General characteristics of elements of group IV, the main subgroup of D. I. Mendeleev’s periodic system
The elements of the main subgroup of group IV include carbon, silicon, germanium, tin, and lead. Metallic properties are enhanced, non-metallic properties are reduced. The outer layer has 4 electrons.
Chemical properties(carbon based)
· Interact with metals
4Al+3C = Al 4 C 3 (reaction occurs at high temperature)
· Interact with non-metals
2H 2 +C = CH 4
· Interact with oxygen
· Interact with water
C+H2O = CO+H2
· Interact with oxides
2Fe 2 O 3 +3C = 3CO 2 +4Fe
· Interact with acids
3C+4HNO3 = 3CO2 +4NO+2H2O
Carbon. Characteristics of carbon, based on its position in the periodic table, allotropy of carbon, adsorption, distribution in nature, production, properties. The most important carbon compounds
Carbon (chemical symbol - C, lat. Carboneum) is a chemical element of the fourteenth group (according to the outdated classification - the main subgroup of the fourth group), the 2nd period of the periodic system of chemical elements. serial number 6, atomic mass - 12.0107. Carbon exists in a variety of allotropes with very diverse physical properties. The variety of modifications is due to the ability of carbon to form chemical bonds of different types.
Natural carbon consists of two stable isotopes - 12C (98.93%) and 13C (1.07%) and one radioactive isotope 14C (β-emitter, T½ = 5730 years), concentrated in the atmosphere and upper part of the earth's crust.
The main and well-studied allotropic modifications of carbon are diamond and graphite. Under normal conditions, only graphite is thermodynamically stable, while diamond and other forms are metastable. Liquid carbon exists only at a certain external pressure.
At pressures above 60 GPa, the formation of a very dense modification C III (density 15-20% higher than the density of diamond), which has metallic conductivity, is assumed.
The crystalline modification of carbon of the hexagonal system with a chain structure of molecules is usually called carbyne. Several forms of carbyne are known, differing in the number of atoms in the unit cell.
Carbyne is a fine-crystalline black powder (density 1.9-2 g/cm³) and has semiconductor properties. Obtained under artificial conditions from long chains of carbon atoms laid parallel to each other.
Carbyne is a linear polymer of carbon. In the carbyne molecule, carbon atoms are connected in chains alternately either by triple and single bonds (polyene structure) or permanently by double bonds (polycumulene structure). Carbyne has semiconducting properties, and its conductivity increases greatly when exposed to light. The first practical application is based on this property - in photocells.
Graphene is a two-dimensional allotropic modification of carbon, formed by a layer of carbon atoms one atom thick, connected through sp² bonds into a hexagonal two-dimensional crystal lattice.
At ordinary temperatures, carbon is chemically inert; at sufficiently high temperatures it combines with many elements and exhibits strong reducing properties. The chemical activity of different forms of carbon decreases in the following order: amorphous carbon, graphite, diamond; in air they ignite at temperatures respectively above 300-500 °C, 600-700 °C and 850-1000 °C.
The combustion products of carbon are CO and CO2 (carbon monoxide and carbon dioxide, respectively). Unstable suboxide carbon C3O2 (melting point −111 °C, boiling point 7 °C) and some other oxides (for example, C12O9, C5O2, C12O12) are also known. Graphite and amorphous carbon begin to react with hydrogen at a temperature of 1200 °C, with fluorine at 900 °C.
Carbon dioxide reacts with water to form weak carbonic acid - H2CO3, which forms salts - carbonates. The most widespread on Earth are calcium carbonates (mineral forms - chalk, marble, calcite, limestone, etc.) and magnesium (mineral form dolomite).
Graphite with halogens, alkali metals, etc.
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substances form inclusion compounds. When an electric discharge is passed between carbon electrodes in a nitrogen atmosphere, cyanogen is formed. At high temperatures, the reaction of carbon with a mixture of H2 and N2 produces hydrocyanic acid:
The reaction of carbon with sulfur produces carbon disulfide CS2; CS and C3S2 are also known. With most metals, carbon forms carbides, for example:
The reaction of carbon with water vapor is important in industry:
When heated, carbon reduces metal oxides to metals. This property is widely used in the metallurgical industry.
