Solid state carbon. The structure of the carbon atom. Carbonic acid and its salts

CARBON
WITH (carboneum), non-metallic chemical element IVA of subgroup (C, Si, Ge, Sn, Pb) of the periodic table of elements. It occurs naturally in the form of diamond crystals (Fig. 1), graphite or fullerene and other forms and is a 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% (see also DIAMOND; FULLERENES).

Carbon is widely used in the form of simple substances. In addition to precious diamonds, which are the subject of jewelry, industrial diamonds are of great importance for the manufacture of grinding and cutting tools. Charcoal and other amorphous forms of carbon are used for decolorization, purification, adsorption of gases, in technical fields where adsorbents with a developed surface are required. Carbides, compounds of carbon with metals, as well as with boron and silicon (for example, Al4C3, SiC, B4C) are characterized by high hardness and are used for the manufacture of abrasive and cutting tools. Carbon is found 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 temperatures (carburizing) significantly increases surface hardness and wear resistance.
See also ALLOYS. There are many different forms of graphite in nature; some are artificially obtained; there are amorphous forms (for example, coke and charcoal). Soot, bone charcoal, lamp soot, acetylene soot are formed when hydrocarbons are burned with a lack of oxygen. The so-called white carbon is obtained by sublimation of pyrolytic graphite under reduced pressure - these are the smallest transparent crystals of graphite sheets with sharp edges.
Historical reference. Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that graphite can be used to mark other material, and the very name "graphite", derived 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 taken for it for example molybdenite (molybdenum sulfide), once considered graphite. Other names for graphite include black lead, carbide iron, and silver lead. In 1779, K. Scheele established that graphite can be oxidized with air to form carbon dioxide. For the first time, diamonds were used 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 developed in 1970, are produced for industrial purposes.
Allotropy. If the structural units of a substance (atoms for monatomic elements or molecules for polyatomic elements and compounds) are able to combine with each other in more than one crystalline form, this phenomenon is called allotropy. Carbon has three allotropic modifications - diamond, graphite and fullerene. In diamond, each carbon atom has 4 tetrahedrally located neighbors, forming a cubic structure (Fig. 1, a). This structure corresponds to the maximum bond covalence, and all 4 electrons of each carbon atom form high-strength C-C bonds, i.e. there are no conduction electrons in the structure. Therefore, diamond is characterized by the absence of conductivity, low thermal conductivity, high hardness; it is the hardest known substance (Fig. 2). Cleavage of the C-C bond (bond length 1.54, hence the covalent radius 1.54 / 2 = 0.77) in a tetrahedral structure requires large energy costs, therefore, diamond, along with exceptional hardness, is characterized by a high melting point (3550 ° C ).

