MOU "Nikiforovskaya average comprehensive school№1"

Carbon and its main inorganic compounds

Essay

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 - chemical element IV group periodic system Mendeleev: 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 a fire glass sunbeams. 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.

ChapterI. 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 does not conduct well 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 physical properties carbine can vary widely. 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 is made up 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 close 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 called absorption by the surface. solids 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.

Carbon is capable of forming several allotropic modifications. These are diamond (the most inert allotropic modification), graphite, fullerene and carbine.

Charcoal and soot are amorphous carbon. Carbon in this state does not have an ordered structure and actually consists of the smallest fragments of graphite layers. Amorphous carbon treated with hot water vapor is called activated carbon. 1 gram of activated carbon, due to the presence of many pores in it, has a total surface of more than three hundred square meters! Due to its ability to absorb various substances, activated carbon is widely used as a filter filler, as well as an enterosorbent in various types poisoning.

From a chemical point of view, amorphous carbon is its most active form, graphite exhibits medium activity, and diamond is an extremely inert substance. For this reason, discussed below Chemical properties carbon should primarily be attributed to amorphous carbon.

Reducing properties of carbon

As a reducing agent, carbon reacts with non-metals such as oxygen, halogens, and sulfur.

Depending on the excess or lack of oxygen during the combustion of coal, carbon monoxide CO or carbon dioxide CO2:

When carbon reacts with fluorine, carbon tetrafluoride is formed:

When carbon is heated with sulfur, carbon disulfide CS 2 is formed:

Carbon is capable of reducing metals after aluminum in the activity series from their oxides. For example:

Carbon also reacts with oxides of active metals, however, in this case, as a rule, not the reduction of the metal is observed, but the formation of its carbide:

Interaction of carbon with non-metal oxides

Carbon enters into a co-proportionation reaction with carbon dioxide CO 2:

One of the most important processes from an industrial point of view is the so-called steam reforming of coal. The process is carried out by passing water vapor through hot coal. In this case, the following reaction takes place:

At high temperatures, carbon is able to reduce even such an inert compound as silicon dioxide. In this case, depending on the conditions, the formation of silicon or silicon carbide is possible ( carborundum):

Also, carbon as a reducing agent reacts with oxidizing acids, in particular, concentrated sulfuric and nitric acid:

Oxidizing properties of carbon

The chemical element carbon is not highly electronegative, so the simple substances it forms rarely exhibit oxidizing properties with respect to other non-metals.

An example of such reactions is the interaction of amorphous carbon with hydrogen when heated in the presence of a catalyst:

as well as with silicon at a temperature of 1200-1300 about C:

Carbon exhibits oxidizing properties in relation to metals. Carbon is able to react with active metals and some metals of intermediate activity. Reactions proceed when heated:

Active metal carbides are hydrolyzed by water:

as well as solutions of non-oxidizing acids:

In this case, hydrocarbons are formed containing carbon in the same oxidation state as in the original carbide.

Chemical properties of silicon

Silicon can exist, as well as carbon in the crystalline and amorphous state, and, just as in the case of carbon, amorphous silicon is significantly more chemically active than crystalline silicon.

Sometimes amorphous and crystalline silicon is called its allotropic modifications, which, strictly speaking, is not entirely true. Amorphous silicon is essentially a conglomerate of the smallest particles of crystalline silicon randomly arranged relative to each other.

Interaction of silicon with simple substances

non-metals

At normal conditions Silicon, due to its inertness, reacts only with fluorine:

Silicon reacts with chlorine, bromine and iodine only when heated. It is characteristic that, depending on the activity of the halogen, a correspondingly different temperature is required:

So with chlorine, the reaction proceeds at 340-420 o C:

With bromine - 620-700 o C:

With iodine - 750-810 o C:

All silicon halides are easily hydrolyzed by water:

as well as alkali solutions:

The reaction of silicon with oxygen proceeds, however, it requires very strong heating (1200-1300 ° C) due to the fact that a strong oxide film makes interaction difficult:

At a temperature of 1200-1500 ° C, silicon slowly interacts with carbon in the form of graphite to form carborundum SiC - a substance with an atomic crystal lattice similar to diamond and almost not inferior to it in strength:

Silicon does not react with hydrogen.

metals

Due to its low electronegativity, silicon can exhibit oxidizing properties only with respect to metals. Of the metals, silicon reacts with active (alkaline and alkaline earth), as well as many metals of medium activity. As a result of this interaction, silicides are formed:

Silicides of active metals are easily hydrolyzed with water or dilute solutions of non-oxidizing acids:

In this case, the gas silane SiH 4 is formed - an analogue of methane CH 4.

Interaction of silicon with complex substances

Silicon does not react with water even when boiling, however, amorphous silicon interacts with superheated water vapor at a temperature of about 400-500 ° C. This produces hydrogen and silicon dioxide:

Of all acids, silicon (in its amorphous state) reacts only with concentrated hydrofluoric acid:

Silicon dissolves in concentrated alkali solutions. The reaction is accompanied by the evolution of hydrogen.

