One of the most amazing elements that can form a huge variety of compounds of organic and inorganic nature is carbon. This element is so unusual in its properties that even Mendeleev predicted a great future for it, speaking of features not yet disclosed.
Later this was practically confirmed. It became known that it is the main biogenic element of our planet, which is part of absolutely all living beings. In addition, it can exist in forms that are radically different in all respects, but at the same time consist only of carbon atoms.
In general, this structure has many features, and we will try to deal with them in the course of the article.
Carbon: formula and position in the system of elements
In the periodic system, the element carbon is located in IV (according to the new model in 14) group, the main subgroup. Its atomic number is 6 and its atomic weight is 12.011. The designation of the element with the sign C indicates its name in Latin - carboneum. There are several different forms in which carbon exists. Therefore, its formula is different and depends on the specific modification.
However, there is, of course, a specific designation for writing reaction equations. In general, when talking about a substance in its pure form, the molecular formula of carbon C is adopted, without indexing.
Element Discovery History
By itself, this element has been known since antiquity. After all, one of the most important minerals in nature is coal. Therefore, for the ancient Greeks, Romans and other nationalities, he was not a secret.
In addition to this variety, diamonds and graphite were also used. There were many confusing situations with the latter for a long time, since often, without analysis of the composition, such compounds were taken for graphite, such as:
- silver lead;
- iron carbide;
- molybdenum sulfide.
All of them were painted black and therefore considered to be graphite. Later, this misunderstanding was cleared up, and this form of carbon became itself.
Since 1725, diamonds have become of great commercial importance, and in 1970, the technology of obtaining them artificially was mastered. Since 1779, thanks to the work of Karl Scheele, the chemical properties that carbon exhibits have been studied. This was the beginning of a number of important discoveries in the field of this element and became the basis for clarifying all of its most unique features.
Isotopes of carbon and distribution in nature
Despite the fact that the element under consideration is one of the most important biogenic, its total content in the mass of the earth's crust is 0.15%. This is due to the fact that it is subjected to constant circulation, the natural cycle in nature.
In general, there are several mineral compounds that contain carbon. These are such natural breeds as:
- dolomites and limestones;
- anthracite;
- oil shale;
- natural gas;
- coal;
- oil;
- brown coal;
- peat;
- bitumen.
In addition, we should not forget about living beings, which are just a repository of carbon compounds. After all, they formed proteins, fats, carbohydrates, nucleic acids, which means the most vital structural molecules. In general, in the conversion of dry body weight out of 70 kg, 15 falls on a pure element. And so it is with every person, not to mention animals, plants and other creatures.
If we also consider water, that is, the hydrosphere as a whole and the atmosphere, then there is a carbon-oxygen mixture expressed by the formula CO 2 . Dioxide or carbon dioxide is one of the main gases that make up the air. It is in this form that the mass fraction of carbon is 0.046%. Even more carbon dioxide is dissolved in the waters of the oceans.
The atomic mass of carbon as an element is 12.011. It is known that this value is calculated as the arithmetic mean between the atomic weights of all isotopic species that exist in nature, taking into account their abundance (as a percentage). This is also the case for the substance in question. There are three main isotopes in which carbon is found. It:
- 12 C - its mass fraction in the vast majority is 98.93%;
- 13 C - 1.07%;
- 14 C - radioactive, half-life 5700 years, stable beta emitter.
In the practice of determining the geochronological age of samples, the radioactive isotope 14 C is widely used, which is an indicator due to its long decay period.
Allotropic modifications of an element
Carbon is an element that exists as a simple substance in several forms. That is, it is capable of forming the largest number of allotropic modifications known today.
1. Crystalline variations - exist in the form of strong structures with regular atomic-type lattices. This group includes varieties such as:
- diamonds;
- fullerenes;
- graphites;
- carbines;
- lonsdaleites;
- and tubes.
All of them differ in lattices, in the nodes of which there is a carbon atom. Hence the completely unique, not similar properties, both physical and chemical.
2. Amorphous forms - they are formed by a carbon atom, which is part of some natural compounds. That is, these are not pure varieties, but with impurities of other elements in small quantities. This group includes:
- Activated carbon;
- stone and wood;
- soot;
- carbon nanofoam;
- anthracite;
- glassy carbon;
- technical kind of substance.
They are also united by structural features of the crystal lattice, which explain and manifest properties.
3. Carbon compounds in the form of clusters. Such a structure, in which atoms are closed in a special conformation hollow from the inside, filled with water or the nuclei of other elements. Examples:
- carbon nanocones;
- astralenes;
- dicarbon.
Physical properties of amorphous carbon
Due to the wide variety of allotropic modifications, it is difficult to identify any common physical properties for carbon. It's easier to talk about a specific form. For example, amorphous carbon has the following characteristics.
- At the heart of all forms are fine-grained varieties of graphite.
- High heat capacity.