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

The graphite structure (Fig. 1b) is a system of condensed hexagonal rings with a bond length of 1.42 (much shorter than in diamond), but each carbon atom has three (and not four, as in diamond) covalent bonds with three neighbors, and the fourth bond (3,4) is too long for a covalent bond and weakly binds the parallel laid layers of graphite to each other. It is the fourth electron of carbon that determines the heat and electrical conductivity of graphite - this longer and less strong bond forms a less compact graphite, which is reflected in its lower hardness in comparison with diamond (graphite density 2.26 g / cm3, diamond - 3.51 g / cm3). For the same reason, graphite is slippery to the touch and easily separates the flakes of the substance, which is used to make lubricants and pencil leads. The lead shine of the lead is mainly due to the presence of graphite. Carbon fibers are highly durable and can be used to make rayon or other high carbon yarns. At high pressures and temperatures, in the presence of a catalyst such as iron, graphite can be converted to diamond. This process has been implemented for the industrial production of artificial diamonds. Diamond crystals grow on the catalyst surface. Equilibrium graphite diamond exists at 15,000 atm and 300 K or at 4000 atm and 1500 K. Artificial diamonds can also be obtained from hydrocarbons. The amorphous forms of carbon that do not form crystals include charcoal obtained by heating wood without air access, lamp and gas soot formed during low-temperature combustion of hydrocarbons with a lack of air and condensed on a cold surface, bone charcoal - an admixture of calcium phosphate in the process of bone destruction fabrics, as well as coal (a natural substance with impurities) and coke, the dry residue obtained by coking fuels by the dry distillation of coal or oil residues (bituminous coals), i.e. heating without air access. Coke is used for smelting pig iron, in ferrous and non-ferrous metallurgy. During coking, gaseous products are also formed - coke oven gas (H2, CH4, CO, etc.) and chemical products that are raw materials for the production of gasoline, paints, fertilizers, medicines, plastics, etc. The diagram of the main apparatus for the production of coke - a coke oven - is shown in Fig. 3. Various types of coal and soot are distinguished by a developed surface and therefore are used as adsorbents for the purification of gases, liquids, and also as catalysts. To obtain various forms of carbon, special methods of chemical technology are used. Artificial graphite is obtained by calcining anthracite or petroleum coke between carbon electrodes at 2260 ° C (Acheson process) and is used in the production of lubricants and electrodes, in particular for the electrolytic production of metals.
The structure of the carbon atom. The nucleus of the most stable carbon isotope with a mass of 12 (abundance 98.9%) has 6 protons and 6 neutrons (12 nucleons) arranged in three quartets, each containing 2 protons and two neutrons, similar to the helium nucleus. Another stable isotope of carbon is 13C (approx. 1.1%), and in trace amounts there exists in nature the unstable isotope 14C with a half-life of 5730 years, which has b-radiation. In the normal carbon cycle of living matter, all three isotopes participate in the form of CO2. After the death of a living organism, the consumption of carbon stops and C-containing objects can be dated by measuring the level of 14C radioactivity. The decrease in the b-radiation of 14CO2 is proportional to the time elapsed since death. In 1960 W. Libby was awarded the Nobel Prize for research with radioactive carbon.
See also RADIOACTIVITY DATING. In the ground state, 6 electrons of carbon form the electronic configuration 1s22s22px12py12pz0. Four electrons of the second level are valence, which corresponds to the position of carbon in the IVA group of the periodic system (see PERIODIC SYSTEM OF ELEMENTS). Since the detachment of an electron from an atom in the gas phase requires high energy (about 1070 kJ / mol), carbon does not form ionic bonds with other elements, since this would require detachment of an electron with the formation of a positive ion. Having electronegativity equal to 2.5, carbon does not show a strong affinity for an electron, therefore, it is not an active electron acceptor. Therefore, it is not inclined to form a particle with a negative charge. But with a partially ionic nature of the bond, some carbon compounds exist, for example, carbides. In compounds, carbon exhibits an oxidation state of 4. In order for four electrons to participate in the formation of bonds, it is necessary to unpair the 2s electrons and jump one of these electrons to the 2pz orbital; in this case, 4 tetrahedral bonds are formed with an angle between them of 109 °. In compounds, the valence electrons of carbon are only partially drawn away from it, so carbon forms strong covalent bonds between neighboring atoms of the C-C type with the help of a common electron pair. The breaking energy of such a bond is 335 kJ / mol, while for the Si-Si bond it is only 210 kJ / mol; therefore, long -Si-Si- chains are unstable. The covalent nature of the bond is retained even in the compounds of highly reactive halogens with carbon, CF4 and CCl4. Carbon atoms are capable of providing more than one electron from each carbon atom for bond formation; this is how double C = C and triple CєC bonds are formed. Other elements also form bonds between their atoms, but only carbon is capable of forming long chains. Therefore, thousands of compounds are known for carbon, called hydrocarbons, in which carbon is bonded to hydrogen and other carbon atoms to form long chains or ring structures.
See ORGANIC CHEMISTRY. In these compounds, it is possible to replace hydrogen with other atoms, most often oxygen, nitrogen and halogens, with the formation of many organic compounds. Hydrocarbons - hydrocarbons in which hydrogen is replaced by fluorine - are of great importance among them. Such compounds are extremely inert, and they are used as plastic and lubricants (fluorocarbons, i.e. hydrocarbons in which all hydrogen atoms are replaced by fluorine atoms) and as low-temperature refrigerants (freons, or freons, fluorochlorocarbons). In the 1980s, physicists in the United States discovered very interesting carbon compounds, in which carbon atoms are connected in 5- or 6-gons, forming a C60 molecule in the shape of a hollow ball, which has the perfect symmetry of a soccer ball. Since this design is at the heart of the "geodesic dome" invented by the American architect and engineer Buckminster Fuller, the new class of compounds was named "Buckminsterfullerenes" or "Fullerenes" (and also more shortly "Faziboles" or "Buckyballs"). Fullerenes - the third modification of pure carbon (except for diamond and graphite), consisting of 60 or 70 (and even more) atoms - was obtained by the action of laser radiation on the smallest particles of carbon. Fullerenes of a more complex shape consist of several hundred carbon atoms. The diameter of the C60 CARBON molecule is 1 nm. There is enough room in the center of such a molecule to house a large uranium atom.
See also FULLERENES.
Standard atomic mass. In 1961, the International Unions of Theoretical and Applied Chemistry (IUPAC) and physics adopted the mass of the carbon isotope 12C as a unit of atomic mass, abolishing the oxygen scale of atomic masses that existed before. The atomic mass of carbon in this system is 12.011, since it is the average for the three natural isotopes of carbon, taking into account their abundance in nature.
See ATOMIC MASS. Chemical properties of carbon and some of its compounds. Some physical and chemical properties of carbon are given in the article CHEMICAL ELEMENTS. The reactivity of carbon depends on its modification, temperature and dispersion. At low temperatures, all forms of carbon are quite inert, but when heated, they are oxidized by atmospheric oxygen, forming oxides:

Finely dispersed carbon in excess of oxygen can explode when heated or from a spark. In addition to direct oxidation, there are more modern methods for producing oxides. Carbon suboxide C3O2 is formed during the dehydration of malonic acid over P4O10:

C3O2 has an unpleasant odor, readily hydrolyzes, again forming malonic acid.
Carbon monoxide (II) CO is formed during the oxidation of any modification of carbon under conditions of oxygen deficiency. The reaction is exothermic, 111.6 kJ / mol is released. At white heat, coke reacts with water: C + H2O = CO + H2; the resulting gas mixture is called "water gas" and is a gaseous fuel. CO is also formed during incomplete combustion of petroleum products, it is found in noticeable quantities in automobile exhaust, it is obtained by thermal dissociation of formic acid:

The oxidation state of carbon in CO is +2, and since carbon is more stable in the oxidation state +4, CO is easily oxidized by oxygen to CO2: CO + O2 (r) CO2, this reaction is highly exothermic (283 kJ / mol). CO is used in industry in a mixture with H2 and other combustible gases as a fuel or gaseous reducing agent. When heated to 500 ° C, CO forms C and CO2 to an appreciable extent, but at 1000 ° C equilibrium is established at low concentrations of CO2. CO reacts with chlorine, forming phosgene - COCl2, similar reactions proceed with other halogens, in the reaction with sulfur, carbonyl sulfide COS is obtained, with metals (M) CO forms carbonyls of various compositions M (CO) x, which are complex compounds. Iron carbonyl is formed by the interaction of blood hemoglobin with CO, preventing the reaction of hemoglobin with oxygen, since iron carbonyl is a stronger compound. As a result, the function of hemoglobin as a carrier of oxygen to cells is blocked, which in this case die (and in the first place, brain cells are affected). (Hence another name for CO - "carbon monoxide"). Already 1% (vol.) CO in the air is dangerous for a person if he is in such an atmosphere for more than 10 minutes. Some of the physical properties of CO are given in the table. Carbon dioxide, or carbon monoxide (IV) CO2 is formed when elemental carbon is burned in an excess of oxygen with the release of heat (395 kJ / mol). CO2 (the trivial name is "carbon dioxide") is also formed during the complete oxidation of CO, petroleum products, gasoline, oils and other organic compounds. When carbonates are dissolved in water, CO2 is also released as a result of hydrolysis:

This reaction is often used in laboratory practice to produce CO2. This gas can also be obtained by calcining metal bicarbonates:

In the case of gas-phase interaction of superheated steam with CO:

When burning hydrocarbons and their oxygen derivatives, for example:

Food products in a living organism are similarly oxidized with the release of heat and other types of energy. In this case, oxidation proceeds under mild conditions through intermediate stages, but the end products are the same - CO2 and H2O, as, for example, during the decomposition of sugars under the action of enzymes, in particular during the fermentation of glucose:

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

CaO is used in large quantities in cement production technology. The thermal stability of carbonates and the consumption of heat for their decomposition according to this scheme increase in the CaCO3 series (see also FIRE PREVENTION AND FIRE PROTECTION). Electronic structure of carbon oxides. The electronic structure of any carbon monoxide can be described by three equiprobable circuits with different positions of electron pairs - three resonant forms:

All carbon oxides are linear.
Carbonic acid. When CO2 interacts with water, carbonic acid H2CO3 is formed. In a saturated solution of CO2 (0.034 mol / l), only some of the molecules form H2CO3, and most of the CO2 is in the hydrated state CO2 * H2O.
Carbonates. Carbonates are formed by the interaction of metal oxides with CO2, for example, Na2O + CO2 -> NaHCO3, which decompose when heated with the release of CO2: 2NaHCO3 -> Na2CO3 + H2O + CO2 Sodium carbonate, or soda, is produced in large quantities in the soda industry, mainly by the Solvay method:

Another method produces soda from CO2 and NaOH.

Carbonate ion CO32- has a planar structure with an O-C-O angle of 120 ° and a CO bond length of 1.31
(see also ALKALI PRODUCTION).
Carbon halides. Carbon reacts directly with halogens when heated to form tetrahalides, but the reaction rate and product yield are slow. Therefore, carbon halides are obtained by other methods, for example, by chlorination of carbon disulfide, CCl4 is obtained: CS2 + 2Cl2 -> CCl4 + 2S temperature is the formation of poisonous phosgene (gaseous poisonous substance). CCl4 itself is also poisonous and, if inhaled in appreciable quantities, can cause liver poisoning. СCl4 is also formed by the photochemical reaction between methane СH4 and Сl2; in this case, the formation of products of incomplete chlorination of methane - CHCl3, CH2Cl2 and CH3Cl - is possible. Reactions with other halogens proceed similarly.
Graphite reactions. Graphite, as a modification of carbon, characterized by large distances between the layers of hexagonal rings, enters into unusual reactions, for example, alkali metals, halogens and some salts (FeCl3) penetrate between the layers, forming compounds of the KC8, KC16 type (called interstitial, inclusion or clathrate compounds). Strong oxidants such as KClO3 in an acidic medium (sulfuric or nitric acid) form substances with a large volume of the crystal lattice (up to 6 between layers), which is explained by the introduction of oxygen atoms and the formation of compounds on the surface of which carboxyl groups (-COOH) are formed as a result of oxidation - compounds such as oxidized graphite or mellitic (benzenehexacarboxylic) acid C6 (COOH) 6. In these compounds, the C: O ratio can vary from 6: 1 to 6: 2.5.
Carbides. Carbon forms various compounds called carbides with metals, boron and silicon. The most active metals (IA-IIIA subgroups) form salt-like carbides, for example Na2C2, CaC2, Mg4C3, Al4C3. In industry, calcium carbide is obtained from coke and limestone by the following reactions:

Carbides are non-conductive, almost colorless, hydrolyzed to form hydrocarbons, for example CaC2 + 2H2O = C2H2 + Ca (OH) 2 The acetylene C2H2 formed by the reaction serves as a feedstock in the production of many organic substances. This process is interesting because it represents the transition from raw materials of an inorganic nature to the synthesis of organic compounds. Carbides that form acetylene during hydrolysis are called acetylenides. In silicon and boron carbides (SiC and B4C), the bond between atoms is covalent. Transition metals (elements of B-subgroups), when heated with carbon, also form carbides of variable composition in cracks on the metal surface; the bond in them is close to metal. Some carbides of this type, for example WC, W2C, TiC and SiC, are characterized by high hardness and refractoriness, and have good electrical conductivity. For example, NbC, TaC and HfC are the most refractory substances (mp = 4000-4200 ° C), diniobium carbide Nb2C is a superconductor at 9.18 K, TiC and W2C are close in hardness to diamond, and the hardness is B4C (a structural analog of diamond ) is 9.5 on the Mohs scale (see Fig. 2). Inert carbides are formed if the radius of the transition metal Nitrogen derivatives of carbon. This group includes urea NH2CONH2 - nitrogen fertilizer used in the form of a solution. Urea is obtained from NH3 and CO2 by heating under pressure:

Dicyan (CN) 2 is similar in many properties to halogens and is often referred to as pseudohalogen. Dicyan is obtained by mild oxidation of the cyanide ion with oxygen, hydrogen peroxide, or the Cu2 + ion: 2CN- -> (CN) 2 + 2e. Cyanide ion, being an electron donor, easily forms complex compounds with transition metal ions. Like CO, cyanide ion is a poison, binding vital iron compounds in a living organism. Cyanide complex ions have the general formula [] -0.5x, where x is the coordination number of the metal (complexing agent), empirically equal to twice the oxidation state of the metal ion. Examples of such complex ions are (the structure of some ions is given below) tetracyanone nickelate (II) -ion [] 2-, hexacyanoferrate (III) [] 3-, dicyanoargentate [] -:

Carbonyls. Carbon monoxide can react directly with many metals or metal ions to form complex compounds called carbonyls, for example Ni (CO) 4, Fe (CO) 5, Fe2 (CO) 9, [] 3, Mo (CO) 6, [] 2. The bond in these compounds is similar to the bond in the cyano complexes described above. Ni (CO) 4 is a volatile substance used to separate nickel from other metals. Deterioration of the structure of cast iron and steel in structures is often associated with the formation of carbonyls. Hydrogen can be a part of carbonyls, forming carbonyl hydrides, such as H2Fe (CO) 4 and HCo (CO) 4, which exhibit acidic properties and react with alkali: H2Fe (CO) 4 + NaOH -> NaHFe (CO) 4 + H2O Known also carbonyl halides, for example Fe (CO) X2, Fe (CO) 2X2, Co (CO) I2, Pt (CO) Cl2, where X is any halogen
(see also ORGANOMETALLIC CONNECTIONS).
Hydrocarbons. A huge number of compounds of carbon with hydrogen are known
(see ORGANIC CHEMISTRY).
LITERATURE
Sunyaev Z.I. Petroleum carbon. M., 1980 Chemistry of hypercoordinated carbon. M., 1990

Collier's Encyclopedia. - Open Society. 2000 .

Synonyms:

See what "CARBON" is in other dictionaries:

Nuclide table General information Name, symbol Carbon 14, 14C Alternative names radiocarbon, radiocarbon Neutrons 8 Protons 6 Nuclide properties Atomic mass ... Wikipedia

Nuclide table General information Name, symbol Carbon 12, 12C Neutrons 6 Protons 6 Nuclide properties Atomic mass 12.0000000 (0) ... Wikipedia

Carbon is capable of forming several allotropic modifications. These are diamond (the most inert allotropic modification), graphite, fullerene, and carbyne.

Charcoal and soot are amorphous carbon. Carbon in this state has no ordered structure and actually consists of the smallest fragments of graphite layers. Amorphous carbon treated with hot steam is called activated carbon. 1 gram of activated carbon due to the presence of many pores in it has a total surface of more than three hundred square meters! Due to its ability to absorb various substances, activated carbon is widely used as a filter filler, as well as an enterosorbent for various types of poisoning.

From a chemical point of view, amorphous carbon is its most active form, graphite is moderately active, and diamond is an extremely inert substance. For this reason, the chemical properties of carbon discussed below should be primarily attributed to amorphous carbon.

Reducing properties of carbon

As a reducing agent, carbon reacts with non-metals such as oxygen, halogens, sulfur.

Depending on the excess or lack of oxygen when burning coal, the formation of carbon monoxide CO or carbon dioxide CO 2 is possible:

When carbon interacts with fluorine, carbon tetrafluoride is formed:

When carbon is heated with sulfur, carbon disulfide CS 2 is formed:

Carbon is capable of reducing metals after aluminum in a series of activities from their oxides. For example:

Carbon also reacts with oxides of active metals, but in this case, as a rule, not the reduction of the metal is observed, but the formation of its carbide:

Interaction of carbon with oxides of non-metals

Carbon enters into a co-proportionation reaction with carbon dioxide CO 2:

One of the most important industrial processes is the so-called steam conversion of coal... The process is carried out by passing water vapor through hot coal. In this case, the following reaction occurs:

At high temperatures, carbon is capable of reducing even such an inert compound as silicon dioxide. In this case, depending on the condition, the formation of silicon or silicon carbide ( carborundum):

Also, carbon as a reducing agent reacts with oxidizing acids, in particular, concentrated sulfuric and nitric acids:

Oxidizing properties of carbon

The chemical element carbon does not have a high electronegativity, therefore, the simple substances it forms rarely exhibit oxidizing properties in relation to other non-metals.

