4 a group chemistry. General characteristics of Group IV A elements. "Tin Plague" Chemical properties. Biological role. Application in medicine and pharmacy. Reactivity of group IV elements

Lesson Plan

General characteristics of elements of group IV A.

Carbon and silicon

Target:

Educational: to form in students a general idea of ​​the elements included in the 4th group, to study their basic properties, to consider their biochemical role and the use of the main compounds of elements.

Developmental: develop skills in written and oral speech, thinking, and the ability to use acquired knowledge to solve various tasks.

Educating: cultivate a sense of the need to learn new things.

During the classes

Repetition of the covered topic:

How many elements are nonmetals? Indicate their place in PSHE?

What elements are classified as organogenic?

Indicate the state of aggregation of all nonmetals.

How many atoms do nonmetal molecules consist of?

What oxides are called non-salt-forming? Write the formulas of non-salt-forming non-metal oxides.

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 192 g of ammonium nitrite was decomposed by the reaction NH 4 NO 2 = N 2 + 2H 2 O, 60 liters of nitrogen were obtained. Find the yield of the product from the theoretically possible.

Learning new material.

Group 4A 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 number of filled electronic layers and the size of the atom in the group from top to bottom, the attraction of outer valence electrons to the nucleus is weakened, therefore the non-metallic properties of the elements in the subgroup from top to bottom are weakened and the metallic properties are enhanced. However, carbon and silicon have significantly different properties from other elements. These are typical non-metals. Germanium has metallic characteristics, and in tin and lead they predominate over non-metallic ones.

In nature carbon found in a free state in the form of diamond and graphite. The carbon content in the earth's crust is about 0.1%. It is part of natural carbonates: limestone, marble, chalk, magnesite, dolomite. Carbon is the main component of 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, carbyne and fullerene, which have sharply different physical properties, which is explained by the structure of their crystal lattices. Carbin – a finely crystalline black powder, first synthesized in the 60s by Soviet chemists, and later found in nature. When heated to 2800º without air access, 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. Reactivity increases with increasing temperature. At high temperatures, carbon reacts 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 CO 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

When exposed to high temperatures, carbon is able to interact with metals, forming carbide, Among them, “methanides” and “acetylenides” are distinguished, depending on what gas is released when they interact with water or acid:

SaS 2 + HCl = CaCl 2 + C 2 H 2

Al 4 C 3 + 12 H 2 O = 2 Al(OH) 3 ↓ + 3 CH 4

Calcium carbide, which is obtained by heating lime CaO and coke in electric furnaces without air access, is of great practical importance:

CaO + 3C = CaC 2 + CO

Calcium carbide is used to produce acetylene:

SaS 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 unification.

Carbon monoxide (CO) is carbon monoxide. Industrially, it is produced by passing carbon dioxide over hot coal at high temperature. In laboratory conditions, CO is obtained by the action of concentrated sulfuric acid on formic acid when heated (sulfuric acid takes away water):

UNSOUN =H 2 O+ CO

Carbon monoxide (CO 2) is carbon dioxide. In the atmosphere, carbon dioxide is 0.03% by volume, or 0.04% by mass. Volcanoes and hot springs supply the atmosphere, and finally, humans burn fossil fuels. The atmosphere constantly exchanges gases with ocean water, which contains 60 times more carbon dioxide than the atmosphere. It is known that carbon dioxide absorbs sunlight well in the infrared region of the spectrum. Thus, carbon dioxide creates Greenhouse effect and regulates global temperature.

In laboratory conditions, carbon dioxide is produced by the action of hydrochloric acid on marble:

CaCO 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. As pressure increases, the solubility of carbon dioxide increases sharply. This is the basis for its use in the production of fizzy drinks.

Carbonic acid exists only in solution. When the solution is heated, it decomposes into carbon monoxide and water. The salts of the acid are stable, although the acid itself is unstable.

The most important reaction to the carbonate ion is the action of dilute mineral acids - hydrochloric or sulfuric. At the same time, bubbles of carbon dioxide are released with hissing, and when it is passed through a solution of calcium hydroxide (limewater), 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 in the form of sand or quartz. In very pure form, silicon oxide occurs as a mineral called rock 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 obtained by reducing 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 reducing 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 steely sheen. The structure of silicon is similar to that of diamond. Silicon is used as a semiconductor. So-called solar panels are made from it, converting light energy into electrical energy. Silicon is used in metallurgy to produce silicon steels, which have 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.