Graphite is used in the pencil industry, but mixed with clay to reduce its softness. Diamond, due to its exceptional hardness, is an indispensable abrasive material. In pharmacology and medicine, various carbon compounds are widely used - derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers and other compounds. Carbon plays a huge role in human life. Its applications are as diverse as this multifaceted element itself. In particular, carbon is an integral component of steel (up to 2.14% wt.) and cast iron (more than 2.14% wt.)
Carbon is part of atmospheric aerosols, due to which the regional climate can change and the number of sunny days can decrease. Carbon enters the environment in the form of soot in the exhaust gases of vehicles when burning coal at thermal power plants, during open coal mines, underground gasification, production of coal concentrates, etc.
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Carbon concentration above combustion sources is 100-400 µg/m³, in large cities 2.4-15.9 µg/m³, in rural areas 0.5 - 0.8 µg/m³. With gas aerosol emissions from nuclear power plants, (6-15)·109 Bq/day 14СО2 enters the atmosphere.
The high carbon content in atmospheric aerosols leads to increased morbidity in the population, especially in the upper respiratory tract and lungs. Occupational diseases - mainly anthracosis and dust bronchitis. In the air of the working area, MPC, mg/m³: diamond 8.0, anthracite and coke 6.0, coal 10.0, carbon black and carbon dust 4.0; in atmospheric air the maximum one-time is 0.15, the average daily is 0.05 mg/m³.
The most important connections. Carbon (II) monoxide (carbon monoxide) CO. Under normal conditions, it is a colorless, odorless, and tasteless gas. The toxicity is explained by the fact that it easily combines with blood hemoglobin Carbon monoxide (IV) CO2. Under normal conditions, it is a colorless gas with a slightly sour smell and taste, one and a half times heavier than air, does not burn and does not support combustion. Carbonic acid H2CO3. Weak acid. Carbonic acid molecules exist only in solution. Phosgene COCl2. Colorless gas with a characteristic odor, boiling point = 8°C, melting point = -118°C. Very poisonous. Slightly soluble in water. Reactive. Used in organic syntheses.
General characteristics of elements of group IV, the main subgroup of D.I. Mendeleev’s periodic system - concept and types. Classification and features of the category "General characteristics of elements of group IV, the main subgroup of the periodic table of D. I. Mendeleev" 2017, 2018.
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active, inactive; b) when interacting with metals, they form salts; d) typical metals; 2. Metal that can be used to produce hydrogen (by reacting it with acid): a) Zn; b) Pt; c) Au; d) Hg; e) Cu; 3. Basic oxides and hydroxides interact with: a) acids; b) reasons; c) both acids and alkalis; 4. From top to bottom in the main subgroups, non-metallic properties: a) increase b) weaken c) remain unchanged 5. Element of the main subgroup of group IV: a) sulfur b) titanium c) silicon d) chromium 6. The number of electrons at the last energy level is determined by: a) by serial number b) by period number c) by group number 7. The structure of atoms of elements with serial numbers 19 and 32 is identical: a) the total number of electrons; c) number of electronic levels; d) the number of electrons at the last energy level; b) number of neutrons; 8. Element with electronic formula 1s22s22p6: a) neon; b) bromine; c) calcium; d) beryllium; 9. The sodium atom has the electronic formula: a) 1s22s22р1 b) 1s22s22p63s1 c) 1s22s22p63s2 10. The atom of which element has the following structure of the last energy level…3s23p2: a) carbon; b) bromine; c) silicon; d) phosphorus; 11. The number of unpaired electrons contains the electron shell of element No. 16 (sulfur): a) 1; b) 2; c) 3; d) 4; 12. Ordinal number of an element whose atoms are capable of forming a higher oxide of the RO type: a) No. 11 (sodium); b) No. 12 (magnesium); c) No. 14 (silicon); 13. An element with the electronic formula 1s22s22p3 forms a volatile hydrogen compound of the type: a) RH4; b) RH3; c) RH2; d) RH; 14. Volume of 4 moles of hydrogen under normal conditions: b) 44.8 l; c) 67.2 l; d) 89.6 l; e) 112 l; 15. The element is located in the