Carbon is the symbol for the chemical element. The structure of the carbon atom
It is called the basis of life. It is found in all organic compounds. Only he is able to form molecules from millions of atoms, such as DNA.
Did you recognize the hero? This carbon. The number of its compounds known to science is close to 10,000,000.
So much will not be typed in all the other elements taken together. Not surprisingly, one of the two branches of chemistry studies exclusively carbon compounds and takes place in the upper grades.
We offer to recall the school curriculum, as well as supplement it with new facts.
What is carbon
Firstly, element carbon- composite. In her new standard, the substance is in the 14th group.
In the outdated version of the system, carbon is in the main subgroup of the 4th group.
The designation of the element is the letter C. The serial number of the substance is 6, it belongs to the group of non-metals.
organic carbon adjacent in nature to the mineral. So, and the fullerene stone is the 6th element in its pure form.
Differences in appearance are due to several types of structure of the crystal lattice. The polar characteristics of mineral carbon also depend on it.
Graphite, for example, is soft, it is not in vain that it is added to writing pencils, but to everyone else on Earth. Therefore, it is logical to consider the properties of carbon itself, and not its modifications.
Properties of carbon
Let's start with the properties common to all nonmetals. They are electronegative, that is, they attract common electron pairs formed with other elements.
It turns out that carbon can reduce non-metal oxides to the state of metals.
However, the 6th element does this only when heated. Under normal conditions, the substance is chemically inert.
The outer electronic levels of non-metals have more electrons than metals.
That is why the atoms of the 6th element tend to complete a fraction of their own orbitals than to give their particles to someone.
For metals, with a minimum of electrons on the outer shells, it is easier to give away distant particles than to pull strangers onto themselves.
The main form of the 6th substance is the atom. In theory, it should be about carbon molecule. Most non-metals are made up of molecules.
However, carbon with and - exceptions, have an atomic structure. It is due to it that the compounds of elements are distinguished by high melting points.
Another distinctive property of many forms of carbon is . For the same one, it is maximum, equal to 10 points for.
Since the conversation turned to the forms of the 6th substance, we point out that the crystalline one is only one of them.
carbon atoms do not always line up in a crystal lattice. There is an amorphous variety.
Examples of this: - wood, coke, glassy carbon. These are compounds, but without an ordered structure.
If the substance is combined with others, gases can also be obtained. Crystalline carbon passes into them at a temperature of 3700 degrees.
Under normal conditions, an element is gaseous if it is, for example, carbon monoxide.
People call it carbon monoxide. However, the reaction of its formation is more active and faster, if, nevertheless, turn on the heat.
gaseous compounds carbon from oxygen several. There is also, for example, monoxide.
This gas is colorless and poisonous, moreover, under normal conditions. Such carbon monoxide has a triple bond in the molecule.
But, back to the pure element. Being quite inert in chemical terms, it, nevertheless, can interact not only with metals, but also with their oxides, and, as can be seen from the conversation about gases, with oxygen.
The reaction is also possible with hydrogen. Carbon will enter into interaction if one of the factors “plays” or all together: temperature, allotropic state, dispersion.
The latter refers to the ratio of the surface area of the particles of a substance to the volume they occupy.
Allotropy is the possibility of several forms of the same substance, that is, it means crystalline, amorphous, or gaseous carbon.
However, no matter how the factors coincide, the element does not react at all with acids and alkalis. Ignores carbon and almost all halogens.
Most often, the 6th substance binds to itself, forming those very large-scale molecules of hundreds and millions of atoms.
molecules formed, carbon react with even fewer elements and compounds.
Application of carbon
The application of the element and its derivatives is as extensive as their number. Carbon content There is more to a person's life than you might think.
Activated charcoal from a pharmacy is the 6th substance. in from - he is.
Graphite in pencils is also carbon, which is also needed in nuclear reactors and electrical machine contacts.
Methane fuel is also on the list. Carbon dioxide needed for production and can be dry ice, that is, a refrigerant.
Carbon dioxide serves as a preservative, filling vegetable stores, and is also needed to produce carbonates.
The latter are used in construction, for example,. And carbonate comes in handy in soap making and glass production.
Formula of carbon also corresponds to coke. He comes in handy metallurgists.
Coke serves as a reducing agent during the smelting of ore, the extraction of metals from it.
Even ordinary soot is carbon used as fertilizer and filler.
Ever wondered why car tires are colored? This is soot. It gives the rubber strength.
Soot is also included in shoe polish, printing ink, and mascara. The common name is not always used. Industrialists call soot technical carbon.
Mass of carbon begins to be used in the field of nanotechnology. Ultra-small transistors were made, as well as tubes that are 6-7 times stronger.
Here's a non-metal. By the way, scientists from . From carbon tubes and graphene, they created an airgel.
It is also a durable material. Sounds hefty. But, in fact, airgel is lighter than air.
IN iron carbon added to get what is called carbon steel. She's tougher than usual.
However, the mass fraction of the 6th element in should not exceed a couple, three percent. Otherwise, the properties of steel are declining.
The list is endless. But, where to take carbon indefinitely? Is it mined or synthesized? We will answer these questions in a separate chapter.
Carbon mining
carbon dioxide, methane, separately carbon, can be obtained chemically, that is, by intentional synthesis. However, this is not beneficial.
carbon gas and its solid modifications are easier and cheaper to mine along with coal.
Approximately 2 billion tons are extracted from the earth's bowels of this fossil annually. Enough to provide the world with carbon black.
As for, they are extracted from kimbirlite pipes. These are vertical geological bodies, fragments of rock cemented by lava.
It is in such that they meet. Therefore, scientists suggest that the mineral is formed at depths of thousands of kilometers, in the same place as magma.
Graphite deposits, on the contrary, are horizontal, located near the surface.
Therefore, the extraction of the mineral is quite simple and not expensive. About 500,000 tons of graphite are extracted from the subsoil annually.
To get activated carbon, you have to heat the coal and process it with a jet of water vapor.
Scientists have even figured out how to recreate the proteins in the human body. Their basis is also carbon. Nitrogen and hydrogen is an amino group adjacent to it.