Under normal conditions, silicon is chemically quite inert. It reacts directly only with fluorine, forming silicon fluoride:

Si + 2 F 2 = SiF 4

Acids (except for a mixture of hydrofluoric acid and nitric acid) have no effect on silicon. But it dissolves in alkali metal hydroxides:

Si + NaOH + H 2 O=Na 2 SiO 3 + 2H 2

At high temperatures in an electric furnace, a mixture of sand and coke produces silicon carbide SiC– carborundum:

SiO 2 + 2C =SiC+ CO 2

Whetstones and grinding wheels are made from silicon carbide.

Compounds of metals 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+ 4NSl = 2 MdCl 2 + SiH 4

Silane is a poisonous gas with an unpleasant odor that is flammable in air.

Silicon compounds. Silica– a solid, refractory substance. In nature, it is distributed 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 either in the form of a gelatinous mass containing water or in the form of a colloidal solution (sol). Silicic acid salts are called silicates. Natural silicates are quite 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 consolidation.

2. Add possible reaction equations and solve the problem.

1 team	2nd team	Team 3
	H2SO4 + HCl -	CaCO 3 +? - ? + 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 iron (III) oxide taken?	Task: How much sodium silicate will be obtained by fusing silicon (IV) oxide with 64.2 kg of soda containing 5% impurities?	Task: The action of hydrochloric acid on 50 g of calcium carbonate produced 20 g of carbon monoxide (IV). What is the yield of carbon monoxide (IV) (in %) of the theoretically possible?

Crossword.

Pabout vertical: 1. Carbonic acid salt.

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 of chemical elements. 6. Salts of carbonic acid containing hydrogen. 7. Natural silicon compound.

Homework: pp.210 – 229.

The elements of the main subgroup of group IV include carbon (C), silicon (Si), germanium (Ge), tin (Sn) and lead (Pb). In the series, the elements differ so much in their chemical nature that when studying their properties, it is advisable to divide them into two subgroups: carbon and silicon form the carbon subgroup, germanium, tin, and lead form the germanium subgroup.

General characteristics of the subgroup

Similarities of elements:

Identical structure of the outer electronic layer of atoms ns 2 nр 2;

P-elements;

Higher S.O. +4;

Typical valencies II, IV.

Valence states of atoms

For atoms of all elements, 2 valence states are possible:

1. Basic (non-excited) ns 2 np 2

2. Excited ns 1 np 3

Simple substances

Elements of the subgroup in the free state form solid substances, in most cases with an atomic crystal lattice. Allotropy is characteristic

Both the physical and chemical properties of simple substances vary significantly, and vertical changes are often non-monotonic. Usually the subgroup is divided into two parts:

1 - carbon and silicon (non-metals);

2 - germanium, tin, lead (metals).

Tin and lead are typical metals; germanium, like silicon, is a semiconductor.

Oxides and hydroxides

Lower oxides EO

CO and SiO are non-salt-forming oxides

GeO, SnO, PbO - amphoteric oxides

Higher oxides EO +2 O

CO 2 and SiO 2 - acid oxides

GeO 2 , SnO 2 , PbO 2 - amphoteric oxides

There are numerous hydroxo derivatives of the EO nH 2 O and EO 2 nH 2 O types, which exhibit weakly acidic or amphoteric properties.

Hydrogen compounds EN 4

Due to the closeness of the EO values, the E-H bonds are covalent and low-polar. Under normal conditions, EN 4 hydrides are gases that are poorly soluble in water.

CH 4 - methane; SiH 4 - silane; GeH 4 - germanium; SnH 4 - stannane; PbH 4 - not received.

Molecular strength ↓

Chemical activity

Regenerative capacity

Methane is chemically inactive, the remaining hydrides are very reactive, they are completely decomposed by water, releasing hydrogen:

EN 4 + 2H 2 O = EO 2 + 4H 2

EN 4 + 6H 2 O = H 2 [E(OH) 6 ] + 4H 2

Methods of obtaining

EN 4 hydrides are obtained indirectly, since direct synthesis from simple substances is possible only in the case of CH 4, but this reaction also occurs reversibly and under very harsh conditions.

Usually, to obtain hydrides, compounds of the corresponding elements with active metals are used, for example:

Al 4 C 3 + 12H 2 O = ZSN 4 + 4Al(OH) 2

Mg 2 Si + 4HCl = SiH 4 + 2MgCl 2

Hydrocarbons, silicon hydrocarbons, germanic hydrocarbons.

Carbon and hydrogen, in addition to CH 4, form countless compounds C x H y - hydrocarbons (the subject of the study of organic chemistry).

