Sinusitis

Common to carbon and silicon is. Physical properties of simple substances carbon and silicon

Silicon is a chemical element of group IV of the Periodic Table of Elements D.I. Mendeleev. Discovered in 1811 by J. Gay-Lusac and L. Ternar. Its serial number is 14, atomic mass 28.08, atomic volume 12.04 10 -6 m 3 /mol. Silicon is a metalloid and belongs to the carbon subgroup. Its oxygen valency is +2 and +4. In terms of abundance in nature, silicon is second only to oxygen. His mass fraction in the earth's crust is 27.6%. The earth's crust, according to V.I. Vernadsky, more than 97% consists of silica and silicates. Oxygen and organic compounds silicon is also found in plants and animals.

Artificially produced silicon can be either amorphous or crystalline. Amorphous silicon is a brown, finely dispersed, highly hygroscopic powder; according to X-ray diffraction data, it consists of tiny silicon crystals. It can be obtained by reducing SiCl 4 with zinc vapor at high temperatures.

Crystalline silicon has a steel-gray color and a metallic luster. The density of crystalline silicon at 20°C is 2.33 g/cm3, liquid silicon at 1723-2.51, and at 1903K - 2.445 g/cm3. The melting point of silicon is 1690 K, boiling point - 3513 K. According to the data, the vapor pressure of silicon at T = 2500÷4000 K is described by the equation log p Si = -20130/ T + 7.736, kPa. Heat of sublimation of silicon 452610, heat of melting 49790, evaporation 385020 J/mol.

Silicon polycrystals are characterized by high hardness (at 20°C HRC = 106). However, silicon is very brittle, therefore it has high compressive strength (σ SZh B ≈690 MPa) and very low tensile strength (σ B ≈ 16.7 MPa).

At room temperature, silicon is inert and reacts only with fluorine, forming volatile 81P4. Of the acids, it reacts only with nitric acid in a mixture with hydrofluoric acid. However, silicon reacts quite easily with alkalis. One of his reactions with alkalis

Si + NaOH + H 2 O = Na 2 SiO 3 + 2H 2

used to produce hydrogen. At the same time, silicon can form a large number of chemically strong compounds with non-metals. Of these compounds, it is necessary to note the halides (from SiX 4 to Si n X 2n+2, where X is a halogen and n ≤ 25), their mixed compounds SiCl 3 B, SiFCl 3, etc., oxychlorides Si 2 OCl 3, Si 3 O2Cl3 and others, nitrides Si 3 N 4, Si 2 N 3, SiN and hydrides with the general formula Si n H 2n+2, and among the compounds found in the production of ferroalloys - volatile sulfides SiS and SiS 2 and refractory carbide SiC.

Silicon is also capable of producing compounds with metals - silicides, the most important of which are silicides of iron, chromium, manganese, molybdenum, zirconium, as well as rare earth metals and alkali metals. This property of silicon - the ability to produce chemically very strong compounds and solutions with metals - is widely used in the production of low-carbon ferroalloys, as well as in the reduction of low-boiling alkaline earth (Ca, Mg, Ba) and difficult-to-reduce metals (Zr, Al, etc.).

Alloys of silicon with iron were studied by P.V. Geld and his school, special attention was addressed to the part of the Fe-Si system related to alloys with its high content. This is due to the fact that, as can be seen from the Fe-Si diagram (Figure 1), a number of transformations occur in alloys of this composition that significantly affect the quality of ferrosilicon of various grades. Thus, FeSi 2 disilicide is stable only at low temperatures (< 918 или 968 °С, см. рисунок 1). При высоких температурах устойчива его высокотемпературная модификация - лебоит. Содержание кремния в этой фазе колеблется в пределах 53-56 %. В дальнейшем лебоит будем обозначать chemical formula Fe 2 Si 5, which practically corresponds to the maximum concentration of silicon in leboite.

When cooling alloys containing > 55.5% Si, leboite at T< 1213 К разлагается по эвтектоидной реакции

Fe 2 Si 5 → FeSi 2 +Si (2)

and alloys 33.86-50.07% Si at T< 1255 К - по перитектоидной реакции

Fe 2 Si 5 + FeSi = 3 FeSi 2 (3)

Alloys of intermediate composition (50.15-55.5% Si) first undergo peritectoid (3) at 1255 K, and then eutectoid (2) transformations at 1213 K. These transformations of Fe 2 Si 5 according to reactions (2) and (3) are accompanied by changes in the volume of silicide. This change is especially large during reaction (2) - approximately 14%, therefore alloys containing leboite lose continuity, crack and even crumble. With slow, equilibrium crystallization (see Figure 1), leboite can be released during the crystallization of both the FS75 and FS45 alloys.

