Chemistry

INORGANIC CHEMISTRY. ELEMENTS AND THEIR CONNECTIONS

7. Carbon

Properties 6 C.

Atomic mass		clarke, at.% (prevalence in nature)
Electronic configuration *		State of aggregation	solid
			diamond - colorless. graphite - gray
Ionization energy			5000 (diamond)
Relative electro- negativity		Density	diamond - 3.51 graphite - 2,2
Possible oxidation states		Standard electrode potential

* The configuration of the external electronic levels of the atom of the element is given. The configuration of the remaining electronic levels coincides with that for the noble gas ending the previous period and indicated in parentheses.

Carbon isotopes.

Carbon has two stable isotopes: 12 C (98.892%) and 13 C (1.108%). The radioactive isotope of carbon is very important 14 C emitting b-rays with half-life T 1/2 = 5570 years old. Using radiocarbon analysis by determining the concentration of the isotope 14 Scientists were able to quite accurately date the age of carbonaceous rocks, archaeological finds, geological events.

Being in nature. In nature, carbon occurs in the form of diamond carbine and graphite, in compounds - in the form of coal and brown coal and oil. Part of natural carbonates: limestone, marble, chalk

CaCO 3, dolomite CaCO 3 H MgCO 3... It is an important component of organic matter.

Physical properties. A carbon atom has 6 electrons, 2 of which form an inner layer

(1s 2), a 4 - external (2s 2 2p 2 ). The bonds of carbon with other elements are predominantly covalent. The usual valence of carbon is IV. A remarkable feature of carbon atoms is the ability to connect with each other to form strong long chains, including closed ones. The number of such compounds is enormous, they all constitute a subject organic chemistry .

The difference in allotropic modifications of carbon is a vivid example of the influence of the crystalline structure of solids on their physical properties. IN graphite carbon atoms are in the state

sp 2 - hybridization and are arranged in parallel layers, forming a hexagonal grid. The atoms are much more strongly bonded inside the layer than between the layers; therefore, the properties of graphite differ greatly in different directions. Thus, the ability of graphite to delaminate is associated with the rupture of weaker interlayer bonds along the slip planes.

At very high pressures and heating without air access, an artificial diamond. In a diamond crystal, carbon atoms are in the state

sp 3 -hybridization, and therefore all bonds are equivalent and very strong. The atoms form a continuous three-dimensional framework. Diamond is the hardest substance found in nature.

Less well known are the other two allotropes of carbon - carbyne and fullerene.

Chemical properties. Free carbon is typical reducing agent. When oxidized with oxygen in excess air, it turns into carbon monoxide (IV):

with a lack of - into carbon monoxide (II):

Both reactions are highly exothermic.

When carbon is heated in an atmosphere of carbon monoxide (IV), carbon monoxide:

Carbon reduces many metals from their oxides:

This is how reactions proceed with oxides of cadmium, copper, lead. When carbon interacts with oxides of alkaline earth metals, aluminum and some other metals, carbides:

This is explained by the fact that active metals are stronger reducing agents than carbon, therefore, when heated, the resulting metals oxidized excess carbon, giving carbides:

Carbon monoxide (II).

Incomplete oxidation of carbon produces carbon monoxide (II) CO - carbon monoxide. It is poorly soluble in water. The formal oxidation state of carbon 2+ does not reflect the structure of the CO molecule. In the CO molecule, in addition to the double bond formed by the sharing of electrons of carbon and oxygen, there is an additional, third bond (shown by the arrow), formed by the donor-acceptor mechanism due to the lone pair of oxygen electrons:

In this regard, the CO molecule is extremely strong. Carbon monoxide (II) is non-salt-forming and does not interact under normal conditions with water, acids and alkalis. At elevated temperatures, it is prone to addition and oxidation-reduction reactions. In air, CO burns with a blue flame:

It recovers metals from their oxides:

Under the influence of irradiation in direct sunlight or in the presence of catalysts, CO combines with

Cl 2 forming phosgene - extremely poisonous gas:

In nature, carbon monoxide (II) is practically not found.

It can be formed during dehydration of formic acid (laboratory production method):

Based on the last transformation purely formal can be considered as CO anhydride, formic acid. This is confirmed by the following reaction, which occurs when CO is passed into the alkali melt at high pressure:

Transition metal carbonyls.

With many metals, CO forms volatile carbonyls:

Covalent bond

Ni- C in the nickel carbonyl molecule is formed by the donor-acceptor mechanism, with the electron density shifting from the carbon atom to the nickel atom. The increase in the negative charge on the metal atom is compensated by the participation of its d-electrons in the bond, so the oxidation state of the metal is 0. When heated, metal carbonyls decompose into metal and carbon monoxide (II), which is used to obtain metals of special purity.

Carbon monoxide (IV). Carbon monoxide (IV) is an anhydride of carbonic acid H

2 CO 3 and has all the properties of acidic oxides.

When dissolved

CO 2 carbonic acid is partially formed in water, while the following equilibrium exists in the solution:

The existence of equilibrium is explained by the fact that carbonic acid is a very weak acid (K

1 = 4H 10 -7, K 2 = 5H 10 -11at 25 ° C). Free carbonic acid is unknown, since it is unstable and easily decomposes.Carbonic acid. In a carbonic acid molecule, hydrogen atoms are linked to oxygen atoms:

As dibasic, it dissociates stepwise. Carbonic acid is a weak electrolyte.

Carbonic acid as dibasic forms medium salts - carbonates and acidic salts - hydrocarbonates. A qualitative reaction to these salts is the action of strong acids on them. In this reaction, carbonic acid is displaced from its salts and decomposes with the release carbon dioxide:

Carbonic acid salts.

Of the salts of carbonic acid, soda Na 2 CO 3 is of the greatest practical importance. ... This salt forms several crystalline hydrates, of which the most stable is Na 2 CO 3 H 10H 2 O(crystalline soda). When crystalline soda is calcined, anhydrous is obtained, or soda ash, soda Na 2 CO 3 ... Also widely used baking soda NaH CO 3 ... Of the salts of other metals, the following are important: K 2 CO 3 ( potash)- white powder, readily soluble in water, contained in plant ash, used in the production of liquid soap, optical refractory glass, pigments; Ca CO 3 (limestone)- occurs naturally in the form of marble, chalk and limestone, which are used in construction. lime and carbon monoxide ( IV).

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The most widespread knowledge about three states of aggregation: liquid, solid, gaseous, sometimes remember about plasma, less often liquid crystal. Recently, a list of 17 phases of a substance, taken from the famous () Stephen Fry, has been circulated on the Internet. Therefore, we will tell you more about them, because you should know a little more about matter, if only in order to better understand the processes taking place in the Universe.

The list of aggregate states of matter given below increases from the coldest states to the hottest, and so on. can be continued. At the same time, it should be understood that the degree of compression of the substance and its pressure (with some reservations for such unexplored hypothetical states such as quantum, radial, or weakly symmetric) increase from the gaseous state (No. 11), the most "unclenched", to both sides of the list. a visual graph of the phase transitions of matter is shown.

1. Quantum- the aggregate state of matter, achieved when the temperature drops to absolute zero, as a result of which internal bonds disappear and matter disintegrates into free quarks.

