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The main subgroup of group IV of the periodic system includes the elements: carbon, silicon, germanium, tin and lead. Carbon and silicon are typical non-metals, while tin and lead are typical metals. Germanium occupies an intermediate position. At ordinary temperatures, it is a semiconductor, has an atomic crystal lattice and is very fragile, showing non-metallic properties. However, at elevated temperatures, germanium acquires characteristic metallic properties, such as ductility and high electrical conductivity.
The atoms of carbon, silicon, germanium, tin and lead in the ground state have a similar structure of the outer electronic layer and belong to p-elements:
Si 3s23p23d0
Ge 3d104s24p24d0
Sn4d105s25p25d0
Pb 4f145d106s26p26d0
However, only germanium, tin and lead are complete electronic analogues - they have the same electronic configuration of both the outer level and the previous sublevel. They have similar chemical properties.
Since the number of unpaired electrons in the ground state is 2, and in the valence-excited state it is 4, then the main valences of all elements are II and IV. Beginning with silicon, group IV p-elements have vacant d-orbitals. This determines the possibility of bond formation by the donor-acceptor mechanism and leads to an increase in valence in coordination compounds up to VI. Due to the absence of a d-sublevel at the carbon atom, its valence in compounds cannot be more than IV, and carbon, unlike Si, Ge, Sn and Pb, is not able to form complex compounds. This circumstance, as well as the smallest size of the atom and the highest electronegativity of carbon, explain why the chemical properties of this element differ significantly not only from the chemical properties of germanium, tin and lead, but also from the chemical properties of silicon.
Due to their electronic structure and average electronegativity values, all elements have characteristic oxidation states -4, +2, +4. As with all elements of the main subgroups of the periodic system, when moving from top to bottom, the stability of compounds of the “extreme” oxidation states (-4 and +4) decreases, and the +2 oxidation states increase.
general characteristics the fourth group of the main subgroup:
a) properties of elements from the point of view of the structure of the atom;
b) oxidation states;
c) properties of oxides;
d) properties of hydroxides;
e) hydrogen compounds.
a) Carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb) - elements of group 4 of the main subgroup of PSE. On the outer electron layer, the atoms of these elements have 4 electrons: ns2np2. In the subgroup, with an increase in the ordinal number of the element, the atomic radius increases, non-metallic properties weaken, and metallic properties increase: carbon and silicon are non-metals, germanium, tin, lead are metals.
b) Elements of this subgroup exhibit both positive and negative oxidation states: -4, +2, +4.
V) Higher oxides carbon and silicon (C02, Si02) have acidic properties, the oxides of the remaining elements of the subgroup are amphoteric (Ge02, Sn02, Pb02).
d) Carbonic and silicic acids (H2CO3, H2SiO3) are weak acids. Hydroxides of germanium, tin and lead are amphoteric, exhibit weak acidic and basic properties: H2GeO3= Ge(OH)4, H2SnO3=Sn(OH)4, H2PbO3=Pb(OH)4.
e) Hydrogen compounds:
CH4; SiH4, GeH4. SnH4, PbH4. Methane - CH4 - strong connection, silane SiH4 - less strong connection.
Schemes of the structure of carbon and silicon atoms, general and distinctive properties.
Si 1S22S22P63S23p2.
Carbon and silicon are non-metals, since there are 4 electrons on the outer electron layer. But since silicon has a larger atomic radius, the ability to donate electrons is more characteristic for it than for carbon. Carbon - reducing agent:
Carbon is a non-metal. The main crystalline modifications of carbon are diamond and graphite.
Silicon is a dark gray non-metal. It makes up 27.6% of the mass of the earth's crust.
Germanium is a silver-gray metal. Density of germanium in solid state equal to 5.327 g/cm3, in liquid - 5.557 g/cm3.
Tin is a malleable, light metal with a silvery-white color.
Lead is a gray malleable metal. The element is quite soft, you can easily cut it with a knife.
Flerovium is an artificial superheavy radioactive element. Of the known isotopes, 289Fl is the most stable. The half-life is about 2.7 seconds for 289Fl and 0.8 seconds for 288Fl.
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IVA-group of the periodic system of elements D.I. Mendeleev are carbon, silicon, germanium, tin, lead. The general electronic formula of the valence shell of atoms of the elements of the IVA group.
The atoms of these elements have four valence electrons in the s- and p-orbitals of the outer energy level. In the unexcited state, two p-electrons are not paired. Therefore, in compounds, these elements can exhibit an oxidation state of +2. But in the excited state, the electrons of the outer energy level acquire the configuration ps1pr3, and all 4 electrons turn out to be unpaired.
For example, for carbon, the transition from the s-sublevel to the p-sublevel can be represented as follows.
In accordance with the electronic structure of the excited state, the elements of the IVA group can exhibit an oxidation state of +4 in compounds. The atomic radii of group IVA elements naturally increase with increasing atomic number. In the same direction, the ionization energy and electronegativity naturally decrease.
Upon transition in the C--Si--Ge--Sn--Pb group, the role of the lone electron pair at the external s-sublevel decreases during the formation chemical bonds. Therefore, if for carbon, silicon and germanium the most characteristic oxidation state is +4, then for lead it is +2.
In a living organism, carbon, silicon and germanium are in the +4 oxidation state, while tin and lead are characterized by the +2 oxidation state.