However, cracking associated with the eutectoid decomposition of leboite is only one of the causes of disintegration. The second reason, apparently the main one, is that the formation of cracks along the grain boundaries creates the opportunity for the liquids released along these boundaries - phosphorus, arsenic, aluminum sulfides and carbides, etc. - to react with air moisture in reactions that result in H 2, PH 3, PH 4, AsH 4, etc. are released into the atmosphere, and in the cracks there are loose oxides Al 2 O 3, SiO 2 and other compounds that burst them. The disintegration of alloys can be prevented by modifying them with magnesium, alloying them with additives of elements that refine the grain (V, Ti, Zg, etc.) or make it more plastic. Grain refinement reduces the concentration of impurities and their compounds at its boundaries and affects the properties of alloys in the same way as general decline in the alloy there are concentrations of impurities (P, Al, Ca) that contribute to disintegration. The thermodynamic properties of Fe-Si alloys (heat of mixing, activity, carbon solubility) have been studied in detail and can be found in the works. Information on the solubility of carbon in Fe-Si alloys is given in Figure 2, on the activity of silicon - in Table 1.

Figure 1. — State diagram of the Fe-Si system

The physicochemical properties of oxygen silicon compounds were studied by P.V. Geld and his staff. Despite the importance of the Si-O system, its diagram has not yet been constructed. Currently, two oxygen compounds of silicon are known - silica SiO 2 and monoxide SiO. There are also indications in the literature about the existence of other oxygen compounds of silicon - Si 2 O 3 and Si 3 O 4, but there is no information about their chemical and physical properties.

In nature, silicon is represented only by silica SiO 2. This silicon compound is different:

1) high hardness (on the Mohs scale 7) and refractoriness (T pl = 1996 K);

2) high boiling point (T KIP = 3532 K). The vapor pressure of silica can be described by the equations (Pa):

3) the formation of a large number of modifications:

A feature of allotropic transformations of SiO 2 is that they are accompanied by significant changes in the density and volume of the substance, which can cause cracking and crushing of the rock;

4) high tendency to hypothermia. Therefore, it is possible, as a result of rapid cooling, to fix the structure of both the liquid melt (glass) and the high-temperature modifications of β-cristobalite and tridymite. On the contrary, with rapid heating it is possible to melt quartz, bypassing the tridymite and cristobalite structures. In this case, the melting point of SiO 2 decreases by approximately 100 °C;

5) high electrical resistance. For example, at 293 K it is 1 10 12 Ohm*m. However, with increasing temperature, the electrical resistance of SiO 2 decreases, and in the liquid state, silica is a good conductor;

6) high viscosity. Thus, at 2073 K the viscosity is 1 10 4 Pa s, and at 2273 K it is 280 Pa s.

The latter, according to N.V. Solomin, is explained by the fact that SiO 2, like organic polymers, is capable of forming chains that at 2073 K consist of 700, and at 2273 K - of 590 SiO 2 molecules;

7) high thermal stability. The Gibbs energy of the formation of SiO 2 from elements, taking into account their aggregate state in accordance with the data, is described with high accuracy by the equations:

These data, as can be seen from Table 2, differ somewhat from the authors’ data. For thermodynamic calculations, two-term equations can also be used:

Silicon monoxide SiO was discovered in 1895 by Potter in the gas phase of electric furnaces. It has now been reliably established that SiO also exists in condensed phases. According to research by P.V. Gelda, the oxide has a low density (2.15 g/cm 3) and high electrical resistance (10 5 -10 6 Ohm*m). The condensed oxide is brittle, its hardness on the Mohs scale is ~5. Due to its high volatility, the melting point could not be determined experimentally. According to O. Kubashevsky, it is equal to 1875 K, according to Berezhny, it is 1883 K. The heat of fusion of SiO is several times higher than ΔH 0 SiO2, according to the data it is equal to 50242 J/mol. Apparently, due to volatility, it is overestimated. It has a glassy fracture, its color varies from white to chocolate, which is probably due to its oxidation by atmospheric oxygen. Fresh SiO fracture usually has a pea-like color with a greasy sheen. The oxide is thermodynamically stable only at high temperatures in the form of SiO(G). When cooled, the oxide disproportions according to the reaction

2SiO (G) = SiO (L) + SiO 2 (6)

The boiling point of SiO can be roughly estimated from the equation:

Silicon oxide gas is thermodynamically very stable. The Gibbs energy of its formation can be described by the equations (see Table 2):

from which it is clear that the chemical strength of SiO, like CO, increases with increasing temperature, which makes it an excellent reducing agent for many substances.

For thermodynamic analysis, two-term equations can also be used:

The composition of gases over SiO 2 was estimated by I.S. Kulikov. Depending on the temperature, the content of SiO over SiO 2 is described by the equations:

Silicon carbide, like SiO, is one of the intermediate compounds formed during the reduction of SiO 2. Carbide has a high melting point.

Depending on the pressure, it is resistant up to 3033-3103 K (Figure 3). At high temperatures, silicon carbide sublimates. However, the vapor pressure of Si (G), Si 2 C (G), SiC 2 (G) above the carbide at T< 2800К невелико, что следует из уравнения

The carbide exists in the form of two modifications - cubic low-temperature β-SiC and hexagonal high-temperature α-SiC. In ferroalloy furnaces, only β-SiC is usually found. As calculations using the data have shown, the Gibbs energy of formation is described by the equations:

which differ markedly from the data. From these equations it follows that carbide is thermally resistant up to 3194 K. In terms of physical properties, carbide is distinguished by high hardness (~ 10), high electrical resistance (at 1273 K p≈0.13 ⋅ 10 4 μOhm ⋅ m), increased density (3.22 g /cm 3) and high resistance in both reducing and oxidizing atmospheres.