- Good conductive properties.
- The density of carbon is about 2 g/cm 3 .
- When heated above 1600 0 C, there is a transition to graphite forms.
Soot, and stone varieties are widely used for engineering purposes. They are not a manifestation of carbon modification in its pure form, but contain it in very large quantities.
Crystalline carbon
There are several options in which carbon is a substance that forms regular crystals of various types, where atoms are connected in series. As a result, the following modifications are formed.
- - cubic, in which four tetrahedra are connected. As a result, all covalent chemical bonds of each atom are maximally saturated and strong. This explains the physical properties: the density of carbon is 3300 kg/m 3 . High hardness, low heat capacity, lack of electrical conductivity - all this is the result of the structure of the crystal lattice. There are technically obtained diamonds. They are formed during the transition of graphite to the next modification under the influence of high temperature and a certain pressure. In general, it is as high as the strength - about 3500 0 С.
- Graphite. The atoms are arranged similarly to the structure of the previous substance, however, only three bonds are saturated, and the fourth one becomes longer and less strong, it connects the "layers" of the hexagonal rings of the lattice. As a result, it turns out that graphite is a soft, greasy black substance to the touch. It has good electrical conductivity and has a high melting point - 3525 0 С. It is capable of sublimation - sublimation from a solid state to a gaseous state, bypassing the liquid state (at a temperature of 3700 0 С). The density of carbon is 2.26 g/cm3, which is much lower than that of diamond. This explains their different properties. Due to the layered structure of the crystal lattice, it is possible to use graphite for the manufacture of pencil leads. When carried over the paper, the scales peel off and leave a black mark on the paper.
- Fullerenes. They were opened only in the 80s of the last century. They are modifications in which carbons are interconnected into a special convex closed structure with a void in the center. And the form of a crystal - a polyhedron, the correct organization. The number of atoms is even. The most famous form of fullerene C 60 . Samples of a similar substance were found during research:
- meteorites;
- bottom sediments;
- folgurites;
- shungites;
- outer space, where they were contained in the form of gases.
All varieties of crystalline carbon are of great practical importance, since they have a number of technically useful properties.
Chemical activity
Molecular carbon exhibits low reactivity due to its stable configuration. It can be forced to enter into reactions only by imparting additional energy to the atom and forcing the electrons of the outer level to evaporate. At this point, the valency becomes 4. Therefore, in compounds, it has an oxidation state of + 2, + 4, - 4.
Almost all reactions with simple substances, both metals and non-metals, proceed under the influence of high temperatures. The element in question can be both an oxidizing agent and a reducing agent. However, the latter properties are especially pronounced in it, and it is on this that its use in the metallurgical and other industries is based.
In general, the ability to enter into a chemical interaction depends on three factors:
- dispersion of carbon;
- allotropic modification;
- reaction temperature.
Thus, in some cases, interaction with the following substances occurs:
- non-metals (hydrogen, oxygen);
- metals (aluminum, iron, calcium and others);
- metal oxides and their salts.
It does not react with acids and alkalis, very rarely with halogens. The most important of the properties of carbon is the ability to form long chains with each other. They can close in a cycle, form branches. This is how the formation of organic compounds, which today number in the millions. The basis of these compounds are two elements - carbon, hydrogen. Other atoms may also be included in the composition: oxygen, nitrogen, sulfur, halogens, phosphorus, metals and others.
Basic compounds and their characteristics
There are many different compounds that contain carbon. The formula of the most famous of them is CO 2 - carbon dioxide. However, in addition to this oxide, there is also CO - monoxide or carbon monoxide, as well as suboxide C 3 O 2.
Among the salts that contain this element, the most common are calcium and magnesium carbonates. So, calcium carbonate has several synonyms in the name, since it occurs in nature in the form of:
- chalk;
- marble;
- limestone;
- dolomite.
The importance of alkaline earth metal carbonates is manifested in the fact that they are active participants in the processes of formation of stalactites and stalagmites, as well as groundwater.
Carbonic acid is another compound that forms carbon. Its formula is H 2 CO 3. However, in its usual form, it is extremely unstable and immediately decomposes into carbon dioxide and water in solution. Therefore, only its salts are known, and not itself, as a solution.
Carbon halides - are obtained mainly indirectly, since direct synthesis occurs only at very high temperatures and with a low product yield. One of the most common - CCL 4 - carbon tetrachloride. A toxic compound that can cause poisoning if inhaled. Obtained by radical photochemical substitution reactions in methane.
Metal carbides are carbon compounds in which it exhibits an oxidation state of 4. Associations with boron and silicon are also possible. The main property of carbides of some metals (aluminum, tungsten, titanium, niobium, tantalum, hafnium) is high strength and excellent electrical conductivity. Boron carbide B 4 C is one of the hardest substances after diamond (9.5 according to Mohs). These compounds are used in engineering, as well as in the chemical industry, as sources for the production of hydrocarbons (calcium carbide with water leads to the formation of acetylene and calcium hydroxide).