An example of such reactions is the interaction of amorphous carbon with hydrogen when heated in the presence of a catalyst:

and also with silicon at a temperature of 1200-1300 ° C:

Carbon exhibits oxidizing properties in relation to metals. Carbon is capable of reacting with active metals and some metals of moderate activity. Reactions take place when heated:

Carbides of active metals are hydrolyzed by water:

as well as solutions of non-oxidizing acids:

This results in the formation of hydrocarbons containing carbon in the same oxidation state as in the original carbide.

Silicon chemical properties

Silicon can exist, like carbon in a crystalline and amorphous state, and, as in the case of carbon, amorphous silicon is significantly more chemically active than crystalline.

Sometimes amorphous and crystalline silicon is called allotropic modifications, which, strictly speaking, is not entirely true. Amorphous silicon is essentially a conglomerate of the smallest particles of crystalline silicon randomly arranged relative to each other.

Interaction of silicon with simple substances

non-metals

Under normal conditions, silicon, due to its inertness, reacts only with fluorine:

Silicon reacts with chlorine, bromine and iodine only when heated. In this case, it is characteristic that, depending on the activity of the halogen, a correspondingly different temperature is required:

So with chlorine, the reaction proceeds at 340-420 ° C:

With bromine - 620-700 o C:

With iodine - 750-810 o C:

All silicon halides are easily hydrolyzed with water:

as well as alkali solutions:

The reaction of silicon with oxygen proceeds, however, it requires very strong heating (1200-1300 ° C) due to the fact that a strong oxide film makes it difficult to interact:

At a temperature of 1200-1500 ° C, silicon slowly interacts with carbon in the form of graphite to form silicon carbide SiC - a substance with an atomic crystal lattice similar to diamond and almost as strong as it:

Silicon does not react with hydrogen.

metals

Due to its low electronegativity, silicon can exhibit oxidizing properties only in relation to metals. Of the metals, silicon reacts with active (alkaline and alkaline-earth) metals, as well as with many metals of medium activity. As a result of this interaction, silicides are formed:

Silicides of active metals are easily hydrolyzed with water or dilute solutions of non-oxidizing acids:

This forms a gas silane SiH 4 - an analogue of methane CH 4.

Interaction of silicon with complex substances

Silicon does not react with water even when boiling, however, amorphous silicon interacts with superheated water vapor at a temperature of about 400-500 o C. In this case, hydrogen and silicon dioxide are formed:

Of all acids, silicon (in an amorphous state) reacts only with concentrated hydrofluoric acid:

Silicon dissolves in concentrated alkali solutions. The reaction is accompanied by the evolution of hydrogen.

Diamond structure (a) and graphite (b)

Carbon(latin Carboneum) - C, chemical element of group IV of the periodic system of Mendeleev, atomic number 6, atomic mass 12.011. It occurs naturally 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 of simple substances. In addition to precious diamonds, which are the subject of jewelry, industrial diamonds are of great importance for the manufacture of grinding and cutting tools. Charcoal and other amorphous forms of carbon are used for decolorization, purification, adsorption of gases, in technical fields where adsorbents with a developed surface are required. Carbides, compounds of carbon with metals, as well as with boron and silicon (for example, Al 4 C 3, SiC, B 4 C) are characterized by high hardness and are used for the manufacture of abrasive and cutting tools. Carbon is found 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 temperatures (carburizing) significantly increases surface hardness and wear resistance.

Historical reference

Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that graphite can be used to mark other material, and the very name "graphite", derived 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 taken for it for example molybdenite (molybdenum sulfide), once considered graphite. Other names for graphite include black lead, carbide iron, and silver lead.

In 1779, K. Scheele established that graphite can be oxidized with air to form carbon dioxide. For the first time, diamonds were used 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 developed in 1970, are produced for industrial purposes.

Properties

Four crystalline modifications of carbon are known:

graphite,
diamond,
carbyne,
lonsdaleite.

Graphite- gray-black, opaque, oily to the touch, scaly, very soft mass with a metallic sheen. At room temperature and normal pressure (0.1 MN / m 2, or 1 kgf / cm 2), graphite is thermodynamically stable.

