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

At ordinary temperatures, carbon is chemically inert; at sufficiently high 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 respectively above 300-500 °C, 600-700 °C and 850-1000 °C.

Isotopes:
Natural carbon consists of two stable isotopes - 12C (98.892%) and 13C (1.108%) and one radioactive isotope 14C (β-emitter, T½ = 5730 years), concentrated in the atmosphere and upper part of the earth's crust. It is constantly formed in the lower layers of the stratosphere as a result of the impact of neutrons from cosmic radiation on nitrogen nuclei according to the reaction: 14N (n, p) 14C, and also, since the mid-1950s, as a man-made product of nuclear power plants and as a result of testing hydrogen bombs.
The formation and decay of 14C is the basis of the radiocarbon dating method, which is widely used in Quaternary geology and archaeology.

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

Tetrahedral, formed by mixing one s- and three p-electrons (sp3 hybridization). The carbon atom is located in the center of the tetrahedron, connected by four equivalent σ-bonds to carbon or other atoms at the vertices of the tetrahedron. The carbon allotropic modifications diamond and lonsdaleite correspond to this geometry of the carbon atom. Carbon exhibits such hybridization, 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 the same plane at an angle of 120° to each other. The p-orbital not involved in hybridization, located perpendicular to the plane of σ bonds, is used to form a π bond with other atoms. This carbon geometry is characteristic of 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 look like asymmetrical dumbbells. The other two p electrons make a π bond. Carbon with such an atomic geometry forms a special allotropic modification - carbyne.

Oxidation states +4, −4, rarely +2 (CO, metal carbides), +3 (C2N2, halocyanates); electron affinity 1.27 eV; The ionization energy during the sequential transition from C0 to C4+ is 11.2604, 24.383, 47.871 and 64.19 eV, respectively.

Chemical properties of carbon
Interaction with fluorine
Carbon has low reactivity; of the halogens, it reacts only with fluorine:

C + 2F2 = CF4.

Interaction with oxygen
When heated, it reacts with oxygen:

2C + O2 = 2CO,

C + O2 = CO2,

forming oxides CO and CO2.

Interaction with other non-metals
Reacts with sulfur:

does not interact with nitrogen and phosphorus.

Reacts with hydrogen in the presence of a nickel catalyst, forming methane:

Interaction with metals
Able to interact with metals, forming carbides:
Ca + 2C = CaC2.

Interaction with water
When water vapor is passed through hot coal, carbon monoxide (II) and hydrogen are formed:
C + H2O = CO + H2.

Restorative properties
Carbon is capable of reducing many metals from their oxides:
2ZnO + C = 2Zn + CO2.

Concentrated sulfuric and nitric acids, when heated, oxidize carbon to carbon monoxide (IV):

C + 2H2SO4 = CO2 + 2SO2 + 2H2O;
C + 4HNO3 = CO2 + 4NO2 + 2H2O.

CARBON, C, chemical element of group IV of the periodic system, atomic weight 12.00, atomic number 6. Until recently, carbon was considered to have no isotopes; Only recently has it been possible, using particularly sensitive methods, to detect the existence of the C 13 isotope. Carbon is one of the most important elements in terms of its prevalence, the number and diversity of its compounds, its biological significance (as an organogen), the extensive technical use of carbon itself and its compounds (as raw materials and as a source of energy for industrial and domestic needs), and finally, in terms of its role in the development of chemical science. Carbon in the free state exhibits a pronounced phenomenon of allotropy, known for more than a century and a half, but still not fully studied, both because of the extreme difficulty of obtaining carbon in a chemically pure form, and because most of the constants of allotropic modifications of carbon vary greatly depending on morphological features of their structure, determined by the method and conditions of production.

Carbon forms two crystalline forms - diamond and graphite and is also known in the amorphous state in the form of the so-called. amorphous coal. The individuality of the latter has been disputed as a result of recent research: coal was identified with graphite, considering both as morphological varieties of the same form - “black carbon”, and the difference in their properties was explained by the physical structure and degree of dispersion of the substance. However, very recently, facts have been obtained confirming the existence of coal as a special allotropic form (see below).

Natural sources and stocks of carbon. In terms of prevalence in nature, carbon ranks 10th among the elements, making up 0.013% of the atmosphere, 0.0025% of the hydrosphere and about 0.35% of the total mass of the earth’s crust. Most of the carbon is in the form of oxygen compounds: atmospheric air contains ~800 billion tons of carbon in the form of CO 2 dioxide; in the water of oceans and seas - up to 50,000 billion tons of carbon in the form of CO 2, carbonic acid ions and bicarbonates; in rocks - insoluble carbonates (calcium, magnesium and other metals), and the share of CaCO 3 alone accounts for ~160·10 6 billion tons of carbon. These colossal reserves, however, do not represent any energy value; much more valuable are combustible carbonaceous materials - fossil coals, peat, then oil, hydrocarbon gases and other natural bitumens. The reserve of these substances in the earth's crust is also quite significant: the total mass of carbon in fossil coals reaches ~6000 billion tons, in oil ~10 billion tons, etc. In the free state, carbon is quite rare (diamond and part of the graphite substance). Fossil coals contain almost or no free carbon: they consist of Ch. arr. of high molecular weight (polycyclic) and very stable compounds of carbon with other elements (H, O, N, S) have still been very little studied. Carbon compounds of living nature (the biosphere of the globe), synthesized in plant and animal cells, are distinguished by an extraordinary variety of properties and composition quantities; the most common substances in the plant world - fiber and lignin - also play a role as energy resources. Carbon maintains a constant distribution in nature thanks to a continuous cycle, the cycle of which consists of the synthesis of complex organic substances in plant and animal cells and the reverse disaggregation of these substances during their oxidative decomposition (combustion, decay, respiration), leading to the formation of CO 2, which is used again plants for synthesis. The general scheme of this cycle could be presented in the following form:

Carbon production. Carbonaceous compounds of plant and animal origin are unstable at high temperatures and, when heated to at least 150-400°C without access to air, decompose, releasing water and volatile carbon compounds and leaving a solid non-volatile residue rich in carbon and usually called coal. This pyrolytic process is called charring, or dry distillation, and is widely used in technology. High-temperature pyrolysis of fossil coals, oil and peat (at a temperature of 450-1150°C) leads to the release of carbon in graphite form (coke, retort coal). The higher the charring temperature of the starting materials, the closer the resulting coal or coke is to free carbon in composition and to graphite in properties.

