Traditional medicine

Application of carbon and silicon compounds. General information about carbon and silicon

Description and properties of silicon

Silicon - element, fourth group, third period in the table of elements. Atomic number 14. Silicon formula- 3s2 3p2. Defined as an element in 1811, and in 1834 received Russian name“silicon”, instead of the previous “sicily”. Melts at 1414º C, boils at 2349º C.

It resembles the molecular structure, but is inferior to it in hardness. Quite fragile, when heated (at least 800º C) it becomes plastic. Translucent with infrared radiation. Monocrystalline silicon has semiconductor properties. According to some characteristics silicon atom similar to the atomic structure of carbon. Silicon electrons have the same valence number as with the carbon structure.

Workers properties of silicon depend on the content of certain contents in it. Silicon has different types of conductivity. In particular, these are the “hole” and “electronic” types. To obtain the first, boron is added to silicon. If you add phosphorus, silicon acquires the second type of conductivity. If silicon is heated together with other metals, specific compounds called “silicides” are formed, for example, in the reaction “ magnesium silicon«.

Silicon used for electronics needs is primarily assessed by the characteristics of its upper layers. Therefore, it is necessary to pay attention to their quality, it directly affects general indicators. The operation of the manufactured device depends on them. To get the most acceptable indicators upper layers of silicon, they are treated with various chemical methods or irradiated.

Compound "sulfur-silicon" forms silicon sulfide, which easily interacts with water and oxygen. When reacting with oxygen, under temperature conditions above 400º C, it turns out silicon dioxide. At the same temperature, reactions with chlorine and iodine, as well as bromine, become possible, during which volatile substances are formed - tetrahalides.

It will not be possible to combine silicon and hydrogen through direct contact; for this, there are indirect methods. At 1000º C, a reaction with nitrogen and boron is possible, resulting in silicon nitride and boride. At the same temperature, by combining silicon with carbon, it is possible to produce silicon carbide, the so-called “carborundum”. This composition has a solid structure, the chemical activity is sluggish. Used as an abrasive.

In connection with iron, silicon forms a special mixture, this allows the melting of these elements, which produces ferrosilicon ceramics. Moreover, its melting point is much lower than if they are melted separately. At temperatures above 1200º C, the formation of silicon oxide, also under certain conditions it turns out silicon hydroxide. When etching silicon, alkaline water-based solutions are used. Their temperature must be at least 60º C.

Silicon deposits and mining

The element is the second most abundant on the planet substance. Silicon makes up almost a third of the volume earth's crust. Only oxygen is more common. It is predominantly expressed by silica, a compound that essentially contains silicon dioxide. The main derivatives of silicon dioxide are flint, various sands, quartz, and field . After them come silicate compounds of silicon. Nativeness is a rare phenomenon for silicon.

Silicon Applications

Silicon, chemical properties which determines the scope of its application, is divided into several types. Less pure silicon is used for metallurgical needs: for example, for additives in aluminum, silicon actively changes its properties, deoxidizers, etc. It actively modifies the properties of metals by adding them to compound. Silicon alloys them, changing the working characteristics, silicon A very small amount is enough.

Also, higher quality derivatives are produced from crude silicon, in particular, mono and polycrystalline silicon, as well as organic silicon - these are silicones and various organic oils. It has also found its use in the cement production and glass industries. He did not bypass brick production, factories producing porcelain also cannot do without it.

Silicon is part of the well-known silicate glue, which is used for repair work, and previously it was used for office needs until more practical substitutes appeared. Some pyrotechnic products also contain silicon. Hydrogen can be produced from it and its iron alloys in the open air.

What is better quality used for? silicon? Plates Solar batteries also contain silicon, naturally non-technical. For these needs, silicon of ideal purity or at least technical silicon of the highest degree of purity is required.

The so-called "electronic silicon" which contains almost 100% silicon, has much better performance. Therefore, it is preferred in the production of ultra-precise electronic devices and complex microcircuits. Their production requires high-quality production circuit, silicon for which should go only highest category. The operation of these devices depends on how much contains silicon unwanted impurities.

Silicon occupies an important place in nature, and most living beings constantly need it. For them, this is a kind of building composition, because it is extremely important for the health of the musculoskeletal system. Every day a person absorbs up to 1 g silicon compounds.

Can silicon be harmful?

Yes, for the reason that silicon dioxide is extremely prone to dust formation. It has an irritating effect on the mucous surfaces of the body and can actively accumulate in the lungs, causing silicosis. For this purpose, in production related to the processing of silicon elements, the use of respirators is mandatory. Their presence is especially important when it comes to silicon monoxide.

Silicon price

As you know, all modern electronic technology, from telecommunications to computer technology, is based on the use of silicon, using its semiconductor properties. Its other analogues are used to a much lesser extent. Unique properties Silicon and its derivatives are still unrivaled for many years to come. Despite the decline in prices in 2001 silicon, sales quickly returned to normal. And already in 2003, trade turnover amounted to 24 thousand tons per year.

For the latest technologies that require almost crystal purity of silicon, its technical analogues are not suitable. And due to him complex system cleaning price accordingly increases significantly. The polycrystalline type of silicon is more common; its monocrystalline prototype is somewhat less in demand. At the same time, the share of silicon used for semiconductors takes up the lion's share of trade turnover.

Product prices vary depending on purity and purpose silicon, buy which can start from 10 cents per kg of crude raw materials and up to $10 and above for “electronic” silicon.

Designation - Si (Silicon);
Period - III;
Group - 14 (IVa);
Atomic mass - 28.0855;
Atomic number - 14;
Atomic radius = 132 pm;
Covalent radius = 111 pm;
Electron distribution - 1s 2 2s 2 2p 6 3s 2 3p 2 ;
melting temperature = 1412°C;
boiling point = 2355°C;
Electronegativity (according to Pauling/according to Alpred and Rochow) = 1.90/1.74;
Oxidation state: +4, +2, 0, -4;
Density (no.) = 2.33 g/cm3;
Molar volume = 12.1 cm 3 /mol.

