Silicon- a very rare mineral species from the class of native elements. In fact, it is surprising how rarely the chemical element silicon, which makes up at least 27.6% of the mass of the earth's crust in a bound form, is found in nature in its pure form. But silicon binds strongly to oxygen and is almost always found in the form of silica - silicon dioxide, SiO 2 (quartz family) or as part of silicates (SiO 4 4-). Native silicon as a mineral was found in products of volcanic vapors and as tiny inclusions in native gold.
See also:
STRUCTURE
The crystal lattice of silicon is cubic face-centered like diamond, parameter a = 0.54307 nm (other polymorphic modifications of silicon have been obtained at high pressures), but due to the longer bond length between Si-Si atoms compared to the length of the C-C bond, the hardness of silicon is significantly less than a diamond. It has a voluminous structure. The nuclei of atoms, together with the electrons in the inner shells, have a positive charge of 4, which is balanced by the negative charges of the four electrons in the outer shell. Together with the electrons of neighboring atoms, they form covalent bonds on the crystal lattice. Thus, the outer shell contains four of its own electrons and four electrons borrowed from four neighboring atoms. At absolute zero temperature, all electrons in the outer shells participate in covalent bonds. At the same time, silicon is an ideal insulator, since it does not have free electrons that create conductivity. PROPERTIES
Silicon is fragile; only when heated above 800 °C does it become a plastic substance. It is transparent to infrared radiation starting at a wavelength of 1.1 microns. The intrinsic concentration of charge carriers is 5.81 10 15 m−3 (for a temperature of 300 K). Melting point 1415 °C, boiling point 2680 °C, density 2.33 g/cm3. It has semiconductor properties, its resistance decreases with increasing temperature.
Amorphous silicon is a brown powder based on a highly disordered diamond-like structure. It is more reactive than crystalline silicon.
MORPHOLOGY
Most often in nature, silicon is found in the form of silica - compounds based on silicon dioxide (IV) SiO 2 (about 12% of the mass of the earth's crust). The main minerals and rocks formed by silicon dioxide are sand (river and quartz), quartz and quartzites, flint, feldspars. The second most common group of silicon compounds in nature are silicates and aluminosilicates. Isolated cases of finding pure silicon in native form have been noted.
ORIGIN
The silicon content in the earth's crust is, according to various sources, 27.6-29.5% by weight. Thus, in terms of abundance in the earth’s crust, silicon ranks second after oxygen. Concentration in sea water is 3 mg/l. Isolated facts of finding pure silicon in native form have been noted - tiny inclusions (nanoindividuals) in ijolites of the Goryachegorsk alkaline gabbro massif (Kuznetsk Alatau, Krasnoyarsk Territory); in Karelia and on the Kola Peninsula (based on the mathematical study of the Kola superdeep well); microscopic crystals in the fumaroles of the Tolbachik and Kudryavy volcanoes (Kamchatka).
APPLICATION
Ultra-pure silicon is primarily used for the production of single-chip electronic devices (nonlinear passive elements of electrical circuits) and single-chip microcircuits. Pure silicon, ultra-pure silicon waste, purified metallurgical silicon in the form of crystalline silicon are the main raw materials for solar energy. Monocrystalline silicon - in addition to electronics and solar energy, is used to make gas laser mirrors.
Compounds of metals with silicon - silicides - are widely used in industry (for example, electronic and nuclear) materials with a wide range of useful chemical, electrical and nuclear properties (resistance to oxidation, neutrons, etc.). Silicides of a number of elements are important thermoelectric materials.
Silicon compounds serve as the basis for the production of glass and cement. The silicate industry produces glass and cement. It also produces silicate ceramics - brick, porcelain, earthenware and products made from them. Silicate glue is widely known, used in construction as a drier, and in pyrotechnics and in everyday life for gluing paper. Silicone oils and silicones - materials based on organosilicon compounds - have become widespread.
Technical silicon finds the following applications:
- raw materials for metallurgical production: alloy component (bronze, silumin);
- deoxidizer (for smelting iron and steel);
- modifier of metal properties or alloying element (for example, adding a certain amount of silicon in the production of transformer steels reduces the coercive force of the finished product), etc.;
- raw materials for the production of purer polycrystalline silicon and purified metallurgical silicon (in the literature “umg-Si”);
- raw materials for the production of silicon organic materials, silanes;
- sometimes commercial grade silicon and its alloy with iron (ferrosilicon) are used to produce hydrogen in the field;
- for the production of solar panels;
- antiblock (anti-adhesive additive) in the plastics industry.
Silicon - Si
CLASSIFICATION
| Strunz (8th edition) | 1/B.05-10 |
| Nickel-Strunz (10th edition) | 1.CB.15 |
| Dana (7th edition) | 1.3.6.1 |
| Dana (8th edition) | 1.3.7.1 |
| Hey's CIM Ref. | 1.28 |
Element characteristics
14 Si 1s 2 2s 2 2p 6 3s 2 3p 2
Isotopes: 28 Si (92.27%); 29 Si (4.68%); 30 Si (3.05%)
Silicon is the second most abundant element in the earth's crust after oxygen (27.6% by mass). It is not found in a free state in nature; it is found mainly in the form of SiO 2 or silicates.
Si compounds are toxic; inhalation of tiny particles of SiO 2 and other silicon compounds (for example, asbestos) causes a dangerous disease - silicosis
In the ground state, the silicon atom has valence = II, and in the excited state = IV.
