Silicium o 2. Some physicochemical properties of silicon and its compounds. Areas of application of pure silicon. The healing properties of silicon and the causes of deficiency in the body

Silicon(lat. silicium), si, chemical element of group IV of the periodic system of Mendeleev; atomic number 14, atomic mass 28.086. In nature, the element is represented by three stable isotopes: 28 si (92.27%), 29 si (4.68%) and 30 si (3.05%).

Historical reference . K compounds, widespread on earth, have been known to man since the Stone Age. The use of stone tools for labor and hunting continued for several millennia. The use of K compounds associated with their processing - production glass - began around 3000 BC. e. (V Ancient Egypt). The earliest known compound of K. is dioxide sio 2 (silica). In the 18th century silica was considered a simple body and referred to as “earths” (as reflected in its name). The complexity of the composition of silica was established by I. Ya. Berzelius. For the first time, in 1825, he obtained elemental calcium from silicon fluoride sif 4, reducing the latter with potassium metal. The new element was given the name “silicon” (from the Latin silex - flint). The Russian name was introduced by G.I. Hess in 1834.

Prevalence in nature . In terms of prevalence in the earth's crust, oxygen is the second element (after oxygen), its average content in the lithosphere is 29.5% (by mass). In the earth's crust, carbon plays the same primary role as carbon in animals and flora. For the geochemistry of oxygen, its extremely strong connection with oxygen is important. About 12% of the lithosphere is silica sio 2 in mineral form quartz and its varieties. 75% of the lithosphere consists of various silicates And aluminosilicates(feldspars, micas, amphiboles, etc.). The total number of minerals containing silica exceeds 400 .

During magmatic processes, weak differentiation of calcium occurs: it accumulates both in granitoids (32.3%) and in ultrabasic rocks (19%). At high temperatures and high pressure, the solubility of sio 2 increases. Its migration with water vapor is also possible, therefore pegmatites of hydrothermal veins are characterized by significant concentrations of quartz, which is often associated with ore elements (gold-quartz, quartz-cassiterite, etc. veins).

Physical and chemical properties. Carbon forms dark gray crystals with a metallic luster, having a face-centered cubic diamond-type lattice with a period a = 5.431 a, and a density of 2.33 g/cm 3 . At very high pressures a new (apparently hexagonal) modification with a density of 2.55 g/cm 3 was obtained. K. melts at 1417°C, boils at 2600°C. Specific heat capacity (at 20-100°C) 800 J/ (kg? K), or 0.191 cal/ (g? deg); thermal conductivity even for the purest samples is not constant and is in the range (25°C) 84-126 W/ (m? K), or 0.20-0.30 cal/ (cm? sec? deg). Temperature coefficient linear expansion 2.33? 10 -6 K -1 ; below 120k it becomes negative. K. is transparent to long-wave infrared rays; refractive index (for l =6 µm) 3.42; dielectric constant 11.7. K. diamagnetic, atomic magnetic susceptibility -0.13? 10 -6. K. hardness according to Mohs 7.0, according to Brinell 2.4 Gn/m2 (240 kgf/mm2), elastic modulus 109 Gn/m2 (10890 kgf/mm2), compressibility coefficient 0.325? 10 -6 cm 2 /kg. K. brittle material; noticeable plastic deformation begins at temperatures above 800°C.

K. is a semiconductor that is finding increasing use. The electrical properties of copper are very dependent on impurities. Own specific volumetric electrical resistivity of a coil at room temperature is taken equal to 2.3? 10 3 ohm? m(2,3 ? 10 5 ohm? cm) .

Semiconductor circuit with conductivity R-type (additives B, al, in or ga) and n-type (additives P, bi, as or sb) has significantly lower resistance. The band gap according to electrical measurements is 1.21 ev at 0 TO and decreases to 1.119 ev at 300 TO.

In accordance with the position of the ring in the periodic table of Mendeleev, the 14 electrons of the ring atom are distributed over three shells: in the first (from the nucleus) 2 electrons, in the second 8, in the third (valence) 4; electron shell configuration 1s 2 2s 2 2p 6 3s 2 3p 2. Successive ionization potentials ( ev): 8.149; 16.34; 33.46 and 45.13. Atomic radius 1.33 a, covalent radius 1.17 a, ionic radii si 4+ 0.39 a, si 4- 1.98 a.

In carbon compounds (similar to carbon) 4-valentene. However, unlike carbon, silica, along with a coordination number of 4, exhibits a coordination number of 6, which is explained by the large volume of its atom (an example of such compounds are silicofluorides containing the 2- group).

