When connecting 28 g of silicon with oxygen. Silicon oxygen compounds
Silicon.General characteristic. The main difference from carbon: the absence of p bonds in compounds. Silicides. Compounds with hydrogen (silanes), oxidation and hydrolysis. Tetrafluoride and silicon tetrachloride, hydrolysis. Hexafluorosilicates. Oxygen compounds. Silicon oxide (IV). Silica gel. Kremnev. acid. Silicates. Solubility and hydrolysis. Natural silicates and aluminosilicates, zeolites. Organosilicon compounds. Silicones and siloxanes. Use of silicon compounds in medicine.
Silicon (lat. Silicium), Si, chemical element of Group IV of the Periodic System; atomic number 14, atomic mass 28.086. Silicon also exhibits sp3 hybridization of electronic
orbitals. On the outer electron layer of the silicon atom there are valence 3d-
orbitals (Si: 3s23p23d0),
Silicon after oxygen is the most common element in the crust. Unlike carbon in a free state, silicon is not found in nature. Its most common compounds are silicon oxide (IV) SiO2 and silicic acid salts, silicates. They form the shell of the earth's crust. Silicon compounds are found in plants and animals. By chemical properties, silicon, like carbon, is a non-metal, but its non-metallicity is less pronounced, since it has a larger atomic radius
Silicon. forms compounds with almost all metals - with icicides (not found compounds only with Bi, Tl, Pb, Hg). More than 250 silicides were obtained, whose composition (MeSi, MeSi2, Me5Si3, Me3Si, Me2Si, etc.) usually does not correspond to classical valencies. Silicides differ in refractoriness and hardness; ferrosilicon (reducing agent in the smelting of special alloys, see Ferroalloys) and molybdenum silicide MoSi2 (heaters of electric furnaces, gas turbine blades, etc.) are of the greatest practical importance.
Silane Under the action of hydrochloric acid on silicides, the simplest hydrogen compound of silicon is silane SiH4:
Silane is a poisonous gas with an unpleasant odor that ignites spontaneously. the air
They are reactive and are strong reducing agents.
react with water at room temperature:
SiH4 + 2H2O → SiO2 + 4H2 ,:
Tetrafluoride Silicon is produced by fluorination of silicon dioxide with elemental fluorine.
The process of fluorination is carried out in two stages in a flame reactor, directing the excess of elemental fluorine from the 1st stage to the 2nd stage.
The technical result is the production of silicon in continuous mode with high yield and product quality.
Silicon tetrafluoride SiF4 is formed by the action of hydrofluoric (hydrofluoric) acid on glass:
Na2SiO3 + 6HF ® 2NaF + SiF4 + 3H2O
Silicon oxygen compounds
The most important oxygen compound of silicon is silicon dioxide SiO2 (silica), which has several crystalline modifications.
The low-temperature modification (up to 1143 K) is called quartz. Quartz has piezoelectric properties. Natural varieties of quartz: rock crystal, topaz, amethyst. The varieties of silica are chalcedony, opal, agate ,. jasper, sand.
Silica is chemically resistant; it is affected only by fluorine, hydrofluoric acid and alkali solutions. It easily goes into a glassy state (quartz glass). Quartz glass is brittle, very chemically and thermally resistant. The corresponding SiO2 silicic acid does not have a specific composition. Typically, silicic acid is recorded as xH2O-ySiO2. Silicic acids were selected: H2SiO3 (H2O-SiO2) - meta-silicon (three-oxo-silicon), H4Si04 (2H20-Si02) - ortho-silicon (tetra-oxo-silicon), H2Si2O5 (H2O * SiO2) - dimethic silicon.
Silicic acids are poorly soluble substances. In accordance with the less metalloid nature of silicon as compared to carbon, H2SiO3 as an electrolyte is weaker than H2CO3.
Corresponding to silicic acids salts-silicates in water are insoluble (except alkali metal silicates). Soluble silicates are hydrolyzed by the equation
2SiO3 - + H20 = Si2O52- + 20H-.
Concentrated solutions of soluble silicates are called liquid glass. The usual window glass silicate of sodium and calcium has a composition of Na20-CaO-6Si02. It is obtained by reaction
A wide variety of silicates (more precisely, oxosilicates) is known. A certain regularity is observed in the structure of oxosilicates: all consist of Si04 tetrahedra, which are connected to each other through an oxygen atom. The most common combinations of tetrahedra are (Si2O76-), (Si3O9) 6-, (Si40l2) 8-, (Si6O1812-), which, as structural units, can be combined into chains, ribbons, nets and skeletons (Fig. 4).