Amorphous coal, formed at temperatures below 800°C, cannot. we consider it as free carbon, because it contains significant amounts of chemically bound other elements, Ch. arr. hydrogen and oxygen. Of the technical products, activated carbon and soot are the closest in properties to amorphous carbon. The purest coal may be obtained by charring pure sugar or piperonal, special treatment of gas soot, etc. Artificial graphite, obtained by electrothermal means, is almost pure carbon in composition. Natural graphite is always contaminated with mineral impurities and also contains a certain amount of bound hydrogen (H) and oxygen (O); in a relatively pure state it might. obtained only after a number of special treatments: mechanical enrichment, washing, treatment with oxidizing agents and calcination at high temperatures until volatile substances are completely removed. In carbon technology one never deals with completely pure carbon; This applies not only to natural carbon raw materials, but also to the products of its enrichment, upgrading and thermal decomposition (pyrolysis). Below is the carbon content of some carbonaceous materials (in %):

Physical properties of carbon. Free carbon is almost completely infusible, nonvolatile, and at ordinary temperatures insoluble in any of the known solvents. It dissolves only in some molten metals, especially at temperatures approaching the boiling point of the latter: in iron (up to 5%), silver (up to 6%) | ruthenium (up to 4%), cobalt, nickel, gold and platinum. In the absence of oxygen, carbon is the most heat-resistant material; The liquid state for pure carbon is unknown, and its transformation into vapor begins only at temperatures above 3000°C. Therefore, the determination of the properties of carbon was carried out exclusively for the solid state of aggregation. Of the carbon modifications, diamond has the most constant physical properties; the properties of graphite in its various samples (even the purest) vary significantly; The properties of amorphous coal are even more variable. The most important physical constants of various carbon modifications are compared in the table.

Diamond is a typical dielectric, while graphite and carbon have metallic electrical conductivity. In absolute value, their conductivity varies over a very wide range, but for coals it is always lower than for graphites; in graphites, the conductivity of real metals approaches. The heat capacity of all carbon modifications at temperatures >1000°C tends to a constant value of 0.47. At temperatures below -180°C, the heat capacity of diamond becomes vanishingly small and at -27°C it practically becomes zero.

Chemical properties of carbon. When heated above 1000°C, both diamond and coal gradually transform into graphite, which therefore should be considered as the most stable (at high temperatures) monotropic form of carbon. The transformation of amorphous coal into graphite apparently begins around 800°C and ends at 1100°C (at this last point, coal loses its adsorption activity and ability to reactivate, and its electrical conductivity increases sharply, remaining almost constant in the future). Free carbon is characterized by inertness at ordinary temperatures and significant activity at high temperatures. Amorphous coal is the most chemically active, while diamond is the most resistant. For example, fluorine reacts with coal at a temperature of 15°C, with graphite only at 500°C, and with diamond at 700°C. When heated in air, porous coal begins to oxidize below 100°C, graphite at about 650°C, and diamond above 800°C. At temperatures of 300°C and above, coal combines with sulfur to form carbon disulfide CS 2. At temperatures above 1800°C, carbon (coal) begins to interact with nitrogen, forming (in small quantities) cyanogen C 2 N 2. The interaction of carbon with hydrogen begins at 1200°C, and in the temperature range 1200-1500°C only methane CH 4 is formed; above 1500°C - a mixture of methane, ethylene (C 2 H 4) and acetylene (C 2 H 2); at temperatures of the order of 3000°C almost exclusively acetylene is obtained. At the temperature of the electric arc, carbon enters into direct combination with metals, silicon and boron, forming the corresponding carbides. Direct or indirect ways may. compounds of carbon with all known elements were obtained, except gases of the zero group. Carbon is a non-metallic element that exhibits some signs of amphotericity. The carbon atom has a diameter of 1.50 Ᾰ (1Ᾰ = 10 -8 cm) and contains in the outer sphere 4 valence electrons, which are equally easily given up or added to 8; therefore, the normal valency of carbon, both oxygen and hydrogen, is four. In the vast majority of its compounds, carbon is tetravalent; Only a small number of compounds of divalent carbon (carbon monoxide and its acetals, isonitriles, fulminate acid and its salts) and trivalent carbon (the so-called “free radical”) are known.

With oxygen, carbon forms two normal oxides: acidic carbon dioxide CO 2 and neutral carbon monoxide CO. In addition, there are a number carbon suboxides containing more than 1 C atom and having no technical significance; Of these, the best known is suboxide of composition C 3 O 2 (a gas with a boiling point of +7 ° C and a melting point of -111 ° C). The first product of combustion of carbon and its compounds is CO 2, formed according to the equation:

C+O 2 = CO 2 +97600 cal.