The chemical bond of a carbon atom with other atoms is usually carried out due to hybrid sp 3 orbitals, but it is also possible to involve two of its five (vacant) 3 d- orbitals, especially when K. is six-coordinate. Having a low electronegativity value of 1.8 (versus 2.5 for carbon; 3.0 for nitrogen, etc.), carbon is electropositive in compounds with nonmetals, and these compounds are polar in nature. High binding energy with oxygen si-o, equal to 464 kJ/mol(111 kcal/mol) , determines the stability of its oxygen compounds (sio 2 and silicates). Si-si binding energy is low, 176 kJ/mol (42 kcal/mol) ; Unlike carbon, carbon is not characterized by the formation of long chains and double bonds between si atoms. In air, due to the formation of a protective oxide film, carbon is stable even at elevated temperatures. In oxygen it oxidizes starting at 400°C, forming silicon dioxide sio 2. Sio monoxide is also known, stable at high temperatures in the form of a gas; as a result of sudden cooling, a solid product can be obtained that easily decomposes into a thin mixture of si and sio 2. K. is resistant to acids and dissolves only in a mixture of nitric and hydrofluoric acids; easily dissolves in hot alkali solutions with the release of hydrogen. K. reacts with fluorine at room temperature and with other halogens when heated to form compounds general formula six 4 . Hydrogen does not react directly with carbon, and silicas(silanes) are obtained by decomposition of silicides (see below). Hydrogen silicones are known from sih 4 to si 8 h 18 (the composition is similar to saturated hydrocarbons). K. forms 2 groups of oxygen-containing silanes - siloxanes and siloxenes. K reacts with nitrogen at temperatures above 1000°C. Of great practical importance is si 3 n 4 nitride, which does not oxidize in air even at 1200°C, is resistant to acids (except nitric) and alkalis, as well as molten metals and slags, which makes it a valuable material for the chemical industry, for production of refractories, etc. Compounds of carbon with carbon are distinguished by their high hardness, as well as thermal and chemical resistance ( silicon carbide sic) and with boron (sib 3, sib 6, sib 12). When heated, chlorine reacts (in the presence of metal catalysts, such as copper) with organochlorine compounds (for example, ch 3 cl) to form organohalosilanes [for example, si (ch 3) 3 ci], which are used for the synthesis of numerous organosilicon compounds.

K. forms compounds with almost all metals - silicides(connections only with bi, tl, pb, hg were not detected). More than 250 silicides have been obtained, the composition of which (mesi, mesi 2, me 5 si 3, me 3 si, me 2 si, etc.) usually does not correspond to classical valencies. Silicides are refractory and hard; Ferrosilicon and molybdenum silicide mosi 2 are of greatest practical importance (electric furnace heaters, gas turbine blades, etc.).

Receipt and application. K. technical purity (95-98%) is obtained in an electric arc by the reduction of silica sio 2 between graphite electrodes. In connection with the development of semiconductor technology, methods have been developed for obtaining pure and especially pure copper. This requires the preliminary synthesis of the purest starting compounds of copper, from which copper is extracted by reduction or thermal decomposition.

Pure semiconductor copper is obtained in two forms: polycrystalline (by reduction of sici 4 or sihcl 3 with zinc or hydrogen, thermal decomposition of sil 4 and sih 4) and single-crystalline (crucible-free zone melting and “pulling” a single crystal from molten copper - the Czochralski method).

Specially doped copper is widely used as a material for the manufacture of semiconductor devices (transistors, thermistors, power rectifiers, controlled diodes - thyristors; solar photocells used in spacecraft, etc.). Since K. is transparent to rays with wavelengths from 1 to 9 µm, it is used in infrared optics .

K. has diverse and ever-expanding areas of application. In metallurgy, oxygen is used to remove oxygen dissolved in molten metals (deoxidation). K. is a component of a large number of alloys of iron and non-ferrous metals. Usually, carbon gives alloys increased resistance to corrosion, improves their casting properties, and increases mechanical strength; however, with a higher content of K. it can cause fragility. The most important are iron, copper, and aluminum alloys containing calcium. An increasing amount of carbon is used for the synthesis of organosilicon compounds and silicides. Silica and many silicates (clays, feldspars, mica, talc, etc.) are processed by the glass, cement, ceramic, electrical, and other industries.

V. P. Barzakovsky.

Silicon is found in the body in the form of various compounds, mainly involved in the formation of hard skeletal parts and tissues. Some marine plants (for example, diatoms) and animals (for example, siliceous sponges, radiolarians) can accumulate especially large amounts of silicon, forming thick deposits of silicon dioxide on the ocean floor when they die. In cold seas and lakes, biogenic silts enriched in potassium predominate; in tropical seas, calcareous silts with a low content of potassium predominate. Among land plants, cereals, sedges, palms, and horsetails accumulate a lot of potassium. In vertebrates, the content of silicon dioxide in ash substances is 0.1-0.5%. In the largest quantities, K. is found in dense connective tissue, kidneys, and pancreas. The daily human diet contains up to 1 G K. When there is a high content of silicon dioxide dust in the air, it enters the human lungs and causes disease - silicosis.

