Silicon Description. Silicon and its compounds. Silicate industry
Silicon and its compounds. Silicate industry
Silicon - Element IVA groupslike carbon. Therefore, on the external energy level, he has four electrons. These four electrons he can give and manifest reducing properties, while its degree of oxidation will be equal to +4 and can attach four electrons and manifest oxidation propertieswhile the degree of oxidation he will have -4 .
In nature silicon is the second chemical element after oxygen. In nature he only found as compounds. The most common silicon compounds are silicon oxide (IV) - SiO 2 - silica. In nature, it forms a mineral quartz. Its variety is rock crystal, amethyst, agate, topaz, opal, jasper, chalcedony, carnelian, which are used as ornamental and semi-precious stones.
Natural silicates - complex substances. Their composition is depicted as several oxides. Silicates, which include aluminum, are called aluminosilicates. it kaolinite, feldspar, mica.
Asbestos It is also silicate and is used for the manufacture of refractory fabrics.
From varieties of minerals based on silicon oxide (IV), primitive people made tools. Silicon has begun stone age, that is, the century of flint tools because of its availability and the ability to form sharp cutting edges.
Silicon oxide (IV) gives strength to plant stems and animal protective covers.
Thanks to this oxide, reeds, reeds, horsetails stand firmly, and sedge leaves cut, stalks of cereals do not fall from rain and wind, and fish scales, insect shells, butterfly wings, feathers of birds and animal hair are strong.
Silicon is a component of diatom algae and radiolarians.
Silicon industry receive recovery of silicon oxide (IV) coke in electric furnaces.
They get it in the lab reduction of silicon oxide (IV) with aluminum or magnesium.
Silicon exists in the form two allotropic modifications: amorphous and crystalline.
Amorphous silicon is a brown powder.
Crystal Silicon - solid dark gray with a metallic sheen. It is fragile and refractory. This is due to the structure of its crystals. The structure of silicon is similar to the structure of diamond, that is, in this crystal, each atom is surrounded by four other atoms and is associated with them. covalent bonds.
Silicon is a semiconductor. With increasing temperature, its electrical conductivity increases. For example, solar batteries are installed on satellites, spacecraft, stations and rooftops. These batteries convert solar energy into electrical energy, due to semiconductor crystals such as silicon.
At room temperature, silicon is inert., but when heated it reacts with metals and non-metals.
Silicon burns in oxygen with the formation of silicon oxide (IV).
In this reaction, silicon increases its oxidation state from 0 to +4, and oxygen decreases from 0 to -2. Therefore, silicon acts as a reducing agent, and oxygen - as an oxidizing agent.
The reducing properties of silicon are used in metallurgy to obtain some metalsfrom their oxides.
Silicon reacts with metals when heated, with the formation of compounds that are called silicides. For example, magnesium silicide is formed in the reaction of magnesium with silicon. In this reaction, magnesium increases its oxidation state from 0 to +2, and silicon lowers from 0 to -4. Therefore, magnesium is a reducing agent, and silicon is an oxidizing agent.
Silicides easily decompose with water or acids.this produces gas silane - hydrogen compound of silicon. So, when magnesium silicide interacts with hydrochloric acid, magnesium chloride and silane gas are formed.
Silane in the air self-ignites and burns with the formation of silicon oxide (IV) and water.
Silicon interacts with concentrated alkaline solutions.. For example, the interaction of silicon with a concentrated solution of sodium hydroxide produces sodium silicate and hydrogen.
Silicon can be obtained heating silica (IV) with magnesium or carbon.
In the reaction with magnesium, magnesium reduces silicon from silicon oxide (IV), and in the reaction of silicon oxide (IV) with carbon, carbon restores silicon from its oxide.
Silicon oxide (IV), silica - SiO 2 is a solid, very refractory substance, insoluble in water. This oxide has atomic crystal lattice, in which nodes there are atoms of silicon and oxygen.
Silicon oxide (IV) is acid oxide, therefore, exhibits all the properties characteristic of these oxides. However, this oxide does not dissolve in water, but it reacts with alkali solutions. Thus, sodium silicate and water are formed in the reaction of silicon oxide (IV) with sodium hydroxide.
Silicon oxide (IV) reacts with basic oxides when heated. Thus, in the reaction with calcium oxide, calcium silicate is formed.
Silicon oxide (IV) interacts when heated with carbonates, so in the reaction with sodium carbonate sodium silicate and carbon dioxide are formed.
Sodium and potassium silicates are called soluble glass. Their aqueous solutions are silicate glue.
Silicon oxide (IV) reacts with hydrogen fluoride and hydrofluoric acid to form gaseous silicon fluoride.