II period. The valency in the higher oxide and hydroxide is I. The compound exhibits basic properties. This element... a) beryllium b) magnesium c) lithium d) fluorine 16. Maximum valency of chlorine (No. 17): a) IV b) V c) VII d) VIII 17. Minimum valency of arsenic (No. 33): a) IV b) III c) V d) VII 18. The molecular weight of a salt obtained by the interaction of two higher oxides of elements with the atomic configuration in them being 1s22s22p3 and 1s22s22p63s1, respectively: a) 85; b) 111; c) 63; d) 101; e) 164; 19. Determine the formula of substance “X”, which is formed as a result of transformations: N2 → N2O5 A; Ba → BaO B; A + B → X + D; a) HNO3 b) Ba(OH)2 c) Ba (NO3)2 d) BaSO4 e) BaOHNO3 20. The sum of the coefficients in the reaction equation, the scheme of which is KMnO4 → K2MnO4 + MnO2 + O2 a) 2; b) 3; c) 4; d) 5; e) 6; 21. Molar mass of potassium oxide (in g/mol): a) 55; b) 56; c) 74; d) 94; e) 112; 22. The number of moles of aluminum oxide constituting 204 g of this compound: a) 1; b) 2; c) 3; d) 4; e) 5; 23. The amount of heat released during the combustion of 2 g of coal (thermochemical equation of the reaction C + O2 = CO2 + 402.24 kJ): a) 67.04 kJ; b) 134.08 kJ; c) 200 kJ; d) 201.12 kJ; e) 301.68 kJ; 24. Under normal conditions, 44.8 liters of oxygen have a mass: a) 8 g; b) 16 g; c) 32 g; d) 64 g; e) 128 g; 25. The mass fraction of hydrogen in the PH3 compound is: a) 5.4%; b) 7.42%; c) 8.82%; d) 78.5%; e) 82.2%; 26. The mass fraction of oxygen in the EO3 compound is 60%. Name of element E in the compound: a) nitrogen; b) phosphorus; c) sulfur; d) silicon; e) selenium; 27. When sodium interacts with 72 g of water, hydrogen is released in volume (n.s.): a) 11.2 l; b) 22.4 l; c) 44.8 l; d) 67.2 l; e) 112 l; 28. Mass of hydrochloric acid required to obtain 224 liters of hydrogen (n.s.): (Ba + 2HCl = BaCl2 + H2): a) 219 g; b) 109.5 g; c) 730 g; d) 64 g; e) 365 g; 29. Mass of sodium hydroxide contained in 200 g of a 30% solution: a) 146 g; b) 196 g; c) 60 g; d) 6 g; e) 200 g; 30. The mass of salt that is formed by the interaction of sodium hydroxide with 400 g of a 75% solution of sulfuric acid: a) 146 g; b) 196 g; c) 360 g; d) 435 g; e) 200 g;
) Position of the element lithium in the Periodic Table of D.I. Mendeleev1) The position of the element aluminum in the Periodic Table of D.I. Mendeleev and the structure of its atoms 2) The nature of a simple substance (metal, non-metal) 3) Comparison of the properties of a simple substance with the properties of simple substances formed by elements neighboring in the subgroup 4) Comparison of the properties of a simple substance with properties of simple substances formed by elements neighboring in the period 5) Composition of the higher oxide, its character (basic, acidic, amphoteric) 6) Composition of the higher hydroxide and its nature (oxygen-containing acid, base, amphoteric hydroxide) 7) composition of the volatile hydrogen compound (for non-metals)
1. The metallic properties of elements of group II with increasing serial number 1) decrease 2) increase 3) do not change 4) change periodically 2.Phosphorus is an oxidizing agent in the reaction: 1) 3Mg+2H3PO4=Mg3(PO4)2+3H2 2) P2O3+O2=P2O5 3) 3Mg+2P=Mg3P2 4) 2P+3Cl2=2PCl3 3. At room temperature, both do not interact with water metal: 1) zinc and iron 2) copper and gold 3) sodium and mercury 4) potassium and calcium 4. Na+ ions are formed and hydrogen gas is released as a result of the reaction of 1) sodium oxide and water 2) sodium oxide with hydrochloric acid 3) chloride sodium with water 4) sodium with hydrochloric acid. 5. When interacting with oxygen, all metals of the group 1) lithium, sodium 2) calcium, strontium 3) barium, potassium 4) potassium, magnesium form oxides 6. The coefficient in front of the oxidizing formula in the equation of sodium with chlorine 1) 1 2) 2 3) 3 4) 4 7. If the reaction products are iron (II) sulfate and water, then the reactants are 1) iron (II) oxide and sulfur (IV) oxide 2) copper (II) sulfate and iron (II) chloride 3) iron and sulfuric acid 4) iron (II) hydroxide and sulfuric acid 8. Lithium is not used to displace sodium from an aqueous solution of its salt, since it 1) interacts with water 2) is in the activity series to the left of copper 3) is a less powerful reducing agent than sodium 4) easily oxidizes in air.