The formation of CO during incomplete combustion of fuel is the result of a secondary reduction process; The reducing agent in this case is carbon itself, which at temperatures above 450°C reacts with CO 2 according to the equation:

CO 2 +C = 2СО -38800 cal;

this reaction is reversible; above 950°C, the conversion of CO 2 into CO becomes almost complete, which is carried out in gas-generating furnaces. The energetic reducing ability of carbon at high temperatures is also used in the production of water gas (H 2 O + C = CO + H 2 -28380 cal) and in metallurgical processes to obtain free metal from its oxide. Allotropic forms of carbon react differently to the action of some oxidizing agents: for example, a mixture of KCIO 3 + HNO 3 has no effect on diamond at all, amorphous coal is completely oxidized into CO 2, while graphite produces aromatic compounds - graphitic acids with the empirical formula (C 2 OH) x onwards mellitic acid C 6 (COOH) 6 . Compounds of carbon with hydrogen - hydrocarbons - are extremely numerous; from them, most other organic compounds are genetically produced, which, in addition to carbon, most often include H, O, N, S and halogens.

The exceptional diversity of organic compounds, of which up to 2 million are known, is due to certain features of carbon as an element. 1) Carbon is characterized by a strong chemical bond with most other elements, both metallic and non-metallic, due to which it forms fairly stable compounds with both. When it combines with other elements, carbon has very little tendency to form ions. Most organic compounds are of the homeopolar type and do not dissociate under normal conditions; Breaking intramolecular bonds in them often requires the expenditure of a significant amount of energy. When judging the strength of connections, one should, however, distinguish; a) absolute bond strength, measured thermochemically, and b) the ability of the bond to break under the influence of various reagents; these two characteristics do not always coincide. 2) Carbon atoms bond with each other with exceptional ease (non-polar), forming carbon chains, open or closed. The length of such chains is apparently not subject to any restrictions; Thus, quite stable molecules with open chains of 64 carbon atoms are known. The lengthening and complexity of open chains does not affect the strength of the connection of their links with each other or with other elements. Among closed chains, 6- and 5-membered rings are most easily formed, although ringed chains containing from 3 to 18 carbon atoms are known. The ability of carbon atoms to interconnect well explains the special properties of graphite and the mechanism of charring processes; it also makes clear the fact that carbon is unknown in the form of diatomic C 2 molecules, which would be expected by analogy with other light non-metallic elements (in vapor form, carbon consists of monatomic molecules). 3) Due to the non-polar nature of the bonds, many carbon compounds have chemical inertness not only externally (slowness of reaction), but also internally (difficulty of intramolecular rearrangements). The presence of large “passive resistances” greatly complicates the spontaneous transformation of unstable forms into stable ones, often reducing the rate of such transformation to zero. The result of this is the possibility of realizing a large number of isomeric forms that are almost equally stable at ordinary temperatures.

Allotropy and atomic structure of carbon . X-ray analysis made it possible to reliably establish the atomic structure of diamond and graphite. The same research method shed light on the question of the existence of a third allotropic modification of carbon, which is essentially a question about the amorphousness or crystallinity of coal: if coal is an amorphous formation, then it cannot. identified neither with graphite nor with diamond, but must be considered as a special form of carbon, as an individual simple substance. In diamond, carbon atoms are arranged in such a way that each atom lies in the center of a tetrahedron, the vertices of which are 4 adjacent atoms; each of the latter in turn is the center of another similar tetrahedron; the distances between adjacent atoms are 1.54 Ᾰ (the edge of an elementary cube of the crystal lattice is 3.55 Ᾰ). This structure is the most compact; it corresponds to the high hardness, density and chemical inertness of diamond (uniform distribution of valence forces). The mutual connection of carbon atoms in the diamond lattice is the same as in the molecules of most organic compounds of the fatty series (tetrahedral model of carbon). In graphite crystals, carbon atoms are arranged in dense layers, spaced 3.35-3.41 Ᾰ from one another; the direction of these layers coincides with the cleavage planes and sliding planes during mechanical deformations. In the plane of each layer, the atoms form a grid with hexagonal cells (companies); the side of such a hexagon is 1.42-1.45 Ᾰ. In adjacent layers, the hexagons do not lie one under the other: their vertical coincidence is repeated only after 2 layers in the third. The three bonds of each carbon atom lie in the same plane, forming angles of 120°; The 4th bond is directed alternately in one direction or another from the plane to the atoms of neighboring layers. The distances between atoms in a layer are strictly constant, but the distance between individual layers can be changed by external influences: for example, when pressed under pressure up to 5000 atm, it decreases to 2.9 Ᾰ, and when graphite swells in concentrated HNO 3, it increases to 8 Ᾰ. In the plane of one layer, carbon atoms are bonded homeopolarly (as in hydrocarbon chains), but the bonds between atoms of adjacent layers are rather metallic in nature; this is evident from the fact that the electrical conductivity of graphite crystals in the direction perpendicular to the layers is ~100 times higher than the conductivity in the direction of the layer. That. graphite has the properties of a metal in one direction and the properties of a non-metal in the other. The arrangement of carbon atoms in each layer of the graphite lattice is exactly the same as in the molecules of complex nuclear aromatic compounds. This configuration well explains the sharp anisotropy of graphite, exceptionally developed cleavage, antifriction properties and the formation of aromatic compounds during its oxidation. The amorphous modification of black carbon apparently exists as an independent form (O. Ruff). For it, the most probable is a foam-like cellular structure, devoid of any regularity; the walls of such cells are formed by layers of active atoms carbon about 3 atoms thick. In practice, the active substance of coal usually lies under a shell of closely spaced inactive carbon atoms, oriented graphitically, and is penetrated by inclusions of very small graphite crystallites. There is probably no specific point of transformation of coal → graphite: between both modifications there is a continuous transition, during which the randomly crowded mass of C-atoms of amorphous coal is transformed into a regular crystal lattice of graphite. Due to their random arrangement, carbon atoms in amorphous coal exhibit a maximum residual affinity, which (according to Langmuir’s ideas about the identity of adsorption forces with valence forces) corresponds to the high adsorption and catalytic activity so characteristic of coal. Carbon atoms oriented in the crystal lattice spend all their affinity (in diamond) or most of it (in graphite) on mutual adhesion; This corresponds to a decrease in chemical activity and adsorption activity. In diamond, adsorption is possible only on the surface of a single crystal, while in graphite, residual valency can appear on both surfaces of each flat lattice (in the “cracks” between layers of atoms), which is confirmed by the fact that graphite can swell in liquids (HNO 3) and the mechanism of its oxidation to graphitic acid.