This property is used for etching on glass inscriptions, drawings and labels.
The composition of silicic acid can be expressed as H 2 SiO 3. Silicic acid is a gelatinous, water-insoluble substance. She refers to very weak acids (even weaker than coal). Upon drying, the solution containing silicic acid forms silica gel, which is used as an adsorbent.
Silicic acid - loose connection and when stored or heated, decomposes into silica (IV) and water.
Qualitative reaction to silicate ion is the reaction of silicates with solutions of strong acids, this forms silicic acid in the form of a gelatinous precipitate. For example, in the reaction of sodium silicate with hydrochloric acid, a salt is formed — sodium chloride and silicic acid in the form of a gelatinous precipitate.
Let's do an experiment. To do this, skip carbon dioxide through a solution of sodium silicate. At the same time, we can observe the formation of a gelatinous sediment. This formed silicic acid. Thus, silicic acid is very weak, even weaker than carbonic acid, which can displace it from the salt solution.
And now to this gelatinous sediment we add a concentrated solution of alkali and heat up a spirit lamp on the flame. The precipitate begins to dissolve due to the formation of a soluble salt, sodium silicate.
Silicon is used for semiconductor materials and acid-resistant alloys. Such a silicon compound as silicon carbide - SiC - used for grinding the incisors of metal-cutting machine tools and polishing precious stones, because in hardness it is inferior only to diamond.
Quartz chemical glassware is manufactured from quartz, which withstands high temperatures and sudden temperature changes.
Water soluble silicates of sodium and potassium (" soluble glass") Used as a refractory agent for impregnating wood and fabrics. For the manufacture of fireproof and insulating textiles are also used natural silicates - asbestos.
By silicate industry include production:
· Glass;
· Ceramic products (porcelain, pottery faience), bricks, tiles, and roofing materials;
· Cement.
Silicon compounds are the basis for the production of glass and cement. For example, ordinary window glass is produced by fusing a mixture of soda, limestone and sand. Glass has the ability to soften and in a molten state to take a different shape, so it is used for the production of dishes.
Certain properties of the glass give additives. For example, if you replace sodium oxide with potassium oxide, you can get a solid bohemian glassby adding lead (II) oxide can be obtained crystal glassby adding chromium (III) oxide can be obtained green glass, by adding cobalt oxide - blue, and adding manganese (II) oxide - purple. Adding salts of gold and selenium, get ruby glassof which the stars are made Moscow Kremlin.
To improve the mechanical properties of the glass is subjected quenching. The quenching is that the glass of a special composition is heated to a temperature of about 600 ° C, and then cooled rapidly. Such hardening allows you to get bulletproof glass.
Glass has been known to man for a long time, three or four thousand years ago, the production of glass was Egypt, Syria, Phenicia, Black Sea.
Glass is an amazing material. AT Ancient rome masters learned how to get colored glass and make mosaic out of their pieces. Stained-glass windows of churches, museums, various mosaic panels are made of glass.
Glass applications extensive: it is a window, bottle, lamp, mirror and optical.
The main raw material in the manufacture of ceramic products is clay. When clay is mixed with water, a pasty mass is formed, which, after drying and firing, is able to maintain its shape. Some pottery covers icing - a thin layer of vitreous material. Glaze makes ceramics waterproof, protects it from contamination, protects against the action of acids and alkalis, adds shine.
An important silicon compound is cement. It is obtained by sintering clay and limestone. If you mix cement powder with water, the so-called " cement mortar, Which then gradually hardens. If you add to the cement sand or gravel, you get concrete. The strength of concrete can be increased if you enter the iron frame, then it turns out reinforced concreteof which wall panels, blocks of overlappings are made.
Silicon was obtained in 1824 year by the Swedish chemist Bercalius. But twelve years before it, silicon got Gay Lussac and Tenar, but it was very polluted with impurities.
Latin name silicium from latin silex - "flint". The Russian name "silicon" comes from the Greek kremnos - "cliff, rock."
In this way, silicon - element IVA groups. It is characterized by oxidation states +4 and -4. In reactions with oxygen and other non-metals, it exhibits reducing properties, and in reactions with metals - oxidizing. In nature, silicon is found in the form of compounds. Its most common compound is silicon oxide (IV) - silica, which is an acid oxide and exhibits properties characteristic of these oxides. Silicon's hydrogen compound is silane - SiH 4 , which is formed by the action of acids or water on silicides - metal compounds with silicon. Silicon oxide (IV) corresponds to silicic acid. This weak dibasic, gelatinous, water-insoluble acid. A qualitative reaction to silicate-ion is the action of strong acids on silicates, since as a result of these reactions a gelatinous precipitate is formed - silicic acid. Silicon oxide (IV) and silicates are widely used in industry. The silicate industry includes the production of glass and cement, ceramic products and bricks.