The periodic system of chemical elements is a classification of chemical elements created by D. I. Mendeleev on the basis of the periodic law discovered by him in 1869.
D. I. Mendeleev
According to the modern formulation of this law, in a continuous series of elements arranged in order of increasing magnitude of the positive charge of the nuclei of their atoms, elements with similar properties periodically repeat.
The periodic table of chemical elements, presented in table form, consists of periods, series and groups.
At the beginning of each period (except for the first), the element has pronounced metallic properties (alkali metal).
Symbols for the color table: 1 - chemical sign of the element; 2 - name; 3 - atomic mass (atomic weight); 4 - serial number; 5 - distribution of electrons across layers.
As the atomic number of an element increases, equal to the positive charge of the nucleus of its atom, metallic properties gradually weaken and non-metallic properties increase. The penultimate element in each period is an element with pronounced non-metallic properties (), and the last is an inert gas. In period I there are 2 elements, in II and III - 8 elements, in IV and V - 18, in VI - 32 and in VII (not completed period) - 17 elements.
The first three periods are called small periods, each of them consists of one horizontal row; the rest - in large periods, each of which (except for the VII period) consists of two horizontal rows - even (upper) and odd (lower). Only metals are found in even rows of large periods. The properties of the elements in these series change slightly with increasing ordinal number. The properties of elements in odd rows of large periods change. In period VI, lanthanum is followed by 14 elements, very similar in chemical properties. These elements, called lanthanides, are listed separately below the main table. Actinides, the elements following actinium, are presented similarly in the table.
The table has nine vertical groups. The group number, with rare exceptions, is equal to the highest positive valence of the elements of this group. Each group, excluding the zero and eighth, is divided into subgroups. - main (located to the right) and secondary. In the main subgroups, with increasing atomic number, the metallic properties of the elements become stronger and the non-metallic properties weaken.
Thus, the chemical and a number of physical properties of elements are determined by the place that a given element occupies in the periodic table.
Biogenic elements, i.e. elements that are part of organisms and perform a certain biological role in it, occupy the top part of the periodic table. Cells occupied by elements that make up the bulk (more than 99%) of living matter are colored blue; cells occupied by microelements are colored pink (see).
The periodic table of chemical elements is the greatest achievement of modern natural science and a vivid expression of the most general dialectical laws of nature.
See also, Atomic weight.
The periodic system of chemical elements is a natural classification of chemical elements created by D. I. Mendeleev on the basis of the periodic law discovered by him in 1869.
In its original formulation, D.I. Mendeleev’s periodic law stated: the properties of chemical elements, as well as the forms and properties of their compounds, are periodically dependent on the atomic weights of the elements. Subsequently, with the development of the doctrine of the structure of the atom, it was shown that a more accurate characteristic of each element is not the atomic weight (see), but the value of the positive charge of the nucleus of the element’s atom, equal to the serial (atomic) number of this element in the periodic system of D. I. Mendeleev . The number of positive charges on the nucleus of an atom is equal to the number of electrons surrounding the nucleus of the atom, since atoms as a whole are electrically neutral. In the light of these data, the periodic law is formulated as follows: the properties of chemical elements, as well as the forms and properties of their compounds, are periodically dependent on the magnitude of the positive charge of the nuclei of their atoms. This means that in a continuous series of elements arranged in order of increasing positive charges of the nuclei of their atoms, elements with similar properties will periodically repeat.