In accordance with the increase in the size of the atoms and the decrease in the ionization energy in the transition from carbon to lead, non-metallic properties weaken, since the ability to attach electrons decreases and the ease of their return increases. Indeed, the first two members of the group: carbon and silicon are typical non-metals, germanium, tin and lead are amphoteric elements with pronounced metallic properties in the latter.
Strengthening of metallic features in the series C--Si--Ge--Sn--Pb also manifests itself in chemical properties simple substances. Under normal conditions, the elements C, Si, Ge and Sn are resistant to air and water. Lead oxidizes in air. In the electrochemical voltage series of metals, Ge is located after hydrogen, and Sn and Pb are located immediately before hydrogen. Therefore, germanium does not react with acids such as HCl and dilute H2SO4.
The electronic structure and size of the atom, the average value of electronegativity explain strength C--C connections and the tendency of carbon atoms to form long homochains:
Due to the intermediate value of electronegativity, carbon forms low-polarity bonds with vital elements - hydrogen, oxygen, nitrogen, sulfur, etc.
Chemical properties of oxygen compounds of carbon and silicon. Among the inorganic compounds of carbon, silicon and their analogs for physicians and biologists, oxygen compounds of these elements are of the greatest interest.
Carbon (IV) and silicon (IV) oxides EO2 are acidic, and their corresponding hydroxides H2EO3 are weak acids. The corresponding oxides and hydroxides of the remaining elements of group IVA are amphoteric.
CO2 carbon dioxide. is constantly formed in the tissues of the body in the process of metabolism and plays an important role in the regulation of respiration and blood circulation. Carbon dioxide is a physiological stimulant of the respiratory center. Large concentrations of CO2 (over 10%) cause severe acidosis - a decrease in blood pH, violent shortness of breath and paralysis of the respiratory center.
Carbon dioxide dissolves in water. In this case, carbonic acid is formed in the solution:
H2O + CO2? H2CO3
The equilibrium is shifted to the left, so most of the carbon dioxide is in the form of CO2 H2O hydrate, and not H2CO3. Carbonic acid H2CO3 exists only in solution. Refers to weak acids.
As a dibasic acid, H2CO3 forms medium and acidic salts: the former are called carbonates: Na2CO3, CaCO3 are sodium and calcium carbonates; the second - bicarbonates: NaHCO3, Ca (HCO3) 2 - sodium and calcium bicarbonates. All bicarbonates are highly soluble in water; from medium salts soluble carbonates alkali metals and ammonium.
Salt solutions carbonic acid due to hydrolysis, they have an alkaline reaction (pH> 7), for example:
Na2CO3 + HOH? NaHCO3 + NaOH
CO32- + HOH? HCO3- + OH-
The hydrogen-carbonate buffer system (H2CO3--HCO3-) serves as the main buffer system of the blood plasma, ensuring the maintenance of acid-base homeostasis, a constant blood pH of about 7.4.
Since the hydrolysis of carbonates and bicarbonates produces an alkaline environment, these compounds are used in medical practice as antacid (acid neutralizing) agents for increased acidity of gastric juice. These include sodium bicarbonate NaHCO3 and calcium carbonate CaCO3:
NaHCO3 + HCl = NaCl + H2O + CO2
CaCO3 + 2HCl = CaCl2 + H2O + CO2
A liquid is added to silicate cement containing SiO2, which is an aqueous solution of phosphoric acid H3PO4, partially neutralized with zinc oxide ZnO and aluminum hydroxide Al(OH)3. The process of "setting" of silicate-cement begins with the decomposition of the powder with phosphoric acid with the formation of colloidal solutions of aluminum phosphate and silicic acids of variable composition xSiO2 yH2O:
Al2O3 + 2H3PO4 = 2AlPO4 + 3H2O
xSiO2 + yH3O+ = xSiO2 yH2O + yH+
During the preparation of fillings, as a result of mixing, chemical reactions occur with the formation of metal phosphates, for example
3CaO + 2H3PO4 \u003d Ca3 (PO4) 2 + 3H2O
Only alkali metal silicates are highly soluble in water. When mineral acids act on silicate solutions, silicic acids are obtained, for example, metasilicic H2SiO3 and orthosilicic H4SiO4.
Silicic acids are weaker than carbonic, they precipitate under the action of CO2 on silicate solutions. The silicates are highly hydrolyzed. This is one of the reasons for the destruction of silicates in nature.
When various mixtures of silicates are fused with each other or with silicon dioxide, transparent amorphous materials are obtained, called glasses.
The composition of the glass can vary over a wide range and depends on the production conditions.
Quartz glass (almost pure silica) tolerates sudden changes in temperature, almost does not delay ultraviolet rays. Such glass is used for the preparation of mercury-arc lamps, which are widely used in physiotherapy, as well as in the sterilization of operating rooms.
Porcelain masses used in orthopedic dentistry consist of quartz SiO2 (15--35%) and aluminosilicates: feldspar E2O Al2O3 6SiO2, where E is K, Na or Ca (60--75%), and kaolin Al2O3 2SiO2 2H2O (3--10%). The ratio of components may vary depending on the purpose of the porcelain mass.
Feldspar K2O Al2O3 6SiO2 is the main material for obtaining dental porcelain masses. When melted, it turns into a viscous mass. The more feldspar, the more transparent the porcelain mass after annealing. During annealing of porcelain masses, feldspar, being more fusible, lowers the melting point of the mixture.
