CARBON, C (a. carbon; n. Kohlenstoff; f. carbone; i. 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 layers of the atmosphere as a result of irradiation of 14 N nuclei by neutrons from cosmic radiation).
Carbon has been known since ancient times. Wood was used to recover metals from ores, and diamond was used as a... The recognition of carbon as a chemical element is associated with the name of the French chemist A. Lavoisier (1789).
Carbon modifications and properties
There are 4 known crystalline modifications of carbon: graphite, diamond, carbyne and lonsdaleite, which differ greatly in their properties. Carbyne is an artificially produced 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 located parallel to each other. Density 3230-3300 kg/m3, heat capacity 11.52 J/mol.K. Lonsdaleite is found in meteorites and obtained artificially; its structure and physical properties have not been fully 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 largely depend on the dispersion of particles and 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 carbon monoxide (CO). The 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 F2 above 900°C), so 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 reacts 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 among themselves, as well as between themselves and other elements. The ability of carbon to form 4 equivalent valence bonds with other carbon atoms allows the construction of carbon skeletons of different types (linear, branched, cyclic); It is these properties that explain the exclusive role of carbon in the structure of all organic compounds and, in particular, all living organisms.
Carbon in nature
The average carbon content in the earth's crust is 2.3.10% (by mass); Moreover, the bulk of carbon is concentrated in sedimentary rocks (1%), while in other rocks there are significantly lower and approximately equal (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. Over 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 that are sorbed by organic matter and precipitated after its burial at the bottom of reservoirs in the form of insoluble compounds. Large quantities of CO 2 dioxide are released into the atmosphere from the Earth during volcanic activity and during the combustion of organic fuels. From the atmosphere, CO 2 is absorbed by plants during the process of photosynthesis and dissolves in sea water, thereby forming the most important links in the overall carbon cycle on Earth. Carbon also plays an important role in space; On the Sun, carbon ranks 4th in abundance after hydrogen, helium and oxygen, participating in nuclear processes.
Application and Use
The most important national economic importance of carbon is determined by the fact that about 90% of all primary sources of energy consumed by humans come from fossil fuels. There is a tendency to use oil not as 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 production), diamonds (jewelry, technology) and graphite (nuclear technology, heat-resistant crucibles, pencils, some types of lubricants and etc.). Based on the specific activity of the 14 C isotope in 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 important - one twelfth of the mass of an atom of this isotope is taken as a unit of atomic mass of chemical elements.
Municipal educational institution "Nikiforovskaya secondary school No. 1"
Carbon and its main inorganic compounds
Essay
Completed by: student of grade 9B
Sidorov Alexander
Teacher: Sakharova L.N.
Dmitrievka 2009
Introduction
Chapter I. All about carbon
1.1. Carbon in nature
1.2. Allotropic modifications of carbon
1.3. Chemical properties of carbon
1.4. Application of carbon
Chapter II. Inorganic carbon compounds
Conclusion
Literature
Introduction
Carbon (lat. Carboneum) C is a chemical element of group IV of the periodic system of Mendeleev: atomic number 6, atomic mass 12.011(1). Let's consider the structure of the carbon atom. The outer energy level of the carbon atom contains four electrons. Let's depict it graphically:
Carbon has been known since ancient times, and the name of the discoverer of this element is unknown.
At the end of the 17th century. Florentine scientists Averani and Tardgioni tried to fuse several small diamonds into one large one and heated them with a burning glass using sunlight. The diamonds disappeared, burning in the air. In 1772, the French chemist A. Lavoisier showed that when diamonds burn, CO 2 is formed. Only in 1797 did the English scientist S. Tennant prove the identity of the nature of graphite and coal. After burning equal amounts of coal and diamond, the volumes of carbon monoxide (IV) turned out to be the same.
The variety of carbon compounds, explained by the ability of its atoms to combine with each other and the atoms of other elements in various ways, determines the special position of carbon among other elements.
Chapter I . All about carbon
1.1. Carbon in nature
Carbon is found in nature, both in a free state and in the form of compounds.
Free carbon occurs in the form of diamond, graphite and carbyne.
