Silicon and its compounds. Silicon: application, chemical and physical properties

As an independent chemical element, silicon became known to mankind only in 1825. Which, of course, did not prevent the use of silicon compounds in such a number of spheres that it is easier to list those where the element is not used. This article will shed light on the physical, mechanical and useful Chemical properties silicon and its compounds, areas of application, we will also talk about how silicon affects the properties of steel and other metals.

To begin with, let's dwell on the general characteristics of silicon. From 27.6 to 29.5% of the mass earth's crust makes up silicon. In sea water, the concentration of the element is also fair - up to 3 mg / l.

In terms of prevalence in the lithosphere, silicon occupies the second place of honor after oxygen. However, its most well-known form, silica, is an oxide, and it is precisely its properties that have become the basis for such a wide application.

This video will tell you what silicon is:

Concept and features

Silicon is a non-metal, but different conditions can exhibit both acidic and basic properties. It is a typical semiconductor and is extremely widely used in electrical engineering. Its physical and chemical properties are largely determined by the allotropic state. Most often, they deal with the crystalline form, since its qualities are more in demand in the national economy.

Silicon is one of the basic macronutrients in human body. Its deficiency is detrimental to the condition bone tissue, hair, skin, nails. In addition, silicon affects the performance of the immune system.
In medicine, the element, or rather, its compounds, found their first use in this capacity. Water from wells lined with flint differed not only in purity, but also had a positive effect on resistance to infectious diseases. Today, compounds with silicon serve as the basis for drugs against tuberculosis, atherosclerosis, and arthritis.
In general, the non-metal is inactive, however, even in pure form it's hard to meet him. This is due to the fact that in air it is quickly passivated by a layer of dioxide and ceases to react. When heated, the chemical activity increases. As a result, humanity is much more familiar with the compounds of matter, and not with itself.

So, silicon forms alloys with almost all metals - silicides. All of them are distinguished by their refractoriness and hardness and are used in their respective areas: gas turbines, furnace heaters.

A non-metal is placed in the table of D. I. Mendeleev in group 6 along with carbon, germanium, which indicates a certain commonality with these substances. So, with carbon, it is “in common” with the ability to form compounds of the organic type. At the same time, silicon, like germanium, can exhibit the properties of a metal in some chemical reactions, which is used in synthesis.

Pros and cons

Like any other substance in terms of application in the national economy, silicon has certain useful or not very qualities. They are important for determining the area of \u200b\u200buse.

A significant advantage of the substance is its availability. In nature, however, it is not in a free form, but still, the technology for obtaining silicon is not so complicated, although it is energy-consuming.
The second most important advantage is multiple compound formation with extraordinary useful properties. These are silanes, and silicides, and dioxide, and, of course, various silicates. The ability of silicon and its compounds to form complex solid solutions is practically infinite, which makes it possible to endlessly obtain a variety of variations of glass, stone and ceramics.
Semiconductor properties non-metal provides him with a place as a base material in electrical and radio engineering.
Nonmetal is non-toxic, which allows application in any industry, and at the same time does not turn the technological process into a potentially dangerous one.

The disadvantages of the material include only relative brittleness with good hardness. Silicon is not used for load-bearing structures, but this combination makes it possible to properly process the surface of crystals, which is important for instrumentation.

Let's now talk about the main properties of silicon.

Properties and characteristics

Since crystalline silicon is most often used in industry, it is precisely its properties that are more important, and it is they that are given in technical specifications. The physical properties of a substance are:

melting point - 1417 C;
boiling point - 2600 C;
density is 2.33 g/cu. see, which indicates fragility;
heat capacity, as well as thermal conductivity, are not constant even on the purest samples: 800 J / (kg K), or 0.191 cal / (g deg) and 84-126 W / (m K), or 0.20-0, 30 cal/(cm sec deg), respectively;
transparent to long-wave infrared radiation, which is used in infrared optics;
dielectric constant - 1.17;
hardness on the Mohs scale - 7.