The tabular form of the periodic table of chemical elements is presented in its modern form. It consists of periods, series and groups. A period represents a successive horizontal series of elements arranged in order of increasing positive charge of the nuclei of their atoms.
At the beginning of each period (except for the first) there is an element with pronounced metallic properties (alkali metal). Then, as the serial number increases, the metallic properties of the elements gradually weaken and the non-metallic properties increase. The penultimate element in each period is an element with pronounced non-metallic properties (halogen), and the last is an inert gas. The first period consists of two elements, the role of an alkali metal and a halogen here is simultaneously performed by hydrogen. Periods II and III include 8 elements each, called typical by Mendeleev. Periods IV and V contain 18 elements each, VI-32. The VII period has not yet been completed and is replenished with artificially created elements; there are currently 17 elements in this period. Periods I, II and III are called small, each of them consists of one horizontal row, IV-VII are large: they (with the exception of VII) include two horizontal rows - even (upper) and odd (lower). In even rows of large periods there are only metals, and the change in the properties of elements in the row from left to right is weakly expressed.
In odd series of large periods, the properties of the elements in the series change in the same way as the properties of typical elements. In the even row of the VI period, after lanthanum, there are 14 elements [called lanthanides (see), lanthanides, rare earth elements], similar in chemical properties to lanthanum and to each other. A list of them is given separately below the table.
The elements following actinium - actinides (actinides) - are listed separately and listed below the table.
In the periodic table of chemical elements, nine groups are located vertically. The group number is equal to the highest positive valency (see) of the elements of this group. The exceptions are fluorine (can only be negatively monovalent) and bromine (cannot be heptavalent); in addition, copper, silver, gold can exhibit a valency greater than +1 (Cu-1 and 2, Ag and Au-1 and 3), and of the elements of group VIII, only osmium and ruthenium have a valence of +8. Each group, with the exception of the eighth and zero, is divided into two subgroups: the main one (located to the right) and the secondary one. The main subgroups include typical elements and elements of long periods, the secondary subgroups include only elements of long periods and, moreover, metals.
In terms of chemical properties, the elements of each subgroup of a given group differ significantly from each other, and only the highest positive valence is the same for all elements of a given group. In the main subgroups, from top to bottom, the metallic properties of elements are strengthened and non-metallic ones are weakened (for example, francium is the element with the most pronounced metallic properties, and fluorine is non-metallic). Thus, the place of an element in Mendeleev’s periodic system (ordinal number) determines its properties, which are the average of the properties of neighboring elements vertically and horizontally.
Some groups of elements have special names. Thus, the elements of the main subgroups of group I are called alkali metals, group II - alkaline earth metals, group VII - halogens, elements located behind uranium - transuranium. Elements that are part of organisms, take part in metabolic processes and have a clear biological role are called biogenic elements. All of them occupy the top part of D.I. Mendeleev’s table. These are primarily O, C, H, N, Ca, P, K, S, Na, Cl, Mg and Fe, which make up the bulk of living matter (more than 99%). The places occupied by these elements in the periodic table are colored light blue. Biogenic elements, of which there are very few in the body (from 10 -3 to 10 -14%), are called microelements (see). The cells of the periodic system, colored yellow, contain microelements, the vital importance of which for humans has been proven.
According to the theory of atomic structure (see Atom), the chemical properties of elements depend mainly on the number of electrons in the outer electron shell. The periodic change in the properties of elements with an increase in the positive charge of atomic nuclei is explained by the periodic repetition of the structure of the outer electron shell (energy level) of the atoms.
In small periods, with an increase in the positive charge of the nucleus, the number of electrons in the outer shell increases from 1 to 2 in period I and from 1 to 8 in periods II and III. Hence the change in the properties of elements in the period from an alkali metal to an inert gas. The outer electron shell, containing 8 electrons, is complete and energetically stable (elements of group zero are chemically inert).