Hydrogen silicones and germanic hydrogens of the general formula E n H 2n+2 have also been obtained. They have no practical significance.

In terms of importance, 2 elements of the main subgroup of group IV occupy a special position. Carbon is the basis of organic compounds, therefore the main element of living matter. Silicon is the main element of all inanimate nature.

8939 0

Group 14 includes C, Si, Ge, Sn, Pb (Tables 1 and 2). Like 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 bonds between the atoms to weaken. Due to the increasing delocalization of the electrons of the outer atomic shells, 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 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 group 14 metals

	Name		Relates, at. weight	Electronic formula	Radius, pm	Main isotopes (%)
	Carbon Carbon [from lat. carbo - coal]				covalent 77 at double bond 67, at triple bond 60	14 C (traces)
	Silicon Silicon [from lat. silicis - flint]				atomic 117, covalent 117
	Germanium Germanium [from lat. Germania - Germany]			3d 10 4s 2 4p 2	atomic 122.5, covalent 122
	Tin Tin [from Anglo-Saxon. tin, lat. stannum]			4d 10 5s 2 5p 2	atomic 140.5, covalent 140
	Lead Lead [from Anglo-Saxon. lead, lat. plumbum]			4f 14 5d 10 6s 2 6р 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 bottom of the group, when, as with divalent compounds, it, on the contrary, increases with such movement. All elements except Si, also form compounds with valency +2, which is due to “ inert couple effect": by retracting 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 (AA) for ships. The first such coatings used Pb, then they began to use Sn(as a bis-tributyl organotin radical bound to 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. Content in the body, toxic (TD) and lethal doses (LD) of group 14 metals

	In the earth's crust (%)	In the ocean (%)	In the human body
			Average (with body weight 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 very toxic
					(0.23-3.3)x10 -4		TD 1 mg, LD 10 g

Carbon (C) - differs 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, to which a separate section of chemistry is devoted - organic chemistry.

The ability of carbon to catenate is explained by several features:

Firstly, strength communications S - S. Thus, the average enthalpy of this bond is about 350 kJ/mol, while the enthalpy of the bond Si-Si- only 226 kJ/mol.

Secondly, the unique ability of carbon atoms to hybridization: education 4 sp 3 -orbitals with 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 linear orientation (ensuring the formation of triple bonds).

Thus, carbon can form 3 types of coordination environments: linear for di- and triatomic molecules, when the element’s CN is 2, plane-triangular in molecules of graphite, fullerenes, alkenes, carbonyl compounds, benzene ring, when the coordination number is 3, and tetrahedral for alkanes and their derivatives with CN = 4.

In nature, carbon is found in the form of allotropes, 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, soot in printing, activated carbon in the purification of water, sugar, etc.

In 2010, the Nobel Prize in Physics was awarded 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 network 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, it is also extremely strong (about 200 times stronger than steel), and has electrical and thermal conductivity. At room temperature, its electrical resistance is the lowest among all known conductors. In the near future, ultra-high-speed computers, flat-panel screens and solar panels, as well as sensitive gas detectors that respond to several gas molecules, will be created based on graphene. Other areas of its use are not excluded.

In oxide form ( CO) and cyanides ( CN-) carbon is very toxic because it disrupts respiration processes. The mechanisms of biological action of these compounds are different. Cyanide inhibits respiratory enzyme cytochrome oxidase, quickly contacting Si- the active center of the enzyme, blocking the electron flow at the final section of the respiratory chain. CO, being a Lewis base, bonds 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 CO form coordination ties with d-metals in low oxidation states leads to the formation of a variety of carbonyl compounds. For example, Fe in a very poisonous substance - psitacarbopyl Fe(CO) 5 - has a zero oxidation state, and in the complex [ Fe(CO) 4 ] 2- — oxidation state -2 (Fig. 1).

Rice. 1.

Stabilization of the metal atom in a low oxidation state in complexes with CO explained by 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-a bond in which metal protrudes donor electrons. This is one of the few exceptions to the general rule of CS formation, where the electron acceptor is a metal.

There is no point in describing the properties of carbon in more detail, since in multielement analysis, as a rule, it is not only not determined, but its impurity 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 background noise and thereby reducing the sensitivity limit for detecting the elements being determined. In mass spectrometry, organic molecules form a large number of molecular fragments with different molecular weights, which cause 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 reducing silica ( SiO 2) carbon forms black amorphous Si. Crystals Si of high purity resemble blue-gray metal. Silicon is used in semiconductors, alloys and polymers. It is important for some forms of life, for example, for the construction of shells in diatoms; It may also be 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 dioxide SiO 2. Despite its chemical inertness and insolubility in water, upon entry into the body it can form silicic acids and organosilicon compounds with implicit biological properties. Toxicity SiO 2 depends on the dispersity of the particles: the smaller they are, the more toxic, although there are correlations between the solubility of various forms SiO 2 and silicogenicity is not observed. The connection between the toxicity of silicic acids and Si proves the complete inertness of diamond dust of the same dispersion.

