The elements carbon C, silicon Si, germanium Ge, tin Sn, and lead Pb make up the IVA group of the Periodic Table of D.I. Mendeleev. The general electronic formula for the valence level of atoms of these elements is n s 2 n p 2, the predominant oxidation states of the elements in compounds are +2 and +4. By electronegativity, the elements C and Si are classified as non-metals, and Ge, Sn and Pb are classified as amphoteric elements, the metallic properties of which increase as the serial number increases. Therefore, in compounds of tin (IV) and lead (IV), chemical bonds are covalent; for lead (II) and, to a lesser extent, for tin (II), ionic crystals are known. In the series of elements from C to Pb, the stability of the +4 oxidation state decreases, and the +2 oxidation state increases. Lead (IV) compounds are strong oxidants, compounds of other elements in the +2 oxidation state are strong reducing agents.

Simple substances carbon, silicon and germanium are chemically quite inert and do not react with water and non-oxidizing acids. Tin and lead also do not react with water, but under the action of non-oxidizing acids they pass into solution in the form of tin (II) and lead (II) aquacations. Alkalis do not transfer carbon into solution, silicon is hardly transferred, and germanium reacts with alkalis only in the presence of oxidants. Tin and lead react with water in an alkaline medium, transforming into tin (II) and lead (II) hydroxo complexes. The reactivity of simple substances of the IVA-group increases with increasing temperature. So, when heated, they all react with metals and non-metals, as well as with oxidizing acids (HNO 3, H 2 SO 4 (conc.), Etc.). In particular, concentrated nitric acid, when heated, oxidizes carbon to CO 2; silicon dissolves chemically in a mixture of HNO 3 and HF, turning into hydrogen hexafluorosilicate H 2. Diluted nitric acid converts tin into tin (II) nitrate, and concentrated one - into hydrated tin (IV) oxide SnO 2 n H 2 O, called β - stannous acid. Lead under the action of hot nitric acid forms lead (II) nitrate, while cold nitric acid passivates the surface of this metal (an oxide film is formed).

Carbon in the form of coke is used in metallurgy as a strong reducing agent that forms CO and CO 2 in air. This makes it possible to obtain free Sn and Pb from their oxides - natural SnO 2 and PbO, obtained by roasting ores containing lead sulfide. Silicon can be obtained by the magnesium-thermal method from SiO 2 (with an excess of magnesium, silicide Mg 2 Si is also formed).

Chemistry carbon- it is mainly the chemistry of organic compounds. Of the inorganic carbon derivatives, carbides are characteristic: salt-like (such as CaC 2 or Al 4 C 3), covalent (SiC) and metal-like (for example, Fe 3 C and WC). Many salt-like carbides are completely hydrolyzed with the release of hydrocarbons (methane, acetylene, etc.).

Carbon forms two oxides: CO and CO 2. Carbon monoxide is used in pyrometallurgy as a strong reducing agent (converts metal oxides into metals). CO is also characterized by addition reactions with the formation of carbonyl complexes, for example. Carbon monoxide is a non-salt-forming oxide; it is poisonous ("carbon monoxide"). Carbon dioxide is an acidic oxide, in an aqueous solution exists in the form of monohydrate CO 2 · H 2 O and weak dibasic carbonic acid H 2 CO 3. Soluble salts of carbonic acid - carbonates and bicarbonates - due to hydrolysis have a pH> 7.

Silicon forms several hydrogen compounds (silanes), which are highly volatile and reactive (self-igniting in air). To obtain silanes, the interaction of silicides (for example, magnesium silicide Mg 2 Si) with water or acids is used.

Silicon in the +4 oxidation state is part of SiO 2 and very numerous and often very complex in structure and composition of silicate ions (SiO 4 4–; Si 2 O 7 6–; Si 3 O 9 6–; Si 4 O 11 6– ; Si 4 O 12 8–, etc.), the elementary fragment of which is the tetrahedral group. Silicon dioxide is an acidic oxide; it reacts with alkalis during fusion (forming polymetasilicates) and in solution (with the formation of orthosilicate ions). From solutions of silicates of alkali metals under the action of acids or carbon dioxide, a precipitate of hydrate of silicon dioxide SiO 2 is released. n H 2 O, in equilibrium with which there is always a weak ortho-silicic acid H 4 SiO 4 in a solution in a low concentration. Aqueous solutions of alkali metal silicates have a pH> 7 due to hydrolysis.