Technical significance of carbon. As for b. or m. of free carbon obtained during the processes of charring and coking, then its use in technology is based on both its chemical (inertness, reducing ability) and its physical properties (heat resistance, electrical conductivity, adsorption capacity). Thus, coke and charcoal, in addition to their partial direct utilization as flameless fuel, are used to produce gaseous fuel (generator gases); in the metallurgy of ferrous and non-ferrous metals - for the reduction of metal oxides (Fe, Cu, Zn, Ni, Cr, Mn, W, Mo, Sn, As, Sb, Bi); in chemical technology - as a reducing agent in the production of sulfides (Na, Ca, Ba) from sulfates, anhydrous chloride salts (Mg, Al), from metal oxides, in the production of soluble glass and phosphorus - as a raw material for the production of calcium carbide, carborundum and other carbides carbon disulfide, etc.; in the construction industry - as a thermal insulating material. Retort coal and coke serve as materials for electrodes of electric furnaces, electrolytic baths and galvanic cells, for the manufacture of arc coals, rheostats, commutator brushes, melting crucibles, etc., and also as a nozzle in tower-type chemical equipment. In addition to the above applications, charcoal is used to produce concentrated carbon monoxide, cyanide salts, for the cementation of steel, is widely used as an adsorbent, as a catalyst for some synthetic reactions, and finally is included in black powder and other explosive and pyrotechnic compositions.

Analytical determination of carbon. Carbon is determined qualitatively by charring a sample of a substance without access to air (which is not suitable for all substances) or, which is much more reliable, by its exhaustive oxidation, for example, by calcination in a mixture with copper oxide, and the formation of CO 2 is proven by ordinary reactions. To quantify carbon, a sample of the substance is burned in an oxygen atmosphere; the resulting CO 2 is captured by an alkali solution and determined by weight or volume using conventional methods of quantitative analysis. This method is suitable for determining carbon not only in organic compounds and technical coals, but also in metals.

Organic chemistry is the chemistry of the carbon atom. The number of organic compounds is tens of times greater than inorganic ones, which can only be explained features of the carbon atom :

a) he is in middle of the electronegativity scale and the second period, therefore it is unprofitable for him to give away his own and accept other people’s electrons and acquire a positive or negative charge;

b) special structure of the electron shell – there are no electron pairs and free orbitals (there is only one more atom with a similar structure - hydrogen, which is probably why carbon and hydrogen form so many compounds - hydrocarbons).

Electronic structure of the carbon atom

C – 1s 2 2s 2 2p 2 or 1s 2 2s 2 2p x 1 2p y 1 2p z 0

In graphical form:

A carbon atom in an excited state has the following electronic formula:

*C – 1s 2 2s 1 2p 3 or 1s 2 2s 1 2p x 1 2p y 1 2p z 1

In the form of cells:

Shape of s- and p-orbitals

Atomic orbital - the region of space where an electron is most likely to be found, with corresponding quantum numbers.

It is a three-dimensional electron "contour map" in which the wave function determines the relative probability of finding an electron at that particular point in the orbital.

The relative sizes of atomic orbitals increase as their energies increase ( principal quantum number- n), and their shape and orientation in space is determined by quantum numbers l and m. Electrons in orbitals are characterized by a spin quantum number. Each orbital can contain no more than 2 electrons with opposite spins.

When forming bonds with other atoms, the carbon atom transforms its electron shell so that the strongest bonds are formed, and, consequently, as much energy as possible is released, and the system acquires the greatest stability.

Changing the electron shell of an atom requires energy, which is then compensated by the formation of stronger bonds.

Electron shell transformation (hybridization) can be mainly of 3 types, depending on the number of atoms with which the carbon atom forms bonds.

Types of hybridization:

sp 3 – an atom forms bonds with 4 neighboring atoms (tetrahedral hybridization):

Electronic formula of sp 3 – hybrid carbon atom:

*С –1s 2 2(sp 3) 4 in the form of cells

The bond angle between the hybrid orbitals is ~109°.

Stereochemical formula of carbon atom:

sp 2 – Hybridization (valence state)– an atom forms bonds with 3 neighboring atoms (trigonal hybridization):

Electronic formula of sp 2 – hybrid carbon atom:

*С –1s 2 2(sp 2) 3 2p 1 in the form of cells

The bond angle between the hybrid orbitals is ~120°.

Stereochemical formula of sp 2 - hybrid carbon atom:

sp– Hybridization (valence state) – an atom forms bonds with 2 neighboring atoms (linear hybridization):

Electronic formula of sp – hybrid carbon atom:

*С –1s 2 2(sp) 2 2p 2 in the form of cells

The bond angle between the hybrid orbitals is ~180°.

Stereochemical formula:

The s-orbital is involved in all types of hybridization, because it has minimal energy.

