Physical properties of sio2. Oxygen compounds. Silicon (II) SiO
Silicon oxide (II) SiO. In nature, it does not occur, but can be obtained by the reaction:
SiO 2 + Si → 2 SiO.
Under normal pressure, the sublimation of silicon monoxide begins at about 1200 ° C (when the starting materials themselves practically do not evaporate yet). In pairs, SiO is an individual compound. The dissociation energy of the elements is 789 kJ / mol. Conversion to a solid state can only be accomplished by rapid cooling (“quenching”) of the gas phase. Otherwise, dismutation by the equation has time to pass:
2 SiO = SiO 2 + Si.
Silicon monoxide is slowly oxidized by atmospheric oxygen and readily dissolves in alkalis to form silicic acid salts and release of hydrogen. It is easily electrified by friction, acquiring a strong negative charge.
Silicon oxide (IV) SiO 2.Silicon oxide (IV) is also called silica. It is a solid refractory substance. (melting point 1700 ° C)widespread in nature in two forms: 1) crystalline silica - in the form of a mineral of quartz and its varieties (rock crystal, chalcedony, agate, jasper, flint); quartz forms the basis of quartz sands widely used in construction and in the silicate industry; 2) amorphous silica - in the form of a mineral opal composition SiO 2 pH 2 O; the earthy forms of amorphous silica are diatomite, tripoli (infusorial earth); An example of artificial amorphous anhydrous silica is silica gel, which is obtained from sodium metasilicate:
Silica gel has a developed surface, and therefore well absorbs moisture.
At 1710 ° quartz melts. With rapid cooling of the molten mass, quartz glass is formed. It has a very low coefficient of expansion, so that hot quartz glass does not crack when the water is rapidly cooled. Laboratory glassware and instruments for scientific research are made from quartz glass.
The structure of SiO 2 in a planar image can be represented as follows:
Each silicon atom is enclosed in a tetrahedron of 4 oxygen atoms. In this case, the silicon atom is located in the center, and oxygen atoms are located at the vertices of the tetrahedron. The entire piece of silica can be considered as a crystal whose formula is (SiO 2) n. Such a structure of silicon oxide (IV) determines its high hardness and refractoriness.
Chemical properties of silicon oxide (IV) SiO 2 refers to acid oxides. When fusing it with solid alkalis, basic oxides and carbonates, silicic acid salts are formed:
Only hydrofluoric acid interacts with silicon oxide (IV) (glass etching):
SiO 2 + HF → SiF 4 + H 2 O
Silicon (IV) oxide does not dissolve in water and does not chemically interact with it. Therefore, silicic acid is obtained indirectly, for example, by hydrolysis:
SiS 2 + H 2 O ↔ H 2 S + H 4 SiO 4 orthosilicon acid.
H 4 SiO 4 is soluble, when heated or standing, a polymerization process is underway:
2 H 4 SiO 4 → H 2 O + H 6 Si 2 O 7 diorthokremnievy acid.
2 H 6 Si 2 O 7 → H 2 O + H 10 Si 4 O 13 tetraorotremilicic acid.
She closes the ring:
H 10 Si 4 O 13 → H 2 O + (H 2 SiO 3) 4 tetramethacilicic acid.
In this case, silicic acid (depending on the concentration of the initial solutions of salt and acid) can be obtained both in the form of a gelatinous mass containing water, and in the form of a colloidal solution (sol). The composition of the obtained silicic acid depends on the starting materials and conditions of preparation. All silicic acids are very weak (weaker than coal).
If carbonic acid in a solution releases silicic acid from its salts, then the reverse reaction occurs during calcination. The first is due to the lower strength (degree of dissociation) of silicic acid, the second - its lower volatility when heated.
When heated polysilicic acids and their gradual dehydration can be obtained fine SiO 2, which is called silica gel . It absorbs water well, I place it in devices to prevent the oxidation of expensive elements.
Germany subgroup
Ge (+4) Sn (+2, +4) Pb(+2) - resistant oxidation states
Germanium was predicted by DI Mendeleev in 1871, and discovered in 1886. Tin and lead belong to the elements that were most known to mankind for a long time: the Egyptians were able to smelt them from ores more than 3000 years BC. e. In India, lead became known about 2500 years, and tin 1500 years BC. e. Smelting tin produced in ancient China.
Receipt.Natural compounds of germanium are converted to GeO 2 and reduced with hydrogen:
GeO 2 + H 2 t → Ge + H 2 O at temperatures of about 1000 ° C.