Carbon in the periodic table of elements is located in the second period in the IVA group. Electronic configuration of the carbon atom ls 2 2s 2 2p 2 . When it is excited, an electronic state is easily achieved in which there are four unpaired electrons in the four outer atomic orbitals:

This explains why carbon in compounds is usually tetravalent. The equality of the number of valence electrons in the carbon atom to the number of valence orbitals, as well as the unique ratio of the nuclear charge and the radius of the atom, give it the ability to equally easily add and donate electrons, depending on the properties of the partner (Sec. 9.3.1). As a result, carbon is characterized by various oxidation states from -4 to +4 and the ease of its hybridization. atomic orbitals type sp3,sp2 And sp 1 during the formation of chemical bonds (section 2.1.3):

All this gives carbon the ability to form single, double and triple bonds not only among themselves, but also with atoms of other organogen elements. The molecules formed in this case can have a linear, branched and cyclic structure.

Due to the mobility of common electrons - MO formed with the participation of carbon atoms, they are shifted towards the atom of a more electronegative element (inductive effect), which leads to the polarity of not only this bond, but the molecule as a whole. However, carbon, due to the average value of electronegativity (0E0 = 2.5), forms weakly polar bonds with atoms of other organogen elements (Table 12.1). In the presence of systems of conjugated bonds in molecules (Sec. 2.1.3), mobile electrons (MOs) and unshared electron pairs are delocalized with the alignment of electron density and bond lengths in these systems.

From the standpoint of the reactivity of compounds, the polarizability of bonds plays an important role (Sec. 2.1.3). The greater the polarizability of a bond, the higher its reactivity. The dependence of the polarizability of carbon-containing bonds on their nature reflects the following series:

All the considered data on the properties of carbon-containing bonds indicate that carbon in compounds forms, on the one hand, sufficiently strong covalent bonds with each other and with other organogens, and, on the other hand, the common electron pairs of these bonds are quite labile. As a result, both an increase in the reactivity of these bonds and stabilization can occur. It is these features of carbon-containing compounds that make carbon the number one organogen.

Acid-base properties of carbon compounds. Carbon monoxide(4) is an acidic oxide, and its corresponding hydroxide, carbonic acid H2CO3, is a weak acid. The carbon monoxide(4) molecule is non-polar, and therefore it is poorly soluble in water (0.03 mol/l at 298 K). In this case, at first, CO2 H2O hydrate is formed in the solution, in which CO2 is in the cavity of an associate of water molecules, and then this hydrate slowly and reversibly turns into H2CO3. Most of the carbon monoxide (4) dissolved in water is in the form of a hydrate.

In the body, in blood erythrocytes, under the action of the enzyme carboanhydrase, the equilibrium between CO2 H2O and H2CO3 hydrate is established very quickly. This makes it possible to neglect the presence of CO2 in the form of a hydrate in the erythrocyte, but not in the blood plasma, where there is no carbonic anhydrase. The resulting H2CO3 dissociates under physiological conditions to a bicarbonate anion, and in a more alkaline environment to a carbonate anion:

Carbonic acid exists only in solution. It forms two series of salts - bicarbonates (NaHCO3, Ca(HC0 3) 2) and carbonates (Na2CO3, CaCO3). Bicarbonates are more soluble in water than carbonates. In aqueous solutions of salt carbonic acid, especially carbonates, are easily hydrolyzed by the anion, creating an alkaline environment:

Substances such as NaHC03 baking soda; chalk CaCO3, white magnesia 4MgC03 * Mg (OH) 2 * H2O, hydrolyzed with formation alkaline environment, are used as antacids (acid neutralizing) agents to reduce the high acidity of gastric juice:

The combination of carbonic acid and bicarbonate ion (Н2СО3, НСО3(-)) forms a bicarbonate buffer system (Section 8.5) - a glorious buffer system of blood plasma, which ensures the constancy of blood pH at pH = 7.40 ± 0.05.

The presence of calcium and magnesium bicarbonates in natural waters determines their temporary hardness. When such water is boiled, its hardness is eliminated. This is due to the hydrolysis of the HCO3 (-) anion), thermal decomposition of carbonic acid and precipitation of calcium and magnesium cations in the form of insoluble CaCO 3 and Mg (OH) 2 compounds:

The formation of Mg(OH) 2 is caused by complete hydrolysis of the magnesium cation, which occurs under these conditions due to the lower solubility of Mg(0H)2 compared to MgC0 3 .

In biomedical practice, in addition to carbonic acid, one has to deal with other carbon-containing acids. This is primarily a large variety of different organic acids, as well as hydrocyanic acid HCN. From the standpoint of acidic properties, the strength of these acids is different:

These differences are due mutual influence atoms in a molecule, the nature of the dissociating bond, and the stability of the anion, i.e., its ability to charge delocalization.