The electrical properties of a non-metal are highly dependent on impurities. In industry, this feature is used by modulating the desired type of semiconductor. At normal temperatures, silicon is brittle, but when heated above 800 C, plastic deformation is possible.

The properties of amorphous silicon are strikingly different: it is highly hygroscopic and reacts much more actively even at normal temperatures.

The structure and chemical composition, as well as the properties of silicon, are discussed in the video below:

Composition and structure

Silicon exists in two allotropic forms, equally stable at normal temperature.

Crystal It has the appearance of a dark gray powder. The substance, although it has a diamond-like crystal lattice, is fragile - due to the too long bond between the atoms. Of interest are its semiconductor properties.
At very high pressures available hexagonal modification with a density of 2.55 g / cu. see However, this phase has not yet found practical significance.
Amorphous- Brown powder. Unlike the crystalline form, it reacts much more actively. This is due not so much to the inertness of the first form, but to the fact that in air the substance is covered with a layer of dioxide.

In addition, it is necessary to take into account another type of classification associated with the size of the silicon crystal, which together form a substance. The crystal lattice, as is known, implies the ordering not only of atoms, but also of the structures that these atoms form - the so-called long-range order. The larger it is, the more homogeneous the substance will be in properties.

monocrystalline– the sample is a single crystal. Its structure is as ordered as possible, the properties are homogeneous and well predictable. It is this material that is most in demand in electrical engineering. However, it also belongs to the most expensive type, since the process of obtaining it is complicated, and the growth rate is low.
Multicrystalline– the sample consists of a number of large crystalline grains. The boundaries between them form additional defective levels, which reduces the performance of the sample as a semiconductor and leads to faster wear. The technology for growing a multicrystal is simpler, and therefore the material is cheaper.
Polycrystalline- comprises a large number grains arranged randomly with respect to each other. This is the purest variety of industrial silicon, used in microelectronics and solar energy. Quite often it is used as a raw material for growing multi- and single crystals.
Amorphous silicon also occupies a separate position in this classification. Here the order of the atoms is maintained only at the shortest distances. However, in electrical engineering, it is still used in the form of thin films.

Non-metal production

It is not so easy to obtain pure silicon, given the inertness of its compounds and the high melting point of most of them. In industry, carbon dioxide reduction is most often used. The reaction is carried out in arc furnaces at a temperature of 1800 C. Thus, a non-metal with a purity of 99.9% is obtained, which is not enough for its use.

The resulting material is chlorinated in order to obtain chlorides and hydrochlorides. The connections are then cleaned with all possible methods from impurities and reduce with hydrogen.

It is also possible to purify the substance by obtaining magnesium silicide. The silicide is exposed to hydrochloric or acetic acid. Silane is obtained, and the latter is purified different ways- sorption, rectification and so on. Then the silane is decomposed into hydrogen and silicon at a temperature of 1000 C. In this case, a substance with an impurity fraction of 10 -8 -10 -6% is obtained.

Substance use

For industry, the electrophysical characteristics of non-metal are of the greatest interest. Its single-crystal form is an indirect-gap semiconductor. Its properties are determined by impurities, which makes it possible to obtain silicon crystals with desired properties. So, the addition of boron, indium makes it possible to grow a crystal with hole conductivity, and the introduction of phosphorus or arsenic - a crystal with electronic conductivity.

