Carbon

In the free state, carbon forms 3 allotropic modifications: diamond, graphite and artificially obtained carbine.

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 ).

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 various forms amorphous carbon, the most important of which are coke, brown and black coals, soot, activated (active) carbon.

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.

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.

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, reduces the anions NO 3 - and SO 4 2- 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

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. Carbides ion type- 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 + 2H 2 → CH 4

The reaction is very reversible and has no practical significance.

Carbon monoxide(II)– CO

(carbon monoxide , carbon monoxide, carbon monoxide)

Physical properties: colorless poisonous gas, tasteless and odorless, burns with a bluish flame, lighter than air, poorly soluble in water. The concentration of carbon monoxide in the air of 12.5-74% is explosive.

Receipt:

1) In industry

C + O 2 \u003d CO 2 + 402 kJ

CO 2 + C \u003d 2CO - 175 kJ

In gas generators, water vapor is sometimes blown through hot coal:

C + H 2 O \u003d CO + H 2 - Q,

a mixture of CO + H 2 - called synthesis - gas.

2) In the laboratory- thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):

HCOOH t˚C, H2SO4 → H2O + CO

H 2 C 2 O 4 t˚C,H2SO4 → CO + CO 2 + H 2 O

Chemical properties:

Under ordinary conditions, CO is inert; when heated - reducing agent;

CO - non-salt-forming oxide.

1) with oxygen

2C +2 O + O 2 t ˚ C → 2C +4 O 2

2) with metal oxides CO + Me x O y \u003d CO 2 + Me

C +2 O + CuO t ˚ C → Сu + C +4 O 2

3) with chlorine (in the light)

CO + Cl 2 light → COCl 2 (phosgene is a poisonous gas)

4)* reacts with alkali melts (under pressure)

CO + NaOH P → HCOONa (sodium formate)

The effect of carbon monoxide on living organisms:

Carbon monoxide is dangerous because it makes it impossible for the blood to carry oxygen to vital organs like the heart and brain. Carbon monoxide combines with hemoglobin, which carries oxygen to the cells of the body, as a result of which it becomes unsuitable for transporting oxygen. Depending on the amount inhaled, carbon monoxide impairs coordination, exacerbates cardiovascular disease and causes fatigue, headache, weakness, The effect of carbon monoxide on human health depends on its concentration and time of exposure to the body. A concentration of carbon monoxide in the air above 0.1% leads to death within one hour, and a concentration of more than 1.2% within three minutes.

Applications of carbon monoxide:

Carbon monoxide is mainly used as a combustible gas mixed with nitrogen, the so-called generator or air gas, or water gas mixed with hydrogen. In metallurgy for the recovery of metals from their ores. To obtain high purity metals by decomposition of carbonyls.

Carbon monoxide (IV) CO2 - carbon dioxide

Physical properties: Carbon dioxide, colorless, odorless, solubility in water - 0.9V CO 2 dissolves in 1V H 2 O (under normal conditions); heavier than air; t°pl.= -78.5°C (solid CO 2 is called "dry ice"); does not support combustion.

Molecule structure:

Carbon dioxide has the following electronic and structural formulas -

3. Combustion of carbonaceous substances:

CH 4 + 2O 2 → 2H2O+CO2

4. With slow oxidation in biochemical processes(breathing, putrefaction, fermentation)

Chemical properties:

• 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 compounds:

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

Carbon has the unique ability to form polymer chains of unlimited length, thereby giving rise to a huge class of compounds, which are studied by a separate branch of chemistry - organic chemistry. organic compounds carbon are the basis of earthly life, therefore, about the importance of carbon as chemical element, it makes no sense to say - he 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.

Such "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. Crystal cell diamond.

Diamond Properties:

• colorless crystalline substance;
• most solid 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, chemical bonds between neighboring carbon atoms are formed by three valence electrons of each atom (shown in blue in the figure below), while the fourth electron (shown in red) of each carbon atom, 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 give electrons and accept them, manifesting in some compounds restorative properties, and in others - oxidizing.

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 the widest 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, a polymerization catalyst etc.).

Carbon monoxide (IV), carbonic acid and their salts

The complex purpose of the module: know the methods of obtaining oxide and hydroxide of carbon (IV); describe them physical properties; know the characteristics of acid-base properties; characterize redox properties.

All elements of the carbon subgroup form oxides with the general formula EO 2 . CO 2 and SiO 2 exhibit acidic properties, GeO 2, SnO 2, PbO 2 exhibit amphoteric properties with a predominance of acidic, and in the subgroup from top to bottom, acidic properties weaken.

The oxidation state (+4) for carbon and silicon is very stable, so the oxidizing properties of the compound are exhibited with great difficulty. In the germanium subgroup, the oxidizing properties of compounds (+4) are enhanced due to destabilization the highest degree oxidation.

Carbon monoxide (IV), carbonic acid and their salts

Carbon dioxide CO 2 (carbon dioxide) - under normal conditions, it is a colorless and odorless gas, slightly sour in taste, about 1.5 times heavier than air, soluble in water, liquefies quite easily - at room temperature it is fashionable to turn it into a liquid under a pressure of about 60 10 5 Pa. When cooled to? 56.2 ° C, liquid carbon dioxide solidifies and turns into a snowy mass.

