The state of carbon. Carbon and its compounds. Interaction of silicon with complex substances

Carbon

CARBON -a; m. Chemical element (C), essential component of all organic substances in nature. Carbon atoms. Carbon percentage. Life is impossible without carbon.

◁ Carbon, th, th. Uth atoms. Carbonaceous, th, th. Containing carbon. Uth steel.

carbon

(lat.Carboneum), chemical element of IV group periodic system... The main crystalline modifications are diamond and graphite. Under normal conditions, carbon is chemically inert; at high temperatures it combines with many elements (strong reducing agent). The carbon content in the earth's crust is 6.5 × 10 16 tons. A significant amount of carbon (about 10 13 tons) is included in the composition of fossil fuels (coal, natural gas, oil, etc.), as well as in the composition of carbon dioxide in the atmosphere (6 × 10 11 t) and hydrosphere (10 14 t). The main carbonaceous minerals are carbonates. Carbon has the unique ability to form an enormous number of compounds, which can be composed of an almost unlimited number of carbon atoms. The variety of carbon compounds determined the emergence of one of the main branches of chemistry - organic chemistry. Carbon is a biogenic element; its compounds play a special role in the life of plant and animal organisms (the average carbon content is 18%). Carbon is abundant in space; on the Sun, it ranks 4th after hydrogen, helium and oxygen.

CARBON

CARBON (lat. Carboneum, from carbo - coal), C (read "tse"), a chemical element with atomic number 6, atomic mass 12.011. Natural carbon consists of two stable nuclides: 12 C, 98.892% by mass and 13 C - 1.108%. In the natural mixture of nuclides, the radioactive nuclide 14 C is always present in trace amounts (b - emitter, half-life 5730 years). It is constantly formed in the lower layers of the atmosphere when cosmic radiation neutrons act on the nitrogen isotope 14 N:
14 7 N + 1 0 n \u003d 14 6 C + 1 1 H.
Carbon is located in group IVA, in the second period of the periodic table. The configuration of the outer electron layer of an atom in the ground state 2 s 2 p 2 ... The most important oxidation states are +2 +4, –4, valencies IV and II.
The radius of the neutral carbon atom is 0.077 nm. The radius of the C 4+ ion is 0.029 nm (coordination number 4), 0.030 nm (coordination number 6). The sequential ionization energies of a neutral atom are 11.260, 24.382, 47.883, 64.492, and 392.09 eV. Pauling electronegativity (cm. POLING Linus) 2,5.
History reference
Carbon has been known since ancient times. Charcoal was used to recover metals from ores, diamond (cm. DIAMOND (mineral)) - like a precious stone. In 1789 the French chemist A.L. Lavoisier (cm. LAVOISIER Antoine Laurent) made a conclusion about the elementary nature of carbon.
Artificial diamonds were first obtained in 1953 by Swedish researchers, but they did not have time to publish the results. In December 1954, artificial diamonds were received, and at the beginning of 1955 the results were published by employees of the General Electric Company. (cm. GENERAL ELECTRIC)
In the USSR, artificial diamonds were first obtained in 1960 by a group of scientists led by V.N.Bakul and L.F. Vereshchagin (cm. Vereshchagin Leonid Fedorovich) .
In 1961, a group of Soviet chemists led by V.V. Korshak synthesized a linear modification of carbon, carbyne. Soon, carbyne was discovered in the Rees meteorite crater (Germany). In 1969 in the USSR, whiskers of diamond were synthesized at ordinary pressure, which have high strength and are practically devoid of defects.
In 1985 G. Kroto (cm. CROTO Harold) discovered a new form of carbon - fullerenes (cm. FULLERENES)C 60 and C 70 in the mass spectrum of graphite evaporated during laser irradiation. Lonsdaleite was obtained at high pressures.
Being in nature
Content in the earth's crust is 0.48% by weight. It accumulates in the biosphere: in living matter 18% of coal, in wood 50%, peat 62%, natural combustible gases 75%, oil shale 78%, bituminous and brown coal 80%, oil 85%, anthracite 96%. A significant part of the coal in the lithosphere is concentrated in limestones and dolomites. Carbon in the +4 oxidation state is part of carbonate rocks and minerals (chalk, limestone, marble, dolomite). Carbon dioxide CO 2 (0.046% by mass) is a permanent component of atmospheric air. Dissolved carbon dioxide is always present in the water of rivers, lakes and seas.
In the atmosphere of stars, planets and in meteorites, substances containing carbon have been found.
Receiving
Since ancient times, coal has been obtained by incomplete combustion of wood. In the 19th century, charcoal in metallurgy was replaced by coal (coke).
Cracking is currently used for industrial production of pure carbon. (cm. CRACKING) natural gas methane (cm. METHANE) CH 4:
CH 4 \u003d C + 2H 2
Coal for medicinal purposes is prepared by burning the skin of coconuts. For laboratory needs, clean coal that does not contain incombustible impurities is obtained by incomplete combustion of sugar.
Physical and chemical properties
Carbon is a non-metal.
The variety of carbon compounds is explained by the ability of its atoms to bond with each other, forming bulk structures, layers, chains, cycles. There are four known allotropic modifications of carbon: diamond, graphite, carbyne, and fullerite. Charcoal consists of the smallest crystals with a disordered structure of graphite. Its density is 1.8-2.1 g / cm 3. The soot is highly micronized graphite.
Diamond is a mineral with a cubic face-centered lattice. The C atoms in the diamond are in sp 3 -hybridized state. Each atom forms 4 covalent s-bonds with four neighboring C atoms located at the vertices of the tetrahedron, in the center of which is the C atom. The distance between the atoms in the tetrahedron is 0.154 nm. There is no electronic conductivity, the band gap is 5.7 eV. Of all the simple substances, diamond has the maximum number of atoms per unit volume. Its density is 3.51 g / cm 3.. Mohs Mineralogical Hardness (cm. MOSA SCALE) taken as 10. A diamond can only be scratched with another diamond; but it is fragile and on impact splits into pieces of irregular shape. It is thermodynamically stable only at high pressures. However, at 1800 ° C, the conversion of diamond to graphite is fast. The reverse transformation of graphite into diamond occurs at 2700 ° C and a pressure of 11-12 GPa.
Graphite is a layered dark gray substance with a hexagonal crystal lattice. Thermodynamically stable in a wide range of temperatures and pressures. It consists of parallel layers formed by regular hexagons of C atoms. The carbon atoms of each layer are located opposite the centers of the hexagons in the adjacent layers; the position of the layers is repeated through one, and each layer is shifted relative to the other in the horizontal direction by 0.1418 nm. Inside the layer, bonds between atoms are covalent, formed sp 2 -hybrid orbitals. The connections between the layers are carried out by weak van der Waals (cm. INTERMOLECULAR INTERACTION) forces, therefore graphite easily exfoliates. This state is stabilized by the fourth delocalized p-bond. Graphite has good electrical conductivity. The density of graphite is 2.1-2.5 kg / dm 3.
In all allotropic modifications, under normal conditions, carbon is chemically inactive. IN chemical reactions enters only when heated. In this case, the chemical activity of carbon decreases in the sequence of soot-charcoal-graphite-diamond. Soot ignites in air when heated to 300 ° C, diamond at 850-1000 ° C. Burning produces carbon dioxide CO 2 and CO. Heating CO 2 with coal also produces carbon monoxide (II) CO:
CO 2 + C \u003d 2CO
C + H 2 O (superheated steam) \u003d CO + H 2
Synthesized carbon monoxide C 2 O 3.
CO 2 is an acidic oxide; it is answered by a weak unstable carbonic acid H 2 CO 3 that exists only in highly dilute cold aqueous solutions. Carbonic acid salts - carbonates (cm. CARBONATES) (K 2 CO 3, CaCO 3) and hydrocarbonates (cm. HYDROCARBONATES) (NaHCO 3, Ca (HCO 3) 2).
With hydrogen (cm. HYDROGEN) graphite and charcoal react at temperatures above 1200 ° C to form a mixture of hydrocarbons. Reacts with fluorine at 900 ° C to form a mixture of fluorocarbon compounds. Cyanogen (CN) 2 gas is produced by passing an electrical discharge between carbon electrodes in a nitrogen atmosphere; if in gas mixture hydrogen is present, hydrocyanic acid HCN is formed. At very high temperatures, graphite reacts with sulfur, (cm. SULFUR) silicon, boron, forming carbides - CS 2, SiC, B 4 C.
Carbides are obtained by the interaction of graphite with metals at high temperatures: sodium carbide Na 2 C 2, calcium carbide CaC 2, magnesium carbide Mg 2 C 3, aluminum carbide Al 4 C 3. These carbides are readily decomposed by water into metal hydroxide and the corresponding hydrocarbon:
Al 4 C 3 + 12H 2 O \u003d 4Al (OH) 3 + 3CH 4
With transition metals, carbon forms metal-like chemically resistant carbides, for example, iron carbide (cementite) Fe 3 C, chromium carbide Cr 2 C 3, tungsten carbide WC. Carbides are crystalline substances, the nature of the chemical bond can be different.
When heated, coal reduces many metals from their oxides:
FeO + C \u003d Fe + CO,
2CuO + C \u003d 2Cu + CO 2
When heated, it reduces sulfur (VI) to sulfur (IV) from concentrated sulfuric acid:
2H 2 SO 4 + C \u003d CO 2 + 2SO 2 + 2H 2 O
At 3500 ° C and normal pressure, carbon sublimes.
Application
Fossil fuels account for over 90% of all primary sources of energy consumed in the world. 10% of the extracted fuel is used as raw material for the main organic and petrochemical synthesis, for the production of plastics.
Physiological action
Carbon - the most important biogenic element, is a structural unit of organic compounds involved in the construction of organisms and ensuring their vital activity (biopolymers, vitamins, hormones, mediators, and others). 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, the oxidative decomposition of organic compounds occurs with the release of CO 2 into the external environment. Carbon dioxide (cm. CARBON DIOXIDE) dissolved in biological fluids and natural waters, participates in maintaining the acidity of the environment optimal for life. As part of CaCO 3, carbon forms the outer skeleton of many invertebrates, it is found in corals, eggshells.
During various industrial processes, particles of coal, soot, graphite, diamond enter the atmosphere and are in it in the form of aerosols. Maximum concentration limit for carbon dust in working rooms is 4.0 mg / m 3, for coal 10 mg / m 3.

