Silicon compounds with hydrogen. Hydrogen compound - silicon

Silicon compounds

Silicon gives two types of oxides - silicon (IV) oxide and silicon (II) oxide. Silicon oxide (IV) is the most durable, does not decompose at high temperatures, and above 223°C goes into a vapor state. Hydrogen does not restore it either. Moreover, silicon itself is sometimes used as a reducing agent, for example, in the production of molybdenum:

2MoO 3 +3Si 3SiO 2 +2Mo

Since an enormous amount of heat is released during the oxidation of silicon, silicon (IV) oxide and molybdenum are obtained in a molten state.

There are no molecules in silicon (IV) oxide, since due to the chemical bond Si--O--Si, a kind of spatial framework is formed. Thus, a piece of quartz represents, as it were, one giant molecule. Quartz is an inorganic polymer and its formula is (SiO 2) n .

Pure silicon oxide (IV) is found in nature in the form of rock crystal, the crystals of which sometimes reach large sizes. The largest crystal found in Kazakhstan weighed 70 tons.

IN large quantities in industry, silica gel is prepared - partially hydrated silicon oxide (IV). To get it into solution liquid glass hydrochloric acid works:

Na 2 SiO 3 + 2HCl 2NaCl nH 2 SiO 3

Precipitated metasilicic acid is washed from sodium chloride with water and dried at 170-180°C. This produces amorphous silicon oxide containing a small amount of chemically bound water. Therefore, silica gel is given the conditional formula SiO 2 nH 2 O. Dried silica gel can adsorb a significant amount of water vapor, it is used for drying gases.

Silicon oxide (IV) is widely used in industry and in scientific research. As quartz sand it is used in the glass industry; SiO 2 is the main component of silicate glasses. Quartz sand is the most important construction material. Quartz sand is used in large quantities for the manufacture of one of the best refractories - dinas. It is obtained by sintering quartz sand, to which 2-2.5% lime is added. Dinas softens only at 1700°C, it is used for laying open-hearth furnaces and various ovens for the production of non-ferrous metals.

Fused quartz (SiO 2) n gives quartz glass, which has an interesting property: it has the lowest thermal expansion coefficient, i.e., when heated, quartz glass practically does not expand. Therefore, with sudden heating or cooling, quartz glassware does not crack. Quartz glassware is used in chemical laboratories. Her widespread hindered by great fragility and significant difficulties in manufacturing (very high melting point of quartz).

Silicon also gives oxide SiO, which is obtained by the interaction of silicon (IV) oxide with silicon:

Silicon oxide SiO is a gray powder; it does not find any application. It is interesting to note that when heated, this oxide decomposes rather quickly:

This indicates that the divalent state for silicon is not as typical as the tetravalent one.

Silicon compounds with hydrogen are called silanes or silanes. Their composition corresponds to the general formula Si n H 2n+2 similar to the general formula of hydrocarbons of the limiting series. The simplest representative of this class - silane SiH 4 - was first obtained by the German chemist D. Wöhler in 1857. Silane and its homologues (H 3 Si - SiH 3 - disilane, H 3 Si - SiH 2 - SiH 3 - trisilane etc.) have a structure similar to methane, ethane and propane. Unsaturated silanes corresponding in structure to hydrocarbons of the ethylene and acetylene series have not yet been isolated in the form of individual compounds. Silanes are obtained most simply by the method developed in 1883 by Russian scientists N. N. Beketov and A. D. Chirikov. The method consists in the decomposition of metal silicides with mineral acids:

Mg 2 Si + 4HCl > 2MgCl 2 + SiH 4

Silane and disilane are gases with bad smell. Trisilane Si 3 H 8, tetrasilane Si 4 H 10, pentasilane Si 5 H 12 and subsequent homologues - at room temperature volatile liquids with an unpleasant odor. Silicon hydrogens are very toxic. Unlike hydrocarbons, silanes are unstable compounds. They ignite spontaneously, sometimes explode in air, and are easily decomposed by alkalis and water in the presence of traces of acids and alkalis:

SiH 4 + 2H 2 O > SiO 2 + 4H 2

Silicon hydrogens are thermally unstable and decompose into silicon and hydrogen already at 400 °C:

SiH 4 > Si + 2H 2

This results in extremely pure silicon.

