1. In all organic compounds, the carbon atom has a valence of 4.

2. Carbon is capable of forming simple and very complex molecules (high molecular weight compounds: proteins, rubbers, plastics).

3. Carbon atoms connect not only with other atoms, but also with each other, forming various carbon - carbon chains - straight, branched, closed:

4. Carbon compounds are characterized by the phenomenon of isomerism, i.e. when substances have the same qualitative and quantitative composition, but different chemical structures, and therefore different properties. For example: the empirical formula C 2 H 6 O corresponds to two different structures of substances:

ethyl alcohol, dimethyl ether,

liquid, t 0 boil. = +78 0 C gas, t 0 boil. = -23.7 0 C

Therefore, ethyl alcohol and dimethyl ether are isomers.

5. Aqueous solutions of most organic substances are non-electrolytes; their molecules do not break down into ions.

Isomerism.

In 1823 the phenomenon was discovered isomerism– the existence of substances with the same molecular composition, but having different properties. What is the reason for the difference between isomers? Since their composition is the same, the reason can only be sought in the different order of connection of atoms in the molecule.

Even before the creation of the theory of chemical structure A.M. Butlerov predicted that for butane C 4 H 10, which has a linear structure CH 3 - CH 2 - CH 2 - CH 3 t 0 (boiling point -0.5 0 C), the existence of another substance with the same molecular formula, but with a different sequence of joining carbon atoms in a molecule:

isobutane

t 0 kip. – 11.7 0 C

So, isomers- these are substances that have the same molecular formula, but different chemical structures, and therefore different properties. There are two main types of isomerism − structural And spatial.

Structural are called isomers that have different orders of atoms in the molecule. There are three types of it:

Carbon skeleton isomerism:

S – S – S – S – S S – S – S – S

Multiple bond isomerism:

C = C – C – C C – C = C – C

- interclass isomerism:

propionic acid

Spatial isomerism. Spatial isomers have identical substituents on each carbon atom. But they differ in their relative location in space. There are two types of this isomerism: geometric and optical. Geometric isomerism is characteristic of compounds that have a planar molecular structure (alkenes, cycloalkanes, alkadienes, etc.). If identical substituents on carbon atoms, for example, in a double bond, are located on one side of the plane of the molecule, then this will be a cis isomer, on opposite sides - a trans isomer:

Optical isomerism– characteristic of compounds having an asymmetric carbon atom, which is bonded to four different substituents. Optical isomers are mirror images of each other. For example:

Electronic structure of the atom.

The structure of the atom is studied in inorganic chemistry and physics. It is known that an atom determines the properties of a chemical element. An atom consists of a positively charged nucleus, in which all its mass is concentrated, and negatively charged electrons surrounding the nucleus.

Since during chemical reactions the nuclei of the reacting atoms do not change, the physical and chemical properties of atoms depend on the structure of the electronic shells of the atoms. Electrons can move from one atom to another, they can combine, etc. Therefore, we will consider in detail the issue of the distribution of electrons in an atom on the basis of the quantum theory of atomic structure. According to this theory, an electron simultaneously has the properties of a particle (mass, charge) and a wave function. For moving electrons, it is impossible to determine the exact location. They are located in space near the atomic nucleus. Can be determined probability location of an electron in different parts of space. The electron is, as it were, “smeared” in this space in the form of a cloud (Figure 1), the density of which decreases.

Picture 1.

The region of space in which the probability of finding an electron is maximum (≈ 95%) is called orbital.

According to quantum mechanics, the state of an electron in an atom is determined by four quantum numbers: main (n), orbital (l), magnetic(m) And spin(s).

Principal quantum number n – characterizes the energy of the electron, the distance of the orbital from the nucleus, i.e. energy level and takes on the values ​​1, 2, 3, etc. or K, L, M, N, etc. The value n = 1 corresponds to the lowest energy. With increase n the electron energy increases. The maximum number of electrons located at an energy level is determined by the formula: N=2n2, where n is the level number, therefore, with:

n = 1 N = 2 n = 3 N = 18

n = 2 N = 8 n = 4 N = 32, etc.