In long periods in even rows, as the positive charge of the nuclei increases, the number of electrons in the outer shell remains constant (1 or 2) and the second outer shell is filled with electrons. Hence the slow change in the properties of elements in even rows. In the odd series of large periods, as the charge of the nuclei increases, the outer shell is filled with electrons (from 1 to 8) and the properties of the elements change in the same way as those of typical elements.
The number of electron shells in an atom is equal to the period number. Atoms of elements of the main subgroups have a number of electrons in their outer shells equal to the group number. Atoms of elements of side subgroups contain one or two electrons in their outer shells. This explains the difference in the properties of the elements of the main and secondary subgroups. The group number indicates the possible number of electrons that can participate in the formation of chemical (valence) bonds (see Molecule), therefore such electrons are called valence. For elements of side subgroups, not only the electrons of the outer shells are valence, but also those of the penultimate ones. The number and structure of electron shells are indicated in the accompanying periodic table of chemical elements.
The periodic law of D.I. Mendeleev and the system based on it are of exceptionally great importance in science and practice. The periodic law and system were the basis for the discovery of new chemical elements, the precise determination of their atomic weights, the development of the doctrine of the structure of atoms, the establishment of geochemical laws of distribution of elements in the earth's crust and the development of modern ideas about living matter, the composition of which and the patterns associated with it are in accordance with the periodic system. The biological activity of elements and their content in the body are also largely determined by the place they occupy in Mendeleev’s periodic table. Thus, with an increase in the serial number in a number of groups, the toxicity of elements increases and their content in the body decreases. The periodic law is a clear expression of the most general dialectical laws of the development of nature.
A group of the periodic system of chemical elements is a sequence of atoms in increasing nuclear charge that have the same type of electronic structure. The group number is determined by the number of electrons on the outer shell of the atom (valence electrons) ... Wikipedia
The fourth period of the periodic system includes elements of the fourth row (or fourth period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) ... ... Wikipedia
The first period of the periodic system includes elements of the first row (or first period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends in... ... Wikipedia
The second period of the periodic system includes elements of the second row (or second period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends in ... Wikipedia
The fifth period of the periodic system includes elements of the fifth row (or fifth period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends in... ... Wikipedia
The third period of the periodic system includes elements of the third row (or third period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends... Wikipedia
The seventh period of the periodic system includes elements of the seventh row (or seventh period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends... Wikipedia
The sixth period of the periodic system includes elements of the sixth row (or sixth period) of the periodic system of chemical elements. The structure of the periodic table is based on rows to illustrate repeating (periodic) trends in... ... Wikipedia
The short form of the periodic table is based on the parallelism of oxidation states of elements of the main and minor subgroups: for example, the maximum oxidation state of vanadium is +5, like phosphorus and arsenic, the maximum oxidation state of chromium is +6 ... Wikipedia
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The main subgroup of group IV of the periodic table of elements consists of carbon, silicon, germanium, tin and lead. Element Number Atomic mass Electronic configuration Carbon b 12.011 l.v!2r2/>; Silicon 14 28.085 1 l-22.yr2/>l3l-33/ї- Germanium 32 72.59 Il^g/^3pV4.r4p2 Tin 50 118.69 b^-2/>Chg3/)l3,4l-4/ >Mg Lead 82 207.2
Electronic configuration./^-elements.
The outer electron layer contains four electrons, the electronic formula of the outer layer is plіr1. Carbon and silicon are non-metals, germanium, tin and lead are transition elements.
Properties. Elements of this subgroup form oxides with the general formula RO and RO, and hydrogen compounds with the formula RH4. From carbon to lead, the properties of the oxides change from acidic (CO, SiO) to amphoteric (SnO, PbO). PbO and SnO are the main oxides. From carbon to lead, the strength of hydrogen compounds decreases. The nature of hydrates also changes: for example, H, CO,. H,SiO)-weak acids: Pb(OH), Sn(OH), Ge(OH), -amphoteric bases. In a subgroup, as the atomic number increases, the ionization energy decreases and the atomic radius increases, i.e., the non-metallic properties weaken and the metallic properties increase.