The instability of silicon hydrogens is confirmed by the fact that homologues above octasilane Si 8 H 18 have not yet been isolated in the free state. Silanes are strong reducing agents and are vigorously oxidized by oxygen:

SiH 4 + 2O 2 > SiO 2 + 2H 2 O

When silanes interact with halogens, all hydrogen atoms are instantly (with an explosion) replaced by halogen atoms. Chlorine and bromine derivatives of silanes are also formed during their catalytic treatment with hydrogen chloride or hydrogen bromide:

SiH 4 + HCl > SiH 3 Cl + H 2

SiH 3 Cl + HCl > SiH 2 Cl 2 + H 2

SiH 2 Cl + HCl > SiHCl 2 + H 2

SiHCl 3 + HCl > SiCl 4 +H 2

For the homologous series of saturated hydrocarbons, a similar reaction with HCl or HBr is unknown. Silicon compounds with hydrogen are of great scientific and practical interest for the chemistry of organosilicon compounds. Silicon halides are obtained by directly combining silicon with halogens, or by halogenation of oxides in the presence of carbon:

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

In the laboratory, silicon chlorination can be carried out in glass tubes with constrictions. The reaction proceeds with slight heating. Liquid condensate is collected in the elbow of the tube. For cleaning, the condensate is distilled by heating into the next elbow of the tube.

Bromination and iodination can also be carried out in glass tubes with constrictions, but a carrier gas such as argon, nitrogen, carbon monoxide (IV) is used to transfer bromine or iodine. The resulting halides are hygroscopic and easily hydrolyzed by air moisture, so they are sealed in one of the tube elbows.

They call nitrides chemical compounds nitrogen with various elements. Group IV is characterized by nitrides with both a covalent bond and those formed by the introduction of nitrogen atoms into the crystal lattice of the element. Nitrides of elements of the main subgroup are very refractory substances with high hardness and thermal conductivity. Nitrides are quite heat-resistant when heated and have relative chemical stability.

Silicon forms a nitride with a crystal lattice in which nitrogen atoms are bonded to silicon atoms covalent bonds. Such a nitride has a formula corresponding to the usual valence of the element, and can be considered as a derivative of ammonia, in which hydrogen atoms are replaced by silicon - Si 3 N 4.

A common way to obtain nitrides is the direct interaction of substances with nitrogen or ammonia:

3Si + 2N 2 > Si 3 N 4

3Si + 4NH 3 > Si 3 N 4 + 6H 2

The reaction is carried out at 1000-1200 ° C in electric ovens. The nitrogen and ammonia used for the reaction should not contain water and oxygen vapors in order to avoid contamination of the nitride with the oxides of the corresponding elements.

The high heat resistance and heat resistance of silicon nitride is used to create alloys with high heat resistance for high temperature technology, energy and other industries. Its exceptional resistance to chemicals, even such as hydrofluoric acid, alkali and metal melts, combined with fire resistance, is used in the chemical industry. It is used to make the lining of bathtubs for the production of metals by electrolysis of molten salts, lined fittings, nozzles for spraying molten metals, crucibles for melting ultrapure metals, etc.

Metasilicic acid H 2 SiO 3 and orthosilicic acid H 4 SiO 4 are the most common silicon acids. Metasilicic acid is obtained by reacting silicates with hydrochloric acid or ammonium chloride:

Na 2 SiO 3 + 2HCl > H 2 SiO 3 + 2NaCl

Na 2 SiO 3 + 2NH 4 Cl > H 2 SiO 3 + 2NaCl + 2NH 3

Free metasilicic acid is known in several forms with variable water content. This acid is weaker than carbonic, it is insoluble in water, but easily forms colloidal solutions - sols. Metasilicic acid is thermally unstable and decomposes when heated:

H 2 SiO 3 > H 2 O + SiO 2

The splitting of water from several molecules of metasilicic acid occurs in aqueous solution and at room temperature with the formation of a transparent gelatinous mass - silicic acid gel. Dried silicic acid gel is called silica gel.

Silica gel has a very large surface - up to 400 m 2 of surface per 1 g of silica gel - and high adsorption capacity. It is produced on an industrial scale and is widely used for the extraction of volatile and odorous substances from vapors and gases, the purification of mineral oils and petroleum, and the decolorization of liquid organic products. Silica gel voraciously absorbs water, and this property is used in the drying of gases and liquids. High-quality grades of silica gel that do not contain impurities are used in medical practice. Silica gel free from impurities is obtained by hydrolysis of silane SiH 4 , silicon tetrachloride SiCl 4 and organosilicon compounds - tetraethoxysilane Si(OC 2 H 5) 4 and others. Silica gel is also used as a catalyst carrier. By introducing silicic acid sols into cellulosic materials, strength, water resistance and fire resistance of the product are achieved.