You also need oxygen. That is, proteins are built on amino acids. She is not widely known, but for life is much more important than the rest.
Popular sulfuric, nitric, hydrochloric acids, for example, the body needs much less.
So carbon is something worth paying for. Let's find out how big the spread of prices for different goods from the 6th element is.
The price of carbon
For life, as it is easy to understand, carbon is priceless. As for other spheres of life, the price tag depends on the name of the product and its quality.
For, for example, they pay more if they do not contain third-party inclusions.
Airgel samples, so far, cost tens of dollars for a few square centimeters.
But, in the future, manufacturers promise to supply the material in rolls and ask for cheap.
Technical carbon, that is, soot, is sold at 5-7 rubles per kilo. For a ton, respectively, they give about 5000-7000 rubles.
However, the carbon tax introduced in most developed countries can drive up prices.
The carbon industry is considered the cause of the greenhouse effect. Companies are required to pay for emissions, in particular CO 2 .
It is the main greenhouse gas and, at the same time, an indicator of atmospheric pollution. This information is a fly in the ointment in a barrel of honey.
It allows you to understand that carbon, like everything else in the world, has a downside, and not just pluses.
(first electron)
The ability of carbon to form polymeric chains gives rise to a huge class of carbon-based compounds called organic, which are much more numerous than inorganic, and are the study of organic chemistry.
History
At the turn of the XVII-XVIII centuries. the phlogiston theory emerged, put forward by Johann Becher and Georg Stahl. This theory recognized the presence in each combustible body of a special elementary substance - a weightless fluid - phlogiston, which evaporates during combustion. Since only a small amount of ash remains when burning a large amount of coal, phlogistics believed that coal is almost pure phlogiston. This was the explanation, in particular, for the “phlogistic” effect of coal, its ability to restore metals from “lime” and ores. Later phlogistics, Réaumur, Bergman and others, had already begun to understand that coal was an elemental substance. However, for the first time, “pure coal” was recognized as such by Antoine Lavoisier, who studied the process of burning coal and other substances in air and oxygen. In the book of Guiton de Morveau, Lavoisier, Berthollet and Fourcroix, The Method of Chemical Nomenclature (1787), the name "carbon" (carbone) appeared instead of the French "pure coal" (charbone pur). Under the same name, carbon appears in the "Table of Simple Bodies" in Lavoisier's "Elementary Textbook of Chemistry".
origin of name
At the beginning of the 19th century, the term "coal" was sometimes used in Russian chemical literature (Sherer, 1807; Severgin, 1815); since 1824, Solovyov introduced the name "carbon". Carbon compounds have a part in their name carb(he)- from lat. carbō (gen. p. carbonis) "coal".
Physical Properties
Carbon exists in many allotropic modifications with very diverse physical properties. The variety of modifications is due to the ability of carbon to form chemical bonds of various types.
Isotopes of carbon
Natural carbon consists of two stable isotopes - 12 C (98.93%) and 13 C (1.07%) and one radioactive isotope 14 C (β-emitter, T ½ = 5730 years), concentrated in the atmosphere and the upper part of the earth bark. It is constantly formed in the lower layers of the stratosphere as a result of the action of cosmic radiation neutrons on nitrogen nuclei by the reaction: 14 N (n, p) 14 C, and also, since the mid-1950s, as a man-made product of nuclear power plants and as a result of testing hydrogen bombs .
Allotropic modifications of carbon
Crystalline carbon
amorphous carbon
- Fossil Coal: Anthracite and Fossil Coal.
- Coal coke, petroleum coke, etc.
In practice, as a rule, the amorphous forms listed above are chemical compounds with a high carbon content, and not a pure allotropic form of carbon.
cluster forms
Structure
Liquid carbon exists only at a certain external pressure. Triple points: graphite - liquid - vapor T= 4130K, R= 10.7 MPa and graphite - diamond - liquid T≈ 4000 K, R≈ 11 GPa. Equilibrium line graphite - liquid at the phase R, T-diagram has a positive slope, which, as it approaches the triple point of graphite - diamond - liquid, becomes negative, which is associated with the unique properties of carbon atoms to create carbon molecules consisting of a different number of atoms (from two to seven). The slope of the diamond-liquid equilibrium line, in the absence of direct experiments at very high temperatures (>4000–5000 K) and pressures (>10–20 GPa), was considered negative for many years. Direct experiments conducted by Japanese researchers and processing of the experimental data obtained, taking into account the anomalous high-temperature heat capacity of diamond, showed that the slope of the diamond-liquid equilibrium line is positive, i.e., diamond is heavier than its liquid (it will sink in the melt, and not float like ice in water) .
Ultrafine diamonds (nanodiamonds)
In the 1980s, it was discovered in the USSR that under conditions of dynamic loading of carbon-containing materials, diamond-like structures can form, which are called ultrafine diamonds (UDDs). Currently, the term "nanodiamonds" is increasingly used. The particle size in such materials is a few nanometers. The conditions for the formation of UDD can be realized during the detonation of explosives with a significant negative oxygen balance, for example, mixtures of TNT with RDX. Such conditions can also be realized when celestial bodies hit the Earth's surface in the presence of carbon-containing materials (organics, peat, coal, etc.). Thus, in the zone of the fall of the Tunguska meteorite, UDDs were found in the forest litter.
Carbine
A crystalline modification of carbon of a hexagonal syngony with a chain structure of molecules is called carbine. The chains are either polyene (−C≡C−) or polycumulene (=C=C=). Several forms of carbine are known, differing in the number of atoms in a unit cell, cell sizes and density (2.68-3.30 g/cm³). Carbin occurs in nature in the form of the mineral chaoite (white streaks and inclusions in graphite) and is obtained artificially - by oxidative dehydropolycondensation of acetylene, by the action of laser radiation on graphite, from hydrocarbons or CCl 4 in low-temperature plasma.
Carbine is a black fine-grained powder (density 1.9-2 g/cm³) with semiconductor properties. Obtained under artificial conditions from long chains of carbon atoms stacked parallel to each other.