Within energy levels, electrons are arranged into sublevels (or subshells). Their number corresponds to the number of the energy level, but they are characterized orbital quantum number l, which determines the shape of the orbital. It takes values ​​from 0 to n-1. At

n=1 l= 0 n = 2 l= 0, 1 n = 3 l= 0, 1, 2 n = 4 l= 0, 1, 2, 3

The maximum number of electrons at a sublevel is determined by the formula: 2(2l + 1). Letter designations are used for sublevels:

l = 1, 2, 3, 4

Therefore, if n = 1, l= 0, sublevel s.

n = 2, l= 0, 1, sublevel s, p.

Maximum number of electrons in sublevels:

N s = 2 N d = 10

N p = 6 N f = 14, etc.

There cannot be more than these numbers of electrons in sublevels. The shape of the electron cloud is determined by the value l. At
l= 0 (s-orbital) the electron cloud has a spherical shape and has no spatial direction.

Figure 2.

At l = 1 (p-orbital), the electron cloud has a dumbbell or figure-of-eight shape:

Figure 3.

Magnetic quantum number m characterizes
arrangement of orbitals in space. It can take the values ​​of any numbers from –l to +l, including 0. The number of possible values ​​of the magnetic quantum number for a given value l equals (2 l+ 1). For example:

l= 0 (s-orbital) m = 0, i.e. The s orbital has only one position in space.

l= 1 (p-orbital) m = -1, 0, +1 (3 values).

l= 2 (d-orbital) m = -2, -1, 0, +1, +2, etc.

p and d orbitals have 3 and 5 states, respectively.

The p orbitals are elongated along the coordinate axes and are designated p x, p y, p z orbitals.

Spin quantum number s- characterizes the rotation of an electron around its own axis clockwise and counterclockwise. It can only have two values ​​+1/2 and -1/2. The structure of the electron shell of an atom is depicted by an electronic formula that shows the distribution of electrons across energy levels and sublevels. In these formulas, energy levels are designated by the numbers 1, 2, 3, 4..., sublevels by the letters s, p, d, f. The number of electrons in a sublevel is written as a power. For example: the maximum number of electrons on s 2, p 6, d 10, f 14.

Electronic formulas are often depicted graphically, which show the distribution of electrons not only across levels and sublevels, but also across orbitals, indicated by a rectangle. Sublevels are divided into quantum cells.

Free quantum cell

Cell with unpaired electron

Cell with paired electrons

There is one quantum cell at the s-sublevel.

There are 3 quantum cells at the p-sublevel.

There are 5 quantum cells at the d-sublevel.

There are 7 quantum cells at the f-sublevel.

The distribution of electrons in atoms is determined Pauli principle And Hund's rule. According to the Pauli principle: An atom cannot have electrons with the same values ​​of all four quantum numbers. In accordance with the Pauli principle, an energy cell can have one, or at most two, electrons with opposite spins. Filling of cells occurs according to Hund's principle, according to which electrons are first located one at a time in each individual cell, then, when all the cells of a given sublevel are occupied, pairing of electrons begins.

The sequence of filling atomic electron orbitals is determined by the rules of V. Klechkovsky, depending on the sum (n + l):

First, those sublevels for which this amount is smaller are filled;

for the same values ​​of the sum (n + l) the sublevel with the lower value is filled first n.

For example:

a) consider filling sublevels 3d and 4s. Let us determine the sum (n + l):

y 3d (n + l) = 3 + 2 = 5, y 4s (n + l) = 4 + 0 = 4, therefore the 4s sublevel is filled first, and then the 3d sublevel.

b) for sublevels 3d, 4p, 5s the sum of values ​​(n + l) = 5. In accordance with Klechkovsky’s rule, filling begins with a smaller value of n, i.e. 3d → 4p → 5s. Filling of energy levels and sublevels of atoms with electrons occurs in the following sequence: valence n = 2 n = 1

Be has a paired pair of electrons in the 2s 2 sublevel. To supply energy from outside, this pair of electrons can be separated and the atom can be made valence. In this case, an electron transitions from one sublevel to another sublevel. This process is called electron excitation. The graphical formula for Be in an excited state will look like:

and valency is 2.

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 and 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 of this, 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.