Hydrocyanic acid, or hydrogen cyanide, HCN - a colorless, volatile liquid (T bale = 26 °C) with the smell of bitter almonds, miscible with water in any ratio. In aqueous solutions, it behaves like a very weak acid, the salts of which are called cyanides. Cyanides of alkali and alkaline earth metals are soluble in water, while they are hydrolyzed by the anion, due to which they aqueous solutions smell of hydrocyanic acid (smell of bitter almonds) and have a pH >12:

With prolonged exposure to CO2 contained in the air, cyanides decompose with the release of hydrocyanic acid:

As a result of this reaction, potassium cyanide (potassium cyanide) and its solutions lose their toxicity during long-term storage. The cyanide anion is one of the strongest inorganic poisons, since it is an active ligand and easily forms stable complex compounds with enzymes containing Fe3+ and Сu2(+) as complexing ions (Sec. 10.4).

redox properties. Since carbon in compounds can exhibit any oxidation state from -4 to +4, during the reaction, free carbon can both donate and add electrons, acting as a reducing agent or oxidizing agent, respectively, depending on the properties of the second reagent:

When strong oxidizing agents interact with organic substances, incomplete or complete oxidation of the carbon atoms of these compounds can occur.

Under conditions of anaerobic oxidation, with a lack or absence of oxygen, carbon atoms of an organic compound, depending on the content of oxygen atoms in these compounds and external conditions, can turn into CO 2, CO, C and even CH 4, and other organogens turn into H2O, NH3 and H2S .

Complete oxidation in the body organic compounds oxygen in the presence of oxidase enzymes (aerobic oxidation) is described by the equation:

From the above equations of oxidation reactions, it can be seen that in organic compounds, only carbon atoms change the oxidation state, while the atoms of other organogens retain their oxidation state.

In hydrogenation reactions, i.e., the addition of hydrogen (reductant) to a multiple bond, the carbon atoms that form it lower their oxidation state (act as oxidizing agents):

Organic substitution reactions with the appearance of a new intercarbon bond, for example, in the Wurtz reaction, are also redox reactions in which carbon atoms act as oxidizing agents and metal atoms as reducing agents:

Similar is observed in the formation reactions organometallic compounds:

At the same time, in alkylation reactions with the formation of a new intercarbon bond, the role of an oxidizing agent and a reducing agent is played by the carbon atoms of the substrate and the reagent, respectively:

As a result of reactions of addition of a polar reagent to a substrate via a multiple intercarbon bond, one of the carbon atoms lowers the degree of oxidation, showing the properties of an oxidizing agent, and the other increases the degree of oxidation, acting as a reducing agent:

In these cases, the reaction of intramolecular oxidation-reduction of carbon atoms of the substrate takes place, i.e., the process dismutations, under the action of a reagent that does not exhibit redox properties.

Typical reactions of intramolecular dismutation of organic compounds at the expense of their carbon atoms are the decarboxylation reactions of amino acids or keto acids, as well as the reactions of rearrangement and isomerization of organic compounds, which were considered in Sec. 9.3. The given examples of organic reactions, as well as the reactions from Sec. 9.3 convincingly indicate that carbon atoms in organic compounds can be both oxidizing and reducing agents.

A carbon atom in a compound- an oxidizing agent, if as a result of the reaction the number of its bonds with atoms of less electronegative elements (hydrogen, metals) increases, because, by attracting the common electrons of these bonds, the carbon atom in question lowers its oxidation state.

A carbon atom in a compound- a reducing agent, if as a result of the reaction the number of its bonds with atoms of more electronegative elements increases(C, O, N, S), because, by pushing away the common electrons of these bonds, the carbon atom in question increases its oxidation state.

Thus, many reactions in organic chemistry, due to the redox duality of carbon atoms, are redox reactions. However, in contrast to these reactions inorganic chemistry, the redistribution of electrons between the oxidizing agent and the reducing agent in organic compounds can only be accompanied by a shift of the common electron pair of the chemical bond to the atom that acts as the oxidizing agent. Wherein this connection can be preserved, but in cases of its strong polarization, it can break.

Complexing properties of carbon compounds. The carbon atom in the compounds does not have unshared electron pairs, and therefore only carbon compounds containing multiple bonds with its participation can act as ligands. Particularly active in the processes of complex formation are the electrons of the triple polar bond of carbon monoxide (2) and the anion of hydrocyanic acid.

In a carbon monoxide(2) molecule, the carbon and oxygen atoms form one and one bond due to the mutual overlap of their two 2p atomic orbitals by the exchange mechanism. The third bond, i.e., one more bond, is formed by the donor-acceptor mechanism. The acceptor is the free 2p atomic orbital of the carbon atom, and the donor is the oxygen atom, which provides a lone pair of electrons from the 2p orbital:

The increased bond multiplicity provides this molecule with high stability and inertness under normal conditions in terms of acid-base (CO - non-salt-forming oxide) and redox properties (CO - reducing agent at T > 1000 K). At the same time, it makes it an active ligand in complex formation reactions with atoms and cations of d-metals, primarily with iron, with which it forms iron pentacarbonyl, a volatile poisonous liquid:

Educational Ability complex compounds with d-metal cations is the cause of the toxicity of carbon monoxide (H) for living systems (Sec. 10.4) due to leakage reversible reactions with hemoglobin and oxyhemoglobin containing Fe 2+ cation to form carboxyhemoglobin:

These equilibria are shifted towards the formation of carboxyhemoglobin HHbCO, the stability of which is 210 times greater than that of oxyhemoglobin HHbO2. This leads to the accumulation of carboxyhemoglobin in the blood and, consequently, to a decrease in its ability to carry oxygen.