2. Bose-Einstein condensate- the aggregate state of matter, which is based on bosons cooled to temperatures close to absolute zero (less than a millionth of a degree above absolute zero). In such a strongly cooled state, a sufficiently large number of atoms find themselves in their minimum possible quantum states and quantum effects begin to manifest themselves at the macroscopic level. Bose-Einstein condensate (often called "Bose condensate", or simply "back") occurs when you cool a particular chemical element to extremely low temperatures (usually to a temperature slightly above absolute zero, minus 273 degrees Celsius , Is the theoretical temperature at which everything stops moving).
This is where completely strange things begin to happen to the substance. Processes normally only seen at the atomic level now take place on a scale large enough to be observed with the naked eye. For example, if you put a "backing" in a beaker and provide the required temperature, the substance will begin to crawl up the wall and eventually will get out by itself.
Apparently, here we are dealing with a futile attempt by the substance to lower its own energy (which is already at the lowest of all possible levels).
Slowing down the atoms using cooling equipment produces a singular quantum state known as a Bose condensate, or Bose-Einstein condensate. This phenomenon was predicted in 1925 by A. Einstein, as a result of a generalization of the work of S. Bose, where statistical mechanics was built for particles ranging from massless photons to atoms with mass (Einstein's manuscript, which was considered lost, was discovered in the library of Leiden University in 2005 ). The result of the efforts of Bose and Einstein was the concept of Bose gas obeying Bose-Einstein statistics, which describes the statistical distribution of identical particles with integer spin, called bosons. Bosons, which are, for example, and individual elementary particles - photons, and whole atoms, can be with each other in the same quantum states. Einstein suggested that cooling boson atoms to very low temperatures would force them to move (or, in other words, condense) into the lowest possible quantum state. The result of such condensation will be the emergence of a new form of matter.
This transition occurs below the critical temperature, which is for a homogeneous three-dimensional gas consisting of non-interacting particles without any internal degrees of freedom.

3. Fermion condensate- the state of aggregation of a substance, similar to the back, but differing in structure. When approaching absolute zero, atoms behave differently depending on the magnitude of the proper angular momentum (spin). Bosons have integer spins, while fermions have multiples of 1/2 (1/2, 3/2, 5/2). Fermions obey the Pauli exclusion principle, according to which two fermions cannot have the same quantum state. There is no such prohibition for bosons, and therefore they have the opportunity to exist in one quantum state and thereby form the so-called Bose-Einstein condensate. The formation of this condensate is responsible for the transition to the superconducting state.
Electrons have spin 1/2 and are therefore fermions. They combine into pairs (called Cooper pairs), which then form a Bose condensate.
American scientists have attempted to obtain a kind of molecule from fermion atoms with deep cooling. The difference from real molecules was that there was no chemical bond between the atoms - they just moved together in a correlated manner. The bond between atoms turned out to be even stronger than between electrons in Cooper pairs. For the formed pairs of fermions, the total spin is no longer a multiple of 1/2; therefore, they already behave like bosons and can form a Bose condensate with a single quantum state. In the course of the experiment, a gas of potassium-40 atoms was cooled to 300 nanokelvin, while the gas was contained in a so-called optical trap. Then an external magnetic field was imposed, with the help of which it was possible to change the nature of interactions between atoms - instead of a strong repulsion, a strong attraction began to be observed. When analyzing the influence of the magnetic field, it was possible to find such a value at which the atoms began to behave like Cooper pairs of electrons. At the next stage of the experiment, scientists propose to obtain the effects of superconductivity for fermion condensate.

4. Superfluid substance- a state in which a substance has virtually no viscosity, and during flow it does not experience friction with a solid surface. The consequence of this is, for example, such an interesting effect as the complete spontaneous "creeping" of superfluid helium from the vessel along its walls against the force of gravity. Of course, there is no violation of the law of conservation of energy. In the absence of friction forces, only gravity, the forces of interatomic interaction between helium and the walls of the vessel and between helium atoms act on helium. So, the forces of interatomic interaction exceed all other forces combined. As a result, helium tends to spread as much as possible over all possible surfaces, and therefore "travels" along the walls of the vessel. In 1938, the Soviet scientist Pyotr Kapitsa proved that helium can exist in a superfluid state.
It is worth noting that many of the unusual properties of helium have been known for quite some time. However, in last years this chemical element "pampers" us with interesting and unexpected effects. So, in 2004, Moses Chan and Eun-Siong Kim from the University of Pennsylvania intrigued the scientific world with the statement that they had managed to obtain a completely new state of helium - a superfluid solid. In this state, some helium atoms in the crystal lattice can flow around others, and thus helium can flow through itself. The "superhardness" effect was theoretically predicted back in 1969. And now in 2004 - as if it was an experimental confirmation. However, later and very interesting experiments showed that not everything is so simple, and, perhaps, such an interpretation of the phenomenon, which was previously taken for the superfluidity of solid helium, is incorrect.
The experiment of scientists led by Humphrey Maris from Brown University in the United States was simple and elegant. Scientists placed a test tube upside down in a closed reservoir of liquid helium. Some of the helium in the test tube and in the reservoir was frozen in such a way that the boundary between liquid and solid inside the test tube was higher than in the reservoir. In other words, in the upper part of the test tube there was liquid helium, in the lower part - solid, it smoothly passed into the solid phase of the reservoir, over which a little liquid helium was poured - lower than the liquid level in the test tube. If liquid helium began to seep through solid, then the level difference would decrease, and then we can talk about solid superfluid helium. And in principle, in three of the 13 experiments, the level difference actually decreased.

5. Superhard substance- an aggregate state in which matter is transparent and can "flow" like a liquid, but in fact it is devoid of viscosity. Such fluids have been known for many years and are called superfluids. The fact is that if the superfluid is stirred, it will circulate almost forever, while the normal liquid will eventually calm down. The first two superfluids were created by the researchers using helium-4 and helium-3. They were cooled to almost absolute zero - to minus 273 degrees Celsius. And from helium-4, American scientists managed to get a superhard body. They compressed the frozen helium by more than 60 times pressure, and then the glass filled with the substance was placed on a rotating disk. At a temperature of 0.175 degrees Celsius, the disk suddenly began to spin more freely, which, according to scientists, indicates that helium has become a superbody.

6. Solid- the aggregate state of matter, characterized by the stability of the form and the nature of the thermal motion of atoms, which perform small vibrations around the equilibrium positions. The stable state of solids is crystalline. Distinguish between solids with ionic, covalent, metallic, and other types of bonds between atoms, which determines the variety of their physical properties. Electrical and some other properties of solids are mainly determined by the nature of the movement of the outer electrons of its atoms. According to their electrical properties, solids are divided into dielectrics, semiconductors and metals, according to their magnetic properties - into diamagnets, paramagnets and bodies with an ordered magnetic structure. Studies of the properties of solids have united into a large area - solid state physics, the development of which is stimulated by the needs of technology.

7. Amorphous solid- condensed aggregate state of matter, characterized by isotropy of physical properties due to the disordered arrangement of atoms and molecules. In amorphous solids, atoms vibrate around randomly located points. In contrast to the crystalline state, the transition from solid amorphous to liquid occurs gradually. Various substances are in the amorphous state: glasses, resins, plastics, etc.