Many metal alloys are made using carbon, thereby significantly increasing their quality and technical characteristics (steel is an alloy of iron and carbon).
Numerous organic carbon compounds deserve special attention, in which carbon is a fundamental element capable of combining with the same atoms into long chains of various structures. These include:
- alkanes;
- alkenes;
- arenas;
- proteins;
- carbohydrates;
- nucleic acids;
- alcohols;
- carboxylic acids and many other classes of substances.
Application of carbon
The importance of carbon compounds and its allotropic modifications in human life is very high. You can name a few of the most global industries to make it clear that this is true.
- This element forms all types of organic fuel from which a person receives energy.
- The metallurgical industry uses carbon as the strongest reducing agent to obtain metals from their compounds. Carbonates are also widely used here.
- Construction and the chemical industry consume a huge amount of carbon compounds for the synthesis of new substances and obtaining the necessary products.
You can also name such sectors of the economy as:
- nuclear industry;
- jewelry business;
- technical equipment (lubricants, heat-resistant crucibles, pencils, etc.);
- determination of the geological age of rocks - radioactive tracer 14 C;
- carbon is an excellent adsorbent, which makes it possible to use it for the manufacture of filters.
Cycle in nature
The mass of carbon found in nature is included in a constant cycle that cycles every second around the globe. Thus, the atmospheric source of carbon - CO 2 - is absorbed by plants and released by all living beings in the process of respiration. Once in the atmosphere, it is absorbed again, and so the cycle does not stop. At the same time, the death of organic residues leads to the release of carbon and its accumulation in the earth, from where it is then again absorbed by living organisms and released into the atmosphere in the form of gas.
organic carbon
(a. organic carbon; n. organischer Kohlenstoff; f. carbone organique; and. carbono organico) - which is part of the organic. substances of the atmosphere, hydrosphere and horn. breeds. Has a biogenic nature. Macca Corg in the earth's crust reaches 7 * 10 15 tons, incl. in sedimentary rocks - 5 * 10 15 t. and coulometric (automatic analyzers) methods. During catagenesis, the content of Corg in rocks decreases (by 30–40% by the end of apocatagenesis), and its share in organic matter decreases. substance increases (from 70% at the stage of protocatagenesis to 80% in mesocatagenesis and 90% in apocatagenesis). In graphite and graphitized organic. substance, it reaches 99%. Within one stage of catagenesis, the content of C in the composition of organic. substances and the value of the parameter H / C at serve as indicators of the type of organic. substances, in the same type of organic. substance - the level of its maturity. The amount of Corg is an important indicator of the oil and gas source potential of rocks. As part of a concentrated organic in-va O. y, contained in the amount of 85-87% (in oils), 58-90% (in coals). Number of O. y. in coals is one of the indicators of the degree of their metamorphism. E. C. Larskaya.
Mountain Encyclopedia. - M.: Soviet Encyclopedia. Edited by E. A. Kozlovsky. 1984-1991 .
See what "Organic carbon" is in other dictionaries:
organic carbon- Carbon, which is part of organic compounds Source: GOST 23740 79: Soils. Laboratory methods for determining the content of organic substances ...
organic carbon- — EN organic carbon Carbon which comes from an animal or plant. (Source: PHC) Topics environmental protection EN organic… … Technical Translator's Handbook
dissolved organic carbon- 3.4 dissolved organic carbon; DOC: Carbon present in water in the form of organic compounds passing through a 0.45 µm membrane filter when filtered. Source: GOST R 52991 2008: Water. Methods for determining ... ... Dictionary-reference book of terms of normative and technical documentation
total organic carbon- 3.3 total organic carbon; TOC: Carbon present in water in the form of organic compounds in the dissolved and undissolved state. Source: GOST R 52991 2008: Water. Methods for determining the content of total and dissolved organic ... ... Dictionary-reference book of terms of normative and technical documentation
total organic carbon, TOC- 3.3 total organic carbon TOC carbon present in water in the form of organic compounds in the dissolved and insoluble state. Source: GOST 31958 2012: Water. Methods for determining the content of general and ... ... Dictionary-reference book of terms of normative and technical documentation
dissolved organic carbon (DOC)- 3.11 dissolved organic carbon (DOC) carbon present in water in the form of organic compounds passing through a membrane filter with a pore diameter of 0.45 µm when filtered.
Scott Steggenborg, Kansas State University, USA
Carbon is the main structural element of all living things. Carbon is present in the atmosphere, plant and animal tissues, inanimate organic matter, fossil fuels, rocks, and it is dissolved in ocean waters. In the growth of plants, and indeed in our lives, its presence is not the last. Everything starts from the root, and if it grows in soil with a lack of carbon, then the situation must be taken under special control, otherwise ... Everything affects the amount of carbon in the soil, even tillage.