Recently, it has been noted that in biological media, silicic acids participate in the formation hydroxylaluminosilicates, and this phenomenon cannot be explained by any connection Si-C, no communication Si-O-S. 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 molecular skeleton of which consists of alternating interconnected atoms Si And O 2. To the atoms Si Silicones have alkyl or aryl groups attached. Availability Si in organosilicon compounds radically changes the properties of substances when they do not contain it. For example, common polysaccharides can be isolated and purified using strong ethanol, which precipitates the polysaccharide from solution. Silicon-containing carbohydrates, on the contrary, do not precipitate even in 90% ethanol. The classification of organosilicon compounds is presented in table. 3.

Table 3. Organosilicon polymers

	Name and structure	Note
		Consist only of Si. Bond energy of a carbon chain S - S is equal to 58.6, and y Si-Si 42.5 kcal/mol, and therefore polyorganosilanes are unstable.
		Communication energy Si - O 89.3 kcal/mol. Therefore, these polymers are durable, resistant to temperature and oxidative degradation. This class of polymers is very diverse in structure. Linear polysilaxanes are widely used as synthetic elastic and heat-resistant rubbers.
		Atoms in the main chain Si separated by chains of carbon atoms.
		The main chain contains siloxane groups separated by carbon chains.
		The main chain consists of atoms WITH, and atoms Si contained in side groups or branches.
		Macromolecular chains include atoms Si, O and metals, where M = Al, Ti, Sb, Sn, B.

The most likely mechanism of development silicosis consider the destruction of phagocytes that have captured particles SiO 2. When interacting with lysosomes, silicon particles destroy the 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 triggered. 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 lesion.

Colloidal silicic acid is a powerful hemolytic, changes the ratio of serum proteins, inhibits a number of respiratory and tissue enzymes, and disrupts the metabolism of many substances, including phosphorus. Recently, much attention has been paid to silylium ions (R3Si+). They reveal the unique ability of the atom Si 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 identify them (Kochina et al., 2006).

Organosilicon polymers (OSPs) were first used as anti-algae self-polishing coatings for ship hulls (Tsukerman and Rukhadze, 1996). However, then various methods of using COPs were proposed in other sectors of the national economy, in particular, in medicine as durable bone prostheses.

Germanium (Ge) - amphoteric semimetal; at ultra-high purity it looks like fragile crystals of silvery-white color. Used in semiconductors, alloys and special glasses for infrared optics. Considered a biological stimulant. In compounds it exhibits oxidation states of +2 and +4.

Absorption of dioxide and halides Ge weak in the intestines, but in the form of germanates M 2 GeO 4 is slightly improved. Germanium does not bind to plasma proteins and is distributed between red blood cells and plasma in a ratio of approximately 2:1. It is quickly eliminated from the body (half-life about 36 hours). Generally low toxic.

Tin (Sn) - soft, ductile metal. It is used in lubricants, alloys, solder, as an additive to polymers, in paints for anti-fouling coatings, and in volatile organotin compounds, which are 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 structure of the gray modification with CN = 6 and density 7.31 g/cm 3 . It is stable under normal conditions, and at low temperatures it slowly transforms into a form that has a diamond-like structure with CN = 4 and a density of 5.75 g/cm 3 . Such a change in metal density depending on the temperature of the environment is extremely rare and can cause dramatic consequences. For example, in cold winter conditions, tin buttons on soldiers' uniforms 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, and muscles. With tin poisoning, erythropoiesis decreases, which is manifested by a decrease in hematocrit, hemoglobin and the number of red blood cells. Inhibition was also noted 5-aminolevulinate dehydratase, one of the enzymes in the heme biosynthesis chain, as well as liver enzymes glutathione reductase And glucose-6-phosphate dehydrogenases, lactate And succinate. Apparently Sn excreted from the body as part of complexes with SH-containing substrates.