V. V. Kovalsky.

Lit.: Berezhnoy A.S., Silicon and its binary systems. K., 1958; Krasyuk B. A., Gribov A. I., Semiconductors - germanium and silicon, M., 1961; Renyan V.R., Technology of semiconductor silicon, trans. from English, M., 1969; Sally I.V., Falkevich E.S., Production of semiconductor silicon, M., 1970; Silicon and germanium. Sat. Art., ed. E. S. Falkevich, D. I. Levinzon, V. 1-2, M., 1969-70; Gladyshevsky E.I., Crystal chemistry of silicides and germanides, M., 1971; wolf N. f., silicon semiconductor data, oxf. - n. y., 1965.

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Physical properties. Silicon is fragile. When heated above 800° C, its ductility increases. It is resistant to acids. In an acidic environment, it is covered with an insoluble oxide film and passivated.

The microelement is transparent to infrared radiation, starting at a wavelength of 1.1 microns.

Chemical properties. Silicon interacts:

• with halogens (fluorine) with the manifestation of reducing properties: Si + 2F2 = SiF4. It reacts with hydrogen chloride at 300° C, with hydrogen bromide – at 500° C;
• with chlorine when heated to 400–600° C: Si + 2Cl2 = SiCl4;
• with oxygen when heated to 400–600° C: Si + O2 = SiO2;
• with other non-metals. At a temperature of 2000° C, it reacts with carbon (Si + C = SiC) and boron (Si + 3B = B3Si);
• with nitrogen at a temperature of 1000° C: 3Si + 2N2 = Si3N4;
• with metals to form silicides: 2Ca + Si = Ca2Si;
• with acids - only with a mixture of hydrofluoric and nitric acids: 3Si + 4HNO3 + 18HF = 3H2 + 4NO + 8H2O;
• with alkali. Silicon dissolves and silicate and hydrogen are formed: Si + 2NaOH + H2O = Na2SiO3 + H2.

Does not interact with hydrogen.

Interaction in the body with vitamins and minerals

Silicon interacts with vitamins, and. The combination of cereals with citrus fruits and green vegetables is considered the healthiest.

Silicon is involved in the fight against free radicals. Interacting with heavy metals (lead), the microelement forms stable compounds. They are excreted by the genitourinary system. The same thing happens with waste and toxic substances.

Silicon improves the absorption of iron (Fe) and calcium (Ca), cobalt (Cb), manganese (Mn), fluorine (F).

A decrease in silicon concentration in connective tissue leads to vascular damage, atherosclerosis, and impaired bone tissue strength.

The role of silicon in the occurrence and course of various diseases

With a lack of silicon in the body, the concentration of cholesterol in the blood increases. Because of this, cholesterol plaques form and the outflow worsens.

When consuming silicon less than 20 mg per day, the immune system weakens. Allergic rashes appear, the skin becomes dry and flaky, and fungus develops.

The hair becomes thinner, the scalp becomes flaky and itchy. The nail plates become deformed.

Performance and mental state deteriorate due to impaired blood flow and oxygen saturation of the brain.

When the amount of silicon in the body decreases to 1.2-1.6%, it is fraught with the occurrence of stroke, heart attack, diabetes mellitus, hepatitis virus and oncology.

An excess of silicon leads to the deposition of salts in the urinary tract and joints, fibrosis and pathologies of blood vessels. In the worst-case scenario, the liver enlarges, the limbs swell, the skin turns blue, and shortness of breath appears.

Functional potential of silicon

The main task of silicon in the body is the formation of bone, cartilage tissue and vessel walls. 90% of the mineral is found in connective and bone tissue, lymph nodes, thyroid gland, hair and skin. However, the functional potential of the chemical element is not limited to this. Thanks to silicon:

• bones and ligaments are strengthened. The more minerals there are in the first one, the stronger it is. A decrease in silicon concentration in bone tissue is fraught with osteoporosis and atherosclerosis. For cartilage tissue, the synthesis of glycosaminoglycans is important;
• degeneration of intervertebral discs is prevented. The latter consist of plates of cartilage tissue. The less silicon, the faster the plate wears out. If a crack forms in it, cerebrospinal fluid will begin to leak. This is fraught with protrusions and hernia;
• bone tissue is restored. Bones, ligaments and tendons grow together very difficult and take a long time;
• the condition of the skin, nails and hair improves. They contain the highest concentration of the chemical element. Dry and flaky skin, brittle and dull hair, peeling nails are signs of silicon deficiency;
• metabolism is stabilized. Thanks to silicon, three quarters of 70% of chemical elements are absorbed. The mineral is involved in protein and carbohydrate metabolism;
• immunity is strengthened. Thanks to silicon, phagocytosis is accelerated - the formation of special cells of the immune system. Their main function is the breakdown of foreign protein structures. If a viral infection enters the body, phagocytes envelop the enemy and destroy them;
• Heavy metals and toxins are removed. Silicon oxide reacts with them, converts them into compounds neutral for the body, which are excreted in the urine;
• strengthens the walls of blood vessels, heart valves, and organ linings gastrointestinal tract. The basis of the vascular wall is elastin, which is synthesized with the help of silicon;
• the permeability of vascular walls decreases, signs of varicose veins, thrombophlebitis and vasculitis decrease;
• cancer diseases are prevented. The antioxidant properties of vitamins C, A, E are enhanced when interacting with silicon. It is easier for the body to fight free radicals;
• brain diseases are prevented. With a lack of silicon, the walls of blood vessels become softer, poorly transport blood to the brain, which leads to hypoxia - oxygen starvation, due to which the brain does not function properly. full power. Brain neurons cannot give and receive commands without silicon. As a result, motor skills are impaired, blood vessels constrict, headaches and dizziness occur, and health deteriorates.