Silicon literally serves as the basis of modern electrical engineering. Transistors, photocells, integrated circuits, diodes and so on are made from it. Moreover, the functionality of the device is almost always determined only by the near-surface layer of the crystal, which leads to very specific requirements for surface treatment.
In metallurgy, technical silicon is used both as an alloy modifier - it gives greater strength, and as a component - in, for example, and as a deoxidizer - in the production of cast iron.
Ultra-pure and refined metallurgical form the basis of solar energy.
Non-metal dioxide is found in nature in very different forms. Its crystalline varieties are opal, agate, carnelian, amethyst, rhinestone, have found their place in the jewelry business. Modifications that are not so attractive in appearance - flint, quartz, are used in metallurgy, and in construction, and in radio electrical engineering.
The compound of a non-metal with carbon - carbide, is used in metallurgy, and in instrument making, and in chemical industry. It is a wide-gap semiconductor, characterized by high hardness - 7 on the Mohs scale, and strength, which allows it to be used as an abrasive material.
Silicates - that is, salts of silicic acid. Unstable, easily decomposed under the influence of temperature. They are remarkable in that they form numerous and varied salts. But the latter are the basis for the production of glass, ceramics, faience, crystal, and. We can safely say that modern construction is based on a variety of silicates.
Glass represents here the most interesting case. It is based on aluminosilicates, but negligible impurities of other substances - usually oxides, give the material a mass different properties, including color. -, earthenware, porcelain, in fact, has the same formula, although with a different ratio of components, and its diversity is also amazing.
A non-metal has another ability: it forms carbon-type compounds, in the form of a long chain of silicon atoms. Such compounds are called organosilicon compounds. The scope of their application is no less known - these are silicones, sealants, lubricants, and so on.

Silicon is a very common element and is extremely important in so many areas. National economy. Moreover, not only the substance itself is actively used, but all its various and numerous compounds.

This video will talk about the properties and applications of silicon:

Introduction

Chapter 2. Chemical compounds of carbon

2.1 Oxygen derivatives of carbon

2.1.1 +2 oxidation state

2.1.2 +4 oxidation state

2.3 Metal carbides

2.3.1 Carbides soluble in water and dilute acids

2.3.2 Carbides insoluble in water and in dilute acids

Chapter 3. Silicon Compounds

3.1 Oxygen silicon compounds

Bibliography

Introduction

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

By definition, D.I. Mendeleev (1871), "chemistry in its present state can ... be called the doctrine of the elements."

The origin of the word "chemistry" is not completely clear. Many researchers believe that it comes from the ancient name of Egypt - Hemia (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 connected both with other natural sciences and with all branches of the national economy.

The qualitative feature of the chemical form of the motion of matter, and its transitions to other forms of motion, determines the versatility of chemical science and its connection with areas of knowledge that study both lower and higher forms of motion. The knowledge of the chemical form of the motion of matter enriches the general doctrine of the development of nature, the evolution of matter in the Universe, and contributes to the formation of an integral 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 exerted and is exerting an influence on the development of philosophy, and has itself experienced and is experiencing its influence.

Historically, two main branches of chemistry have developed: inorganic chemistry, which studies primarily the chemical elements and the simple and complex substances they form (except carbon compounds), and organic chemistry, the subject of which is the compounds of carbon 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. Starting from the 19th century. these terms have come to indicate the presence or absence of carbon in a given 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 represents 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 the sciences of living nature. At the junction between inorganic and organic chemistry is the area of organoelement compounds.

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

Study of chemical objects and phenomena physical methods, establishing the laws of chemical transformations, based on general principles physics, underlies 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, the doctrine of catalysis, chemical equilibrium, solutions and others. analytical chemistry, whose methods 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, medical chemistry, forensic chemistry, etc., arose.

As mentioned above, chemistry considers the 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 paper.

Chapter 1. Silicon and carbon - chemical elements

1.1 Introduction to carbon and silicon

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

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 (Ca, Zn, Mg, Fe, etc.) that are very common in nature, exists in the atmosphere in the form of CO 2, occurs 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 (Fig. 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.

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

Figure 1. The structure of a diamond (a); graphite structure (b)

Carbon and silicon have their own specific derivatives.

Table 2. The most characteristic 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 in an especially pure state after reduction, the substance is transferred to tetrachloride and again reduced (with hydrogen). Then it is melted into ingots and subjected to cleaning by zone melting. An ingot of metal is heated from 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 one, is removed, and thus the metal is purified.

Carbon is inert, but at a very high temperature (in the 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 \u003d CaC 2, C + 3Fe \u003d Fe 3 C,

Silicon is more reactive. It reacts with fluorine already at ordinary temperature: Si + 2F 2 \u003d SiF 4

Silicon has a very high affinity for oxygen as well:

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 \u003d Na 2 Si0 3 + 2H 2.