Kaolin (white clay) is an essential part of dental porcelain. The addition of kaolin reduces the fluidity of the porcelain mass.
Quartz, which is part of dental porcelain, strengthens the ceramic product, gives it greater hardness and chemical resistance.
CO carbon monoxide. Of the compounds of the IVA-group elements, in which they exhibit an oxidation state of +2, carbon monoxide (II) CO is of interest to physicians and biologists. This compound is poisonous and extremely dangerous because it is odorless.
Carbon monoxide (II) - carbon monoxide - a product of incomplete oxidation of carbon. Paradoxically, one of the sources of CO is the person himself, whose body produces and releases into the external environment (with exhaled air) about 10 ml of CO per day. This is the so-called endogenous carbon monoxide (II), which is formed in the processes of hematopoiesis.
Penetrating into the lungs with air, carbon monoxide (II) quickly passes through the alveolar-capillary membrane, dissolves in the blood plasma, diffuses into erythrocytes and enters into a reversible chemical interaction with both oxidized HbO2 and reduced hemoglobin Hb:
HbO2 + CO? HbCO + O2
Hb + CO? HbCO
The resulting carbonyl hemoglobin HbCO is not able to attach oxygen to itself. As a result, it becomes impossible to transfer oxygen from the lungs to the tissues.
The high chemical affinity of carbon monoxide (II) CO for ferrous iron is the main reason for the interaction of CO with hemoglobin. It can be assumed that other bioinorganic compounds containing Fe2+ ions should also react with this poison.
Since the reaction of interaction of oxyhemoglobin with carbon monoxide is reversible, an increase in the partial pressure of O2 in the respiratory medium will accelerate the dissociation of carbonylhemoglobin and the release of CO from the body (the equilibrium will shift to the left according to the Le Chatelier principle):
HbO2 + CO? HbCO + O2
Currently, there are medicinal preparations that are used as antidotes for poisoning the body with carbon monoxide (II). For example, the introduction of reduced iron sharply accelerates the removal of CO from the body in the form, obviously, of iron carbonyl. The action of this drug is based on the ability of CO to act as a ligand in various complexes.
Chemical properties of tin and lead compounds. The oxides of tin (II) and lead (II), SnO and PbO are amphoteric, as are the corresponding hydroxides Sn(OH)2 and Pb(OH)2.
Pb2+ salts - acetate, nitrate - are highly soluble in water, chloride and fluoride are sparingly soluble, sulfate, carbonate, chromate, sulfide are practically insoluble. All lead(II) compounds, especially soluble ones, are poisonous.
The biological activity of lead is determined by its ability to penetrate into the body and accumulate in it.
Lead and its compounds are poisons that act primarily on the neurovascular system and directly on the blood. The chemistry of the toxic action of lead is very complex. The Pb2+ ions are strong complexing agents compared to the cations of the other p-elements of the IVA group. They form strong complexes with bioligands.
Pb2+ ions are able to interact and block the sulfhydryl groups of SH proteins in the molecules of enzymes involved in the synthesis of porphyrins, regulating the synthesis of theme and other biomolecules:
R--SH + Pb2+ + HS--R > R--S--Pb--S--R + 2H+
Often, Pb2+ ions displace natural M2+ ions, inhibiting EM2+ metalloenzymes:
EM2+ + Pb2+ > EPb2+ + M2+
Reacting with the cytoplasm of microbial cells and tissues, lead ions form gel-like albuminates. In small doses, lead salts have an astringent effect, causing gelation of proteins. The formation of gels makes it difficult for microbes to enter the cells and reduces the inflammatory response. The action of lead lotions is based on this.
As the concentration of Pb2+ ions increases, the formation of albuminates becomes irreversible, albuminates of R-COOH proteins of surface tissues accumulate:
Рb2+ + 2R--СООН = Рb(R--СОО)2 + 2Н+
Therefore, lead (II) preparations have a predominantly astringent effect on tissues. They are prescribed exclusively for external use, because, being absorbed in the gastrointestinal tract or respiratory tract, they exhibit high toxicity.
Inorganic tin(II) compounds are not very toxic, in contrast to organic tin compounds.
Lesson Plan
General characteristics of the elements of IV A group.
Carbon and silicon
Target:
Educational: to form in students a general idea of the elements that make up the 4th group, to study their basic properties, to consider their biochemical role and the use of the main compounds of elements.
Developing: develop the skills of writing and speaking, thinking, the ability to use the acquired knowledge to solve various tasks.
Nurturing: develop a sense of the need for new knowledge.
During the classes
Repetition of the topic covered:
How many elements are non-metals? Indicate their place in the PSCE?
What elements are organogenic?
Specify state of aggregation all nonmetals.
How many atoms make up non-metal molecules?
What oxides are called non-salt-forming? Write formulas for non-salt-forming oxides of non-metals.
Cl 2 → HCl → CuCl 2 → ZnCl 2 → AgCl
Write the last reaction equation in ionic form.
Add possible reaction equations:
1) H 2 + Cl 2 = 6) CuO + H 2 =
2) Fe + Cl 2 = 7) KBr + I 2 =
3) NaCl + Br 2 = 8) Al + I 2 =
4) Br 2 + KI = 9) F 2 + H 2 O =
5) Ca + H 2 = 10) SiO 2 + HF =
Write down the reaction equations for the interaction of nitrogen with a) calcium; b) with hydrogen; c) with oxygen.