Soil organic carbon
The transition of carbon molecules from one form to another is known as the carbon cycle (Fig. 1). Plants obtain carbon from the atmosphere, which is involved in the process of photosynthesis. Using the energy of the sun and carbon dioxide (CO2) from the atmosphere, plants convert CO2 into organic carbon, which promotes the growth of stems, leaves, and roots. The result of the life cycle and death of plants is the accumulation and decomposition of plant tissue both on the soil surface and below it (plant roots) and the production of a significant amount of soil organic carbon.
Soils differ in the amount of soil organic carbon in them, the range of variation is from less than 1% in sandy soils to more than 20% in waterlogged soils. The natural level of soil organic carbon in the soils of Kansas varies between 1-4%. Today, most cultivated land in Kansas has organic carbon levels of 0.5-2%.
Fig. 1. Modern carbon cycle. All figures are expressed in gigatons and gigatons per year.
In Kansas, steppe grasses contributed to the formation of a thick fertile soil layer. The roots of these and other types of cereals are fibrous. They can penetrate to great depths, producing much of their biomass underground. Consequently, high levels of organic carbon in soils under natural grasslands occur at depths of up to several centimeters. The black color associated with soil fertility is an indicator of organic carbon content. As the content of organic carbon decreases, the color of the soil becomes lighter and reflects its mineral composition. Thus, the red color of soils in southeast Kansas and northeast Oklahoma is an indicator of higher iron concentration and lower soil carbon content. Soils that form under forests tend to have high levels of soil organic carbon in the upper layer, but lower levels in deeper layers. This difference is primarily due to the accumulation of fallen leaves, as well as branches of shrubs and trees on the soil surface.
atmospheric carbon
Using data from an ice core study, as well as data accumulated from long-term monitoring of atmospheric CO2 levels, the scientists found significant fluctuations in atmospheric CO2 levels over 200,000 years. In the last 1000 years, the atmospheric content of CO2 has increased significantly (Fig. 2). Today (2000) the level of CO2 is approximately 369 mg/l, and this figure is higher than at any time in the last millennium. Most importantly, such unprecedented growth rates are so great that the ecosystem may not be able to adapt to them. This increase in CO2 is due to the expansion of fossil fuel use, land clearing and land-use changes that are occurring around the world. The most significant factor that causes an increase in CO2 content in the atmosphere is the use of fossil fuels. At the current pace of this process, amounting to 1 trillion. kg, fossil fuel reserves will be exhausted in the next 300-400 years. As the use of fossil fuels increases, carbon that has been out of circulation for millions of years is being released directly into the atmosphere. Over time, atmospheric carbon will be converted back into organic carbon, or it will end up in the ocean - and a new balance will be reached, but this process can take thousands of years. In the near future, "new" carbon will remain in the atmosphere in the form of CO2. Based on current atmospheric models, it can be concluded that the full use of fossil fuels will lead to an increase in the concentration of atmospheric CO2 to a peak of about 1,200 mg/l. Some scientists believe that these concentrations will be even higher. This rise in CO2 levels has led many scientists to speculate that average global temperatures will begin to rise. In the popular press, this process is called global warming. The so-called greenhouse gases - CO2, methane (CH4) and nitric oxide (N 2 O), which are contained in the atmosphere, contribute to the retention of heat, which, as a rule, is reflected from the earth's surface. At higher concentrations of these gases, heat may not be released, resulting in higher global temperatures. At the moment, changes in global temperatures are not significant and there are no definite trends to this, but changes in the level of CO2 content are fully documented and recognized by most scientists.
What can be done to slow down the CO2 increase? If we think about where CO2 comes from and where it goes next, the most obvious solution is to reduce its supply by reducing the use of fossil fuels. This will reduce the release of CO2 into the atmosphere. Over time, more efficient and cleaner energy sources will be required, but the current economics of fossil fuels limit the uptake and development of alternative sources. In the future, when we develop alternative energy technologies, the massive use of carbon sinks may help stabilize the level of CO2 in the atmosphere. The description of the world's carbon pools (Figure 1) demonstrates that carbon pools in the deep ocean are the main pool, but changes can take millions of years. In addition, our ability to manage this reserve is limited. The next largest reserve is soil organic carbon. The amount of soil organic carbon is twice the amount of carbon contained in plant biomass (plants, trees, crops, grasses, etc.). One way to stabilize atmospheric carbon would be to introduce technologies around the world that increase soil carbon. How much carbon can be held in Kansas soil? The question is simple, but there is no simple answer to it. The storage potential for this type of soil depends on the level of soil carbon at the moment, the concentration of CO2 in the atmosphere and the applied agricultural practices. In many soils in Kansas, significant loss of topsoil from erosion and extensive tillage has resulted in carbon levels being more than doubled from baseline. With proper management, the content of organic carbon in many soils can be increased. Soil carbon losses that occurred in the first half of the 20th century were partially offset in the second half with improvements in conservation technologies and intensification of cropping systems (Figure 3). Proper fertilization and cultivation of improved hybrids and varieties also played a role in the accumulation of soil organic carbon. Higher yields and intensity of cultivation increase the amount of biomass that enters the soil, providing more material that can be converted into soil carbon. On fig. 3 shows projections of soil carbon levels by no-till level for 1990. Soils that are no-till cultivated and that use intensified cultivation systems can increase soil carbon by 1% per year. Currently, 10% of agricultural land in Kansas is under no-till cultivation (a total area of 8.2 million hectares), and these areas should sequester an additional 19,000 tons of carbon per year. With increased use of no-till technology and the use of intensified cropping systems, carbon would be sequestered in large quantities. There is no potential in the world to use soil as a carbon sink, this option remains a short-term solution. Over a period of time, perhaps 30-50 years, a new level of soil CO2 balance will be reached at which it will be difficult to achieve further carbon storage. A longer-term solution to stabilize atmospheric CO2 levels could be to reduce our dependence on fossil fuels for energy.