Silicon compounds:

Silicon was first isolated in its pure form in 1811 (the French J. L. Gay-Lussac and L. J. Tenard). Pure elemental silicon was obtained in 1825 (Swede J. J. Berzelius). The chemical element received its name “silicon” (translated from ancient Greek as mountain) in 1834 (Russian chemist G. I. Hess).

Silicon is the most common (after oxygen) chemical element on Earth (content in the earth's crust is 28-29% by weight). In nature, silicon is most often present in the form of silica (sand, quartz, flint, feldspars), as well as in silicates and aluminosilicates. In its pure form, silicon is extremely rare. Many natural silicates in their pure form are precious stones: emerald, topaz, aquamary - all this is silicon. Pure crystalline silicon(IV) oxide occurs in the form of rock crystal and quartz. Silicon oxide, which contains various impurities, forms precious and semi-precious stones- amethyst, agate, jasper.

Rice. Structure of the silicon atom.

The electronic configuration of silicon is 1s 2 2s 2 2p 6 3s 2 3p 2 (see Electronic structure of atoms). At the outer energy level, silicon has 4 electrons: 2 paired in the 3s sublevel + 2 unpaired in p-orbitals. When a silicon atom transitions to an excited state, one electron from the s-sublevel “leaves” its pair and moves to the p-sublevel, where there is one free orbital. Thus, in excited state the electronic configuration of the silicon atom takes the following form: 1s 2 2s 2 2p 6 3s 1 3p 3.

Rice. Transition of a silicon atom to an excited state.

Thus, silicon in compounds can exhibit a valency of 4 (most often) or 2 (see Valency). Silicon (as well as carbon), reacting with other elements, forms chemical bonds in which it can both give up its electrons and accept them, but at the same time the ability to accept electrons in silicon atoms is less pronounced than in carbon atoms, due to larger size silicon atom.

Silicon oxidation states:

-4 : SiH 4 (silane), Ca 2 Si, Mg 2 Si (metal silicates);
+4 - the most stable: SiO 2 (silicon oxide), H 2 SiO 3 (silicic acid), silicates and silicon halides;
0 : Si (simple substance)

Silicon as a simple substance

Silicon is a dark gray crystalline substance with metallic shine. Crystalline silicon is a semiconductor.

Silicon forms only one allotropic modification, similar to diamond, but not as strong, since the Si-Si bonds are not as strong as in the diamond carbon molecule (See Diamond).

Amorphous silicon- brown powder, with a melting point of 1420°C.

Crystalline silicon is obtained from amorphous silicon by recrystallization. Unlike amorphous silicon, which is quite active chemical, crystalline silicon is more inert in terms of interaction with other substances.

The structure of the crystal lattice of silicon repeats the structure of diamond - each atom is surrounded by four other atoms located at the vertices of a tetrahedron. The atoms are held together by covalent bonds, which are not as strong as the carbon bonds in diamond. For this reason, even at no. Some covalent bonds in crystalline silicon are broken, resulting in the release of some electrons, causing silicon to have little electrical conductivity. As silicon heats up, in the light or when certain impurities are added, the number of broken covalent bonds increases, as a result of which the number of free electrons increases, and therefore the electrical conductivity of silicon increases.

Chemical properties of silicon

Like carbon, silicon can be both a reducing agent and an oxidizing agent, depending on what substance it reacts with.

At no. silicon interacts only with fluorine, which is explained by the fairly strong crystal lattice of silicon.

Silicon reacts with chlorine and bromine at temperatures exceeding 400°C.

Silicon interacts with carbon and nitrogen only at very high temperatures.

In reactions with nonmetals, silicon acts as reducing agent:
- at normal conditions Of the non-metals, silicon reacts only with fluorine, forming silicon halide:
  Si + 2F 2 = SiF 4
- at high temperatures, silicon reacts with chlorine (400°C), oxygen (600°C), nitrogen (1000°C), carbon (2000°C):
  - Si + 2Cl 2 = SiCl 4 - silicon halide;
  - Si + O 2 = SiO 2 - silicon oxide;
  - 3Si + 2N 2 = Si 3 N 4 - silicon nitride;
  - Si + C = SiC - carborundum (silicon carbide)
In reactions with metals, silicon is oxidizing agent(formed salicids:
Si + 2Mg = Mg 2 Si
In reactions with concentrated solutions of alkalis, silicon reacts with the release of hydrogen, forming soluble salts of silicic acid, called silicates:
Si + 2NaOH + H 2 O = Na 2 SiO 3 + 2H 2
Silicon does not react with acids (except for HF).

Preparation and use of silicon

Obtaining silicon:

in the laboratory - from silica (aluminum therapy):
3SiO 2 + 4Al = 3Si + 2Al 2 O 3
in industry - by reduction of silicon oxide with coke (technically pure silicon) at high temperature:
SiO 2 + 2C = Si + 2CO
The purest silicon is obtained by reducing silicon tetrachloride with hydrogen (zinc) at high temperature:
SiCl 4 +2H 2 = Si+4HCl

Silicon Application:

production of semiconductor radioelements;
as metallurgical additives in the production of heat-resistant and acid-resistant compounds;
in the production of photocells for solar batteries;
as AC rectifiers.

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 form of the following 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, crystal lattice which is like the lattice of a 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 when mixed with water (in some cases with solutions of salts, acids, alkalis) form 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. 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 sealed, as a rule, with aqueous solutions of 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.

In binary compounds of silicon with carbon, each silicon atom is directly bonded to four neighboring carbon atoms located at the vertices of a tetrahedron, the center of which is the silicon atom. At the same time, each carbon atom is in turn connected to four neighboring silicon atoms located at the vertices of a tetrahedron, the center of which is a carbon atom. This mutual arrangement of silicon and carbon atoms is based on the silicon-carbon bond Si - C- and forms a dense and very strong crystalline structure.

Currently, only two binary compounds of silicon and carbon are known. This is a very rare mineral moissanite, which has no practical use yet, and an artificially produced carborundum SiC, which is sometimes called silund, refrax, carbofrax, cristolan, etc.