The most stable oxidation state of Si is +4. In compounds with metals (silicides) S.O. -4.
Methods for obtaining silicon
The most common natural silicon compound is silica (silicon dioxide) SiO 2 . It is the main raw material for producing silicon.
1) Reduction of SiO 2 with carbon in arc furnaces at 1800 "C: SiO 2 + 2C = Si + 2CO
2) High-purity Si from a technical product is obtained according to the scheme:
a) Si → SiCl 2 → Si
b) Si → Mg 2 Si → SiH 4 → Si
Physical properties of silicon. Allotropic modifications of silicon
1) Crystalline silicon - a silver-gray substance with a metallic sheen, a diamond-type crystal lattice; m.p. 1415"C, boiling point 3249"C, density 2.33 g/cm3; is a semiconductor.
2) Amorphous silicon - brown powder.
Chemical properties of silicon
In most reactions, Si acts as a reducing agent:
At low temperatures, silicon is chemically inert; when heated, its reactivity increases sharply.
1. Reacts with oxygen at temperatures above 400°C:
Si + O 2 = SiO 2 silicon oxide
2. Reacts with fluorine already at room temperature:
Si + 2F 2 = SiF 4 silicon tetrafluoride
3. Reactions with other halogens occur at temperature = 300 - 500°C
Si + 2Hal 2 = SiHal 4
4. With sulfur vapor at 600°C it forms a disulfide:
5. Reaction with nitrogen occurs above 1000°C:
3Si + 2N 2 = Si 3 N 4 silicon nitride
6. At temperature = 1150°C reacts with carbon:
SiO 2 + 3С = SiС + 2СО
Carborundum is close to diamond in hardness.
7. Silicon does not react directly with hydrogen.
8. Silicon is resistant to acids. Interacts only with a mixture of nitric and hydrofluoric (hydrofluoric) acids:
3Si + 12HF + 4HNO 3 = 3SiF 4 + 4NO + 8H 2 O
9. reacts with alkali solutions to form silicates and release hydrogen:
Si + 2NaOH + H 2 O = Na 2 SiO 3 + 2H 2
10. The reducing properties of silicon are used to isolate metals from their oxides:
2MgO = Si = 2Mg + SiO 2
In reactions with metals, Si is an oxidizing agent:
Silicon forms silicides with s-metals and most d-metals.
The composition of silicides of a given metal may vary. (For example, FeSi and FeSi 2 ; Ni 2 Si and NiSi 2 .) One of the most well-known silicides is magnesium silicide, which can be obtained by direct interaction of simple substances:
2Mg + Si = Mg 2 Si
Silane (monosilane) SiH 4
Silanes (hydrogen silicas) Si n H 2n + 2, (cf. alkanes), where n = 1-8. Silanes are analogs of alkanes; they differ from them in the instability of the -Si-Si- chains.
Monosilane SiH 4 is a colorless gas with an unpleasant odor; soluble in ethanol, gasoline.
Methods of obtaining:
1. Decomposition of magnesium silicide with hydrochloric acid: Mg 2 Si + 4HCI = 2MgCI 2 + SiH 4
2. Reduction of Si halides with lithium aluminum hydride: SiCl 4 + LiAlH 4 = SiH 4 + LiCl + AlCl 3
Chemical properties.
Silane is a strong reducing agent.
1.SiH 4 is oxidized by oxygen even at very low temperatures:
SiH 4 + 2O 2 = SiO 2 + 2H 2 O
2. SiH 4 is easily hydrolyzed, especially in an alkaline environment:
SiH 4 + 2H 2 O = SiO 2 + 4H 2
SiH 4 + 2NaOH + H 2 O = Na 2 SiO 3 + 4H 2
Silicon (IV) oxide (silica) SiO 2
Silica exists in various forms: crystalline, amorphous and glassy. The most common crystalline form is quartz. When quartz rocks are destroyed, quartz sands are formed. Quartz single crystals are transparent, colorless (rock crystal) or colored with impurities in various colors (amethyst, agate, jasper, etc.).
Amorphous SiO 2 is found in the form of the opal mineral: silica gel is artificially produced, consisting of colloidal particles of SiO 2 and being a very good adsorbent. Glassy SiO 2 is known as quartz glass.
Physical properties
SiO 2 dissolves very slightly in water, and is also practically insoluble in organic solvents. Silica is a dielectric.
Chemical properties
1. SiO 2 is an acidic oxide, therefore amorphous silica dissolves slowly in aqueous solutions of alkalis:
SiO 2 + 2NaOH = Na 2 SiO 3 + H 2 O
2. SiO 2 also interacts with basic oxides when heated:
SiO 2 + K 2 O = K 2 SiO 3;
SiO 2 + CaO = CaSiO 3
3. Being a non-volatile oxide, SiO 2 displaces carbon dioxide from Na 2 CO 3 (during fusion):
SiO 2 + Na 2 CO 3 = Na 2 SiO 3 + CO 2
4. Silica reacts with hydrofluoric acid, forming hydrofluorosilicic acid H 2 SiF 6:
SiO 2 + 6HF = H 2 SiF 6 + 2H 2 O
5. At 250 - 400°C, SiO 2 interacts with gaseous HF and F 2, forming tetrafluorosilane (silicon tetrafluoride):
SiO 2 + 4HF (gas.) = SiF 4 + 2H 2 O
SiO 2 + 2F 2 = SiF 4 + O 2
Silicic acids
Known:
Orthosilicic acid H 4 SiO 4 ;
Metasilicon (silicic) acid H 2 SiO 3 ;
Di- and polysilicic acids.