Tin is obtained from natural mineral cassiterite(SnO 2):
SnO 2 + C → Sn + CO.
The simplest scheme for industrial lead reduction is based on two successive reactions:
PbS + O 2 → SO 2 + PbO Galena(PbS) is burned and then reduced with coal:
PbO + С → СO + Pb.
Application.All three elements are very important for modern technology. Some compounds of tin and lead are also of considerable use. Lead derivatives are highly toxic.
Germanium is a typical semiconductor (n-type with a bandgap width of 0.75 eV) and finds various uses in electrical engineering. It is most widely used for the manufacture of AC rectifiers.. This application is based on unipolar conductivity arising from the contact between pure germanium and germanium alloy with indium. The current (electron flow) passes in such an installation practically only from germanium to the alloy, but not vice versa. Germanium rectifiers are characterized by extremely high (about 98%) efficiency and a very large (with proper operation) service life. The main disadvantage of such rectifiers is their sensitivity to heating - above 70 ° C, their efficiency quickly drops.
Important use area germany is an infrared optics, since the rays with a wavelength greater than 2 microns, it practically does not delay. On the contrary, in the light and close to it ranges (0.2? 2 microns), germanium intensively absorbs energy. If a shiny metal surface (which stores heat well, but does not heat up well) is covered with germanium film, then the surface heats up much more than without a film. It was reported that in a barrel prepared in this way under the action of sunlight, boiling water can be obtained.
Tin is mainly used for iron tinning in order to protect it from rusting. (tinplate for the canning industry). The thickness of such tin coatings is very small - on the order of microns. In the form of thin sheets (so-called. Stannioles) tin is consumed for the manufacture of capacitors in the electrical industry . Lead is used for the manufacture of battery plates, plates of electrical cables, bullets and shot, to protect against X-rays and g-rays, as well as in the chemical industry (pipelines, etc.). Very large quantities of tin and lead are spent on the manufacture of a number of technically important alloys.
The most important of them are various bronzes (Cu and Sn alloys), alloys for bearings (babbits, usually made on the basis of Pb or Sn and also containing Sb and Cu), typographical alloys (5-30% Sn, 10-20% Sb, the rest is Pb) and the usual “soft” solder (30-70% Sn, 70-30% Pb). It can often be replaced by a cheaper alloy of 90% Pb, 6% Sn, 4% Sb. Of great importance are alloys for bearings with an approximate composition of 98% Pb, 1% Ca, 1% Na.
Silica (silica, silica) is a substance consisting of colorless crystals with high strength, hardness and refractoriness. Silicon dioxide is resistant to acids and does not interact with water. With an increase in the reaction temperature, the substance interacts with alkalis, dissolves in hydrofluoric acid, is an excellent dielectric.
In nature, silicon dioxide is widely distributed: crystalline silicon oxide is represented by such minerals as jasper, agate (crystalline silicon dioxide compounds), rock crystal (large crystals of matter), quartz (free silicon dioxide), chalcedony, amethyst, morion, topaz (colored crystals silica).
Under normal conditions (at natural ambient temperature and pressure), there are three crystalline modifications of silicon dioxide — tridymite, quartz, and cristobalite. When the temperature rises, silicon dioxide first turns into coesite, and then into stishovite (a mineral found in 1962 in a meteorite crater). According to studies, it is stishovit, a derivative of silicon dioxide, that lines a large part of the Earth’s mantle.
The chemical formula of the substance - SiO 2
Preparation of silica
Silicon dioxide is produced industrially at quartz plants producing pure quartz concentrate, which is then used in the chemical and electronics industry, in the manufacture of optics, rubber and paint and varnish fillers, jewelry making, etc. Natural silicon dioxide, otherwise called silica, is widely used in construction (concrete, sand, sound and heat insulation materials).
Synthesis of silicon dioxide by a synthetic method is carried out by the action of acids on sodium silicate, in some cases on other soluble silicates or by the method of coagulation of colloidal silica under the influence of ions. In addition, silicon dioxide is produced by the oxidation of silicon with oxygen at a temperature of about 500 degrees Celsius.
Silicon dioxide application
Silicon-containing materials are widely used both in the field of high technologies and in everyday life. Silicon dioxide is used in the manufacture of glass, ceramics, concrete products, abrasive materials, as well as in radio engineering, ultrasonic installations, lighters, etc. In combination with a number of ingredients, silica is used in the manufacture of fiber optic cables.