In laboratory practice and in technology, carborundum is obtained by reducing silica with carbon according to the reaction equation

SiO 2 + 3C = 2СО + SiC

In addition to finely ground quartz or pure quartz line and coke, table salt and sawdust are added to the mixture to produce carborundum. During firing, sawdust loosens the charge, and table salt, reacting with ferrous and aluminum impurities, transforms them into volatile chlorides FeCl 3 and AlC1 3, which are removed from the reaction zone at 1000-1200 ° C. In fact, the reaction between silica and coke begins already at 1150° C, but proceeds extremely slowly. As the temperature rises to 1220° C, its speed increases. In the temperature range from 1220 to 1340 ° C it becomes exothermic and proceeds violently. As a result of the reaction, a mixture is first formed consisting of tiny crystals and an amorphous variety of carborundum. With an increase in temperature to 1800-2000 ° C, the mixture recrystallizes and turns into well-developed, tabular-shaped, rarely colorless, often colored green, gray and even black with a diamond shine and iridescent hexagonal crystals, containing about 98-99.5% carborundum. The process of obtaining carborundum from the charge is carried out in electric furnaces burning at 2000-2200 ° C. To obtain chemically pure carborundum, the product obtained by firing the charge is treated with an alkali, which dissolves unreacted silica.

Crystalline carborundum is a very hard substance; its hardness is 9. The ohmic resistance of polycrystalline carborundum decreases with increasing temperature and at 1500 0 C becomes insignificant.

In air at temperatures above 1000 0 C, carborundum begins to oxidize, first slowly, and then vigorously with an increase in temperature above 1700 ° C. In this case, silica and carbon monoxide are formed:

2SiC + ZO 2 = 2SiO 2 + 2CO

The silicon dioxide formed on the surface of the carborundum is a protective film that somewhat slows down the further oxidation of the carborundum. In an environment of water vapor, the oxidation of carborundum under the same conditions proceeds more vigorously.

Mineral acids, with the exception of orthophosphoric acid, have no effect on carborundum; chlorine at 100° C decomposes it according to the reaction equation

SiC + 2Cl 2 = SiCl 4 + C

and at 1000° C, instead of carbon, CC1 4 is released:

SiC + 4C1 2 = SiCl + CC1 4

Molten metals, reacting with carborundum, form the corresponding silicides:

SiC + Fe =FeSl + C

At temperatures above 810° C, carborundum reduces oxides to metal alkaline earth metals, above 1000 ° C it reduces iron (III) oxide Fe 2 O 3 and above 1300-1370 ° C iron (II) oxide FeO, nickel (II) oxide NiO and manganese oxide MnO.

Molten caustic alkalis and their carbonates in the presence of atmospheric oxygen completely decompose carborundum with the formation of the corresponding silicates:

SiC + 2KOH + 2O 2 = K 2 SiO 3 + H 2 O + CO 2

SiC + Na 2 CO 3 + 2O 2 = Na 2 SiO 3 + 2CO 2

Carborundum can also react with sodium peroxide, lead (II) oxide and phosphoric acid.

Due to the fact that carborundum has high hardness, it is widely used as abrasive powders for grinding metal, as well as for the manufacture of carborundum abrasive wheels, whetstones and sanding paper. The electrical conductivity of carborundum at high temperatures makes it possible to use it as the main material in the manufacture of so-called silit rods, which are resistance elements in electric furnaces. For this purpose, a mixture of carborundum and silicon is mixed with glycerin or another organic cementing substance and rods are formed from the resulting mass, which are fired at 1400-1500 ° C in an atmosphere of carbon monoxide or in a nitrogen atmosphere. During firing, the cementing agent organic matter decomposes, the released carbon, combining with silicon, turns it into carborundum and gives the rods the required strength.

Special fireproof crucibles are made from carborundum
for melting metals produced by hot pressing
carborundum at 2500° C under a pressure of 42-70 MPa. Also known
We have refractories made from mixtures of carborundum and nitrides
boron, steatite, molybdenum-containing bonds and other substances
creatures.

SILICON HYDRIDES, OR SILANES

Hydrogen compounds of silicon are usually called silicon hydrides, or silanes. Like saturated hydrocarbons, silicon hydrides form a homologous series in which the silicon atoms are connected to each other by a single bond

Si-Si -Si -Si -Si- etc.

The simplest.representative

of this homologous series is monosilane, or simply silane, SiH 4, the molecular structure of which is similar to the structure of methane, followed by

disilane H 3 Si-SiH 3, which is similar in molecular structure to ethane, then trisilane H 3 Si-SiH 2 -SiH 3,

tetrasilane H 3 Si-SiH 2 -SiH 2 -SiH 3,

pentasilane H 3 Si-SiH 2 -SiH 2 -SiH 2 ^--SiH 3 and the last of the obtained silanes of this homologous series

hexasilane H 3 Si-SiH 2 -SiH 2 -SiH 2 -SiH 2 -SiH 3. Silanes do not occur in pure form in nature. They are obtained artificially:

1. Decomposition of metal silicides with acids or alkalis according to the reaction equation

Mg 2 Si+ 4HCI = 2MgCl 2 + SiH 4

this produces a mixture of silanes, which is then separated by fractional distillation at very low temperatures.

2. Reduction of halogenosilanes with lithium hydride or lithium aluminum hydride:

SiCl 4 + 4 LiH = 4LiCl + SiH 4

This method of producing siles was first described in 1947.

3. Reduction of halogenosilanes with hydrogen. The reaction takes place at 300 - 400 ° C in reaction tubes filled with a contact mixture containing silicon, copper metal and 1 - 2% aluminum halides as catalysts.

Despite the similarity in the molecular structure of sitanes and saturated hydrocarbons, physical properties they are different.