Carry out a chain of transformations:
N 2 → Li 3 N → NH 3 → NO → NO 2 → HNO 3
When decomposing 192 g of ammonium nitrite by the reaction NH 4 NO 2 \u003d N 2 + 2H 2 O, 60 l of nitrogen were obtained. Find the output of the product from the theoretically possible.
Learning new material.
Group 4 A includes p-elements: carbon, silicon, germanium, tin and lead. Differing in the number of energy levels, their unexcited atoms have 4 electrons at the outer level. Due to the increase in the group from top to bottom of the number of filled electron layers and the size of the atom, the attraction of external valence electrons to the nucleus is weakened, therefore, the non-metallic properties of elements in the subgroup are weakened from top to bottom and metallic properties are enhanced. However, carbon and silicon differ significantly in properties from other elements. These are typical non-metals. Germanium has metallic features, while tin and lead predominate over non-metallic ones.
In nature carbon occurs in the free state in the form of diamond and graphite. Carbon content in earth's crust is about 0.1%. It is part of natural carbonates: limestone, marble, chalk, magnesite, dolomite. Carbon is the main integral part organic matter. Coal, peat, oil, wood and natural gas are usually considered combustible materials used as fuel.
physical properties. Carbon as a simple substance exists in several allotropic forms: diamond, graphite, carbine and fullerene, which have sharply different physical properties, which is explained by the structure of their crystal lattices. Carbin - fine-crystalline black powder, first synthesized in the 60s by Soviet chemists, later found in nature. When heated to 2800º without air, it turns into graphite. Fullerene - in the 80s, spherical structures formed by carbon atoms were synthesized, called fullerenes. They are closed structures consisting of a certain number of carbon atoms - C 60, C 70.
Chemical properties. Chemically, carbon is inert under normal conditions. The reactivity increases with increasing temperature. At high temperatures, carbon interacts with hydrogen, oxygen, nitrogen, halogens, water, and some metals and acids.
When water vapor is passed through hot coal or coke, a mixture of carbon monoxide (II) and hydrogen is obtained:
C + H 2 O = CO + H 2 ( water vapor ),
This reaction takes place at 1200º, at temperatures below 1000º oxidation occurs to SO 2 :
C + 2H 2 O= CO 2 + 2 H 2 .
An industrially important process is the conversion of water gas to methanol (methyl alcohol):
CO + 2H 2 = CH 3 HE
Under the influence of high temperatures, carbon is able to interact with metals, forming carbide, among them, "methanides" and "acetylenides" are distinguished, depending on which gas is released when they interact with water or acid:
CaS 2 + HCl = CaCl 2 + C 2 H 2
Al 4 C 3 + 12 H 2 O = 2 Al(Oh) 3 ↓ + 3 CH 4
big practical value has calcium carbide, which is obtained by heating lime CaO and coke in electric furnaces without air access:
CaO + 3C = CaC 2 + CO
Calcium carbide is used to produce acetylene:
CaS 2 + 2 H 2 O= Ca(OH) 2 + C 2 H 2
However, carbon is characterized by reactions in which it exhibits reducing properties:
2 ZnO + C = Zn+ CO 2
Ccarbon compounds.
Carbon monoxide (CO) is carbon monoxide. In industry, it is obtained by passing carbon dioxide over hot coal at high temperature. Under laboratory conditions, CO is obtained by the action of concentric sulfuric acid on formic acid when heated (sulfuric acid takes away water):
UNSD =H 2 O+ CO
Carbon monoxide (CO 2) is carbon dioxide. In an atmosphere of carbon dioxide, 0.03% by volume, or 0.04% by mass, is small. Volcanoes and hot springs supply the atmosphere, and, finally, a person burns fossil fuels. The atmosphere is constantly exchanging gases with ocean water, which contains 60 times more carbon dioxide than the atmosphere. It is known that carbon dioxide absorbs solar radiation well in the infrared region of the spectrum. Thus, carbon dioxide creates Greenhouse effect and regulates the global temperature.
In the laboratory, carbon dioxide is produced by the action of of hydrochloric acid for marble:
SaCO 3 + 2 HCl = CaCl 2 + H 2 O+ CO 2
The property of carbon dioxide not to support combustion is used in fire fighting devices. With increasing pressure, the solubility of carbon dioxide increases sharply. This is the basis for its use in the manufacture of fizzy drinks.
Carbonic acid exists only in solution. When the solution is heated, it decomposes into carbon monoxide and water. Salts of the acid are stable, although the acid itself is unstable.
The most important reaction to a carbonate ion is the action of dilute mineral acids - hydrochloric or sulfuric. At the same time, bubbles of carbon dioxide are emitted with a hiss, and when it is passed through a solution of calcium hydroxide (lime water), it becomes cloudy as a result of the formation of calcium carbonate.
Silicon. After oxygen, it is the most abundant element on Earth. It makes up 25.7% of the mass of the earth's crust. A significant part of it is represented by silicon oxide, called silica, which occurs as sand or quartz. Silicon oxide occurs in very pure form as a mineral called mountain crystal. Crystalline silicon oxide, colored with various impurities, forms precious and semi-precious stones: agate, amethyst, jasper. Another group of natural silicon compounds is silicates - derivatives silicic acid.