Diamonds are very rare. The largest known diamond, the Cullinan, was found in 1905 in South Africa, weighed 621.2 g and measured 10x6.5x5 cm. The Diamond Fund in Moscow houses one of the largest and most beautiful diamonds in world – “Orlov” (37.92 g).
Diamond got its name from the Greek. "adamas" - invincible, indestructible. The most significant diamond deposits are located in South Africa, Brazil, and Yakutia.
Large deposits of graphite are located in Germany, Sri Lanka, Siberia, and Altai.
The main carbon-containing minerals are: magnesite MgCO 3, calcite (lime spar, limestone, marble, chalk) CaCO 3, dolomite CaMg(CO 3) 2, etc.
All fossil fuels - oil, gas, peat, coal and brown coal, shale - are built on a carbon basis. Some fossil coals, containing up to 99% C, are close in composition to carbon.
Carbon accounts for 0.1% of the earth's crust.
In the form of carbon monoxide (IV) CO 2, carbon enters the atmosphere. A large amount of CO 2 is dissolved in the hydrosphere.
1.2. Allotropic modifications of carbon
Elementary carbon forms three allotropic modifications: diamond, graphite, carbine.
1. Diamond is a colorless, transparent crystalline substance that refracts light rays extremely strongly. Carbon atoms in diamond are in a state of sp 3 hybridization. In the excited state, the valence electrons in the carbon atoms are paired and four unpaired electrons are formed. When chemical bonds are formed, the electron clouds acquire the same elongated shape and are located in space so that their axes are directed towards the vertices of the tetrahedron. When the tops of these clouds overlap with clouds of other carbon atoms, covalent bonds occur at an angle of 109°28", and an atomic crystal lattice characteristic of diamond is formed.
Each carbon atom in diamond is surrounded by four others, located from it in directions from the center of the tetrahedrons to the vertices. The distance between atoms in tetrahedra is 0.154 nm. The strength of all connections is the same. Thus, the atoms in diamond are “packed” very tightly. At 20°C, the density of diamond is 3.515 g/cm 3 . This explains its exceptional hardness. Diamond is a poor conductor of electricity.
In 1961, the Soviet Union began industrial production of synthetic diamonds from graphite.
In the industrial synthesis of diamonds, pressures of thousands of MPa and temperatures from 1500 to 3000°C are used. The process is carried out in the presence of catalysts, which can be some metals, for example Ni. The bulk of the diamonds formed are small crystals and diamond dust.
When heated without access to air above 1000°C, diamond turns into graphite. At 1750°C, the transformation of diamond into graphite occurs quickly.
Diamond structure
2. Graphite is a gray-black crystalline substance with a metallic sheen, greasy to the touch, and inferior in hardness even to paper.
Carbon atoms in graphite crystals are in a state of sp 2 hybridization: each of them forms three covalent σ bonds with neighboring atoms. The angles between the bond directions are 120°. The result is a grid made up of regular hexagons. The distance between adjacent nuclei of carbon atoms inside the layer is 0.142 nm. The fourth electron in the outer layer of each carbon atom in graphite occupies a p orbital that does not participate in hybridization.
Non-hybrid electron clouds of carbon atoms are oriented perpendicular to the plane of the layer and, overlapping each other, form delocalized σ bonds. Adjacent layers in a graphite crystal are located at a distance of 0.335 nm from each other and are weakly connected to each other, mainly by van der Waals forces. Therefore, graphite has low mechanical strength and easily splits into flakes, which themselves are very strong. The bond between layers of carbon atoms in graphite is partially metallic in nature. This explains the fact that graphite conducts electricity well, but not as well as metals.
Graphite structure
Physical properties in graphite vary greatly in directions - perpendicular and parallel to the layers of carbon atoms.
When heated without air access, graphite does not undergo any changes up to 3700°C. At the specified temperature, it sublimes without melting.
Artificial graphite is produced from the best grades of coal at 3000°C in electric furnaces without air access.
Graphite is thermodynamically stable over a wide range of temperatures and pressures, so it is accepted as the standard state of carbon. The density of graphite is 2.265 g/cm3.