8. Liquid crystal Is a specific aggregate state of a substance in which it simultaneously exhibits the properties of a crystal and a liquid. Immediately it is necessary to make a reservation that not all substances can be in a liquid crystal state. However, some organic substances with complex molecules can form a specific aggregate state - liquid crystal. This state occurs when crystals of some substances melt. When they melt, a liquid crystal phase is formed, which differs from ordinary liquids. This phase exists in the range from the melting point of the crystal to some higher temperature, when heated to which the liquid crystal transforms into an ordinary liquid.
How does a liquid crystal differ from a liquid and an ordinary crystal, and how is it similar to them? Like an ordinary liquid, a liquid crystal is fluid and takes the form of a vessel in which it is placed. In this it differs from the crystals known to all. However, despite this property, which unites it with a liquid, it has a property characteristic of crystals. This is the ordering in space of the molecules that form the crystal. True, this ordering is not as complete as in ordinary crystals, but, nevertheless, it significantly affects the properties of liquid crystals, which distinguishes them from ordinary liquids. Incomplete spatial ordering of molecules that form a liquid crystal is manifested in the fact that in liquid crystals there is no complete order in the spatial arrangement of the centers of gravity of molecules, although there may be a partial order. This means that they do not have a rigid crystal lattice. Therefore, liquid crystals, like ordinary liquids, have the property of fluidity.
An obligatory property of liquid crystals, bringing them closer to ordinary crystals, is the presence of the order of the spatial orientation of molecules. This order in orientation can manifest itself, for example, in the fact that all long axes of molecules in a liquid crystal sample are oriented in the same way. These molecules must be elongated. In addition to the simplest named ordering of the molecular axes, a more complex orientational order of molecules can be realized in a liquid crystal.
Depending on the type of ordering of the molecular axes, liquid crystals are divided into three types: nematic, smectic, and cholesteric.
Research in the physics of liquid crystals and their applications is currently being carried out on a broad front in all the most developed countries the world. Domestic research is concentrated in both academic and industrial research institutions and has a long tradition. The works of V.K. Fredericksz to V.N. Tsvetkova. In recent years, the vigorous study of liquid crystals, Russian researchers have also made a significant contribution to the development of the theory of liquid crystals in general and, in particular, of the optics of liquid crystals. Thus, the works of I.G. Chistyakova, A.P. Kapustina, S.A. Brazovsky, S.A. Pikina, L.M. Blinov and many other Soviet researchers are widely known to the scientific community and serve as the foundation for a number of effective technical applications of liquid crystals.
The existence of liquid crystals was established a very long time ago, namely in 1888, that is, almost a century ago. Although scientists were faced with this state of matter before 1888, it was officially discovered later.
The first to discover liquid crystals was the Austrian botanist Reinitzer. Investigating the new substance he synthesized, cholesteryl benzoate, he found that at a temperature of 145 ° C, the crystals of this substance melt, forming a turbid liquid that strongly scatters light. As the heating continues, upon reaching a temperature of 179 ° C, the liquid clears up, that is, it begins to behave optically like an ordinary liquid, for example water. Cholesteryl benzoate exhibited unexpected properties in a cloudy phase. Examining this phase under a polarizing microscope, Rey-nitzer discovered that it has birefringence. This means that the refractive index of light, that is, the speed of light in this phase, depends on the polarization.

9. Liquid- the state of aggregation of a substance, combining the features of a solid state (retention of volume, a certain tensile strength) and gaseous (variability of shape). A liquid is characterized by short-range order in the arrangement of particles (molecules, atoms) and a small difference in the kinetic energy of the thermal motion of molecules and their potential interaction energy. The thermal motion of liquid molecules consists of oscillations about equilibrium positions and relatively rare jumps from one equilibrium position to another, which is associated with the fluidity of the liquid.

10. Supercritical fluid(SCF) - the state of aggregation of a substance, in which the difference between the liquid and gas phases disappears. Any substance at a temperature and pressure above the critical point is a supercritical fluid. The properties of a substance in a supercritical state are intermediate between its properties in the gas and liquid phases. So, SCF has a high density, close to a liquid, and a low viscosity, like gases. In this case, the diffusion coefficient has an intermediate value between liquid and gas. Supercritical substances can be used as substitutes for organic solvents in laboratory and industrial processes. Supercritical water and supercritical carbon dioxide have received the greatest interest and distribution in connection with certain properties.
One of the most important properties of the supercritical state is the ability to dissolve substances. By changing the temperature or pressure of the fluid, you can change its properties in a wide range. So, you can get a fluid that is close in properties to either a liquid or a gas. Thus, the dissolving power of a fluid increases with increasing density (at a constant temperature). Since the density increases with increasing pressure, changing the pressure can affect the dissolving ability of the fluid (at constant temperature). In the case of temperature, the envy of the properties of the fluid is somewhat more complicated - at a constant density, the dissolving ability of the fluid also increases, however, near the critical point, a slight increase in temperature can lead to a sharp drop in density, and, accordingly, in the dissolving ability. Supercritical fluids mix indefinitely with each other, therefore, when the critical point of the mixture is reached, the system will always be single-phase. The approximate critical temperature of a binary mixture can be calculated as the arithmetic mean of the critical parameters of substances Tc (mix) = (mole fraction A) x TcA + (mole fraction B) x TcB.

11. Gaseous- (French gaz, from the Greek chaos - chaos), the state of aggregation of matter, in which the kinetic energy of the thermal motion of its particles (molecules, atoms, ions) significantly exceeds the potential energy of interactions between them, and therefore the particles move freely, evenly filling, in the absence of external fields, the entire volume provided to them.

12. Plasma- (from the Greek. Plasma - sculpted, shaped), the state of matter, which is an ionized gas, in which the concentrations of positive and negative charges are equal (quasineutrality). The overwhelming part of the substance of the Universe is in the state of plasma: stars, galactic nebulae and the interstellar medium. Plasma exists near the Earth in the form of the solar wind, magnetosphere and ionosphere. High-temperature plasma (T ~ 106 - 108K) from a mixture of deuterium and tritium is being investigated for the purpose of controlled thermonuclear fusion. Low-temperature plasma (T Ј 105K) is used in various gas-discharge devices (gas lasers, ion devices, MHD generators, plasmatrons, plasma engines, etc.), as well as in technology (see Plasma metallurgy, Plasma drilling, Plasma technology) ...

13. Degenerate substance- is an intermediate stage between plasma and neutronium. It is observed in white dwarfs and plays an important role in the evolution of stars. When atoms are under extremely high temperatures and pressures, they lose their electrons (they go into electron gas). In other words, they are completely ionized (plasma). The pressure of such a gas (plasma) is determined by the pressure of the electrons. If the density is very high, all the particles are forced to approach each other. Electrons can be in states with certain energies, and two electrons cannot have the same energy (unless their spins are opposite). Thus, in a dense gas, all the lower energy levels are filled with electrons. Such a gas is called degenerate. In this state, electrons exhibit degenerate electron pressure that opposes the forces of gravity.

14. Neutronium- the state of aggregation, into which matter passes at ultrahigh pressure, which is unattainable in the laboratory, but exists inside neutron stars. During the transition to the neutron state, the electrons of a substance interact with protons and turn into neutrons. As a result, the substance in the neutron state consists entirely of neutrons and has a density of the order of the nuclear one. In this case, the temperature of the substance should not be too high (in energy equivalent, no more than a hundred MeV).
With a strong increase in temperature (hundreds of MeV and above), various mesons begin to be produced and annihilated in the neutron state. With a further increase in temperature, deconfinement occurs, and the substance passes into the state of a quark-gluon plasma. It no longer consists of hadrons, but of quarks and gluons that are constantly being born and disappearing.

15. Quark-gluon plasma(chromoplasm) - the aggregate state of matter in high-energy physics and elementary particle physics, in which hadronic matter passes into a state similar to the state in which electrons and ions are in ordinary plasma.
Usually matter in hadrons is in the so-called colorless ("white") state. That is, quarks of different colors cancel each other out. Ordinary matter has a similar state - when all atoms are electrically neutral, that is,
positive charges in them are compensated by negative ones. At high temperatures, ionization of atoms can occur, while the charges are separated, and the substance becomes, as they say, "quasineutral". That is, the entire cloud of matter as a whole remains neutral, and its individual particles cease to be neutral. Exactly the same, apparently, can happen with hadronic matter - at very high energies, the color is released and makes the matter "quasi-colorless".
Presumably, the substance of the Universe was in the state of a quark-gluon plasma in the first moments after the Big Bang. Now quark-gluon plasma can be formed for a short time by collisions of particles of very high energies.
Quark-gluon plasma was obtained experimentally at the RHIC accelerator at Brookhaven National Laboratory in 2005. The maximum plasma temperature of 4 trillion degrees Celsius was obtained there in February 2010.