The most important natural silicates are, for example, talc (3MgO * H20-4Si02) and asbestos (SmgO * H2O * SiO2). As with SiO2, the glassy (amorphous) state is characteristic of silicates. With the controlled crystallization of glass, it is possible to obtain a fine-crystalline state (sitalls). Sitalls are characterized by increased strength.
In addition to silicates, aluminosilicates are widespread in nature. Aluminosilicates - frame oxosilicates, in which a part of silicon atoms is replaced by trivalent Al; eg Na12 [(Si, Al) 04] 12.
For the silicic acid, a colloidal state is characteristic when the salts of the acid H2SiO3 are not affected immediately. Colloidal solutions of silicic acid (sols) under certain conditions (for example, when heated) can be converted into a transparent, homogeneous gel-like mass-gel of silicic acid. Gels are high-molecular compounds with a spatial, very loose structure formed by SiO2 molecules, the voids of which are filled with H2O molecules. When dehydrating silica gel, silica gel is obtained - a porous product with high adsorption capacity.
Silicon oxide (IV) (silica) - the most common compound in the earth's crust, making up 12% of its mass in the form of various minerals. Distinguish between crystalline and amorphous silica. The simplest formula for silicon oxide (IV) is SiO2. It crystallizes in the atomic lattice.
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 the opal mineral composition SiO2 nH2O; 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:
Na2SiO3 + 2HCl = 2NaCl + H2SiO3
Silica gel has a developed surface that is why it absorbs moisture well.
Silica gel is a dried gel formed from supersaturated solutions of silicic acid (nSiO2 · mH2O) at pH\u003e 5-6. Solid hydrophilic sorbent.
Getting
It is obtained by acidification of alkali metal silicate solutions, followed by washing and drying the gel formed:
Silicic acid. SiO2 is the anhydride of a number of silicic acids
Silicic acid is built from tetrahedral structural units (in each such unit, the silicon atom is in the center of the tetrahedron, and there are oxygen atoms in the tops). Structural links, uniting in chains, form more stable polysilicon acids:
The composition of such a compound can be expressed by the formula (H2SiO3) n. However, silicic acid is usually represented by the formula H2SiO3. H2SiO3 - the acid is very weak, little soluble in water. When heated, it easily decomposes in the same way as carbonic acid:
All silicic acids are very weak (weaker than coal).
Silicates. Salts of all silicic acids are called silicates, although, as a rule, in educational literature, silicates imply salts of metacrystalline acid. Their composition is usually represented by the formula in the form of compounds of oxides of elements. For example, calcium silicate CaSiO3 can be expressed as: CaO × SiO2.
The silicates of composition R2O × nSiO2, where R2O is sodium or potassium oxides, are called soluble glass, and their concentrated aqueous solutions are called liquid glass. The most important is sodium soluble glass.
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 SiO32-.
Silicates are obtained by fusing silica with alkalis or carbonates:
Silicic acid solubility and the rate of its dissolution depends on several factors, of which the most important are the modification of silicon dioxide taken, its degree of dispersion, and temperature. When shaking silica gel with water, the solubility equilibrium is established in a few hours; in the case of quartz, many months and even years are needed.
NATURAL SILICATES (from the Latin. silex, genus. case of silicis - flint * a. natural silicates; N. naturliche Silikate; F. silicates naturels; and. silicatos naturales) - a class of minerals, salts of silicic, iso- and heteropolycrystalline acids. The share of natural silicates accounts for up to 75% of the mass of the earth's crust and about 25% of mineral species. In nature, more than 700 natural silicates are known, including the most important rock-forming minerals (feldspars, pyroxenes, amphiboles, micas, etc.)
Aluminosilicates - a group of natural and synthetic silicates, the complex anions of which contain silicon and aluminum. Examples of complex anions: -, -, 2 -. Na +, K +, Mg2 +, Ca2 +, and sometimes Ba2 + and Li + act as cations.
Natural aluminosilicates are the most common minerals, they account for up to 50% of the mass of the earth's crust. These include feldspars (albite, orthoclase, anortite), clay minerals and mica.