Pure carbide is colorless in appearance and has semiconducting properties that are retained at high temperatures. Technical silicon carbide contains impurities and is therefore colored green or black. Thus, green carbide contains 0.5-1.3% impurities (0.1-0.3% C, 0.2-1.2% Si + SiO 2, 0.05-0.20% Fe 2 O 3 , 0.01-0.08% Al 2 O 3, etc.). Black carbide has a higher impurity content (1-2%).

Carbon is used as a reducing agent in the production of silicon alloys. It is also the main substance from which electrodes and linings of electric furnaces that melt silicon and its alloys are made. Carbon is quite common in nature, its content in the earth's crust is 0.14%. In nature, it is found both in a free state and in the form of organic and inorganic compounds (mainly carbonates).

Carbon (graphite) has a hexagonal cubic lattice. X-ray density of graphite is 2.666 g/cm3, pycnometric - 2.253 g/cm3. It is characterized by high melting points (~ 4000 °C) and boiling points (~ 4200 °C), increasing with increasing temperature electrical resistance (at 873 K p≈9.6 μOhm⋅m, at 2273 K p≈ 15.0 μOhm⋅m) , quite durable. Its temporary resistance on the whiskers can be 480-500 MPa. However, electrode graphite has σ in = 3.4÷17.2 MPa. The hardness of graphite on the Mohs scale is ~ 1.

Carbon is an excellent reducing agent. This is due to the fact that the strength of one of its oxygen compounds (CO) increases with increasing temperature. This is evident from the Gibbs energy of its formation, which, as shown by our calculations using the data, is well described as a three-term

and two-term equations:

Carbon dioxide CO 2 is thermodynamically strong only up to 1300 K. The Gibbs energy of CO 2 formation is described by the equations:

One of the most common elements in nature is silicium, or silicon. Such a wide distribution indicates the importance and significance of this substance. This was quickly understood and learned by people who learned how to properly use silicon for their purposes. Its use is based on special properties, which we will discuss further.

Silicon - chemical element

If we characterize a given element by position in the periodic table, we can identify the following important points:

Serial number - 14.
The period is the third small one.
Group - IV.
The subgroup is the main one.
External structure electron shell is expressed by the formula 3s 2 3p 2.
The element silicon is represented by the chemical symbol Si, which is pronounced "silicium".
The oxidation states it exhibits are: -4; +2; +4.
The valency of the atom is IV.
The atomic mass of silicon is 28.086.
In nature, there are three stable isotopes of this element with mass numbers 28, 29 and 30.

Thus, from a chemical point of view, the silicon atom is a fairly studied element; many of its different properties have been described.

History of discovery

Since various compounds of the element in question are very popular and abundant in nature, since ancient times people have used and known about the properties of many of them. Pure silicon for a long time remained beyond human knowledge in chemistry.

The most popular compounds used in everyday life and industry by peoples of ancient cultures (Egyptians, Romans, Chinese, Russians, Persians and others) were precious and ornamental stones based on silicon oxide. These include:

opal;
rhinestone;
topaz;
chrysoprase;
onyx;
chalcedony and others.

It has also been customary to use quartz in construction since ancient times. However, elemental silicon itself remained undiscovered until the 19th century, although many scientists tried in vain to isolate it from various compounds, using catalysts, high temperatures, and even electric current. These are such bright minds as:

Karl Scheele;
Gay-Lussac;
Thenar;
Humphry Davy;
Antoine Lavoisier.

Jens Jacobs Berzelius succeeded in obtaining silicon in its pure form in 1823. To do this, he conducted an experiment on fusing vapors of silicon fluoride and potassium metal. As a result, I obtained an amorphous modification of the element in question. The same scientists were asked Latin name open atom.

A little later, in 1855, another scientist - Sainte-Clair-Deville - managed to synthesize another allotropic variety - crystalline silicon. Since then, knowledge about this element and its properties began to expand very quickly. People realized that it has unique features that can be very intelligently used to meet their own needs. Therefore, today one of the most popular elements in electronics and technology is silicon. Its use only expands its boundaries every year.

The Russian name for the atom was given by the scientist Hess in 1831. This is what has stuck to this day.

In terms of abundance in nature, silicon ranks second after oxygen. His percentage in comparison with other atoms in the earth's crust - 29.5%. Additionally, carbon and silicon are two special elements that can form chains by bonding with each other. That is why more than 400 different natural minerals are known for the latter, in which it is found in the lithosphere, hydrosphere and biomass.

Where exactly is silicon found?

In deep layers of soil.
In rocks, deposits and massifs.
At the bottom of bodies of water, especially seas and oceans.
In plants and marine life of the animal kingdom.
In the human body and terrestrial animals.

We can identify several of the most common minerals and rocks, which contain large quantities silicon is present. Their chemistry is such that the mass content of the pure element in them reaches 75%. However, the specific figure depends on the type of material. So, rocks and minerals containing silicon:

feldspars;
mica;
amphiboles;
opals;
chalcedony;
silicates;
sandstones;
aluminosilicates;
clays and others.

Accumulating in the shells and exoskeletons of marine animals, silicon eventually forms powerful silica deposits at the bottom of water bodies. This is one of the natural sources of this element.