All silicic acids are slightly soluble in water and easily form colloidal solutions.
Receipt methods
1. Precipitation with acids from solutions of alkali metal silicates:
Na 2 SiO 3 + 2HCl = H 2 SiO 3 ↓ + 2NaCl
2. Hydrolysis of chlorosilanes: SiCl 4 + 4H 2 O = H 4 SiO 4 + 4HCl
Chemical properties
Silicic acids are very weak acids (weaker than carbonic acid).
When heated, they dehydrate to form silica as the final product.
H 4 SiO 4 → H 2 SiO 3 → SiO 2
Silicates - salts of silicic acids
Since silicic acids are extremely weak, their salts in aqueous solutions are highly hydrolyzed:
Na 2 SiO 3 + H 2 O = NaHSiO 3 + NaOH
SiO 3 2- + H 2 O = HSiO 3 - + OH - (alkaline medium)
For the same reason, when carbon dioxide is passed through silicate solutions, silicic acid is displaced from them:
K 2 SiO 3 + CO 2 + H 2 O = H 2 SiO 3 ↓ + K 2 CO 3
SiO 3 + CO 2 + H 2 O = H 2 SiO 3 ↓ + CO 3
This reaction can be considered as a qualitative reaction to silicate ions.
Among silicates, only Na 2 SiO 3 and K 2 SiO 3 are highly soluble, which are called soluble glass, and their aqueous solutions are called liquid glass.
Glass
Ordinary window glass has the composition Na 2 O CaO 6 SiO 2, i.e., it is a mixture of sodium and calcium silicates. It is obtained by fusing Na 2 CO 3 soda, CaCO 3 limestone and SiO 2 sand;
Na 2 CO 3 + CaCO 3 + 6SiO 2 = Na 2 O CaO 6SiO 2 + 2СO 2
Cement
A powdery binding material that, when interacting with water, forms a plastic mass that turns over time into a solid, stone-like body; main building material.
The chemical composition of the most common Portland cement (in % by weight) is 20 - 23% SiO 2; 62 - 76% CaO; 4 - 7% Al 2 O 3; 2-5% Fe 2 O 3; 1-5% MgO.
In this lesson you will study the topic "Silicon". Consider information about silicon: its electronic structure, where silicon is found in nature, study the allotropy of silicon, explain its physical and chemical properties. You will learn about where silicon is used in industry and other areas and how it is produced. You will get acquainted with silicon dioxides, silicic acid and its salts - silicates.
Topic: Basic metals and non-metals
Lesson: Silicon. Noble gases
Silicon is one of the most common chemical elements in the earth's crust. Its content is almost 30%. In nature, it is mainly found in various forms of silica, silicates and aluminosilicates.
In almost all of its compounds, silicon is tetravalent. In this case, the silicon atoms are in an excited state. Rice. 1.
Rice. 1
To transition to this state, one of the 3s electrons occupies a vacant position in the 3p orbital. In this case, instead of 2 unpaired electrons in the ground state, the silicon atom in the excited state will have 4 unpaired electrons. It will be able to form 4 by the exchange mechanism.
Rice. 2
Rice. 3
Silicon atoms are not prone to forming multiple bonds, but form compounds with single bonds -Si-O-. Silicon, unlike carbon, is not characterized by allotropy.
One of allotropic modifications is crystalline silicon, in which each silicon atom is in sp 3 hybridization. Rice. 2, 3. Crystalline silicon is a hard, refractory and durable crystalline substance of dark gray color with a metallic luster. Under normal conditions - a semiconductor. Sometimes amorphous silicon is isolated as another allotropic modification of silicon. It is a dark brown powder that is more chemically active than crystalline silicon. Whether it is an allotropic modification is a controversial issue.
Chemical properties of silicon
1. Interaction with halogens
Si + 2F 2 → SiF 4
2. When heated, silicon burns in oxygen, forming silicon (IV) oxide.
Si + O 2 → SiO 2
3. At high temperatures, silicon reacts with nitrogen or carbon.
3Si + 2N 2 → Si 3 N 4
4. Silicon does not react with aqueous solutions of acids. But it dissolves in alkalis.
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2
5. When silicon is fused with metals, silicides are formed.
Si + 2Mg → Mg 2 Si
6. Silicon does not interact directly with hydrogen, but hydrogen compounds of silicon can be obtained by reacting silicides with water.
Mg 2 Si + 4H 2 O → 2Mg(OH) 2 + SiH 4 (silane)
Silanes are similar in structure to alkanes, but are significantly reactive. The most stable monosilane ignites in air.
SiH 4 +2 O 2 → SiO 2 + 2H 2 O
Getting silicon
Silicon is obtained by reduction from silicon(IV) oxide
SiO 2 + 2Mg → Si + 2MgO
One of the tasks is to obtain high-purity silicon. For this purpose, technical silicon is converted into silicon tetrachloride. The resulting tetrachloride is reduced to silane, and the silane decomposes when heated into silicon and hydrogen.
Silicon is capable of forming two oxides: SiO 2 - silicon oxide (IV) and SiO - silicon oxide (II).
Rice. 4
SiO - silicon oxide (II) - it is an amorphous dark brown substance that is formed when silicon reacts with silicon (IV) oxide
Si + SiO 2 → 2 SiO.
Despite its stability, this substance is almost never used.