16. Strange substance- the state of aggregation, in which matter is compressed to the limiting density values, it can exist in the form of a "quark soup". A cubic centimeter of matter in this state will weigh billions of tons; moreover, it will transform any normal substance with which it comes into contact into the same "strange" form with the release of a significant amount of energy.
The energy that can be released during the transformation of the matter of the star's core into "strange matter" will lead to a super-powerful explosion of the "quark nova" - and, according to Leahy and Wyed, it was his astronomers who observed in September 2006.
The process of the formation of this substance began with an ordinary supernova, into which a massive star turned. As a result of the first explosion, a neutron star was formed. But, according to Leahy and Uyed, it did not last long - as its rotation seemed to be slowed down by its own magnetic field, it began to shrink even more, with the formation of a lump of "strange matter", which led to an even more powerful release of energy than in an ordinary supernova explosion - and the outer layers of the substance of the former neutron star, scattering into the surrounding space at a speed close to the speed of light ...

17. Strongly symmetrical substance Is a substance compressed to such an extent that the microparticles inside it are layered on top of each other, and the body itself collapses into a black hole. The term "symmetry" is explained as follows: Let's take the aggregate states of matter known to everyone from school - solid, liquid, gaseous. For definiteness, consider an ideal infinite crystal as a solid. It has a certain so-called discrete symmetry with respect to transfer. This means that if you move the crystal lattice by a distance equal to the interval between two atoms, nothing will change in it - the crystal will coincide with itself. If the crystal is melted, then the symmetry of the resulting liquid will be different: it will increase. In the crystal, only points were equivalent, which were distant from each other at certain distances, the so-called nodes of the crystal lattice, in which the same atoms were located.
The liquid is homogeneous throughout the volume, all its points are indistinguishable from one another. This means that the liquid can be displaced at any arbitrary distance (and not only at some discrete, as in a crystal) or rotated at any arbitrary angles (which cannot be done in crystals at all) and it will coincide with itself. The degree of its symmetry is higher. The gas is even more symmetrical: the liquid occupies a certain volume in the vessel and asymmetry is observed inside the vessel, where there is liquid, and points where it is not. Gas occupies the entire volume provided to it, and in this sense, all its points are indistinguishable from one another. Still, here it would be more correct to speak not about points, but about small, but macroscopic elements, because there are still differences at the microscopic level. At some points at a given time there are atoms or molecules, while others do not. Symmetry is observed only on average, either over some macroscopic volume parameters, or over time.
But there is still no instantaneous symmetry at the microscopic level. If the substance is compressed very strongly, up to pressures that are unacceptable in everyday life, compress so that the atoms were crushed, their shells penetrated each other, and the nuclei began to touch, symmetry arises at the microscopic level. All nuclei are the same and pressed against each other, not only interatomic, but also internuclear distances are absent, and the substance becomes homogeneous (strange substance).
But there is also a submicroscopic level. Nuclei are made up of protons and neutrons that move inside the nucleus. There is also some space between them. If you continue to squeeze so that the nuclei will be crushed too, the nucleons will tightly press against each other. Then, at the submicroscopic level, symmetry will appear, which is not even inside ordinary nuclei.
From what has been said, a quite definite tendency can be discerned: the higher the temperature and the higher the pressure, the more symmetrical the substance becomes. Based on these considerations, the substance compressed to the maximum is called strongly symmetric.

18. Weakly symmetric substance- a state opposite to a strongly symmetric substance in its properties, which was present in a very early Universe at a temperature close to the Planck temperature, perhaps 10-12 seconds after the Big Bang, when strong, weak and electromagnetic forces were a single superpower. In this state, matter is compressed to such an extent that its mass is converted into energy, which begins to influence, that is, to expand indefinitely. It is not yet possible to reach energies for the experimental obtaining of superpower and transfer of matter into this phase under terrestrial conditions, although such attempts were made at the Large Hadron Collider in order to study the early universe. Due to the absence of gravitational interaction in the composition of the super-force that forms this substance, the super-force is not sufficiently symmetric in comparison with the supersymmetric force, which contains all 4 types of interactions. Therefore, this state of aggregation has received such a name.

19. Beam matter- this, in fact, is no longer a substance at all, but energy in its pure form. However, it is this hypothetical state of aggregation that a body will assume when it has reached the speed of light. It can also be obtained by heating the body to the Planck temperature (1032K), that is, by accelerating the molecules of the substance to the speed of light. As follows from the theory of relativity, when a speed of more than 0.99 s is reached, the body's mass begins to grow much faster than during "normal" acceleration, in addition, the body lengthens, heats up, that is, begins to radiate in the infrared spectrum. Upon crossing the threshold of 0.999 s, the body changes dramatically and begins a rapid phase transition up to the ray state. As follows from Einstein's formula, taken in full form, the growing mass of the final substance consists of masses that are separated from the body in the form of thermal, X-ray, optical and other radiation, the energy of each of which is described by the next term in the formula. Thus, a body approaching the speed of light will begin to emit in all spectra, grow in length and slow down in time, thinning to the Planck length, that is, upon reaching speed c, the body will turn into an infinitely long and thin ray moving at the speed of light and consisting of photons that have no length, and its infinite mass is completely converted into energy. Therefore, such a substance is called ray.

DEFINITION

Carbon- the sixth element of the Periodic Table. Designation - C from the Latin "carboneum". Located in the second period, IVA group. Refers to non-metals. The core has a charge of 6.

Carbon is found in nature both in a free state and in the form of numerous compounds. Free carbon occurs in the form of diamond and graphite. In addition to fossil coal, there are large accumulations of oil in the bowels of the Earth. In the earth's crust, there are huge amounts of carbonic acid salts, especially calcium carbonate. There is always carbon dioxide in the air. Finally, plant and animal organisms are composed of substances in the formation of which carbon takes part. Thus, this element is one of the most widespread on Earth, although its total content in the earth's crust is only about 0.1% (mass.).

Atomic and molecular weight of carbon

The relative molecular weight of a substance (M r) is a number that shows how many times the mass of a given molecule is greater than 1/12 of the mass of a carbon atom, and the relative atomic mass element (Ar) - how many times the average mass of atoms of a chemical element is more than 1/12 of the mass of a carbon atom.

Since in the free state carbon exists in the form of monatomic molecules C, the values ​​of its atomic and molecular weight match up. They are equal to 12.0064.

Allotropy and allotropic modifications of carbon

In the free state, carbon exists in the form of diamond crystallizing in the cubic and hexagonal (lonsdaleite) system, and graphite belonging to the hexagonal system (Fig. 1). Forms of carbon such as charcoal, coke, or soot have a disordered structure. There are also allotropic modifications obtained synthetically - these are carbyne and polycumulene - varieties of carbon built from linear chain polymers such as -C = C- or = C = C =.

Rice. 1. Allotropic modifications of carbon.

Allotropic modifications of carbon are also known, which have the following names: graphene, fullerene, nanotubes, nanofibers, astralen, glassy carbon, colossal nanotubes; amorphous carbon, carbon nanobodules and carbon nanofoam.

Carbon isotopes

In nature, carbon exists in the form of two stable isotopes 12 C (98.98%) and 13 C (1.07%). Their mass numbers are 12 and 13, respectively. The nucleus of the carbon 12 C isotope contains six protons and six neutrons, while the 13 C isotope contains the same number of protons and five neutrons.