The restructuring of the electron cloud allows the formation of the strongest possible bonds and minimal interaction of atoms in the resulting molecule. Wherein hybrid orbitals may not be identical, but bond angles may be different, for example CH 2 Cl 2 and CCl 4

2. Covalent bonds in carbon compounds

Covalent bonds, properties, methods and reasons for formation - school curriculum.

Let me just remind you:

1. Education Communications between atoms can be considered as a result of the overlap of their atomic orbitals, and the more effective it is (the larger the overlap integral), the stronger the bond.

According to calculated data, the relative overlap efficiencies of atomic orbitals S rel increase as follows:

Therefore, using hybrid orbitals, such as sp 3 carbon orbitals, to form bonds with four hydrogen atoms results in stronger bonds.

2. Covalent bonds in carbon compounds are formed in two ways:

A)If two atomic orbitals overlap along their principal axes, the resulting bond is called - σ bond.

Geometry. Thus, when bonds are formed with hydrogen atoms in methane, four hybrid sp 3 ~ orbitals of the carbon atom overlap with the s-orbitals of four hydrogen atoms, forming four identical strong σ bonds located at an angle of 109°28" to each other (standard tetrahedral angle) A similar strictly symmetric tetrahedral structure also arises, for example, during the formation of CCl 4; if the atoms forming bonds with carbon are unequal, for example in the case of CH 2 C1 2, the spatial structure will differ somewhat from completely symmetrical, although essentially it remains tetrahedral .

σ bond length between carbon atoms depends on the hybridization of atoms and decreases during the transition from sp 3 - hybridization to sp. This is explained by the fact that the s orbital is closer to the nucleus than the p orbital, therefore, the larger its share in the hybrid orbital, the shorter it is, and therefore the shorter the bond formed

B) If two atomic p -orbitals located parallel to each other carry out lateral overlap above and below the plane where the atoms are located, then the resulting bond is called - π (pi) -communication

Lateral overlap atomic orbitals is less efficient than overlap along the major axis, so π - connections are less strong than σ - connections. This is manifested, in particular, in the fact that the energy of a double carbon-carbon bond is less than twice the energy of a single bond. Thus, the C-C bond energy in ethane is 347 kJ/mol, while the C = C bond energy in ethene is only 598 kJ/mol, and not ~ 700 kJ/mol.

Degree of lateral overlap of two atomic 2p orbitals , and therefore strength π -bonds are maximum if there are two carbon atoms and four bonded to them atoms are located strictly in one plane, i.e. if they coplanar , since only in this case the atomic 2p orbitals are exactly parallel to one another and are therefore capable of maximum overlap. Any deviation from the coplanar state due to rotation around σ -bond connecting two carbon atoms will lead to a decrease in the degree of overlap and, accordingly, to a decrease in strength π -bond, which thus helps maintain the flatness of the molecule.

Rotation around a carbon-carbon double bond is not possible.

Distribution π -electrons above and below the plane of the molecule means the existence areas of negative charge, ready to interact with any electron-deficient reagents.

Atoms of oxygen, nitrogen, etc. also have different valence states (hybridization), and their electron pairs can be in both hybrid and p-orbitals.

Carbon in the periodic table of elements is located in the second period in group IVA. Electronic configuration of carbon atom ls 2 2s 2 2p 2 . When it is excited, 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 charge of the nucleus and the radius of the atom, gives it the ability to equally easily attach and give up 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 according to the type sp 3, sp 2 And sp 1 during the formation of chemical bonds (section 2.1.3):

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

Due to the mobility of common electrons -MOs formed with the participation of carbon atoms, they are shifted 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 electronegativity value (0E0 = 2.5), forms weakly polar bonds with atoms of other organogenic elements (Table 12.1). If there are systems of conjugated bonds in 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 point of view of the reactivity of 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 is reflected in the following series:

All the considered data on the properties of carbon-containing bonds indicate that carbon in compounds forms, on the one hand, fairly strong covalent bonds with each other and with other organogens, and on the other hand, the common electron pairs of these bonds are quite 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 its corresponding hydroxide - carbonic acid H2CO3 - is a weak acid. The carbon monoxide(4) molecule is non-polar, and therefore it is poorly soluble in water (0.03 mol/l at 298 K). In this case, first, the hydrate CO2 H2O is formed in the solution, in which CO2 is located in the cavity of the associate of water molecules, and then this hydrate slowly and reversibly turns into H2CO3. Most of the carbon monoxide (4) dissolved in water is in the form of hydrate.

In the body, in red blood cells, under the action of the enzyme carboanhydrase, the equilibrium between CO2 hydrate H2O and H2CO3 is established very quickly. This allows us to neglect the presence of CO2 in the form of hydrate in the erythrocyte, but not in the blood plasma, where there is no carbonic anhydrase. The resulting H2CO3 dissociates under physiological conditions to a hydrocarbonate anion, and in a more alkaline environment to a carbonate anion:

Carbonic acid exists only in solution. It forms two series of salts - hydrocarbonates (NaHCO3, Ca(HC0 3)2) and carbonates (Na2CO3, CaCO3). Hydrocarbonates are more soluble in water than carbonates. In aqueous solutions, carbonic acid salts, especially carbonates, easily hydrolyze at the anion, creating an alkaline environment:

Substances such as baking soda NaHC03; chalk CaCO3, white magnesia 4MgC03 * Mg(OH)2 * H2O, hydrolyzed to form an alkaline environment, are used as antacids (acid neutralizers) 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 nice buffer system of the blood plasma, which ensures a constant blood pH at pH = 7.40 ± 0.05.