Carbon

CARBON-A; m. Chemical element (C), the most important component of all organic substances in nature. Carbon atoms. Carbon content percentage. Without carbon, life is impossible.

◁ Carbon, oh, oh. Y atoms. Carbon, oh, oh. Containing carbon. Uh steel.

carbon

(lat. Carboneum), chemical element of group IV of the periodic table. The main crystal 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 atmospheric carbon dioxide (6 10 11 t) and hydrosphere (10 14 t). The main carbon-containing minerals are carbonates. Carbon has the unique ability to form a huge number of compounds, which can consist 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 (average carbon content - 18%). Carbon is widespread in space; on the Sun it ranks 4th after hydrogen, helium and oxygen.

CARBON

CARBON (Latin Carboneum, from carbo - coal), C (read “ce”), a chemical element with atomic number 6, atomic weight 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 (b - emitter, half-life 5730 years) is always present in negligible quantities. It is constantly formed in the lower layers of the atmosphere under the action of neutrons from cosmic radiation on the nitrogen isotope 14 N:
14 7 N + 1 0 n = 14 6 C + 1 1 H. Carbon is located in group IVA, in the second period of the periodic table. Configuration of the outer electron layer of an atom in ground state 2 2 s 2 p
. The most important oxidation states are +2 +4, –4, valences IV and II. (The radius of a 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. Electronegativity according to Pauling cm. 2,5.
PAULING Linus)
Historical reference (The radius of a 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. Electronegativity according to Pauling Carbon has been known since ancient times. Charcoal was used to recover metals from ores, diamond DIAMOND (mineral)) (The radius of a 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. Electronegativity according to Pauling- like a precious stone. In 1789, the French chemist A. L. Lavoisier LAVOISIER Antoine Laurent)
made a conclusion about the elemental nature of carbon. (The radius of a 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. Electronegativity according to Pauling Synthetic diamonds were first obtained in 1953 by Swedish researchers, but they did not manage to publish the results. In December 1954, artificial diamonds were obtained, and at the beginning of 1955, employees of the General Electric company published the results.
GENERAL ELECTRIC) (The radius of a 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. Electronegativity according to Pauling In the USSR, artificial diamonds were first obtained in 1960 by a group of scientists led by V. N. Bakul and L. F. Vereshchagin .
VERESHCHAGIN Leonid Fedorovich)
In 1961, a group of Soviet chemists under the leadership of V.V. Korshak synthesized a linear modification of carbon - carbyne. Soon after, carbine was discovered in the Ries meteorite crater (Germany). In 1969, in the USSR, whisker-like diamond crystals were synthesized at normal pressure, possessing high strength and practically free of defects. (The radius of a 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. Electronegativity according to Pauling In 1985, Croteau CUTE Harold) (The radius of a 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. Electronegativity according to Pauling discovered a new form of carbon - fullerenes FULLERENES)
C 60 and C 70 in the mass spectrum of graphite evaporated during laser irradiation. Lonsdaleite was obtained at high pressures.
Content in the earth's crust is 0.48% by weight. Accumulates in the biosphere: in living matter 18% coal, in wood 50%, peat 62%, natural combustible gases 75%, oil shale 78%, hard and brown coal 80%, oil 85%, anthracite 96%. A significant part of the coal of 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 weight) is a permanent component of atmospheric air. Carbon dioxide is always present in dissolved form in the water of rivers, lakes and seas.
Substances containing carbon have been discovered in the atmosphere of stars, planets and meteorites.
Receipt
Since ancient times, coal has been produced by incomplete combustion of wood. In the 19th century, charcoal was replaced by bituminous coal (coke) in metallurgy.
Currently, cracking is used for industrial production of pure carbon. (The radius of a 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. Electronegativity according to Pauling CRACKING) natural gas methane (The radius of a 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. Electronegativity according to Pauling METHANE) CH 4:
CH 4 = C + 2H 2
Charcoal for medicinal purposes is prepared by burning coconut shells. For laboratory needs, pure coal that does not contain non-combustible 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 three-dimensional structures, layers, chains, and cycles. Four allotropic modifications of carbon are known: diamond, graphite, carbyne and fullerite. Charcoal consists of tiny crystals with a disordered graphite structure. Its density is 1.8-2.1 g/cm3. Soot is highly ground graphite.