In industry, silicon is produced by the reduction of silicon oxide with coke in electric furnaces:
SiO 2 + 2 C = Si + 2 CO
In laboratories, magnesium or aluminum is used as reducing agents:
SiO 2 + 2Mg = Si + 2MgO
3 SiO 2 + 4Al = Si + 2Al 2 O 3 .
The purest silicon is obtained by reduction of silicon tetrachloride with zinc vapor:
SiCl 4 + 2 Zn = Si + 2 ZnCl 2
physical properties. Crystalline silicon is a brittle substance of dark gray color with a steel sheen. The structure of silicon is similar to that of diamond. Silicon is used as a semiconductor. It is used to make the so-called solar panels, which convert light energy into electrical energy. Silicon is used in metallurgy to obtain silicon steels with high heat resistance and acid resistance.
Chemical properties. In terms of chemical properties, silicon, like carbon, is a non-metal, but its non-metallicity is less pronounced, since it has a large atomic radius.
Silicon at normal conditions chemically quite inert. It directly interacts only with fluorine, forming silicon fluoride:
Si + 2 F 2 = SiF 4
Acids (except for a mixture of hydrofluoric HF and nitric acid) do not act on silicon. But it dissolves in alkali metal hydroxides:
Si+NaOH+H 2 O = Na 2 SiO 3 + 2H 2
At high temperature in an electric furnace, silicon carbide is obtained from a mixture of sand and coke. SiC– carborundum:
SiO 2 + 2C =SiC+ CO 2
Grinding stones and grinding wheels are made from silicon carbide.
Metal compounds with silicon are called silicides:
Si + 2 mg = mg 2 Si
When magnesium silicide is treated with hydrochloric acid, the simplest hydrogen compound of silicon is obtained silane -SiH 4 :
mg 2 Si+ 4HCl = 2 MdCl 2 + SiH 4
Silane is a poisonous gas with an unpleasant odor, self-igniting in air.
silicon compounds. Silica- solid refractory substance. It occurs in nature in two forms. crystalline and amorphous silica. Silicic acid- is a weak acid, when heated, it easily decomposes into water and silicon dioxide. It can be obtained both in the form of a gelatinous mass containing water, and in the form of a colloidal solution (sol). Silicic acid salts called silicates. Natural silicates are rather complex compounds, their composition is usually depicted as a combination of several oxides. Only sodium and potassium silicates are soluble in water. They are called soluble glass, and their solution - liquid glass.
Tasks for fixing.
2. Add possible reaction equations, solve the problem.
| 1 team
| 2 team
| 3 team
|
| H 2 SO 4 + HCl - | CaCO3+? - ? + CO 2 + H 2 O |
|
| NaOH + H 2 SO 4 - | CaCO 3 + H 2 SO 4 - | K 2 SO 4 + CO 2 + H 2 O - |
| CaCl 2 + Na 2 Si O 3 - |
||
| Si O 2 + H 2 SO 4 - | ||
| Ca 2+ + CO 3 -2 - | CaCl 2 ++ NaOH - |
|
| Task: When iron oxide (111) was reduced with carbon, 10.08 g of iron was obtained, which was 90% of the theoretically possible yield. What is the mass of the taken iron oxide (III)? | Task: How much sodium silicate will be obtained by fusing silicon (IV) oxide with 64.2 kg of soda containing 5% impurities? | Task: Under the action of hydrochloric acid on 50 g of calcium carbonate, 20 g of carbon monoxide (IV) was obtained. What is the yield of carbon monoxide (IV) (in%) from the theoretically possible? |
Crossword.
Pabout vertical: 1. Salt of carbonic acid.
Horizontally: 1. The hardest natural substance on Earth. 2. Construction material. 3. Substance used to make dough. 4. Silicon compounds with metals. 5. Element of the main subgroup 1V of the PS group chemical elements. 6. Salts of carbonic acid containing hydrogen. 7. Natural silicon compound.
Homework: pp.210 – 229.
8939 0
Group 14 includes C, Si, Ge, Sn, Pb (Tables 1 and 2). Like the elements of the 3A subgroup, these are p-elements with a similar electronic configuration of the outer shell - s 2 p 2. As you move down the group, the atomic radius increases, causing the bond between the atoms to weaken. Due to the increasing delocalization of the electrons of the outer atomic shells, the electrical conductivity increases in the same direction, so the properties of the elements change from non-metallic to metallic. Carbon (C) in the form of a diamond is an insulator (dielectric), Si and Ge are semimetals, Sn and Pb are metals and good conductors.
Table 1. Some physical and chemical properties of metals of group 14
|
|
Name |
Refers, at. weight |
Radius, pm |
Main isotopes (%) |
||
|
Carbon Carbon [from lat. carbo - coal] |
covalent 77 with double bond 67, with triple bond 60 |
14 C (traces) |
||||
|
Silicon Silicon [from lat. silicis - flint] |
atomic 117, covalent 117 | |||||
|
Germanium Germanium [from lat. Germany] |
3d 10 4s 2 4p 2 |
atomic 122.5, covalent 122 | ||||
|
Tin Tin [from the Anglo-Sax. tin, lat. stannum] |
4d 10 5s 2 5p 2 |
atomic 140.5, covalent 140 | ||||
|
Lead Lead [from Anglo-Sax. lead, lat. plumbum] |
4f 14 5d 10 6s 2 6r 2 |
atomic 175, covalent 154 |
All elements of this group form compounds with an oxidation state of +4. The stability of these compounds decreases when moving to the lower part of the group, while, as in divalent compounds, it, on the contrary, increases with such a movement. All elements except Si, also form compounds with a valence of +2, which is due to " inert pair effect»: by pulling in a pair of external s-elements into the inner electron shell due to worse shielding of outer electrons d- And f-electrons compared to s- And R-electrons of the inner shells of large atoms of the lower members of the group.
