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 salty carbides are not fully ionic compounds.

Organometallic compounds

Organometallic compounds, by definition, contain at least one carbon-metal bond. There is a wide variety of such compounds; major classes include simple alkyl metal compounds (eg tetraethylelide), η2-alkene compounds (eg Zeise salt), and η3-allyl compounds (eg allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands (eg ferrocene); and carbene complexes of transition metals. There are many metal carbonyls (eg tetracarbonylnickel); some workers believe that the carbon monoxide ligand is a purely inorganic, rather than organometallic, compound. While carbon is thought to exclusively form four bonds, an interesting compound has been reported containing an octahedral hexacoordinate carbon atom. The cation of this compound is 2+. This phenomenon is explained by the aurophilicity of the gold ligands. In 2016, it was confirmed that hexamethylbenzene contains a carbon atom with six bonds and not the usual four.

History and etymology

The English name for carbon (carbon) comes from the Latin carbo, meaning "coal" and "charcoal", hence the French word charbon, which means "charcoal". In German, Dutch and Danish, the names for carbon are Kohlenstoff, koolstof and kulstof respectively, all literally meaning coal. Carbon was discovered in prehistoric times and was known in the forms of soot and charcoal in the earliest human civilizations. Diamonds were probably already known as early as 2500 BC. in China, and carbon in the form of charcoal was made in Roman times by the same chemistry as today, by heating wood in a pyramid covered with clay to exclude air. In 1722, René Antoine Fercho de Réamour demonstrated that iron is converted to steel through the absorption of a substance now known as carbon. In 1772, Antoine Lavoisier showed that diamonds are a form of carbon; when he burned samples of charcoal and diamond and found that neither produced any water, and that both substances released an equal amount of carbon dioxide per gram. In 1779, Karl 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.Vandermond confirmed that graphite was primarily carbon, oxidized in oxygen in much the same way as Lavoisier did with diamond. A certain amount of iron remained again, which, according to the French scientists, was necessary for the structure of the graphite. In their publication, they proposed the name carbone (the Latin word for carbonum) for an element in graphite that was released as a gas when graphite was burned. Antoine Lavoisier then listed carbon as an element in his 1789 textbook. A new carbon allotrope, fullerene, which was discovered in 1985, includes nanostructural forms such as backyballs and nanotubes. Their pioneers - 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 deposits of graphite are found in many parts of the world, but the most economically important sources are found in China, India, Brazil, and North Korea. Graphite deposits are of metamorphic origin, found in combination 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. The graphite stocks in Borrowdale, Cumberland, England were initially of sufficient size and purity that, until the 19th century, pencils were made simply by sawing natural graphite blocks into strips before gluing the strips into the wood. Today, smaller deposits of graphite are produced by crushing the parent rock and floating the lighter graphite on water. There are three types of natural graphite - amorphous, flake, or crystalline. Amorphous graphite is of the lowest quality and is the most abundant. Unlike science, in industry, "amorphous" refers to a very small crystal size, rather than a complete absence of a crystal structure. The word "amorphous" is used for 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 United States. Flat graphite is less common and of a higher quality than amorphous graphite; it looks like separate plates that crystallize in metamorphic rocks. The price of granular graphite can be four times higher than the price of amorphous. Good quality flaked graphite can be processed into expandable graphite for many applications such as flame retardants. Primary deposits of graphite are found in Austria, Brazil, Canada, China, Germany and Madagascar. Liquid or lumpy graphite is the rarest, most valuable and highest quality type of natural graphite. It is found in veins along intrusive contacts in solid lumps, and is only commercially mined in Sri Lanka. According to the USGS, the world production of natural graphite in 2010 was 1.1 million tonnes, with 800,000 tonnes in China, 130,000 tonnes in India, 76,000 tonnes in Brazil, 30,000 tonnes in North Korea, and Canada 25,000 tonnes. No natural graphite was mined in the United States, but 118,000 tonnes of synthetic graphite were mined in 2009 with an estimated value of US $ 998 million.