Sources of silicon

• brown rice – 1240;
• oatmeal – 1000;
• millet – 754;
• barley – 600;
• soybean – 177;
• buckwheat – 120;
• beans – 92;
• Peas – 83;
• Jerusalem artichoke – 80;
• Corn – 60;
• Hazelnuts – 51;
• Spinach – 42;
• Ryazhenka – 34;
• Parsley – 31;
• Cauliflower – 24;
• Green leaf salad – 18;
• Peach – 10;
• Honeysuckle – 10.

Advice! Do you want to quickly replenish silicon reserves in your body? Forget about meat with side dishes. Meat itself, although it contains a sufficient amount of silicon (30-50 mg per 100 g), interferes with its absorption from other products. Separate nutrition is the opposite. Combine brown rice, barley, millet, millet, buckwheat with vegetables and fruits. Arrange “fasting” days on apricots, pears and cherries

Combination with other nutrients

Avoid combining silicon with aluminum. The action of the latter is opposite to the action of silicon.

Silicon, together with other microelements, participates in chemical reactions in the synthesis of collagen and elastin, which are part of the connective tissue of the skin, hair and nails.

Silicon enhances the antioxidant properties of vitamins C, A, E. The latter fight free radicals that cause cancer.

To prevent cancer, consume the following foods together (described in the table)

Silicon oxide interacts in the body with heavy metals (lead) and toxins. As a result of the chemical reaction, stable compounds are formed, which are excreted from the body by the kidneys.

Daily norm

The daily intake of silicon (given below) is calculated for adults only. The upper permissible level of silicon intake for children and adolescents has not been established.

• Children under 6 months and after 7 months – absent.

• From 1 to 13 years – absent.
• Adolescents (male and female) – absent.
• Adults – 20-50 mg.

When using silicon-containing drugs (Atoxil), the daily dosage in children over 7 years of age and adults is 12 g. The maximum dose of the drug is 24 grams per day. For children from one year to 7 years – 150-200 mg of the drug per kilogram of body weight.

Deficiency and excess of silicon

Silicon deficiency can be caused by:

A lack of silicon in the body is dangerous due to the following conditions:

• high concentration of cholesterol in the blood. Cholesterol clogs blood vessels (zolesterol “plaques” form), the blood becomes more viscous and its outflow worsens;
• predisposition to fungal diseases. The less silicon, the weaker the immune system. When a viral infection enters the body, phagocytes (special cells of the immune system) are produced in insufficient quantities;
• dandruff, hair loss and thinning. The elasticity of hair and skin is the merit of elastin and collagen, which are synthesized thanks to silicon. Its deficiency affects the condition of the skin, hair and nails;
• mood swings. Not only the performance, but also the mental state of a person depends on the saturation of the brain with oxygen. Due to weakened vessel walls, blood flows poorly to the brain. There is not enough oxygen to perform habitual mental operations. Mood swings and deterioration in performance are the result of a lack of silicon. The same thing happens when the weather changes;
• cardiovascular diseases. The reason is the same - weakened vascular walls;
• diabetes mellitus The reason is an increase in the concentration of glucose in the blood and the body’s inability to reduce it.

• from 1.2 to 4.7% – stroke and heart attack;
• 1.4% or less – diabetes mellitus;
• 1.6% or less – hepatitis virus;
• 1.3% - cancer.

Advice! Silicon is involved in all types of exchange. Stored in the walls of blood vessels, the microelement protects them from the penetration of fats into the blood plasma and blocks the bloodstream

Increase the amount of silicon-containing foods in your diet during:

• physical and emotional fatigue. A serving of cereals for breakfast, a large plate of green salad for lunch and a glass of fermented baked milk or kefir before bed guarantee a boost of energy;
• pregnancy and breastfeeding The immunity of the baby and mother depends on the correct diet. 20-50 mg of silicon per day will make bones strong and skin elastic;
• preparation for competitions. The more energy consumption, the more silicon-containing products should be in the diet. They will prevent brittle bones and sprained ligaments and tendons;
• puberty. Pain in the knees (Schlatter's disease) is common. Bone cells divide faster than connective tissue cells. The latter not only maintains the bone in an anatomically correct position, but also protects against mechanical damage. Cranberries, walnuts and pears are great snacks for teenagers.