3. Carbin is a fine-crystalline black powder. In its crystal structure, carbon atoms are connected by alternating single and triple bonds in linear chains:
−С≡С−С≡С−С≡С−
This substance was first obtained by V.V. Korshak, A.M. Sladkov, V.I. Kasatochkin, Yu.P. Kudryavtsev in the early 60s of the XX century.
It was subsequently shown that carbyne can exist in different forms and contains both polyacetylene and polycumulene chains in which the carbon atoms are linked by double bonds:
C=C=C=C=C=C=
Later, carbyne was found in nature - in meteorite matter.
Carbyne has semiconducting properties; when exposed to light, its conductivity increases greatly. Due to the existence of different types of bonds and different ways of laying chains of carbon atoms in the crystal lattice, the physical properties of carbyne can vary within wide limits. When heated without access to air above 2000°C, carbine is stable; at temperatures around 2300°C, its transition to graphite is observed.
Natural carbon consists of two isotopes
(98.892%) and (1.108%). In addition, minor admixtures of a radioactive isotope, which is produced artificially, were found in the atmosphere.Previously, it was believed that charcoal, soot and coke are similar in composition to pure carbon and differ in properties from diamond and graphite, representing an independent allotropic modification of carbon (“amorphous carbon”). However, it was found that these substances consist of tiny crystalline particles in which the carbon atoms are bonded in the same way as in graphite.
4. Coal – finely ground graphite. It is formed during the thermal decomposition of carbon-containing compounds without air access. Coals vary significantly in properties depending on the substance from which they are obtained and the method of production. They always contain impurities that affect their properties. The most important types of coal are coke, charcoal, and soot.
Coke is produced by heating coal without access to air.
Charcoal is formed when wood is heated without access to air.
Soot is a very fine graphite crystalline powder. Formed by the combustion of hydrocarbons (natural gas, acetylene, turpentine, etc.) with limited air access.
Activated carbons are porous industrial adsorbents consisting mainly of carbon. Adsorption is the absorption of gases and dissolved substances by the surface of solids. Activated carbons are obtained from solid fuel (peat, brown and hard coal, anthracite), wood and its processed products (charcoal, sawdust, paper waste), leather industry waste, and animal materials, such as bones. Coals, characterized by high mechanical strength, are produced from the shells of coconuts and other nuts, and from fruit seeds. The structure of coals is represented by pores of all sizes, however, the adsorption capacity and adsorption rate are determined by the content of micropores per unit mass or volume of granules. When producing active carbon, the starting material is first subjected to heat treatment without access to air, as a result of which moisture and partially resins are removed from it. In this case, a large-porous structure of coal is formed. To obtain a microporous structure, activation is carried out either by oxidation with gas or steam, or by treatment with chemical reagents.
Carbon is perhaps one of the most impressive elements of chemistry on our planet, which has the unique ability to form a huge variety of different organic and inorganic bonds.
In a word, carbon compounds that have unique characteristics are the basis of life on our planet.
What is carbon
In the chemical table D.I. Mendeleev's carbon is number six, belongs to group 14 and is designated “C”.
Physical properties
It is a hydrogen compound belonging to the group of biological molecules, the molar mass and molecular weight of which is 12.011, and the melting point is 3550 degrees.
The oxidation state of a given element can be: +4, +3, +2, +1, 0, -1, -2, -3, -4, and the density is 2.25 g/cm3.
In the aggregate state, carbon is a solid, and the crystal lattice is atomic.
Carbon has the following allotropic modifications:
- graphite;
- fullerene;
- carbine
Atomic structure
An atom of a substance has an electronic configuration of the form - 1S 2 2S 2 2P 2. At the outer level, an atom has 4 electrons located in two different orbitals.
If we take the excited state of the element, then its configuration becomes 1S 2 2S 1 2P 3.
In addition, an atom of a substance can be primary, secondary, tertiary and quaternary.
Chemical properties
Being in normal conditions, the element is inert and interacts with metals and non-metals at elevated temperatures:
- interacts with metals, resulting in the formation of carbides;
- reacts with fluorine (halogen);
- at elevated temperatures interacts with hydrogen and sulfur;
- when the temperature rises, it ensures the reduction of metals and non-metals from oxides;
- at 1000 degrees it interacts with water;
- lights up when the temperature rises.