Compared to hydrocarbons, silanes are less stable. The most stable of them is monosilane SiH4, which decomposes into silicon and hydrogen only at red heat. Other silanes with high content silicon at much lower temperatures form lower derivatives. For example, disilane Si 2 H 6 gives silane and a solid polymer at 300 ° C, and hexasilane Si 6 H 14 decomposes slowly even at normal temperatures. When in contact with oxygen, silanes easily oxidize, and some of them, for example monosilane SiH 4, spontaneously ignite at -180 ° C. Silanes easily hydrolyze into silicon dioxide and hydrogen:

SiH 4 + 2H 2 0 = SiO 2 + 4H 2

In higher silanes this process occurs with splitting

bonds - Si - Si - Si - between silicon atoms. For example, three

silane Si 3 H 8 gives three molecules of SiO 2 and ten molecules of hydrogen gas:

H 3 Si - SiH 2 - SiH 3 + 6H 3 O = 3SiO 2 + 10H 2

In the presence of caustic alkalis, hydrolysis of silanes results in the formation of silicate of the corresponding alkali metal and hydrogen:

SiH 4 + 2NaOH + H 2 0 = Na 2 Si0 3 + 4H 2

SILICON HALIDES

Binary silicon compounds also include halogenosilanes. Like silicon hydrides - silanes - they form a homologous series of chemical compounds in which halide atoms are directly connected to silicon atoms connected to each other by single bonds

etc. in chains of appropriate length. Due to this similarity, halogenosilanes can be considered as products of the replacement of hydrogen in silanes with the corresponding halogen. In this case, replacement can be complete or incomplete. In the latter case, halogen derivatives of silanes are obtained. The highest halogenosilane known to date is considered to be chlorosilane Si 25 Cl 52. Halogenosilanes and their halogen derivatives do not occur in nature in pure form and can only be obtained artificially.

1. Direct combination of elemental silicon with halogens. For example, SiCl 4 is obtained from ferrosilicon containing from 35 to 50% silicon, treating it at 350-500 ° C with dry chlorine. In this case, SiCl 4 is obtained as the main product in a mixture with other more complex halogenosilanes Si 2 C1 6, Si 3 Cl 8, etc. according to the reaction equation

Si + 2Cl 2 = SiCl 4

The same compound can be obtained by chlorinating a mixture of silica and coke at high temperatures. The reaction proceeds according to the scheme

SiO 2 + 2C=Si +2CO

Si + 2C1 2 = SiС1 4

SiO 2 + 2C + 2Cl 2 = 2CO + SiCl 4

Tetrabromosilane is obtained by bromination of elemental silicon at red heat with bromine vapor:

Si + 2Br 2 = SiBr 4

or a mixture of silica and coke:

SiO 2 + 2C = Si+2CO

Si + 2Br 3 = SiBi 4

SiO 2 + 2C + 2Br 2 = 2CO + SiBr 4

In this case, simultaneously with tetrasilanes, the formation of silanes is possible higher degrees. For example, when chlorinating magnesium silicide, 80% SiCI 4, 20% SiCl 6 and 0.5-1% Si 3 Cl 8 are obtained; when chlorinating calcium silicide, the composition of the reaction products is expressed as follows: 65% SiC1 4; 30% Si 2 Cl 6 ; 4% Si 3 Cl 8 .

2. Halogenation of silanes with hydrogen halides in the presence of AlBr 3 catalysts at temperatures above 100° C. The reaction proceeds according to the scheme

SiH 4 + HBr = SiH 3 Br + H 2

SiH 4 + 2HBr = SiH 2 Br 2 + 2H 2

3. Halogenation of silanes with chloroform in the presence of AlCl 3 catalysts:

Si 3 H 8 + 4СН1 3 = Si 3 H 4 Cl 4 + 4СН 2 С1 3

Si 3 H 8 + 5CHCl 3 = Si 3 H 3 C1 5 + 5CH 2 C1 2

4. Silicon tetrafluoride is obtained by treating silica with hydrofluoric acid:

SiO 2 + 4HF= SiF 4 + 2H 2 0

5. Some polyhalosilanes can be prepared from the simplest halogenosilanes by halogenating them with the appropriate halide. For example, tetraiodosilane in a sealed tube at 200-300 ° C, reacting with silver, releases hexaiododisilane according to

Iodosilanes can be obtained by reacting iodine with silanes in carbon tetrachloride or chloroform, as well as V the presence of an AlI 3 catalyst during the interaction of silane with hydrogen iodide

Halogenosilanes are less durable than structurally similar halogenated hydrocarbons. They easily hydrolyze, forming silica gel and hydrohalic acid:

SiCl 4 + 2H 2 O = Si0 2 + 4HCl

The simplest representatives of halogenosilanes are SiF 4 , SiCl 4 , SiBr 4 and SiI 4 . Of these, tetrafluorosilane and tetrachlorosilane are mainly used in technology. Tetrafluorosilane SiF 4 is a colorless gas with a pungent odor, fumes in air, and hydrolyzes into hydrosilicic acid and silica gel. SiF 4 is obtained by the action of hydrofluoric acid on silica according to the reaction equation

SiO 2 + 4HF = SlF 4 + 2H 2 0

For industrial production. SiF 4 uses fluorspar CaF 2, silica SiO 2 and sulfuric acid H 2 SO 4. The reaction occurs in two phases:

2CaF 2 + 2H 3 SO 4 = 2CaSO 4 + 4HF

SiO 2 + 4HF = 2H 2 O + SiF 4

2CaF 2 + 2H 2 S0 4 + SiO 2 = 2CaSO 4 + 2H 2 O + SiF 4

The gaseous state and volatility of tetrafluorosilane is used for etching sodium-lime silicate glasses with hydrogen fluoride. When hydrogen fluoride reacts with glass, tetrafluorosilane, calcium fluoride, sodium fluoride and water are formed. Tetrafluorosilane, evaporating, releases new deeper layers of glass for reaction with hydrogen fluoride. At the site of the reaction, CaF 2 and NaF remain, which dissolve in water and thereby free up access for hydrogen fluoride for further penetration to the freshly exposed glass surface. The etched surface can be matte or transparent. Matte etching is obtained by the action of gaseous hydrogen fluoride on glass, transparent - by etching with aqueous solutions of hydrofluoric acid. If you pass tetrafluorosilane into water, you get H 2 SiF 6 and silica in the form of a gel:

3SiF 4 + 2H 2 O = 2H 2 SiF 6 + Si0 2

Hydrofluorosilicic acid is a strong dibasic acid; it is not obtained in a free state; upon evaporation it decomposes into SiF 4 and 2HF, which volatilize; with caustic alkalis forms acidic and normal salts:

H 2 SlF 6 + 2NaOH.= Na 2 SiF 6 + 2H 2 O

with excess alkalis gives alkali metal fluoride, silica and water:

H 2 SiF 6 + 6NaOH = 6NaF + SiO 2 + 4H 2 O

The silica released in this reaction reacts with caustic
fog and leads to the formation of silicate:

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

Salts of hydrofluorosilicic acid are called silicofluorides or fluates. Currently known silicofluorides are Na, H, Rb, Cs, NH 4, Cu, Ag, Hg, Mg, Ca, Sr, Ba, Cd, Zn, Mn, Ni, Co, Al, Fe, Cr, Pb and etc.