If the condition of your skin, hair and nails is unsatisfactory, lean on cereals and juices. Grape juice for tomorrow, cranberry juice for lunch and pear juice for dinner is the first step to elastic and tightened skin.

What are the dangers of excess silicon?

It is impossible to get sick due to excess silicon in the diet, but residents of areas with high silicon content in soil or water are at risk.

Due to the high concentration of silicon in the body:

• salts are deposited in the urinary tract, joints and other organs;
• fibrosis develops in the blood vessels and throughout the body as a whole. Symptoms: rapid breathing with light exertion, decreased vital capacity, low blood pressure;
• the right ventricle expands and hypertrophies (“cor pulmonale”);
• the liver enlarges, the limbs swell, the skin turns blue;
• irritability increases, asthenic syndrome develops;
• the risk of upper respiratory tract diseases increases. The most common of these is silicosis. The disease develops due to inhalation of dust containing silicon dioxide and occurs in chronic form. As the disease progresses, connective tissue grows in the patient's lungs. Normal gas exchange is disrupted, and tuberculosis, emphysema or lung cancer develop against its background.

At risk are workers in mines, foundries, and manufacturers of refractory materials and ceramic products. The disease is signaled by difficulty breathing, shortness of breath and cough. Symptoms worsen with physical activity. Porcelain and earthenware, glass production, deposits of non-ferrous ores and precious metals, sandblasting of castings are potentially dangerous objects.

An excess of silicon is indicated by a decrease and increase in body temperature, depression, general fatigue and drowsiness.

For such symptoms, include carrots, beets, potatoes, Jerusalem artichokes, as well as apricots, cherries, bananas and strawberries in your diet.

Preparations containing silicon

Despite the fact that the adult body contains 1-2 g of silicon, an additional portion will not hurt. An adult consumes about 3.5 mg of silicon per day, with food and water. An adult spends three times more on basal metabolism - about 9 mg. The reasons for the increased consumption of silicon are poor ecology, oxidative processes that provoke the formation of free radicals, and stress. You can’t get by with silicon-containing products alone – stock up on medications or medicinal plants.

Record holders for silicon content are juniper, horsetail, tansy, wormwood, and ginkgo biloba. And also field chamomile, thyme, Chinese walnut and eucalyptus.

You can replenish silicon deficiency with silicon water. One of the properties of a microelement is the structuring of water molecules. Such water is not suitable for the life of pathogenic microorganisms, protozoa, fungi, toxins and foreign chemical elements.

Silicon water resembles melt water in taste and freshness.

To purify and enrich water with silicon at home, you need to:

• buy flint pebbles at a pharmacy store - the smaller the better (the larger the area of ​​contact between the flint and the water);
• put in water at the rate of 50 g of stones per 3 liters of water;
• Infuse water in a glass container at room temperature in a dark place for 3-4 days. The longer the water is infused, the more pronounced the therapeutic effect;
• pour the finished water into another container, leaving a bottom layer 3–4 cm deep (it cannot be used due to the accumulation of toxins).
• In an airtight container, water is stored for up to one and a half years.
• You can drink silicon water in any quantity to prevent atherosclerosis, hypertension and urolithiasis, skin pathology and diabetes, infectious and oncological diseases, varicose veins and even neuropsychiatric diseases.

Atoxil. The active ingredient of Atoxyl is silicon dioxide.

Release form:

• powder for preparing a suspension;
• bottles of 12 g of the drug;
• bottles of 10 mg of the drug;
• sachet bags of 2 g, 20 sachets per pack.

Pharmachologic effect. Acts as an enterosorbent, has a wound-healing, antiallergic, antimicrobial, bacteriostatic and detoxification effect.

In the organs of the gastrointestinal tract, the drug absorbs exogenous and endogenous toxins (bacterial and food allergens, endotoxins of microorganisms, toxic substances) and removes them.

Accelerates the transport of toxins from the blood, lymph and tissues into the digestive tract.

Indications: diarrhea, salmonellosis, viral hepatitis A and B, allergic diseases (diathesis, atopic dermatitis), burns, trophic ulcers, purulent wounds.

It is used for kidney diseases, enterocolitis, toxic hepatitis, liver cirrhosis, hepatocholecystitis, drug and alcohol intoxication, skin diseases (eczema, dermatitis, neurodermatitis), intoxication during purulent-septic processes and burn disease.

How to use:

• Bottle. Open the bottle (vial) with the powder, add to the 250 ml mark in clean drinking water, shake until smooth.
• Sachet bag. Dissolve 1-2 sachets in 100-150 ml of clean drinking water. Take one hour before meals or medications.

The duration of treatment for acute intestinal infections is 3-5 days. The course of therapy is up to 15 days. When treating viral hepatitis – 7-10 days.

Side effects effects: constipation.