Carbon production
Carbon can be found in nature in the form of black graphite or, very rarely, in the form of diamond. Unnatural graphite is produced by reacting coke with silica.
Unnatural diamonds are produced by applying heat and pressure along with catalysts. This melts the metal, and the resulting diamond comes out as a precipitate.
Adding nitrogen results in yellowish diamonds, while adding boron produces bluish diamonds.
History of discovery
Carbon has been used by people since ancient times. The Greeks knew graphite and coal, and diamonds were first found in India. By the way, people often took similar-looking compounds as graphite. But even despite this, graphite was widely used for writing, because even the word “grapho” is translated from Greek as “I write.”
Currently, graphite is also used in writing, in particular it can be found in pencils. At the beginning of the 18th century, diamond trade began in Brazil, many deposits were discovered, and already in the second half of the 20th century, people learned to obtain unnatural gemstones.
Currently, non-natural diamonds are used in industry, and real diamonds are used in jewelry.
The role of carbon in the human body
Carbon enters the human body along with food, during the day - 300 g. And the total amount of the substance in the human body is 21% of body weight.
This element consists of 2/3 muscles and 1/3 bones. And the gas is removed from the body along with exhaled air or with urea.
It is worth noting: Without this substance, life on Earth is impossible, because carbon forms bonds that help the body fight the destructive influence of the surrounding world.
Thus, the element is capable of forming long chains or rings of atoms, which provide the basis for many other important bonds.
Occurrence of carbon in nature
The element and its compounds can be found everywhere. First of all, we note that the substance makes up 0.032% of the total amount of the earth’s crust.
A single element can be found in coal. And the crystalline element is found in allotropic modifications. Also, the amount of carbon dioxide in the air is constantly increasing.
Large concentrations of the element in the environment can be found as compounds with various elements. For example, carbon dioxide is contained in the air in an amount of 0.03%. Minerals such as limestone or marble contain carbonates.
All living organisms contain compounds of carbon with other elements. In addition, the remains of living organisms become deposits such as oil and bitumen.
Application of carbon
Compounds of this element are widely used in all areas of our lives and the list of them can be endless, so we will indicate a few of them:
- graphite is used in pencil leads and electrodes;
- diamonds are widely used in jewelry and drilling;
- carbon is used as a reducing agent to remove elements such as iron ore and silicon;
- activated carbon, consisting mainly of this element, is widely used in the medical field, industry and everyday life.
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 physical and chemical characteristics of carbon and the features of its properties.
Place of the element in the periodic table 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 these elements have the same structure of the outer 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 divalent, and when their atoms go into an excited state, they exhibit a valency of 4. The physical and chemical properties of carbon depend on the state of the electronic shells of its atom. Thus, in a reaction with oxygen, an element whose particles are in an unexcited state forms the indifferent oxide CO. Carbon atoms in an excited state are oxidized to carbon dioxide, which exhibits acidic properties.
Forms of carbon in nature
Diamond, graphite and carbyne 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 conduct heat poorly 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 physical and chemical properties of the carbon that forms graphite. It is a dark gray crystalline substance that is greasy to the touch. It has a layer-by-layer 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 exfoliates into thin flakes. They leave a dark mark on the 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 the substance. In it, carbon particles are bonded to three others using strong covalent chemical bonds. The fourth valence electron of each atom remains free and is able to move throughout the substance. The directed movement of negatively charged particles causes the appearance of electric current. The areas of application of graphite are varied. Thus, it is used for the manufacture of electrodes in electrical engineering and for carrying out the electrolysis process, through which, for example, alkali metals are obtained in their pure form. Graphite has found application in nuclear reactors to control the speed of chain reactions occurring in them as a neutron moderator. It is known to use the substance as slate rods or lubricant in rubbing parts of mechanisms.
What is carbyne?
Black crystalline powder with a glassy sheen is carbine. It was synthesized in the mid-20th century in Russia. The substance is superior to graphite in hardness, chemically passive, has semiconductor properties and is the most stable modification of carbon. The connection is stronger than graphite. There are also forms of carbon whose chemical properties differ from each other. These are soot, charcoal and coke.
