Element characteristic

6 C 1s 2 2s 2 2p 2

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

Clark in the earth's crust 0.48% by weight. Location forms:

in free form (coal, diamonds);

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

in the composition of fossil fuels (coal, oil, gas);

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

in the oceans - in the form of HCO 3 - anions;

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

The chemistry of carbon compounds is basically organic chemistry. In the course of inorganic chemistry, the following C-containing substances are studied: 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 obtained carbine. These modifications of carbon differ in crystal-chemical structure and physical characteristics.

Diamond

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

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 refractive substance. It has the highest hardness among all known substances. Diamond is brittle, refractory, poorly conducts heat and electricity. Small distances between adjacent carbon atoms (0.154 nm) determine the rather high density of diamond (3.5 g/cm 3 ).

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 atom, carbon, 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 adjacent 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 a gray-black color with a metallic sheen; conducts heat and electricity well. Graphite has a lower density than diamond and is easily split into thin flakes.

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

Carbine

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

C=C-C=C-... and...=C=C=C=

Carbin has semiconductor properties.

Chemical properties of carbon

At ordinary temperature, 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:

1. Interaction with oxygen

C + O 2 \u003d CO 2 + 393.5 kJ (in excess O 2)

2C + O 2 \u003d 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 \u003d CS 2 carbon disulfide

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

ZS + Fe 2 O 3 \u003d 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 carbide. For example: 3C + CaO \u003d CaC 2 + CO calcium carbide

5. Coke is also used to obtain silicon:

2C + SiO 2 \u003d Si + 2CO

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

Obtaining "water gas" (solid fuel gasification)

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

C + H 2 O \u003d CO + H 2

7. Reactions with oxidizing acids.

Activated or charcoal, when heated, restores NO 3 - and SO 4 2- anions from concentrated acids:

C + 4HNO 3 \u003d CO 2 + 4NO 2 + 2H 2 O

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

8. Reactions with molten alkali metal nitrates

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

5C + 4KNO 3 \u003d 2K 2 CO 3 + ZSO 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 the reducing functions.

2. Only in reactions with active metals, carbon atoms pass into negatively charged ions C -4 and (C \u003d C) 2-, forming salt-like carbides:

ZS + 4Al \u003d Al 4 C 3 aluminum carbide

2C + Ca \u003d CaC 2 calcium carbide

3. Ionic type 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 \u003d ZSN 4 + 4Al (OH) 3

CaC 2 + 2H 2 O \u003d 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 substances in general are close to alloys. Such carbides are highly resistant, 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 + 2HH 2 → CNN 4

The reaction is very reversible and has no practical significance.

• Designation - C (Carbon);
• Period - II;
• Group - 14 (IVa);
• Atomic mass - 12.011;
• Atomic number - 6;
• Radius of an atom = 77 pm;
• Covalent radius = 77 pm;
• The distribution of electrons - 1s 2 2s 2 2p 2;
• melting point = 3550°C;
• boiling point = 4827°C;
• Electronegativity (according to Pauling / according to Alpred and Rochov) = 2.55 / 2.50;
• Oxidation state: +4, +3, +2, +1, 0, -1, -2, -3, -4;
• Density (n.a.) \u003d 2.25 g / cm 3 (graphite);
• Molar volume = 5.3 cm 3 / mol.

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

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

Now consider carbon from the point of view of inorganic chemistry.

Rice. The structure of the carbon atom.

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

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

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

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

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

Carbon as a simple substance

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

• Diamond
• Graphite
• fullerene
• Carbine

Diamond

Rice. The crystal lattice of diamond.

Diamond Properties:

• colorless crystalline substance;
• the hardest substance in nature;
• has a strong refractive effect;
• poor conductor of heat and electricity.

Rice. Diamond tetrahedron.

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

Graphite

Rice. Graphite crystal lattice.

Graphite properties:

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

In graphite, carbon atoms form regular hexagons lying in the same plane, organized into infinite layers.

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

Rice. Distribution of orbitals of carbon atom in graphite.

fullerene

Rice. Fullerene crystal lattice.

Fullerene properties:

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

Carbine

Carbine properties:

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

Chemical properties of carbon

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

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

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

• when heated in air, it burns (with an excess of oxygen with the formation of carbon dioxide; with its lack - carbon monoxide (II)):
  C + O 2 \u003d CO 2;
  2C + O 2 \u003d 2CO.
• reacts at high temperatures with sulfur vapor, easily interacts with chlorine, fluorine:
  C+2S=CS2
  C + 2Cl 2 = CCl 4
  2F2+C=CF4
• when heated, it restores many metals and non-metals from oxides:
  C 0 + Cu +2 O \u003d Cu 0 + C +2 O;
  C 0 + C +4 O 2 \u003d 2C +2 O
• reacts with water at a temperature of 1000°C (gasification process) to form water gas:
  C + H 2 O \u003d CO + H 2;

Carbon exhibits oxidizing properties in reactions with metals and hydrogen:

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

Carbon is obtained by thermal decomposition of its compounds or by pyrolysis of methane (at high temperature):
CH 4 \u003d C + 2H 2.

