Silicon. Properties of silicon

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Historical reference .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. (in 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 the animal and plant world. 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 of 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. is diamagnetic, atomic magnetic susceptibility is -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. The intrinsic specific volumetric electrical resistivity of a cell at room temperature is taken to be 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 of the general formula six 4 . Hydrogen does not react directly with carbon, and silicic acids(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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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).

(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).

SILICON (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 (valence 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 the 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 .

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 table, 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. There are 3 stable isotopes found in nature: 28Si (92.27), 29Si (4.68%), 30Si (3 ... Geological encyclopedia

Instructions

The periodic system is a multi-story “house” containing a large number of apartments. Each “tenant” or in his own apartment under a certain number, which is permanent. In addition, the element has a “surname” or name, such as oxygen, boron or nitrogen. In addition to this data, each “apartment” contains information such as relative atomic mass, which may have exact or rounded values.

As in any house, there are “entrances”, namely groups. Moreover, in groups the elements are located on the left and right, forming. Depending on which side there are more of them, that side is called the main one. The other subgroup, accordingly, will be secondary. The table also has “floors” or periods. Moreover, periods can be both large (consist of two rows) and small (have only one row).

The table shows the structure of an atom of an element, each of which has a positively charged nucleus consisting of protons and neutrons, as well as negatively charged electrons rotating around it. The number of protons and electrons is numerically the same and is determined in the table by the serial number of the element. For example, the chemical element sulfur is #16, therefore it will have 16 protons and 16 electrons.

To determine the number of neutrons (neutral particles also located in the nucleus), subtract its atomic number from the relative atomic mass of the element. For example, iron has a relative atomic mass of 56 and an atomic number of 26. Therefore, 56 – 26 = 30 protons for iron.

Electrons are located at different distances from the nucleus, forming electron levels. To determine the number of electronic (or energy) levels, you need to look at the number of the period in which the element is located. For example, aluminum is in the 3rd period, therefore it will have 3 levels.

By the group number (but only for the main subgroup) you can determine the highest valence. For example, elements of the first group of the main subgroup (lithium, sodium, potassium, etc.) have a valence of 1. Accordingly, elements of the second group (beryllium, magnesium, calcium, etc.) will have a valence of 2.

You can also use the table to analyze the properties of elements. From left to right, metallic properties weaken, and non-metallic properties increase. This is clearly seen in the example of period 2: it begins with the alkali metal sodium, then the alkaline earth metal magnesium, after it the amphoteric element aluminum, then the non-metals silicon, phosphorus, sulfur and the period ends with gaseous substances - chlorine and argon. In the next period, a similar dependence is observed.

From top to bottom, a pattern is also observed - metallic properties increase, and non-metallic properties weaken. That is, for example, cesium is much more active compared to sodium.

DEFINITION

Silicon- the fourteenth element of the Periodic Table. Designation - Si from the Latin "silicium". Located in the third period, group IVA. Refers to non-metals. The nuclear charge is 14.

Silicon is one of the most common elements in the earth's crust. It makes up 27% (wt.) of the part of the earth’s crust accessible to our study, ranking second in abundance after oxygen. In nature, silicon is found only in compounds: in the form of silicon dioxide SiO 2, called silicon anhydride or silica, in the form of salts of silicic acids (silicates). Aluminosilicates are the most widespread in nature, i.e. silicates containing aluminum. These include feldspars, micas, kaolin, etc.

Like carbon, which is part of all organic substances, silicon is the most important element of the plant and animal kingdom.

Under normal conditions, silicon is a dark gray substance (Fig. 1). It looks like metal. Refractory - melting point is 1415 o C. Characterized by high hardness.

Rice. 1. Silicon. Appearance.

Atomic and molecular mass of silicon

The relative molecular mass of a substance (M r) is a number showing how many times the mass of a given molecule is greater than 1/12 the mass of a carbon atom, and the relative atomic mass of an element (A r) is how many times the average mass of atoms of a chemical element is greater than 1/12 mass of a carbon atom.