encyclopedic Dictionary. 2009 .

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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

Nuclide table General information Name, symbol Carbon 13, 13C Neutrons 7 Protons 6 Nuclide properties Atomic mass 13,0033548378 (10)… Wikipedia

- (lat. Carboneum) C, chemical. element of group IV of Mendeleev's periodic system, atomic number 6, atomic mass 12.011. The main crystalline modifications are diamond and graphite. Under normal conditions, carbon is chemically inert; at high ... ... Big Encyclopedic Dictionary

- (Carboneum), C, chemical element of group IV of the periodic system, atomic number 6, atomic mass 12.011; non-metal. Content in the earth's crust is 2.3 × 10 2% by weight. The main crystalline forms of carbon are diamond and graphite. Carbon is the main component ... ... Modern encyclopedia

Carbon - (Carboneum), C, chemical element of group IV of the periodic system, atomic number 6, atomic mass 12.011; non-metal. Content in the earth's crust is 2.3 × 10 2% by weight. The main crystalline forms of carbon are diamond and graphite. Carbon is the main component ... ... Illustrated Encyclopedic Dictionary

CARBON - (1) chem. element, symbol C (Latin Carboneum), at. and. 6, at. m. 12.011. It exists in several allotropic modifications (forms) (diamond, graphite and rarely carbyne, chaoite and lonsdaleite in meteorite craters). Since 1961 / the mass of the atom of the isotope 12C is adopted ... Big Polytechnic Encyclopedia

- (symbol C), a widespread non-metallic element of the fourth group of the periodic table. Carbon forms a huge number of compounds, which together with hydrocarbons and other non-metallic substances form the basis ... ... Scientific and technical encyclopedic dictionary

Carbon in the periodic table of elements is located in the second period in group IVA. Electronic configuration of a carbon atom ls 2 2s 2 2p 2.Upon its excitation, an electronic state is easily achieved, in which there are four unpaired electrons in the four outer atomic orbitals:

This explains why carbon in compounds is usually tetravalent. The equality of the number of valence electrons in the carbon atom to the number of valence orbitals, as well as the unique ratio of the nuclear charge and the radius of the atom, give it the ability to equally easily attach and donate electrons, depending on the properties of the partner (Section 9.3.1). As a result, carbon is characterized by various oxidation states from -4 to +4 and the ease of hybridization of its atomic orbitals of the type sp 3, sp 2and sp 1during the formation of chemical bonds (Section 2.1.3):

All this gives carbon the ability to form ordinary, double and triple bonds not only with each other, but also with the atoms of other organogenic elements. The molecules formed in this case can have a linear, branched and cyclic structure.

Due to the mobility of common -MO electrons formed with the participation of carbon atoms, they are displaced towards the atom of a more electronegative element (inductive effect), which leads to the polarity of not only this bond, but also the molecule as a whole. However, carbon, due to the average value of electronegativity (0E0 \u003d 2.5), forms weakly polar bonds with the atoms of other organogenic elements (Table 12.1). In the presence of conjugated bond systems in the molecules (Section 2.1.3), delocalization of mobile electrons - MO and lone electron pairs occurs with equalization of the electron density and bond lengths in these systems.

From the position reactivity compounds, the polarizability of bonds plays an important role (Section 2.1.3). The greater the polarizability of a bond, the higher its reactivity. The dependence of the polarizability of carbon-containing bonds on their nature reflects the following series:

All the considered data on the properties of carbon-containing bonds indicate that carbon in the compounds forms, on the one hand, rather strong covalent bonds with each other and with other organogens, and on the other hand, the common electronic pairs of these bonds are rather labile. As a result, both an increase in the reactivity of these bonds and stabilization can occur. It is these features of carbon-containing compounds that make carbon the number one organogen.

Acid-base properties of carbon compounds.Carbon monoxide (4) is an acidic oxide, and the corresponding hydroxide, carbonic acid Н2СО3, is a weak acid. The molecule of carbon monoxide (4) is non-polar, and therefore it is poorly soluble in water (0.03 mol / l at 298 K). In this case, the hydrate CO2 H2O is first formed in the solution, in which CO2 is in the cavity of the associate of water molecules, and then this hydrate is slowly and reversibly converted into H2CO3. Most of the carbon monoxide (4) dissolved in water is in the form of a hydrate.

In the body in erythrocytes of blood under the action of the enzyme carbonic anhydrase, the balance between the hydrate CO2 H2O and H2CO3 is established very quickly. This makes it possible to neglect the presence of CO2 in the form of a hydrate in the erythrocyte, but not in the blood plasma, where there is no carbonic anhydrase. The resulting Н2СО3 dissociates under physiological conditions to a bicarbonate anion, and in a more alkaline medium, to a carbonate anion:

Carbonic acid exists only in solution. It forms two series of salts - bicarbonates (NaHCO3, Ca (HCO 3) 2) and carbonates (Na2CO3, CaCO3). Hydrocarbonates dissolve better in water than carbonates. In aqueous solutions, carbonic acid salts, especially carbonates, are easily hydrolyzed by the anion, creating an alkaline environment:

Substances such as baking soda NaHC03; chalk CaCO3, white magnesia 4MgC03 * Mg (OH) 2 * H2O, hydrolyzing with the formation of an alkaline medium, are used as antacid (neutralizing acids) agents to reduce the increased acidity of gastric juice:

The combination of carbonic acid and bicarbonate ion (H2CO3, HCO3 (-)) forms a bicarbonate buffer system (Section 8.5) - a glorious blood plasma buffer system, which ensures the constancy of blood pH at pH \u003d 7.40 ± 0.05.

The presence of calcium and magnesium bicarbonates in natural waters causes their temporary hardness. By boiling such water, its hardness is eliminated. This is due to the hydrolysis of the HCO3 (-)) anion, thermal decomposition of carbonic acid, and precipitation of calcium and magnesium cations in the form of insoluble compounds CaCO 3 and Mg (OH) 2:

The formation of Mg (OH) 2 is caused by complete hydrolysis of the magnesium cation, which proceeds under these conditions due to the lower solubility of Mg (0H) 2 compared to MgCO 3.

In medical and biological practice, in addition to carbonic acid, one has to deal with other carbon-containing acids. This is primarily a large variety of different organic acids, as well as hydrocyanic acid HCN. From the point of view of acidic properties, the strength of these acids is different:

These differences are due to the mutual influence of atoms in the molecule, the nature of the dissociating bond and the stability of the anion, that is, its ability to delocalize the charge.