SiO 2 - silicon oxide (IV)
Rice. 5
Rice. 6
This substance accounts for 12% of the earth's crust. Rice. 4. It is represented by minerals such as rock crystal, quartz, amethyst, citrine, jasper, chalcedony. Rice. 5.
SiO 2 - silicon oxide (IV) is a substance of non-molecular structure.
Its crystal lattice is atomic. Rice. 6. SiO 2 crystals have the shape of a tetrahedron, which are interconnected by oxygen atoms. The formula of the molecule (SiO 2)n would be more correct. Since SiO 2 forms a substance of atomic structure, and CO 2 forms a substance of molecular structure, the difference in their properties is obvious. CO 2 is a gas, and SiO 2 is a solid transparent crystalline substance, insoluble in water and refractory.
Chemical propertiesSiO 2
1. Silicon (IV) oxide SiO 2 is an acidic oxide. It does not react with water. Silicic acid cannot be obtained by hydration of SiO 2. Its salts - silicates - can be obtained by reacting SiO 2 with hot alkali solutions.
SiO 2 + 2NaOH Na 2 SiO 3 + H 2 O
2. Reacts with carbonates of alkali and alkaline earth metals.
CaCO 3 + SiO 2 CaSiO 3 + CO 2
3. Interacts with metals.
SiO 2 + 2Mg → Si + 2MgO
4. Reaction with hydrofluoric acid.
SiO 2 + 4HF → SiF 4 + 2H 2 O
Homework
1. No. 2-4 (p. 138) Rudzitis G.E. Chemistry. Fundamentals of general chemistry. 11th grade: textbook for general education institutions: basic level / G.E. Rudzitis, F.G. Feldman. - 14th ed. - M.: Education, 2012.
2. Name the areas of application of polyorganosiloxanes.
3. Compare the properties of allotropic modifications of silicon.
It is located in the main subgroup of group IV, in the third period. This is an analogue of carbon. The electronic configuration of the electronic layers of the silicon atom is ls 2 2s 2 2p 6 3s 2 3p 2. Structure of the outer electronic layer
The structure of the outer electronic layer is similar to the structure of the carbon atom.
It occurs in the form of two allotropic modifications - amorphous and crystalline.
Amorphous - a brownish powder with slightly greater chemical activity than crystalline. At normal temperature it reacts with fluorine:
Si + 2F2 = SiF4 at 400° - with oxygen
Si + O2 = SiO2
in melts - with metals:
2Mg + Si = Mg2Si
Silicon is
Crystalline silicon is a hard, brittle substance with a metallic luster. It has good thermal and electrical conductivity and easily dissolves in molten metals, forming. An alloy of silicon with aluminum is called silumin, an alloy of silicon with iron is called ferrosilicon. Silicon density is 2.4. Melting point 1415°, boiling point 2360°. Crystalline silicon is a rather inert substance and enters into chemical reactions with difficulty. Despite its clearly visible metallic properties, silicon does not react with acids, but reacts with alkalis, forming silicic acid salts and:
Si + 2KOH + H2O = K2SiO2 + 2H2
■ 36. What are the similarities and differences between the electronic structures of silicon and carbon atoms?
37. How can we explain from the point of view of the electronic structure of the silicon atom why metallic properties are more characteristic of silicon than of carbon?
38. List the chemical properties of silicon.
Silicon in nature. Silica
In nature, silicon is very widespread. Approximately 25% of the earth's crust is made up of silicon. A significant part of natural silicon is represented by silicon dioxide SiO2. In a very pure crystalline state, silicon dioxide occurs as a mineral called rock crystal. Silicon dioxide and carbon dioxide are chemically analogous, but carbon dioxide is a gas and silica is a solid. Unlike the molecular crystal lattice of CO2, silicon dioxide SiO2 crystallizes in the form of an atomic crystal lattice, each cell of which is a tetrahedron with a silicon atom in the center and oxygen atoms at the corners. This is explained by the fact that the silicon atom has a larger radius than the carbon atom, and not 2, but 4 oxygen atoms can be placed around it. The difference in the structure of the crystal lattice explains the difference in the properties of these substances. In Fig. 69 shows the appearance of a natural quartz crystal consisting of pure silicon dioxide and its structural formula.
Rice. 60. Structural formula of silicon dioxide (a) and natural quartz crystals (b)
Crystalline silica most often occurs in the form of sand, which is white unless contaminated with yellow clay impurities. Besides sand, silica is often found in the form of a very hard mineral, silica (hydrated silica). Crystalline silicon dioxide, colored with various impurities, forms precious and semi-precious stones - agate, amethyst, jasper. Almost pure silicon dioxide also occurs in the form of quartz and quartzite. Free silicon dioxide in the earth's crust is 12%, in the composition of various rocks - about 43%. In total, more than 50% of the earth's crust is made of silicon dioxide.
Silicon is part of a wide variety of rocks and minerals - clay, granites, syenites, micas, feldspars, etc.
Solid carbon dioxide, without melting, sublimes at -78.5°. The melting point of silicon dioxide is about 1.713°. She is quite refractory. Density 2.65. The expansion coefficient of silicon dioxide is very small. This is very important when using quartz glassware. Silicon dioxide does not dissolve in water and does not react with it, despite the fact that it is an acidic oxide and its corresponding silicic acid is H2SiO3. Carbon dioxide is known to be soluble in water. Silicon dioxide does not react with acids, except hydrofluoric acid HF, and gives salts with alkalis.