Diamond is a mineral with a cubic face-centered lattice. The C atoms in diamond are located 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 distances between the atoms in the tetrahedron are 0.154 nm. There is no electronic conductivity, the band gap is 5.7 eV. Of all simple substances, diamond has the maximum number of atoms per unit volume. Its density is 3.51 g/cm 3. . Hardness on the Mohs mineralogical scale (The radius of a 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. Electronegativity according to Pauling MOHS SCALE) taken as 10. A diamond can only be scratched by another diamond; but it is fragile and upon impact breaks into pieces of irregular shape. Thermodynamically stable only at high pressures. However, at 1800 °C the transformation of diamond into graphite occurs quickly. 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 over a wide range of temperatures and pressures. 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 located in adjacent layers; the position of the layers is repeated every other one, and each layer is shifted relative to the other in the horizontal direction by 0.1418 nm. Inside the layer, the bonds between atoms are covalent, formed sp 2 -hybrid orbitals. The connections between the layers are carried out by weak van der Waals (The radius of a 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. Electronegativity according to Pauling INTERMOLECULAR INTERACTION) forces, so graphite is easily exfoliated. This state is stabilized by the fourth delocalized p-bond. Graphite has good electrical conductivity. Graphite density is 2.1-2.5 kg/dm3.
In all allotropic modifications, under normal conditions, carbon is chemically inactive. It enters into chemical reactions only when heated. In this case, the chemical activity of carbon decreases in the series soot-charcoal-graphite-diamond. Soot in air ignites when heated to 300°C, diamond - at 850-1000°C. During combustion, carbon dioxide CO 2 and CO are formed. By heating CO 2 with coal, carbon monoxide (II) CO is also obtained:
CO 2 + C = 2CO
C + H 2 O (superheated steam) = CO + H 2
Carbon monoxide C 2 O 3 was synthesized.
CO 2 is an acidic oxide; it is associated with weak, unstable carbonic acid H 2 CO 3, which exists only in highly dilute cold aqueous solutions. Salts of carbonic acid - carbonates (The radius of a 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. Electronegativity according to Pauling CARBONATES)(K 2 CO 3, CaCO 3) and bicarbonates (The radius of a 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. Electronegativity according to Pauling HYDROCARBONATES)(NaHCO 3, Ca(HCO 3) 2).
With hydrogen (The radius of a 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. Electronegativity according to Pauling HYDROGEN) graphite and charcoal react at temperatures above 1200°C to form a mixture of hydrocarbons. Reacting with fluorine at 900°C, it forms a mixture of fluorocarbon compounds. By passing an electric discharge between carbon electrodes in a nitrogen atmosphere, cyanogen gas (CN) 2 is obtained; If hydrogen is present in the gas mixture, hydrocyanic acid HCN is formed. At very high temperatures, graphite reacts with sulfur, (The radius of a 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. Electronegativity according to Pauling SULFUR) silicon, boron, forming carbides - CS 2, SiC, B 4 C.
Carbides are produced 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 easily decomposed by water into metal hydroxide and the corresponding hydrocarbon:
Al 4 C 3 + 12H 2 O = 4Al(OH) 3 + 3CH 4
With transition metals, carbon forms metal-like chemically stable 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 = Fe + CO,
2CuO+ C = 2Cu+ CO 2
When heated, it reduces sulfur(VI) to sulfur(IV) from concentrated sulfuric acid:
2H 2 SO 4 + C = CO 2 + 2SO 2 + 2H 2 O
At 3500°C and normal pressure, carbon sublimates.
Application
Over 90% of all primary sources of energy consumed in the world come from fossil fuels. 10% of the extracted fuel is used as raw material for basic organic and petrochemical synthesis to produce plastics.
Physiological action
Carbon is the most important biogenic element; it is a structural unit of organic compounds involved in the construction of organisms and ensuring their vital functions (biopolymers, vitamins, hormones, mediators and others). The carbon content in living organisms on a dry matter basis is 34.5-40% for aquatic plants and animals, 45.4-46.5% for terrestrial plants and animals, and 54% for bacteria. During the life of organisms, oxidative decomposition of organic compounds occurs with the release of CO 2 into the external environment. Carbon dioxide (The radius of a 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. Electronegativity according to Pauling CARBON DIOXIDE), dissolved in biological fluids and natural waters, participates in maintaining the optimal acidity of the environment for life. Carbon in CaCO 3 forms the exoskeleton of many invertebrates and is found in corals and eggshells.
During various production processes, particles of coal, soot, graphite, and diamond enter the atmosphere and are found in it in the form of aerosols. MPC for carbon dust in work areas is 4.0 mg/m 3, for coal 10 mg/m 3.

encyclopedic Dictionary. 2009 .