Carbyne is a linear polymer of carbon. In a carbine molecule, carbon atoms are connected in chains alternately either by triple and single bonds (polyene structure), or permanently by double bonds (polycumulene structure). This substance was first obtained by Soviet chemists V. V. Korshak, A. M. Sladkov, V. I. Kasatochkin and Yu. P. Kudryavtsev in the early 1960s at the USSR Academy of Sciences. Carbin has semiconductor properties, and under the influence of light, its conductivity increases greatly. The first practical application is based on this property - in photovoltaic cells.
Fullerenes and carbon nanotubes
Carbon is also known in the form of cluster particles C 60 , C 70 , C 80 , C 90 , C 100 and the like (fullerenes), as well as graphenes, nanotubes and complex structures - astralenes.
Amorphous carbon (structure)
The structure of amorphous carbon is based on the disordered structure of single-crystal (always contains impurities) graphite. These are coke, brown and hard coals, carbon black, soot, activated carbon.
Graphene
Graphene is a two-dimensional allotropic modification of carbon, formed by a layer of carbon atoms one atom thick, connected by means of sp² bonds into a hexagonal two-dimensional crystal lattice.
Being in nature
It has been estimated that the Earth as a whole is composed of 730 ppm of carbon, with 2000 ppm in the core and 120 ppm in the mantle and crust. Since the mass of the Earth is 5.972⋅10 24 kg , this implies the presence of 4360 million gigatonnes of carbon.
Most carbon compounds, and above all hydrocarbons, have a pronounced character of covalent compounds. The strength of simple, double and triple bonds of C atoms among themselves, the ability to form stable chains and cycles from C atoms determine the existence of a huge number of carbon-containing compounds studied by organic chemistry. In nature, the mineral shungite is found, which contains both solid carbon (≈25%) and significant amounts of silicon oxide (≈35%). Chemical propertiesAt ordinary temperatures, carbon is chemically inert, at sufficiently high temperatures it combines with many elements, and exhibits strong reducing properties. The chemical activity of different forms of carbon decreases in the following order: amorphous carbon, graphite, diamond, in air they ignite at temperatures above 300-501 °C, 600-700 °C and 800-1000 °C, respectively. The oxidation state ranges from −4 to +4. Electron affinity 1.27 eV; the ionization energy during the successive transition from C 0 to C 4+ is 11.2604, 24.383, 47.871 and 64.19 eV, respectively. inorganic compoundsCarbon reacts with many elements. Compounds with non-metals have their own names - methane, tetrafluoromethane. The combustion products of carbon are CO and CO 2 (carbon monoxide and carbon dioxide, respectively). Also known is unstable carbon suboxide C 3 O 2 (melting point −111 ° C, boiling point 7 ° C) and some other oxides (for example, C 12 O 9, C 5 O 2, C 12 O 12). Graphite and amorphous carbon begin to react with hydrogen at a temperature of 1200 °C, with fluorine at 900 °C. Graphite forms inclusion compounds with halogens, alkali metals, and other substances. When an electric discharge is passed between carbon electrodes in a nitrogen atmosphere, cyanide is formed. At high temperatures, the interaction of carbon with a mixture of H 2 and N 2 gives |
Organic life on Earth is represented by carbon compounds. The element is part of the main components of cellular structures: proteins, carbohydrates and fats, and also forms the basis of the substance of heredity - deoxyribonucleic acid. In inorganic nature, carbon is one of the most common elements that form the earth's crust and atmosphere of the planet. Organic chemistry as a branch of chemical science is entirely devoted to the properties of the chemical element carbon and its compounds. Our article will consider the physicochemical characteristics of carbon and the features of its properties.
The place of the element in the periodic system of Mendeleev
The carbon subgroup is the main subgroup of group IV, which, in addition to carbon, also includes silicon, germanium, tin and lead. All of the listed elements have the same structure of the external energy level, on which four electrons are located. This determines the similarity of their chemical properties. In the normal state, the elements of the subgroup are bivalent, and when their atoms go into an excited state, they exhibit a valence equal to 4. The physical and chemical properties of carbon depend on the state of the electron shells of its atom. Thus, in reaction with oxygen, an element whose particles are in an unexcited state forms an indifferent oxide CO. Carbon atoms in the excited state are oxidized to carbon dioxide, which exhibits acidic properties.
Forms of carbon in nature
Diamond, graphite and carbine are three allotropic modifications of carbon as a simple substance. Transparent crystals with a high degree of refraction of light rays, which are the hardest compounds in nature, are diamonds. They are poor conductors of heat and are dielectrics. The crystal lattice is atomic, very strong. In it, each atom of an element is surrounded by four other particles, forming a regular tetrahedron.
Completely different physicochemical properties of carbon forming graphite. It is greasy to the touch crystalline substance of dark gray color. It has a layered structure, the distances between the layers of atoms are quite large, while their attractive forces are weak. Therefore, when pressing on a graphite rod, the substance is stratified into thin flakes. They leave a dark mark on paper. Graphite is thermally conductive and slightly inferior to metals in electrical conductivity.
The ability to conduct electric current is explained by the structure of the crystal of a substance. In it, carbon particles are bound to three others using strong covalent chemical bonds. The fourth valence electron of each atom remains free and is able to move in the thickness of the substance. The directed movement of negatively charged particles causes the appearance of an electric current. The fields of application of graphite are diverse. So, it is used for the manufacture of electrodes in electrical engineering and for carrying out the electrolysis process, with the help of which, for example, pure alkali metals are obtained. Graphite has found application in nuclear reactors to control the rate of chain reactions taking place in them as a neutron moderator. It is known to use the substance as slate rods or lubricants in the rubbing parts of mechanisms.
What is carbin?
The black crystalline powder with a glassy sheen is carbine. It was synthesized in the middle of the 20th century in Russia. The substance surpasses graphite in hardness, is chemically passive, has the properties of a semiconductor and is the most stable modification of carbon. The connection is stronger than graphite. There are also such forms of carbon, the chemical properties of which differ from each other. These are soot, charcoal and coke.
Various characteristics of allotropic modifications of carbon are explained by the structure of their crystal lattices. It is a refractory substance, colorless and odorless. It is insoluble in organic solvents, but it is capable of forming solid solutions - alloys, for example, with iron.