Diamond- a very hard, 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 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 air access causes them to turn into graphite.

The physical properties of "amorphous" carbon very strongly depend 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 those of graphite.

Carbin obtained artificially. It is a fine-crystalline black powder (density 1.9-2 g / cm 3). Built from long chains of atoms WITH laid parallel to each other.

Lonsdaleite found in meteorites and obtained artificially; its structure and properties have not been definitively established.

Carbon properties
Atomic number		6
Atomic mass		12,011
Isotopes:	stable	12, 13
Isotopes:	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 forge forges, for the production of gunpowder (75% KNO 3 + 13% C + 12% S), for the absorption of 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 electrochemical cells. Glassy carbon is used for the manufacture of equipment for highly corrosive environments, as well as in aviation and astronautics.

Activated carbon absorbs harmful substances from gases and liquids: it is filled with gas masks, purification systems, it is used in medicine for poisoning.

Carbon is the basis of all organic matter. Any living organism is made up largely of carbon. Carbon is the basis of life. The carbon source 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 each other's remains and thereby extract carbon to build their own bodies. The biological carbon cycle ends with either oxidation and re-entry into the atmosphere, or disposal in the form of coal or oil.

The use of the 14 C radioactive isotope contributed to the advances in molecular biology in the study of the mechanisms of protein biosynthesis and the 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.

Sources of

Chemical elements and materials
Chemical elements	Nitrogen Argon. Hydrogen. Helium. Iron . Calcium Oxygen. Silicon. Magnesium Manganese

Designation - C (Carbon);
Period - II;
Group - 14 (IVa);
Atomic mass - 12.011;
Atomic number - 6;
Atom radius = 77 pm;
Covalent radius = 77 pm;
Distribution of electrons - 1s 2 2s 2 2p 2;
melting point = 3550 ° C;
boiling point = 4827 ° C;
Electronegativity (Pauling / Alpred and Rohov) = 2.55 / 2.50;
Oxidation state: +4, +3, +2, +1, 0, -1, -2, -3, -4;
Density (n. At.) = 2.25 g / cm 3 (graphite);
Molar volume = 5.3 cm 3 / mol.

Carbon compounds:

Carbon in the form of charcoal has been known to man since time immemorial, therefore, it makes no sense to talk about the date of its discovery. Actually its name "carbon" got in 1787, when the book "Method of chemical nomenclature" was published, in which instead of the French name "pure coal" (charbone pur) the term "carbon" (carbone) appeared.

Carbon has the unique ability to form polymer chains of unlimited length, thus giving rise to a huge class of compounds, which are studied in a separate branch of chemistry - organic chemistry. Organic carbon compounds are the basis of life on Earth, therefore, it makes no sense to talk about the importance of carbon as a chemical element - it is the basis of life on Earth.

Now let's look at carbon from the point of view of inorganic chemistry.

Rice. The structure of the carbon atom.

The electronic configuration of carbon is 1s 2 2s 2 2p 2 (see. Electronic structure of atoms). At the external energy level, carbon has 4 electrons: 2 paired at the s-sublevel + 2 unpaired at p-orbitals. When a carbon atom passes into an excited state (requires energy consumption), one electron from the s-sublevel "leaves" its pair and goes to the p-sublevel, where there is one free orbital. Thus, in an excited state, the electronic configuration of a carbon atom takes the following form: 1s 2 2s 1 2p 3.

Rice. The transition of a carbon atom to an excited state.

Such "castling" significantly expands the valence capabilities of carbon atoms, which can take the oxidation state from +4 (in compounds with active non-metals) to -4 (in compounds with metals).

In the unexcited state, the carbon atom in the compounds has a valence of 2, for example, CO (II), and in the excited state it has a valence of 4: CO 2 (IV).

The "uniqueness" of the carbon atom lies in the fact that there are 4 electrons on its external energy level, therefore, to complete the level (which, in fact, the atoms of any chemical element strive for), it can, with the same "success", both give and attach electrons with the formation of covalent bonds (see. Covalent bond).

Carbon as a simple substance

As a simple substance, carbon can be in the form of several allotropic modifications:

Diamond
Graphite
Fullerene
Carbin

Diamond

Rice. The crystal lattice of a diamond.

Diamond properties:

colorless crystalline substance;
the hardest substance in nature;
has a strong refractive effect;
poorly conducts heat and electricity.