Hydrocyanic acid anion CN- also contains easily polarizable - electrons, because of which it effectively forms complexes with d-metals, including life metals that are part of enzymes. Therefore, cyanides are highly toxic compounds (Section 10.4).

The carbon cycle in nature. The carbon cycle in nature is mainly based on the reactions of oxidation and reduction of carbon (Fig. 12.3).

Plants assimilate (1) carbon monoxide (4) from the atmosphere and hydrosphere. Part of the plant mass is consumed (2) by man and animals. The respiration of animals and the rotting of their remains (3), as well as the respiration of plants, the rotting of dead plants and the burning of wood (4) return CO2 to the atmosphere and hydrosphere. The process of mineralization of the remains of plants (5) and animals (6) with the formation of peat, fossil coals, oil, gas leads to the transition of carbon into natural resources. Acid-base reactions (7) proceeding between CO2 and various rocks with the formation of carbonates (medium, acid and basic) act in the same direction:

This inorganic part of the cycle leads to CO2 losses in the atmosphere and hydrosphere. Human activity in burning and processing coal, oil, gas (8), firewood (4), on the contrary, enriches the environment with carbon monoxide (4). For a long time, it was believed that photosynthesis kept the concentration of CO2 in the atmosphere constant. However, at present, the increase in the CO2 content in the atmosphere due to human activities is not compensated by its natural decrease. Total income CO2 in the atmosphere rises in geometric progression by 4-5% per year. According to calculations, in 2000 the content of CO2 in the atmosphere will reach approximately 0.04% instead of 0.03% (1990).

After considering the properties and characteristics of carbon-containing compounds, the leading role of carbon should be emphasized once again.

Rice. 12.3. The carbon cycle in nature

organogen No. 1: firstly, carbon atoms form the skeleton of molecules of organic compounds; secondly, carbon atoms play a key role in redox processes, since among the atoms of all organogens, it is for carbon that redox duality is most characteristic. For more information about the properties of organic compounds, see module IV "Fundamentals of Bioorganic Chemistry".

general characteristics and the biological role of p-elements of group IVA. The electronic analogues of carbon are the IVA group elements: silicon Si, germanium Ge, tin Sn and lead Pb (see Table 1.2). The atomic radii of these elements naturally increase with increasing atomic number, while their ionization energy and electronegativity naturally decrease in this case (Sec. 1.3). Therefore, the first two elements of the group: carbon and silicon are typical non-metals, and germanium, tin, lead are metals, since they are most characterized by the return of electrons. In the series Ge - Sn - Pb, the metallic properties are enhanced.

From the standpoint of redox properties, the elements C, Si, Ge, Sn and Pb under normal conditions are quite stable with respect to air and water (metals Sn and Pb - due to the formation of an oxide film on the surface). At the same time, lead(4) compounds are strong oxidizing agents:

The complexing properties are most characteristic of lead, since its Pb 2+ cations are strong complexing agents compared to the cations of the other p-elements of group IVA. Lead cations form strong complexes with bioligands.

Elements of the IVA group differ sharply both in content in the body and in their biological role. Carbon plays a fundamental role in the life of the organism, where its content is about 20%. The content in the body of the remaining elements of the IVA group is in the range of 10 -6 -10 -3%. At the same time, if silicon and germanium undoubtedly play important role in the life of the organism, then tin and especially lead are toxic. Thus, with an increase in the atomic mass of group IVA elements, the toxicity of their compounds increases.

Dust, consisting of particles of coal or silicon dioxide SiO2, when systematically exposed to the lungs, causes diseases - pneumoconiosis. In the case of coal dust, this is anthracosis, an occupational disease of miners. Silicosis occurs when dust containing Si02 is inhaled. The mechanism of development of pneumoconiosis has not yet been established. It is assumed that upon prolonged contact of silicate grains with biological fluids, polysilicic acid Si02 yH2O is formed in a gel-like state, the deposition of which in cells leads to their death.