Diamond

The diamond supply 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 fraction of diamond ore is made up of real diamonds. The ore is crushed, during which it is necessary to take measures 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. Before the spread of the use of X-rays, separation was carried out with lubricating belts; it is known that diamonds were found only in alluvial deposits in southern India. It is known that diamonds are more prone to adhere to the mass than other minerals in the ore. India was the leader in diamond production from their discovery around the 9th century BC to the mid-18th century AD, but the commercial potential of these sources was exhausted by the end of the 18th century, and by then India was overshadowed by Brazil, where the first diamonds were found. in 1725. Diamond production of primary deposits (kimberlites and lamproites) began only in the 1870s, after the discovery of diamond deposits in South Africa. Diamond production has increased over time, 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 begun production, and 4 more are awaiting their imminent discovery. Most of these deposits are located in Canada, Zimbabwe, Angola and one in Russia. In the United States, diamonds have been found in Arkansas, Colorado, and Montana. In 2004, the startling discovery of a microscopic diamond in the United States led to the release in January 2008 of a massive sampling of kimberlite pipes in remote Montana. Today, most commercially viable diamond deposits are located in Russia, Botswana, Australia and the Democratic Republic of the Congo. In 2005, Russia produced nearly one-fifth of the world's diamonds, according to the British Geological Survey. In Australia, the richest diamantated pipe reached peak production levels of 42 metric tons (41 tonnes, 46 short tons) per year in the 1990s. There are also commercial fields, the active production of which is carried out in the Northwest Territories of Canada, Siberia (mainly in Yakutia, for example, in the Mir pipe and in the Udachnaya pipe), in Brazil, as well as in Northern and Western Australia.

Applications

Carbon is essential for all known living systems. Without it, the existence of life, such as we know it, is impossible. The main economic uses of carbon, apart from food and wood, are in 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 natural 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 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 feedstock for many of these synthetics comes from crude oil. The use of carbon and its compounds is extremely varied. Carbon can form alloys with iron, the most common of which is carbon steel. Graphite combines with clays to form the "lead" used in pencils used for writing and drawing. It is also used as a lubricant and pigment, as a molding material in glass making, in electrodes for dry batteries and electroplating and electroplating, in brushes for electric motors, and as a neutron moderator in nuclear reactors. Coal is used as a material for artwork, as a barbecue grill, for smelting iron, and has many other uses. Wood, coal and oil are used as fuels for energy production and for heating. High quality diamonds are used in jewelry making, while industrial diamonds are used for drilling, cutting and polishing tools for working metals and stone. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolysis of synthetic polyester fibers, is used to reinforce plastics to form advanced, lightweight composites. Carbon fiber is made by pyrolysis of extruded and stretched polyacrylonitrile (PAN) filaments and other organics. 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 that resembles narrow strands of graphite, but heat treatment can reorder the structure into a continuous sheet. As a result, the fibers have a higher tensile strength than steel. Carbon black is used as a black pigment in printing inks, artist oil paints and watercolors, carbon paper, automotive trimmings, inks, and laser printers. Carbon black is also used as a filler in rubber products such as tires and in plastic joints. Activated carbon is used as an absorbent and adsorbent in filter media in applications as diverse as gas masks, water purification and cooker hoods, as well as in medicine to absorb toxins, poisons or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore to iron (smelting). Solidification of steel is achieved by heating the finished steel components in carbon powder. Silicon, tungsten, boron and titanium carbides are among the hardest materials and are used as abrasives for cutting and grinding. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and nearly all interior surfaces in environments other than glass, stone, and metal.

Diamonds

The diamond industry is divided into two categories, one of which is high quality diamonds (gemstones) and the other is industrial grade diamonds. While there is a lot of trade in both types of diamonds, both markets operate in very different ways. Unlike precious metals such as gold or platinum, gemstone diamonds are not traded as a commodity: there is a significant premium in the sale of diamonds and the resale market for diamonds is not very active. Industrial diamonds are prized primarily 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 (scrap diamond). Synthetic diamonds, invented in the 1950s, found industrial applications almost immediately; 3 billion carats (600 tons) of synthetic diamonds are produced annually. The dominant industrial uses for diamond are cutting, drilling, grinding and polishing. Most of these applications do not require large diamonds; in fact, most gem quality diamonds, with the exception of small diamonds, can be used in industry. Diamonds are inserted into drill tips or saw blades, or ground into powder for use in grinding and polishing. Specialized applications include laboratory use as storage for high pressure experiments, high performance bearings, and limited use in specialized windows. With advances in synthetic diamond manufacturing, new applications are becoming feasible. Much attention is paid to the possible use of diamond as a semiconductor suitable for microchips and because of its exceptional thermal conductivity as a heat sink in electronics.