The presence of calcium and magnesium hydrocarbonates in natural waters causes their temporary hardness. When such water is boiled, its hardness is eliminated. This occurs due to the hydrolysis of the HCO3(-) anion, the thermal decomposition of carbonic acid and the precipitation of calcium and magnesium cations in the form of insoluble compounds CaC03 and Mg(OH)2:

The formation of Mg(OH)2 is caused by complete hydrolysis of the magnesium cation, which occurs under these conditions due to the lower solubility of Mg(0H)2 compared to MgC03.

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 standpoint of acidic properties, the strength of these acids is different:

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

Hydrocyanic acid, or hydrogen cyanide, HCN - colorless, highly volatile liquid (T kip = 26 °C) with the smell of bitter almonds, miscible with water in any ratio. In aqueous solutions it behaves as a very weak acid, the salts of which are called cyanides. Alkali and alkaline earth metal cyanides are soluble in water, but they hydrolyze at the anion, which is why their aqueous solutions smell like hydrocyanic acid (the smell of bitter almonds) and have a pH >12:

With prolonged exposure to CO2 contained in the air, cyanide decomposes to release hydrocyanic acid:

As a result of this reaction, potassium cyanide (potassium cyanide) and its solutions lose their toxicity during long-term storage. 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 Fe 3+ and Cu2(+) as complexing ions (Sect. 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 gain electrons, acting as a reducing agent or an oxidizing agent, respectively, depending on the properties of the second reagent:

When strong oxidizing agents interact with organic substances, incomplete or complete oxidation of the carbon atoms of these compounds may occur.

Under conditions of anaerobic oxidation with a lack or absence of oxygen, carbon atoms of an organic compound, depending on the content of oxygen atoms in these compounds and external conditions, can turn into C0 2, CO, C and even CH 4, and other organogens turn into H2O, NH3 and H2S .

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

From the given equations of oxidation reactions it is clear that in organic compounds only carbon atoms change the oxidation state, while the atoms of other organogens retain their oxidation state.

During hydrogenation reactions, i.e., the addition of hydrogen (a reducing agent) to a multiple bond, the carbon atoms that form it reduce 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:

A similar thing is observed in the reactions of the formation of organometallic compounds:

At the same time, in alkylation reactions with the emergence of a new intercarbon bond, the role of oxidizer and reducer is played by the carbon atoms of the substrate and reagent, respectively:

As a result of the reactions of addition of a polar reagent to the substrate via 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 degree, acting as a reducing agent:

In these cases, an intramolecular oxidation-reduction reaction 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 decarboxylation reactions of amino acids or keto acids, as well as the rearrangement and isomerization reactions of organic compounds, which were discussed in section. 9.3. The given examples of organic reactions, as well as reactions from Sect. 9.3 convincingly indicate that carbon atoms in organic compounds can be both oxidizing agents 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- a 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 shared electrons of these bonds, the carbon atom in question increases its oxidation state.

Thus, many reactions in organic chemistry, due to the redox duality of carbon atoms, are redox. However, unlike 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 strong polarization it can be broken.

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

In the carbon monoxide molecule (2), the carbon and oxygen atoms form one and one -bond due to the mutual overlap of their two 2p-atomic orbitals according to the exchange mechanism. The third bond, i.e., another -bond, is formed according to 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 a lone pair of electrons from the 2p orbital:

The increased bond ratio 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 > 1000 K). At the same time, it makes it an active ligand in complexation reactions with atoms and cations of d-metals, primarily with iron, with which it forms iron pentacarbonyl, a volatile toxic liquid:

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

These equilibria are shifted towards the formation of carboxyhemoglobin ННbСО, the stability of which is 210 times greater than that of oxyhemoglobin ННbО2. This leads to the accumulation of carboxyhemoglobin in the blood and, consequently, to a decrease in its ability to carry oxygen.

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

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

Plants assimilate (1) carbon monoxide (4) from the atmosphere and hydrosphere. Part of the plant mass is consumed (2) by humans and animals. The respiration of animals and the decay of their remains (3), as well as the respiration of plants, the rotting of dead plants and the combustion 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 coals, oil, gas leads to the transition of carbon into natural resources. Acid-base reactions (7) operate in the same direction, occurring between CO2 and various rocks with the formation of carbonates (medium, acidic and basic):

This inorganic part of the cycle leads to loss of CO2 in the atmosphere and hydrosphere. Human activity in the combustion and processing of coal, oil, gas (8), firewood (4), on the contrary, abundantly enriches the environment with 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 CO2 content in the atmosphere due to human activity is not compensated by its natural decrease. 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 characteristics of carbon-containing compounds, the leading role of carbon should once again be emphasized

Rice. 12.3. Carbon cycle in nature

Organogen No. 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 carbon that is most characterized by redox duality. For more information about the properties of organic compounds, see module IV "Fundamentals of Bioorganic Chemistry".

General characteristics and biological role of p-elements of group IVA. Electronic analogues 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 increasing atomic 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, and lead are metals, since they are most characterized by the loss of electrons. In the series Ge - Sn - Pb, metallic properties increase.

From the point of view 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 - due to the formation of an oxide film on the surface). At the same time, lead compounds (4) are strong oxidizing agents:

Complexing properties are most characteristic of lead, since its Pb 2+ cations are strong complexing agents compared to the cations of other p-elements of group IVA. 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 of other group IVA elements in the body is within 10 -6 -10 -3%. At the same time, if silicon and germanium undoubtedly play an important role in the life of the body, then tin and especially lead are toxic. Thus, with increasing atomic mass of group IVA elements, the toxicity of their compounds increases.