The toxic effect of lead has been known to mankind for a very long time. The use of lead for the manufacture of dishes and water pipes led to mass poisoning of people. Currently, lead continues to be one of the main pollutants environment, since the release of lead compounds into the atmosphere is over 400,000 tons annually. Lead accumulates mainly in the skeleton in the form of the poorly soluble phosphate Pb3(PO4)2, and during bone demineralization it has a regular toxic effect on the body. Therefore, lead is classified as a cumulative poison. The toxicity of lead compounds is associated primarily with its complexing properties and high affinity for bioligands, especially those containing sulfhydryl groups (-SH):

The formation of complex compounds of lead ions with proteins, phospholipids and nucleotides leads to their denaturation. Lead ions often inhibit EM 2+ metalloenzymes, displacing life metal cations from them:

Lead and its compounds are poisons that act primarily on nervous system, blood vessels and blood. At the same time, lead compounds affect protein synthesis, the energy balance of cells and their genetic apparatus.

In medicine, they are used as astringent external antiseptics: lead acetate Pb (CH3COO) 2 ZH2O (lead lotions) and lead (2) oxide PbO (lead plaster). Lead ions of these compounds react with proteins (albumins) of the cytoplasm of microbial cells and tissues, forming gel-like albuminates. The formation of gels kills microbes and, in addition, makes it difficult for them to penetrate into tissue cells, which reduces the local inflammatory response.

Important area practical application latest discoveries in the field of physics, chemistry and even astronomy - the creation and study of new materials with unusual, sometimes unique properties. About the directions in which these works are being carried out and what scientists have already managed to achieve, we will tell in a series of articles created in partnership with the Ural Federal University. Our first text is devoted to unusual materials that can be obtained from the most common substance - carbon.

If you ask a chemist which element is the most important, you can get a lot of different answers. Someone will say about hydrogen - the most common element in the universe, someone about oxygen - the most common element in the earth's crust. But most often you will hear the answer "carbon" - it is he who underlies all organic substances, from DNA and proteins to alcohols and hydrocarbons.

Our article is devoted to the diverse appearances of this element: it turns out that dozens of different materials can be built from only its atoms - from graphite to diamond, from carbyne to fullerenes and nanotubes. Although they all consist of exactly the same carbon atoms, their properties are radically different - and the arrangement of atoms in the material plays a major role in this.

Graphite

Most often in nature, pure carbon can be found in the form of graphite - a soft black material that easily exfoliates and seems to be slippery to the touch. Many may recall that pencil leads are made from graphite - but this is not always true. Often the lead is made from a composite of graphite chips and glue, but there are also completely graphite pencils. Interestingly, more than one-twentieth of the world's production of natural graphite is spent on pencils.

What is special about graphite? First of all, it conducts electricity well - although carbon itself is not like other metals. If we take a graphite plate, it turns out that the conductivity along its plane is about a hundred times greater than in the transverse direction. This is directly related to how the carbon atoms in the material are organized.

If we look at the structure of graphite, we will see that it consists of separate layers one atom thick. Each of the layers is a grid of hexagons, resembling a honeycomb. The carbon atoms within the layer are linked by covalent chemical bonds. Moreover, some of the electrons that provide the chemical bond are "smeared" over the entire plane. The ease of their movement determines the high conductivity of graphite along the plane of carbon flakes.

Separate layers are interconnected due to van der Waals forces - they are much weaker than the usual chemical bond, but sufficient to ensure that the graphite crystal does not delaminate spontaneously. Such a discrepancy leads to the fact that it is much more difficult for electrons to move perpendicular to the planes - the electrical resistance increases by 100 times.

Due to its electrical conductivity, as well as the ability to embed atoms of other elements between layers, graphite is used as anodes for lithium-ion batteries and other current sources. Graphite electrodes are essential for the production of metallic aluminum - and even trolleybuses use graphite sliding contacts of current collectors.

In addition, graphite is a diamagnet with one of the highest susceptibilities per unit mass. This means that if you place a piece of graphite in a magnetic field, then it will try in every possible way to push this field out of itself - to the point that graphite can levitate over a sufficiently strong magnet.

And the last important property of graphite is its incredible refractoriness. The most refractory substance today is one of the hafnium carbides with a melting point of about 4000 degrees Celsius. However, if you try to melt graphite, then at pressures of about one hundred atmospheres, it will retain hardness up to 4800 degrees Celsius (at atmospheric pressure, graphite sublimates - evaporates, bypassing the liquid phase). As a result, graphite-based materials are used, for example, in rocket nozzle bodies.

Diamond

Many materials under pressure begin to change their atomic structure - a phase transition occurs. Graphite in this sense is no different from other materials. At pressures of one hundred thousand atmospheres and a temperature of 1–2 thousand degrees Celsius, the layers of carbon begin to approach each other, chemical bonds, and once smooth planes become corrugated. A diamond is formed, one of the most beautiful forms of carbon.

The properties of diamond are radically different from those of graphite - it is a hard transparent material. It is extremely difficult to scratch (the owner of 10 on the Mohs hardness scale, this is the maximum hardness). At the same time, the electrical conductivity of diamond and graphite differs by a factor of quintillion (this is a number with 18 zeros).

Diamond in rock

Wikimedia Commons

This determines the use of diamonds: most of the mined and artificial diamonds are used in metalworking and other industries. For example, grinding wheels and cutting tools with diamond powder or coating are widespread. Diamond coatings are used even in surgery - for scalpels. The use of these stones in the jewelry industry is well known to everyone.