Rice. Diamond tetrahedron.

The exceptional hardness of diamond is explained by the structure of its crystal lattice, which has the shape of a tetrahedron - in the center of the tetrahedron there is a carbon atom, which is bonded by equally strong bonds with four neighboring atoms that form the vertices of the tetrahedron (see the figure above). This "construction", in turn, is associated with neighboring tetrahedra.

Graphite

Rice. Crystal lattice of graphite.

Graphite properties:

a soft crystalline gray substance of a layered structure;
has a metallic luster;
conducts electricity well.

In graphite, carbon atoms form regular hexagons lying in one plane, organized in endless layers.

In graphite, chemical bonds between adjacent carbon atoms are formed by three valence electrons of each atom (shown in blue in the figure below), while the fourth electron (shown in red) of each carbon atom is located on a p-orbital lying perpendicular to the plane of the graphite layer. does not participate in the formation of covalent bonds in the plane of the layer. Its "purpose" is different - interacting with its "brother" lying in the adjacent layer, it provides a bond between the graphite layers, and the high mobility of p-electrons determines the good electrical conductivity of graphite.

Rice. Distribution of the orbitals of the carbon atom in graphite.

Fullerene

Rice. Fullerene crystal lattice.

Fullerene properties:

a fullerene molecule is a collection of carbon atoms enclosed in hollow spheres such as a soccer ball;
it is a yellow-orange fine crystalline substance;
melting point = 500-600 ° C;
semiconductor;
is part of the shungite mineral.

Carbin

Carbine properties:

inert black substance;
consists of polymeric linear molecules in which atoms are linked by alternating single and triple bonds;
semiconductor.

Chemical properties of carbon

Under normal conditions, carbon is an inert substance, but when heated, it can react with a variety of simple and complex substances.

It has already been said above that at the external energy level of carbon there are 4 electrons (neither there nor here), therefore carbon can both donate and receive electrons, exhibiting reducing properties in some compounds, and oxidizing in others.

Carbon is reducing agent in reactions with oxygen and other elements with a higher electronegativity (see the table of electronegativity of elements):

when heated in air, it burns (with an excess of oxygen with the formation of carbon dioxide; with a lack of it - carbon monoxide (II)):
C + O 2 = CO 2;
2C + O 2 = 2CO.
reacts at high temperatures with sulfur vapors, easily interacts with chlorine, fluorine:
C + 2S = CS 2
C + 2Cl 2 = CCl 4
2F 2 + C = CF 4
when heated, it reduces many metals and non-metals from oxides:
C 0 + Cu +2 O = Cu 0 + C +2 O;
C 0 + C +4 O 2 = 2C +2 O
at a temperature of 1000 ° C, it reacts with water (gasification process), with the formation of water gas:
C + H 2 O = CO + H 2;

Carbon exhibits oxidizing properties in reactions with metals and hydrogen:

reacts with metals to form carbides:
Ca + 2C = CaC 2
interacting with hydrogen, carbon forms methane:
C + 2H 2 = CH 4

Carbon is obtained by thermal decomposition of its compounds or by pyrolysis of methane (at high temperatures):
CH 4 = C + 2H 2.

Application of carbon

Carbon compounds have found the widest application in the national economy, it is not possible to list all of them, we will indicate only a few:

graphite is used for the manufacture of pencil leads, electrodes, melting crucibles, as a neutron moderator in nuclear reactors, as a lubricant;
diamonds are used in jewelry, as a cutting tool, in drilling equipment, as an abrasive material;
as a reducing agent, carbon is used to obtain certain metals and non-metals (iron, silicon);
carbon makes up the bulk of activated carbon, which has found widespread use both in everyday life (for example, as an adsorbent for purifying air and solutions), and in medicine (activated carbon tablets) and in industry (as a carrier for catalytic additives, polymerization catalyst etc.).

C (carboneum), a non-metallic chemical element of group IVA (C, Si, Ge, Sn, Pb) of the periodic table of elements. It occurs naturally in the form of diamond crystals (Fig. 1), graphite or fullerene and other forms and is a 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% ( see also DIAMOND; FULLERENES).

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

Sunyaev Z.I. Petroleum carbon... M., 1980
The chemistry of hypercoordinated carbon... M., 1990

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