Chemical properties of carbon
Depending on the substance with which carbon reacts, it can exhibit dual properties: both a reducing agent and an oxidizing agent. For example, by fusing coke with metals, their compounds are obtained - carbides. In reaction with hydrogen, hydrocarbons are formed. These are organic compounds, for example, methane, ethylene, acetylene, in which, as in the case of metals, carbon has an oxidation state of -4. Reductive chemical reactions of carbon, whose properties we are studying, appear during its interaction with oxygen, halogens, water and basic oxides.
Oxides of carbon
By burning coal in air with a low oxygen content, carbon monoxide is obtained - oxide of divalent carbon. It is colorless, odorless and highly toxic. Combining with blood hemoglobin during respiration, carbon monoxide is carried throughout the human body, causing poisoning, and then death from suffocation. In the classification, a substance takes the place of indifferent oxides, does not react with water, and neither a base nor an acid corresponds to it. The chemical properties of carbon having a valency of 4 differ from the previously discussed characteristics.
Carbon dioxide
A colorless gaseous substance at a temperature of 15 and a pressure of one atmosphere passes into a solid phase. It's called dry ice. CO 2 molecules are non-polar, although the covalent bond between oxygen and carbon atoms is polar. The compound belongs to acidic oxides. When interacting with water, it forms carbonic acid. Reactions between carbon dioxide and simple substances are known: metals and non-metals, for example, with magnesium, calcium or coke. In them, it plays the role of an oxidizing agent.
Qualitative reaction to carbon dioxide
To make sure that the gas under study is really carbon monoxide CO 2, the following experiment is carried out in inorganic chemistry: the substance is passed through a transparent solution of lime water. Observation of the cloudiness of the solution due to the precipitation of a white precipitate of calcium carbonate confirms the presence of carbon dioxide molecules in the reagent mixture. With further passage of gas through a solution of calcium hydroxide, the CaCO 3 precipitate dissolves due to its transformation into calcium bicarbonate, a water-soluble salt.
The role of carbon in the blast furnace process
The chemical properties of carbon are used in the industrial production of iron from its ores: magnetic, red or brown iron ore. Chief among them will be the reducing properties of carbon and oxides - carbon monoxide and carbon dioxide. The processes occurring in the blast furnace can be represented as the following sequence of reactions:
- First, coke burns in a stream of air heated to 1,850 °C with the formation of carbon dioxide: C + O 2 = CO 2.
- Passing through hot carbon, it is reduced to carbon monoxide: CO 2 + C = 2CO.
- Carbon monoxide reacts with iron ore, resulting in iron oxide: 3Fe 2 O 3 + CO \u003d 2Fe 3 O 4 + CO 2, Fe 3 O 4 + CO \u003d 3FeO + CO 2.
- The iron production reaction will have the following form: FeO + CO \u003d Fe + CO 2
Molten iron dissolves a mixture of carbon and carbon monoxide in itself, resulting in a substance - cementite.
Cast iron smelted in a blast furnace, in addition to iron, contains up to 4.5% carbon and other impurities: manganese, phosphorus, sulfur. Steel, which differs from cast iron in a number of ways, such as the ability to roll and forge, has only 0.3 to 1.7% carbon in its composition. Steel products are widely used in almost all industries: mechanical engineering, metallurgy, and medicine.
In our article, we found out what chemical properties of carbon and its compounds are used in various areas of human activity.
MOU "Nikiforovskaya secondary school No. 1"
Carbon and its main inorganic compounds
abstract
Completed by: student of class 9B
Sidorov Alexander
Teacher: Sakharova L.N.
Dmitrievka 2009
Introduction
Chapter I. All About Carbon
1.1. carbon in nature
1.2. Allotropic modifications of carbon
1.3. Chemical properties of carbon
1.4. Application of carbon
Chapter II. Inorganic carbon compounds
Conclusion
Literature
Introduction
Carbon (lat. Carboneum) C is a chemical element of Group IV of the Mendeleev periodic system: atomic number 6, atomic mass 12.011(1). Consider the structure of the carbon atom. There are four electrons in the outer energy level of the carbon atom. Let's graph it:
Carbon has been known since ancient times, and the name of the discoverer of this element is unknown.
At the end of the XVII century. Florentine scientists Averani and Targioni tried to fuse several small diamonds into one large one and heated them with the help of burning glass with the sun's rays. The diamonds disappeared after burning in the air. In 1772, the French chemist A. Lavoisier showed that CO 2 is formed during the combustion of diamond. Only in 1797, the English scientist S. Tennant proved the identity of the nature of graphite and coal. After burning equal amounts of coal and diamond, the volumes of carbon monoxide (IV) turned out to be the same.
The variety of carbon compounds, which is explained by the ability of its atoms to combine with each other and with atoms of other elements in various ways, determines the special position of carbon among other elements.
Chapter I . All about carbon
1.1. carbon in nature
Carbon is found in nature both in the free state and in the form of compounds.
Free carbon occurs as diamond, graphite, and carbine.
Diamonds are very rare. The largest known diamond - "Cullinan" was found in 1905 in South Africa, weighed 621.2 g and measured 10 × 6.5 × 5 cm. The Diamond Fund in Moscow holds one of the largest and most beautiful diamonds in world - "Orlov" (37.92 g).
The diamond got its name from the Greek. "adamas" - invincible, indestructible. The most significant diamond deposits are located in South Africa, Brazil, and Yakutia.
Large deposits of graphite are located in Germany, in Sri Lanka, in Siberia, in Altai.
The main carbon-bearing minerals are: magnesite MgCO 3, calcite (lime spar, limestone, marble, chalk) CaCO 3, dolomite CaMg (CO 3) 2, etc.
All fossil fuels - oil, gas, peat, hard and brown coal, shale - are built on a carbon basis. Close in composition to carbon are some fossil coals containing up to 99% C.
Carbon accounts for 0.1% of the earth's crust.
In the form of carbon monoxide (IV) CO 2 carbon is part of the atmosphere. A large amount of CO 2 is dissolved in the hydrosphere.
1.2. Allotropic modifications of carbon
Elemental carbon forms three allotropic modifications: diamond, graphite, carbine.
1. Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly. Carbon atoms in diamond are in a state of sp 3 hybridization. In the excited state, the valence electrons in the carbon atoms are depaired and four unpaired electrons are formed. When chemical bonds are formed, electron clouds acquire the same elongated shape and are located in space so that their axes are directed towards the vertices of the tetrahedron. When the tops of these clouds overlap with clouds of other carbon atoms, covalent bonds appear at an angle of 109°28", and an atomic crystal lattice is formed, which is characteristic of diamond.
Each carbon atom in a diamond is surrounded by four others located from it in directions from the center of the tetrahedra to the vertices. The distance between atoms in tetrahedra is 0.154 nm. The strength of all bonds is the same. Thus, the atoms in a diamond are "packed" very tightly. At 20°C, the density of diamond is 3.515 g/cm 3 . This explains its exceptional hardness. Diamond is a poor conductor of electricity.
In 1961, the industrial production of synthetic diamonds from graphite began in the Soviet Union.
In the industrial synthesis of diamonds, pressures of thousands of MPa and temperatures from 1500 to 3000°C are used. The process is carried out in the presence of catalysts, which can be some metals, such as Ni. The bulk of the formed diamonds are small crystals and diamond dust.
Diamond, when heated without access to air above 1000 ° C, turns into graphite. At 1750°C, the transformation of diamond into graphite occurs rapidly.
Structure of a diamond
2. Graphite is a gray-black crystalline substance with a metallic sheen, greasy to the touch, inferior in hardness even to paper.
Carbon atoms in graphite crystals are in a state of sp 2 hybridization: each of them forms three covalent σ bonds with neighboring atoms. The angles between the bond directions are 120°. The result is a grid composed of regular hexagons. The distance between adjacent nuclei of carbon atoms within the layer is 0.142 nm. The fourth electron of the outer layer of each carbon atom in graphite occupies a p-orbital, which is not involved in hybridization.
Non-hybrid electron clouds of carbon atoms are oriented perpendicular to the plane of the layer, and overlapping with each other, form delocalized σ-bonds. Neighboring layers in a graphite crystal are located at a distance of 0.335 nm from each other and are weakly interconnected, mainly by van der Waals forces. Therefore, graphite has low mechanical strength and is easily split into flakes, which are very strong in themselves. The bond between the layers of carbon atoms in graphite is partially metallic. This explains the fact that graphite conducts electricity well, but still not as well as metals.
graphite structure
Physical properties in graphite differ greatly in directions - perpendicular and parallel to the layers of carbon atoms.
When heated without access to air, graphite does not undergo any changes up to 3700°C. At this temperature, it sublimates without melting.
Artificial graphite is obtained from the best grades of hard coal at 3000°C in electric furnaces without air access.
Graphite is thermodynamically stable over a wide range of temperatures and pressures, so it is accepted as the standard state of carbon. The density of graphite is 2.265 g/cm 3 .
3. Carbin - fine-grained black powder. In its crystal structure, carbon atoms are connected by alternating single and triple bonds into linear chains:
−С≡С−С≡С−С≡С−
This substance was first obtained by V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin, Yu.P. Kudryavtsev in the early 1960s.
Subsequently, it was shown that carbine can exist in different forms and contains both polyacetylene and polycumulene chains in which carbon atoms are linked by double bonds:
C=C=C=C=C=C=
Later, carbine was found in nature - in meteorite matter.
Carbyne has semiconductor properties; under the action of light, its conductivity increases greatly. Due to the existence of different types of bonds and different ways of stacking chains of carbon atoms in the crystal lattice, the physical properties of carbine can vary over a wide range. When heated without access to air above 2000°C, carbine is stable; at temperatures of about 2300°C, its transition to graphite is observed.
Natural carbon consists of two isotopes (98.892%) and (1.108%). In addition, minor impurities of a radioactive isotope, which are obtained artificially, were found in the atmosphere.
Previously, it was believed that charcoal, soot and coke are similar in composition to pure carbon and differ in properties from diamond and graphite, represent an independent allotropic modification of carbon (“amorphous carbon”). However, it was found that these substances consist of the smallest crystalline particles in which carbon atoms are connected in the same way as in graphite.
4. Coal - finely divided graphite. It is formed during the thermal decomposition of carbon-containing compounds without air access. Coals differ significantly in properties depending on the substance from which they are obtained and the method of preparation. They always contain impurities that affect their properties. The most important grades of coal are coke, charcoal, and soot.
Coke is obtained by heating coal in the absence of air.
Charcoal is formed when wood is heated in the absence of air.
Soot is a very fine graphite crystalline powder. It is formed during the combustion of hydrocarbons (natural gas, acetylene, turpentine, etc.) with limited air access.
Activated carbons are porous industrial adsorbents consisting mainly of carbon. Adsorption is the absorption by the surface of solids of gases and dissolved substances. Active carbons are obtained from solid fuels (peat, brown and hard coal, anthracite), wood and its products (charcoal, sawdust, paper production waste), leather industry waste, animal materials, such as bones. Coals, characterized by high mechanical strength, are produced from the shells of coconuts and other nuts, from the seeds of fruits. The structure of coals is represented by pores of all sizes, however, the adsorption capacity and adsorption rate are determined by the content of micropores per unit mass or volume of granules. In the production of active carbon, the raw material is first subjected to heat treatment without air access, as a result of which moisture and partially resins are removed from it. In this case, a large-pore structure of coal is formed. To obtain a microporous structure, activation is carried out either by oxidation with gas or steam, or by treatment with chemical reagents.
1.3. Chemical properties of carbon
At ordinary temperatures diamond, graphite, coal are chemically inert, but at high temperatures their activity increases. As follows from the structure of the main forms of carbon, coal reacts more easily than graphite and even more so diamond. Graphite is not only more reactive than diamond, but, reacting with certain substances, it can form products that diamond does not form.
1. As an oxidizing agent, carbon reacts with certain metals at high temperatures to form carbides:
ZS + 4Al \u003d Al 4 C 3 (aluminum carbide).