In technology, for various purposes, sodium silicofluorides Na 2 SiF 6, magnesium MgSiF 6 * 6HgO, zinc ZnSiF 6 * 6H 2 O, aluminum Al 2 (SiF 6) 3, lead PbSiF 6, barium BaSiF 6, etc. are used. Silico fluorides have antiseptic and sealing properties; at the same time they are fire retardants. Because of this, they are used to impregnate wood to prevent premature decay and protect it from ignition during fires. Artificial and natural stones for construction purposes are also impregnated with silicofluoride to compact them. The essence of impregnation is that a solution of silicofluoride, penetrating into the pores and cracks of the stone, reacts with calcium carbonate and some other compounds and forms insoluble salts that are deposited in the pores and seal them. This significantly increases the stone's resistance to weathering. Materials that do not contain calcium carbonate at all or contain little of it are pre-treated with avanfluates, i.e. substances containing dissolved calcium salts, alkali metal silicates and other substances capable of forming insoluble precipitates with fluates. Silicofluorides of magnesium, zinc and aluminum are used as fluates. The fluting process can be represented as follows:

MgSiF 6 + 2CaCO 3 = MgF 2 + 2CaF 2 + SiO 2 + 2CO 2

ZnSiF 6 + ZCaС0 3 = 3CaF 6 + ZnCO 3 + SiO 2 + 2CO 2

Al 2 (SiF 6) 3 + 6CaCO 3 =. 2A1F 3 + 6CaF 2 + 3SiO 2 + 6CO 2

Silicofluorides of alkali metals are obtained by reacting hydrofluorosilicic acid with solutions of salts of these metals:

2NaCl + H 2 SiF 6 = Na 2 SlF 6 + 2HC1

These are gelatinous precipitates, soluble in water and practically insoluble in absolute alcohol. Therefore they are used in quantitative analysis when determining silica by volumetric method. For technical purposes, sodium silicofluoride is used, which is obtained in the form of a white powder as by-product in the production of superphosphate. From a mixture of Na 2 SiF 6 and Al 2 About 3 at 800° C, cryolite 3NaF٠AlF 3 is formed, which is widely used in the production of dental cements and is a good opacifier both in glassmaking and in the manufacture of opaque glazes and enamels.

Sodium silicofluoride, as one of the components, is introduced into the composition of chemically resistant putties produced on liquid glass:

Na 2 SiF 6 + 2Na 2 SiO 3 = 6NaF + 3SiO 2

The silica released by this reaction gives the hardened putty chemical resistance. At the same time, Na 2 SiF 6 is a hardening accelerator. Sodium silicofluoride is also introduced as a mineralizer into raw mixtures in the production of cements.

Tetrachlorosilane SiCl 4 is a colorless, fuming in air, easily hydrolyzed liquid obtained by chlorinating carborundum or ferrosilicon by acting on silanes at elevated temperatures

Tetrachlorosilane is the main starting product for the production of many organosilicon compounds.

Tetrabromosilane SiBr 4 is a colorless liquid that fumes in air, easily hydrolyzes into SiO 2 and HBr, obtained at a red-hot temperature when bromine vapor is passed over hot elemental silicon.

Tetraiodosilane SiI 4 is a white crystalline substance obtained by passing a mixture of iodine vapor and carbon dioxide over hot elemental silicon.

Silicon borides and nitrides

Silicon borides are compounds of silicon and boron. Currently, two silicon borons are known: silicon triboride B 3 Si and silicon hexaboride B 6 Si. These are extremely hard, chemically resistant and fire-resistant substances. They are obtained by fusing in an electric current a finely ground mixture consisting of 5 wt. parts of elemental silicon and 1 wt. h. boron. The cured mass is cleaned with molten potassium carbonate. G. M. Samsonov and V. P. Latyshev obtained silicon triboride by hot pressing at 1600-1800 0 C.

Silicon triboride with pl. 2.52 g/cm 3 forms black plates -
fine structure rhombic crystals, translucent
in a thin layer in yellow-brown tones. Silicon hexaboride with pl.
2.47 g/cm 3 is obtained in the form of opaque opaque grains
fork shape.

Silicon borides melt at about 2000° C, but oxidize very slowly even at high temperatures. This makes it possible to use them as special refractories. The hardness of silicon borides is very high, and in this respect they are close to carborundum.

Silicon compounds with nitrogen are called silicon nitrides. The following nitrides are known: Si 3 N 4, Si 2 N 3 and SIN. Silicon nitrides are obtained by calcining elemental silicon in an atmosphere of pure nitrogen in the temperature range from 1300 to 1500 ° C. Normal silicon nitride Si 3 N 4 can be obtained from a mixture of silica with coke, calcined in an atmosphere of pure nitrogen at 1400-1500 ° C:

6С + 3Si0 2 + 2N 3 ͢ Si 3 N 4 + 6CO

Si 3 N 4 is a grayish-white fireproof and acid-resistant powder that volatilizes only above 1900° C. Silicon nitride hydrolyzes to release silica and ammonia:

Si 3 N 4 + 6H 2 O = 3SiO 2 + 4NH 3

Concentrated sulfuric acid when heated, it slowly decomposes Si 3 N 4, and diluted hydrofluorosilicic acid decomposes it more energetically.

Silicon nitride of the composition Si 2 N 3 is also obtained by the action of nitrogen at high temperatures on elemental silicon or on carbonitrogen silicon C 2 Si 2 N + N 2 = 2C + Si2N 3 .