Zeolites - These are aqueous aluminosilicates of calcium, sodium, potassium, barium and some other elements. The group of zeolites includes more than forty minerals, which differ in composition (especially in the number of water molecules in the crystalline hydrate), and of course in physical and chemical properties. But almost all representatives of this group of minerals have a common feature - they are good sorbents, possess ion-exchange properties, are able to change the mobility of individual ions and work as molecular sieves. And relatively recently, these minerals have found a completely unexpected use - they began to be used in agriculture.
Organosilicon compounds - compounds in whose molecules there is a bond between silicon and carbon atoms. Organosilicon compounds are sometimes called silicones, from the Latin silicon name "silicon". Organosilicon compounds are used to produce lubricants, polymers, rubbers, rubbers, silicone fluids and emulsions. Organosilicon compounds are used in cosmetics, household chemicals, paints and varnishes, detergents. A distinctive feature of products based on organosilicon compounds from products based on common organic compounds are, as a rule, higher performance characteristics and characteristics, as well as the safety of human use. Silicone polymers can be used to make molds in cooking. Polymerization of organosilicon compounds and sealants is safe for humans and does not require extraction.
Siloxanes - compounds containing alternating silicon and oxygen atoms in a molecule. The highest have high molecular weight siloxanes - polyorganosiloxanes; see Silicone polymers.
Silicones (polyorganosiloxanes) - oxygenated high molecular weight organosilicon compounds with the chemical formula n, where R = organic group (methyl, ethyl or phenyl). Now this definition is extremely rarely adhered to, and polyorganosiloxanes (for example, PMS type silicone oils, NGL type water repellents or low molecular weight SKTN rubbers) and even organosilicon monomers (various silanes) are also combined into "silicones", erasing the distinction between "silicones" and " silicone. "
Metallic silicon 
Crystal Silicon
Silicon (Si). This chemical element is 1/4 of the composition of the earth's crust. Quartz, rock crystal, sand, clay, granite, mica, asbestos - all this chemical compounds of silicon
Silicon is an intermediate element (amphoteric) and can exhibit both metallic and non-metallic properties. It can form chemical compounds, both with metals and non-metals.
Pure silicon - a chemically simple substance of gray color, hard, refractory and brittle. Crystal Silicon It has a metallic luster and is widely used in the semiconductor industry (it is a semiconductor).
Silicon can stretch like in a crystalline state ( crystalline silicon), and in the amorphous state ( amorphous silicon). Crystalline silicon is formed by cooling a solution of amorphous silicon in a molten metal. In turn, crystalline silicon is a very brittle material and is easily crushed into an amorphous powder. Thus, amorphous silicon is a fragment of crystals of crystalline silicon.
In the free state, silicon is quite difficult to obtain. Its industrial production is associated with the recovery of quartz, whose chemical formula is SiO 2, the reduction reaction is produced by hot coke (carbon).
SiO 2 + C → CO 2 + Si
In the laboratory, pure silicon is reduced from silica sand with metallic magnesium using the following reaction:
SiO 2 + 2Mg → Si + 2MgO.
During this reaction, a brown powder of amorphous silicon is formed. When heated, the powder can slowly react with concentrated solutions of alkalis (for example, sodium hydroxide NaOH)
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2, - the resulting complex substance - also called liquid glass.
It is interesting that the chemical activity of silicon depends on the size of its crystals. Co-crystalline silicon is less chemically active than amorphous. The latter reacts easily with fluorine even at ordinary temperature, and at a temperature of 400 - 600 0 C it reacts with oxygen, chlorine, bromine, sulfur to form the corresponding chemical compounds. At very high temperatures, silicon reacts with nitrogen and carbon to form, respectively, nitride and silicon carbide.
If you try to dissolve silicon in a mixture of hydrofluoric HF (hydrofluoric) and nitric HNO 3 acids, then the reaction will not proceed. But if you conduct a chemical reaction with an alkali, for example, with potassium hydroxide, then the reaction will take place with the formation of a salt of silicic acid
Si + KOH → K 2 SiO 3 + H 2
If calcined in the furnace silica (sand) with coke, it turns out a very solid crystalline substance. Carborundum SiC
SiO 2 + 3C → SiC + 2CO
Carborundum - very hard and refractory substance. In industry, it is produced in large quantities due to these properties. Interestingly, the carborundum crystal lattice is similar to the lattice of the hardest substance - diamond, but in it individual carbon atoms are uniformly replaced by silicon atoms.
At high temperatures, as well as during chemical reactions under the action of acids on metal compounds with silicon, silane SiH 4.
Silane - it is a self-igniting colorless gas. It can ignite in air to form silica and water.