Hydrocyanic acid, or hydrogen cyanide, HCN - colorless, highly volatile liquid (T bale \u003d26 ° C) with the smell of bitter almonds, miscible with water in any ratio. In aqueous solutions, it behaves like a very weak acid, the salts of which are called cyanides. Cyanides of alkali and alkaline earth metals are soluble in water, while they are hydrolyzed by the anion, which is why they aqueous solutions they smell like hydrocyanic acid (the smell of bitter almonds) and have a pH\u003e 12:

With prolonged exposure to CO2 contained in the air, cyanides decompose with the release of hydrocyanic acid:

As a result of this reaction, potassium cyanide (potassium cyanide) and its solutions lose their toxicity during long-term storage. The cyanide anion is one of the most powerful inorganic poisons, since it is an active ligand and easily forms stable complex compounds with enzymes containing complexing agents Fe 3+ and Cu2 (+) as ions (Sec. 10.4).

Redox properties.Since carbon in compounds can exhibit any oxidation state from -4 to +4, during the reaction, free carbon can both donate and attach electrons, acting as a reducing agent or oxidizing agent, respectively, depending on the properties of the second reagent:

When strong oxidants interact with organic substances, incomplete or complete oxidation of carbon atoms of these compounds can occur.

Under conditions of anaerobic oxidation with a lack or in the absence of oxygen, the carbon atoms of an organic compound, depending on the content of oxygen atoms in these compounds and external conditions, can turn into CO2, CO, C, and even CH4, and the rest of the organogens are converted into H2O, NH3 and H2S ...

In the body, complete oxidation of organic compounds with oxygen in the presence of oxidase enzymes (aerobic oxidation) is described by the equation:

From the above equations of oxidation reactions, it can be seen that in organic compounds, the oxidation state is changed only by carbon atoms, while the atoms of the remaining organogens retain their oxidation state.

In hydrogenation reactions, i.e., the addition of hydrogen (reducing agent) to a multiple bond, the carbon atoms forming it lower their oxidation state (act as oxidizing agents):

Organic substitution reactions with the emergence of a new intercarbon bond, for example, in the Wurtz reaction, are also redox reactions, in which carbon atoms act as oxidizing agents and metal atoms act as reducing agents:

This is observed in the reactions of formation of organometallic compounds:

At the same time, in alkylation reactions with the formation of a new intercarbon bond, the role of an oxidizing agent and a reducing agent is played by the carbon atoms of the substrate and reagent, respectively:

As a result of the reactions of the addition of a polar reagent to the substrate at a multiple intercarbon bond, one of the carbon atoms lowers the oxidation state, exhibiting the properties of an oxidizing agent, and the other increases the oxidation state, acting as a reducing agent:

In these cases, the reaction of intramolecular oxidation-reduction of carbon atoms of the substrate takes place, i.e., the process dismutation,under the influence of a reagent that does not exhibit redox properties.

Typical reactions of intramolecular dismutation of organic compounds due to their carbon atoms are the reactions of decarboxylation of amino acids or keto acids, as well as the reactions of rearrangement and isomerization of organic compounds, which were considered in Sec. 9.3. Examples given organic reactions, as well as the reactions from Sec. 9.3 strongly suggests that carbon atoms in organic compounds can be both oxidizing and reducing agents.

Carbon atom in a compound- an oxidizing agent, if, as a result of the reaction, the number of its bonds with atoms of less electronegative elements (hydrogen, metals) increases, because by attracting the common electrons of these bonds to itself, the carbon atom in question lowers its oxidation state.

Carbon atom in a compound- reducing agent, if as a result of the reaction the number of its bonds with atoms of more electronegative elements increases(C, O, N, S), because by pushing away the common electrons of these bonds, the carbon atom in question increases its oxidation state.

Thus, many reactions in organic chemistry are redox due to the redox duality of carbon atoms. However, in contrast to similar reactions in inorganic chemistry, the redistribution of electrons between the oxidizing agent and the reducing agent in organic compounds can only be accompanied by a displacement of the common electron pair of the chemical bond to the atom acting as the oxidizing agent. In this case, this connection can be preserved, but in cases of its strong polarization, it can break.

Complexing properties of carbon compounds.The carbon atom in the compounds does not have lone electron pairs, and therefore only carbon compounds containing multiple bonds with its participation can act as ligands. The electrons of the triple polar bond of carbon monoxide (2) and the anion of hydrocyanic acid are especially active in the processes of complexation.

In a molecule of carbon monoxide (2), carbon and oxygen atoms form one and one β-bond due to the mutual overlap of their two 2p-atomic orbitals by the exchange mechanism. The third bond, that is, another -bond, is formed by the donor-acceptor mechanism. The acceptor is the free 2p-atomic orbital of the carbon atom, and the donor is the oxygen atom, which provides the lone pair of electrons from the 2p-orbital:

The increased multiplicity of the bond provides this molecule with high stability and inertness under normal conditions in terms of acid-base (CO is a non-salt-forming oxide) and redox properties (CO is a reducing agent at T\u003e1000 K). At the same time, it makes it an active ligand in complexation reactions with d-metal atoms and cations, primarily with iron, with which it forms iron pentacarbonyl, a volatile poisonous liquid:

The ability to form complex compounds with d-metal cations is the reason for the toxicity of carbon monoxide (H) for living systems (Sec. 10.4) due to the occurrence of reversible reactions with hemoglobin and oxyhemoglobin containing the cation Fe 2+, with the formation of carboxyhemoglobin:

These equilibria are shifted towards the formation of carboxyhemoglobin HHbCO, the stability of which is 210 times greater than that of oxyhemoglobin HHbO2. This leads to the accumulation of carboxyhemoglobin in the blood and, consequently, to a decrease in its ability to carry oxygen.

The anion of hydrocyanic acid CN- also contains easily polarizable electrons, which is why it effectively forms complexes with d-metals, including the life metals that are part of enzymes. Therefore, cyanides are highly toxic compounds (Section 10.4).

The carbon cycle in nature.The carbon cycle in nature is mainly based on the oxidation and reduction of carbon (Figure 12.3).

Plants assimilate (1) carbon monoxide from the atmosphere and hydrosphere (4). Part of the plant mass is consumed (2) by humans and animals. Respiration of animals and decay of their remains (3), as well as respiration of plants, decay of dead plants and burning of wood (4) return CO2 to the atmosphere and hydrosphere. The process of mineralization of the remains of plants (5) and animals (6) with the formation of peat, fossil coal, oil, gas leads to the transition of carbon into natural resources. Acid-base reactions act in the same direction (7), occurring between CO2 and various rocks with the formation of carbonates (medium, acidic and basic):

This inorganic part of the cycle leads to CO2 losses in the atmosphere and hydrosphere. Human activities for the combustion and processing of coal, oil, gas (8), firewood (4), on the contrary, enrich environment carbon monoxide (4). For a long time, there was confidence that, thanks to photosynthesis, the concentration of CO2 in the atmosphere remains constant. However, at present, the increase in the content of CO2 in the atmosphere due to human activity is not compensated by its natural loss. The total release of CO2 into the atmosphere is growing exponentially by 4-5% per year. According to calculations in 2000, the CO2 content in the atmosphere will reach approximately 0.04% instead of 0.03% (1990).

After considering the properties and features of carbon-containing compounds, the leading role of carbon should be emphasized once again.

Figure: 12.3.The carbon cycle in nature

organogen number 1: firstly, carbon atoms form the skeleton of molecules of organic compounds; secondly, carbon atoms play a key role in redox processes, since among the atoms of all organogens, it is for carbon that redox duality is most characteristic. For more details on the properties of organic compounds, see module IV "Fundamentals of Bioorganic Chemistry".

General characteristics and biological role of p-elements of group IVA.Electronic analogs of carbon are elements of group IVA: silicon Si, germanium Ge, tin Sn and lead Pb (see Table 1.2). The radii of the atoms of these elements naturally increase with an increase in the serial number, and their ionization energy and electronegativity naturally decrease (Section 1.3). Therefore, the first two elements of the group: carbon and silicon are typical non-metals, and germanium, tin, lead are metals, since they are most characterized by the return of electrons. In the Ge - Sn - Pb series, the metallic properties are enhanced.

From the standpoint of redox properties, the elements C, Si, Ge, Sn and Pb under normal conditions are quite stable with respect to air and water (the metals Sn and Pb are due to the formation of an oxide film on the surface). At the same time, lead compounds (4) are strong oxidants:

Complexing properties are most characteristic of lead, since its Pb 2+ cations are strong complexing agents in comparison with the cations of the other p-elements of IVA group. Lead cations form strong complexes with bioligands.

Elements of group IVA differ sharply both in their content in the body and in their biological role. Carbon plays a fundamental role in the life of the body, where its content is about 20%. The content in the body of other elements of the IVA group is in the range of 10 -6 -10 -3%. At the same time, while silicon and germanium undoubtedly play an important role in the vital activity of the organism, then tin and especially lead are toxic. Thus, with an increase in the atomic mass of group IVA elements, the toxicity of their compounds increases.