Rice. 69. Structural formula of silicon dioxide (a) and natural quartz crystals (b).
When silicon dioxide is heated with coal, silicon is reduced, and then it combines with carbon and carborundum is formed according to the equation:
SiO2 + 2C = SiC + CO2. Carborundum has high hardness, is resistant to acids, and is destroyed by alkalis.
■ 39. By what properties of silicon dioxide can one judge its crystal lattice?
40. In what minerals does silicon dioxide occur in nature?
41. What is carborundum?
Silicic acid. Silicates
Silicic acid H2SiO3 is a very weak and unstable acid. When heated, it gradually decomposes into water and silicon dioxide:
H2SiO3 = H2O + SiO2
Silicic acid is practically insoluble in water, but can easily give.
Silicic acid forms salts called silicates. widely found in nature. Natural ones are quite complex. Their composition is usually depicted as a combination of several oxides. If natural silicates contain aluminum oxide, they are called aluminosilicates. These are white clay, (kaolin) Al2O3 2SiO2 2H2O, feldspar K2O Al2O3 6SiO2, mica
К2O · Al2O3 · 6SiO2 · 2Н2O. Many natural stones in their pure form are precious stones, such as aquamarine, emerald, etc.
Of the artificial silicates, sodium silicate Na2SiO3 should be noted - one of the few silicates soluble in water. It is called soluble glass, and the solution is called liquid glass.
Silicates are widely used in technology. Soluble glass is used to impregnate fabrics and wood to protect them from fire. The liquid is included in fire-resistant putties for gluing glass, porcelain, and stone. Silicates are the basis in the production of glass, porcelain, earthenware, cement, concrete, brick and various ceramic products. In solution, silicates are easily hydrolyzed.
■ 42. What is ? How are they different from silicates?
43. What is liquid and for what purposes is it used?
Glass
The raw materials for glass production are Na2CO3 soda, CaCO3 limestone and SiO2 sand. All components of the glass charge are thoroughly cleaned, mixed and fused at a temperature of about 1400°. During the fusion process the following reactions occur:
Na2CO3 + SiO2= Na2SiO3 + CO2
CaCO3 + SiO2 = CaSiO 3+ CO2
In fact, glass contains sodium and calcium silicates, as well as excess SO2, so the composition of ordinary window glass is: Na2O · CaO · 6SiO2. The glass mixture is heated at a temperature of 1500° until carbon dioxide is completely removed. Then it is cooled to a temperature of 1200°, at which it becomes viscous. Like any amorphous substance, glass softens and hardens gradually, so it is a good plastic material. The viscous glass mass is passed through the slit, resulting in a glass sheet. The hot glass sheet is pulled out with rollers, brought to a certain size and gradually cooled by a current of air. Then it is trimmed along the edges and cut into sheets of a certain format.
■ 44. Give the equations for the reactions that occur during the production of glass and the composition of window glass.
Glass- the substance is amorphous, transparent, practically insoluble in water, but if it is crushed into fine dust and mixed with a small amount of water, an alkali can be detected in the resulting mixture with the help of phenolphthalein. When storing alkalis in glass containers for a long time, excess SiO2 in the glass reacts very slowly with the alkali and the glass gradually loses its transparency.
Glass became known to people more than 3000 BC. In ancient times, glass was obtained with almost the same composition as today, but the ancient masters were guided only by their own intuition. In 1750, M.V. was able to develop the scientific basis for producing glass. Over the course of 4 years, M.V. collected many recipes for making various glasses, especially colored ones. The glass factory he built produced a large number of glass samples that have survived to this day. Currently, glasses of different compositions with different properties are used.
Quartz glass consists of almost pure silicon dioxide and is melted from rock crystal. Its very important feature is that its expansion coefficient is insignificant, almost 15 times less than that of ordinary glass. Dishes made from such glass can be heated red-hot in the flame of a burner and then lowered into cold water; in this case, no changes will occur to the glass. Quartz glass does not block ultraviolet rays, and if you paint it black with nickel salts, it will block all visible rays of the spectrum, but will remain transparent to ultraviolet rays.
Quartz glass is not affected by acids and alkalis, but alkalis noticeably corrode it. Quartz glass is more fragile than regular glass. Laboratory glass contains about 70% SiO2, 9% Na2O, 5% K2O, 8% CaO, 5% Al2O3, 3% B2O3 (the composition of the glasses is not given for memorization purposes).
Jena and Pyrex glass are used in industry. Jena glass contains about 65% Si02, 15% B2O3, 12% BaO, 4% ZnO, 4% Al2O3. It is durable, resistant to mechanical stress, has a low expansion coefficient, and is resistant to alkalis.
Pyrex glass contains 81% SiO2, 12% B2O3, 4% Na2O, 2% Al2O3, 0.5% As2O3, 0.2% K2O, 0.3% CaO. It has the same properties as Jena glass, but to an even greater extent, especially after tempering, but is less resistant to alkalis. Pyrex glass is used to make household items that are exposed to heat, as well as parts of some industrial installations that operate at low and high temperatures.
Certain additives give different qualities to glass. For example, admixtures of vanadium oxides produce glass that completely blocks ultraviolet rays.
Glass painted in various colors is also produced. M.V. also produced several thousand samples of colored glass of different colors and shades for his mosaic paintings. Currently, glass painting methods have been developed in detail. Manganese compounds color glass violet, cobalt compounds blue. , dispersed in the glass mass in the form of colloidal particles, gives it a ruby color, etc. Lead compounds give the glass a shine similar to that of rock crystal, which is why it is called crystal. This type of glass can be easily processed and cut. Products made from it refract light very beautifully. By coloring this glass with various additives, colored crystal glass is obtained.