Amazing hardness is also used in scientific research - it is with the help of high-quality diamonds that laboratories study materials at pressures of millions of atmospheres. You can read more about this in our material "".

Graphene

Instead of compressing and heating graphite, we, following Andrey Geim and Konstantin Novoselov, will stick a piece of adhesive tape to the graphite crystal. Then peel it off - a thin layer of graphite will remain on the adhesive tape. Let's repeat this operation one more time - apply the tape to a thin layer and peel it off again. The layer will become even thinner. By repeating the procedure a few more times, we get graphene - the material for which the aforementioned British physicists received the Nobel Prize in 2010.

Graphene is a flat monolayer of carbon atoms, completely identical to the atomic layers of graphite. Its popularity is due to the unusual behavior of the electrons in it. They move as if they have no mass at all. In reality, of course, the mass of electrons remains the same as in any substance. The carbon atoms of the graphene frame are to blame for everything, attracting charged particles and forming a special periodic field.

Graphene based device. In the background of the photo are gold contacts, above them is graphene, above is a thin layer of polymethyl methacrylate

Engineering at Cambridge / flickr.com

The consequence of this behavior was the high mobility of electrons - they move in graphene much faster than in silicon. For this reason, many scientists hope that graphene will become the basis of the electronics of the future.

Interestingly, graphene has carbon counterparts - and. The first of these consists of slightly distorted pentagonal sections and, unlike graphene, is a poor conductor of electricity. Fagraphene consists of five-, six- and heptagonal sections. If the properties of graphene are the same in all directions, then phagraphene will have a pronounced anisotropy of properties. Both of these materials were predicted theoretically, but do not yet exist in reality.

A fragment of a silicon single crystal (in the foreground) on a vertical array of carbon nanotubes

carbon nanotubes

Imagine that you rolled a small piece of graphene sheet into a tube and glued the ends together. The result was a hollow structure, consisting of the same hexagons of carbon atoms as graphene and graphite - a carbon nanotube. This material is in many ways related to graphene - it has high mechanical strength (once it was proposed to build an elevator into space from carbon nanotubes), high electron mobility.

However, there is one unusual feature. The graphene sheet can be twisted parallel to an imaginary edge (the side of one of the hexagons) or at an angle. It turns out that how we twist a carbon nanotube will greatly affect its electronic properties, namely: it will look more like a semiconductor with a band gap or a metal.

Multilayer carbon nanotube

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When carbon nanotubes were first observed is not known for certain. In the 1950s–1980s, various groups of researchers involved in the catalysis of reactions involving hydrocarbons (for example, methane pyrolysis) paid attention to elongated structures in the soot that coated the catalyst. Now, in order to synthesize carbon nanotubes of only a specific type (of a specific chirality), chemists suggest using special seeds. These are small molecules in the form of rings, which in turn consist of hexagonal benzene rings. You can read about work on their synthesis, for example,.

Like graphene, carbon nanotubes can find great applications in microelectronics. The first transistors based on nanotubes have already been created, which are traditional silicon devices in terms of their properties. In addition, nanotubes formed the basis of the transistor with.

Carbine

Speaking of elongated structures of carbon atoms, one cannot fail to mention carbines. These are linear chains, which, according to theorists, may turn out to be the strongest possible material (we are talking about specific strength). For example, the Young's modulus for carbine is estimated at 10 giganewtons per kilogram. For steel, this figure is 400 times less, for graphene - at least two times less.

Thin thread stretching to the iron particle below - carbine

Wikimedia Commons

Carbynes are of two types, depending on how the bonds between the carbon atoms are arranged. If all the bonds in the chain are the same, then we are talking about cumulene, but if the bonds alternate (single-triple-single-triple, and so on), then we are talking about polyynes. Physicists have shown that carbine thread can be "switched" between these two types by deformation - when stretched, cumulene turns into polyyne. Interestingly, this radically changes electrical properties carbine. If polyyne conducts electricity, then cumulene is a dielectric.

The main difficulty in studying carbynes is that they are very difficult to synthesize. It's chemical active substances and are easily oxidized. Today, chains are only six thousand atoms long. To achieve this, chemists had to grow carbyne inside a carbon nanotube. In addition, the synthesis of carbine will help break the gate size record in a transistor - it can be reduced to one atom.

Fullerenes

Although the hexagon is one of the most stable configurations that carbon atoms can form, there is a whole class of compact objects where regular pentagon from carbon. These objects are called fullerenes.

In 1985, Harold Kroto, Robert Curl, and Richard Smalley investigated carbon vapor and what fragments carbon atoms stick together into when cooled. It turned out that there are two classes of objects in the gas phase. The first one is clusters consisting of 2–25 atoms: chains, rings, and other simple structures. The second is clusters consisting of 40–150 atoms, which have not been observed before. Over the next five years, chemists were able to prove that this second class was a hollow framework of carbon atoms, the most stable of which consisted of 60 atoms and was shaped like a soccer ball. C 60 , or buckminsterfullerene, consisted of twenty hexagonal sections and 12 pentagonal sections fastened together into a sphere.