In addition, it was found that silicon can exist in its pure native form - in the form of crystals. But such deposits are very rare.

Physical properties of silicon

If we characterize the element under consideration according to a set of physical and chemical properties, then first of all it is necessary to designate the physical parameters. Here are a few main ones:

It exists in the form of two allotropic modifications - amorphous and crystalline, which differ in all properties.
The crystal lattice is very similar to that of diamond, because carbon and silicon are practically the same in this regard. However, the distance between the atoms is different (silicon is larger), so diamond is much harder and stronger. Lattice type - cubic face-centered.
The substance is very brittle and becomes plastic at high temperatures.
The melting point is 1415˚C.
Boiling point - 3250˚С.
The density of the substance is 2.33 g/cm3.
The color of the compound is silver-gray, with a characteristic metallic luster.
It has good semiconductor properties, which can vary with the addition of certain agents.
Insoluble in water, organic solvents and acids.
Specifically soluble in alkalis.

The identified physical properties of silicon allow people to manipulate it and use it to create various products. For example, the use of pure silicon in electronics is based on the properties of semiconductivity.

Chemical properties

Chemical properties silicon very much depend on the reaction conditions. If we talk about standard parameters, then we need to indicate very low activity. Both crystalline and amorphous silicon are very inert. They do not interact with strong oxidizing agents (except fluorine) or with strong reducing agents.

This is due to the fact that an oxide film of SiO 2 is instantly formed on the surface of the substance, which prevents further interactions. It can be formed under the influence of water, air, and vapor.

If you change the standard conditions and heat silicon to a temperature above 400˚C, then its chemical activity will greatly increase. In this case, it will react with:

oxygen;
all types of halogens;
hydrogen.

With a further increase in temperature, the formation of products by interaction with boron, nitrogen and carbon is possible. Special significance has carborundum - SiC, as it is a good abrasive material.

Also, the chemical properties of silicon are clearly visible in reactions with metals. In relation to them, it is an oxidizing agent, which is why the products are called silicides. Similar compounds are known for:

alkaline;
alkaline earth;
transition metals.

The compound obtained by fusing iron and silicon has unusual properties. It is called ferrosilicon ceramics and is successfully used in industry.

Silicon does not interact with complex substances, therefore, of all their varieties, it can dissolve only in:

aqua regia (a mixture of nitric and hydrochloric acids);
caustic alkalis.

In this case, the temperature of the solution must be at least 60˚C. All this once again confirms physical basis substances - a diamond-like stable crystal lattice, giving it strength and inertness.

Methods of obtaining

Obtaining silicon in its pure form is a fairly costly process economically. In addition, due to its properties, any method gives only a 90-99% pure product, while impurities in the form of metals and carbon remain all the same. Therefore, simply obtaining the substance is not enough. It should also be thoroughly cleaned of foreign elements.

In general, silicon production is carried out in two main ways:

From white sand, which is pure silicon oxide SiO 2. When it is calcined with active metals (most often magnesium), a free element is formed in the form of an amorphous modification. The purity of this method is high, the product is obtained with a 99.9 percent yield.
A more widespread method on an industrial scale is the sintering of molten sand with coke in specialized thermal kilns. This method was developed by the Russian scientist N. N. Beketov.

Further processing involves subjecting the products to purification methods. For this purpose, acids or halogens (chlorine, fluorine) are used.

Amorphous silicon

The characterization of silicon will be incomplete if each of its allotropic modifications is not considered separately. The first of them is amorphous. In this state, the substance we are considering is a brownish-brown powder, finely dispersed. Possesses high degree hygroscopicity, exhibits fairly high chemical activity when heated. Under standard conditions, it is able to interact only with the strongest oxidizing agent - fluorine.

It is not entirely correct to call amorphous silicon a type of crystalline silicon. Its lattice shows that this substance is only a form of finely dispersed silicon, existing in the form of crystals. Therefore, as such, these modifications are one and the same compound.

However, their properties differ, which is why it is customary to talk about allotropy. Amorphous silicon itself has a high light absorption capacity. Moreover, under certain conditions this indicator is several times higher than that of the crystalline form. Therefore, it is used for technical purposes. In this form (powder), the compound is easily applied to any surface, be it plastic or glass. This is why amorphous silicon is so convenient to use. Application based on different sizes.

Although batteries of this type wear out quite quickly, which is associated with the abrasion of a thin film of the substance, their use and demand are only growing. After all, even over a short service life, solar batteries based on amorphous silicon can provide energy to entire enterprises. In addition, the production of such a substance is waste-free, which makes it very economical.

This modification is obtained by reducing compounds with active metals, for example, sodium or magnesium.

Crystalline silicon

Silver-gray shiny modification of the element in question. This form is the most common and most in demand. This is explained by the set quality properties, which this substance possesses.

The characteristics of silicon with a crystal lattice include the classification of its types, since there are several of them:

Electronic quality - the purest and highest quality. This type is used in electronics to create particularly sensitive devices.
Sunny quality. The name itself determines the area of use. This is also silicon of fairly high purity, the use of which is necessary to create high-quality and long-lasting silicon. solar panels. Photoelectric converters created on the basis of a crystalline structure are of higher quality and wear-resistant than those created using an amorphous modification by sputtering onto various types of substrates.
Technical silicon. This variety includes those samples of the substance that contain about 98% of the pure element. Everything else goes to various kinds of impurities:

aluminum;
chlorine;
carbon;
phosphorus and others.