Carbon (C)- typical non-metal; in the periodic system is in the 2nd period of the IV group, the main subgroup. Atomic number 6, Ar = 12.011 amu, nuclear charge +6.

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 on separate p-orbitals and are unpaired. In principle, this pair could occupy one orbital, but in this case the electron-electron repulsion strongly increases. For this reason, one of them takes 2p x, and the other, or 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 the free one 2p. A valence state with 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 arising functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three p-p- and one s-s-link. In addition to sp 3 hybridization at the carbon atom, sp 2 and sp hybridization is also observed . In the first case, there is a mutual overlap s- and two p-orbitals. Three equivalent sp 2 - hybrid orbitals are formed, located in one plane at an angle of 120 ° to each other. The third orbital p is unchanged and directed perpendicular to the plane sp 2.

During sp hybridization, the s and p orbitals overlap. An angle of 180 ° arises between the two formed equivalent hybrid orbitals, 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 bonded to three adjacent sp 2 -hybrid bonds. The connection between the parallel planes is carried out by 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 valence state in which carbon atoms are in a substance, the properties of this substance depend.

Chemical properties of carbon

The most typical oxidation states are +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 ° = 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 water vapor
C 0 + H 2 O - 1200 ° = C +2 O + H 2 water gas

- with metal oxides. Thus, metal is smelted from ore.
C 0 + 2CuO - t ° = 2Cu + C +4 O 2

- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) = C +4 O 2 + 2SO 2 + 2H 2 O
C 0 + 4HNO 3 (conc.) = C +4 O 2 + 4NO 2 + 2H 2 O

- forms carbon disulfide with sulfur:
C + 2S 2 = CS 2.

Carbon as an oxidizing agent:

- forms carbides with some metals

4Al + 3C 0 = Al 4 C 3

Ca + 2C 0 = CaC 2 -4

- with hydrogen - methane (as well as a huge amount of organic compounds)

C 0 + 2H 2 = CH 4

- with silicon, forms carborundum (at 2000 ° C in an electric furnace):

Finding carbon in nature

Free carbon occurs in the form of diamond and graphite. In the form of compounds, carbon is in the composition of minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 * CaCO 3; hydrocarbonates - Mg (HCO 3) 2 and Ca (HCO 3) 2, CO 2 is part of the air; carbon is the main constituent part of natural organic compounds - gas, oil, coal, peat; it is part of organic substances, proteins, fats, carbohydrates, amino acids that make up living organisms.

Inorganic carbon compounds

Neither C 4+ nor C 4- ions are formed under any ordinary chemical processes: there are covalent bonds of different polarity in carbon compounds.

Carbon monoxide (II) CO

Carbon monoxide; colorless, odorless, slightly soluble in water, soluble in organic solvents, poisonous, bale temperature = -192 ° C; t pl. = -205 ° C.

Receiving
1) In industry (in gas generators):
C + O 2 = CO 2

2) In the laboratory - by thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):
HCOOH = H 2 O + CO

H 2 C 2 O 4 = CO + CO 2 + H 2 O

Chemical properties

CO is inert under normal conditions; when heated - a reducing agent; non-salt-forming oxide.

1) with oxygen

2C +2 O + O 2 = 2C +4 O 2

2) with metal oxides

C +2 O + CuO = Cu + C +4 O 2

3) with chlorine (in the light)

CO + Cl 2 - hn = 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.