Synonyms:

See what “carbon” is in other dictionaries:

Table of nuclides General information Name, symbol Carbon 14, 14C Alternative names radiocarbon, radiocarbon Neutrons 8 Protons 6 Properties of the nuclide 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 the Mendeleev periodic system, atomic number 6, atomic mass 12.011. The main crystal 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 table, atomic number 6, atomic mass 12.011; non-metal. The content in the earth's crust is 2.3×10 2% by mass. 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 table, atomic number 6, atomic mass 12.011; non-metal. The 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 (lat. Carboneum), at. And. 6, at. m. 12,011. It exists in several allotropic modifications (forms) (diamond, graphite and rarely carbine, chaoite and lonsdaleite in meteorite craters). Since 1961 / the mass of an atom of the 12C isotope has been 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

DEFINITION

Carbon- the sixth element of the Periodic Table. Designation - C from the Latin “carboneum”. Located in the second period, group IVA. Refers to non-metals. The nuclear charge is 6.

Carbon is found in nature both in a free state and in the form of numerous compounds. Free carbon occurs in the form of diamond and graphite. In addition to fossil coal, there are large accumulations of oil in the depths of the Earth. Carbonic acid salts, especially calcium carbonate, are found in huge quantities in the earth's crust. There is always carbon dioxide in the air. Finally, plant and animal organisms consist of substances in the formation of which carbon takes part. Thus, this element is one of the most common on Earth, although its total content in the earth’s crust is only about 0.1% (wt.).

Atomic and molecular mass of carbon

The relative molecular mass of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and the relative atomic mass of an element (A r) is how many times the average mass of atoms of a chemical element is greater than 1/12 mass of a carbon atom.

Since in the free state carbon exists in the form of monatomic C molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 12.0064.

Allotropy and allotropic modifications of carbon

In the free state, carbon exists in the form of diamond, which crystallizes in the cubic and hexagonal (lonsdaleite) system, and graphite, which belongs to the hexagonal system (Fig. 1). Forms of carbon such as charcoal, coke or soot have a disordered structure. There are also allotropic modifications obtained synthetically - these are carbyne and polycumulene - varieties of carbon built from linear chain polymers of the type -C= C- or = C = C=.

Rice. 1. Allotropic modifications of carbon.

Allotropic modifications of carbon are also known, having the following names: graphene, fullerene, nanotubes, nanofibers, astralen, glassy carbon, colossal nanotubes; amorphous carbon, carbon nanobuds and carbon nanofoam.

Carbon isotopes

In nature, carbon exists in the form of two stable isotopes 12 C (98.98%) and 13 C (1.07%). Their mass numbers are 12 and 13, respectively. The nucleus of an atom of the 12 C carbon isotope contains six protons and six neutrons, and the 13 C isotope contains the same number of protons and five neutrons.

There is one artificial (radioactive) isotope of carbon, 14 C, with a half-life of 5730 years.

Carbon ions

The outer energy level of the carbon atom has four electrons, which are valence electrons:

1s 2 2s 2 2p 2 .

As a result of chemical interaction, carbon can lose its valence electrons, i.e. be their donor, and turn into positively charged ions or accept electrons from another atom, i.e. be their acceptor and turn into negatively charged ions:

C 0 -2e → C 2+ ;

C 0 -4e → C 4+ ;

C 0 +4e → C 4- .

Molecule and carbon atom

In the free state, carbon exists in the form of monatomic molecules C. Here are some properties characterizing the carbon atom and molecule:

Carbon alloys

The most famous carbon alloys around the world are steel and cast iron. Steel is an alloy of iron and carbon, the carbon content of which does not exceed 2%. In cast iron (also an alloy of iron and carbon), the carbon content is higher - from 2 to 4%.