The last type of the substance in question is used to obtain polycrystals of silicon. For this purpose, recrystallization processes are carried out. As a result, in terms of purity, products are obtained that can be classified as solar and electronic quality.

By its nature, polysilicon is an intermediate product between the amorphous and crystalline modifications. This option is easier to work with, it is better processed and cleaned with fluorine and chlorine.

The resulting products can be classified as follows:

multisilicon;
monocrystalline;
profiled crystals;
silicon scrap;
technical silicon;
production waste in the form of fragments and scraps of matter.

Each of them finds application in industry and is fully used by humans. Therefore, those that touch silicon are considered non-waste. This significantly reduces its economic cost without affecting quality.

Using pure silicon

Industrial silicon production is quite well established, and its scale is quite large. This is due to the fact that this element, both pure and in the form of various compounds, is widespread and in demand in various branches of science and technology.

Where is crystalline and amorphous silicon used in its pure form?

In metallurgy, as an alloying additive capable of changing the properties of metals and their alloys. Thus, it is used in the smelting of steel and cast iron.
Different types of substances are used to make a purer version - polysilicon.
Silicon compounds are a whole chemical industry that has gained particular popularity today. Organosilicon materials are used in medicine, in the manufacture of dishes, tools and much more.
Manufacturing of various solar panels. This method of obtaining energy is one of the most promising in the future. Environmentally friendly, economically beneficial and wear-resistant are the main advantages of this type of electricity generation.
Silicon has been used for lighters for a very long time. Even in ancient times, people used flint to produce a spark when lighting a fire. This principle is the basis for the production of various types of lighters. Today there are types in which flint is replaced by an alloy of a certain composition, which gives an even faster result (sparking).
Electronics and solar energy.
Manufacturing of mirrors in gas laser devices.

Thus, pure silicon has a lot of advantageous and special properties that allow it to be used to create important and necessary products.

Application of silicon compounds

In addition to the simple substance, various silicon compounds are also used, and very widely. There is a whole industry called silicate. It is based on the use various substances, which contain this amazing element. What are these compounds and what is produced from them?

Quartz, or river sand - SiO 2. Used to make construction and decorative materials such as cement and glass. Everyone knows where these materials are used. No construction can be completed without these components, which confirms the importance of silicon compounds.
Silicate ceramics, which includes materials such as earthenware, porcelain, brick and products based on them. These components are used in medicine, in the manufacture of dishes, decorative jewelry, household items, in construction and other everyday areas of human activity.
- silicones, silica gels, silicone oils.
Silicate glue - used as stationery, in pyrotechnics and construction.

Silicon, the price of which varies on the world market, but does not cross from top to bottom the mark of 100 Russian rubles per kilogram (per crystalline), is a sought-after and valuable substance. Naturally, compounds of this element are also widespread and applicable.

Biological role of silicon

From the point of view of its importance for the body, silicon is important. Its content and distribution in tissues is as follows:

0.002% - muscle;
0.000017% - bone;
blood - 3.9 mg/l.

About one gram of silicon must be ingested every day, otherwise diseases will begin to develop. None of them are mortally dangerous, but prolonged silicon starvation leads to:

hair loss;
the appearance of acne and pimples;
fragility and brittleness of bones;
easy capillary permeability;
fatigue and headaches;
the appearance of numerous bruises and bruises.

For plants silicon - important trace element required for normal height and development. Experiments on animals have shown that those individuals that consume daily grow better. sufficient quantity silicon

A brief comparative description of the elements carbon and silicon is presented in Table 6.

Table 6

Comparative characteristics carbon and silicon

Comparison criteria	Carbon – C	Silicon – Si
position in the periodic table of chemical elements	, 2nd period, IV group, main subgroup	, 3rd period, IV group, main subgroup
electron configuration of atoms
valence possibilities	II – in a stationary state IV – in an excited state
possible oxidation states	, , , , ,	,
higher oxide	, acidic	, acidic
higher hydroxide	– weak unstable acid	() or – weak acid, has a polymer structure
hydrogen connection	– methane (hydrocarbon)	– silane, unstable

Carbon. The carbon element is characterized by allotropy. Carbon exists in the following forms simple substances: diamond, graphite, carbyne, fullerene, of which only graphite is thermodynamically stable. Coal and soot can be considered as amorphous varieties of graphite.

Graphite is refractory, slightly volatile, chemically inert at ordinary temperatures, and is an opaque, soft substance that weakly conducts current. The structure of graphite is layered.

Alamaz is an extremely hard, chemically inert (up to 900 °C) substance, does not conduct current and conducts heat poorly. The structure of diamond is tetrahedral (each atom in a tetrahedron is surrounded by four atoms, etc.). Therefore, diamond is the simplest polymer, the macromolecule of which consists of only carbon atoms.

Carbyne has a linear structure ( – carbyne, polyyne) or ( – carbyne, polyene). It is a black powder and has semiconductor properties. Under the influence of light, the electrical conductivity of carbyne increases, and at temperature carbyne turns into graphite. Chemically more active than graphite. Synthesized in the early 60s of the 20th century, it was later discovered in some meteorites.