In addition to binary compounds of silicon with nitrogen, many other more complex compounds are currently known, which are based on the direct bond of silicon atoms with nitrogen atoms, for example: 1) aminosilanes SiH 3 NH 2, SiH 2 (NH 2) 2, SiH(NH 2) 3, Si(NH 2) 4; 2) silylamines NH 2 (SiH 3), NH(SiH 3) 2, N(SiH 3) 3; 3) nitrogen-containing silicon compounds of a more complex composition.

GENERAL VIEWS

Introduction

2.1.1 Oxidation state +2

2.1.2 Oxidation state +4

2.3 Metal carbides

Chapter 3. Silicon compounds

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 forms of motion. 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 it itself has experienced and is experiencing its influence.

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, corresponding disciplines emerged and became isolated: chemistry of complex compounds, polymers, crystal chemistry, studies of dispersed systems and surface phenomena, alloys, etc.

Studying chemical objects and phenomena using physical methods, establishing patterns of 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, colloid 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. Analytical chemistry has acquired an independent character , whose methods are widely used in all areas of chemistry and 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. The 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 occurs at about 500 K. At very high temperatures, silicon reacts 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

Graphite is widely used to make crucibles. Graphite rods are used as electrodes. A lot of graphite is used to make pencils. Carbon and silicon are used to produce various types of cast iron. In metallurgy, carbon is used as a reducing agent, and silicon, due to its high affinity for oxygen, is used as a deoxidizing agent. Crystalline silicon in a particularly pure state (no more than 10 -9 at.% impurity) is used as a semiconductor in various devices and devices, including as transistors and thermistors (devices for very fine temperature measurements), as well as in photocells, the operation of which is based on the ability of a semiconductor to conduct current when illuminated.

Chapter 2. Chemical compounds of carbon

Carbon is characterized by strong covalent bonds between its own atoms (C-C) and with the hydrogen atom (C-H), which is reflected in the abundance of organic compounds (several hundred million). In addition to strong C-H and C-C bonds in various classes of organic and inorganic compounds, carbon bonds with nitrogen, sulfur, oxygen, halogens, and metals are widely represented (see Table 5). Such high possibilities of bond formation are due to the small size of the carbon atom, which allows its valence orbitals 2s 2, 2p 2 to overlap as much as possible. The most important inorganic compounds are described in Table 3.

Among inorganic carbon compounds, nitrogen-containing derivatives are unique in composition and structure.

In inorganic chemistry, derivatives of acetic CH3COOH and oxalic H 2 C 2 O 4 acids are widely represented - acetates (type M "CH3COO) and oxalates (type M I 2 C 2 O 4).

Table 3. The most important inorganic carbon compounds.

2.1 Oxygen derivatives of carbon

2.1.1 Oxidation state +2

Carbon monoxide CO (carbon monoxide): according to the structure of molecular orbitals (Table 4).

CO is similar to the N2 molecule. Like nitrogen, CO has a high dissociation energy (1069 kJ/mol), has a low melting point (69 K) and boiling point (81.5 K), is poorly soluble in water, and is chemically inert. CO enters into reactions only at high temperatures, including:

CO+Cl 2 =COCl 2 (phosgene),

CO + Br 2 = COBg 2, Cr + 6CO = Cr (CO) 6 - chromium carbonyl,

Ni+4CO=Ni (CO) 4 - nickel carbonyl

CO + H 2 0 pairs = HCOOH (formic acid).

At the same time, the CO molecule has a high affinity for oxygen:

CO +1/202 = C0 2 +282 kJ/mol.

Due to its high affinity for oxygen, carbon monoxide (II) is used as a reducing agent for the oxides of many heavy metals (Fe, Co, Pb, etc.). In the laboratory, CO oxide is obtained by dehydrating formic acid

In technology, carbon monoxide (II) is produced by the reduction of CO 2 with coal (C + C0 2 = 2CO) or the oxidation of methane (2CH 4 + ZO 2 = 4H 2 0 + 2CO).

Among CO derivatives, metal carbonyls (for the production of pure metals) are of great theoretical and certain practical interest.

Chemical bonds in carbonyls are formed mainly by the donor-acceptor mechanism due to free orbitals d- element and electron pair of the CO molecule, there is also an l-overlap by the dative mechanism (metal CO). All metal carbonyls are diamagnetic substances characterized by low strength. Like carbon(II) monoxide, metal carbonyls are toxic.

Table 4. Distribution of electrons over the orbitals of the CO molecule

2.1.2 Oxidation state +4

Carbon dioxide C0 2 (carbon dioxide). The C0 2 molecule is linear. The energy scheme for the formation of orbitals of the CO 2 molecule is shown in Fig. 2. Carbon (IV) monoxide can react with ammonia by reaction.

When this salt is heated, a valuable fertilizer is obtained - urea CO (MH 2) 2:

Urea is decomposed by water

CO (NH 2) 2 +2HaO= (MH 4) 2CO3.

Figure 2. Enphetic diagram of the formation of molecular orbitals of C0 2.

In technology, CO 2 oxide is obtained by the decomposition of calcium carbonate or sodium bicarbonate:

In laboratory conditions, it is usually obtained by the reaction (in the Kipp apparatus)

CaCO3+2HC1=CaC12+CO2+H20.

The most important derivatives of CO 2 are weak carbonic acid H 2 CO 3 and its salts: M I 2 CO 3 and M I H CO 3 (carbonates and bicarbonates, respectively).

Most carbonates are insoluble in water. Water-soluble carbonates undergo significant hydrolysis:

CO3- +H 2 0 CO3-+OH - (I stage).

Due to complete hydrolysis, carbonates Cr 3+, ai 3+, Ti 4+, Zr 4+, etc. cannot be isolated from aqueous solutions.

The practically important ones are Ka 2 CO3 (soda), K 2 CO3 (potash) and CaCO3 (chalk, marble, limestone). Hydrocarbonates, unlike carbonates, are soluble in water. From hydrocarbonates practical application finds NaHCO 3 (baking soda). Important basic carbonates are 2CuCO3-Cu (OH) 2, PbCO 3 X XRb (OH) 2.