Dust consisting of particles of coal or silicon dioxide SiO2, when systematically exposed to the lungs, causes diseases - pneumoconiosis. In the case of coal dust, this is anthracosis, an occupational disease of miners. When dust containing Si02 is inhaled, silicosis occurs. The mechanism of development of pneumoconiosis has not yet been established. It is assumed that with prolonged contact of silicate sand grains with biological fluids, polysilicic acid Si02 yH2O is formed in a gel-like 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. The use of lead to make dishes and water pipes led to massive poisoning of people. Currently, lead continues to be one of the main environmental pollutants, since the release of lead compounds into the atmosphere amounts to over 400,000 tons annually. Lead accumulates mainly in the skeleton in the form of poorly soluble phosphate Pb3(PO4)2, and when bones are demineralized, it has a regular toxic effect on the body. Therefore, lead is classified as a cumulative poison. The toxicity of lead compounds is associated primarily 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 life metal cations from them:

Lead and its compounds are poisons that act primarily on the 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, the following external antiseptics are used as astringents: lead acetate Pb(CH3COO)2 ZH2O (lead lotions) and lead(2) oxide PbO (lead plaster). The lead ions of these compounds react with proteins (albumin) in the cytoplasm of microbial cells and tissues, forming gel-like albuminates. The formation of gels kills microbes and, in addition, makes it difficult for them to penetrate into tissue cells, which reduces the local inflammatory response.

Municipal educational institution "Nikiforovskaya secondary school No. 1"

Carbon and its main inorganic compounds

Essay

Completed by: student of grade 9B

Sidorov Alexander

Teacher: Sakharova L.N.

Dmitrievka 2009

Introduction

Chapter I. All about carbon

1.1. Carbon in nature

1.2. Allotropic modifications of carbon

1.3. Chemical properties of carbon

1.4. Application of carbon

Chapter II. Inorganic carbon compounds

Conclusion

Literature

Introduction

Carbon (lat. Carboneum) C is a chemical element of group IV of the periodic system of Mendeleev: atomic number 6, atomic mass 12.011(1). Let's consider the structure of the carbon atom. The outer energy level of the carbon atom contains four electrons. Let's depict it graphically:

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 Tardgioni tried to fuse several small diamonds into one large one and heated them with a burning glass using sunlight. The diamonds disappeared, burning in the air. In 1772, the French chemist A. Lavoisier showed that when diamonds burn, CO 2 is formed. Only in 1797 did the English scientist S. Tennant prove the identity of the nature of graphite and coal. After burning equal amounts of coal and diamond, the volumes of carbon monoxide (IV) turned out to be the same.

The variety of carbon compounds, explained by the ability of its atoms to combine with each other and 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, the Cullinan, was found in 1905 in South Africa, weighed 621.2 g and measured 10x6.5x5 cm. The Diamond Fund in Moscow houses one of the largest and most beautiful diamonds in world – “Orlov” (37.92 g).

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

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

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

All fossil fuels - oil, gas, peat, coal and brown coal, shale - are built on a carbon basis. Some fossil coals, containing up to 99% C, are close in composition to carbon.

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

In the form of carbon monoxide (IV) CO 2, carbon enters 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, carbine.

1. Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly. Carbon atoms in diamond are in a state of sp 3 hybridization. In the excited state, the valence electrons in the carbon atoms are paired 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 towards the vertices of the tetrahedron. When the tops of these clouds overlap with clouds of other carbon atoms, covalent bonds occur at an angle of 109°28", and an atomic crystal lattice characteristic of diamond is formed.

Each carbon atom in diamond is surrounded by four others, located from it in directions from the center of the tetrahedrons to the vertices. The distance between atoms in tetrahedra is 0.154 nm. The strength of all connections is the same. Thus, the atoms in diamond are “packed” very tightly. At 20°C, the density of diamond is 3.515 g/cm 3 . This explains its exceptional hardness. Diamond is a poor conductor of electricity.

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

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

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

Diamond structure

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

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

Non-hybrid electron clouds of carbon atoms are oriented perpendicular to the plane of the layer and, overlapping each other, form delocalized σ bonds. Adjacent layers in a graphite crystal are located 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 themselves are very strong. The bond between layers of carbon atoms in graphite is partially metallic in nature. This explains the fact that graphite conducts electricity well, but not as well as metals.

Graphite structure

Physical properties in graphite vary 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 specified temperature, it sublimes without melting.

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

Graphite is thermodynamically stable over a wide range of temperatures and pressures, so it is accepted as the standard state of carbon. The density of graphite is 2.265 g/cm3.

3. Carbin 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.

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

C=C=C=C=C=C=

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

Carbyne has semiconducting properties; when exposed to light, its conductivity increases greatly. Due to the existence of different types of bonds and different ways of laying chains of carbon atoms in the crystal lattice, the physical properties of carbyne can vary within wide limits. When heated without access to air above 2000°C, carbine is stable; at temperatures around 2300°C, its transition to graphite is observed.

Natural carbon consists of two isotopes (98.892%) and (1.108%). In addition, minor admixtures of a radioactive isotope, which is produced artificially, were found in the atmosphere.

Previously, it was believed that charcoal, soot and coke are similar in composition to pure carbon and differ in properties from diamond and graphite, representing an independent allotropic modification of carbon (“amorphous carbon”). However, it was found that these substances consist of tiny crystalline particles in which the carbon atoms are bonded in the same way as in graphite.

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

Coke is produced by heating coal without access to air.

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

Soot is a very fine graphite crystalline powder. Formed by the combustion of hydrocarbons (natural gas, acetylene, turpentine, etc.) with limited air access.