SiH 4 + 2O 2\u003e → SiO 2 + 2H 2 O
If silicon oxide SiO 2 is heated in the presence of carbon in a stream of chlorine, a chemical reaction takes place with the formation of silicon chloride
SiO 2 + 2C + 2 Cl 2 → SiCl 4 + 2CO
Silicon chloride - it is a liquid, the boiling temperature of which is only 54 0 C. Silicon chloride is easily dissolved in water with the formation of a solution of two acids: silicic and hydrochloric
SiCl 4 + H 2 O → H 2 SiO 3 + HCl
If this chemical reaction proceeds in an atmosphere of humid air, thick smoke will appear during the formation of two acids.
Silicon fluoride SiF 4 - formed as a result of a chemical reaction of hydrofluoric acid and silicon oxide
SiO 2 + 4HF → SiF 4 + 2H 2 O
Silicon fluoride is a colorless gas with a "strong" odor. As well as silicon chloride, in water this gas forms two acids: silicon and hydrofluoric. But interestingly, silicon fluoride can interact with hydrofluoric acid to form hexafluorosilicic acid whose chemical formula is H 2 SiF 6. Its salts and the acid itself are poisonous.
Silicon
Base metals and non-metals
In this lesson you will study the topic of "Silicon". Consider information about silicon: its electronic structure, where silicon is in nature, study silicon allotropy, explain its physical and chemical properties. Learn where silicon is used in industry and other areas, how it is produced. You will get acquainted with silica, silicic acid and its salts - silicates.
Topic: Base 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 the form of various forms of silicon dioxide, silicates and aluminosilicates.
Silicon is tetravalent in almost all of its compounds. In this case, the silicon atoms are in the excited state. Fig. one.
To go into this state, one of the 3s electrons occupies a vacant place on the 3p orbitals. In this case, instead of 2 unpaired electrons in the ground state, the silicon atom in the excited state will have 4 unpaired electrons. He will be able to form 4 covalent bonds by the exchange mechanism.
Silicon atoms are not prone to the formation of multiple bonds, but form compounds with single bonds-Si-O-. Silicon, unlike carbon, is not typical of allotropy.
One of allotropic modification is crystalline siliconin which each silicon atom is in sp 3 hybridization. Fig. 2, 3. Crystalline silicon is a solid, refractory and durable crystalline substance of dark gray with a metallic luster. Under normal conditions - a semiconductor. Sometimes, amorphous silicon is also emitted as another allotropic modification of silicon. It is a dark brown powder, more chemically active than crystalline silicon. Whether it is an allotropic modification is a moot point.
Chemical properties of silicon
1. Interaction with halogens
Si + 2F 2 → SiF 4
2. When heated, silicon burns in oxygen, silica (IV) is formed.
Si + O 2 → SiO 2
3. At high temperatures, silicon interacts 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 directly interact with hydrogen, but hydrogen compounds of silicon can be obtained by the interaction of silicides with water.
Mg 2 Si + 4H 2 O → 2Mg (OH) 2 + SiH 4 (silane)
Silanes are similar in structure to alkanes, but are considerably reactive. The most stable monosilane is flammable in air.
SiH 4 + 2 O 2 → SiO 2 + 2H 2 O
Getting silicon
Silicon is obtained by reduction from silicon oxide (IV)
SiO 2 + 2Mg → Si + 2MgO
One of the tasks is to obtain high-purity silicon. For this purpose, technical silicon is transferred to silicon tetrachloride. The resulting tetrachloride is reduced to silane, and silane decomposes into silicon and hydrogen when heated.
Silicon is able to form two oxides: SiO 2 - silicon oxide (IV) and SiO - silicon oxide (II).
SiO - silicon oxide (II) - this is an amorphous dark brown substance, which is formed by the interaction of silicon with silicon oxide (IV)
Si + Sio 2 → 2 Sio.
Despite its stability, this substance is almost never used.
SiO 2 - silicon oxide (IV)
This substance accounts for 12% of the earth's crust. Fig. 4. It is represented by such minerals as rock crystal, quartz, amethyst, citrine, jasper, chalcedony. Fig. five.
SiO 2 - silicon oxide (IV) - a substance of non-molecular structure.