In all states of aggregation consists of non-polar linear molecules. The chemical structure of CO 2 is determined by the sp hybridization of the central carbon atom and the formation of additional p rr-bonds: O = C = O

Some of the CO 2 dissolved in the will interacts with it by the formation of carbonic acid

CO 2 + H 2 O - CO 2 H 2 O - H 2 CO 3.

Carbon dioxide is very easily absorbed by alkali solutions with the formation of carbonates and bicarbonates:

CO 2 + 2NaOH \u003d Na 2 CO 3 + H 2 O;

CO 2 + NaOH \u003d NaHCO 3.

CO 2 molecules are very stable thermally, decomposition begins only at a temperature of 2000ºC. Therefore, carbon dioxide does not burn and does not support the combustion of conventional fuels. But in its atmosphere some are burning simple substances, whose atoms show a high affinity for oxygen, for example, magnesium, when heated, ignites in an atmosphere of CO 2.

Carbonic acid and its salts

Carbonic acid H 2 CO 3 - the connection is fragile, exists only in aqueous solutions. Most of the carbon dioxide dissolved in water is in the form of hydrated CO 2 molecules, the smaller part forms carbonic acid.

Aqueous solutions in equilibrium with atmospheric CO 2 are acidic: = 0.04 M and pH? four.

Carbonic acid is dibasic, belongs to weak electrolytes, dissociates in steps (K 1 \u003d 4.4 10 -7; K 2 \u003d 4.8 10 -11). When CO 2 is dissolved in water, the following dynamic equilibrium is established:

H 2 O + CO 2 - CO 2 H 2 O - H 2 CO 3 - H + + HCO 3?

When heated aqueous solution carbon dioxide, the solubility of the gas decreases, CO 2 is released from the solution, and the equilibrium shifts to the left.

Salts of carbonic acid

Being dibasic, carbonic acid forms two series of salts: medium salts (carbonates) and acidic (hydrocarbonates). Most salts of carbonic acid are colorless. Of the carbonates, only alkali metal and ammonium salts are soluble in water.

In water, carbonates undergo hydrolysis, and therefore their solutions have an alkaline reaction:

Na 2 CO 3 + H 2 O - NaHCO 3 + NaOH.

Further hydrolysis with the formation of carbonic acid practically does not occur under normal conditions.

The dissolution of bicarbonates in water is also accompanied by hydrolysis, but to a much lesser extent, and the medium is slightly alkaline (pH? 8).

Ammonium carbonate (NH 4) 2 CO 3 is highly volatile at elevated and even normal temperatures, especially in the presence of water vapor, which causes strong hydrolysis

Strong acids and even weak acetic acid displace carbonic acid from carbonates:

K 2 CO 3 + H 2 SO 4 \u003d K 2 SO 4 + H 2 O + CO 2 ^.

Unlike most carbonates, all hydrocarbons are soluble in water. They are less stable than carbonates of the same metals and easily decompose when heated, turning into the corresponding carbonates:

2KHCO 3 \u003d K 2 CO 3 + H 2 O + CO 2 ^;

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

strong acids bicarbonates decompose, like carbonates:

KHCO 3 + H 2 SO 4 \u003d KHSO 4 + H 2 O + CO 2

From salts of carbonic acid highest value have: sodium carbonate (soda), potassium carbonate (potash), calcium carbonate (chalk, marble, limestone), sodium bicarbonate (baking soda) and basic copper carbonate (CuOH) 2 CO 3 (malachite).

The basic salts of carbonic acid are practically insoluble in water and easily decompose when heated:

(CuOH) 2 CO 3 \u003d 2CuO + CO 2 + H 2 O.

In general, the thermal stability of carbonates depends on the polarization properties of the ions that make up the carbonate. The greater the polarizing effect of the cation on the carbonate ion, the lower the decomposition temperature of the salt. If the cation can be easily deformed, then the carbonate ion itself will also have a polarizing effect on the cation, which will lead to a sharp decrease in the salt decomposition temperature.

Sodium and potassium carbonates melt without decomposition, while most of the remaining carbonates decompose into metal oxide and carbon dioxide when heated.

(IV) (CO 2, carbon dioxide, carbon dioxide) It is a colorless, tasteless, odorless gas that is heavier than air and soluble in water.

Under normal conditions, solid carbon dioxide passes immediately into a gaseous state, bypassing the liquid state.

With a large amount of carbon monoxide, people begin to suffocate. Concentrations of more than 3% lead to rapid breathing, and more than 10% there is loss of consciousness and death.

Chemical properties of carbon monoxide.

carbon monoxide - it is carbonic anhydride H 2 CO 3.

When carbon monoxide is passed through calcium hydroxide (lime water), a white precipitate is observed:

Ca(Oh) 2 + CO 2 = CaCO 3 ↓ + H 2 O

If carbon dioxide is taken in excess, then the formation of hydrocarbonates is observed, which dissolve in water:

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

which then decompose when heated.

2KNCO 3 \u003d K 2 CO 3 + H 2 O + CO 2

The use of carbon monoxide.

Carbon dioxide is used in various industries. In chemical production - as a refrigerant.

AT Food Industry use it as a preservative E290. Although he was assigned "conditionally safe", in fact it is not. Doctors have proven that frequent eating of E290 leads to the accumulation of a toxic poisonous compound. Therefore, you need to carefully read the labels on the products.