Dust, consisting of particles of coal or silicon dioxide SiO2, with systematic exposure to the lungs causes diseases - pneumoconiosis. In the case of coal dust, it is anthracosis, an occupational disease of miners. When dust containing SiO2 is inhaled, silicosis occurs. The mechanism of development of pneumoconiosis has not yet been established. It is assumed that during prolonged contact of silicate grains of sand with biological fluids, polysilicic acid SiO2 yH2O is formed in a gel state, the deposition of which in cells leads to their death.

The toxic effect of lead has been known to mankind for a very long time. Use of lead for cookware and water pipes led to mass poisoning of people. Today, lead continues to be one of the main pollutants in the environment, as it releases over 400,000 tons of lead compounds into the atmosphere annually. Lead accumulates mainly in the skeleton in the form of poorly soluble phosphate Pb3 (PO4) 2, and with demineralization of bones, it has a regular toxic effect on the body. Therefore, lead is classified as a cumulative poison. The toxicity of lead compounds is primarily associated with its complexing properties and high affinity for bioligands, especially those containing sulfhydryl groups (-SH):

The formation of complex compounds of lead ions with proteins, phospholipids and nucleotides leads to their denaturation. Often, lead ions inhibit EM 2+ metalloenzymes, displacing from them the cations of the metals of life:

Lead and its compounds are poisons that act mainly on nervous system, blood vessels and blood. At the same time, lead compounds affect protein synthesis, the energy balance of cells and their genetic apparatus.

In medicine, they are used as astringent external antiseptics: lead acetate Pb (CH3COO) 2 ZH2O (lead lotions) and lead (2) oxide PbO (lead plaster). Lead ions of these compounds react with proteins (albumin) of the cytoplasm of microbial cells and tissues, forming gelatinous albuminates. The formation of gels kills microbes and also makes it difficult for them to penetrate into tissue cells, which reduces the local inflammatory response.

Carbon is the sixth element in Mendeleev's periodic table. Its atomic weight is 12.

Carbon is in the second period of the Mendeleev system and in the fourth group of this system.

The period number tells us that the six electrons of carbon are located on two energy levels.

And the fourth number of the group says that on the external energy level carbon has four electrons. Two of them are paired s-electrons, and the other two are not paired r-electrons.

The structure of the outer electron layer of a carbon atom can be expressed by the following schemes:

Each cell in these diagrams represents a separate electron orbital, the arrow represents an electron in orbital. Two arrows inside one cell are two electrons located in the same orbital, but having oppositely directed spins.

When an atom is excited (when energy is imparted to it), one of the paired S-electrons takes r-orbital.

An excited carbon atom can participate in the formation of four covalent bonds. Therefore, in the overwhelming majority of its compounds, carbon exhibits a valency equal to four.

So, the simplest organic compound hydrocarbon methane has the composition CH 4... Its structure can be expressed by structural or electronic formulas:

The electronic formula shows that the carbon atom in the methane molecule has a stable eight-electron outer shell, and the hydrogen atoms have a stable two-electron shell.

All four covalent bonds of carbon in methane (and in other similar compounds) are equivalent and symmetrically directed in space. The carbon atom is, as it were, in the center of a tetrahedron (a regular quadrangular pyramid), and the four atoms connected to it (in the case of methane, four hydrogen atoms) are at the vertices of the tetrahedron.

The angles between the directions of any pair of bonds are the same and amount to 109 degrees 28 minutes.

This is because in a carbon atom, when it forms covalent bonds with four other atoms, from one s- and three p-orbitals as a result sp 3-hybridizations are formed four symmetrically located in space hybrid sp 3-orbitals, elongated towards the vertices of the tetrahedron.

Feature of the properties of carbon.

The number of electrons at the external energy level is the main factor that determines the chemical properties of an element.

On the left side of the periodic table are elements with a low-filled external electronic level. The elements of the first group on the outer level have one electron, the elements of the second group have two.

The elements of these two groups are metals... They are easily oxidized, i.e. lose their outer electrons and are converted into positive ions.

On the right side of the periodic system, on the contrary, there are non-metals (oxidants)... Compared to metals, they have a nucleus with a large number of protons. Such a massive core provides a much stronger attraction for its electron cloud.

Such elements with great difficulty lose their electrons, but it is not averse to attach additional electrons of other atoms to themselves, i.e. oxidize them, and themselves, at the same time, turn into a negative ion.

The metallic properties of the elements, as the group number in the periodic system increases, weaken, and their ability to oxidize other elements increases.

Carbon is in the fourth group, i.e. just in the middle between metals that easily donate electrons and non-metals that easily attach these electrons.

For this reason carbon does not have a pronounced tendency to give or attach electrons.

Carbon chains.

The exclusive property of carbon, which determines the variety of organic compounds, is the ability of its atoms to bond with strong covalent bonds with each other, forming carbon schemes of practically unlimited length.

In addition to carbon, a chain of identical atoms forms its analog from group IV - silicon. However, such chains contain no more than six Si atoms. Long chains of sulfur atoms are known, but the compounds containing them are fragile.

The valences of carbon atoms, which are not used for interconnection, are used to attach other atoms or groups (in hydrocarbons, to attach hydrogen).

So hydrocarbons ethane ( C 2 H 6) and propane ( C 3 H 8) contain chains of two and three carbon atoms, respectively. Their structure is expressed by the following structural and electronic formulas:

Known compounds containing hundreds or more carbon atoms in chains.

Due to the tetrahedral orientation of carbon bonds, its atoms included in the chain are located not on a straight line, but in a zigzag pattern. Moreover, due to the possibility of rotation of atoms around the bond axis, the chain in space can take various forms (conformations):

This chain structure makes it possible for terminal or other non-adjacent carbon atoms to approach each other. As a result of the formation of a bond between these atoms, carbon chains can be closed into rings (cycles), for example:

Thus, the variety of organic compounds is determined by the fact that with the same number of carbon atoms in a molecule, compounds with an open open chain of carbon atoms are possible, as well as substances whose molecules contain cycles.

Simple and multiple links.

Covalent bonds between carbon atoms formed by one pair of generalized electrons are called simple bonds.

The bond between carbon atoms can be carried out not by one, but by two or three common pairs of electrons. Then chains with multiple - double or triple bonds are obtained. These connections can be depicted as follows:

The simplest compounds containing multiple bonds are hydrocarbons ethylene (double bond) and acetylene (with triple bond):

Hydrocarbons with multiple bonds are called unsaturated or unsaturated. Ethylene and acetylene are the first representatives of two homologous series - ethylene and acetylene hydrocarbons.

(first electron)

Carbon (chemical symbol C) chemical element of the 4th group of the main subgroup of the 2nd period of the periodic system of Mendeleev, serial number 6, atomic mass of the natural mixture of isotopes 12.0107 g / mol.

History

Carbon in the form of charcoal was used in ancient times for smelting metals. Allotropic modifications of carbon — diamond and graphite — have long been known. The elementary nature of carbon was established by A. Lavoisier in the late 1780s.

origin of name

International name: carbō - coal.

Physical properties

Carbon exists in many allotropic modifications with very different physical properties. The variety of modifications is due to the ability of carbon to form chemical bonds of different types.

Carbon isotopes

Natural carbon consists of two stable isotopes - 12 С (98.892%) and 13 С (1.108%) and one radioactive isotope 14 С (β-emitter, Т ½ \u003d 5730 years), concentrated in the atmosphere and the upper part of the earth's crust. It is constantly formed in the lower layers of the stratosphere as a result of the action of cosmic radiation neutrons on nitrogen nuclei according to the reaction: 14 N (n, p) 14 C, as well as, since the mid-1950s, as a technogenic product of the operation of nuclear power plants and as a result of testing hydrogen bombs ...

The formation and decay of 14 C is based on the method of radiocarbon dating, which is widely used in Quaternary geology and archeology.

Allotropic modifications of carbon

Diagrams of the structure of various modifications of carbon
a: diamond, b: graphite, c: lonsdaleite
d: fullerene - bukyball C 60, e: fullerene C 540, f: fullerene C 70
g: amorphous carbon, h: carbon nanotube

Allotropy of carbon

lonsdaleite

fullerenes

carbon nanotubes

amorphous carbon

Coal carbon black soot

The electron orbitals of a carbon atom can have different geometries, depending on the degree of hybridization of its electron orbitals. There are three main geometries for the carbon atom.