Receiving

1. Thermal decomposition of carbonic acid salts (carbonates). Limestone roasting:

CaCO 3 - t ° = CaO + CO 2

1. The action of strong acids on carbonates and bicarbonates:

CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2

NaHCO 3 + HCl = NaCl + H 2 O + CO 2

ChemicalpropertiesCO2
Acidic Oxide: Reacts with basic oxides and bases to form carbonic acid salts

Na 2 O + CO 2 = Na 2 CO 3

2NaOH + CO 2 = Na 2 CO 3 + H 2 O

NaOH + CO 2 = NaHCO 3

May exhibit oxidizing properties at elevated temperatures

С +4 O 2 + 2Mg - t ° = 2Mg +2 O + C 0

Qualitative reaction

Turbidity of lime water:

Ca (OH) 2 + CO 2 = CaCO 3 ¯ (white precipitate) + H 2 O

It disappears with prolonged passage of CO 2 through lime water, because insoluble calcium carbonate transforms into soluble bicarbonate:

CaCO 3 + H 2 O + CO 2 = Ca (HCO 3) 2

Carbonic acid and itssalt

H 2CO 3 - The acid is weak, exists only in aqueous solution:

CO 2 + H 2 O ↔ H 2 CO 3

Two-base:
H 2 CO 3 ↔ H + + HCO 3 - Acid salts - bicarbonates, hydrocarbons
HCO 3 - ↔ H + + CO 3 2- Medium salts - carbonates

All properties of acids are characteristic.

Carbonates and hydrocarbons can be converted into each other:

2NaHCO 3 - t ° = Na 2 CO 3 + H 2 O + CO 2

Na 2 CO 3 + H 2 O + CO 2 = 2NaHCO 3

Metal carbonates (except for alkali metals) decarboxylate when heated to form an oxide:

CuCO 3 - t ° = CuO + CO 2

Qualitative reaction- "boiling" under the action of a strong acid:

Na 2 CO 3 + 2HCl = 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 = 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 = 2La (OH) 3 + 2 C 2 H 2 + H 2.

Be 2 C and Al 4 C 3 decompose with water to form methane:

Al 4 C 3 + 12 H 2 O = 4 Al (OH) 3 = 3 CH 4.

In technology, titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum as an abrasive and a material for heaters) are used.

Cyanide

obtained by heating soda in an atmosphere of ammonia and carbon monoxide:

Na 2 CO 3 + 2 NH 3 + 3 CO = 2 NaCN + 2 H 2 O + H 2 + 2 CO 2

Hydrocyanic acid HCN is an important product of the chemical industry and is widely used in organic synthesis. Its world production reaches 200 thousand tons per year. The electronic structure of the cyanide anion is similar 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 = 2 K + 2 KOH.

When boiling solutions of cyanide with sulfur or fusion of solids, thiocyanates:
KCN + S = KSCN.

When cyanides of low-activity metals are heated, cyanogen is obtained: Hg (CN) 2 = Hg + (CN) 2. Cyanide solutions are oxidized to cyanates:

2 KCN + O 2 = 2 KOCN.

Cyanic acid comes 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 = CO (NH 2) 2 by evaporation of an aqueous solution.

This event is usually seen as the victory of synthetic chemistry over "vitalist theory".

There is an isomer of cyanic acid - volatile acid

H-O-N = C.
Its salts (explosive mercury Hg (ONC) 2) are used in impact ignitors.

Synthesis urea(urea):

CO 2 + 2 NH 3 = CO (NH 2) 2 + H 2 O. At 130 0 С and 100 atm.

Urea is an amide of carbonic acid, there is also its "nitrogen analogue" - guanidine.

Carbonates

The most important inorganic carbon compounds are carbonic acid salts (carbonates). H 2 CO 3 is a weak acid (K 1 = 1.3 · 10 -4; K 2 = 5 · 10 -11). Carbonate buffer supports carbon dioxide equilibrium in the atmosphere. The oceans have a huge buffer capacity because they are an open system. The main buffer reaction is equilibrium in 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, dissolution of carbonate rocks (shells, chalk and limestone deposits in the ocean) occurs; this compensates for the loss of hydrocarbonate ions:

H + + CO 3 2- ↔ HCO 3 -

CaCO 3 (solid) ↔ Ca 2+ + CO 3 2-

Solid carbonates are converted into soluble hydrocarbonates. It is this process of chemical dissolution of excess carbon dioxide that counteracts the "greenhouse effect" - global warming due to the absorption of thermal radiation from the Earth by carbon dioxide. About a third of the world's soda (sodium carbonate Na 2 CO 3) is used in glass production.