The 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 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. The reaction with hydrogen produces hydrocarbons. 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, the properties of which we study, appear during its interaction with oxygen, halogens, water and basic oxides.
Carbon oxides
By burning coal in air with a low oxygen content, carbon monoxide is produced - divalent carbon oxide. It is colorless, odorless and highly toxic. Combining with hemoglobin in the blood during respiration, carbon monoxide spreads throughout the human body, causing poisoning and then death from suffocation. In the classification, the substance takes the place of indifferent oxides, does not react with water, and does not correspond to either a base or an acid. The chemical properties of carbon, which has a valence 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 the solid phase. It's called dry ice. CO 2 molecules are nonpolar, although the covalent bond between the oxygen and carbon atoms is polar. The compound belongs to the acid oxides. Interacting with water, it forms carbonate 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 indeed carbon monoxide CO 2, the following experiment is carried out in inorganic chemistry: the substance is passed through a clear solution of lime water. Observation of turbidity of the solution due to the precipitation of a white precipitate of calcium carbonate confirms the presence of carbon dioxide molecules in the mixture of reagents. When the gas is further passed 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 dioxide 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 = 2Fe 3 O 4 + CO 2, Fe 3 O 4 + CO = 3FeO + CO 2.
- The reaction for producing iron will have the following form: FeO + CO = Fe + CO 2
Molten iron dissolves a mixture of carbon and carbon monoxide, 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 its ability to be rolled and forged, contains only 0.3 to 1.7% carbon. Steel products are widely used in almost all industries: mechanical engineering, metallurgy, medicine.
In our article, we found out what chemical properties of carbon and its compounds are used in various areas of human activity.
Carbon (C)– typical non-metal; in the periodic table it is in the 2nd period of group IV, the main subgroup. Serial number 6, Ar = 12.011 amu, nuclear charge +6.Physical properties: carbon forms many allotropic modifications: diamond- one of the hardest substances graphite, coal, soot.
A carbon atom has 6 electrons: 1s 2 2s 2 2p 2 . The last two electrons are located in separate p-orbitals and are unpaired. In principle, this pair could occupy the same orbital, but in this case the interelectron repulsion greatly increases. For this reason, one of them takes 2p x, and the other, either 2p y , or 2p z orbitals.
The difference in the energy of the s- and p-sublevels of the outer layer is small, so the atom quite easily goes into an excited state, in which one of the two electrons from the 2s orbital passes to a free one 2 rub. A valence state appears with the configuration 1s 2 2s 1 2p x 1 2p y 1 2p z 1 . It is this state of the carbon atom that is characteristic of the diamond lattice—tetrahedral spatial arrangement of hybrid orbitals, identical length and energy of bonds.
This phenomenon is known to be called sp 3 -hybridization, and the emerging functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three r-r- and one s-s-connection. In addition to sp 3 hybridization, sp 2 and sp hybridization is also observed at the carbon atom . In the first case, mutual overlap occurs s- and two p-orbitals. Three equivalent sp 2 hybrid orbitals are formed, located in the same plane at an angle of 120° to each other. The third orbital p is unchanged and directed perpendicular to the plane sp2.
During sp hybridization, the s and p orbitals overlap. An angle of 180° arises between the two equivalent hybrid orbitals that are formed, while the two p-orbitals of each atom remain unchanged.
Allotropy of carbon. Diamond and graphite
In a graphite crystal, carbon atoms are located in parallel planes, occupying the vertices of regular hexagons. Each carbon atom is connected to three neighboring sp 2 hybrid bonds. The connection between parallel planes is carried out due to van der Waals forces. The free p-orbitals of each atom are directed perpendicular to the planes of covalent bonds. Their overlap explains the additional π bond between the carbon atoms. Thus, from the valence state in which the carbon atoms in a substance are located determines the properties of this substance.
Chemical properties of carbon
The most characteristic oxidation states are: +4, +2.
At low temperatures carbon is inert, but when heated its activity increases.