Orthosilicic acid is obtained by hydrolysis of silicon tetrachloride:

SiCl 4 + 4H 2 O > Si (OH) 4 + 4HCl

In structure, orthosilicic acid is close to quartz: the silicon atom is surrounded by a tetrahedron of four oxygen atoms with hydrogen attached to oxygen. Salts of orthosilicic acid are also called silicates. Alkali metal salts of silicic acids are soluble in water, silicates of other elements are insoluble. The molecular weight of freshly isolated silicic acid (formula Si (OH) 4) is about 100 cu. e. In a few days, the molecular weight of the acid will reach 1000 cu. e. and more. This is due to the extreme ease of self-condensation of the acid, accompanied by the release of water.

Silicon forms acidic, amphoteric and basic hydroxides. All of them are insoluble in water. Silicon oxide (IV) and the oxides of its analogues practically do not react with water, therefore it is impossible to obtain acids by this method.

Silicates are refractory and passive substances. Most of them are insoluble in water. They exist in gaseous, liquid and solid form, and also form highly dispersed, or colloidal, systems with a particle size of silicates from 10 - 6 to 10 - 9 m. Colloidal systems are similar to solutions, but unlike them, they have an interface between silicate particles dispersion medium, i.e., the medium in which the substance is dissolved. Examples of colloidal systems are chalcedony and opal. The range of composition of silicates is extremely wide (aluminosilicates, hydrosilicates, etc.)

There are no systematic names for silicate minerals, so the names reflect them. appearance and properties. Plagioclase in translation from the ancient Greek "obliquely splitting", pyroxene - "refractory". The names are also given by the names of the people who discovered these minerals.

At different times, ideas about the structure of silicates were different. The first scientific theory was polysilicon. It played an important role in the middle of the 19th century. - 1920s According to this theory, silicates are salts of silicic acids. All silicic acids can be given by the formula n SiO 2 m H 2 O. Examples are metasilicic acid H 2 SiO 3 (n=1, m=1), orthosilicic acid H 4 SiO 4 (n=1, m=2), disilicic acid H 2 Si 2 O 5 (n=2 m=1), pyrosilicic acid H 6 Si 2 O 7 (n=2, m=2). The respective names of silicates are still used today, although the polysilicon theory is no longer popular.

Due to the colloidal nature of silicates, they cannot be obtained in pure form. Therefore, the question arises about the salt-like nature of silicates. But that's not all. Let us consider two silicates similar in structure: jadeite Na Al and leucite K Al. According to the polysilicon theory, they are salts of metasilicic acid, and, therefore, should have similar properties. But by their very nature, they are two completely different substances. This theory does not explain the relationship between the composition and properties of substances, although this is its main task.

More D.I. Mendeleev noted the shortcomings of this theory. He suggested isomorphism in silicate crystals, i.e. the ability of atoms to replace each other in crystal structures. Moreover, it can be atoms not only of the same type, but also of different ones. Thus, it manifests itself in aluminosilicate crystals, although aluminum and silicon are atoms of different types. DI. Mendeleev called such crystals "indefinite compounds", similar to alloys, but these alloys are not simple substances, and close oxides. Polymeric silicon salts exist not because of the existence of polymeric acids, but because of the polymerization of silicon compounds. Research D.I. Mendeleev played an important role in shaping views on this problem.

In 1925-1931. W.L. Bragg studied aluminosilicate crystals, including with the help of X-rays. He proposed a structural classification of silicates. In his opinion, silicates were polymer structures consisting of tetrahedra - silicon oxides, atoms that replaced it. They are connected with the help of oxygen atoms, which have become "common" for two tetrahedra. Such oxygen atoms are called bridging, and those that do not participate in the formation of such bonds are called non-bridging. Thus, bonds Si - O - Si or Si - O - Al are created. The variety of silicates is explained different ways compounds of these tetrahedra.

Bragg proposed to classify silicates according to the types of silicon-oxygen radicals:

1. Orthosilicates 4 - In this radical, all oxygen atoms are non-bridging.

2. Island 6 -, 6 -, 8 -. Two oxygens in each tetrahedron serve to form the ring, while the other two are non-bridged.

3. Isolated 2 - and doubled 6 - radicals form infinite chains

4. Layered structures with radicals 2 -

5. Frame structures

Consider the structure of sodium orthosilicate. Its formula is 2Na 2 O SiO 2 . This orthosilicate belongs to the first group. In it, tetrahedra 4 - are interconnected by sodium ions.