Carbon sequestration: 9 most asked questions
1. What is meant by carbon sequestration?
Carbon sequestration is generally the process of converting carbon in the air (carbon dioxide or TO2) into soil carbon. Carbon dioxide is taken up by plants during photosynthesis and is also taken up by living plants. When the plant dies, the carbon in the leaves, stem, and roots enters the soil and becomes soil organic matter.
2. How can carbon sequestration help tackle global warming?
Atmospheric carbon dioxide and other greenhouse gases trap heat that escapes from the earth's surface. This accumulation of heat can lead to global warming. Through carbon sequestration, atmospheric carbon dioxide levels are reduced and soil organic matter levels are increased. If left untouched, soil organic carbon can remain in the ground for many years as a stable organic matter. This carbon is sequestered later or moved to storage to become available for recycling to the atmosphere. This process reduces the level of CO2, as well as the possibility of global warming.
3. What impact can carbon sequestration have on greenhouse gases?
It has been found that it is possible to reduce CO2 emissions by 20% or more through agricultural soil carbon sequestration.
4. What can farmers do to improve carbon sequestration?
There are several ways to achieve this:
- no-till or minimum tillage;
- intensive increase in crop rotations and exclusion of summer fallow;
— buffer zones;
— measures for the protection of nature, which will help reduce erosion;
- the use of crops that give a lot of residues (corn, sorghum, as well as wheat);
— use of cover crops;
- selection of species and hybrids that store more carbon.
5. What can farmers do to improve carbon sequestration?
Farmers can increase carbon sequestration by:
- improving the quality of forage;
- maintaining a sufficient amount of crop residues;
— reducing overgrazing.
6. Will agricultural workers be rewarded for carbon sequestration?
There may be a commercial system for providing credit to farmers who increase carbon sequestration. It is also possible that the government will apply some incentives to producers to encourage carbon sequestration. But even if there were no payments, farmers would see a positive effect from the introduction of methods to increase soil organic matter:
– improving the structure and quality of the soil;
- increasing soil fertility by increasing organic matter;
— reduction of erosion due to improved soil structure;
— improving water quality due to reduced erosion.
7. What is soil organic matter, where does it come from and where does it go?
Soil organic matter consists of decayed plants and animal waste. They allow soil mineral particles to be combined into lumps, which are called soil aggregates. Increasing soil organic matter levels leads to more stable soil aggregates, more resistant to wind erosion, better infiltration and aeration, less compaction, and higher fertility. Organic matter helps hold soil nutrients together so they are not washed out or leached out. If left untouched, soil organic matter can turn into humus, a very stable form of organic matter. However, if the soil is tilled, the soil organic matter will be oxidized and the carbon will dissolve into the atmosphere as CO2. If the soil is eroded, the soil organic matter will be washed out by the water.
8. What affects the level of soil organic matter?
The natural levels of soil organic matter for any given location are in most cases determined by latitude as well as annual rainfall. Natural levels of soil organic matter will increase as you move north to south from the equator. On the Great Plains, the level of organic matter increases from west to east, taking into account the amount of precipitation. Management can change soil organic matter levels. In general, as crop intensity increases, the level of soil organic matter increases. As the frequency of mechanical tillage increases, the level of soil organic matter decreases. For the Kansas growers, the use of no-till technology and the elimination of steam offered the greatest potential for achieving this goal.
9. What is Kansas doing to increase carbon sequestration?
Scientists at Kansas State are working to develop better management practices that will increase carbon sequestration. Research is being conducted to test the results of mechanical tillage, various crop rotations, soil conservation practices, and soil carbon management practices.
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 one orbital, but in this case the interelectron repulsion strongly increases. For this reason, one of them takes 2p x, and the other, either 2p y , or 2p z-orbitals.