Non-porous amorphous silicon dioxide is also used in the food industry as an additive, registered under the number E551, preventing clumping and caking of the main product. Dioxide 
silicon food is used in the pharmaceutical industry as a drug enterosorbent, in the manufacture of toothpastes. The substance is found in chips, crackers, corn sticks, instant coffee, etc.
Silica Harm
Officially confirmed that the substance of silicon dioxide passes through the gastrointestinal tract unchanged, after which it is completely removed from the body. According to a 15-year study by French experts, drinking high-alumina drinking water reduces the risk of developing Alzheimer's disease by 10%.
Thus, information about the dangers of silicon dioxide, which is a chemically inert substance, is false: the E551 dietary supplement, ingested orally, is completely safe for health.
Silicon oxide SiO 2 is a solid, very refractory substance (melting point more than 1700 ° C), widely distributed in nature, where it is found mainly in the form of the quartz mineral, as well as cristobalite and tridymite.
At usual temperatures, quartz is a stable modification, with increasing temperature polymorphic transformations are observed:
Silica of all modifications in the form of a monomer does not exist; it is always polymeric and “built” of tetrahedra forming a very strong atomic lattice
Each silicon atom in (SiO 2) n crystals is tetrahedrally surrounded by four oxygen atoms, each of which is bridged. Through a common oxygen atom, tetrahedra at different angles bind to each other, forming a continuous three-dimensional lattice; the mutual arrangement of tetrahedra in space determines one or another modification of silica.
In different modifications of silica bond strength varies. This affects the magnitude of the Si-O-Si angles and the Si-O distances, for example, the Si-O-Si bond angle in various modifications of silica varies from 120 to 180 °. Quartz-tridymite-cristobalite transitions are accompanied by breaking and transformation of bonds, which can occur only at high temperatures.
Quartz. Often found in nature in the form of extremely well-formed crystals, sometimes of considerable size. The crystals are formed from tetrahedra arranged in a spiral shape around the central axis, in the form of a spiral. In the same crystal, the direction of the helix may be opposite. Such crystals are optical isomers. They rotate the plane of polarization of light, and can be both right-and left-handed. Those and other crystals differ as a subject from their mirror image.
Quartz is used in various fields of science and technology, and its crystals are often grown artificially. Some types of quartz have special names. Transparent colorless crystals are called rock crystal. There are also colored varieties of quartz: rose quartz, violet (amethyst), dark brown (smoky topaz), green (chrysoprase), etc. The crystalline modification of quartz with admixtures of other substances is called chalcedony. The varieties of chalcedony are agate, jasper, and others. Rock crystal and colored varieties of quartz are used as precious and semiprecious stones.
Tridimite occurs in volcanic rocks, but in very small quantities. Known tridymite and meteorite origin.
Cristobalite in nature is sometimes found in the form of small crystals embedded in lava, like tridimite. Tridimite and cristobalite have a more "loose" structure than quartz. Thus, the density of cristobalite, tridymite, and quartz is 2.32; 2.26 and 2.65 g / cm 3, respectively.
Silica melt with slow cooling easily forms amorphous quartz glass. Silica in the form of glass is also found in nature. The density of amorphous glass is 2.20 g / cm 3 - lower than that of all crystalline modifications. Quartz glass has a slight temperature coefficient of expansion, therefore, it is used to prepare laboratory glassware resistant to sudden changes in temperature.
All modifications of silica in water are practically insoluble (at a temperature of 25 ° C, the solubility of quartz is 7, cristobalite - 12, tridymite - 16, quartz glass - 83 mg / l). Therefore, under normal conditions, only alkaline solutions and hydrofluoric acid act on them:
SiO 2 + 2KO = K 2 SiO 3 + H 2 O, (1)
SiO 2 + 4HF = SiF 4 + 2H 2 O. (2)
The latter reaction is used in the "etching" of glass.
The added silica reacts with basic oxides, alkalis (reaction (1)) and carbonates to form silicates:
SiO 2 + CaO = СaSiO 3, (3)
SiO 2 + Na 2 CO 3 = Na 2 SiO 3 + CO 2. (four)
Reactions (3) and (4) underlie the industrial production of various glasses, as well as cement. Thus, the composition of ordinary glass (for example, window, for the manufacture of dishes) is expressed by the formula Na 2 O. CaO. 6SiO 2. Such glass is produced by fusing a mixture of soda, sand and limestone. The process is carried out at a temperature of ~ 1400 ° C until the complete removal of gases:
Na 2 CO 3 + CaCO 3 + 6SiO 2 = Na 2 O. CaO. 6SiO 2 + 2CO 2.