There is one artificial (radioactive) isotope of carbon 14 C with a half-life of 5730 years.

Carbon ions

At the outer energy level of the carbon atom, there are four electrons that are valence:

1s 2 2s 2 2p 2.

As a result of chemical interaction, carbon can lose its valence electrons, i.e. be their donor, and turn into positively charged ions or accept electrons of another atom, i.e. be their acceptor, and turn into negatively charged ions:

C 0 -2e → C 2+;

C 0 -4e → C 4+;

C 0 + 4e → C 4-.

Molecule and carbon atom

In the free state, carbon exists in the form of monatomic molecules C. Let us give some properties that characterize the atom and molecule of carbon:

Carbon alloys

The most famous carbon alloys around the world are steel and cast iron. Steel is an alloy of iron with carbon, the carbon content of which does not exceed 2%. In cast iron (also an alloy of iron with carbon), the carbon content is higher - from 2 to 4%.

Examples of problem solving

EXAMPLE 1

The task	What volume of carbon monoxide (IV) will be released (n.o.) when firing 500 g of limestone containing 0.1 mass fraction of impurities.
Solution	Let us write the equation for the reaction of limestone roasting: CaCO 3 = CaO + CO 2 -. Let's find a mass of pure limestone. To do this, first determine its mass fraction without impurities: w clear (CaCO 3) = 1 - w impurity = 1 - 0.1 = 0.9. m clear (CaCO 3) = m (CaCO 3) × w clear (CaCO 3); m clear (CaCO 3) = 500 × 0.9 = 450 g. Let's calculate the amount of limestone substance: n (CaCO 3) = m clear (CaCO 3) / M (CaCO 3); n (CaCO 3) = 450/100 = 4.5 mol. According to the reaction equation n (CaCO 3): n (CO 2) = 1: 1, which means n (CaCO 3) = n (CO 2) = 4.5 mol. Then, the volume of released carbon monoxide (IV) will be equal to: V (CO 2) = n (CO 2) × V m; V (CO 2) = 4.5 × 22.4 = 100.8 liters.
Answer	100.8 l

EXAMPLE 2

The task	How much of a solution containing 0.05 parts by weight, or 5% hydrogen chloride, is required to neutralize 11.2 g of calcium carbonate?
Solution	Let us write the equation for the reaction of neutralization of calcium carbonate with hydrogen chloride: CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2 -. Find the amount of calcium carbonate substance: M (CaCO 3) = A r (Ca) + A r (C) + 3 × A r (O); M (CaCO 3) = 40 + 12 + 3 × 16 = 52 + 48 = 100 g / mol. n (CaCO 3) = m (CaCO 3) / M (CaCO 3); n (CaCO 3) = 11.2 / 100 = 0.112 mol. According to the reaction equation n (CaCO 3): n (HCl) = 1: 2, which means n (HCl) = 2 × n (CaCO 3) = 2 × 0.224 mol. Determine the mass of the hydrogen chloride substance contained in the solution: M (HCl) = A r (H) + A r (Cl) = 1 + 35.5 = 36.5 g / mol. m (HCl) = n (HCl) × M (HCl) = 0.224 × 36.5 = 8.176 g. Calculate the mass of the hydrogen chloride solution: m solution (HCl) = m (HCl) x 100 / w (HCl); m solution (HCl) = 8.176 × 100/5 = 163.52 g.
Answer	163.52 g

Carbon (C)- typical non-metal; in the periodic system is in the 2nd period of the IV group, main subgroup... Atomic number 6, Ar = 12.011 amu, nuclear charge +6.

Physical properties: carbon forms many allotropic modifications: diamond- one of the hardest substances graphite, coal, soot.

A carbon atom has 6 electrons: 1s 2 2s 2 2p 2 . The last two electrons are located on separate p-orbitals and are unpaired. In principle, this pair could occupy one orbital, but in this case the electron-electron repulsion greatly increases. For this reason, one of them takes 2p x, and the other, or 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 goes over to the free one. 2p. A valence state with the configuration 1s 2 2s 1 2p x 1 2p y 1 2p z 1 . It is this state of the carbon atom that is characteristic of the diamond lattice - the tetrahedral spatial arrangement of hybrid orbitals, the same bond length and energy.

This phenomenon is known to be called sp 3 -hybridization, and the arising functions are sp 3 -hybrid . The formation of four sp 3 bonds provides the carbon atom with a more stable state than three p-p- and one s-s-link. In addition to sp 3 hybridization at the carbon atom, sp 2 and sp hybridization is also observed . In the first case, there is a mutual overlap s- and two p-orbitals. Three equivalent sp 2 - hybrid orbitals are formed, located in one plane at an angle of 120 ° to each other. The third orbital p is unchanged and directed perpendicular to the plane sp 2.

During sp-hybridization, the s and p orbitals overlap. An angle of 180 ° arises between the two formed equivalent hybrid orbitals, while the two p-orbitals for 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 bonded to three adjacent sp 2 -hybrid bonds. The connection between the parallel planes is carried out by 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 in a substance are located, the properties of this substance depend.

Chemical properties of carbon

The most typical oxidation states are +4, +2.

At low temperatures, carbon is inert, but when heated, its activity increases.

Carbon as a reducing agent:

- with oxygen
C 0 + O 2 - t ° = CO 2 carbon dioxide
with a lack of oxygen - incomplete combustion:
2C 0 + O 2 - t ° = 2C +2 O carbon monoxide

- with fluorine
C + 2F 2 = CF 4

- with water vapor
C 0 + H 2 O - 1200 ° = C +2 O + H 2 water gas

- with metal oxides. Thus, metal is smelted from ore.
C 0 + 2CuO - t ° = 2Cu + C +4 O 2

- with acids - oxidizing agents:
C 0 + 2H 2 SO 4 (conc.) = C +4 O 2 + 2SO 2 + 2H 2 O
C 0 + 4HNO 3 (conc.) = C +4 O 2 + 4NO 2 + 2H 2 O

- forms carbon disulfide with sulfur:
C + 2S 2 = CS 2.

Carbon as an oxidizing agent:

- forms carbides with some metals

4Al + 3C 0 = Al 4 C 3

Ca + 2C 0 = CaC 2 -4

- with hydrogen - methane (as well as a huge amount of organic compounds)

C 0 + 2H 2 = CH 4

- with silicon, forms carborundum (at 2000 ° C in an electric furnace):

Finding carbon in nature

Free carbon occurs in the form of diamond and graphite. In the form of compounds, carbon is in the composition of minerals: chalk, marble, limestone - CaCO 3, dolomite - MgCO 3 * CaCO 3; hydrocarbonates - Mg (HCO 3) 2 and Ca (HCO 3) 2, CO 2 is part of the air; carbon is the main constituent part of natural organic compounds - gas, oil, coal, peat, is a part of organic substances, proteins, fats, carbohydrates, amino acids that make up living organisms.

Inorganic carbon compounds

Neither C 4+ nor C 4- ions are formed under any ordinary chemical processes: there are covalent bonds of different polarity in carbon compounds.

Carbon monoxide (II) CO

Carbon monoxide; colorless, odorless, slightly soluble in water, soluble in organic solvents, poisonous, t ° bale = -192 ° C; t pl. = -205 ° C.

Receiving
1) In industry (in gas generators):
C + O 2 = CO 2

2) In the laboratory - by thermal decomposition of formic or oxalic acid in the presence of H 2 SO 4 (conc.):
HCOOH = H 2 O + CO

H 2 C 2 O 4 = CO + CO 2 + H 2 O

Chemical properties

CO is inert under normal conditions; when heated - a reducing agent; non-salt-forming oxide.