Representatives of silicates of the third group are pyroxenes with the formula LiAl. In them, one silicon atom out of three was replaced by an aluminum atom. Pyroxenes form endless chains different structure(Fig. 3). The structure of the chain determines the properties of pyroxene.

Si is one of the most abundant elements in the earth's crust. The most common after O2. In nature, Si occurs only in the form of a compound: SiO2. Essential element plant and animal kingdom.

Receiving: Technical: SiO2 + 2C ==== Si + 2CO. Pure: SiCl4 + 2H2 = Si + 4HCl. SiH4 =(t)Si + 2H2. Used in metallurgy and semiconductor technology. To remove O2 from molten Me and serves integral part alloys. For the manufacture of photocells, amplifiers, rectifiers.

Physical properties aza. Silicon - gray-steel color. brittle, only when heated above 800 ° C, it becomes a plastic substance. Transparent to infrared radiation, semiconductor. The crystal lattice is cubic like diamond, but due to greater length bonds between Si-Si atoms compared to the length C-C connections silicon is much less hard than diamond. Allotropic Si-powder of gray color.

Chemical properties: At n. y. Si is inactive and reacts only with gaseous fluorine: Si + 2F2 = SiF4

Amorphous Si is more reactive, molten Si is very active.

When heated to a temperature of 400-500 °C, silicon reacts with O2, Cl2, Br2, S: Si + O2 = SiO2 . Si + 2 Cl2 = SiCl4

With nitrogen, silicon at a temperature of about 1000 ° C forms the nitride Si3N4,

with boron - thermally and chemically resistant borides SiB3, SiB6 and SiB12.,

with carbon - silicon carbide SiC (carborundum).

When silicon is heated with metals, silicides can form.

Si does not react with acids, only with a mixture of HNO3 and HF oxidizes it to hexafluorosilicic acid: 3Si + 8HNO3 + 18HF = 3H2 + 4NO + 8H2O

It dissolves vigorously in alkali solutions in the cold (non-metallic properties): Si + 2NaOH + H2O = Na2SiO3 + 2 H2

At high temperatures, it slowly interacts with water: Si + 3H2O = H2SiO3 + 2H2

Hydrogen compoundsSi.Silicon does not directly react with hydrogen, silicon compounds with hydrogen - silanes with the general formula SinH2n+2 is obtained indirectly. Monosilane SiH4 Ca2Si + 4HCl → 2CaCl2 + SiH4 admixture of other silanes, disilane Si2H6 and trisilane Si3H8.

Polysilanes are toxic, have bad smell, less thermally stable compared to CnH2n+2 Reducing agents SiH4 + O2 = SiO2 + 2 H2O

Hydrolyze in water SiH4 + 2H2O = SiO2 + 4H2

Silicon compounds with metals - SILICIDES

I.Ion-covalent: silicides of alkali, alkaline earth metals and magnesium Ca2Si, Mg2Si

Easily destroyed by water: Na2Si + 3H2O = Na2SiO3 + 3 H2

Decomposed by acids: Ca2Si + 2H2SO4 = 2CaSO4 + SiH4

II. Metal-like: transition metal silicides. Chemically stable and do not decompose under the action of acids, resistant to oxygen even at high temperatures. They have high Tm (up to 2000 °C). Many are metallically conductive. The most common are MeSi, Me3Si2, Me2Si3, Me5Si3 and MeSi2.

Silicides of d-elements are used to obtain heat-resistant and acid-resistant alloys. Lanthanide silicides are used in nuclear power engineering as neutron absorbers.

SiC - carborundum Solid, refractory substance. The crystal lattice is similar to that of a diamond. It is a semiconductor. Used to make artificial gems

Silica easily reacts with F2 and HF: SiO2 + 4HF = SiF4 + 2 H2O. SiO2 + F2 = SiF4 + O2 Does not dissolve in water.

Dissolves in alkali solutions when heated: SiO2 + 2NaOH = Na2SiO3 + H2O

Sintered with salts: SiO2 + Na2CO3 = Na2SiO3 + CO2. SiO2 + PbO = PbSiO3

Silicic acids Very weak, slightly soluble acids in water. Silicic acids form colloidal solutions in water.