Being in nature. Silicon is not found in free form; it occurs only in the form of compounds. The most stable silicon compound is silicon (IV) oxide, or silica. Crystalline silica occurs in nature primarily as the mineral quartz. At the bottom of the seas there are deposits of thin, porous amorphous silica, which is called tripoli, diatomaceous earth or infusor earth. Silicon is part of feldspar, mica, clay, asbestos
Physical properties. Silicon is a dark gray substance with a metallic luster. It is fragile and, like carbon, refractory. Has semiconductor properties.
Chemical properties. Reducing agent. Reacts directly only with fluorine: Si + 2F, = SiF4 (silicon fluoride).
Silicon does not interact with acids (except for a mixture of hydrofluoric and nitric acids), while it reacts very vigorously with alkalis: Si + 2NaOH + H,0 = Na,SiO, + +2H,T.
When heated, silicon combines with oxygen: Si + O, = SiO,.
Silicon also forms a compound with hydrogen - silane: SiH4: Si + 2H, = SiH4.
With carbon, silicon forms carborundum (silicon carbide) - a crystalline substance built like a diamond: Si02 + 2C = SiC + C02.
Silicon compounds with metals are called silicides: Si + 2Mg = Mg,Si (magnesium silicide).
Application. Silicon is used mainly for the manufacture of semiconductor devices, the production of alloys, and the reduction of metals from oxides.
Receipt. Silicon is obtained by reducing it from silica: SiO, + 2Mg = 2MgO + Si.
In industry, silica is reduced with coal in electric furnaces: SiO, + 2C = Si + 2CO.
Silicon compounds
Silicon (IV) oxide and silica.
A solid, very refractory crystalline substance, insoluble in water and does not interact with it. According to its chemical properties, silicon (IV) oxide belongs to the acidic oxides. Only hydrofluoric acid reacts directly with silicon (IV) oxide: SiO, + 4HF = SiF4 + 2H.O.
When silicon (IV) oxide is fused with alkalis, basic oxides and carbonates, silicic acid salts are formed - silicates:
SiO, + 2NaOH = Na,SiO, + H,0; SiO, + CaO = CaSiO,;
Si02 + K2CO, = K,Si03 + CO,T.
Silicic acid. Refers to weak acids; slightly soluble in water. Silicic acid molecules practically do not dissociate in aqueous solutions. The formula H,Si03 is conditional. In fact, silicic acid exists in the form of a compound (H,SiOJn or polysilicic acids. During long-term storage, water molecules are split off from silicic acid and it turns into SiO. When heated, silicic acid also decomposes into silicon oxide (IV) and water: H2Si03 = H20 + SiO,.
Silicate industry
The silicate industry consists mainly of ceramic, glass and cement production.
Ceramics production. Ceramics are materials and products made from refractory substances - clay, carbides and oxides of some metals. Ceramic products include bricks, tiles, facing tiles, pottery, porcelain and earthenware.
The process of making ceramic products consists of preparing the ceramic mass, molding, drying and firing. During firing, sintering occurs due to chemical reactions in the solid phase. Firing is usually carried out at a temperature of 900 °C. Sintering is carried out according to a strictly defined regime and leads to the production of a material with specified properties. Glass production. Window glass consists primarily of sodium and potassium silicates fused with silicon (IV) oxide. the composition is approximately expressed by the formula Na20 CaO 6Si02. The raw materials for its production are white sand, soda, limestone or chalk. When these substances fuse, the following reactions occur:
CaCO, + SiO, = CaSiO, + CO,T; Na,COi + SiO, = Na,SiO, + CO,1\
Sodium and calcium silicates, together with silica, are fused into a mass that gradually cools:
Na,SiO, + CaSiO, + 4SiO, = Nap CaO CSiOr
Cement production. Cement is one of the most important materials produced by the silicate industry. It is used in huge quantities in construction work. Conventional cement (silica cement or Portland cement) is produced by firing a mixture of clay and limestone. When firing a cement mixture, calcium carbonate decomposes into carbon monoxide (IV) and calcium oxide: the latter reacts with clay. In this case, calcium silicates and aluminates are formed.