Acids other than hydrofluoric do not affect it. With HF there is a reaction

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

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

Introduction

2.1.1 +2 oxidation state

2.1.2 +4 oxidation state

2.3 Metal carbides

Chapter 3. Silicon Compounds

Bibliography

Introduction

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

By definition, D.I. Mendeleev (1871), "chemistry in its present state can ... be called the doctrine of the elements."

Modern chemistry is closely connected both with other natural sciences and with all branches of the national economy.

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. Starting from the 19th century. these terms have come to indicate the presence or absence of carbon in a given 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 the sciences of living nature. At the junction between inorganic and organic chemistry is the area of organoelement compounds.

The study of chemical objects and phenomena by physical methods, the establishment of patterns of chemical transformations, based on the general principles of physics, underlies 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, the doctrine of catalysis, chemical equilibrium, solutions and others. Analytical chemistry acquired an independent character , whose methods 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, medical chemistry, forensic chemistry, etc., arose.

Chapter 1. Silicon and carbon - chemical elements

1.1 Introduction to carbon and silicon

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

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.

Figure 1. The structure of a diamond (a); graphite structure (b)

Carbon and silicon have their own specific derivatives.

Table 2. The most characteristic derivatives of carbon and silicon

1.2 Preparation, chemical properties and use of simple substances

2C + Ca \u003d CaC 2, C + 3Fe \u003d Fe 3 C,

Silicon is more reactive. It reacts with fluorine already at ordinary temperature: Si + 2F 2 \u003d SiF 4

Silicon has a very high affinity for oxygen as well:

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

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

Si + 2NaOH + H 2 0 \u003d Na 2 Si0 3 + 2H 2.

Acids other than hydrofluoric do not affect it. With HF there is a reaction

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

Carbon in the composition of various coals, oil, natural (mainly CH4), as well as artificially obtained 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 goes to the production of pencils. Carbon and silicon are used to produce various grades of cast iron. In metallurgy, carbon is used as a reducing agent, and silicon, due to its high affinity for oxygen, as a deoxidizer. Crystalline silicon in an especially 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 It 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 durable C-H connections, C-C 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 compounds of carbon.

2.1 Oxygen derivatives of carbon

2.1.1 +2 oxidation state

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

CO is similar to the N 2 molecule. Like nitrogen, CO has a high dissociation energy (1069 kJ/mol), has a low Tm (69 K) and Tbp (81.5 K), is poorly soluble in water, and is chemically inert. CO reacts only at high temperatures, including:

CO + Cl 2 \u003d COCl 2 (phosgene),

CO + Br 2 \u003d SOVg 2, Cr + 6CO \u003d Cr (CO) 6 -chromium carbonyl,

Ni + 4CO \u003d Ni (CO) 4 - nickel carbonyl

CO + H 2 0 pairs \u003d HCOOH (formic acid).

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

CO +1/202 \u003d 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 obtained by reducing CO 2 with coal (C + CO 2 \u003d 2CO) or by oxidizing methane (2CH 4 + 3O 2 \u003d \u003d 4H 2 0 + 2CO).

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

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

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

2.1.2 +4 oxidation state

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

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

Urea is decomposed by water

CO (NH 2) 2 + 2HaO \u003d (MH 4) 2COz.

Figure 2. Energy diagram of the formation of CO 2 molecular orbitals.

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

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

CaCO3 + 2HC1 = CaC12 + CO2 + H20.

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

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

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

Due to the complete hydrolysis of aqueous solutions it is impossible to isolate carbonates Cr 3+ , ai 3 + , Ti 4+ , Zr 4+ etc.