If molten glass is mixed with substances that, when decomposed, form a large amount of gases, the latter, when released, foam the glass, forming foam glass. This glass is very light, can be processed well, and is an excellent electrical and thermal insulator. It was first obtained by Prof. I. I. Kitaygorodsky.
By pulling threads from glass, you can get so-called fiberglass. If you impregnate fiberglass laid in layers with synthetic resins, you get a very durable, rot-resistant, easily processed building material, the so-called fiberglass laminate. Interestingly, the thinner the fiberglass, the higher its strength. Fiberglass is also used to make workwear.
Glass wool is a valuable material through which strong acids and alkalis can be filtered that cannot be filtered through paper. In addition, glass wool is a good thermal insulator.
■ 44. What determines the properties of different types of glass?
Ceramics
Of the aluminosilicates, white clay is especially important - kaolin, which is the basis for the production of porcelain and earthenware. Porcelain production is an extremely ancient industry. The birthplace of porcelain is China. In Russia, porcelain was produced for the first time in the 18th century. D, I. Vinogradov.
The raw materials for producing porcelain and earthenware, in addition to kaolin, are sand and. A mixture of kaolin, sand and water is subjected to thorough fine grinding in ball mills, then excess water is filtered out and the well-mixed plastic mass is sent for molding of products. After molding, the products are dried and fired in continuous tunnel kilns, where they are first heated, then fired and finally cooled. After this, the products undergo further processing - glazing and painting with ceramic paints. After each stage, the products are fired. The result is porcelain that is white, smooth and shiny. In thin layers it shines through. Earthenware is porous and does not shine through.
Red clay is used to make bricks, tiles, pottery, ceramic rings for attachment in absorption and washing towers of various chemical industries, and flower pots. They are also fired so that they are not softened by water and become mechanically strong.
Cement. Concrete
Silicon compounds serve as the basis for the production of cement, a binding material indispensable in construction. The raw materials for producing cement are clay and limestone. This mixture is fired in a huge inclined tubular rotary kiln into which raw materials are continuously fed. After firing at 1200-1300°, a sintered mass - clinker - continuously emerges from a hole located at the other end of the kiln. After grinding, clinker turns into. The composition of cement consists mainly of silicates. If mixed with water to form a thick slurry and then left in the air for some time, it will react with cement substances, forming crystalline hydrates and other solid compounds, which leads to hardening (“setting”) of the cement. Such
Silicon
SILICON-I; m.[from Greek krēmnos - cliff, rock] Chemical element (Si), dark gray crystals with a metallic sheen are found in most rocks.
◁ Silicon, oh, oh. K salts. Siliceous (see 2.K.; 1 mark).
silicon(lat. Silicium), chemical element of group IV of the periodic table. Dark gray crystals with a metallic luster; density 2.33 g/cm 3, t pl 1415ºC. Resistant to chemical influences. It makes up 27.6% of the mass of the earth's crust (2nd place among elements), the main minerals are silica and silicates. One of the most important semiconductor materials (transistors, thermistors, photocells). An integral part of many steels and other alloys (increases mechanical strength and corrosion resistance, improves casting properties).
SILICONSILICON (lat. Silicium from silex - flint), Si (read “silicium”, but nowadays quite often as “si”), chemical element with atomic number 14, atomic mass 28.0855. The Russian name comes from the Greek kremnos - cliff, mountain.
Natural silicon consists of a mixture of three stable nuclides (cm. NUCLIDE) with mass numbers 28 (prevails in the mixture, it contains 92.27% by mass), 29 (4.68%) and 30 (3.05%). Configuration of the outer electronic layer of a neutral unexcited silicon atom 3 s 2
R 2
. In compounds it usually exhibits an oxidation state of +4 (valency IV) and very rarely +3, +2 and +1 (valency III, II and I, respectively). In the periodic table of Mendeleev, silicon is located in group IVA (in the carbon group), in the third period.
The radius of a neutral silicon atom is 0.133 nm. The sequential ionization energies of the silicon atom are 8.1517, 16.342, 33.46 and 45.13 eV, and the electron affinity is 1.22 eV. The radius of the Si 4+ ion with a coordination number of 4 (the most common in the case of silicon) is 0.040 nm, with a coordination number of 6 - 0.054 nm. According to the Pauling scale, the electronegativity of silicon is 1.9. Although silicon is usually classified as a non-metal, in a number of properties it occupies an intermediate position between metals and non-metals.
In free form - brown powder or light gray compact material with a metallic sheen.
History of discovery
Silicon compounds have been known to man since time immemorial. But man became acquainted with the simple substance silicon only about 200 years ago. In fact, the first researchers to obtain silicon were the French J. L. Gay-Lussac (cm. GAY LUSSAC Joseph Louis) and L. J. Tenard (cm. TENAR Louis Jacques). They discovered in 1811 that heating silicon fluoride with potassium metal leads to the formation of a brown-brown substance:
SiF 4 + 4K = Si + 4KF, however, the researchers themselves did not draw the correct conclusion about obtaining a new simple substance. The honor of discovering a new element belongs to the Swedish chemist J. Berzelius (cm. BERZELIUS Jens Jacob), who also heated a compound of composition K 2 SiF 6 with potassium metal to produce silicon. He obtained the same amorphous powder as the French chemists, and in 1824 announced a new elemental substance, which he called “silicon.” Crystalline silicon was obtained only in 1854 by the French chemist A. E. Sainte-Clair Deville (cm. SAINT-CLAIR DEVILLE Henri Etienne) .