The difference between the energies of the s- and p-sublevels of the outer layer is small, therefore, the atom quite easily passes into an excited state, in which one of the two electrons from the 2s-orbital passes to a free 2r. A valence state arises having 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 - the tetrahedral spatial arrangement of hybrid orbitals, the same length and energy of bonds.
This phenomenon is known to be called sp 3 -hybridization, and the resulting functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three rr- and one s-s-bond. In addition to sp 3 hybridization, sp 2 and sp hybridization are also observed at the carbon atom . In the first case, there is a mutual overlap 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.
In sp hybridization, the s and p orbitals overlap. An angle of 180° arises between the two equivalent hybrid orbitals formed, while the two p-orbitals of each of the atoms 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 in them. Each of the carbon atoms is linked to three adjacent sp 2 hybrid bonds. Between parallel planes, the connection is carried out due to van der Waals forces. Free p-orbitals of each of the atoms are directed perpendicular to the planes of covalent bonds. Their overlap explains the additional π-bond between carbon atoms. So from the valence state in which carbon atoms are in a substance, the properties of this substance depend.
Chemical properties of carbon
The most characteristic oxidation states: +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 ° \u003d 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 steam
C 0 + H 2 O - 1200 ° \u003d C + 2 O + H 2 water gas
— with metal oxides. In this way metal is smelted from ore.
C 0 + 2CuO - t ° \u003d 2Cu + C +4 O 2
- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) \u003d C +4 O 2 + 2SO 2 + 2H 2 O
С 0 + 4HNO 3 (conc.) = С +4 O 2 + 4NO 2 + 2H 2 O
- forms carbon disulfide with sulfur:
C + 2S 2 \u003d CS 2.
Carbon as an oxidizing agent:
- forms carbides with some metals
4Al + 3C 0 \u003d Al 4 C 3
Ca + 2C 0 \u003d CaC 2 -4
- with hydrogen - methane (as well as a huge amount of organic compounds)
C 0 + 2H 2 \u003d CH 4
- with silicon, forms carborundum (at 2000 ° C in an electric furnace):
Finding carbon in nature
Free carbon occurs as diamond and graphite. In the form of compounds, carbon is found in minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 *CaCO 3; bicarbonates - 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, is part of organic substances, proteins, fats, carbohydrates, amino acids that are part of living organisms.
Inorganic carbon compounds
Neither C 4+ nor C 4- ions are formed in any conventional chemical processes: there are covalent bonds of different polarity in carbon compounds.
Carbon monoxide (II) SO
Carbon monoxide; colorless, odorless, sparingly soluble in water, soluble in organic solvents, poisonous, bp = -192°C; t sq. = -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 \u003d CO + CO 2 + H 2 O
Chemical properties
Under ordinary conditions, CO is inert; when heated - reducing agent; non-salt-forming oxide.
1) with oxygen
2C +2 O + O 2 \u003d 2C +4 O 2
2) with metal oxides
C +2 O + CuO \u003d Cu + C +4 O 2
3) with chlorine (in the light)
CO + Cl 2 - hn \u003d 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 salts of carbonic acid (carbonates). Limestone firing:
CaCO 3 - t ° \u003d CaO + CO 2
- The action of strong acids on carbonates and bicarbonates:
CaCO 3 + 2HCl \u003d CaCl 2 + H 2 O + CO 2
NaHCO 3 + HCl \u003d 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 \u003d Na 2 CO 3
2NaOH + CO 2 \u003d Na 2 CO 3 + H 2 O
NaOH + CO 2 \u003d NaHCO 3
May exhibit oxidizing properties at elevated temperatures
C +4 O 2 + 2Mg - t ° \u003d 2Mg +2 O + C 0
Qualitative reaction
Turbidity of lime water:
Ca (OH) 2 + CO 2 \u003d 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 is converted to soluble bicarbonate:
CaCO 3 + H 2 O + CO 2 \u003d Ca (HCO 3) 2
carbonic acid and itssalt
H2CO3 — Weak acid, exists only in aqueous solution:
CO 2 + H 2 O ↔ H 2 CO 3
Dual base:
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 be converted into each other:
2NaHCO 3 - t ° \u003d Na 2 CO 3 + H 2 O + CO 2
Na 2 CO 3 + H 2 O + CO 2 \u003d 2NaHCO 3
Metal carbonates (except alkali metals) decarboxylate when heated to form an oxide:
CuCO 3 - t ° \u003d CuO + CO 2
Qualitative reaction- "boiling" under the action of a strong acid:
Na 2 CO 3 + 2HCl \u003d 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 \u003d 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 \u003d 2La (OH) 3 + 2 C 2 H 2 + H 2.
Be 2 C and Al 4 C 3 are decomposed by water to form methane:
Al 4 C 3 + 12 H 2 O \u003d 4 Al (OH) 3 \u003d 3 CH 4.
Titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum - as an abrasive and material for heaters) are used in technology.
cyanides
obtained by heating soda in an atmosphere of ammonia and carbon monoxide:
Na 2 CO 3 + 2 NH 3 + 3 CO \u003d 2 NaCN + 2 H 2 O + H 2 + 2 CO 2
Hydrocyanic acid HCN is an important chemical industry product widely used in organic synthesis. Its world 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 \u003d 2 K + 2 KOH.
When cyanide solutions are boiled with sulfur or when solids are fused, thiocyanates:
KCN + S = KSCN.
When cyanides of low-active metals are heated, cyanide is obtained: Hg (CN) 2 \u003d Hg + (CN) 2. cyanide solutions are oxidized to cyanates:
2KCN + O2 = 2KOCN.
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 \u003d CO (NH 2) 2 by evaporating an aqueous solution.
This event is usually seen as the victory of synthetic chemistry over "vitalistic theory".
There is an isomer of cyanic acid - fulminic acid
H-O-N=C.
Its salts (mercury fulminate Hg(ONC) 2) are used in impact igniters.
Synthesis urea(carbamide):
CO 2 + 2 NH 3 \u003d CO (NH 2) 2 + H 2 O. At 130 0 C and 100 atm.
Urea is an amide of carbonic acid, there is also its "nitrogen analogue" - guanidine.
Carbonates
The most important inorganic compounds of carbon are salts of carbonic acid (carbonates). H 2 CO 3 is a weak acid (K 1 \u003d 1.3 10 -4; K 2 \u003d 5 10 -11). Carbonate buffer supports carbon dioxide balance in the atmosphere. The oceans have a huge 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 -.
With a decrease in acidity, additional absorption of carbon dioxide from the atmosphere occurs with the formation of acid:
CO 2 + H 2 O ↔ H 2 CO 3.
With an increase in acidity, carbonate rocks (shells, chalk and limestone deposits in the ocean) dissolve; this compensates for the loss of hydrocarbonate ions:
H + + CO 3 2- ↔ HCO 3 -
CaCO 3 (tv.) ↔ Ca 2+ + CO 3 2-
Solid carbonates are converted into soluble hydrocarbons. It is this process of chemical dissolution of excess carbon dioxide that counteracts the "greenhouse effect" - global warming due to the absorption of Earth's thermal radiation by carbon dioxide. Approximately one third of the world's production of soda (sodium carbonate Na 2 CO 3) is used in the manufacture of glass.
It is called the basis of life. It is found in all organic compounds. Only he is able to form molecules from millions of atoms, such as DNA.
Did you recognize the hero? it carbon. The number of its compounds known to science is close to 10,000,000.
So much will not be typed in all the other elements taken together. Not surprisingly, one of the two branches of chemistry studies exclusively carbon compounds and takes place in the upper grades.
We offer to recall the school curriculum, as well as supplement it with new facts.
What is carbon
Firstly, element carbon- composite. In her new standard, the substance is in the 14th group.
In the outdated version of the system, carbon is in the main subgroup of the 4th group.
The designation of the element is the letter C. The serial number of the substance is 6, it belongs to the group of non-metals.
organic carbon adjacent in nature to the mineral. So, and the fullerene stone is the 6th element in its pure form.
Differences in appearance are due to several types of structure of the crystal lattice. The polar characteristics of mineral carbon also depend on it.
Graphite, for example, is soft, it is not in vain that it is added to writing pencils, but to everyone else on Earth. Therefore, it is logical to consider the properties of carbon itself, and not its modifications.
Properties of carbon
Let's start with the properties common to all nonmetals. They are electronegative, that is, they attract common electron pairs formed with other elements.
It turns out that carbon can reduce non-metal oxides to the state of metals.
However, the 6th element does this only when heated. Under normal conditions, the substance is chemically inert.
The outer electronic levels of non-metals have more electrons than metals.
That is why the atoms of the 6th element tend to complete a fraction of their own orbitals than to give their particles to someone.
For metals, with a minimum of electrons on the outer shells, it is easier to give away distant particles than to pull strangers onto themselves.
The main form of the 6th substance is the atom. In theory, it should be about carbon molecule. Most non-metals are made up of molecules.
However, carbon with and - exceptions, have an atomic structure. It is due to it that the compounds of elements are distinguished by high melting points.
Another distinctive property of many forms of carbon is . For the same one, it is maximum, equal to 10 points for.
Since the conversation turned to the forms of the 6th substance, we point out that the crystalline one is only one of them.
carbon atoms do not always line up in a crystal lattice. There is an amorphous variety.
Examples of this: - wood, coke, glassy carbon. These are compounds, but without an ordered structure.
If the substance is combined with others, gases can also be obtained. Crystalline carbon passes into them at a temperature of 3700 degrees.
Under normal conditions, an element is gaseous if it is, for example, carbon monoxide.