Practically important are Ka 2 CO3 (soda), K 2 CO3 (potash) and CaCO3 (chalk, marble, limestone). Bicarbonates, unlike carbonates, are soluble in water. From bicarbonates practical use finds NaHCO 3 ( drinking soda). Important basic carbonates are 2CuCO3-Cu (OH) 2 , PbCO 3 X XPb (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. AT normal conditions CCI 4 is chemically inert. It is used as a non-flammable and non-flammable solvent for resins, varnishes, fats, as well as for obtaining freon CF 2 CI 2 (T bp = 303 K):

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

CS 2 +30 2 \u003d C0 2 + 2S0 2 +258 kcal / mol,

CS 2 + 3Cl 2 \u003d CCl 4 -S 2 Cl 2, CS 2 + 2H 2 0 \u003d\u003d C0 2 + 2H 2 S, CS 2 + K 2 S \u003d K 2 CS 3 (salt of thiocarbonic acid H 2 CSz).

Vapors of carbon disulfide are poisonous.

Hydrocyanic (hydrocyanic) acid HCN (H-C \u003d 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 obtained by the reaction

Hydrocyanic acid dissolves in water; at the same time, it weakly dissociates

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

Hydrocyanic acid salts (cyanides) in some reactions resemble chlorides. For example, CH - -ion with Ag + ions gives a white precipitate of silver cyanide AgCN, poorly soluble in mineral acids. Cyanides of alkali and alkaline earth metals are soluble in water. Due to hydrolysis, their solutions smell of 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 Kz [Re (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; interacts with water to form cyanic (HOCN) and hydrocyanic (HCN) acids:

(HCN) acids:

(CN) 2 + H 2 0 \u003d\u003d HOCN + HCN.

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

CO + (CN) 2 \u003d 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). Rhodohydrogen acid HSCN is a colorless, oily, volatile, easily solidifying liquid (Tm=278 K). In the pure state, it is very unstable; when it decomposes, HCN is released. Unlike hydrocyanic acid, HSCN is a rather strong acid (K=0.14). HSCN is characterized by tautomeric equilibrium:

H-N \u003d C \u003d S \u003d H-S-C \u003d N.

SCN - blood-red ion (reagent for Fe 3+ ion). HSCN-derived rhodanide salts - easily obtained from cyanides by addition of sulfur:

Most thiocyanates are soluble in water. Salts of Hg, Au, Ag, Cu 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. Dirodan (SCN) 2 - light yellow crystals, melting - 271 K. Get (SCN) 2 by reaction

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

Of the 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. By solubility, carbides are divided into two classes: carbides that are soluble in water (or dilute acids) and carbides that are insoluble in water (or dilute acids).

2.3.1 Carbides soluble in water and dilute acids

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

CaC 2 + 2H 2 0 \u003d Ca (OH) 2 + C 2 H 2, ThC 2 + 4H 2 0 \u003d Th (OH) 4 + H 2 C 2 + H 2.

ANSz + 12H 2 0 \u003d 4Al (OH) s + ZSN 4, Be 2 C + 4H 2 0 \u003d 2Be (OH) 2 + CH 4. According to their properties, Mn z C is close to them:

Mn s C + 6H 2 0 \u003d ZMn (OH) 2 + CH 4 + H 2.

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

2.3.2 Carbides insoluble in water and in 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 \u003d HVF 6 + CO 2 + 3NO + 4H 2 0, SiC + 4KOH + 2C0 2 \u003d K 2 Si0 3 + K 2 C0 3 + 2H 2 0.

Figure 3. Icosahedron B 12

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

B 4 C - polymer. The boron carbide lattice is built from linearly arranged three carbon atoms and groups containing 12 B atoms arranged in the form 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), silicon bonds with oxygen Si-O-Si and fluorine Si-F (Table 17.23) are stronger than those of carbon, and due to bigger size of the Si atom, compared to the C atom, the 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 silicon hydrogens SinH2n+2 (silanes) analogous to hydrocarbons was obtained only up to the composition Si4Hio. Due to the larger size, the Si atom also has a weakly expressed ability for n-overlapping; therefore, not only triple, but also double bonds are of little character for it.

When silicon interacts with metals, silicides are formed (Ca 2 Si, Mg 2 Si, BaSi 2, Cr 3 Si, CrSi 2, etc.), similar in many respects to carbides. Silicides are not characteristic of group I elements (except for Li). Silicon halides (Table 5) are stronger compounds than carbon halides; however, they are decomposed by water.