Contraindications: exacerbation of duodenal and gastric ulcers, erosions and ulcers of the mucous membrane of the large and small intestines, intestinal obstruction, hypersensitivity to silicon dioxide.

The drug is not prescribed to children under one year of age, pregnant or breastfeeding women.

Interactions with drugs:

• with Acetylsalicylic acid (Aspirin) – increased platelet disaggregation;
• with Simvastatin and Nicotinic acid – a decrease in the blood of atherogenic fractions of lipid spectrum indicators and an increase in the level of lipoproteins VP and cholesterol;
• with antiseptics (Trifuran, Furacillin, Chlorhexidine, Bifuran, etc.) – increasing the effectiveness of therapy for purulent-inflammatory processes.

Chemical element

Silicon- chemical element No. \(14\). It is located in Group IV of the Periodic Table.

Si 14 14) 2e) 8e) 4e

The outer layer of a silicon atom contains four valence electrons. Four electrons are missing before it is completed. Therefore, in compounds with metals, silicon is characterized by an oxidation state of \(–4\), and when interacting with more electronegative non-metals, it exhibits positive oxidation states of \(+2\) or \(+4\).

In terms of content in the earth's crust, silicon ranks second place after oxygen. More than half of the earth's crust is formed by silicon compounds. Distributed silicon oxide (IV) Si O 2 , silicates And aluminosilicates . Sand, quartz, rock crystal, and amethyst are composed of oxide. Granite, feldspar, and clay are silicates and aluminosilicates.

Silicon is also found in living organisms. Its compounds give strength to plant stems, are found in the outer integument of animals, and form the shells and skeletons of some inhabitants of the aquatic environment. In humans, silicon is present in hair and nails.

Radiolarian skeletons

Simple substance

Silicon has an atomic crystal lattice similar to that of diamond. Each silicon atom in its crystals is connected by four covalent bonds to neighboring atoms. Thanks to this structure, it has high hardness.

The radius of a silicon atom is greater than the radius of a carbon atom, therefore electrons in its crystals are more free compared to diamond. Silicon conducts electricity, and its electrical conductivity increases with temperature or light. Such substances belong to semiconductors .

Unlike diamond, silicon is a black-gray opaque substance. It has a high melting point (\(1428\) °C).

Silicon

Silicon is obtained by reducing its oxide with coke in electric furnaces:

Si O 2 + 2C = t Si + 2CO.

Chemical properties

In chemical reactions, silicon can also exhibit oxidative , And restorative properties. The oxidizing properties of silicon are less pronounced than those of other non-metals.

• Interaction with metals.

At high temperatures, silicon reacts with metals to form silicides:

2Mg 0 Si 0 = t Mg 2 2 Si − 4 .

In this reaction, silicon is oxidizer .

• Does not react with hydrogen.

Silicon practically does not react with hydrogen due to the instability of the hydrogen compound. silane SiH4. Silane can be obtained by hydrolysis of silicides:

Mg 2 Si 4H 2 O = 2Mg (OH) 2 ↓ Si H 4.

It spontaneously ignites in air and burns to form silicon oxide (\(IV\)) and water:

SiH 4 2O 2 = Si O 2 2H 2 O.

• Interaction with oxygen.

Silicon burns in oxygen and exhibits in this reaction restorative properties.

Silicon (Si) – stands in period 3, group IV of the main subgroup of the periodic table. Physical properties: silicon exists in two modifications: amorphous and crystalline. Amorphous silicon is a brown powder with a density of 2.33 g/cm3, soluble in metal melts. Crystalline silicon is dark gray crystals with a steely luster, hard and brittle, with a density of 2.4 g/cm3. Silicon consists of three isotopes: Si (28), Si (29), Si (30).

Chemical properties: electronic configuration: 1s22s22p63 s23p2 . Silicon is a non-metal. At the outer energy level, silicon has 4 electrons, which determines its oxidation states: +4, -4, -2. Valency – 2.4. Amorphous silicon has greater reactivity than crystalline silicon. Under normal conditions, it interacts with fluorine: Si + 2F2 = SiF4. At 1000 °C Si reacts with non-metals: CL2, N2, C, S.

Of the acids, silicon reacts only with a mixture of nitric and hydrofluoric acids:

It behaves differently in relation to metals: in molten Zn, Al, Sn, Pb it dissolves well, but does not react with them; Silicon interacts with other metal melts - with Mg, Cu, Fe - to form silicides: Si + 2Mg = Mg2Si. Silicon burns in oxygen: Si + O2 = SiO2 (sand).

Silicon dioxide or silica– stable connection Si, widely distributed in nature. It reacts by fusing it with alkalis and basic oxides, forming silicic acid salts - silicates. Receipt: In industry, silicon in its pure form is obtained by reducing silicon dioxide with coke in electric furnaces: SiO2 + 2C = Si + 2CO?.