Silicon is obtained by reducing its oxide with an excess of magnesium when heated:
Of the two allotropic modifications of silicon, crystalline and amorphous, amorphous silicon is more chemically active. It reacts with oxygen when heated, forming
and also with all halogens, for example:
At high temperature, silicon combines with carbon, forming carborundum - a substance that is close in hardness to diamond:
In reactions with active metals occurring with the formation of silicides, silicon acts as an oxidizing agent:
Under the action of hydrochloric acid on silicides, the simplest hydrogen compound silicon silane is obtained.
Silicon oxide and silicic acids.
Silicon oxide is a solid, very refractory substance (melting point, widely distributed in nature. It is found in the form of two modifications - crystalline and amorphous silica. It is an anhydride of a number of silicic acids whose composition can be expressed by the general formula where x and y are integers:
1), i.e. - metasilicic acid;
2), i.e. - orthocremaic acid;
3), i.e. - dimetacrytic acid.
Silicic acids, the molecules of which contain more than one molecule belong to polysilicon. The simplest silicic acid is often called simply silicic acid.
All silicic acids are very weak (weaker than coal). Salts of all silicic acids are called silicates, although, as a rule, in educational literature, silicates imply salts of methacilicic acid. When standing in air, the solutions of silicates grow turbid, since carbon dioxide (IV) in the air displaces silicic acid from its salts:
Silicic acid is practically insoluble in water - this property is used as a qualitative reaction to the ion.
Silicates are obtained by fusing silica with alkalis or carbonates:
The most widely used silicates are sodium and potassium. Concentrated solutions of these salts are called liquid glass; they have a strongly alkaline reaction due to hydrolysis. Liquid glass is used in the manufacture of glue and waterproof fabrics.
- silicon element characteristic: electronic structure, possible oxidation states, main compounds: oxide, hydroxide. Amorphous and crystalline silicon.
Silicon- an element of the 3rd period and the IVA-group of the Periodic system, the serial number is 14. The electronic formula of the atom is 1s 2 2s 2 2p 6 3s 2 3p 2 = [10 Ne] 3s 2 3p 2. The characteristic degree of oxidation in compounds + IV.
The scale of oxidation of silicon:
Silicon electronegativity is not high for non-metals (2.25). Shows non-metal (acid) properties; forms oxides, silicic acids, a very large number of salts - silicates in the form of chains, ribbons and three-dimensional tetrahedron networks, binary compounds. At present, the chemistry of organic silicon compounds with Si – C bonds and silicone organic polymers — silicones and silicone rubbers with Si – Si, Si – O and Si – C bonds, is widely developed.
The most important element of inanimate nature, secondby chemical prevalence. It is found only in a related form. A vital element for many organisms.
Silicon Si -Simple substance. Coarse-crystalline - dark gray, with a metallic luster, very hard, very fragile, opaque, refractory, a common semiconductor. The crystal lattice is atomic, the Si – Si bonds are very strong. Amorphous - white or tan (with impurities, mainly Fe), more chemically active. It is steady on air (it is covered with a strong oxide film), does not react with water. Reacts with HF (conc.), Alkalis. It is oxidized by oxygen, chlorine. Recovered by magnesium. Sintered with graphite. Industrially important is alloy with iron - ferrosilicon(12–90% Si). It is used as an alloying additive in steel and non-ferrous metal alloys, a component of semiconductor materials for microelectronics, a base of silicones.
The equations of the most important reactions:
Gettingin industry: the restoration of SiCl 4 or SiO 2 during calcination:
SiCl 4 + 2Zn = Si+ 2ZnCl 2
SiO 2 + 2Mg = Si+ 2MgO
(The last reaction can be carried out in the laboratory; amorphous silicon remains after treatment with hydrochloric acid).
Silicon dioxide SiO 2 -Acid oxide. White powder (quartz sand)and clear crystals, natural product colored with impurities (silica) - in the form of ordinary sand and stone (flint).The crystal lattice is atomic, each silicon atom is surrounded by four oxygen atoms, and each oxygen atom is surrounded by two silicon atoms. It has several crystal modifications (all minerals), the most important - quartz, tridimichi cristobalite,rare and artificially obtained - kitit, coesit, stishovit, melanophlogite, fibrous silica. refractory, with slow cooling of the melt, an amorphous form is formed - quartz glass(in nature, the mineral lechateleit).The most chemically active amorphous form.