Salts of silicic acids are called silicates. SiO2 corresponds to silicic acid, which can be obtained by the action of a strong acid on silicateNa2SiO3 + HCl = H2SiO3 + NaCl

H2SiO3 - metasilicic, or silicic acid. H4SiO4 - orthosilicic acid exist only in solution and irreversibly turn into SiO2 if water is evaporated.

silicates-salts of silicic acids, each Si atom surrounds a tetrahedrally located O2 atom around it. Close relationship between Si and O2.

Hydrogen silicon compounds - silanes (SiH4, Si2H6, etc.) spontaneously ignite in air.
Hydrogen silicon compounds - silanes (SiH4, Si2He, etc.) spontaneously ignite in air.
Therefore, all hydrogen compounds of silicon tend to be converted into oxygen compounds. Consequently, in the collision of silicon hydrogen molecules with molecules of oxygen and other substances, active complexes are easily formed, which ensure the rapid course of reactions. Apparently, for this reason, silicon hydrogens, unlike hydrocarbons, ignite spontaneously in air, and SiF / i, unlike Cr, rapidly hydrolyze.
What are known hydrogen compounds of silicon. How they are obtained, what properties they have.
Therefore, all hydrogen compounds of silicon tend to be converted into oxygen compounds.
Write the formulas for the hydrogen compounds of silicon, phosphorus, sulfur and chlorine.
The reducing properties of silicon hydrogen compounds are preserved even when they contain at least one hydrogen atom directly bonded to silicon.
What explains the instability of silicon hydrogen compounds.
Some silicides, such as magnesium and manganese silicides, when decomposed by acids, along with elemental hydrogen, also form silicon hydrogen compounds - silanes.
But just as the hydrogen compound of sulfur H2S is incomparably less stable than the hydrogen compound of oxygen lizO, and the hydrogen compounds of phosphorus PH3 and P3H4 are incomparably less stable than the hydrogen compounds of nitrogen NH3 and N2H4, so are the hydrogen compounds of silicon, in accordance with periodic law, are incomparably less stable than hydrogen compounds of carbon.
But just as the hydrogen compound of sulfur SH2 is incomparably less stable than the hydrogen compound of oxygen H2O, and the hydrogen compounds of phosphorus PH3 and P2H4 - - than the hydrogen compounds of nitrogen NH3 and N2H4, so the hydrogen compounds of silicon, in accordance with the periodic law, are incomparably less stable than hydrogen compounds of carbon.
Hydrogen does not chemically interact with silicon. Hydrogen compounds of silicon - silanes, or silanes, -: can be obtained by the action of hydrochloric acid on magnesium silicide. By its structure and physical properties silanes are similar to hydrocarbons of the methane homologous series. However, in terms of chemical properties, silanes differ sharply from fatty hydrocarbons. In contrast to the latter, silanes are unstable, therefore, reactive. They are easily oxidized in air and the better, the greater their molecular weight. All silanes have a specific odor and are highly toxic.
A mixture of hydrogen compounds of silicon - silanes, or silanes - is formed by the action of dilute hydrochloric acid on magnesium silicide.
A mixture of hydrogen compounds of silicon - silanes or silanes - are formed by the action of dilute hydrochloric acid on magnesium silicide.

A mixture of hydrogen compounds of silicon - silicon hydrogens or silanes - are formed by the action of dilute hydrochloric acid on magnesium silicide.
A mixture of hydrogen compounds of silicon - silicon hydrogens, or silanes - is formed by the action of dilute hydrochloric acid on magnesium silicide.
Therefore, all hydrogen compounds of silicon tend to be converted into oxygen compounds. Consequently, in the collision of silicon hydrogen molecules with molecules of oxygen and other substances, active complexes are easily formed, which ensure the rapid course of reactions. Apparently, for this reason, silicon hydrogens, unlike hydrocarbons, spontaneously ignite in air, and Sir4, unlike SG4, quickly hydrolyzes.
The main mineral and rocks containing silicon. Hydrogen compounds of silicon (si-lanes), their preparation and properties.
Silicon ranks in the fourth group periodic system directly below the carbon, and therefore similar in form to carbon. However, the properties of the metalloid in silicon should obviously be less pronounced than in carbon, which is confirmed in reality. Silicon is already more prone to donate its four valence electrons than to join. Therefore, silicon oxygen compounds are typically stable. Hydrogen silicon compounds are very unstable and decompose under normal conditions.