2. With hydrogen, coal and graphite form hydrocarbons. The simplest representative - methane CH 4 - can be obtained in the presence of a Ni catalyst at a high temperature (600-1000 ° C):
C + 2H 2 CH 4.
3. When interacting with oxygen, carbon exhibits reducing properties. With the complete combustion of carbon of any allotropic modification, carbon monoxide (IV) is formed:
C + O 2 \u003d CO 2.
Incomplete combustion produces carbon monoxide (II) CO:
C + O 2 \u003d 2CO.
Both reactions are exothermic.
4. The reducing properties of coal are especially pronounced when interacting with metal oxides (zinc, copper, lead, etc.), for example:
C + 2CuO \u003d CO 2 + 2Cu,
C + 2ZnO = CO 2 + 2Zn.
The most important process of metallurgy is based on these reactions - the smelting of metals from ores.
In other cases, for example, when interacting with calcium oxide, carbides are formed:
CaO + 3C \u003d CaC 2 + CO.
5. Coal is oxidized with hot concentrated sulfuric and nitric acids:
C + 2H 2 SO 4 \u003d CO 2 + 2SO 2 + 2H 2 O,
ZS + 4HNO 3 \u003d ZSO 2 + 4NO + 2H 2 O.
All forms of carbon are resistant to alkalis!
1.4. Application of carbon
Diamonds are used for processing various hard materials, for cutting, grinding, drilling and engraving glass, for drilling rocks. Diamonds after grinding and cutting turn into diamonds used as jewelry.
Graphite is the most valuable material for modern industry. Graphite is used to make molds, melting crucibles and other refractory products. Due to its high chemical resistance, graphite is used for the manufacture of pipes and apparatus lined with graphite plates from the inside. Significant amounts of graphite are used in the electrical industry, for example, in the manufacture of electrodes. Graphite is used to make pencils and some paints, as a lubricant. Very pure graphite is used in nuclear reactors to moderate neutrons.
A linear polymer of carbon, carbine, is attracting the attention of scientists as a promising material for the manufacture of semiconductors that can operate at high temperatures and ultra-strong fibers.
Charcoal is used in the metallurgical industry, in blacksmithing.
Coke is used as a reducing agent in the smelting of metals from ores.
Soot is used as a filler for rubber to increase strength, so car tires are black. Soot is also used as a component of printing inks, ink, and shoe polish.
Activated carbons are used to purify, extract and separate various substances. Activated carbons are used as fillers for gas masks and as a sorbent agent in medicine.
Chapter II . Inorganic carbon compounds
Carbon forms two oxides - carbon monoxide (II) CO and carbon monoxide (IV) CO 2.
Carbon monoxide (II) CO is a colorless, odorless gas, slightly soluble in water. It is called carbon monoxide because it is very poisonous. Getting into the blood during breathing, it quickly combines with hemoglobin, forming a strong carboxyhemoglobin compound, thereby depriving hemoglobin of the ability to carry oxygen.
When inhaling air containing 0.1% CO, a person can suddenly lose consciousness and die. Carbon monoxide is formed during incomplete combustion of fuel, which is why premature closing of chimneys is so dangerous.
Carbon monoxide (II) is referred, as you already know, to non-salt-forming oxides, since, being a non-metal oxide, it must react with alkalis and basic oxides to form salt and water, but this is not observed.
2CO + O 2 \u003d 2CO 2.
Carbon monoxide (II) is able to take oxygen from metal oxides, i.e. recover metals from their oxides.
Fe 2 O 3 + ZSO \u003d 2Fe + ZSO 2.
It is this property of carbon monoxide (II) that is used in metallurgy for iron smelting.
Carbon monoxide (IV) CO 2 - commonly known as carbon dioxide - is a colorless, odorless gas. It is about one and a half times heavier than air. Under normal conditions, 1 volume of carbon dioxide dissolves in 1 volume of water.
At a pressure of about 60 atm, carbon dioxide turns into a colorless liquid. When liquid carbon dioxide evaporates, part of it turns into a solid snow-like mass, which is pressed in industry - this is the “dry ice” you know, which is used to store food. You already know that solid carbon dioxide has a molecular lattice and is capable of sublimation.
Carbon dioxide CO 2 is a typical acidic oxide: it reacts with alkalis (for example, causes lime water to become cloudy), with basic oxides and with water.
It does not burn and does not support combustion and therefore is used to extinguish fires. However, magnesium continues to burn in carbon dioxide to form oxide and release carbon as soot.
CO 2 + 2Mg \u003d 2MgO + C.
Carbon dioxide is obtained by acting on salts of carbonic acid - carbonates with solutions of hydrochloric, nitric and even acetic acids. In the laboratory, carbon dioxide is produced by the action of hydrochloric acid on chalk or marble.
CaCO 3 + 2HCl \u003d CaCl 2 + H 2 0 + C0 2.
In industry, carbon dioxide is produced by burning limestone:
CaCO 3 \u003d CaO + C0 2.
Carbon dioxide, in addition to the already mentioned field of application, is also used for the manufacture of fizzy drinks and for the production of soda.
When carbon monoxide (IV) is dissolved in water, carbonic acid H 2 CO 3 is formed, which is very unstable and easily decomposes into its original components - carbon dioxide and water.
As a dibasic acid, carbonic acid forms two series of salts: medium - carbonates, for example CaCO 3, and acidic - bicarbonates, for example Ca (HCO 3) 2. Of the carbonates, only potassium, sodium and ammonium salts are soluble in water. Acid salts are usually soluble in water.
With an excess of carbon dioxide in the presence of water, carbonates can turn into hydrocarbons. So, if carbon dioxide is passed through lime water, then it will first become cloudy due to the precipitation of water-insoluble calcium carbonate, however, with further passage of carbon dioxide, the cloudiness disappears as a result of the formation of soluble calcium bicarbonate:
CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2.
It is the presence of this salt that explains the temporary hardness of water. Why temporary? Because when heated, soluble calcium bicarbonate turns back into insoluble carbonate:
Ca (HCO 3) 2 \u003d CaCO 3 ↓ + H 2 0 + C0 2.