1) with oxygen

2C +2 O + O 2 = 2C +4 O 2

2) with metal oxides

C +2 O + CuO = Cu + C +4 O 2

3) with chlorine (in the light)

CO + Cl 2 - hn = COCl 2 (phosgene)

4) reacts with alkali melts (under pressure)

CO + NaOH = HCOONa (sodium formate)

5) forms carbonyls with transition metals

Ni + 4CO - t ° = Ni (CO) 4

Fe + 5CO - t ° = Fe (CO) 5

Carbon monoxide (IV) CO2

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

Receiving

1. Thermal decomposition of carbonic acid salts (carbonates). Limestone roasting:

CaCO 3 - t ° = CaO + CO 2

1. The action of strong acids on carbonates and bicarbonates:

CaCO 3 + 2HCl = CaCl 2 + H 2 O + CO 2

NaHCO 3 + HCl = NaCl + H 2 O + CO 2

ChemicalpropertiesCO2
Acidic Oxide: Reacts with basic oxides and bases to form carbonic acid salts

Na 2 O + CO 2 = Na 2 CO 3

2NaOH + CO 2 = Na 2 CO 3 + H 2 O

NaOH + CO 2 = NaHCO 3

May exhibit oxidizing properties at elevated temperatures

С +4 O 2 + 2Mg - t ° = 2Mg +2 O + C 0

Qualitative reaction

Turbidity of lime water:

Ca (OH) 2 + CO 2 = CaCO 3 ¯ (white precipitate) + H 2 O

It disappears with prolonged passage of CO 2 through lime water, because insoluble calcium carbonate transforms into soluble bicarbonate:

CaCO 3 + H 2 O + CO 2 = Ca (HCO 3) 2

Carbonic acid and itssalt

H 2CO 3 - The acid is weak, exists only in aqueous solution:

CO 2 + H 2 O ↔ H 2 CO 3

Two-base:
H 2 CO 3 ↔ H + + HCO 3 - Acid salts - bicarbonates, hydrocarbonates
HCO 3 - ↔ H + + CO 3 2- Medium salts - carbonates

All properties of acids are characteristic.

Carbonates and hydrocarbons can be converted into each other:

2NaHCO 3 - t ° = Na 2 CO 3 + H 2 O + CO 2

Na 2 CO 3 + H 2 O + CO 2 = 2NaHCO 3

Metal carbonates (except for alkali metals) decarboxylate when heated to form an oxide:

CuCO 3 - t ° = CuO + CO 2

Qualitative reaction- "boiling" under the action of a strong acid:

Na 2 CO 3 + 2HCl = 2NaCl + H 2 O + CO 2

CO 3 2- + 2H + = H 2 O + CO 2

Carbides

Calcium carbide:

CaO + 3 C = CaC 2 + CO

CaC 2 + 2 H 2 O = Ca (OH) 2 + C 2 H 2.

Acetylene is released when zinc, cadmium, lanthanum and cerium carbides react with water:

2 LaC 2 + 6 H 2 O = 2La (OH) 3 + 2 C 2 H 2 + H 2.

Be 2 C and Al 4 C 3 decompose with water to form methane:

Al 4 C 3 + 12 H 2 O = 4 Al (OH) 3 = 3 CH 4.

In technology, titanium carbides TiC, tungsten W 2 C (hard alloys), silicon SiC (carborundum - as an abrasive and a material for heaters) are used.

Cyanide

obtained by heating soda in an atmosphere of ammonia and carbon monoxide:

Na 2 CO 3 + 2 NH 3 + 3 CO = 2 NaCN + 2 H 2 O + H 2 + 2 CO 2

Hydrocyanic acid HCN is an important product of the chemical industry and is widely used in organic synthesis. Its 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% water solution) are used in gold mining:

2 Au + 4 KCN + H 2 O + 0.5 O 2 = 2 K + 2 KOH.

When boiling solutions of cyanide with sulfur or fusing solids, thiocyanates:
KCN + S = KSCN.

When cyanides of low-activity metals are heated, cyanogen is obtained: Hg (CN) 2 = Hg + (CN) 2. Cyanide solutions are oxidized to cyanates:

2 KCN + O 2 = 2 KOCN.

Cyanic acid comes in two forms:

H-N = C = O; H-O-C = N:

In 1828, Friedrich Wöhler (1800-1882) obtained urea from ammonium cyanate: NH 4 OCN = CO (NH 2) 2 by evaporation of an aqueous solution.

This event is usually seen as the victory of synthetic chemistry over "vitalist theory".

There is an isomer of cyanic acid - oxyhydrogen

H-O-N = C.
Its salts (explosive mercury Hg (ONC) 2) are used in impact ignitors.

Synthesis urea(urea):

CO 2 + 2 NH 3 = CO (NH 2) 2 + H 2 O. At 130 0 С and 100 atm.

Urea is an amide of carbonic acid; there is also its "nitrogen analogue" - guanidine.

Carbonates

The most important inorganic carbon compounds are carbonic acid salts (carbonates). H 2 CO 3 is a weak acid (K 1 = 1.3 · 10 -4; K 2 = 5 · 10 -11). Carbonate buffer supports carbon dioxide equilibrium in the atmosphere. The oceans have a huge buffer capacity because they are open system... The main buffer reaction is equilibrium in 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, dissolution of carbonate rocks (shells, chalk and limestone deposits in the ocean) occurs; this compensates for the loss of hydrocarbonate ions:

H + + CO 3 2- ↔ HCO 3 -

CaCO 3 (solid) ↔ Ca 2+ + CO 3 2-

Solid carbonates are converted into soluble hydrocarbonates. It is this process of chemical dissolution of excess carbon dioxide that counteracts the "greenhouse effect" - global warming due to the absorption of thermal radiation from the Earth by carbon dioxide. About a third of the world's soda production (sodium carbonate Na 2 CO 3) is used in glass production.

CARBON, С, chemical element of group IV of the periodic system, atomic weight 12.00, ordinal number 6. Until recently, carbon was considered to have no isotopes; only recently was it possible with the help of especially sensitive methods to detect the existence of the isotope C 13. Carbon is one of the most important elements in terms of abundance, the abundance and diversity of its compounds, and biological significance(as an organogen), in the vastness of the technical use of carbon itself and its compounds (as raw materials and as a source of energy for industrial and domestic needs) and, finally, in terms of its role in the development of chemical science. Carbon in a free state reveals a pronounced phenomenon of allotropy, which has been known for more than a century and a half, but has not yet been fully studied, both due to the extreme difficulty of obtaining carbon in a chemically pure form, and because most of the constants of allotropic modifications of carbon vary greatly depending on morphological features of their structure, due to the method and conditions of obtaining.

Carbon forms two crystalline forms - diamond and graphite and is also known in the amorphous state in the form of the so-called. amorphous coal. The individuality of the latter, as a result of recent studies, was disputed: coal was identified with graphite, considering both as morphological varieties of one form - "black carbon", and the difference in their properties was explained by the physical structure and degree of dispersion of the substance. However, very recently, facts have been obtained that confirm the existence of coal as a special allotropic form (see below).