In the laboratory, silicon is obtained by calcination of white sand with magnesium or aluminum:

SiO2 + 2Mg = 2MgO + Si.

3SiO2 + 4Al = Al2O3 + 3Si.

Silicon forms acids: H2 SiO3 – meta-silicic acid; H2 Si2O5 is dimethasilicic acid.

Finding in nature: quartz mineral – SiO2. Quartz crystals are shaped like a hexagonal prism, colorless and transparent, and are called rock crystal. Amethyst is a rock crystal colored purple with impurities; smoky topaz is brownish in color; agate and jasper are crystalline varieties of quartz. Amorphous silica is less common and exists in the form of the opal mineral – SiO2 nH2O. Diatomite, tripoli or kieselguhr (diatomaceous earth) are earthy forms of amorphous silicon.

42. The concept of colloidal solutions

Colloidal solutions– highly dispersed two-phase systems, consisting of a dispersion medium and a dispersed phase. The particle sizes are intermediate between true solutions, suspensions and emulsions. U colloidal particles molecular or ionic composition.

There are three types of internal structure of primary particles.

1. Suspensoids (or irreversible colloids)– heterogeneous systems, the properties of which can be determined by the developed interphase surface. Compared to suspensions, they are more highly dispersed. They cannot exist for a long time without a dispersion stabilizer. They are called irreversible colloids due to the fact that their sediments do not form sols again after evaporation. Their concentration is low - 0.1%. They differ slightly from the viscosity of the dispersed medium.

Suspensoids can be obtained:

1) methods of dispersion (crushing large bodies);

2) condensation methods (production of insoluble compounds using exchange reactions, hydrolysis, etc.).

The spontaneous decrease in dispersity in suspensions depends on the free surface energy. To obtain a long-lasting suspension, conditions are necessary to stabilize it.

Stable disperse systems:

1) dispersion medium;

2) dispersed phase;

3) stabilizer of the dispersed system.

The stabilizer can be ionic, molecular, but most often high-molecular.

Protective colloids– high-molecular compounds that are added for stabilization (proteins, peptides, polyvinyl alcohol, etc.).

2. Associative (or micellar colloids) – semicolloids that arise when there is a sufficient concentration of molecules consisting of hydrocarbon radicals (diphilic molecules) of low molecular weight substances when they associate into aggregates of molecules (micelles). Micelles are formed in aqueous solutions of detergents (soaps), organic dyes.

3. Molecular colloids (reversible or lyophilic colloids) – natural and synthetic high-molecular substances with high molecular weight. Their molecules have the size of colloidal particles (macromolecules).

Dilute solutions of colloids of high molecular weight compounds are homogeneous solutions. When highly diluted, these solutions obey the laws of dilute solutions.

Non-polar macromolecules dissolve in hydrocarbons, polar ones - in polar solvents.

Reversible colloids– substances, the dry residue of which, when adding a new portion of the solvent, goes back into solution.

Silicon and its compounds, like carbon and its compounds, are widely used in various fields. Silicon is used to make microelectronic devices. Silica is used in the production of glass and cement. The uses of silicates are varied (Table 15.8). All of these examples use sodium silicates. Finally, silicones are used to produce synthetic rubbers, polishes and manufacturing materials. protective coatings. We will now look in some detail at three of these applications.

Table 15.8. Some uses of silicates

Revolution in microelectronics

In the last two to three decades, silicon has become extremely important as a semiconductor material used for the manufacture of microelectronic devices called “ICs.”

A semiconductor is a substance electrical resistance which has an intermediate value between those characteristic of electrical insulators (dielectrics) and conductors (Table 15.9).

Semiconductors are often deliberately introduced with impurities by doping them with controlled amounts of impurity substances. Doping, as it were, reduces the gap between the conduction band and the valence band of the semiconductor (see Section 2.1), and therefore reduces its resistance. A -type (negative type) semiconductor is obtained by doping pure silicon or germanium with any element

Table 15.9. Semiconductor properties of silicon

Rice. 15.9. Doped silicon, a - schematic representation of Al, Si atoms with their outer electrons; b - semiconductor: each pair of electrons forms a covalent bond; c - impurity-type semiconductor: the presence in the crystal lattice of silicon of an impurity atom of a group V element, for example phosphorus, introduces an excess electron into it, and this reduces the electrical resistance of silicon; d - impurity p-type semiconductor: the presence in the crystal lattice of silicon of an impurity atom of a group III element, for example aluminum, leads to the appearance of an electron “hole” in the lattice.

Group V, for example phosphorus. Since the phosphorus atom has five electrons in its outer shell, the presence of phosphorus atoms in the silicon crystal lattice leads to the appearance of excess electrons and, consequently, to the appearance of an effective negative charge (Fig. 15.9).

A p-type semiconductor (positive type) has an effective positive charge due to the presence in its crystal lattice of impurity atoms belonging to some Group III element, for example aluminum. Each aluminum atom creates an electron hole in the silicon lattice, i.e., a positive charge.