This reaction leads to the formation of scale on the walls of boilers, steam heating pipes and domestic kettles, and in nature, as a result of this reaction, bizarre stalactites hanging down are formed in caves, towards which stalagmites grow from below.
Other calcium and magnesium salts, in particular chlorides and sulfates, give the water permanent hardness. Boiling permanent water hardness cannot be eliminated. You have to use another carbonate - soda.
Na 2 CO 3, which precipitates these Ca 2+ ions, for example:
CaCl 2 + Na 2 CO 3 \u003d CaCO 3 ↓ + 2NaCl.
Soda can also be used to eliminate temporary hardness of water.
Carbonates and bicarbonates can be detected using acid solutions: when exposed to acids, a characteristic “boiling” is observed due to the released carbon dioxide.
This reaction is a qualitative reaction to carbonic acid salts.
Conclusion
All life on earth is based on carbon. Each molecule of a living organism is built on the basis of a carbon skeleton. Carbon atoms are constantly migrating from one part of the biosphere (the narrow shell of the Earth where life exists) to another. Using the example of the carbon cycle in nature, one can trace the dynamics of life on our planet in dynamics.
The main carbon reserves on Earth are in the form of carbon dioxide contained in the atmosphere and dissolved in the oceans, that is, carbon dioxide (CO 2). Consider first the carbon dioxide molecules in the atmosphere. Plants absorb these molecules, then in the process of photosynthesis the carbon atom is converted into a variety of organic compounds and thus included in the structure of plants. Following are several options:
1. Carbon can remain in plants until the plants die. Then their molecules will be eaten by decomposers (organisms that feed on dead organic matter and at the same time break it down to simple inorganic compounds), such as fungi and termites. Eventually the carbon will return to the atmosphere as CO 2 ;
2. Plants can be eaten by herbivores. In this case, carbon will either return to the atmosphere (during the respiration of animals and during their decomposition after death), or herbivores will be eaten by carnivores (and then carbon will again return to the atmosphere in the same ways);
3. Plants may die and end up underground. Then eventually they will turn into fossil fuels - for example, into coal.
In the case of dissolution of the original CO 2 molecule in sea water, several options are also possible:
Carbon dioxide can simply return to the atmosphere (this type of mutual gas exchange between the oceans and the atmosphere occurs all the time);
Carbon can enter the tissues of marine plants or animals. Then it will gradually accumulate in the form of sediments on the bottom of the oceans and eventually turn into limestone or again pass from the sediments into sea water.
Once carbon is incorporated into sediments or fossil fuels, it is removed from the atmosphere. Throughout the existence of the Earth, the carbon withdrawn in this way was replaced by carbon dioxide released into the atmosphere during volcanic eruptions and other geothermal processes. In modern conditions, emissions from human combustion of fossil fuels are also added to these natural factors. Due to the influence of CO 2 on the greenhouse effect, the study of the carbon cycle has become an important task for atmospheric scientists.
An integral part of these searches is to determine the amount of CO 2 present in plant tissues (for example, in a newly planted forest) - scientists call this carbon sink. As governments around the world try to reach an international agreement to limit CO 2 emissions, the issue of a balance between carbon sinks and carbon emissions in individual countries has become a major bone of contention for industrial countries. However, scientists doubt that the accumulation of carbon dioxide in the atmosphere can be stopped by forest plantations alone.
Carbon constantly circulates in the earth's biosphere along closed interconnected pathways. Currently, the effects of burning fossil fuels are being added to natural processes.
Literature:
1. Akhmetov N.S. Chemistry grade 9: textbook. for general education textbook establishments. - 2nd ed. – M.: Enlightenment, 1999. – 175 p.: ill.
2. Gabrielyan O.S. Chemistry grade 9: textbook. for general education textbook establishments. - 4th ed. - M.: Bustard, 2001. - 224 p.: ill.
3. Gabrielyan O.S. Chemistry grades 8-9: method. allowance. - 4th ed. – M.: Bustard, 2001. – 128 p.
4. Eroshin D.P., Shishkin E.A. Methods for solving problems in chemistry: textbook. allowance. – M.: Enlightenment, 1989. – 176 p.: ill.
5. Kremenchugskaya M. Chemistry: Schoolchildren's Handbook. – M.: Philol. Society "WORD": LLC "Publishing House AST", 2001. - 478 p.
6. Kritsman V.A. Reading book on inorganic chemistry. – M.: Enlightenment, 1986. – 273 p.
Carbon (lat. Carboneum) - a chemical element of the 14th group of the 2nd period of the periodic system of Mendeleev (group IV in the old numbering); atomic number 6, atomic mass 12.011.
Carbon is a very special chemical element. A powerful tree of organic chemistry has grown out of the chemistry of carbon, with its most complex syntheses and an immense range of studied compounds. New branches of organic chemistry are emerging. All living things that make up the biosphere are built from carbon compounds. And the trees, which had died down a long time ago, millions of years ago, turned into fuel containing carbon - coal, peat, etc. Let's take the most ordinary pencil - an object familiar to everyone. Isn't it amazing that a humble graphite rod is related to a sparkling diamond, the hardest substance in nature? Diamond, graphite, carbine are allotropic modifications of carbon (see Allotropy). The structure of graphite (1), diamond (2), carbine (3).
The history of human acquaintance with this substance goes far into the depths of centuries. The name of the person who discovered carbon is unknown, it is not known which form of pure carbon - graphite or diamond - was discovered earlier. Only at the end of the XVIII century. It was recognized that carbon is an independent chemical element.
The carbon content in the earth's crust is 0.023% by mass. Carbon is the main component of the plant and animal world. All fossil fuels - oil, gas, peat, shale - are built on a carbon basis, coal is especially rich in carbon. Most of the carbon is concentrated in minerals - limestone CaCO 3 and dolomite CaMg (CO 3) 2, which are salts of alkaline earth metals and weak carbonic acid H 2 CO 3.
Among the vital elements, carbon is one of the most important: life on our planet is built on a carbon basis. Why? We find the answer to this question in the Fundamentals of Chemistry by D. I. Mendeleev: “Carbon is found in nature both in the free and in the connecting state, in very different forms and types ... The ability of carbon atoms to combine with each other and give complex particles is manifested in all carbon compounds ... In none of the elements ... the ability to complicate is not developed to such an extent as in carbon ... No pair of elements gives as many compounds as carbon and hydrogen.