The discovery of fullerenes aroused great interest among chemists. Subsequently, an unusual class of endofullerenes was synthesized - fullerenes, in the cavity of which there was some foreign atom or a small molecule. For example, just a year ago, a molecule of hydrofluoric acid was introduced into fullerene for the first time, which made it possible to very accurately determine its electronic properties.

Fullerites - fullerene crystals

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In 1991, it turned out that fullerides - fullerene crystals, in which part of the cavities between neighboring polyhedra are occupied by metals - are molecular superconductors with a record high transition temperature for this class, namely 18 kelvin (for K 3 C 60). Later, fullerides were found with an even higher transition temperature - 33 kelvin, Cs 2 RbC 60 . Such properties turned out to be directly related to the electronic structure of matter.

Q-carbon

Among the recently discovered forms of carbon, the so-called Q-carbon can be noted. He was first American Materials Scientists from the University of North Carolina in 2015. Scientists irradiated amorphous carbon with a powerful laser, locally heating the material to 4000 degrees Celsius. As a result, about a quarter of all carbon atoms in the substance took sp 2 hybridization, that is, the same electronic state as in graphite. The remaining Q-carbon atoms retained the hybridization characteristic of diamond.

Q-carbon

Unlike diamond, graphite, and other forms of carbon, Q-carbon is a ferromagnet such as magnetite or iron. At the same time, its Curie temperature was about 220 degrees Celsius - only with such heating did the material lose its magnetic properties. And when Q-carbon was doped with boron, physicists obtained another carbon superconductor, with a transition temperature of about 58 kelvins.

***

Listed are not all known forms of carbon. Moreover, right now theorists and experimenters are creating and studying new carbon materials. In particular, such work is being carried out in the Ural federal university. We turned to Anatoly Fedorovich Zatsepin, Associate Professor and Chief Researcher at the Ural Federal University's Institute of Physics and Technology, to find out how to predict the properties of yet unsynthesized materials and create new forms of carbon.

Anatoly Zatsepin is working on one of six breakthrough scientific projects Ural Federal University "Development of the fundamental foundations of new functional materials based on low-dimensional modifications of carbon”. The work is carried out with academic and industrial partners in Russia and the world.

The project is being implemented by the Institute of Physics and Technology of UrFU, a strategic academic unit (SAU) of the university. The position of the university in Russian and international rankings, especially in the subject.

N+1: The properties of carbon nanomaterials are highly structure dependent and vary widely. Is it possible to somehow predict the properties of a material from its structure in advance?

Anatoly Zatsepin: It is possible to predict, and we are doing it. There are computer simulation methods that perform first-principles calculations ( ab initio) - we lay down a certain structure, model and take all the fundamental characteristics of the atoms that make up this structure. As a result, those properties are obtained that the material or new substance that we are modeling can have. In particular, with regard to carbon, we were able to model new modifications not known to nature. They can be created artificially.

In particular, our laboratory at the Ural Federal University is currently developing, synthesizing and researching the properties of a new type of carbon. It can be called as follows: two-dimensionally ordered linear chain carbon. Such a long name is due to the fact that this material is a so-called 2D structure. These are films composed of separate carbon chains, and within each chain the carbon atoms are in the same " chemical form» - sp 1 -hybridization. This gives completely unusual properties to the material; in sp 1 -carbon chains, the strength exceeds the strength of diamond and other carbon modifications.

When we form films from these chains, we get new material, which has the properties inherent in carbon chains, plus the combination of these ordered chains forms a two-dimensional structure or superlattice on a special substrate. Such a material has great prospects not only due to its mechanical properties. Most importantly, carbon chains in a certain configuration can be closed into a ring, and very interesting properties arise, such as superconductivity, and the magnetic properties of such materials can be better than those of existing ferromagnets.

The challenge remains to actually create them. Our simulation shows the way to go.

How much do the actual and predicted properties of materials differ?

The error always exists, but the fact is that first principles calculations and modeling use the fundamental characteristics of individual atoms - quantum properties. And when structures are formed from these quantum atoms at such a micro- and nanolevel, then errors are associated with existing limitation theory and those models that exist. For example, it is known that the Schrödinger equation can be exactly solved only for the hydrogen atom, while for heavier atoms certain approximations must be used if we are talking about solids or more complex systems.

On the other hand, errors can occur due to computer calculations. With all this, gross errors are excluded, and accuracy is quite enough to predict one or another property or effect that will be inherent in a given material.

How many materials can be predicted in such ways?

When it comes to carbon materials, there are many variations, and I am sure that much has not yet been explored and discovered. UrFU has everything for researching new carbon materials, and there is a lot of work ahead.

We also deal with other objects, for example, silicon materials for microelectronics. Silicon and carbon are, by the way, analogues, they are in the same group in the periodic table.