Table 5. Strength of some bonds of carbon and silicon

The most durable silicon halide is SiF 4 (it decomposes only under the action 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, as a rule, are soluble in water. Alkali metal fluorosilicates (except for Li and NH 4) are poorly soluble. Fluorosilicates are used as pesticides (insecticides).

Practically important halide is SiCO 4 . It is used to obtain organosilicon compounds. So, SiCL 4 easily interacts with alcohols to form silicic acid esters HaSiO 3:

SiCl 4 + 4C 2 H 5 OH \u003d Si (OC 2 H 5) 4 + 4HCl 4

Table 6. Carbon and silicon halides

Silicic acid esters, hydrolyzing, form silicones - polymeric substances of a chain structure:

(R-organic radical), which have found application in the production of rubbers, oils and lubricants.

Silicon sulfide (SiS 2) n-polymer substance; stable at normal temperature; decomposed by water:

SiS 2 + ZN 2 O \u003d 2H 2 S + H 2 SiO 3.

3.1 Oxygen silicon compounds

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

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 passes into a glassy state (quartz glass). Quartz glass is brittle, chemically and thermally quite resistant. Silicic acid corresponding to SiO 2 does not have a definite composition. Silicic acid is usually written as xH 2 O-ySiO 2 . Silicic acids have been isolated: H 2 SiO 3 (H 2 O-SiO 2) - metasilicon (tri-oxosilicon), H 4 Si0 4 (2H 2 0-Si0 2) - orthosilicon (tetra-oxosilicon), H 2 Si2O 5 (H 2 O * SiO 2) - dimethosilicon.

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 alkali metal silicates). Soluble silicates are hydrolyzed according to the equation

2SiOz 2 - + H 2 0 \u003d 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 from the reaction

A wide variety of silicates (more precisely, oxosilicates) is known. A certain regularity 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 (Fig. 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, it is possible to obtain a finely crystalline state (sitalls). Sitalls are characterized by increased strength.

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

For silicic acid, a colloidal state is characteristic when exposed to its salts of acids 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 a high adsorption capacity.

Figure 4. The structure of silicates.

conclusions

Having examined chemical compounds based on silicon and carbon in my work, I came to the conclusion that carbon, being a quantitatively not very common element, is the most important component of earthly life, its compounds exist in air, oil, and also 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 compounds of carbon are: oxides, acids, salts, halides, nitrogen-containing derivatives, sulfides, carbides.

Speaking of silicon, it is necessary to note the large amounts of its reserves on earth, it is the basis of the earth's crust and is found in a huge variety of silicates, sand, etc. At present, the use of silicon due to its semiconductor properties is on the rise. It is used in electronics in the manufacture 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). In nature, there is a wide variety of silicates - talc, asbestos, aluminosilicates are also common.

Bibliography

1. Great Soviet Encyclopedia. Third edition. T.28. - M.: Soviet Encyclopedia, 1970.

2. Zhiryakov V.G. Organic chemistry. 4th ed. - M., "Chemistry", 1971.

3. Brief chemical encyclopedia. - M. "Soviet Encyclopedia", 1967.

4. General chemistry / Ed. EAT. Sokolovskaya, L.S. Guzeya. 3rd ed. - M.: Publishing House of Moscow. un-ta, 1989.

5. The world of inanimate nature. - M., "Science", 1983.

6. Potapov V.M., Tatarinchik S.N. Organic chemistry. Textbook.4th ed. - M.: "Chemistry", 1989.

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

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

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

Reducing properties of carbon

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

Depending on the excess or lack of oxygen during the combustion of coal, the formation of carbon monoxide CO or carbon dioxide CO 2 is possible:

When carbon reacts with fluorine, carbon tetrafluoride is formed:

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

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

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

Interaction of carbon with non-metal oxides

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

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

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

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

Oxidizing properties of carbon

The chemical element carbon does not have a high electronegativity, therefore, formed by it simple substances rarely show oxidizing properties in relation to other non-metals.