Tetrahedral -is formed by mixing one s- and three p-electrons (sp 3 -hybridization). The carbon atom is located in the center of the tetrahedron, bonded by four equivalent σ-bonds with carbon atoms or others at the vertices of the tetrahedron. This geometry of the carbon atom corresponds to the allotropic modifications of carbon, diamond and lonsdaleite. This hybridization is possessed by carbon, for example, in methane and other hydrocarbons.

Trigonal - formed by mixing one s- and two p-electron orbitals (sp²-hybridization). The carbon atom has three equivalent σ-bonds located in one plane at an angle of 120 ° to each other. The p-orbital that does not participate in hybridization, located perpendicular to the plane of σ-bonds, is used to form a π-bond with other atoms. This carbon geometry is typical for graphite, phenol, etc.

Digonal -formed by mixing one s- and one p-electrons (sp-hybridization). In this case, two electron clouds are elongated along one direction and have the form of asymmetric dumbbells. The other two p-electrons give π-bonds. Carbon with such an atomic geometry forms a special allotropic modification - carbyne.

Graphite and diamond

The main and well-studied crystalline modifications of carbon are diamond and graphite. Under normal conditions, only graphite is thermodynamically stable, while diamond and other forms are metastable. At atmospheric pressure and temperatures above 1200 K, the diamond begins to transform into graphite; above 2100 K, the transformation takes place in seconds. ΔН 0 transition - 1.898 kJ / mol. Under normal pressure, carbon sublimes at 3780 K. Liquid carbon exists only at a certain external pressure. Triple points: graphite-liquid-vapor Т \u003d 4130 K, р \u003d 10.7 MPa. The direct transition of graphite to diamond occurs at 3000 K and a pressure of 11–12 GPa.

At pressures above 60 GPa, the formation of a very dense C III modification (the density is 15–20% higher than that of diamond) with metallic conductivity is assumed. At high pressures and relatively low temperatures (about 1200 K), a hexagonal carbon modification with a crystal lattice of the wurtzite-lonsdaleite type is formed from highly oriented graphite (a \u003d 0.252 nm, c \u003d 0.412 nm, space group P6 3 / mts), density 3.51 g / cm³, that is, the same as that of a diamond. Lonsdaleite is also found in meteorites.

Ultrafine diamonds (nanodiamonds)

In the 1980s. In the USSR, it was discovered that under dynamic loading of carbon-containing materials, diamond-like structures, called ultradispersed diamonds (UDD), can form. Nowadays, the term "nanodiamonds" is increasingly used. The particle size in such materials is in the order of nanometers. The conditions for the formation of UDD can be realized upon detonation of explosives with a significant negative oxygen balance, for example, mixtures of TNT with RDX. Such conditions can also be realized when celestial bodies strike the Earth's surface in the presence of carbon-containing materials (organic matter, peat, coal, etc.). So, in the zone of the fall of the Tunguska meteorite, UDDs were found in the forest floor.

Carbin

The crystalline modification of hexagonal carbon with a chain molecular structure is called carbyne. The chains have either a polyene structure (—C≡C—) or a polycumulene (\u003d C \u003d C \u003d). Several forms of carbyne are known, differing in the number of atoms in the unit cell, cell size and density (2.68-3.30 g / cm³). Carbyne occurs naturally in the form of the mineral chaoite (white streaks and inclusions in graphite) and is obtained artificially by oxidative dehydro-polycondensation of acetylene, the action of laser radiation on graphite, from hydrocarbons or CCl 4 in low-temperature plasma.

Carbyne is a fine-crystalline black powder (density 1.9-2 g / cm³), has semiconducting properties. Received in artificial conditions from long chains of atoms carbonlaid parallel to each other.

Carbyne is a linear polymer of carbon. In a carbyne molecule, carbon atoms are connected in chains alternately either by triple and single bonds (polyene structure), or permanently double bonds (polycumulene structure). This substance was first obtained by Soviet chemists V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin and Yu.P. Kudryavtsev in the early 60s. in Institute of Organoelement Compounds of the USSR Academy of Sciences . Carbine has semiconducting properties, and under the influence of light, its conductivity is greatly increased. The first practical application, in photocells, is based on this property.

Fullerenes and carbon nanotubes

Carbon is also known in the form of cluster particles C 60, C 70, C 80, C 90, C 100 and the like (fullerenes), as well as graphenes and nanotubes.

Amorphous carbon

The structure of amorphous carbon is based on the disordered structure of monocrystalline (always contains impurities) graphite. These are coke, brown and bituminous coals, carbon black, soot, active coal.

Being in nature

The carbon content in the earth's crust is 0.1% by mass. Free carbon is found naturally in the form of diamond and graphite. The bulk of carbon in the form of natural carbonates (limestone and dolomite), combustible minerals - anthracite (94-97% C), brown coal (64-80% C), bituminous coals (76-95% C), oil shale (56- 78% C), oil (82-87% C), combustible natural gases (up to 99% methane), peat (53-56% C), as well as bitumen, etc. In the atmosphere and hydrosphere is in the form of carbon dioxide CO 2 , in the air 0.046% CO 2 by mass, in the waters of rivers, seas and oceans ~ 60 times more. Carbon is found in plants and animals (~ 18%).
Carbon enters the human body with food (normally about 300 g per day). The total carbon content in the human body reaches about 21% (15kg per 70kg of body weight). Carbon accounts for 2/3 of muscle mass and 1/3 of bone mass. Excreted from the body mainly with exhaled air (carbon dioxide) and urine (urea)
The carbon cycle in nature includes a biological cycle, the release of CO 2 into the atmosphere during the combustion of fossil fuels, from volcanic gases, hot mineral springs, from the surface layers of ocean waters, etc. The biological cycle consists in the fact that carbon in the form of CO 2 is absorbed from the troposphere by plants ... Then, from the biosphere, it returns to the geosphere: with plants, carbon enters the body of animals and humans, and then, during the decay of animal and plant materials, into the soil and, in the form of CO 2, into the atmosphere.

In the vapor state and in the form of compounds with nitrogen and hydrogen, carbon is found in the atmosphere of the Sun, planets, it is found in stone and iron meteorites.

Most carbon compounds, and above all hydrocarbons, have a pronounced covalent character. The strength of simple, double and triple bonds of C atoms with each other, the ability to form stable chains and cycles from C atoms determine the existence of a huge number of carbon-containing compounds studied by organic chemistry.

Chemical properties

At ordinary temperatures, carbon is chemically inert; at high enough temperatures, it combines with many elements and exhibits strong reducing properties. The chemical activity of different forms of carbon decreases in the following order: amorphous carbon, graphite, diamond; in air they ignite at temperatures above 300–500 ° C, 600–700 ° C, and 850–1000 ° C, respectively.

Oxidation states +4, −4, rarely +2 (CO, metal carbides), +3 (C 2 N 2, halocyanines); electron affinity 1.27 eV; the ionization energy during the successive transition from C 0 to C 4+ is 11.2604, 24.383, 47.871 and 64.19 eV, respectively.

Inorganic compounds

Carbon reacts with many elements to form carbides.

Combustion products are carbon monoxide CO and carbon dioxide CO 2. Also known unstable oxide С 3 О 2 (melting point −111 ° C, boiling point 7 ° C) and some other oxides. Graphite and amorphous carbon begin to react with H 2 at 1200 ° C, with F 2, respectively, 900 ° C.

CO 2 with water forms a weak carbonic acid - H 2 CO 3, which forms salts - carbonates. On Earth, the most widespread carbonates are calcium (chalk, marble, calcite, limestone and other minerals) and magnesium (dolomite).

Graphite with halogens, alkali metals and other substances forms inclusion compounds. When an electric discharge is passed between carbon electrodes in an N 2 medium, cyanogen is formed; at high temperatures, hydrocyanic acid is obtained by the interaction of carbon with a mixture of N 2 and N 2. With sulfur, carbon gives carbon disulfide CS 2, CS and C 3 S 2 are also known. With most metals, boron and silicon, carbon forms carbides. The reaction of carbon with water vapor is important in industry: C + H 2 O \u003d CO + H 2 (Gasification of solid fuels). When heated, carbon reduces metal oxides to metals, which is widely used in metallurgy.

Organic compounds

Due to the ability of carbon to form polymer chains, there is a huge class of carbon-based compounds, which are much more numerous than inorganic ones, and which are studied by organic chemistry. Among them are the most extensive groups: hydrocarbons, proteins, fats, etc.

Carbon compounds form the basis of life on earth, and their properties largely determine the range of conditions in which such life forms can exist. In terms of the number of atoms in living cells, the proportion of carbon is about 25%, in terms of mass fraction, about 18%.