The properties of the elements of this group made it possible to use them as anti-algae coatings (AP) for ships. The first such coatings used Pb, then began to apply sn(in the form of a bis-tributyl organotin radical associated with a carbon polymer). For environmental reasons, in 1989 the use of these, as well as other toxic metals in PP ( Hg, Cd, As) was banned, replaced by PP based on organosilicon polymers.
Table 2. The content in the body, toxic (TD) and lethal doses (LD) of metals of the 14th group
|
|
In the earth's crust (%) |
In the ocean (%) |
In the human body | ||||
|
Average (with a body weight of 70 kg) |
Blood (mg/l) |
||||||
|
usually non-toxic, but in the form of CO and CN cyanides it is very toxic |
|||||||
|
(0.03-4.09)x10 -4 |
Non-toxic |
||||||
|
(0.07-7)x10 -10 |
Non-toxic |
||||||
|
(2.3-8.8)x10 -10 |
(0.33-2.4)x10 -4 |
TD 2 g, LD nd, some organotin. compounds are highly toxic |
|||||
|
(0.23-3.3)x10 -4 |
TD 1 mg, LD 10 g |
||||||
Carbon (C) - different from all other elements of the so-called catenation, that is, the ability to form compounds in which its atoms are linked to each other in long chains or rings. This property explains the formation of millions of compounds called organic, which is devoted to a separate section of chemistry - organic chemistry.
The ability of carbon to catenation is explained by several features:
Firstly, strength connections C - C. Thus, the average enthalpy of this bond is about 350 kJ/mol, while the enthalpy of bond Si - Si— only 226 kJ/mol.
Secondly, the unique ability of carbon atoms to hybridization: education 4 sp 3 orbitals with a tetrahedral orientation (ensuring the formation of simple covalent bonds), or 3 sp 2 orbitals oriented in the same plane (providing the formation of double bonds), or 2 sp-orbitals with a linear orientation (providing the formation of triple bonds).
Thus, carbon can form 3 types of coordination environment: linear for two- and three-atomic molecules, when the CN of the element is 2, plane triangular for graphite molecules, fullerenes, alkenes, carbonyl compounds, benzene ring, when the CN is 3, and tetrahedral for alkanes and their derivatives with CN = 4.
In nature, carbon occurs in the form of allotropic, that is, various structural forms (graphite, diamond, fullerenes), as well as in the form of limestone and hydrocarbon raw materials (coal, oil and gas). It is used in the form of coke in steel smelting, carbon black in printing, activated carbon in the purification of water, sugar, etc.
Awarded in 2010 Nobel Prize in physics for the study of a unique form WITH- graphene. The laureates - natives of Russia - A. Geim and K. Novoselov managed to obtain this material from graphite. It is a two-dimensional crystal, that is, it looks like a grid of C atoms one atom thick, wave-like structure, which ensures the stability of the crystal. Its properties are very promising: it is the thinnest transparent material of all currently known, moreover, it is extremely strong (about 200 times stronger than steel), has electrical and thermal conductivity. At room temperature, its electrical resistance is the lowest among all known conductors. In the not-too-distant future, ultra-high-speed computers, flat-panel screens and solar panels, as well as sensitive gas detectors that react to several gas molecules, will be based on graphene. Other areas of its use are not excluded.
In the form of an oxide ( SO) and cyanides ( CN-) carbon is very toxic because it disrupts the processes of respiration. The mechanisms of biological action of these compounds are different. Cyanide inhibits the respiratory enzyme cytochrome oxidase quickly contacting Xi- the active center of the enzyme, blocking the electron flow at the end of the respiratory chain. SO, being a Lewis base, binds to an atom Fe in the hemoglobin molecule is stronger than O 2 , forming carbonylhemoglobin devoid of the ability to bind and carry O 2. Ability SO form links with d-metals in low oxidation states leads to the formation of diverse carbonyl compounds. For example, Fe in a very toxic substance - psitacarbopile Fe(CO) 5 has a zero oxidation state, and in the complex [ Fe(CO) 4 ] 2- is the oxidation state -2 (Fig. 1).
Rice. 1.
Stabilization of a metal atom in a low oxidation state in complexes with SO due to the ability of carbon to protrude due to the structure of low-lying R*-orbitals in the role acceptor ligand. These orbitals overlap with the occupied orbitals of the metal, forming a coordination R-bond in which the metal acts donor electrons. This is one of the few exceptions to general rule the formation of a CS, where the electron acceptor is a metal.
It makes no sense to describe the properties of carbon in more detail, since, as a rule, it is not only not determined in multielement analysis, but its admixture in the sample is also considered undesirable and subject to maximum removal during sample preparation. In optical emission analysis, it gives a very wide spectrum, increasing the noise background and thereby reducing the sensitivity limit for detecting the elements being determined. With mass spectrometry organic molecules form a large number of fragments of molecules with different molecular weights, which give significant interference in the analysis. Therefore, in the vast majority of cases, all carbon-containing substances are removed during sample preparation.