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

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

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

Active metal carbides are hydrolyzed by water:

as well as solutions of non-oxidizing acids:

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

Chemical properties of silicon

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

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

Interaction of silicon with simple substances

non-metals

Under normal conditions, silicon, due to its inertness, reacts only with fluorine:

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

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

With bromine - 620-700 o C:

With iodine - 750-810 o C:

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

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

Silicon does not react with hydrogen.

metals

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

Interaction of silicon with complex substances

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

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

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

Under normal conditions, the allotropic modifications of carbon - graphite and diamond - are rather inert. But with an increase in t, they actively enter into chemical reactions with simple and complex substances.

Chemical properties of carbon

Since the electronegativity of carbon is low, simple substances are good reducing agents. It is easier to oxidize fine-crystalline carbon, more difficult - graphite, even more difficult - diamond.

Allotropic modifications of carbon are oxidized by oxygen (burn) at certain ignition temperatures: graphite ignites at 600 °C, diamond at 850-1000 °C. If oxygen is in excess, carbon monoxide (IV) is formed, if there is a deficiency, carbon monoxide (II):

C + O2 = CO2

2C + O2 = 2CO

Carbon reduces metal oxides. In this case, metals are obtained in a free form. For example, when lead oxide is calcined with coke, lead is smelted:

PbO + C = Pb + CO

reducing agent: C0 - 2e => C+2

oxidizer: Pb+2 + 2e => Pb0

Carbon also exhibits oxidizing properties with respect to metals. At the same time, it forms various kinds of carbides. So, aluminum undergoes reactions at high temperatures:

3C + 4Al = Al4C3

C0 + 4e => C-4 3

Al0 – 3e => Al+3 4

Chemical properties of carbon compounds

1) Since the strength of carbon monoxide is high, it enters into chemical reactions at high temperatures. With significant heating, high reducing properties of carbon monoxide are manifested. So, it reacts with metal oxides:

CuO + CO => Cu + CO2

At elevated temperature(700 °C) it ignites in oxygen and burns with a blue flame. From this flame, you can find out that carbon dioxide is formed as a result of the reaction:

CO + O2 => CO2

2) Double bonds in the carbon dioxide molecule are strong enough. Their rupture requires significant energy (525.6 kJ/mol). Therefore, carbon dioxide is rather inert. The reactions it enters into often occur at high temperatures.

Carbon dioxide exhibits acidic properties when it reacts with water. This forms a solution of carbonic acid. The reaction is reversible.

Carbon dioxide, as an acidic oxide, reacts with alkalis and basic oxides. When carbon dioxide is passed through an alkali solution, either an average or an acid salt can be formed.

3) Carbonic acid has all the properties of acids and interacts with alkalis and basic oxides.

Chemical properties of silicon

Silicon more active than carbon, and is oxidized by oxygen already at 400 °C. Other non-metals can oxidize silicon. These reactions usually take place at a higher temperature than with oxygen. Under such conditions, silicon interacts with carbon, in particular with graphite. In this case, carborundum SiC is formed - a very hard substance, inferior in hardness only to diamond.

Silicon can also be an oxidizing agent. This is manifested in reactions with active metals. For example:

Si + 2Mg = Mg2Si

The higher activity of silicon compared to carbon is manifested in the fact that, unlike carbon, it reacts with alkalis:

Si + NaOH + H2O => Na2SiO3 + H2

Chemical properties of silicon compounds

1) Strong bonds between atoms in the crystal lattice of silicon dioxide explain the low chemical activity. The reactions that this oxide enters into take place at high temperatures.

Silicon oxide is an acidic oxide. As you know, it does not react with water. Its acidic nature is manifested in the reaction with alkalis and basic oxides:

SiO2 + 2NaOH = Na2SiO3 + H2O

Reactions with basic oxides take place at high temperatures.

Silicon oxide exhibits weak oxidizing properties. It is reduced by some active metals.