Application

Graphite is used in the pencil industry. It is also used as a lubricant at extremely high or low temperatures.

Diamond, thanks to its exceptional hardness, is an irreplaceable abrasive material. Grinding nozzles of drills have diamond dusting. In addition, cut diamonds are used as precious stones in jewelry. Due to its rarity, high decorative qualities and a coincidence of historical circumstances, the diamond is invariably the most expensive gemstone. The exceptionally high thermal conductivity of diamond (up to 2000 W / m.K) makes it a promising material for semiconductor technology as substrates for processors. But the relatively high price (about $ 50 / gram) and the complexity of diamond processing limit its use in this area.
In pharmacology and medicine, various carbon compounds are widely used — derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers, and other compounds. Thus, carbolene (activated carbon) is used to absorb and remove various toxins from the body; graphite (in the form of ointments) - for the treatment of skin diseases; radioactive isotopes of carbon - for scientific research (radiocarbon analysis).

Carbon plays a huge role in human life. Its applications are as varied as the many-sided element itself.

Carbon is the basis of all organic matter. Any living organism is composed 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 devour 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.

Carbon in the form of fossil fuels: coal and hydrocarbons (oil, natural gas) - one of the most important sources of energy for humanity.

Toxic effect

Carbon is a part of atmospheric aerosols, as a result of which the regional climate can change, the number of sunny days can decrease. Carbon enters the environment in the form of soot in the exhaust gases of vehicles, when coal is burned at thermal power plants, during opencast coal mining, its underground gasification, coal concentrates production, etc. The concentration of carbon over combustion sources is 100-400 μg / m³, in large cities 2, 4-15.9 µg / m³, in rural areas 0.5–0.8 µg / m³. With gas-aerosol emissions from nuclear power plants (6-15) .10 9 Bq / day 14 СО 2.

The high carbon content in atmospheric aerosols leads to an increase in the incidence of the population, especially the upper respiratory tract and lungs. Occupational diseases are mainly anthracosis and dust bronchitis. In the air of the working area MPC, mg / m³: diamond 8.0, anthracite and coke 6.0, coal 10.0, carbon black and carbon dust 4.0; in the atmospheric air the maximum one-time 0.15, the daily average 0.05 mg / m³.

The toxic effect of 14 C, included in the composition of protein molecules (especially in DNA and RNA), is determined by the radiation effect of beta particles and nitrogen recoil nuclei (14 C (β) → 14 N) and the transmutation effect - a change chemical composition molecules as a result of the transformation of atom C into atom N. The permissible concentration of 14 C in the air of the working area DK A 1.3 Bq / l, in the atmospheric air DK B 4.4 Bq / l, in water 3.0.10 4 Bq / l, maximum admissible intake through the respiratory system 3.2.10 8 Bq / year.

Additional Information

- Carbon compounds
- Radiocarbon analysis
- Orthocarboxylic acid

Allotropic forms of carbon:

Diamond
Graphene
Graphite
Carbin
Lonsdaleite
Carbon nanotubes
Fullerenes

Amorphous forms:

Soot
Carbon black
Coal

Carbon isotopes:

Unstable (less than a day): 8C: Carbon-8, 9C: Carbon-9, 10C: Carbon-10, 11C: Carbon-11
Stable: 12C: Carbon-12, 13C: Carbon-13
10-10,000 years: 14C: Carbon-14
Unstable (less than a day): 15C: Carbon-15, 16C: Carbon-16, 17C: Carbon-17, 18C: Carbon-18, 19C: Carbon-19, 20C: Carbon-20, 21C: Carbon-21, 22C: Carbon-22

Nuclide table

Carbon, Carboneum, C (6)
Carbon (English Carbon, French Carbone, German Kohlenstoff) in the form of coal, soot and soot has been known to mankind since time immemorial; about 100 thousand years ago, when our ancestors mastered fire, they dealt with coal and soot every day. Probably, very early on, people became acquainted with the allotropic modifications of carbon - diamond and graphite, as well as with fossil coal. Not surprisingly, the combustion of carbonaceous substances was one of the first chemical processes to interest humans. Since the burning substance disappeared, being devoured by the fire, combustion was considered a process of decomposition of the substance, and therefore coal (or carbon) was not considered an element. The element was fire, a phenomenon that accompanies combustion; in the teachings of the elements of antiquity, fire usually appears as one of the elements. At the turn of the XVII - XVIII centuries. arose the theory of phlogiston, put forward by Becher and Stahl. This theory recognized the presence in each combustible body of a special elementary substance - a weightless fluid - phlogiston, which evaporates during combustion.

When a large amount of coal is burned, only a little ash remains, phlogists believed that coal is almost pure phlogiston. This explains, in particular, the "phlogistic" effect of coal - its ability to reduce metals from "lime" and ores. Later phlogists, Reaumur, Bergman and others, already began to understand that coal is an elementary substance. However, for the first time, Lavoisier was recognized as such "clean coal", who studied the process of combustion of coal and other substances in air and oxygen. In the book of Guiton de Morveaux, Lavoisier, Berthollet and Furcroix "Method of chemical nomenclature" (1787), the name "carbon" (carbone) appeared instead of the French "pure coal" (charbone pur). Under the same name, carbon appears in the "Table of Simple Bodies" in Lavoisier's "Elementary Textbook of Chemistry". In 1791 the English chemist Tennant was the first to obtain free carbon; he passed phosphorus vapors over the calcined chalk, resulting in the formation of calcium phosphate and carbon. It has been known for a long time that a diamond burns out without residue when heated strongly. Back in 1751, the French king Franz I agreed to give diamond and ruby \u200b\u200bfor burning experiments, after which these experiments even became fashionable. It turned out that only diamond burns, and ruby \u200b\u200b(aluminum oxide with an admixture of chromium) can withstand prolonged heating at the focus of the incendiary lens without damage. Lavoisier set up a new experiment on burning a diamond using a large incendiary machine, came to the conclusion that a diamond is crystalline carbon. The second carbon allotrope - graphite in the alchemical period was considered a modified lead luster and was called plumbago; it was only in 1740 that Pott discovered the absence of any lead impurity in graphite. Scheele investigated graphite (1779) and, being a phlogist, considered it a sulfurous body of a special kind, a special mineral coal containing bound "air acid" (CO2) and a large amount of phlogiston.

Twenty years later, Guiton de Morveaux, by careful heating, turned the diamond into graphite and then into carbonic acid.

The international name Carboneum comes from lat. carbo (coal). The word is of very ancient origin. It is compared with cremare - to burn; root sag, cal, Russian gar, gal, gol, Sanskrit hundred means to boil, to boil. The word "carbo" is associated with the names of carbon in other European languages \u200b\u200b(carbon, charbone, etc.). German Kohlenstoff comes from Kohle - coal (Old German kolo, Swedish kylla - to heat). Old Russian ugorati, or ugarati (to burn, scorch) has the root gar, or mountains, with a possible transition to a goal; coal in Old Russian is yugl, or coal, of the same origin. The word diamond (Diamante) comes from ancient Greek - indestructible, unyielding, hard, and graphite from Greek - I write.

At the beginning of the XIX century. the old word coal in Russian chemical literature was sometimes replaced by the word ugletvor (Sherer, 1807; Severgin, 1815); since 1824 Soloviev introduced the name carbon.

MOU "Nikiforovskaya secondary school №1"

Carbon and its main inorganic compounds

abstract

Completed: student of grade 9B

Alexander Sidorov

Teacher: Sakharova L.N.

Dmitrievka 2009

Introduction

Chapter I. All About Carbon

1.1. Carbon in nature

1.2. Allotropic modifications of carbon

1.3. Chemical properties of carbon

1.4. Application of carbon

Chapter II. Inorganic carbon compounds

Conclusion

Literature

Introduction

Carbon (Latin Carboneum) C is a chemical element of group IV of Mendeleev's periodic system: atomic number 6, atomic mass 12.011 (1). Consider the structure of the carbon atom. There are four electrons on the outer energy level of the carbon atom. Let's graphically depict:

Carbon has been known since ancient times, and the name of the discoverer of this element is unknown.

At the end of the 17th century. Florentine scientists Averani and Targioni tried to fuse several small diamonds into one large one and heated them with incendiary glass sunbeams... The diamonds disappeared by burning in the air. In 1772, the French chemist A. Lavoisier showed that the combustion of diamond produces CO 2. Only in 1797 the English scientist S. Tennant proved the identity of the nature of graphite and coal. After combustion of equal amounts of coal and diamond, the volumes of carbon monoxide (IV) were the same.