Application of carbon

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

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

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

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

Modifications and properties of carbon

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

Chemical properties of carbon

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

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

carbon in nature

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

Application and use

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

Free carbon is a typical reducing agent. When oxidized with oxygen in excess air, it turns into carbon monoxide (IV):

with a deficiency - in carbon monoxide (II):

Both reactions are highly exothermic.

When carbon is heated in an atmosphere of carbon monoxide (IV), carbon monoxide is formed:

Carbon reduces many metals from their oxides:

This is how reactions with oxides of cadmium, copper, and lead proceed. When carbon interacts with oxides of alkaline earth metals, aluminum and some other metals, carbides are formed:

This is explained by the fact that active metals are stronger reducing agents than carbon, therefore, when heated, the resulting metals are oxidized by excess carbon:

Carbon monoxide (II).

With incomplete oxidation of carbon, carbon monoxide (II) CO is formed - carbon monoxide. It is poorly soluble in water. The formal oxidation state of carbon 2+ does not reflect the structure of the CO molecule.

In the CO molecule, in addition to the double bond formed by the sharing of carbon and oxygen electrons, there is an additional, third bond (shown by an arrow), formed by the donor-acceptor mechanism due to the lone pair of oxygen electrons

In this regard, the CO molecule is extremely strong. Carbon monoxide (II) is non-salt-forming and does not interact under normal conditions with water, acids and alkalis. At elevated temperatures, it is prone to addition and redox reactions. In air, CO burns with a blue flame:

It restores metals from their oxides:

Under the action of irradiation in direct sunlight or in the presence of catalysts, CO combines with forming phosgene - an extremely poisonous gas:

With many metals, CO forms volatile carbonyls:

The covalent bond in the nickel carbonyl molecule is formed by the donor-acceptor mechanism, with the electron density shifting from the carbon atom to the nickel atom. The increase in the negative charge on the metal atom is compensated by the participation of its d-electrons in the bond, so the oxidation state of the metal is 0. When heated, metal carbonyls decompose into metal and carbon monoxide (II), which is used to obtain high purity metals.

In nature, carbon monoxide (II) practically does not occur. It can be formed during the dehydration of formic acid (laboratory method of preparation):

Based on the last transformation, purely formally, CO can be considered an anhydride of formic acid. This is confirmed by the following reaction, which occurs when CO is passed into an alkali melt at high pressure:

Carbon monoxide (IV) and carbonic acid. Carbon monoxide (IV) is anhydride of carbonic acid and has all the properties of acidic oxides (see § 8).

When dissolved in water, carbonic acid is partially formed, while the following equilibrium exists in the solution.

CHEMICAL PROPERTIES OF CARBON

Carbon is inactive, in the cold it reacts only with fluorine; chemical activity is manifested at high temperatures.

Reminder! "Chemical properties"

Adsorption

The reverse process - the release of these absorbed substances - desorption.

Application of adsorption

Purification of impurities (in the production of sugar, etc.), for the protection of respiratory organs (gas masks), in medicine (tablets "Karbolen"), etc.

Application of carbon

Diamonds are widely used for cutting rocks and grinding especially hard materials. Jewelry is made from diamonds during cutting. Graphite is used to make inert electrodes and pencil leads. Mixed with technical oils as a lubricant. Melting crucibles are made from a mixture of graphite and clay. Graphite is used in the nuclear industry as a neutron absorber.

Coke is used in metallurgy as a reducing agent. Charcoal - in forges, to obtain gunpowder (75% KNO 3 + 13% C + 12% S), to absorb gases (adsorption), as well as in everyday life. Soot is used as a rubber filler, for the manufacture of black paints - printing ink and ink, as well as in dry galvanic cells. Glassy carbon is used for the manufacture of equipment for highly aggressive environments, as well as in aviation and astronautics.

Activated charcoal absorbs harmful substances from gases and liquids: they fill gas masks, purification systems, it is used in medicine for poisoning.

CHARCOAL

Charcoal- a microporous high-carbon product formed during the decomposition of wood without air access. It is used in the production of crystalline silicon, carbon disulfide, ferrous and non-ferrous metals, activated carbon, etc., as well as domestic fuel (specific heat of combustion 31.5-34 MJ/kg).

TASKS FOR REINFORCEMENT

No. 1. Complete the reaction equations, draw up an electronic balance, indicate the oxidizing agent and reducing agent for each reaction:

C + O 2 (ex) \u003d

C + O 2 (missing) \u003d

C + H 2 \u003d

C + Ca =

C + Al =