Carbon as a reducing agent:
- with oxygen
C 0 + O 2 – t° = CO 2 carbon dioxide
with a lack of oxygen - incomplete combustion:
2C 0 + O 2 – t° = 2C +2 O carbon monoxide
- with fluorine
C + 2F 2 = CF 4
- with water vapor
C 0 + H 2 O – 1200° = C +2 O + H 2 water gas
- with metal oxides. This is how metal is smelted from ore.
C 0 + 2CuO – t° = 2Cu + C +4 O 2
- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) = C +4 O 2 + 2SO 2 + 2H 2 O
C 0 + 4HNO 3 (conc.) = C +4 O 2 + 4NO 2 + 2H 2 O
- forms carbon disulfide with sulfur:
C + 2S 2 = CS 2.
Carbon as an oxidizing agent:
- forms carbides with some metals
4Al + 3C 0 = Al 4 C 3
Ca + 2C 0 = CaC 2 -4
- with hydrogen - methane (as well as a huge number of organic compounds)
C0 + 2H2 = CH4
— with silicon, forms carborundum (at 2000 °C in an electric furnace):
Finding carbon in nature
Free carbon occurs in the form of diamond and graphite. In the form of compounds, carbon is found in minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 *CaCO 3; hydrocarbonates - Mg(HCO 3) 2 and Ca(HCO 3) 2, CO 2 is part of the air; Carbon is the main component of natural organic compounds - gas, oil, coal, peat, and is part of organic substances, proteins, fats, carbohydrates, amino acids that make up living organisms.
Inorganic carbon compounds
Neither C 4+ nor C 4- ions are formed during any conventional chemical processes: carbon compounds contain covalent bonds of different polarities.
Carbon monoxide CO
Carbon monoxide; colorless, odorless, slightly soluble in water, soluble in organic solvents, toxic, boiling point = -192°C; t pl. = -205°C.
Receipt
1) In industry (in gas generators):
C + O 2 = CO 2
2) In the laboratory - thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):
HCOOH = H2O + CO
H 2 C 2 O 4 = CO + CO 2 + H 2 O
Chemical properties
Under normal conditions, CO is inert; when heated - a reducing agent; non-salt-forming oxide.
1) with oxygen
2C +2 O + O 2 = 2C +4 O 2
2) with metal oxides
C +2 O + CuO = Cu + C +4 O 2
3) with chlorine (in the light)
CO + Cl 2 – hn = COCl 2 (phosgene)
4) reacts with alkali melts (under pressure)
CO + NaOH = HCOONa (sodium formate)
5) forms carbonyls with transition metals
Ni + 4CO – t° = Ni(CO) 4
Fe + 5CO – t° = Fe(CO) 5
Carbon monoxide (IV) CO2
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.
Receipt
- Thermal decomposition of carbonic acid salts (carbonates). Limestone firing:
CaCO 3 – t° = CaO + CO 2
- The action of strong acids on carbonates and bicarbonates:
CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2
NaHCO 3 + HCl = NaCl + H 2 O + CO 2
ChemicalpropertiesCO2
Acid oxide: Reacts with basic oxides and bases to form carbonic acid salts
Na 2 O + CO 2 = Na 2 CO 3
2NaOH + CO 2 = Na 2 CO 3 + H 2 O
NaOH + CO 2 = NaHCO 3
At elevated temperatures may exhibit oxidizing properties
C +4 O 2 + 2Mg – t° = 2Mg +2 O + C 0
Qualitative reaction
Cloudiness of lime water:
Ca(OH) 2 + CO 2 = CaCO 3 ¯ (white precipitate) + H 2 O
It disappears when CO 2 is passed through lime water for a long time, because insoluble calcium carbonate turns into soluble bicarbonate:
CaCO 3 + H 2 O + CO 2 = Ca(HCO 3) 2
Carbonic acid and itssalt
H 2CO 3 - A weak acid, it exists only in aqueous solution:
CO 2 + H 2 O ↔ H 2 CO 3
Dibasic:
H 2 CO 3 ↔ H + + HCO 3 - Acid salts - bicarbonates, bicarbonates
HCO 3 - ↔ H + + CO 3 2- Medium salts - carbonates
All properties of acids are characteristic.