Indeed, carbon atoms can combine in a variety of ways with each other and with atoms of many other elements, forming a huge variety of substances. Their chemical bonds can arise and break under the influence of natural factors. This is how the carbon cycle arises in nature: from the atmosphere to plants, from plants to animal organisms, from them to inanimate nature, etc. Where there is carbon, there is a variety of substances, where there is carbon, there are structures of the most diverse molecular architecture (see .Hydrocarbons).
The accumulation of carbon in the earth's crust is associated with the accumulation of many other elements that precipitate in the form of insoluble carbonates, etc. CO 2 and carbonic acid play an important geochemical role in the earth's crust. A huge amount of CO 2 is released during volcanism - in the history of the Earth it was the main source of carbon for the biosphere.
Inorganic carbon compounds are much smaller in number than organic ones. Carbon in the form of diamond, graphite, coal enters into a compound only when heated. At high temperatures, it combines with metals and some non-metals, such as boron, to form carbides.
Of the inorganic compounds of carbon, the most famous are salts of carbonic acid, carbon dioxide CO 2 (carbon dioxide) and carbon monoxide CO. Much less known is the third oxide C 3 O 2 - a colorless gas with an unpleasant pungent odor.
The Earth's atmosphere contains 2.3 10 12 tons of CO 2 dioxide, a product of respiration and combustion. It is the main source of carbon for plant development. Carbon monoxide CO, known as carbon monoxide, is produced by the incomplete combustion of fuels: in the exhaust gases of cars, etc.
In industry, carbon monoxide CO is used as a reducing agent (for example, in iron smelting in blast furnaces) and for the synthesis of organic substances (for example, methyl alcohol by the reaction: CO + 2H 2 → CH 3 (OH).
The most famous allotropic modifications of elemental carbon: diamond- inorganic polymer of spatial, volumetric structure; graphite- polymer of planar structure; carbine- a linear polymer of carbon that exists in two forms, differing in the nature and alternation of chemical bonds; two-dimensional modification graphene; carbon nanotubes cylindrical structure. (see Allotropy).
Diamond- a crystalline form of carbon, a rare mineral, surpassing in hardness all natural and all, except for crystalline boron nitride, artificial materials. Large diamond crystals after cutting turn into the most precious of stones - diamonds.
At the end of the XVII century. Florentine scientists Averani and Targioni tried to fuse several small diamonds into one large one, heated them with sunlight using a burning glass. Diamonds disappeared by burning in the air ... It took about a hundred years before the French chemist A. Lavoisier in 1772 not only repeated this experiment, but also explained the reasons for the disappearance of the diamond: a precious diamond crystal burned out in the same way as pieces burned in other experiments phosphorus and coal. And only in 1797, the English scientist S. Tennant proved the identity of the nature of diamond and coal. He found that the volumes of carbon dioxide after the combustion of equal masses of coal and diamond turned out to be the same. After that, many attempts were made to obtain diamond artificially from graphite, coal and carbon-containing materials at high temperatures and pressures. Sometimes, after these experiments, small diamond-like crystals were found, but it was never possible to carry out successful experiments.
The synthesis of diamond became possible after the Soviet physicist O. I. Leipunsky in 1939 calculated the conditions under which graphite can turn into diamond (pressure about 60,000 atm, temperature 1600-2000 ° C). In the 50s. of our century, almost simultaneously in several countries, including the USSR, artificial diamonds were obtained under industrial conditions. Today, 2,000 carats of artificial diamonds are produced daily from one domestic industrial installation (1 carat = 0.2 g). Diamond crowns of drilling rigs, diamond cutting tools, grinding wheels with diamond chips work reliably and for a long time. Artificial diamonds, as well as natural crystals, are widely used in modern technology.
Another pure carbon polymer is even more widely used in practice - graphite. In a graphite crystal, carbon atoms lying in the same plane are firmly bound into regular hexagons. Hexagons with common faces form bundle planes. The bonds between carbon atoms of different packs are weak. In addition, the distance between carbon atoms of different planes is almost 2.5 times greater than between neighboring atoms of the same plane. Therefore, a slight effort is enough to split the graphite crystal into separate flakes. That's why the graphite lead of a pencil leaves a mark on paper. It is incomparably more difficult to break the bond between carbon atoms lying in the same plane. The strength of these bonds is the reason for the high chemical resistance of graphite. It is not affected even by hot alkalis and acids, with the exception of concentrated nitric acid.
In addition to high chemical resistance, graphite is also characterized by high heat resistance: products made from it can be used at temperatures up to 3700 °C. The ability to conduct electric current has determined many applications of graphite. It is needed in electrical engineering, metallurgy, the production of gunpowder, nuclear technology. Graphite of the highest purity is used in reactor building - as an effective neutron moderator.
Linear polymer of carbon - carbine has so far been used in practice to a limited extent. In a carbine molecule, carbon atoms are connected in chains alternately by triple and single bonds:
−C≡C−C≡C−C≡C−C≡C−C≡C−
This substance was first obtained by Soviet chemists V. V. Korshak, A. M. Sladkov, V. I. Kasatochkin and Yu. P. Kudryavtsev in the early 1960s. at the Institute of Organoelement Compounds of the USSR Academy of Sciences. Carbyne has semiconductor properties, and under the action of light its conductivity is greatly increased. The first practical application is based on this property - in photocells.
In the molecule of another form of carbine - polycumulene (β-carbine), also obtained for the first time in our country, carbon atoms are connected differently than in carbine - only by double bonds:
═C═C═C═C═C═C═C═C═C═
The number of organic compounds known to science - carbon compounds - exceeds 7 million. The chemistry of polymers - natural and synthetic - is also primarily the chemistry of carbon compounds. Organic carbon compounds are studied by such independent sciences as organic chemistry, biochemistry, and the chemistry of natural compounds.
The importance of carbon compounds in human life is invaluable - bound carbon surrounds us everywhere: in the atmosphere and lithosphere, in plants and animals, in our clothes and food.