Examples of problem solving

EXAMPLE 1

Exercise	What volume of carbon monoxide (IV) will be released (n.s.) when burning 500 g of limestone containing 0.1 mass fraction of impurities.
Solution	Let us write the reaction equation for limestone firing: CaCO 3 = CaO + CO 2 -. Let's find a mass of pure limestone. To do this, we first determine its mass fraction without impurities: w clear (CaCO 3) = 1 - w impurity = 1 - 0.1 = 0.9. m clear (CaCO 3) = m (CaCO 3) × w clear (CaCO 3); m clear (CaCO 3) = 500 × 0.9 = 450 g. Let's calculate the amount of limestone substance: n(CaCO 3) = m clear (CaCO 3) / M(CaCO 3); n(CaCO 3) = 450 / 100 = 4.5 mol. According to the reaction equation n(CaCO 3) :n(CO 2) = 1:1, it means n(CaCO 3) = n(CO 2) = 4.5 mol. Then, the volume of carbon monoxide (IV) released will be equal to: V(CO 2) = n(CO 2) ×V m; V(CO 2) = 4.5 × 22.4 = 100.8 l.
Answer	100.8 l

EXAMPLE 2

Exercise	How much of a solution containing 0.05 parts by mass, or 5% hydrogen chloride, is required to neutralize 11.2 g of calcium carbonate?
Solution	Let us write the equation for the reaction of neutralization of calcium carbonate with hydrogen chloride: CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2 -. Let's find the amount of calcium carbonate: M(CaCO 3) = A r (Ca) + A r (C) + 3×A r (O); M(CaCO 3) = 40 + 12 + 3×16 = 52 + 48 = 100 g/mol. n(CaCO 3) = m (CaCO 3) / M(CaCO 3); n(CaCO 3) = 11.2 / 100 = 0.112 mol. According to the reaction equation n(CaCO 3) :n(HCl) = 1:2, which means n(HCl) = 2 ×n(CaCO 3) = 2 ×0.224 mol. Let us determine the mass of hydrogen chloride contained in the solution: M(HCl) = A r (H) + A r (Cl) = 1 + 35.5 = 36.5 g/mol. m(HCl) = n(HCl) × M(HCl) = 0.224 × 36.5 = 8.176 g. Let's calculate the mass of the hydrogen chloride solution: m solution (HCl) = m(HCl)× 100 / w(HCl); m solution (HCl) = 8.176 × 100 / 5 = 163.52 g.
Answer	163.52 g

Element characteristics

6 C 1s 2 2s 2 2p 2

Isotopes: 12 C (98.892%); 13 C (1.108%); 14 C (radioactive)

Clarke in the earth's crust is 0.48% by mass. Forms of location:

in free form (coal, diamonds);

in the composition of carbonates (CaCO 3, MgCO 3, etc.);

as part of fossil fuels (coal, oil, gas);

in the form of CO 2 - in the atmosphere (0.03% by volume);

in the World Ocean - in the form of HCO 3 - anions;

in the composition of living matter (-18% carbon).

The chemistry of carbon compounds is mainly organic chemistry. The following C-containing substances are studied in the course of inorganic chemistry: free carbon, oxides (CO and CO 2), carbonic acid, carbonates and bicarbonates.

Free carbon. Allotropy.

In the free state, carbon forms 3 allotropic modifications: diamond, graphite and artificially produced carbyne. These modifications of carbon differ in crystal chemical structure and physical characteristics.

Diamond

In a diamond crystal, each carbon atom is connected by strong covalent bonds to four others placed around it at equal distances.

All carbon atoms are in a state of sp 3 hybridization. The atomic crystal lattice of diamond has a tetrahedral structure.

Diamond is a colorless, transparent, highly refracting substance. It has the greatest hardness among all known substances. Diamond is brittle, refractory, and does not conduct heat or electricity well. The small distances between neighboring carbon atoms (0.154 nm) determine the rather high density of diamond (3.5 g/cm3).