Silicon (Si) - semimetal. When silica is reduced ( SiO 2) black amorphous is formed by carbon Si. crystals Si high purity resemble a gray-blue metal. Silicon is used in semiconductors, alloys and polymers. It is important for some forms of life, for example, for building shells in diatoms; possibly important for the human body. Some silicates are carcinogenic, some cause silicosis.
In all connections Si tetravalent, forms chemical bonds of a covalent nature. The most common oxide SiO 2. Despite the chemical inertness and insolubility in water, when ingested, it can form silicic acids and organosilicon compounds with implicitly expressed biological properties. Toxicity SiO 2 depends on the dispersion of particles: the smaller they are, the more toxic, although the correlations between the solubility of various forms SiO 2 and silicogenicity is not observed. The relationship of the toxicity of silicic acids with Si proves the complete inertness of diamond dust of the same fineness.
Recently, it has been noted that in biological media, silicic acids are involved in the formation hydroxylaluminosilicates, and this phenomenon cannot be explained by the relation Si-C, no connection Si-O-C. As industrial use expands Al and its compounds via aluminosilicates Al increasingly involved in many biochemical reactions. In particular, functional oxygen- and fluorine-containing groups easily form highly stable complex compounds with Al perverting their metabolism.
The most studied among organosilicon compounds silicones- polymers, the skeleton of the molecule of which consists of alternating interconnected atoms Si And O 2. To atoms Si in silicones, alkyl or aryl groups are attached. Availability Si in organosilicon compounds, it radically changes the properties of substances when they do not contain it. For example, conventional polysaccharides can be isolated and purified using strong ethanol, which precipitates the polysaccharide out of solution. Silicon-containing carbohydrates, on the other hand, do not precipitate even in 90% ethanol. The classification of organosilicon compounds is presented in Table. 3.
Table 3 Silicone polymers
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Consist only of Si. The binding energy of a carbon chain C - C is 58.6, and Si - Si 42.5 kcal/mol, and therefore polyorganosilanes are unstable. |
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Bond energy Si-O 89.3 kcal/mol. Therefore, these polymers are strong, resistant to temperature and oxidative degradation. This class of polymers is very diverse in structure. Linear polysiloxanes are widely used as synthetic elastic and heat-resistant rubbers. |
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Atoms in the main chain Si separated by chains of carbon atoms. |
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The main chain contains siloxane groups separated by carbon chains. |
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The backbone is made up of atoms WITH, and the atoms Si contained in side groups or offshoots. |
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Macromolecular chains include atoms Si, O and metals, where M = Al, Ti, Sb, Sn, B. |
The most likely development mechanism silicosis consider the destruction of phagocytes that have captured particles SiO 2. When interacting with lysosomes, silicon particles destroy lysosomes and the phagocyte cell itself, causing the release of enzymes and fragments of organelle molecules. They interact with other phagocytes, that is, a chain process of phagocyte death is launched. If there is a certain amount of silicic acids in the cell, this process is accelerated. The accumulation of dead macrophages initiates the production of collagen in the surrounding fibroblasts, as a result of which sclerosis develops in the focus.
Colloidal silicic acid is a powerful hemolytic, changes the ratio of serum proteins, inhibits a number of respiratory and tissue enzymes, disrupts the metabolism of many substances, including phosphorus. Last time great attention give silylium ions (R 3 Si+). They show the unique ability of the atom Si to expand its coordination sphere, in the form of increasing its electrophilicity. It interacts with any nucleophiles, including ions of opposite charge (including reactive metabolic intermediates) and solvent molecules. Therefore, in condensed phases, they become “elusive” and it is difficult to detect them (Kochina et al., 2006).
Organosilicon polymers (OSPs) were first used as anti-algae self-polishing ship hull coatings (Tsukerman and Rukhadze, 1996). However, then various methods were proposed for the use of COP in other sectors of the national economy, in particular, in medicine as strong bone prostheses.
Germanium (Ge) — amphoteric semimetal; at ultra-high purity, it appears as brittle silver-white crystals. It is used in semiconductors, alloys and special glasses for infrared optics. It is considered a biological stimulant. In compounds, it exhibits an oxidation state of +2 and +4.
Absorption of dioxide and halides Ge weak in the intestine, but in the form of germanates M 2 GeO 4 is somewhat improved. Germanium does not bind to plasma proteins, and is distributed between erythrocytes and plasma in a ratio of approximately 2:1. Quickly (half-life of about 36 hours) is excreted from the body. Generally low toxicity.
Tin (Sn) - soft, ductile metal. It is used in lubricants, alloys, solder, as an additive to polymers, in paints for antifouling coatings, in composition of volatile organotin compounds highly toxic to lower plants and animals. In the form of inorganic compounds, it is non-toxic.
Has two enantiotrope, "gray" (b) and "white" (c) tin, that is, different allotropic forms that are stable in a certain range of conditions. The transition temperature between these forms at a pressure of 1 atm. equal to 286.2°K (13.2°C). White tin has a distorted gray modification structure with CN = 6 and a density of 7.31 g/cm 3 . It is stable under normal conditions, and at low temperature it slowly transforms into a form having a diamond-like structure with CN = 4 and a density of 5.75 g/cm 3 . Such a change in the density of the metal depending on the temperature of the medium is extremely rare and can cause dramatic consequences. For example, in the conditions of cold winters, tin buttons on the uniforms of soldiers were destroyed, and in 1851, in the church of Seitz, the tin pipes of the organ turned into powder.