A semiconductor diode is obtained at the junction of two semiconductor electrodes, one of which belongs to the n-type and the other to the p-type (Fig. 15.10). Electrons flowing through a p-type electrode stop at the junction (junction) between the two electrodes, which is called a -junction. Electrons flowing in reverse

Rice. 15.10. Semiconductor Diode: Excess electrons from the -type semiconductor electrode flow through the -junction to fill the "holes" in the -type semiconductor electrode.

Rice. 15.11. Transistors, a - transistor -type; b - transistor-type.

direction pass through this transition as they move from a lattice with excess electrons to a lattice with a deficiency of electrons. The same flow of electrical charge can be thought of as the opposite movement of electron holes, or positive charge, from -type electrode to -type electrode.

Silicon semiconductor diodes are used as AC rectifiers that convert it into DC current. The controlled silicon rectifier consists of -type and -type electrodes, as well as a third electrode, which acts as a diode valve. Such a rectifier converts alternating current to constant only if a small voltage is applied to the diode valve.

A transistor is a three-electrode semiconductor device in which a thin layer of -type (or -type) semiconductor is sandwiched between two -type (or -type) semiconductor electrodes (Fig. 15.11). This device allows you to control the flow electric current great force by applying little tension to it. A -type transistor has hole conductivity, and an -type transistor has electronic conductivity.

Before the beginning, all transistors were placed in an individual metal or plastic shell. They were subsequently replaced by integrated circuits. Currently, a single tiny piece of silicon in a software pocket calculator can contain over 30,000 transistors connected into a single integrated circuit.

Glass

Silicate glass is formed when molten silicates solidify. Soda glass consists of a mixture of calcium silicate and sodium silicate. Its manufacture was mentioned in the previous chapter. Soda glass is used to make window glass and various types of flat glass.

Borosilicate glass contains approximately boron oxide and small amounts of sodium and aluminum oxides. Borosilicate glass can withstand temperatures up to and is highly resistant to chemicals such as alkalis. The most common type of borosilicate glass is Pyrex. Borosilicate glass is used to make kitchen utensils and laboratory glassware.

Lead glass has a high refractive index and is used to make crystal glass products. Typical lead glass contains about 8% oxide; good crystal glass contains more lead.

Fiberglass is obtained different ways, for example, dripping molten glass onto a rotating disk of fireproof material. The glass flies away from the disk, forming thin threads. Fiberglass is used to make thermal insulation panels in the automotive industry, as well as parts for instrument housings in the aircraft industry.

To impart color to glass, oxides of various d-metals are introduced into it during the manufacturing process. Cobalt gives glass a blue or pink color depending on the amount of basic oxides present in the glass, such as. Brown or green color inexpensive varieties The iron content of glass used to make wine and beer bottles is due to the iron compounds present in the sand used to make such glass.

Optical fibers are made from quartz glass. Quartz glass is made by melting quartz. Quartz glass has excellent optical transparency. However, the quartz glass used to make optical fiber must be extremely pure. The amount of impurities in it, such as iron and copper, should be reduced to such a level that it does not exceed one part per 10°. For this reason, quartz glass used to make optical fiber is obtained directly from the reaction of oxygen with chloride in the gas phase. The chloride can be obtained in extremely high purity, characterized as "electronic purity".

An optical fiber has a core, which allows light to pass through, and a cladding with a lower refractive index, which prevents light loss through the sides. The fiber, which is the thickness of a human hair, is surrounded by a protective coating of silicon or organic polymer material.

Optical fibers are used to transmit television programs, telephone conversations, and output from computers and other devices. According to some predictions, optical fibers will gradually replace copper wire cables, which are usually used for these purposes.

Liquid glass is an aqueous solution of sodium silicate. It is obtained by fusing silica with some alkali, for example sodium hydroxide, or sodium carbonate. Sodium silicate is a strong base. When it acidifies, a gel forms. It is a polymeric acid, which has the following structure:

When this material is heated, it dehydrates and forms silica gel. Silica gel has a very developed surface. It is used as a drying agent and also as an inert carrier for some finely divided catalysts.

Silicones

This is the name given to organosilicon polymer compounds, the skeleton of which is formed by alternating silicon and oxygen atoms bonded to each other. Alkyl or aryl groups are attached to the silicon atoms (see Chapter 17). Let's take the following structure as an example:

Silicones are oily, fatty, resinous or rubbery substances. They are obtained by hydrolysis of chlorosilanes, for example dimethylchlorosilane. Alkyl or aryl chlorosilanes are prepared using Grignard reagents (see Section 19.1) or by passing alkyl or aryl halide vapors over silicon granules in the presence of a copper catalyst at a temperature of about 300 ° C:

Silicones are thermally stable and react with most chemicals. They have good water-repellent properties and are used as moisture-proof materials. In addition, they are used as technical oils, lubricants and insulators, as well as oil varnishes, paints and polishes.