For special grades of glass - refractory, "unbreakable" - when cooking, add oxides of barium, lead, boron. To obtain colored glasses, various additives are also introduced, for example, the addition of cobalt oxide Co 2 O 3 gives a blue color, chromium oxide Cr 2 O 3 - green, manganese dioxide MnO 2 - pink.
SiO 2 oxide is an anhydride of a number of silicic acids, whose composition can be expressed by the general formula xSiO 2 ∙ yH 2 O, where x and y are integer numbers: 1) x = 1, y = 1: SiO 2. H 2 Oh, i.e. H 2 SiO 3 - meta-silicon acid; 1) x = 1, y = 2: SiO 2. 2H 2 O, i.e. orthosilicic acid; 1) x = 2, y = 1: 2SiO 2. H 2 Oh, i.e. H 2 Si 2 O 5 - bimeta silicic acid.
Acids whose molecules contain more than one SiO 2 molecule belong to polysilicon.
The simplest of silicic acids is H 2 SiO 3, which is often called simply silicon, and its salts are silicates. Of silicates, only sodium and potassium silicates are soluble in water, the remaining silicates are refractory, water-insoluble substances.
Solutions of silicates grow turbid when standing in air, since the CO 2 contained in it displaces silicic acid from its salts (H 2 SiO 3 is weaker than carbonic acid; the dissociation constant of H 2 SiO 3 in the first stage is equal to K 1 = 2.2. 10 -10 ).
H 2 SiO 3 is practically insoluble in water - this property is used as a qualitative reaction for the detection of silicate ions:
Na 2 SiO 3 + CO 2 + H 2 O = Na 2 CO 3 + H 2 SiO 3 ↓.
Silicates are obtained by fusing SiO 2 with alkalis or carbonates.
Concentrated solutions of sodium and potassium silicates are called liquid glass, they have a strongly alkaline reaction due to the fact that they are highly hydrolyzed:
K 2 SiO 3 + H 2 O 2KON + H 2 SiO 3 ↓.
Liquid glass is used, for example, for the manufacture of glue, waterproof fabrics.
Cement is very widely used in construction as a binder, which when mixed with water hardens. Usually, cement is produced in large rotary kilns where various silicates are roasted and ground (at a temperature of -1000 ° C).
There are several types of cement, however, it is conditionally possible to distinguish two types of cement according to the principle of their “coagulation” - ordinary cement and Portland cement. The process of "setting" conventional cement consisting of calcium silicate, occurs due to the formation of calcium carbonate due to carbon dioxide in the air:
Cao. SiO 2 + CO 2 + H 2 O = CaCO 3 ↓ + H 2 SiO 3 ↓.
When setting Portland cement carbon dioxide is not involved in the process, and the hydrolysis of silicates occurs with the subsequent formation of insoluble crystalline hydrates:
Ca 3 SiO 5 + H 2 O = Ca 2 SiO 4 + Ca (OH) 2,
Ca 2 SiO 4 + 4H 2 O = Ca 2 SiO 4. 4H 2 O ↓.
· Carbides and silicides
· Carbon and silicon compounds with metals - carbides and silicides, in addition to the considered reactions, are also obtained by the interaction of silicon with metal hydrides, for example:
· 2CaH 2 + Si = Ca 2 Si + 2H 2.
· All these reactions take place at high temperatures. Among the carbides emit the so-called "methanides" and "acetylene". The first are considered as methane derivatives containing carbon in oxidation state -4 (Be 2 C, Al 4 C 3), the second - as acetylene derivatives with a degree of carbon oxidation -1 (Li 2 C 2, Ag 2 C 2, Cu 2 C 2 , CAC 2). Acetylides of silver and copper (I) can be easily obtained by passing acetylene through an ammonia solution of silver oxide or copper (I) chloride. Most methanides and acetylides actively react with water (especially with acids), releasing the corresponding hydrocarbons:
· СаС 2 + 2Н 2 О = Са (ОН) 2 + С 2 Н 2,
· Al 4 C 3 + 12H 2 O = 4Al (OH) 3 ↓ + 3CH 4,
· Ag 2 C 2 + 2HCl = 2AgCl ↓ + C 2 H 2.
· Unlike carbides, only silicides of alkali or alkaline-earth metals interact with water and acids, producing the simplest hydrogen compound silicon monosilane, which is often called simply silane SiН 4:
· Ca 2 Si + 4HCl = 2CaCl 2 + SiH 4.