Fullerene is an allotropic modification of carbon formed by molecules having a “football” type structure. Molecules and other fullerenes were synthesized. All fullerenes are closed structures of carbon atoms in a hybrid state. Unhybridized bond electrons are delocalized as in aromatic compounds. Fullerene crystals are of the molecular type.

Silicon. Silicon is not characterized by bonds and does not exist in a hybrid state. Therefore, there is only one stable allotropic modification of silicon, the crystal lattice of which is similar to that of diamond. Silicon is hard (on the Mohs scale, hardness is 7), refractory ( ), a very fragile substance of dark gray color with a metallic luster under standard conditions - a semiconductor. Chemical activity depends on the size of the crystals (large crystalline ones are less active than amorphous ones).

The reactivity of carbon depends on the allotropic modification. Carbon in the form of diamond and graphite is quite inert, resistant to acids and alkalis, which makes it possible to make crucibles, electrodes, etc. from graphite. Carbon exhibits higher reactivity in the form of coal and soot.

Crystalline silicon is quite inert; in amorphous form it is more active.

The main types of reactions reflecting the chemical properties of carbon and silicon are given in Table 7.

Table 7

Basic chemical properties of carbon and silicon

reaction with	carbon	reaction with	silicon
simple substances	oxygen		oxygen
halogens		halogens
gray		carbon
hydrogen		hydrogen	doesn't respond
metals		metals
complex substances	metal oxides		alkalis
water vapor		acids	doesn't respond
acids

Cementing materials

Cementing materials – mineral or organic building materials, used for the manufacture of concrete, fastening individual elements of building structures, waterproofing, etc..

Mineral binders(MVM)– finely ground powdery materials (cements, gypsum, lime, etc.), which form when mixed with water (in in some cases– with solutions of salts, acids, alkalis) a plastic, workable mass that hardens into a durable stone-like body and binds particles of solid aggregates and reinforcement into a monolithic whole.

Hardening of MVM occurs due to dissolution processes, the formation of a supersaturated solution and colloidal mass; the latter partially or completely crystallizes.

MVM classification:

1. hydraulic binders:

When mixed with water (mixing), they harden and continue to maintain or increase their strength in water. These include various cements and hydraulic lime. When hydraulic lime hardens, CaO interacts with water and carbon dioxide in the air and the resulting product crystallizes. They are used in the construction of above-ground, underground and hydraulic structures exposed to constant exposure to water.

2. air binders:

When mixed with water, they harden and retain their strength only in air. These include aerated lime, gypsum-anhydrite and magnesia aerated binders.

3. acid-resistant binders:

They consist mainly of acid-resistant cement containing a finely ground mixture of quartz sand and; They are usually locked aqueous solutions sodium or potassium silicate, they retain their strength for a long time when exposed to acids. During hardening, a reaction occurs. Used for the production of acid-resistant putties, mortars and concrete in the construction of chemical plants.

4. Autoclave hardening binders:

They consist of calc-siliceous and calc-nepheline binders (lime, quartz sand, nepheline sludge) and harden when processed in an autoclave (6-10 hours, steam pressure 0.9-1.3 MPa). These also include sandy Portland cements and other binders based on lime, ash and low-active sludge. Used in the production of silicate concrete products (blocks, sand-lime bricks, etc.).

5. Phosphate binders:

Consist of special cements; they are sealed with phosphoric acid to form a plastic mass that gradually hardens into a monolithic body and retains its strength at temperatures above 1000 °C. Usually titanophosphate, zinc phosphate, aluminophosphate and other cements are used. Used for the manufacture of refractory lining mass and sealants for high-temperature protection of metal parts and structures in the production of refractory concrete, etc.

Organic binders(OBM)– substances organic origin, capable of transitioning from a plastic state to a solid or low-plasticity state as a result of polymerization or polycondensation.

Compared to MVM, they are less brittle and have greater tensile strength. These include products formed during oil refining (asphalt, bitumen), products of thermal decomposition of wood (tar), as well as synthetic thermosetting polyester, epoxy, phenol-formaldehyde resins. They are used in the construction of roads, bridges, floors of industrial premises, rolled roofing materials, asphalt polymer concrete, etc.

Introduction

Chapter 2. Chemical compounds of carbon

2.1 Oxygen derivatives of carbon

2.1.1 Oxidation state +2

2.1.2 Oxidation state +4

2.3 Metal carbides

2.3.1 Carbides soluble in water and dilute acids

2.3.2 Carbides insoluble in water and dilute acids

Chapter 3. Silicon compounds

3.1 Oxygen compounds of silicon

References

Introduction

Chemistry is one of the branches of natural science, the subject of study of which is chemical elements (atoms), the simple and complex substances (molecules) they form, their transformations and the laws to which these transformations are subject.

By definition D.I. Mendeleev (1871), “chemistry in its modern state can... be called the study of elements.”

The origin of the word "chemistry" is not completely clear. Many researchers believe that it comes from the ancient name of Egypt - Chemia (Greek Chemia, found in Plutarch), which is derived from "hem" or "hame" - black and means "science of the black earth" (Egypt), "Egyptian science".