Activated carbons are porous industrial adsorbents consisting mainly of carbon. Adsorption is the absorption of gases and dissolved substances by the surface of solids. Activated carbons are obtained from solid fuel (peat, brown and hard coal, anthracite), wood and its processed products (charcoal, sawdust, paper waste), leather industry waste, and animal materials, such as bones. Coals, characterized by high mechanical strength, are produced from the shells of coconuts and other nuts, and from fruit seeds. The structure of coals is represented by pores of all sizes, however, the adsorption capacity and adsorption rate are determined by the content of micropores per unit mass or volume of granules. When producing active carbon, the starting material is first subjected to heat treatment without access to air, as a result of which moisture and partially resins are removed from it. In this case, a large-porous structure of coal is formed. To obtain a microporous structure, activation is carried out either by oxidation with gas or steam, or by treatment with chemical reagents.

1.3. Chemical properties of carbon

At ordinary temperatures, diamond, graphite, 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, especially, diamond. Graphite is not only more reactive than diamond, but when reacting with certain substances, it can form products that diamond does not form.

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

ZS + 4Al = Al 4 C 3 (aluminum carbide).

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

C + 2H 2 CH 4.

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

C + O 2 = CO 2.

Incomplete combustion produces carbon monoxide (II) CO:

C + O 2 = 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 = CO 2 + 2Cu,

C + 2ZnO = CO 2 + 2Zn.

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

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

CaO + 3S = CaC 2 + CO.

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

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

3S + 4HNO 3 = 3SO 2 + 4NO + 2H 2 O.

Any form of carbon is resistant to alkalis!

1.4. Application of carbon

Diamonds are used for processing various hard materials, for cutting, grinding, drilling and engraving glass, and for drilling rocks. Diamonds, after being polished and cut, are transformed into diamonds used as jewelry.

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

A linear carbon polymer, carbyne, is attracting the attention of scientists as a promising material for the manufacture of semiconductors that can operate at high temperatures and ultra-strong fibers.

Charcoal is used in the metallurgical industry and 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 strength, which is why car tires are black. Soot is also used as a component of printing inks, ink, and shoe polish.

Activated carbons are used to purify, extract and separate various substances. Activated carbons are used as fillers in gas masks and as a sorbent in medicine.

Chapter II . Inorganic carbon compounds

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

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

If air containing 0.1% CO is inhaled, a person may suddenly lose consciousness and die. Carbon monoxide is formed during incomplete combustion of fuel, which is why premature closing of chimneys is so dangerous.

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

2CO + O 2 = 2CO 2.

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

Fe 2 O 3 + ZSO = 2Fe + ZSO 2.

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

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

At a pressure of approximately 60 atm, carbon dioxide turns into a colorless liquid. When liquid carbon dioxide evaporates, part of it turns into a solid snow-like mass, which is pressed in industry - this is the “dry ice” you know, which is used for storing 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, it causes cloudiness in lime water), with basic oxides and water.

It does not burn and does not support combustion and is therefore used to extinguish fires. However, magnesium continues to burn in carbon dioxide, forming an oxide and releasing carbon in the form of soot.

CO 2 + 2Mg = 2MgO + C.

Carbon dioxide is produced by reacting 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 = CaCl 2 + H 2 0 + C0 2.

In industry, carbon dioxide is produced by burning limestone:

CaCO 3 = CaO + C0 2.

In addition to the application already mentioned, carbon dioxide is also used to make fizzy drinks and to produce soda.

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

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

When there is an excess of carbon dioxide in the presence of water, carbonates can turn into bicarbonates. So, if carbon dioxide is passed through lime water, it will first become cloudy due to the precipitation of water-insoluble calcium carbonate, but with further passage of carbon dioxide, the cloudiness disappears as a result of the formation of soluble calcium bicarbonate:

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

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

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

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

Other calcium and magnesium salts, in particular chlorides and sulfates, give water permanent hardness. Constant hardness of water cannot be eliminated by boiling. You have to use another carbonate - soda.

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

CaCl 2 + Na 2 CO 3 = CaCO 3 ↓ + 2NaCl.

Baking soda can also be used to eliminate temporary water hardness.

Carbonates and bicarbonates can be detected using acid solutions: when exposed to acids, a characteristic “boiling” is observed due to the release of carbon dioxide.

This reaction is a qualitative reaction to carbonic acid salts.

Conclusion

All life on earth is based on carbon. Each molecule of a living organism is built on the basis of a carbon skeleton. Carbon atoms 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, we can trace the dynamics of life on our planet.

The main carbon reserves on Earth are in the form of carbon dioxide contained in the atmosphere and dissolved in the World Ocean, that is, carbon dioxide (CO 2). Let us first consider the carbon dioxide molecules in the atmosphere. Plants absorb these molecules, then, through the process of photosynthesis, the carbon atom is converted into a variety of organic compounds and thus incorporated into the plant structure. There are several options below:

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 destroy it into simple inorganic compounds), such as fungi and termites. Eventually the carbon will return to the atmosphere as CO2;

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

3. plants may die and end up underground. Then they will eventually turn into fossil fuels such as coal.

In the case of dissolving the original CO 2 molecule in sea water, several options are also possible:

Carbon dioxide can simply return to the atmosphere (this type of mutual gas exchange between the 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 on the bottom of the world's oceans and eventually turn into limestone or from the sediments will again pass into sea water.

If carbon is incorporated into sediments 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 released into the atmosphere during volcanic eruptions and other geothermal processes. In modern conditions, these natural factors are also supplemented by 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 involved in the study of the atmosphere.

Part of this search is to determine the amount of CO 2 found in plant tissue (for example, in a newly planted forest) - scientists call this a carbon sink. As governments try to reach an international agreement to limit CO 2 emissions, the issue of balancing carbon sinks and emissions in individual countries has become a major bone of contention for industrialized countries. However, scientists doubt that the accumulation of carbon dioxide in the atmosphere can be stopped by forest planting alone.

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

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