Its crystal lattice is atomic. Fig. 6. SiO 2 crystals have the form of a tetrahedron, which are interconnected by oxygen atoms. The formula of the (SiO 2) n molecule would be more correct. Since SiO 2 forms a substance of atomic structure, and CO 2 - of a 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 propertiesSiAbout 2
1. Silicon oxide (IV) SiO 2 is an acid oxide. It does not react with water. Silicic acid cannot be obtained by the 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
SiF 4 + 2HF → H 2
Chemical properties of silicic acid and silicates
Getting silicic acid
Silicic acid precipitates as a polymeric compound. Silicic Acid Formulas -
H 2 SiO 3 (meta form) and H 4 SiO 4 (ortho form) - reflect the ratio of the elements, but not the true composition. Conventionally, on the plane, the composition of silicic acid is depicted as Fig. 7
For silicic acid, the formula H 2 SiO 3 is always used.
1. H 2 Sio 3 decomposes when heated
H 2 SiO 3 H 2 O + SiO 2 (silica gel)
2. Interacts with alkali solutions
H 2 SiO 3 + 2NaOH Na 2 SiO 3 + 2H 2 O
Silicic acid salts - silicates - refer to ionic compounds. These are solid colorless substances. Only alkali metal silicates, except lithium, are soluble in water.
1. Soluble silicates are hydrolyzed by anion
Na 2 SiO 3 + H 2 O ⇆ NaHSio 3 + NaOH
2. Soluble silicates interact with strong acids.
Na 2 SiO 3 + 2HCl → H 2 SiO 3 ↓ + 2NaCl
Polyorganosiloxanes (silicones)
Polyorganosiloxanes (silicones) are oxygenated, high molecular weight organosilicon compounds.
R 2 [ Sio] n
R is an organic group (methyl, ethyl or phenyl). The basis of the structure of siloxanes is a chain of alternating silicon atoms and oxygen. Fig.8. By varying the length of the chain and the organic groups, silicones with different properties can be obtained. By changing the conditions of polymerization, you can get molecules of different lengths.
Short chain polymers are liquids, longer ones are valuable lubricants. Fig. 9, which retain their properties in a huge temperature range from
100 0 С to + 300 0 С. Longer molecules form rubbers that do not lose their elasticity at low temperatures. Possess high resistance to attrition, are chemically inert. Fig. 10. It causes various variants of their application. They can be used to create artificial heart or kidney machines, and can be used as shoes for shoes. Siloxane polymers are used in medicine to create various soft tissue implants, since such polymers are chemically inert and are not rejected by the body. They are not moistened with water. It is used in creams. When applying this cream on his hands, he will replace the rubber gloves.
Inorganic Garden
In a transparent beaker filled with sodium silicate, dip the crystals of colored salts, for example, copper sulphate. After some time, it can be seen that thin hollow tubes formed from the crystals, which consist of insoluble silicates. Fig. eleven.
Getting "stupid" putty
Equal volumes of sodium silicate and medical alcohol are mixed. The precipitate is filtered and squeezed out so as not to drip alcohol. This is putty. Fig. 12. It is named so because it was planned to use it as a putty for windows. But it turned out that it has such properties that it could not be used for its intended purpose. If you roll the ball and throw it on the floor, it will bounce off like a rubber ball. If put on the table, it will spread like a liquid. If you hit a solid object, it will shatter like a solid body. After a while, when the alcohol dries, this putty will just crumble.
Summing up the lesson
In this lesson, you have studied the topic "Silicon." We examined information about silicon: its electronic structure, where silicon is located in nature, studied the allotropy of silicon, explained its physical and chemical properties. They learned about where silicon is used in industry and other areas, how it is produced. You met with silica, silicic acid and its salts - silicates.
Bibliography
1. Rudzitis G.E. Chemistry. Basics of general chemistry. Grade 11: textbook for educational institutions: basic level / G.E. Rudzitis, F.G. Feldman. - 14th ed. - M .: Enlightenment, 2012.
2. Popel P.P. Chemistry: 8 cl. Textbook for secondary schools / PP. Popel, L.S. - К .: ИЦ "Academy", 2008. - 240 p.: Ill.
3. Gabrielyan O.S. Chemistry. Grade 11. A basic level of. 2nd ed., Sr. - M .: Drofa, 2007. - 220 p.
Homework
1. №№2-4 (p. 138) Rudzitis G.E. Chemistry. Basics of general chemistry. Grade 11: textbook for educational institutions: basic level / G.E. Rudzitis, F.G. Feldman. - 14th ed. - M .: Enlightenment, 2012.
2. What are the applications of polyorganosiloxanes.
3. Compare the properties of allotropic modifications of silicon.