The variety of carbon compounds, explained by the ability of its atoms to combine with each other and with the atoms of other elements in various ways, determines the special position of carbon among other elements.

Chapter I ... All about carbon

1.1. Carbon in nature

Carbon is found in nature, both in a free state and in the form of compounds.

Free carbon occurs in the form of diamond, graphite, and carbyne.

Diamonds are very rare. The largest known diamond - "Cullinan" was found in 1905 in South Africa, weighed 621.2 g and had dimensions 10 × 6.5 × 5 cm. The Diamond Fund in Moscow stores one of the largest and most beautiful diamonds in the world - "Orlov" (37.92 g).

The diamond got its name from the Greek. "Adamas" - invincible, indestructible. The most significant diamond deposits are located in South Africa, Brazil, and Yakutia.

Large deposits of graphite are located in the Federal Republic of Germany, Sri Lanka, Siberia, and Altai.

The main carbon-containing minerals are: magnesite MgCO 3, calcite (limestone, limestone, marble, chalk) CaCO 3, dolomite CaMg (CO 3) 2, etc.

All fossil fuels - oil, gas, peat, bituminous and brown coal, shale - are carbon-based. Some fossil coals are similar in composition to carbon, containing up to 99% C.

Carbon accounts for 0.1% of the earth's crust.

In the form of carbon monoxide (IV) CO 2, carbon is part of the atmosphere. A large amount of CO 2 is dissolved in the hydrosphere.

1.2. Allotropic modifications of carbon

Elementary carbon forms three allotropic modifications: diamond, graphite, and carbyne.

1. Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly. Carbon atoms in diamond are in the state of sp 3 -hybridization. In an excited state, the valence electrons in carbon atoms are unpaired and four unpaired electrons are formed. When chemical bonds are formed, the electron clouds acquire the same elongated shape and are located in space so that their axes are directed to the vertices of the tetrahedron. When the tops of these clouds overlap with the clouds of other carbon atoms, covalent bonds appear at an angle of 109 ° 28 ", and an atomic crystal lattice, characteristic of diamond, is formed.

Each carbon atom in a diamond is surrounded by four others, located from it in the directions from the center of the tetrahedrons to the vertices. The distance between atoms in tetrahedra is 0.154 nm. The strength of all bonds is the same. Thus, the atoms in a diamond are packed very tightly. At 20 ° C, the density of diamond is 3.515 g / cm 3. This explains its exceptional hardness. Diamond does not conduct electric current well.

In 1961, the industrial production of synthetic diamonds from graphite began in the Soviet Union.

In the industrial synthesis of diamonds, pressures of thousands of MPa and temperatures from 1500 to 3000 ° C are used. The process is carried out in the presence of catalysts, which can be some metals, for example Ni. The bulk of the formed diamonds are small crystals and diamond dust.

When heated without air access above 1000 ° C, diamond turns into graphite. At 1750 ° C, the transformation of diamond into graphite occurs rapidly.

Diamond structure

2. Graphite is a gray-black crystalline substance with a metallic luster, greasy to the touch, inferior in hardness even to paper.

Carbon atoms in graphite crystals are in the state of sp 2 -hybridization: each of them forms three covalent σ-bonds with neighboring atoms. The angles between the directions of the bonds are equal to 120 °. The result is a grid made up of regular hexagons. The distance between adjacent nuclei of carbon atoms inside the layer is 0.142 nm. The fourth electron of the outer layer of each carbon atom in graphite is occupied by the p-orbital, which does not participate in hybridization.

Non-hybrid electron clouds of carbon atoms are oriented perpendicular to the plane of the layer, and overlap with each other, form delocalized σ-bonds. Adjacent layers in a graphite crystal are at a distance of 0.335 nm from each other and are weakly connected to each other, mainly by van der Waals forces. Therefore, graphite has low mechanical strength and easily splits into flakes, which are very strong in themselves. The bond between layers of carbon atoms in graphite is partially metallic. This explains the fact that graphite conducts electric current well, but still not as well as metals.

Graphite structure

The physical properties in graphite differ greatly in directions - perpendicular and parallel to the layers of carbon atoms.

When heated without air access, graphite does not undergo any changes up to 3700 ° C. At the indicated temperature, it sublimes without melting.

Artificial graphite is obtained from the best grades of coal at 3000 ° C in electric furnaces without access to air.

Graphite is thermodynamically stable over a wide range of temperatures and pressures; therefore, it is taken as the standard state of carbon. The density of graphite is 2.265 g / cm 3.

3. Carbyne is a fine crystalline black powder. In its crystal structure, carbon atoms are connected by alternating single and triple bonds in linear chains:

−С≡С − С≡С − С≡С−

This substance was first obtained by V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin, Yu.P. Kudryavtsev in the early 60s of the XX century.

Subsequently, it was shown that carbyne can exist in different forms and contains both polyacetylene and polycumulene chains, in which carbon atoms are linked by double bonds:

C \u003d C \u003d C \u003d C \u003d C \u003d C \u003d

Later, carbyne was found in nature - in meteorite matter.

Carbyne has semiconducting properties; under the influence of light, its conductivity is greatly increased. Due to existence different types bonds and different ways of stacking chains of carbon atoms in the crystal lattice physical properties carbyne can vary widely. When heated without air access above 2000 ° C, carbyne is stable; at temperatures around 2300 ° C, its transition to graphite is observed.

Natural carbon is composed of two isotopes (98.892%) and (1.108%). In addition, insignificant admixtures of a radioactive isotope, which are obtained artificially, have been found in the atmosphere.

Previously, it was believed that charcoal, soot and coke are close in composition to pure carbon and differ in properties from diamond and graphite, represent an independent allotropic modification of carbon ("amorphous carbon"). However, it was found that these substances are composed of the smallest crystalline particles, in which carbon atoms are linked in the same way as in graphite.

4. Coal - finely ground graphite. Formed by thermal decomposition of carbon-containing compounds without air access. Coals differ significantly in properties depending on the substance from which they are obtained and the method of obtaining. They always contain impurities that affect their properties. The most important types of coal are coke, charcoal, and soot.

Coke is produced by heating coal without air.

Charcoal is formed when wood is heated without access to air.

Soot is a very fine graphite crystalline powder. Formed when burning hydrocarbons (natural gas, acetylene, turpentine, etc.) with limited air access.

Active carbons are porous industrial adsorbents, consisting mainly of carbon. Adsorption is the absorption by the surface of solids of gases and solutes. Activated carbons are obtained from solid fuels (peat, brown and coal, anthracite), wood and products of its processing (charcoal, sawdust, paper waste), tanning industry waste, animal materials, such as bones. Coals with high mechanical strength are produced from the shells of coconut and other nuts, from the seeds of fruits. The structure of coals is represented by pores of all sizes; however, the adsorption capacity and the rate of adsorption are determined by the content of micropores per unit of mass or volume of granules. In the production of active carbon, the starting material is first subjected to heat treatment without access to air, as a result of which moisture and partly tar is removed from it. In this case, a large-pore structure of coal is formed. To obtain a microporous structure, activation is performed either by oxidation with gas or steam, or by treatment with chemical reagents.

1.3. Chemical properties of carbon

At ordinary temperatures, diamond, graphite, and coal are chemically inert, but at high temperatures their activity increases. As follows from the structure of the main forms of carbon, coal reacts more easily than graphite and even more so diamond. Graphite is not only more reactive than diamond, but by reacting with certain substances, it can form products that diamond does not.

1. As an oxidizing agent, carbon reacts with some metals at high temperatures to form carbides:

ЗС + 4Аl \u003d Аl 4 С 3 (aluminum carbide).

2. With hydrogen, coal and graphite form hydrocarbons. The simplest representative - methane CH 4 - can be obtained in the presence of a Ni catalyst at a high temperature (600-1000 ° C):

C + 2H 2 CH 4.

3. When interacting with oxygen, carbon exhibits reducing properties. With the complete combustion of carbon of any allotropic modification, carbon monoxide (IV) is formed:

C + O 2 \u003d CO 2.

With incomplete combustion, carbon monoxide (II) CO is formed:

C + O 2 \u003d 2CO.

Both reactions are exothermic.

4. The reducing properties of coal are especially pronounced when interacting with metal oxides (zinc, copper, lead, etc.), for example:

C + 2CuO \u003d CO 2 + 2Cu,

C + 2ZnO \u003d CO 2 + 2Zn.

The most important process of metallurgy is based on these reactions - the smelting of metals from ores.