The properties of carbon halides are given in Table 6. Of the carbon halides, the most important is a colorless, rather toxic liquid. Under normal conditions, CCI 4 is chemically inert. It is used as a non-flammable and non-flammable solvent for resins, varnishes, fats, and also for the production of freon CF 2 CI 2 (T bp = 303 K):

Another organic solvent used in practice is carbon disulfide CSa (colorless, volatile liquid with boiling point = 319 K) - a reactive substance:

CS 2 +30 2 =C0 2 +2S0 2 +258 kcal/mol,

CS 2 +3Cl 2 =CCl 4 -S 2 Cl 2, CS 2 +2H 2 0==C0 2 +2H 2 S, CS 2 +K 2 S=K 2 CS 3 (thiocarbonic acid salt H 2 CS3).

Carbon disulfide vapors are poisonous.

Hydrocyanic (hydrocyanic) acid HCN (H-C = N) is a colorless, easily mobile liquid, boiling at 299.5 K. At 283 K it solidifies. HCN and its derivatives are extremely poisonous. HCN can be prepared by the reaction

Hydrocyanic acid dissolves in water; however, it weakly dissociates

HCN=H++CN-, K=6.2.10- 10.

Salts of hydrocyanic acid (cyanides) resemble chlorides in some reactions. For example, CH -- -ion with Ag+ ions gives a white precipitate of silver cyanide AgCN, which is poorly soluble in mineral acids. Alkali and alkaline earth metal cyanides are soluble in water. Due to hydrolysis, their solutions smell like hydrocyanic acid (the smell of bitter almonds). Heavy metal cyanides are poorly soluble in water. CN is a strong ligand; the most important complex compounds are K 4 and K3 [Fe (CN) 6 ].

Cyanides are fragile compounds; with prolonged exposure to CO 2 contained in the air, cyanides decompose

2KCN+C0 2 +H 2 0=K 2 C0 3 +2HCN.

(CN) 2 - cyanogen (N=C-C=N) –

colorless poisonous gas; reacts with water to form cyanic (HOCN) and hydrocyanic (HCN) acids:

(HCN) acids:

(CN) 2 +H 2 0==HOCN+HCN.

In this, as in the reaction below, (CN)2 is similar to a halogen:

CO+ (CN) 2 =CO (CN) 2 (analogue of phosgene).

Cyanic acid is known in two tautomeric forms:

H-N=C=O==H-0-C=N.

The isomer is the acid H-0=N=C (explosive acid). HONC salts explode (used as detonators). Rhodane acid HSCN is a colorless, oily, volatile, easily solidifying (Tm=278 K) liquid. In its pure state it is very unstable; when it decomposes, HCN is released. Unlike hydrocyanic acid, HSCN is sufficiently strong acid(K=0.14). HSCN is characterized by tautomeric equilibrium:

H-N = C = S=H-S-C =N.

SCN is a blood-red ion (reagent for Fe 3+ ion). Rhodanide salts derived from HSCN are easily obtained from cyanides by adding sulfur:

Most thiocyanates are soluble in water. Hg, Au, Ag, Cu salts are insoluble in water. The SCN- ion, like CN-, tends to give complexes of the type M3 1 M" (SCN) 6, where M" "Cu, Mg and some others. Dirodane (SCN) 2 are light yellow crystals, melting at 271 K. They are obtained (SCN) 2 by reaction

2AgSCN+Br 2 ==2AgBr+ (SCN) 2.

Among other nitrogen-containing compounds, cyanamide should be indicated

and its derivative, calcium cyanamide CaCN 2 (Ca=N-C=N), which is used as a fertilizer.

2.3 Metal carbides

Carbides are the products of the interaction of carbon with metals, silicon and boron. Carbides are divided into two classes based on solubility: carbides soluble in water (or in dilute acids) and carbides insoluble in water (or in dilute acids).

2.3.1 Carbides soluble in water and dilute acids

A. Carbides that, when dissolved, form C 2 H 2 This group includes metal carbides of the first two main groups; Carbides Zn, Cd, La, Ce, Th of composition MC 2 (LaC 2, CeC 2, ТhC 2.) are also close to them.

CaC 2 +2H 2 0=Ca (OH) 2 +C 2 H 2, ThC 2 +4H 2 0=Th (OH) 4 +H 2 C 2 +H 2.

ANS3+ 12H 2 0=4Al (OH) 3+3CH 4, Be 2 C+4H 2 0=2Be (OH) 2 +CH 4. In terms of properties, Mn 3 C is close to them:

Mn 3 C + 6H 2 0 = 3Mn (OH) 2 + CH 4 + H 2.

B. Carbides, when dissolved, form a mixture of hydrocarbons and hydrogen. These include most rare earth metal carbides.

2.3.2 Carbides insoluble in water and dilute acids

This group includes most transition metal carbides (W, Mo, Ta, etc.), as well as SiC, B 4 C.

They dissolve in oxidizing environments, for example:

VC + 3HN0 3 + 6HF = HVF 6 + CO 2 + 3NO + 4H 2 0, SiC + 4KOH + 2C0 2 = K 2 Si0 3 + K 2 C0 3 + 2H 2 0.

Figure 3. Icosahedron B 12

Practically important are carbides of transition metals, as well as silicon carbides SiC and boron B 4 C. SiC - carborundum - colorless crystals with a diamond lattice, in hardness approaching diamond (technical SiC has a dark color due to impurities). SiC is highly refractory, thermally and electrically conductive at high temperatures, and chemically extremely inert; it can only be destroyed by fusion in air with alkalis.

B 4 C is a polymer. The boron carbide lattice is built from linearly arranged three carbon atoms and groups containing 12 B atoms, arranged in the shape of an icosahedron (Fig. 3); The hardness of B4C is higher than that of SiC.