Graphite

In the crystal lattice of graphite, each carbon atom is in a state of sp 2 hybridization and forms three strong covalent bonds with carbon atoms located in the same layer. Three electrons of each carbon atom participate in the formation of these bonds, and the fourth valence electrons form n-bonds and are relatively free (mobile). They determine the electrical and thermal conductivity of graphite.

The length of the covalent bond between neighboring carbon atoms in the same plane is 0.152 nm, and the distance between C atoms in different layers is 2.5 times greater, so the bonds between them are weak.

Graphite is an opaque, soft, greasy to the touch substance of gray-black color with a metallic sheen; conducts heat and electricity well.

Graphite has a lower density compared to diamond and easily splits into thin flakes.

The disordered structure of fine-crystalline graphite underlies the structure of various forms of amorphous carbon, the most important of which are coke, brown and black coals, soot, and activated carbon.

Carbin

This allotropic modification of carbon is obtained by catalytic oxidation (dehydropolycondensation) of acetylene. Carbyne is a chain polymer that comes in two forms:

С=С-С=С-... and...=С=С=С=

Carbyne has semiconducting properties.

Chemical properties of carbon

At ordinary temperatures, both modifications of carbon (diamond and graphite) are chemically inert. Fine-crystalline forms of graphite - coke, soot, activated carbon - are more reactive, but, as a rule, after they are preheated to a high temperature.

C - active reducing agent:

C + O 2 = CO 2 + 393.5 kJ (in excess O 2)

2C + O 2 = 2CO + 221 kJ (with a lack of O 2)

Coal combustion is one of the most important sources of energy.

2. Interaction with fluorine and sulfur.

C + 2F 2 = CF 4 carbon tetrafluoride

C + 2S = CS 2 carbon disulfide

3. Coke is one of the most important reducing agents used in industry. In metallurgy, it is used to obtain metals from oxides, for example:

ZS + Fe 2 O 3 = 2Fe + ZSO

C + ZnO = Zn + CO

4. When carbon interacts with oxides of alkali and alkaline earth metals, the reduced metal combines with carbon to form a carbide. For example: 3S + CaO = CaC 2 + CO calcium carbide

5. Coke is also used to produce silicon:

2C + SiO 2 = Si + 2СО

6. If there is an excess of coke, silicon carbide (carborundum) SiC is formed.

Production of “water gas” (gasification of solid fuel)

By passing water vapor through hot coal, a flammable mixture of CO and H 2, called water gas, is obtained:

C + H 2 O = CO + H 2

7. Reactions with oxidizing acids.

When heated, activated charcoal or charcoal reduces the NO 3 - and SO 4 2- anions from concentrated acids:

C + 4HNO 3 = CO 2 + 4NO 2 + 2H 2 O

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

8. Reactions with molten alkali metal nitrates

In KNO 3 and NaNO 3 melts, crushed coal burns intensely with the formation of a dazzling flame:

5C + 4KNO 3 = 2K 2 CO 3 + ZCO 2 + 2N 2

C - low-active oxidizing agent:

1. Formation of salt-like carbides with active metals.

A significant weakening of the non-metallic properties of carbon is expressed in the fact that its functions as an oxidizing agent are manifested to a much lesser extent than its reducing functions.

2. Only in reactions with active metals do carbon atoms transform into negatively charged ions C -4 and (C=C) 2-, forming salt-like carbides:

ZS + 4Al = Al 4 C 3 aluminum carbide

2C + Ca = CaC 2 calcium carbide

3. Ionic carbides are very unstable compounds; they easily decompose under the action of acids and water, which indicates the instability of negatively charged carbon anions:

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

CaC 2 + 2H 2 O = C 2 H 2 + Ca(OH) 2

4. Formation of covalent compounds with metals

In melts of mixtures of carbon with transition metals, carbides are formed predominantly with a covalent type of bond. Their molecules have a variable composition, and the substances as a whole are close to alloys. Such carbides are highly stable; they are chemically inert with respect to water, acids, alkalis and many other reagents.

5. Interaction with hydrogen

At high T and P, in the presence of a nickel catalyst, carbon combines with hydrogen:

C + 2НН 2 → СНН 4

The reaction is highly reversible and has no practical significance.