Being in nature
In terms of abundance in the earth's crust, silicon ranks second among all elements (after oxygen). Silicon accounts for 27.7% of the mass of the earth's crust. Silicon is a component of several hundred different natural silicates (cm. SILICATES) and aluminosilicates (cm. ALUMINUM SILICATES). Silica, or silicon dioxide, is also widespread (cm. SILICON DIOXIDE) SiO 2 (river sand (cm. SAND), quartz (cm. QUARTZ), flint (cm. FLINT) etc.), constituting about 12% of the earth's crust (by mass). Silicon does not occur in free form in nature.
Receipt
In industry, silicon is produced by reducing the SiO 2 melt with coke at a temperature of about 1800°C in arc furnaces. The purity of the silicon obtained in this way is about 99.9%. Since silicon of higher purity is needed for practical use, the resulting silicon is chlorinated. Compounds of the composition SiCl 4 and SiCl 3 H are formed. These chlorides are further purified in various ways from impurities and at the final stage they are reduced with pure hydrogen. It is also possible to purify silicon by first obtaining magnesium silicide Mg 2 Si. Next, volatile monosilane SiH 4 is obtained from magnesium silicide using hydrochloric or acetic acids. Monosilane is further purified by rectification, sorption and other methods, and then decomposed into silicon and hydrogen at a temperature of about 1000°C. The impurity content in silicon obtained by these methods is reduced to 10 -8 -10 -6% by weight.
Physical and chemical properties
Crystal lattice of silicon face-centered cubic diamond type, parameter a = 0.54307 nm (other polymorphic modifications of silicon have been obtained at high pressures), but due to the longer bond length between Si-Si atoms compared to the length of the C-C bond, the hardness of silicon is significantly less than that of diamond.
Silicon density is 2.33 kg/dm3. Melting point 1410°C, boiling point 2355°C. Silicon is fragile, only when heated above 800°C does it become a plastic substance. Interestingly, silicon is transparent to infrared (IR) radiation.
Elemental silicon is a typical semiconductor (cm. SEMICONDUCTORS). The band gap at room temperature is 1.09 eV. The concentration of current carriers in silicon with intrinsic conductivity at room temperature is 1.5·10 16 m -3. The electrical properties of crystalline silicon are greatly influenced by the microimpurities it contains. To obtain silicon single crystals with hole conductivity, additives of group III elements - boron - are introduced into silicon. (cm. BOR (chemical element)), aluminum (cm. ALUMINUM), gallium (cm. GALLIUM) and India (cm. INDIUM), with electronic conductivity - additions of elements of group V - phosphorus (cm. PHOSPHORUS), arsenic (cm. ARSENIC) or antimony (cm. ANTIMONY). The electrical properties of silicon can be varied by changing the processing conditions of single crystals, in particular, by treating the silicon surface with various chemical agents.
Chemically, silicon is inactive. At room temperature it reacts only with fluorine gas, resulting in the formation of volatile silicon tetrafluoride SiF 4 . When heated to a temperature of 400-500°C, silicon reacts with oxygen to form dioxide SiO 2, with chlorine, bromine and iodine to form the corresponding highly volatile tetrahalides SiHal 4.
Silicon does not react directly with hydrogen; silicon compounds with hydrogen are silanes (cm. SILANS) with the general formula Si n H 2n+2 - obtained indirectly. Monosilane SiH 4 (often called simply silane) is released when metal silicides react with acid solutions, for example:
Ca 2 Si + 4HCl = 2CaCl 2 + SiH 4
The silane SiH 4 formed in this reaction contains an admixture of other silanes, in particular, disilane Si 2 H 6 and trisilane Si 3 H 8, in which there is a chain of silicon atoms interconnected by single bonds (-Si-Si-Si-) .
With nitrogen, silicon at a temperature of about 1000°C forms the nitride Si 3 N 4, with boron - the thermally and chemically stable borides SiB 3, SiB 6 and SiB 12. A compound of silicon and its closest analogue according to the periodic table - carbon - silicon carbide SiC (carborundum (cm. CARBORUNDUM)) is characterized by high hardness and low chemical reactivity. Carborundum is widely used as an abrasive material.
When silicon is heated with metals, silicides form (cm. SILICIDES). Silicides can be divided into two groups: ionic-covalent (silicides of alkali, alkaline earth metals and magnesium such as Ca 2 Si, Mg 2 Si, etc.) and metal-like (silicides of transition metals). Silicides of active metals decompose under the influence of acids; silicides of transition metals are chemically stable and do not decompose under the influence of acids. Metal-like silicides have high melting points (up to 2000°C). The most commonly formed metal-like silicides are the compositions MSi, M 3 Si 2, M 2 Si 3, M 5 Si 3 and MSi 2. Metal-like silicides are chemically inert and resistant to oxygen even at high temperatures.
Silicon dioxide SiO 2 is an acidic oxide that does not react with water. Exists in the form of several polymorphs (quartz (cm. QUARTZ), tridymite, cristobalite, glassy SiO 2). Of these modifications, quartz is of greatest practical importance. Quartz has piezoelectric properties (cm. PIEZOELECTRIC MATERIALS), it is transparent to ultraviolet (UV) radiation. It is characterized by a very low coefficient of thermal expansion, so dishes made from quartz do not crack under temperature changes of up to 1000 degrees.