Modern chemistry is closely related, as with other natural sciences, and with all sectors of the national economy.

The qualitative feature of the chemical form of motion of matter, and its transitions into other forms of motion, determines the versatility of chemical science and its connections with areas of knowledge that study both lower and higher higher forms movements. Knowledge of the chemical form of the movement of matter enriches general doctrine about the development of nature, the evolution of matter in the Universe, contributes to the formation of a holistic materialistic picture of the world. The contact of chemistry with other sciences gives rise to specific areas of their mutual penetration. Thus, the areas of transition between chemistry and physics are represented by physical chemistry and chemical physics. Between chemistry and biology, chemistry and geology, special border areas arose - geochemistry, biochemistry, biogeochemistry, molecular biology. The most important laws of chemistry are formulated in mathematical language, and theoretical chemistry cannot develop without mathematics. Chemistry has had and continues to influence the development of philosophy, and has itself been and is being influenced by it.

Historically, two main branches of chemistry have developed: inorganic chemistry, which studies primarily chemical elements and the simple and complex substances they form (except for carbon compounds), and organic chemistry, the subject of which is the study of carbon compounds with other elements (organic substances).

Until the end of the 18th century, the terms “inorganic chemistry” and “organic chemistry” indicated only from which “kingdom” of nature (mineral, plant or animal) certain compounds were obtained. Since the 19th century. these terms came to indicate the presence or absence of carbon in this substance. Then they acquired a new, broader meaning. Inorganic chemistry comes into contact primarily with geochemistry and then with mineralogy and geology, i.e. with the sciences of inorganic nature. Organic chemistry is a branch of chemistry that studies a variety of carbon compounds up to the most complex biopolymer substances. Through organic and bioorganic chemistry, chemistry borders on biochemistry and further on biology, i.e. with the totality of sciences about living nature. At the interface between inorganic and organic chemistry is the field of organoelement compounds.

In chemistry, ideas about the structural levels of organization of matter gradually formed. The complication of a substance, starting from the lowest, atomic, goes through the stages of molecular, macromolecular, or high-molecular compounds (polymer), then intermolecular (complex, clathrate, catenane), finally, diverse macrostructures (crystal, micelle) up to indefinite non-stoichiometric formations. Gradually, the corresponding disciplines emerged and became isolated: chemistry complex compounds, polymers, crystal chemistry, studies of dispersed systems and surface phenomena, alloys, etc.

Study of chemical objects and phenomena by physical methods, establishing patterns chemical transformations, based on general principles physics, is the basis of physical chemistry. This area of chemistry includes a number of largely independent disciplines: chemical thermodynamics, chemical kinetics, electrochemistry, colloidal chemistry, quantum chemistry and the study of the structure and properties of molecules, ions, radicals, radiation chemistry, photochemistry, studies of catalysis, chemical equilibria, solutions, etc. Has acquired an independent character analytical chemistry, the methods of which are widely used in all areas of chemistry and the chemical industry. In the areas of practical application of chemistry, such sciences and scientific disciplines as chemical technology with its many branches, metallurgy, agricultural chemistry, medicinal chemistry, forensic chemistry, etc. arose.

As mentioned above, chemistry examines chemical elements and the substances they form, as well as the laws that govern these transformations. One of these aspects (namely, chemical compounds based on silicon and carbon) and will be considered by me in this work.

Chapter 1. Silicon and carbon - chemical elements

1.1 General information about carbon and silicon

Carbon (C) and silicon (Si) are members of group IVA.

Carbon is not a very common element. Despite this, its significance is enormous. Carbon is the basis of life on earth. It is part of carbonates that are very common in nature (Ca, Zn, Mg, Fe, etc.), exists in the atmosphere in the form of CO 2, and is found in the form of natural coals (amorphous graphite), oil and natural gas, as well as simple substances (diamond, graphite).

Silicon is the second most abundant element in the earth's crust (after oxygen). If carbon is the basis of life, then silicon is the basis of the earth's crust. It is found in a huge variety of silicates (Figure 4) and aluminosilicates, sand.

Amorphous silicon is a brown powder. The latter is easy to obtain in the crystalline state in the form of gray hard but rather brittle crystals. Crystalline silicon is a semiconductor.

Table 1. General chemical data on carbon and silicon.

A modification of carbon that is stable at ordinary temperatures, graphite, is an opaque, gray, fatty mass. Diamond is the hardest substance on earth - colorless and transparent. The crystal structures of graphite and diamond are shown in Fig. 1.

Figure 1. Diamond structure (a); graphite structure (b)

Carbon and silicon have their own specific derivatives.

Table 2. The most typical derivatives of carbon and silicon

1.2 Preparation, chemical properties and use of simple substances

Silicon is obtained by reduction of oxides with carbon; to obtain a particularly pure state after reduction, the substance is transferred to tetrachloride and reduced again (with hydrogen). Then they are melted into ingots and subjected to purification using the zone melting method. A metal ingot is heated at one end so that a zone of molten metal is formed in it. When the zone moves to the other end of the ingot, the impurity, dissolving in the molten metal better than in the solid metal, is removed, and thereby the metal is cleaned.