Carbonates and bicarbonates can transform into each other:
2NaHCO 3 – t° = Na 2 CO 3 + H 2 O + CO 2
Na 2 CO 3 + H 2 O + CO 2 = 2NaHCO 3
Metal carbonates (except alkali metals) decarboxylate when heated to form an oxide:
CuCO 3 – t° = CuO + CO 2
Qualitative reaction- “boiling” under the influence of a strong acid:
Na 2 CO 3 + 2HCl = 2NaCl + H 2 O + CO 2
CO 3 2- + 2H + = H 2 O + CO 2
Carbides
Calcium carbide:
CaO + 3 C = CaC 2 + CO
CaC 2 + 2 H 2 O = Ca(OH) 2 + C 2 H 2.
Acetylene is released when zinc, cadmium, lanthanum and cerium carbides react with water:
2 LaC 2 + 6 H 2 O = 2La(OH) 3 + 2 C 2 H 2 + H 2.
Be 2 C and Al 4 C 3 decompose with water to form methane:
Al 4 C 3 + 12 H 2 O = 4 Al(OH) 3 = 3 CH 4.
In technology, titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum - as an abrasive and material for heaters) are used.
Cyanide
obtained by heating soda in an atmosphere of ammonia and carbon monoxide:
Na 2 CO 3 + 2 NH 3 + 3 CO = 2 NaCN + 2 H 2 O + H 2 + 2 CO 2
Hydrocyanic acid HCN is an important product of the chemical industry and is widely used in organic synthesis. Its global production reaches 200 thousand tons per year. The electronic structure of the cyanide anion is similar to carbon monoxide (II); such particles are called isoelectronic:
C = O: [:C = N:] –
Cyanides (0.1-0.2% aqueous solution) are used in gold mining:
2 Au + 4 KCN + H 2 O + 0.5 O 2 = 2 K + 2 KOH.
When boiling solutions of cyanide with sulfur or melting solids, they form thiocyanates:
KCN + S = KSCN.
When cyanides of low-active metals are heated, cyanide is obtained: Hg(CN) 2 = Hg + (CN) 2. Cyanide solutions are oxidized to cyanates:
2 KCN + O 2 = 2 KOCN.
Cyanic acid exists in two forms:
H-N=C=O; H-O-C = N:
In 1828, Friedrich Wöhler (1800-1882) obtained urea from ammonium cyanate: NH 4 OCN = CO(NH 2) 2 by evaporating an aqueous solution.
This event is usually regarded as the victory of synthetic chemistry over "vitalistic theory".
There is an isomer of cyanic acid - explosive acid
H-O-N=C.
Its salts (mercuric fulminate Hg(ONC) 2) are used in impact igniters.
Synthesis urea(urea):
CO 2 + 2 NH 3 = CO(NH 2) 2 + H 2 O. At 130 0 C and 100 atm.
Urea is a carbonic acid amide; there is also its “nitrogen analogue” – guanidine.
Carbonates
The most important inorganic carbon compounds are salts of carbonic acid (carbonates). H 2 CO 3 is a weak acid (K 1 = 1.3 10 -4; K 2 = 5 10 -11). Carbonate buffer supports carbon dioxide balance in the atmosphere. The world's oceans have enormous buffer capacity because they are an open system. The main buffer reaction is the equilibrium during the dissociation of carbonic acid:
H 2 CO 3 ↔ H + + HCO 3 - .
When acidity decreases, additional absorption of carbon dioxide from the atmosphere occurs with the formation of acid:
CO 2 + H 2 O ↔ H 2 CO 3 .
As acidity increases, carbonate rocks (shells, chalk and limestone sediments in the ocean) dissolve; this compensates for the loss of hydrocarbonate ions:
H + + CO 3 2- ↔ HCO 3 —
CaCO 3 (solid) ↔ Ca 2+ + CO 3 2-
Solid carbonates turn into soluble bicarbonates. It is this process of chemical dissolution of excess carbon dioxide that counteracts the “greenhouse effect” - global warming due to the absorption of thermal radiation from the Earth by carbon dioxide. About a third of the world's production of soda (sodium carbonate Na 2 CO 3) is used in glass production.