Since in the free state silicon exists in the form of monatomic Si molecules, the values ​​of its atomic and molecular masses coincide. They are equal to 28.084.

Allotropy and allotropic modifications of silicon

Silicon can exist in the form of two allotropic modifications: diamond-like (cubic) (stable) and graphite-like (unstable). Diamond-like silicon is in a solid aggregate state, and graphite-like silicon is in an amorphous state. They also differ in appearance and chemical activity.

Crystalline silicon is a dark gray substance with a metallic luster, and amorphous silicon is a brown powder. The second modification is more reactive than the first.

Isotopes of silicon

It is known that in nature silicon can be found in the form of three stable isotopes 28 Si, 29 Si and 30 Si. Their mass numbers are 28, 29 and 30, respectively. The nucleus of an atom of the silicon isotope 28 Si contains fourteen protons and fourteen neutrons, and the isotopes 29 Si and 30 Si contain the same number of protons, fifteen and sixteen neutrons, respectively.

There are artificial isotopes of silicon with mass numbers from 22 to 44, among which the longest-lived is 32 Si with a half-life of 170 years.

Silicon ions

At the outer energy level of the silicon atom there are four electrons, which are valence:

1s 2 2s 2 2p 6 3s 2 3p 2 .

As a result of chemical interaction, silicon can give up its valence electrons, i.e. be their donor and turn into a positively charged ion, or accept electrons from another atom, i.e. be an acceptor, and turns into a negatively charged ion:

Si 0 -4e → Si 4+ ;

Si 0 +4e → Si 4- .

Silicon molecule and atom

In the free state, silicon exists in the form of monatomic Si molecules. Here are some properties characterizing the silicon atom and molecule:

Silicon alloys

Silicon is used in metallurgy. It serves as a component of many alloys. The most important of them are alloys based on iron, copper and aluminum.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2

• Designation - Si (Silicon);
• Period - III;
• Group - 14 (IVa);
• Atomic mass - 28.0855;
• Atomic number - 14;
• Atomic radius = 132 pm;
• Covalent radius = 111 pm;
• Electron distribution - 1s 2 2s 2 2p 6 3s 2 3p 2 ;
• melting temperature = 1412°C;
• boiling point = 2355°C;
• Electronegativity (according to Pauling/according to Alpred and Rochow) = 1.90/1.74;
• Oxidation state: +4, +2, 0, -4;
• Density (no.) = 2.33 g/cm3;
• Molar volume = 12.1 cm 3 /mol.

Silicon compounds:

Silicon was first isolated in its pure form in 1811 (the French J. L. Gay-Lussac and L. J. Tenard). Pure elemental silicon was obtained in 1825 (Swede J. J. Berzelius). The chemical element received its name “silicon” (translated from ancient Greek as mountain) in 1834 (Russian chemist G. I. Hess).

Silicon is the most common (after oxygen) chemical element on Earth (content in the earth's crust is 28-29% by weight). In nature, silicon is most often present in the form of silica (sand, quartz, flint, feldspars), as well as in silicates and aluminosilicates. In its pure form, silicon is extremely rare. Many natural silicates in their pure form are precious stones: emerald, topaz, aquamary - all this is silicon. Pure crystalline silicon(IV) oxide occurs in the form of rock crystal and quartz. Silicon oxide, which contains various impurities, forms precious and semi-precious stones - amethyst, agate, jasper.

Rice. Structure of the silicon atom.

The electronic configuration of silicon is 1s 2 2s 2 2p 6 3s 2 3p 2 (see Electronic structure of atoms). At the outer energy level, silicon has 4 electrons: 2 paired in the 3s sublevel + 2 unpaired in p-orbitals. When a silicon atom transitions to an excited state, one electron from the s-sublevel “leaves” its pair and moves to the p-sublevel, where there is one free orbital. Thus, in the excited state, the electronic configuration of the silicon atom takes the following form: 1s 2 2s 2 2p 6 3s 1 3p 3.