In the body it is deposited in the liver, kidneys, bones, muscles. With tin poisoning, erythropoiesis decreases, which is manifested by a decrease in hematocrit, hemoglobin, and the number of red blood cells. There has also been an inhibition 5-aminolevulinate dehydratase, one of the enzymes in the heme biosynthesis chain, as well as liver enzymes glutathione reductase And dehydrogenase glucose-6-phosphate, lactate And succinate. Apparently sn excreted from the body as part of complexes with SH containing substrates.
Lead (Pb) - soft, malleable, ductile metal. In moist air it is covered with an oxide film, resistant to oxygen and water. Used in batteries, cables, paints, glass, lubricants, gasoline and radiation protection products. It is a toxic metal of hazard group 1, as it accumulates in the body in bone tissue with impaired renal function and the cardiovascular system. In developed countries, its content is controlled with mandatory medical examination of the population. Causes various diseases.
Medical bioinorganics. G.K. Barashkov
Group IV p-elements include carbon C, silicon Si, germanium Ge, tin Sn, and lead Pb. According to the electronic configurations of their atoms, carbon and silicon are typical elements, while germanium, tin, and lead form a subgroup of germanium. Carbon differs significantly from other p-elements of the group by its high ionization energy. Carbon is a typical non-metallic element. In the C-Si-Ge-Sn-Pb series, the ionization energy decreases, and, consequently, the non-metallic features of the elements weaken, the metallic ones increase. A secondary periodicity is manifested in the change in the properties of atoms and compounds in this series. In most inorganic compounds, carbon exhibits oxidation states -4, +4, +2. In nature, carbon exists in the form of two stable isotopes: 12C (98.892%) and 13C (1.108%). Its content in the earth's crust is 0.15% (mole fraction). In the earth's crust, carbon is found in carbonate minerals (primarily CaCO 3 and MgCO 3), coal, oil, as well as in the form of graphite and, more rarely, diamond. Carbon- the main component of the animal and flora. Allotropic modifications : Diamond- a crystalline substance with an atomic coordination cubic lattice. Graphite- layered crystalline substance with a hexagonal structure. Carbon atoms combine into C 2∞ macromolecules, which are infinite layers of six-membered rings. K a r b i n- black powder (ρ=1.9-2 g/cm3); its lattice is hexagonal, constructed from rectilinear C ∞ chains, in which each atom forms two σ- and π-bonds. Fullerene molecules consist of 60, 70 atoms, forming a sphere - a geodesic dome. Fullerene was obtained by evaporating graphite and condensing its vapors in a helium atmosphere at high pressure. Fullerene is chemically stable. Due to the spherical shape of C 60 and C 70 molecules, fullerene is very hard. Silicon- electronic analogue of carbon. The oxidation state of silicon in its compounds varies from -4 to +4. In silicon compounds, during the formation of covalent bonds, its coordination number does not exceed six. Germanium Ge, tin Sn and lead Pb are complete electronic analogues. Like the typical elements of the group, they have valence s 2 p 2 electrons. In the Ge-Sn-Pb series, the role of the external s-electron pair in the formation of chemical bonds decreases. The change in the characteristic oxidation states in the C-Si-Ge- -Sn-Pb series can be explained by the secondary periodicity in the difference in the energy of the ns- and np-orbitals.
In the Ge-Sn-Pb series, the metallic properties of simple substances are clearly enhanced. Germanium- a silvery-gray substance with a metallic sheen, outwardly similar to metal, but has a diamond-like lattice. Tin is polymorphic. Under normal conditions, it exists in the form of a β-modification (white tin), which is stable above 14 °C. On cooling, white tin transforms into the α-modification (grey tin) with a diamond-like structure. The transition β → α is accompanied by an increase in the specific volume (by 25%), in connection with which the tin crumbles into powder. Lead- dark gray metal with a face-centered cube structure typical of metals. The compounds of carbon and hydrogen are called hydrocarbons. Methane CH 4 - Its molecule has a tetrahedral shape. Methane- a colorless, odorless gas (mp. -182.49 ° C, b.p. -161.56 ° C), chemically very inert due to the valence and coordination saturation of the molecule. It is not affected by acids and alkalis. However, it catches fire easily; its mixtures with air are extremely explosive. Methane- the main component of natural (60-90%) mine and swamp gas. Found in the form of clathrates in the earth's crust. In large quantities, it is formed during the coking of coal. Methane-rich gases are used as a high-calorie fuel and feedstock for the production of water gas. Ethane C 2 H 6, ethylene C 2 H 4 and acetylene C 2 H 2 are gases under normal conditions. Due to the high bond strength of C 2 H 6 (E \u003d 347 kJ / mol), C 2 H 4 (E \u003d 598 kJ / mol) and C 2 H 2 (E \u003d 811 kJ / mol), unlike H 2 0, N 2 H 4 and especially N 2 H 2 are quite stable and chemically inactive. Silanes, compounds of silicon with hydrogen of the general formula Si n H 2n+2 - Silanes were obtained to octa-silane Si 8 Hi 18 . The low strength of the Si-Si bond is due to the limited homologous series of silicon hydrogens. At room temperature, the first two silanes - monosilane SiH 4 and disilane Si 2 H 6 - are gaseous, Si 3 H 8 is a liquid, the rest are solids. All silanes are colorless, have an unpleasant odor, and are poisonous. Unlike communication S-N connection Si-H has a more ionic character. Self-igniting in air. Silanes do not occur in nature.