Quartz is chemically resistant to acids, but reacts with hydrofluoric acid:
SiO 2 + 6HF =H 2 + 2H 2 O
and hydrogen fluoride gas HF:
SiO 2 + 4HF = SiF 4 + 2H 2 O
These two reactions are widely used for glass etching.
When SiO 2 fuses with alkalis and basic oxides, as well as with carbonates of active metals, silicates are formed (cm. SILICATES)- salts of very weak water-insoluble silicic acids that do not have a constant composition (cm. SILICIC ACIDS) general formula xH 2 O ySiO 2 (quite often in the literature they write not very accurately not about silicic acids, but about silicic acid, although in fact they are talking about the same thing). For example, sodium orthosilicate can be obtained:
SiO 2 + 4NaOH = (2Na 2 O) SiO 2 + 2H 2 O,
calcium metasilicate:
SiO 2 + CaO = CaO SiO 2
or mixed calcium and sodium silicate:
Na 2 CO 3 + CaCO 3 + 6SiO 2 = Na 2 O CaO 6SiO 2 + 2CO 2
Window glass is made from Na 2 O·CaO·6SiO 2 silicate.
It should be noted that most silicates do not have a constant composition. Of all the silicates, only sodium and potassium silicates are soluble in water. Solutions of these silicates in water are called soluble glass. Due to hydrolysis, these solutions are characterized by a highly alkaline environment. Hydrolyzed silicates are characterized by the formation of not true, but colloidal solutions. When solutions of sodium or potassium silicates are acidified, a gelatinous white precipitate of hydrated silicic acids precipitates.
The main structural element of both solid silicon dioxide and all silicates is the group, in which the silicon atom Si is surrounded by a tetrahedron of four oxygen atoms O. In this case, each oxygen atom is connected to two silicon atoms. Fragments can be connected to each other in different ways. Among silicates, according to the nature of the connections in their fragments, they are divided into island, chain, ribbon, layered, frame and others.
When SiO 2 is reduced by silicon at high temperatures, silicon monoxide of the composition SiO is formed.
Silicon is characterized by the formation of organosilicon compounds (cm. ORGANOSILONE COMPOUNDS), in which silicon atoms are connected in long chains due to bridging oxygen atoms -O-, and to each silicon atom, in addition to two O atoms, two more organic radicals R 1 and R 2 = CH 3, C 2 H 5, C 6 are attached H 5, CH 2 CH 2 CF 3, etc.
Application
Silicon is used as a semiconductor material. Quartz is used as a piezoelectric, as a material for the manufacture of heat-resistant chemical (quartz) cookware, and UV lamps. Silicates are widely used as building materials. Window glasses are amorphous silicates. Organosilicon materials are characterized by high wear resistance and are widely used in practice as silicone oils, adhesives, rubbers, and varnishes.
Biological role
For some organisms, silicon is an important biogenic element (cm. BIOGENIC ELEMENTS). It is part of the supporting structures in plants and skeletal structures in animals. Silicon is concentrated in large quantities by marine organisms - diatoms. (cm. DIATOM ALGAE), radiolarians (cm. RADIOLARIA), sponges (cm. SPONGS). Human muscle tissue contains (1-2) 10 -2% silicon, bone tissue - 17 10 -4%, blood - 3.9 mg/l. Up to 1 g of silicon enters the human body with food every day.
Silicon compounds are not poisonous. But inhalation of highly dispersed particles of both silicates and silicon dioxide, formed, for example, during blasting operations, when chiseling rocks in mines, during the operation of sandblasting machines, etc., is very dangerous. SiO 2 microparticles that enter the lungs crystallize in them, and the resulting crystals destroy the lung tissue and cause a serious illness - silicosis (cm. SILICOSIS). To prevent this dangerous dust from entering your lungs, you should use a respirator to protect your respiratory system.
encyclopedic Dictionary. 2009 .
Synonyms:See what “silicon” is in other dictionaries:
- (symbol Si), a widespread gray chemical element of group IV of the periodic table, non-metal. It was first isolated by Jens BERZELIUS in 1824. Silicon is found only in compounds such as SILICA (silicon dioxide) or in... ... Scientific and technical encyclopedic dictionary
Silicon- is produced almost exclusively by carbothermal reduction of silica using electric arc furnaces. It is a poor conductor of heat and electricity, harder than glass, usually in the form of a powder or more often shapeless pieces... ... Official terminology
SILICON- chem. element, non-metal, symbol Si (lat. Silicium), at. n. 14, at. m. 28.08; amorphous and crystalline silicon (which is built from the same type of crystals as diamond) are known. Amorphous K. brown powder with cubic structure in highly dispersed... ... Big Polytechnic Encyclopedia
- (Silicium), Si, chemical element of group IV of the periodic system, atomic number 14, atomic mass 28.0855; non-metal, melting point 1415°C. Silicon is the second most abundant element on Earth after oxygen, its content in the earth’s crust is 27.6% by weight.… … Modern encyclopedia
Si (lat. Silicium * a. silicium, silicon; n. Silizium; f. silicium; i. siliseo), chemical. element of group IV periodic. Mendeleev system, at. n. 14, at. m. 28,086. In nature there are 3 stable isotopes 28Si (92.27), 29Si (4.68%), 30Si (3 ... Geological encyclopedia