· Silane is a colorless gas that has the smell of mold, spontaneously flammable in air, burning to SiO 2 and water:
· SiH 4 + 2O 2 = SiO 2 + 2H 2 O.
· Alkalis very easily decompose silane by the equation:
· SiH 4 + 2KON + H 2 O = K 2 SiO 3 + 4H 2,
· Water also hydrolyzes silane, but much slower:
· SiH 4 + 2H 2 O = SiO 2 + 4H 2.
· When heated above 400 ° C without air access, silane decomposes into silicon and hydrogen (one of the methods for producing silicon):
· SiH 4 = Si + 2H 2.
· In addition to monosilane, disilane Si 2 H 6, trisilane Si 3 H 8, tetrasilane Si 4 H 10, etc. are also known. In the individual state, compounds were isolated only up to Si 6 H 14 inclusive. All these compounds belong to the homologous series of silanes, to which the general formula Si n H 2 n + 2 corresponds. Like alkanes, silanes are colorless, the first members of the homologous series are gaseous under normal conditions, the following are liquids. The chemical activity of silanes and hydrocarbons is different: in contrast to sufficiently inert alkanes, silane all reactive. This is due to the lower silicon affinity for hydrogen compared to carbon and the very high affinity of silicon for oxygen. Moreover, Si-Si bonds are less durable than С-С bonds. In contrast to the C – H bond, the Si – H bond has a more ionic character.
· The energy of Si-E and CE bonds.
· The low strength of the Si-Si bond is due to the limitedness of the homologous series of silanes.
· Among carbides and silicides, a special place is occupied by carborundum SiC, which can be called both silicon carbide and carbon silicide. Carborundum has a high melting point due to its diamond-like structure; its hardness is close to that of diamond. Chemically, SiC is very stable.
· The concept of colloidal solutions
In nature and technology, dispersed systems are often found in which one substance is evenly distributed as particles inside another substance.
In dispersed systems, there is a dispersed phase — a finely divided substance and a dispersion medium — a homogeneous substance in which the dispersed phase is distributed. Disperse systems include ordinary (true) solutions, colloidal solutions, as well as suspensions and emulsions. They differ from each other primarily in particle sizes, i.e. the degree of dispersion (fragmentation).
Systems with a particle size of less than 1 nm are true solutions consisting of solute molecules or ions. They should be considered as a single phase system. Systems with particle sizes greater than 100 nm are coarse-dispersed systems — suspensions and emulsions.
Suspensions are dispersed systems in which the dispersed phase is a solid and the dispersion medium is a liquid, and the solid is practically insoluble in the liquid.
Emulsions are dispersed systems in which both the dispersed phase and the dispersion medium are liquids that are not mutually miscible. An example of an emulsion is milk, in which small balls of fat are floating in a liquid.
Suspensions and emulsions are biphasic systems.
Colloidal solutions are highly dispersed two-phase systems consisting of a dispersion medium and a dispersed phase, and the linear dimensions of the particles of the latter lie in the range from 1 to 100 nm. As can be seen, colloidal solutions by particle size are intermediate between true solutions and suspensions and emulsions. Colloidal particles usually consist of a large number of molecules or ions.
Colloidal solutions are also called sols. They are obtained by dispersion and condensation methods. Dispersing is most often performed using special “colloid mills”. In the condensation method, colloidal particles are formed by combining atoms or molecules into aggregates. During the course of many chemical reactions, condensation occurs and highly dispersed systems are formed (precipitation, hydrolysis, oxidation-reduction reactions, etc.).
1 nm - nanometer (1 nm = 10 -9 m).
In contrast to true solutions, sinds are characterized by the Tyndall effect, i.e., the scattering of light by colloidal particles. When a light cone appears through a beam of light, it appears in a darkened room. 
. So you can recognize whether this solution is colloidal or true.
One of the important properties of sols is that their particles have electric charges of the same sign. Due to this, they do not merge into larger particles and do not precipitate. At the same time, the particles of some sols, for example, metals, sulfides, silicic and tin acids, have a negative charge, while others, for example hydroxides, metal oxides, have a positive charge. The appearance of a charge is explained by the adsorption of ions from the solution by colloidal particles.
To precipitate a sol, it is necessary for its particles to merge into larger aggregates. The combination of particles into larger aggregates is called coagulation, and their sedimentation under the influence of gravity is called sedimentation.
Usually coagulation occurs when adding to the sols: 1) electrolyte, 2) another sol whose particles have an opposite charge, and 3) when heated.