Carbon is inert, but at very high temperatures (in an amorphous state) it interacts with most metals to form solid solutions or carbides (CaC 2, Fe 3 C, etc.), as well as with many metalloids, for example:

2C+ Ca = CaC 2, C + 3Fe = Fe 3 C,

Silicon is more reactive. It reacts with fluorine already at ordinary temperature: Si+2F 2 = SiF 4

Silicon also has a very high affinity for oxygen:

The reaction with chlorine and sulfur proceeds at about 500 K. At very high temperature silicon interacts with nitrogen and carbon:

Silicon does not interact directly with hydrogen. Silicon dissolves in alkalis:

Si+2NaOH+H 2 0=Na 2 Si0 3 +2H 2.

Acids other than hydrofluoric acid have no effect on it. There is a reaction with HF

Si+6HF=H 2 +2H 2.

Carbon in the composition of various coals, oil, natural (mainly CH4), as well as artificially produced gases is the most important fuel base of our planet

General characteristics of the fourth group of the main subgroup:

a) properties of elements from the point of view of atomic structure;
b) oxidation state;
c) properties of oxides;
d) properties of hydroxides;
e) hydrogen compounds.

a) Carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb) - elements of group 4 of the main subgroup of PSE. On the outer electron layer, the atoms of these elements have 4 electrons: ns 2 np 2. In a subgroup, as the atomic number of an element increases, the atomic radius increases, non-metallic properties weaken, and metallic properties increase: carbon and silicon are non-metals, germanium, tin, lead are metals.

b) Elements of this subgroup exhibit both positive and negative oxidation states: -4, +2, +4.

c) Higher oxides of carbon and silicon (C0 2, Si0 2) have acidic properties, oxides of the remaining elements of the subgroup are amphoteric (Ge0 2, Sn0 2, Pb0 2).

d) Carbonic and silicic acids (H 2 CO 3, H 2 SiO 3) are weak acids. Germanium, tin and lead hydroxides are amphoteric and exhibit weak acidic and basic properties: H 2 GeO 3 = Ge(OH) 4, H 2 SnO 3 = Sn(OH) 4, H 2 PbO 3 = Pb(OH) 4.

e) Hydrogen compounds:

CH 4; SiH 4, GeH 4. SnH4, PbH4. Methane - CH 4 is a strong compound, silane SiH 4 is a less strong compound.

Schemes of the structure of carbon and silicon atoms, general and distinctive properties.

With lS 2 2S 2 2p 2 ;

Si 1S 2 2S 2 2P 6 3S 2 3p 2 .

Carbon and silicon are non-metals because there are 4 electrons in the outer electron layer. But since silicon has a larger atomic radius, it is more likely to donate electrons than carbon. Carbon - reducing agent:

Task. How to prove that graphite and diamond are allotropic modifications of the same thing chemical element? How can we explain the differences in their properties?

Solution. Both diamond and graphite, when burned in oxygen, form carbon monoxide (IV) C0 2, which, when passed through lime water, produces a white precipitate of calcium carbonate CaC0 3

C + 0 2 = CO 2; C0 2 + Ca(OH) 2 = CaCO 3 v - H 2 O.

In addition, diamond can be obtained from graphite by heating under high pressure. Consequently, both graphite and diamond contain only carbon. The difference in the properties of graphite and diamond is explained by the difference in the structure of the crystal lattice.

IN crystal lattice In diamond, each carbon atom is surrounded by four others. The atoms are located at equal distances from each other and are very tightly connected to each other by covalent bonds. This explains the great hardness of diamond.

Graphite has carbon atoms arranged in parallel layers. The distance between adjacent layers is much greater than between adjacent atoms in a layer. This causes low bond strength between the layers, and therefore graphite easily splits into thin flakes, which themselves are very strong.

Compounds with hydrogen that form carbon. Empirical formulas, type of hybridization of carbon atoms, valence and oxidation states of each element.

The oxidation state of hydrogen in all compounds is +1.

The valence of hydrogen is one, the valency of carbon is four.

Formulas of carbonic and silicic acids, their chemical properties in relation to metals, oxides, bases, specific properties.

H 2 CO 3 - carbonic acid,

H 2 SiO 3 - silicic acid.

H 2 CO 3 - exists only in solution:

H 2 C0 3 = H 2 O + C0 2

H 2 SiO 3 is a solid substance, practically insoluble in water, therefore hydrogen cations in water are practically not split off. In this regard, this general property H 2 SiO 3 does not detect acids as an effect on indicators; it is even weaker than carbonic acid.

H 2 SiO 3 is a fragile acid and gradually decomposes when heated:

H 2 SiO 3 = Si0 2 + H 2 0.

H 2 CO 3 reacts with metals, metal oxides, bases:

a) H 2 CO 3 + Mg = MgCO 3 + H 2

b) H 2 CO 3 + CaO = CaCO 3 + H 2 0

c) H 2 CO 3 + 2NaOH = Na 2 CO 3 + 2H 2 0

Chemical properties of carbonic acid:

1) common with other acids,
2) specific properties.

Confirm your answer with reaction equations.

1) reacts with active metals:

Task. Using chemical transformations, separate the mixture of silicon (IV) oxide, calcium carbonate and silver, sequentially dissolving the components of the mixture. Describe the sequence of actions.

Solution.

1) a solution of hydrochloric acid was added to the mixture.