Lead (Pb) - soft, malleable, ductile metal. In humid air it becomes covered with an oxide film and is 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 and cardiovascular function. In developed countries, its content is controlled during mandatory medical examination of the population. Causes a variety of 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 classified as typical elements, while germanium, tin and lead form a subgroup of germanium. Carbon differs significantly from other p-elements of the group in its high ionization energy. Carbon is a typical non-metallic element. In the series C-Si-Ge-Sn-Pb, the ionization energy decreases, and therefore, the non-metallic characteristics of the elements weaken, and the metallic ones increase. Secondary periodicity manifests itself in changes in the properties of atoms and compounds in this series. In most inorganic compounds, carbon exhibits oxidation states -4, +4, +2. In nature, carbon is found in the form of two stable isotopes: 12C (98.892%) and 13C (1.108%). Its content in the earth's crust is 0.15% (mol fraction). In the earth's crust, carbon is found in carbonate minerals (primarily CaC0 3 and MgCO 3), coal, oil, and also in the form of graphite and, less commonly, diamond. Carbon- the main component of the animal and plant world. Allotropic modifications : Diamond- a crystalline substance with an atomic coordination cubic lattice. Graphite- layered crystalline substance with a hexagonal structure. Carbon atoms are combined into C 2∞ macromolecules, which are endless layers of six-membered rings. Karbin- black powder (ρ=1.9-2 g/cm3); its lattice is hexagonal, built from straight chains C ∞, in which each atom forms two σ- and π-bonds. Fullerene molecules consist of 60, 70 atoms forming a sphere - a geodesic dome. Fullerene is obtained by evaporation of graphite and condensation of its vapor in a helium atmosphere at high pressure. Fullerene is chemically resistant. Due to the spherical shape of the 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, when covalent bonds are formed, its coordination number does not exceed six. Germanium Ge, tin Sn and lead Pb are complete electronic analogues. Like typical elements of the group, their valence electrons are 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 characteristic oxidation states in the C-Si-Ge- -Sn-Pb series can be explained by 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 luster, looks like metal, but has a diamond-like lattice. Tin is polymorphic. Under normal conditions, it exists in the form of a β-modification (white tin), stable above 14 °C. When cooled, white tin transforms into the α-modification (gray tin) with a diamond-type structure. The transition β→α is accompanied by an increase in specific volume (by 25%), and therefore the tin crumbles into powder. Lead- dark gray metal with a face-centered cube structure typical of metals. 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, bp -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. Contained in the form of clathrates in the earth's crust. It is formed in large quantities during the coking of coal. Methane-rich gases are used as high-calorie fuels and raw materials 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 = 347 kJ/mol), C 2 H 4 (E = 598 kJ/mol) and C 2 H 2 (E = 811 kJ/mol), in contrast to 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 up to octa-silane Si 8 Hi 18 have been obtained. The low strength of the Si-Si bond is due to the limited homologous series of hydrogen silicas. At room temperature, the first two silanes - monosilane SiH 4 and disilane Si 2 H 6 - are gaseous, Si 3 H 8 are liquid, and the rest are solids. All silanes are colorless, have an unpleasant odor, and are poisonous. Unlike the C-H bond, the Si-H bond is more ionic in nature. They ignite spontaneously in air. Silanes do not occur in nature.

Carbon, silicon, germanium, tin and lead form the main subgroup of group IV. The outer energy levels of p-elements of group IV contain four electrons (configuration ns 2 np 2), of which two are paired s-electrons and two unpaired p-electrons.

In an unexcited state, elements of this subgroup exhibit a valency of two. Upon transition to an excited state, accompanied by the transition of one of the s-electrons of the outer level to a free cell of the p-sublevel of the same level, all electrons of the outer layer become unpaired, and the valence increases to 4.

The energy expended for the electron transition is more than compensated by the energy released during the formation of four bonds.

In compounds, elements of the carbon subgroup exhibit an oxidation state of +4 or -4, as well as +2, the latter becoming more characteristic with increasing nuclear charge. For carbon, silicon and germanium, the most typical oxidation state is +4, for lead - +2. The -4 oxidation state in the C - Pb sequence is becoming less and less common.

Elements of the carbon subgroup form oxides of the general formula RO 2 and RO, and hydrogen compounds of the formula - RH 4. Hydrates of higher oxides of carbon and silicon have acidic properties, hydrates of other elements are amphoteric, and acidic properties are more pronounced in germanium hydrates, and basic ones are more pronounced in lead hydrates. From carbon to lead, the strength of hydrogen compounds RH 4 decreases: CH 4 is a strong substance, and PbH 4 is not isolated in free form.

When moving from carbon to lead, the radii of neutral atoms increase, and the ionization energy decreases, therefore, from carbon to lead, non-metallic properties decrease, and metallic ones increase. Non-metals are carbon and silicon (see Table 24).