Vladimir Korolev

Structure of a diamond (A) and graphite (b)

Carbon(Latin carboneum) - C, a chemical element of the IV group of the periodic system of Mendeleev, atomic number 6, atomic mass 12.011. It occurs in nature in the form of crystals of diamond, graphite or fullerene and other forms and is part of organic (coal, oil, animal and plant organisms, etc.) and inorganic substances (limestone, baking soda, etc.). Carbon is widespread, but its content in the earth's crust is only 0.19%.

Carbon is widely used in the form of simple substances. In addition to precious diamonds, which are the subject of jewelry, great importance have industrial diamonds - for the manufacture of grinding and cutting tools. Charcoal and other amorphous forms of carbon are used for decolorization, purification, adsorption of gases, in areas of technology where adsorbents with a developed surface are required. Carbides, compounds of carbon with metals, as well as with boron and silicon (for example, Al 4 C 3, SiC, B 4 C) are highly hard and are used to make abrasive and cutting tools. Carbon is present in steels and alloys in the elemental state and in the form of carbides. Saturation of the surface of steel castings with carbon at high temperature (carburizing) significantly increases the surface hardness and wear resistance.

Historical reference

Graphite, diamond and amorphous carbon have been known since antiquity. It has long been known that other material can be marked with graphite, and the very name "graphite", which comes from the Greek word meaning "to write", was proposed by A. Werner in 1789. However, the history of graphite is confused, often substances with similar external physical properties were mistaken for it. , such as molybdenite (molybdenum sulfide), at one time considered graphite. Among other names of graphite, "black lead", "iron carbide", "silver lead" are known.

In 1779, K. Scheele found that graphite can be oxidized with air to form carbon dioxide. For the first time, diamonds found use in India, and in Brazil, precious stones acquired commercial importance in 1725; deposits in South Africa were discovered in 1867.

In the 20th century The main diamond producers are South Africa, Zaire, Botswana, Namibia, Angola, Sierra Leone, Tanzania and Russia. Artificial diamonds, the technology of which was created in 1970, are produced for industrial purposes.

Properties

Four crystalline modifications of carbon are known:

• graphite,
• diamond,
• carbine,
• lonsdaleite.

Graphite- gray-black, opaque, greasy to the touch, scaly, very soft mass with a metallic sheen. At room temperature and normal pressure (0.1 MN/m2, or 1 kgf/cm2), graphite is thermodynamically stable.

Diamond- very solid, crystalline substance. Crystals have a cubic face-centered lattice. At room temperature and normal pressure, diamond is metastable. A noticeable transformation of diamond into graphite is observed at temperatures above 1400°C in vacuum or in an inert atmosphere. At atmospheric pressure and a temperature of about 3700 ° C, graphite sublimates.

Liquid carbon can be obtained at pressures above 10.5 MN/m2 (105 kgf/cm2) and temperatures above 3700°C. Solid carbon (coke, soot, charcoal) is also characterized by a state with a disordered structure - the so-called "amorphous" carbon, which is not an independent modification; its structure is based on the structure of fine-grained graphite. Heating some varieties of "amorphous" carbon above 1500-1600 ° C without air causes their transformation into graphite.

The physical properties of "amorphous" carbon depend very strongly on the dispersion of particles and the presence of impurities. Density, heat capacity, thermal conductivity and electrical conductivity of "amorphous" carbon is always higher than graphite.

Carbine obtained artificially. It is a finely crystalline powder of black color (density 1.9-2 g / cm 3). Built from long chains of atoms WITH laid parallel to each other.

Lonsdaleite found in meteorites and obtained artificially; its structure and properties have not been finally established.

Properties of carbon
atomic number		6
Atomic mass		12,011
Isotopes:	stable	12, 13
	unstable	8, 9, 10, 11, 14, 15, 16, 17, 18, 19, 20, 21, 22
Melting temperature		3550°C
Boiling temperature		4200°C
Density		1.9-2.3 g / cm 3 (graphite) 3.5-3.53 g / cm 3 (diamond)
Hardness (Mohs)		1-2
Content in the earth's crust (mass.)		0,19%
Oxidation states		-4; +2; +4

Alloys

Steel

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

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

Carbon is the basis of all organic substances. Every living organism is made up largely of carbon. Carbon is the basis of life. The source of carbon for living organisms is usually CO 2 from the atmosphere or water. As a result of photosynthesis, it enters biological food chains in which living things eat each other or the remains of each other and thereby extract carbon to build their own body. The biological cycle of carbon ends either with oxidation and return to the atmosphere, or with disposal in the form of coal or oil.

The use of the radioactive isotope 14 C contributed to the success molecular biology in the study of the mechanisms of protein biosynthesis and the transmission of hereditary information. Determination of the specific activity of 14 C in carbonaceous organic remains makes it possible to judge their age, which is used in paleontology and archeology.

Sources

Chemical elements and materials
Chemical elements	Nitrogen. Argon. Hydrogen. Helium. Iron . Calcium. Oxygen. Silicon. Magnesium. Manganese.