Rice. Transition of a silicon atom to an excited state.

Thus, silicon in compounds can exhibit a valence of 4 (most often) or 2 (see Valency). Silicon (as well as carbon), reacting with other elements, forms chemical bonds in which it can both give up its electrons and accept them, but the ability to accept electrons in silicon atoms is less pronounced than in carbon atoms, due to larger silicon atom.

Silicon oxidation states:

• -4 : SiH 4 (silane), Ca 2 Si, Mg 2 Si (metal silicates);
• +4 - the most stable: SiO 2 (silicon oxide), H 2 SiO 3 (silicic acid), silicates and silicon halides;
• 0 : Si (simple substance)

Silicon as a simple substance

Silicon is a dark gray crystalline substance with a metallic luster. Crystalline silicon is a semiconductor.

Silicon forms only one allotropic modification, similar to diamond, but not as strong, since the Si-Si bonds are not as strong as in the diamond carbon molecule (See Diamond).

Amorphous silicon- brown powder, with a melting point of 1420°C.

Crystalline silicon is obtained from amorphous silicon by recrystallization. Unlike amorphous silicon, which is a fairly active chemical, crystalline silicon is more inert in terms of interaction with other substances.

The structure of the crystal lattice of silicon repeats the structure of diamond - each atom is surrounded by four other atoms located at the vertices of a tetrahedron. The atoms are held together by covalent bonds, which are not as strong as the carbon bonds in diamond. For this reason, even at no. Some covalent bonds in crystalline silicon are broken, resulting in the release of some electrons, causing silicon to have little electrical conductivity. As silicon heats up, in the light or when certain impurities are added, the number of broken covalent bonds increases, as a result of which the number of free electrons increases, and therefore the electrical conductivity of silicon also increases.

Chemical properties of silicon

Like carbon, silicon can be both a reducing agent and an oxidizing agent, depending on what substance it reacts with.

At no. silicon interacts only with fluorine, which is explained by the fairly strong crystal lattice of silicon.

Silicon reacts with chlorine and bromine at temperatures exceeding 400°C.

Silicon interacts with carbon and nitrogen only at very high temperatures.

• In reactions with nonmetals, silicon acts as reducing agent:
  • under normal conditions, from non-metals, silicon reacts only with fluorine, forming silicon halide:
    Si + 2F 2 = SiF 4
  • at high temperatures, silicon reacts with chlorine (400°C), oxygen (600°C), nitrogen (1000°C), carbon (2000°C):
    • Si + 2Cl 2 = SiCl 4 - silicon halide;
    • Si + O 2 = SiO 2 - silicon oxide;
    • 3Si + 2N 2 = Si 3 N 4 - silicon nitride;
    • Si + C = SiC - carborundum (silicon carbide)
• In reactions with metals, silicon is oxidizing agent(formed salicids:
  Si + 2Mg = Mg 2 Si
• In reactions with concentrated solutions of alkalis, silicon reacts with the release of hydrogen, forming soluble salts of silicic acid, called silicates:
  Si + 2NaOH + H 2 O = Na 2 SiO 3 + 2H 2
• Silicon does not react with acids (except for HF).

Preparation and use of silicon

Obtaining silicon:

• in the laboratory - from silica (aluminum therapy):
  3SiO 2 + 4Al = 3Si + 2Al 2 O 3
• in industry - by reduction of silicon oxide with coke (technically pure silicon) at high temperature:
  SiO 2 + 2C = Si + 2CO
• The purest silicon is obtained by reducing silicon tetrachloride with hydrogen (zinc) at high temperature:
  SiCl 4 +2H 2 = Si+4HCl

Silicon Application:

• production of semiconductor radioelements;
• as metallurgical additives in the production of heat-resistant and acid-resistant compounds;
• in the production of photocells for solar batteries;
• as AC rectifiers.