Practically does not react with water (hydrate SiO 2 nH 2 O precipitates from the solution), common acids. Quartz glass corrodes in HF (conc.). Reacts with alkalis in solution (forms orthosilicates)and when fusing (products - metasilicates).It is easily chlorinated in the presence of coke. Recovered by coke, magnesium, iron (in the blast furnace process).
It is used as an industrial raw material in the production of silicon, ordinary, thermo– and chemically resistant glass,
porcelain, ceramics, abrasives and adsorbents, rubber filler, lubricants, adhesives and paints, components of building bonding solutions, in the form of quartz single crystals are the basis of ultrasound generators and precise movements of quartz watches. Varieties of quartz ( rock crystal, rose quartz, amethyst, smoky quartz, chalcedony, onyxy etc.) - precious, semi-precious or ornamental stones.
The equations of the most important reactions:
Silicon dioxide polyhydrate SiO 2 nH 2 O -Silicic acids with variable content of SiO 2 and H 2 O. White, amorphous (vitreous) polymer with a chain, ribbon, sheet, mesh and frame structure. When heated, it gradually decomposes. Very little soluble in water. Above the precipitate in solution there is a monomeric weak silicon siliconacid H 4 SiO 4 (tetrahedral structure, sp 3 hybridization), solubility of 0.00673 g / 100 g H 2 O at 20 ° C. Upon standing of the solution, polycondensation occurs and silicic acids H 6 Si 2 O 7, H 2 Si 2 O 5, H 10 Si 2 O 9, and then the hydrosol n (sol metasiliconacids) and, finally, the hydrogel SiO 2 nH 2 O (n< 2). При высушивании гидрогель переходит в силикагель SiO 2 nН 2 O (n < 1). Скорость гелеобразования максимальна в слабокислотной среде.
It is converted into solution by the action of concentrated alkalis. The other chemical properties are similar to SiO 2. Minerals in nature opaland chalcedony (agate, jasper).Monomeric meta-silicic acid H 2 SiO 3 was not obtained.
The equations of the most important reactions:
Getting: displacement by strong acid from silicate solution, for example:
K 2 SiO 3 + 2НCl + (n - 1) Н 2 O = 2КCl + SiO 2 nH 2 O↓
Sodium metasilicate Na 2 SiO 3 -Saline White, when heated melts without decomposition. It dissolves in cold water (strong anion hydrolysis). Concentrated solution - colloidal (“liquid glass”, contains SiO 2 nH 2 O hydrosol). It decomposes in hot water, reacts with acids, alkalis, carbon dioxide.
It is used as a component of the charge in the production of glass, special cements and concretes, it is part of silicate paints and glue, cold glazes, aluminosilicate catalysts, in the manufacture of paper and cardboard, silica gel, and synthetic zeolites. The equations of the most important reactions:
Getting: fusion of soda with sand
Na 2 SiO 3 + SiO 2 = CO 2 + Na 2 SiO 3(1150 ° C)
Silicates.Silicon in oxidation state + IV is, in addition to SiO 2, in very numerous and often very complex in composition and structure silicate ions(so, except zetasilicate ionSiO 3 2- and orthosilicate ionSiO 4 4-known ions Si 2 O 7 6-, Si 3 O 9 6-, Si 2 O 10 4-, etc.). For ease of recording, all silicates are depicted as containing ion SiO 3 2-.
A saturated solution of sodium and potassium silicates (viscous "liquid glass") is used as silicate glue.
Silicates of sodium and calcium are part of the glass; it is obtained by fusing silica quartz SiO 2, limestone CaCO 3 and soda Na 2 CO 3:
Often the glass composition is expressed in terms of oxides, for example, ordinary glass Na 2 O CaO 6SiO 2.
Among silicate minerals we note clay (aluminosilicates), very clean clay - kaolinAl 2 O 3 2SiO 2 2Н 2 O is used to make porcelain.
Silicates and aluminosilicates are used in industry for the production of ceramics, cement, concrete and other building materials.
Silicon SiCl 4.Binary connection. Colorless liquid, has a wide range of liquid state. The molecule has a tetrahedral structure (sp 3 hybridization). Thermally resistant. "Smokes" in humid air. Fully hydrolyzed with water. Decomposed by alkalis. Restored by hydrogen, sodium, zinc. Chlorinates alumina.
Used in the manufacture of high purity silicon for semiconductor technology.
The equations of the most important reactions:
Gettingat industry- Chlorination of silicon or silica sand SiO 2.
Crystalline silicon is the main form in which silicon is used in the production of photoelectric converters and solid-state electronic devices using planar technology. The use of silicon in the form of thin films (epitaxial layers) of a crystalline and amorphous structure on various substrates is actively developing.