Natural sources and stocks of carbon... In terms of prevalence in nature, carbon occupies the 10th place among the elements, making up 0.013% of the atmosphere, 0.0025% of the hydrosphere and about 0.35% of the total mass of the earth's crust. Most of the carbon is in the form of oxygen compounds: the atmospheric air contains ~ 800 billion tons of carbon in the form of CO 2 dioxide; in the water of the oceans and seas - up to 50,000 billion tons of carbon in the form of CO 2, carbonic acid ion and bicarbonates; in rocks - insoluble carbonates (calcium, magnesium and other metals), and the share of CaCO 3 alone accounts for ~ 160 · 10 6 billion tons of carbon. These colossal reserves, however, are of no energy value; much more valuable are combustible carbonaceous materials - fossil coals, peat, then oil, hydrocarbon gases and other natural bitumens. The supply of these substances in the earth's crust is also quite significant: the total mass of carbon in fossil coals reaches ~ 6000 billion tons, in oil ~ 10 billion tons, etc. In a free state, carbon is quite rare (diamond and part of the graphite matter). Fossil coals contain little or no free carbon: they consist of hl. arr. from high-molecular (polycyclic) and very stable compounds of carbon with other elements (H, O, N, S) are still very little studied. Carbonaceous compounds of living nature (the biosphere of the earth), synthesized in plant and animal cells, are distinguished by an extraordinary variety of properties and amounts of composition; The most abundant substances in the plant world - fiber and lignin - also play a role as energy resources.

Carbon retains a constant distribution in nature due to the continuous circulation, the cycle of which is composed of the synthesis of complex organic substances in plant and animal cells and from the reverse disaggregation of these substances during their oxidative decay (combustion, decay, respiration), leading to the formation of CO 2, which is again used plants for synthesis. The general scheme of this cycle can be used. presented in the following form:

Carbon production... Carbonaceous compounds of plant and animal origin are unstable at high temperatures and, when heated to at least 150-400 ° C without access to air, decompose, releasing water and volatile carbon compounds and leaving a solid non-volatile residue, rich in carbon and commonly called coal. This pyrolytic process is called charring, or dry distillation, and is widely used in technology. High-temperature pyrolysis of fossil coal, oil and peat (at a temperature of 450-1150 ° C) leads to the release of carbon in a graphite-like form (coke, retort coal). The higher the carbonization temperature of the starting materials, the more the resulting coal or coke is closer in composition to free carbon, and in properties to graphite.

Amorphous coal, formed at temperatures below 800 ° C, can not be. we consider it as free carbon, because it contains significant amounts of chemically bound other elements, Ch. arr. hydrogen and oxygen. Among technical products, activated carbon and soot are the closest in properties to amorphous carbon. The purest coal m. B. obtained by carbonization of pure sugar or piperonal, special processing of gas soot, etc. Artificial graphite obtained by electrothermal means is almost pure carbon in composition. Natural graphite is always contaminated with mineral impurities and, in addition, contains a certain amount of bound hydrogen (H) and oxygen (O); in a relatively clean state, he might b. obtained only after a number of special treatments: mechanical enrichment, washing, treatment with oxidizing agents and calcining at high temperatures until the complete removal of volatile substances. Carbon technology never deals with perfectly pure carbon; this applies not only to natural carbon raw materials, but also to the products of its enrichment, upgrading and thermal decomposition (pyrolysis). Below is the carbon content of some carbonaceous materials (in%):

Physical properties of carbon... Free carbon is practically completely infusible, non-volatile, and at ordinary temperatures it is insoluble in any of the known solvents. It dissolves only in some molten metals, especially at temperatures approaching the boiling point of the latter: in iron (up to 5%), silver (up to 6%) | ruthenium (up to 4%), cobalt, nickel, gold and platinum. In the absence of oxygen, carbon is the most refractory material; the liquid state for pure carbon is unknown, and its transformation into vapor begins only at temperatures above 3000 ° C. Therefore, the determination of the properties of carbon was made exclusively for the solid state of aggregation. Of the carbon modifications, diamond has the most permanent physical properties; the properties of graphite in its various samples (even the purest ones) vary considerably; the properties of amorphous coal are even more inconsistent. The most important physical constants of various carbon modifications are compared in the table.

Diamond is a typical dielectric, while graphite and coal have metallic electrical conductivity. In absolute value, their conductivity varies over a very wide range, but for coals it is always lower than for graphites; for graphites it approaches the conductivity of real metals. The heat capacity of all carbon modifications at temperatures> 1000 ° С tends to a constant value of 0.47. At temperatures below -180 ° C, the heat capacity of diamond becomes vanishingly small, and at -27 ° C it becomes practically zero.

Chemical properties of carbon... When heated above 1000 ° C, both diamond and coal gradually transform into graphite, which should therefore be considered as the most stable (at high temperatures) monotropic form of carbon. The transformation of amorphous coal into graphite apparently begins at about 800 ° C and ends at 1100 ° C (at this last point, coal loses its adsorption activity and ability to reactivate, and its electrical conductivity increases sharply, remaining almost constant in the future). Free carbon is characterized by inertness at ordinary temperatures and significant activity at high temperatures. Amorphous coal is the most chemically active, while diamond has the greatest resistance. For example, fluorine reacts with coal at a temperature of 15 ° C, with graphite only at 500 ° C, and with diamond at 700 ° C. When heated in air, porous coal begins to oxidize below 100 ° C, graphite around 650 ° C, and diamond above 800 ° C. At temperatures of 300 ° C and above, coal combines with sulfur to form carbon disulfide CS 2. At temperatures above 1800 ° C, carbon (coal) begins to interact with nitrogen, forming (in small amounts) cyanogen C 2 N 2. The interaction of carbon with hydrogen begins at 1200 ° C, and in the temperature range 1200-1500 ° C, only methane CH 4 is formed; above 1500 ° C - a mixture of methane, ethylene (C 2 H 4) and acetylene (C 2 H 2); at a temperature of the order of 3000 ° C, almost exclusively acetylene is obtained. At the temperature of the electric arc, carbon enters into direct connection with metals, silicon and boron, forming the corresponding carbides. Direct or indirect ways m. B. compounds of carbon with all known elements, except for gases of the zero group, were obtained. Carbon is a non-metallic element that exhibits some signs of amphotericity. The carbon atom has a diameter of 1.50 Ᾰ (1Ᾰ = 10 -8 cm) and contains 4 valence electrons in the outer sphere, which are given or supplemented with equal ease to 8; therefore, the normal valence of carbon, both oxygen and hydrogen, is four. In the overwhelming majority of its compounds, carbon is tetravalent; only a few are known compounds of divalent carbon (carbon monoxide and its acetals, isonitriles, explosive acid and its salts) and trivalent (so-called "free radical").

With oxygen, carbon forms two normal oxides: carbon dioxide CO 2 of an acidic nature and neutral carbon monoxide CO. In addition, there are a number of carbon deficiency containing more than 1 C atom, of no technical importance; Of these, the most famous is a suboxide of the composition C 3 O 2 (gas with a boiling point of + 7 ° C and a melting point of -111 ° C). The first product of combustion of carbon and its compounds is CO 2, which is formed according to the equation:

C + O 2 = CO 2 +97600 cal.

The formation of CO during incomplete combustion of fuel is the result of the secondary reduction process; the reducing agent in this case is carbon itself, which at temperatures above 450 ° C reacts with CO 2 according to the equation:

CO 2 + C = 2CO -38800 cal;

this reaction is reversible; above 950 ° C, the conversion of CO 2 into CO becomes almost complete, which is carried out in gas-generating furnaces. The energetic reductive capacity of carbon at high temperatures is also used in the production of water gas (H 2 O + C = CO + H 2 -28380 cal) and in metallurgical processes - to obtain a free metal from its oxide. Allotropic forms of carbon relate differently to the action of some oxidants: for example, a mixture of KCIO 3 + HNO 3 does not act on diamond at all, amorphous coal is completely oxidized by it in CO 2, while graphite gives aromatic compounds - graphitic acids with the empirical formula (C 2 OH) x and beyond mellitic acid C 6 (COOH) 6. Compounds of carbon with hydrogen - hydrocarbons - are extremely numerous; most of the other organic compounds are genetically produced from them, which, in addition to carbon, most often include H, O, N, S and halogens.