People call it carbon monoxide. However, the reaction of its formation is more active and faster, if, nevertheless, turn on the heat.
gaseous compounds carbon With oxygen several. There is also, for example, monoxide.
This gas is colorless and poisonous, moreover, under normal conditions. Such carbon monoxide has a triple bond in the molecule.
But, back to the pure element. Being quite inert in chemical terms, it, nevertheless, can interact not only with metals, but also with their oxides, and, as can be seen from the conversation about gases, with oxygen.
The reaction is also possible with hydrogen. Carbon will enter into interaction if one of the factors “plays” or all together: temperature, allotropic state, dispersion.
The latter refers to the ratio of the surface area of the particles of a substance to the volume they occupy.
Allotropy is the possibility of several forms of the same substance, that is, it means crystalline, amorphous, or gaseous carbon.
However, no matter how the factors coincide, the element does not react at all with acids and alkalis. Ignores carbon and almost all halogens.
Most often, the 6th substance binds to itself, forming those very large-scale molecules of hundreds and millions of atoms.
molecules formed, carbon react with even fewer elements and compounds.
Application of carbon
The application of the element and its derivatives is as extensive as their number. Carbon content There is more to a person's life than you might think.
Activated charcoal from a pharmacy is the 6th substance. in from - he is.
Graphite in pencils is also carbon, which is also needed in nuclear reactors and electrical machine contacts.
Methane fuel is also on the list. Carbon dioxide needed for production and can be dry ice, that is, a refrigerant.
Carbon dioxide serves as a preservative, filling vegetable stores, and is also needed to produce carbonates.
The latter are used in construction, for example,. And carbonate comes in handy in soap making and glass production.
Formula of carbon also corresponds to coke. He comes in handy metallurgists.
Coke serves as a reducing agent during the smelting of ore, the extraction of metals from it.
Even ordinary soot is carbon used as fertilizer and filler.
Ever wondered why car tires are colored? This is soot. It gives the rubber strength.
Soot is also included in shoe polish, printing ink, and mascara. The common name is not always used. Industrialists call soot technical carbon.
Mass of carbon begins to be used in the field of nanotechnology. Ultra-small transistors were made, as well as tubes that are 6-7 times stronger.
Here's a non-metal. By the way, scientists from . From carbon tubes and graphene, they created an airgel.
It is also a durable material. Sounds hefty. But, in fact, airgel is lighter than air.
AT iron carbon added to get what is called carbon steel. She's tougher than usual.
However, the mass fraction of the 6th element in should not exceed a couple, three percent. Otherwise, the properties of steel are declining.
The list is endless. But, where to take carbon indefinitely? Is it mined or synthesized? We will answer these questions in a separate chapter.
Carbon mining
carbon dioxide, methane, separately carbon, can be obtained chemically, that is, by intentional synthesis. However, this is not beneficial.
carbon gas and its solid modifications are easier and cheaper to mine along with coal.
Approximately 2 billion tons are extracted from the earth's bowels of this fossil annually. Enough to provide the world with carbon black.
As for, they are extracted from kimbirlite pipes. These are vertical geological bodies, fragments of rock cemented by lava.
It is in such that they meet. Therefore, scientists suggest that the mineral is formed at depths of thousands of kilometers, in the same place as magma.
Graphite deposits, on the contrary, are horizontal, located near the surface.
Therefore, the extraction of the mineral is quite simple and not expensive. About 500,000 tons of graphite are extracted from the subsoil annually.
To get activated carbon, you have to heat the coal and process it with a jet of water vapor.
Scientists have even figured out how to recreate the proteins in the human body. Their basis is also carbon. Nitrogen and hydrogen is an amino group adjacent to it.
You also need oxygen. That is, proteins are built on amino acids. She is not widely known, but for life is much more important than the rest.
Popular sulfuric, nitric, hydrochloric acids, for example, the body needs much less.
So carbon is something worth paying for. Let's find out how big the spread of prices for different goods from the 6th element is.
The price of carbon
For life, as it is easy to understand, carbon is priceless. As for other spheres of life, the price tag depends on the name of the product and its quality.
For, for example, they pay more if they do not contain third-party inclusions.
Airgel samples, so far, cost tens of dollars for a few square centimeters.
But, in the future, manufacturers promise to supply the material in rolls and ask for cheap.
Technical carbon, that is, soot, is sold at 5-7 rubles per kilo. For a ton, respectively, they give about 5000-7000 rubles.
However, the carbon tax introduced in most developed countries can drive up prices.
The carbon industry is considered the cause of the greenhouse effect. Companies are required to pay for emissions, in particular CO 2 .
It is the main greenhouse gas and, at the same time, an indicator of atmospheric pollution. This information is a fly in the ointment in a barrel of honey.
It allows you to understand that carbon, like everything else in the world, has a downside, and not just pluses.