Chapter 3. Silicon compounds

The difference between the chemistry of silicon and carbon is mainly due to the large size of its atom and the possibility of using free 3d orbitals. Due to additional binding (according to the donor-acceptor mechanism), the bonds of silicon with oxygen Si-O-Si and fluorine Si-F (Table 17.23) are stronger than those of carbon, and due to the larger size of the Si atom compared to the Si-F atom C Si-H and Si-Si bonds are less strong than those of carbon. Silicon atoms are practically incapable of forming chains. The homologous series of silicic acids SinH2n+2 (silanes), similar to hydrocarbons, was obtained only up to the composition Si4Hio. Due to its larger size, the Si atom has a weakly expressed ability to overlap; therefore, not only triple but also double bonds are uncharacteristic for it.

When silicon interacts with metals, silicides are formed (Ca 2 Si, Mg 2 Si, BaSi 2, Cr 3 Si, CrSi 2, etc.), which are in many ways similar to carbides. Silicides are not typical for group I elements (except for Li). Silicon halides (Table 5) are stronger compounds than carbon halides; at the same time, they decompose with water.

Table 5. Strength of some bonds between carbon and silicon

The most durable silicon halide is SiF 4 (it decomposes only under the influence of an electric discharge), but, like other halides, it undergoes hydrolysis. When SiF 4 interacts with HF, hexafluorosilicic acid is formed:

SiF 4 +2HF=H 2.

H 2 SiF 6 is close in strength to H 2 S0 4 . Derivatives of this acid - fluorosilicates, are usually soluble in water. Fluorosilicates of alkali metals (except Li and NH 4) are poorly soluble. Fluorosilicates are used as pesticides (insecticides).

The practically important halide is SiCO 4 . It is used to produce organosilicon compounds. Thus, SiCL 4 easily interacts with alcohols to form silicic acid esters HaSiO 3:

SiCl 4 +4C 2 H 5 OH=Si (OC 2 H 5) 4 +4HCl 4

Table 6. Carbon and silicon halides

Esters of silicic acid, hydrolyzing, form silicones - polymer substances with a chain structure:

(R-organic radical), which are used for the production of rubbers, oils and lubricants.

Silicon sulfide (SiS 2) n-polymer substance; stable at normal temperatures; decomposes with water:

SiS 2 + ZN 2 O = 2H 2 S + H 2 SiO 3.

3.1 Oxygen compounds of silicon

The most important oxygen compound of silicon is silicon dioxide SiO 2 (silica), which has several crystalline modifications.

The low-temperature modification (up to 1143 K) is called quartz. Quartz has piezoelectric properties. Natural varieties of quartz: rock crystal, topaz, amethyst. Varieties of silica are chalcedony, opal, agate,. jasper, sand.

Silica is chemically resistant; only fluorine, hydrofluoric acid and alkali solutions act on it. It easily transforms into a glassy state (quartz glass). Quartz glass is fragile, chemically and thermally very resistant. The corresponding SiO 2 silicic acid does not have a specific composition. Typically, silicic acid is written as xH 2 O-ySiO 2 . The following silicic acids have been identified: H 2 SiO 3 (H 2 O-SiO 2) - metasilicon (tri-oxo-silicon), H 4 Si0 4 (2H 2 0-Si0 2) - ortho-silicon (tetra-oxo-silicon), H 2 Si2O 5 (H 2 O * SiO 2) - dimethacilicon.

Silicic acids are poorly soluble substances. In accordance with the less metalloid nature of silicon compared to carbon, H 2 SiO 3 as an electrolyte is weaker than H 2 CO3.

The silicate salts corresponding to silicic acids are insoluble in water (except for alkali metal silicates). Soluble silicates hydrolyze according to the equation

2SiO3 2 -+H 2 0=Si 2 O 5 2 -+20H-.

Concentrated solutions of soluble silicates are called liquid glass. Ordinary window glass - sodium and calcium silicate - has the composition Na 2 0-CaO-6Si0 2. It is obtained by reaction

Known great variety silicates (more precisely, oxosilicates). A certain pattern is observed in the structure of oxosilicates: they all consist of Si0 4 tetrahedra, which are connected to each other through an oxygen atom. The most common combinations of tetrahedra are (Si 2 O 7 6 -), (Si 3 O 9) 6 -, (Si 4 0 l2) 8-, (Si 6 O 18 12 -), which as structural units can be combined into chains, tapes, meshes and frames (Figure 4).

The most important natural silicates are, for example, talc (3MgO * H 2 0-4Si0 2) and asbestos (SmgO * H 2 O * SiO 2). Like SiO 2, silicates are characterized by a glassy (amorphous) state. With controlled crystallization of glass, a fine-crystalline state (ceramic glass) can be obtained. Sitalls are characterized by increased strength.

In addition to silicates, aluminosilicates are widespread in nature. Aluminosilicates are framework oxosilicates in which some of the silicon atoms are replaced by trivalent Al; for example Na 12 [ (Si, Al) 0 4 ] 12 .

Silicic acid is characterized by a colloidal state; when exposed to acid salts, H 2 SiO 3 does not precipitate immediately. Colloidal solutions of silicic acid (sols) under certain conditions (for example, when heated) can be converted into a transparent, homogeneous gelatinous mass-gel of silicic acid. Gels are high-molecular compounds with a spatial, very loose structure formed by Si0 2 molecules, the voids of which are filled with H 2 O molecules. When silicic acid gels are dehydrated, silica gel is obtained - a porous product with high adsorption capacity.

Figure 4. Structure of silicates.

Conclusions

Having examined in my work chemical compounds based on silicon and carbon, I came to the conclusion that carbon, being a not very widespread element in quantity, is the most important component of earthly life; its compounds exist in the air, oil, as well as in such simple substances as diamond and graphite. One of the most important characteristics Carbon has strong covalent bonds between atoms, as well as the hydrogen atom. The most important inorganic carbon compounds are: oxides, acids, salts, halides, nitrogen-containing derivatives, sulfides, carbides.

Speaking about silicon, it should be noted large quantities its reserves on earth, it is the basis of the earth's crust and is found in a huge variety of silicates, sand, etc. Currently, the use of silicon due to its semiconductor properties is increasing. It is used in electronics in the production of computer processors, microcircuits and chips. Silicon compounds with metals form silicides; the most important oxygen compound of silicon is silicon oxide SiO 2 (silica). There is a wide variety of silicates in nature - talc, asbestos, and aluminosilicates are also common.