The exceptional variety of organic compounds, of which up to 2 million are known, is due to some of the characteristics of carbon as an element. 1) Carbon is characterized by the strength of a chemical bond with most of the other elements, both metallic and non-metallic, due to which it forms fairly stable compounds with both. Combining with other elements, carbon has very little inclination to form ions. Most of the organic compounds are of the homeopolar type and do not dissociate under normal conditions; the rupture of intramolecular bonds in them often requires the expenditure of a significant amount of energy. When judging the strength of bonds, however, one should distinguish; a) the absolute bond strength, measured by the thermochemical method, and b) the ability of the bond to break under the action of various reagents; these two characteristics do not always coincide. 2) Carbon atoms bond with each other with exceptional ease (non-polarity), forming carbon chains, open or closed. The length of such chains does not appear to be subject to any restrictions; thus, quite stable molecules with open chains of 64 carbon atoms are known. The lengthening and complication of open chains does not affect the strength of the connection of their links with each other or with other elements. Among the closed chains, 6- and 5-membered rings are most easily formed, although ring chains containing from 3 to 18 carbon atoms are known. The ability of carbon atoms to interconnect well explains the special properties of graphite and the mechanism of carbonization processes; it also makes it clear that carbon is unknown in the form of diatomic C 2 molecules, which might be expected by analogy with other light non-metallic elements (in vapor form, carbon consists of monoatomic molecules). 3) Due to the non-polar nature of the bonds, many carbon compounds have chemical inertness not only external (slow reaction), but also internal (difficulty of intramolecular rearrangements). The presence of large "passive resistances" greatly complicates the spontaneous transformation of unstable forms into stable ones, often reducing the rate of such transformation to zero. This results in the possibility of realizing a large number of isomeric forms that are practically equally stable at ordinary temperatures.

Allotropy and atomic structure of carbon... X-ray analysis made it possible to reliably establish the atomic structure of diamond and graphite. The same research method shed light on the question of the existence of the third allotropic modification of carbon, which is essentially a question about the amorphousness or crystallinity of coal: if coal is an amorphous formation, then it cannot be. identified with neither graphite nor diamond, but should be considered as special form carbon as an individual simple substance. In a diamond, carbon atoms are located so that each atom lies in the center of a tetrahedron, the vertices of which are 4 adjacent atoms; each of the latter, in turn, is the center of another similar tetrahedron; the distances between adjacent atoms are equal to 1.54 Ᾰ (the edge of the elementary cube of the crystal lattice is 3.55). This structure is the most compact; it corresponds to the high hardness, density and chemical inertness of diamond (uniform distribution of valence forces). The interconnection of carbon atoms in the diamond lattice is the same as in the molecules of most fatty organic compounds (tetrahedral carbon model). In graphite crystals, carbon atoms are located in dense layers spaced from one another by 3.35-3.41 Ᾰ; the direction of these layers coincides with the cleavage planes and slip planes during mechanical deformations. In the plane of each layer, the atoms form a grid with hexagonal cells (companies); the side of such a hexagon is 1.42-1.45 Ᾰ. In adjacent layers, the hexagons do not lie one below the other: their coincidence vertically is repeated only after 2 layers in the third. Three bonds of each carbon atom lie in the same plane, forming angles of 120 °; The 4th bond is directed alternately in one direction or the other from the plane to the atoms of the neighboring layers. The distances between the atoms in the layer are strictly constant, while the distance between the individual layers m. B. changed by external influences: for example, when pressed under pressure up to 5000 atm, it decreases to 2.9 Ᾰ, and when graphite swells in concentrated HNO 3, it increases to 8 Ᾰ. In the plane of one layer, the carbon atoms are linked homeopolarly (as in hydrocarbon chains), while the bonds between the atoms of adjacent layers are rather metallic in nature; This can be seen from the fact that the electrical conductivity of graphite crystals in the direction perpendicular to the layers is ~ 100 times higher than the conductivity in the direction of the layer. That. graphite has the properties of a metal in one direction and properties of a non-metal in the other. The arrangement of carbon atoms in each layer of the graphite lattice is exactly the same as in the molecules of complex aromatic compounds. This configuration well explains the sharp anisotropy of graphite, extremely developed cleavage, antifriction properties, and the formation of aromatic compounds during its oxidation. The amorphous modification of black carbon apparently exists as an independent form (O. Ruff). For her, the most probable is a foamy cellular structure, devoid of any regularity; the walls of such cells are formed by layers of active atoms carbon about 3 atoms thick. In practice, the active substance of coal usually lies under a shell of closely spaced inactive carbon atoms oriented graphitically and is permeated with inclusions of very small graphite crystallites. There is probably no definite point of transformation coal → graphite: a continuous transition occurs between both modifications, during which the randomly packed mass of C-atoms of amorphous coal is reorganized into the correct one. crystal lattice graphite. Due to their random arrangement, carbon atoms in amorphous coal exhibit a maximum residual affinity, which (according to Langmuir's ideas about the identity of adsorption forces with valence forces) corresponds to the high adsorption and catalytic activity so characteristic of coal. Carbon atoms oriented in the crystal lattice spend all their affinity (in diamond) or most of it (in graphite) on mutual adhesion; this corresponds to a decrease in the chemical activity and adsorption activity. In diamond, adsorption is possible only on the surface of a single crystal, while in graphite, residual valence can manifest itself on both surfaces of each planar lattice (in “gaps” between layers of atoms), which is confirmed by the fact that graphite is capable of swelling in liquids (HNO 3) and the mechanism of its oxidation to graphitic acid.

Carbon technical value... As for b. or m. free carbon obtained during the processes of charring and coking, then its application in technology is based both on chemical (inertness, reducing ability) and on its physical properties (heat resistance, electrical conductivity, adsorption capacity). So, coke and charcoal, in addition to their partial direct utilization as a flameless fuel, are used to obtain gaseous fuel (generator gases); in metallurgy of ferrous and non-ferrous metals - for the reduction of metal oxides (Fe, Cu, Zn, Ni, Cr, Mn, W, Mo, Sn, As, Sb, Bi); in chemical technology - as a reducing agent in the production of sulfides (Na, Ca, Ba) from sulfates, anhydrous chloride salts (Mg, Al), from metal oxides, in the production of soluble glass and phosphorus - as a raw material for the production of calcium carbide, carborundum and other carbides carbon disulfide, etc .; in the construction business - as a thermal insulating material. Retort coal and coke serve as a material for electrodes of electric furnaces, electrolytic baths and galvanic cells, for the manufacture of arc coals, rheostats, collector brushes, melting crucibles, etc., as well as packing in tower-type chemical equipment. Charcoal, in addition to the above applications, is used to obtain concentrated carbon monoxide, cyanide salts, for carburizing steel, is widely used as an adsorbent, as a catalyst for some synthetic reactions, and finally it is part of black powder and other explosive and pyrotechnic compositions.

Analytical determination of carbon... Qualitatively, carbon is determined by charring a sample of a substance without air access (which is far from suitable for all substances) or, which is much more reliable, by its exhaustive oxidation, for example, by calcining it in a mixture with copper oxide, and the formation of CO 2 is proved by conventional reactions. For the quantitative determination of carbon, a sample of the substance is burned in an oxygen atmosphere; the resulting CO 2 is captured by the alkali solution and determined by weight or volume by conventional methods of quantitative analysis. This method is suitable for determining carbon not only in organic compounds and industrial coals, but also in metals.