In other cases, for example, when interacting with calcium oxide, carbides are formed:

CaO + 3C \u003d CaC 2 + CO.

5. Coal is oxidized with hot concentrated sulfuric and nitric acids:

C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O,

ЗС + 4НNО 3 \u003d ЗСО 2 + 4NO + 2Н 2 О.

All forms of carbon are resistant to alkalis!

1.4. Application of carbon

Diamonds are used for processing various hard materials, for cutting, grinding, drilling and engraving glass, for drilling rocks. After polishing and cutting, diamonds are transformed into diamonds used as jewelry.

Graphite is the most valuable material for modern industry. Casting molds, melting crucibles and other refractory products are made from graphite. Due to its high chemical resistance, graphite is used for the manufacture of pipes and apparatus lined with graphite plates from the inside. Significant amounts of graphite are used in the electrical industry, for example, in the manufacture of electrodes. Graphite is used to make pencils and some paints as a lubricant. Very pure graphite is used in nuclear reactors to slow down neutrons.

Linear polymer of carbon - carbyne - attracts the attention of scientists as a promising material for the manufacture of semiconductors that can operate at high temperatures and ultra-strong fibers.

Charcoal is used in the metallurgical industry, in blacksmithing.

Coke is used as a reducing agent in the smelting of metals from ores.

Carbon black is used as a rubber filler to increase durability, which is why car tires are black. Carbon black is also used as a component of printing inks, mascara, and shoe polish.

Active carbons are used for the purification, recovery and separation of various substances. Active carbons are used as fillers for gas masks and as a sorbing agent in medicine.

Chapter II ... Inorganic carbon compounds

Carbon forms two oxides - carbon monoxide (II) CO and carbon monoxide (IV) CO 2.

Carbon monoxide (II) CO is a colorless, odorless gas, slightly soluble in water. It is called carbon monoxide because it is highly toxic. Getting into the blood during breathing, it quickly combines with hemoglobin, forming a strong compound carboxyhemoglobin, thereby depriving hemoglobin of the ability to carry oxygen.

If air containing 0.1% CO is inhaled, a person may suddenly faint and die. Carbon monoxide is formed when the fuel is incompletely burned, which is why premature closing of chimneys is so dangerous.

Carbon monoxide (II) is referred, as you already know, to non-salt-forming oxides, since, as a non-metal oxide, it must react with alkalis and basic oxides to form salt and water, but this is not observed.

2CO + O 2 \u003d 2CO 2.

Carbon monoxide (II) is capable of removing oxygen from metal oxides, i.e. recover metals from their oxides.

Fe 2 О 3 + ЗСО \u003d 2Fe + ЗСО 2.

It is this property of carbon monoxide (II) that is used in metallurgy when smelting pig iron.

Carbon monoxide (IV) CO 2 - commonly known as carbon dioxide - is a colorless, odorless gas. It is about one and a half times heavier than air. Under normal conditions, 1 volume of water dissolves 1 volume of carbon dioxide.

At a pressure of about 60 atm, carbon dioxide turns into a colorless liquid. When liquid carbon dioxide evaporates, part of it turns into a solid snow-like mass, which is compressed in industry - this is the "dry ice" you know, which is used to store food. You already know that solid carbon dioxide has a molecular lattice and is capable of sublimation.

Carbon dioxide CO 2 is a typical acidic oxide: it interacts with alkalis (for example, causes turbidity of lime water), with basic oxides and water.

It does not burn and does not support combustion and therefore is used to extinguish fires. However, magnesium continues to burn in carbon dioxide to form oxide and release carbon as soot.

CO 2 + 2Mg \u003d 2MgO + C.

Carbon dioxide is produced by acting on carbonic acid salts - carbonates with solutions of hydrochloric, nitric and even acetic acids. In the laboratory, carbon dioxide is produced by the action of hydrochloric acid on chalk or marble.

CaCO 3 + 2HCl \u003d CaCl 2 + H 2 0 + CO 2.

In industry, carbon dioxide is obtained by burning limestone:

CaCO 3 \u003d CaO + CO 2.

Carbon dioxide, in addition to the already mentioned field of application, is also used for the production of effervescent drinks and for the production of soda.

When carbon monoxide (IV) dissolves in water, carbonic acid H 2 CO 3 is formed, which is very unstable and easily decomposes into its original components - carbon dioxide and water.

As a dibasic acid, carbonic acid forms two series of salts: medium - carbonates, for example CaCO 3, and acidic - bicarbonates, for example Ca (HCO 3) 2. Of the carbonates, only potassium, sodium and ammonium salts are soluble in water. Acid salts are generally water soluble.

With an excess of carbon dioxide in the presence of water, carbonates can be converted to bicarbonates. So, if carbon dioxide is passed through lime water, it will first become cloudy due to precipitated water-insoluble calcium carbonate, but with further passing of carbon dioxide, the turbidity disappears as a result of the formation of soluble calcium bicarbonate:

CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2.

It is the presence of this salt that explains the temporary hardness of the water. Why temporary? Because when heated, soluble calcium bicarbonate again turns into insoluble carbonate:

Ca (HCO 3) 2 \u003d CaCO 3 ↓ + H 2 0 + C0 2.

This reaction leads to the formation of scale on the walls of boilers, steam heating pipes and domestic kettles, and in nature, as a result of this reaction, bizarre stalactites hanging down in caves are formed, towards which stalagmites grow from below.

Other calcium and magnesium salts, in particular chlorides and sulphates, impart permanent hardness to water. The constant hardness of water cannot be eliminated by boiling. We have to use another carbonate - soda.

Na 2 CO 3, which converts these Ca 2+ ions into a precipitate, for example:

CaCl 2 + Na 2 CO 3 \u003d CaCO 3 ↓ + 2NaCl.

Soda can also be used to eliminate temporary water hardness.

Carbonates and bicarbonates can be detected using acid solutions: under the action of acids on them, a characteristic "boiling" is observed due to the emitted carbon dioxide.

This reaction is a qualitative reaction for carbonic acid salts.

Conclusion

All life on earth is carbon-based. Each molecule of a living organism is built on the basis of a carbon skeleton. Carbon atoms constantly migrate from one part of the biosphere (the narrow shell of the Earth where life exists) to another. Using the example of the carbon cycle in nature, one can trace the dynamics of the picture of life on our planet.

The main reserves of carbon on Earth are in the form of carbon dioxide, that is, carbon dioxide (CO 2), contained in the atmosphere and dissolved in the oceans. Consider first the molecules of carbon dioxide in the atmosphere. Plants absorb these molecules, then, in the process of photosynthesis, the carbon atom turns into various organic compounds and thus is included in the structure of plants. Further, several options are possible:

1. Carbon can remain in plants until the plants die. Then their molecules will go into food for decomposers (organisms that feed on dead organic matter and at the same time break it down to simple inorganic compounds), such as mushrooms and termites. Eventually, the carbon will return to the atmosphere as CO 2;

2. Plants can be eaten by herbivores. In this case, the carbon will either return to the atmosphere (during the respiration of animals and during their decomposition after death), or the herbivores will be eaten by the carnivores (and then the carbon will return to the atmosphere in the same ways);

3. Plants may die and end up underground. Then they will eventually turn into fossil fuels - for example, coal.

In the case of dissolution of the original CO 2 molecule in seawater, several options are also possible:

Carbon dioxide can simply return to the atmosphere (this type of mutual gas exchange between the World Ocean and the atmosphere occurs constantly);

Carbon can enter the tissues of marine plants or animals. Then it will gradually accumulate in the form of sediments at the bottom of the World Ocean and eventually turn into limestone or from sediments will again pass into sea water.

When carbon is incorporated into sediment or fossil fuels, it is removed from the atmosphere. Throughout the existence of the Earth, the carbon removed in this way was replaced by carbon dioxide that entered the atmosphere during volcanic eruptions and other geothermal processes. In modern conditions, these natural factors also add emissions from human combustion of fossil fuels. Due to the influence of CO 2 on the greenhouse effect, the study of the carbon cycle has become an important task for scientists studying the atmosphere.

An integral part This quest is to determine the amount of CO 2 in plant tissues (for example, in a newly planted forest) - scientists call this carbon sink. Since governments different countries trying to reach an international agreement on limiting CO 2 emissions, the issue of a balanced ratio of sinks and carbon emissions in individual states has become the main bone of contention for industrial countries. However, scientists doubt that the accumulation of carbon dioxide in the atmosphere can be stopped by planting forests alone.

Carbon constantly circulates in the earth's biosphere along closed interconnected paths. Nowadays, the consequences of burning fossil fuels are added to natural processes.

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