Tin and lead in the oxidation state +2 form oxides SnO and PbO. Tin (II) oxide is thermally unstable and decomposes into SnO 2 and Sn. Lead (II) oxide, on the other hand, is very stable. It is formed when lead is burned in air and occurs naturally. Tin (II) and lead (II) hydroxides are amphoteric.

Tin (II) aquacation exhibits strong acidic properties and is therefore stable only at pH< 1 в среде хлорной или азотной кислот, анионы которых не обладают заметной склонностью вхо­дить в состав комплексов олова(II) в качестве лигандов. При раз­бавлении таких растворов выпадают осадки основных солей раз­личного состава. Галогениды олова(II) – ковалентные соединения, поэтому при растворении в воде, например, SnCl 2 протекает внача­ле гидратация с образованием , а затем гидролиз до выпадения осадка вещества условного состава SnCl(OH). При наличии избытка хлороводородной кислоты, SnCl 2 нахо­дится в растворе в виде комплекса – . Большинство солей свинца(II) (например, иодид, хлорид, сульфат, хромат, карбонат, сульфид) малорастворимы в воде.

Tin (IV) and lead (IV) oxides are amphoteric with predominantly acidic properties. They are answered by polyhydrates EO 2 n H 2 O, passing into solution in the form of hydroxo complexes under the action of an excess of alkalis. Tin (IV) oxide is formed by combustion of tin in air, and lead (IV) oxide can be obtained only when lead (II) compounds are exposed to strong oxidants (for example, calcium hypochlorite).

Covalent tin (IV) chloride is completely hydrolyzed by water with the release of SnO 2, and lead (IV) chloride decomposes under the action of water, releasing chlorine and reducing to lead (II) chloride.

Tin (II) compounds exhibit reducing properties, which are especially strong in an alkaline medium, and lead (IV) compounds exhibit oxidizing properties, which are especially strong in an acidic medium. A common lead compound is its double oxide (Pb 2 II Pb IV) O 4. This compound decomposes under the action of nitric acid, and lead (II) goes into solution in the form of a cation, and lead (IV) oxide precipitates. Lead (IV) found in double oxide is responsible for the strong oxidizing properties of this compound.

Sulfides of germanium (IV) and tin (IV), due to the amphotericity of these elements, when an excess of sodium sulfide is added, form soluble thiosalts, for example, Na 2 GeS 3 or Na 2 SnS 3. The same tin (IV) thiosalt can be obtained from tin (II) sulfide SnS by oxidation with sodium polysulfide. Thiosalts are destroyed under the action of strong acids with the release of gaseous H 2 S and a precipitate of GeS 2 or SnS 2. Lead (II) sulfide does not react with polysulfides, and lead (IV) sulfide is unknown.

IVA group of chemical elements of the periodic table D.I. Mendeleev includes non-metals (carbon and silicon), as well as metals (germanium, tin, lead). The atoms of these elements contain four electrons at the external energy level (ns 2 np 2), two of which are not paired. Therefore, the atoms of these elements in compounds can exhibit valence II. Atoms of group IVA elements can pass into an excited state and increase the number of unpaired electrons to 4 and, accordingly, in compounds exhibit a higher valence equal to the number of group IV. Carbon in compounds exhibits oxidation states from –4 to +4, for the rest, oxidation states are stabilized: –4, 0, +2, +4.

In a carbon atom, unlike all other elements, the number of valence electrons is equal to the number of valence orbitals. This is one of the main reasons for the stability of the C – C bond and the exceptional tendency of carbon to form homochains, as well as the existence of a large number of carbon compounds.

In the change in the properties of atoms and compounds in the series C – Si – Ge – Sn – Pb, secondary peridicity is manifested (Table 5).

Table 5 - Characteristics of atoms of group IV elements

	6 C	1 4 Si	3 2 Ge	50 Sn	82 Pb
Atomic mass	12,01115	28,086	72,59	118,69	207,19
Valence electrons	2s 2 2p 2	3s 2 3p 2	4s 2 4p 2	5s 2 5p 2	6s 2 6p 2
Atom covalent radius, Ǻ	0,077	0,117	0,122	0,140	–
Metallic radius of an atom, Ǻ	–	0,134	0,139	0,158	0,175
Conditional ion radius, E 2+, nm	–	–	0,065	0,102	0,126
Conditional ion radius E 4+, nm	–	0,034	0,044	0,067	0,076
Ionization energy E 0 - E +, ev	11,26	8,15	7,90	7,34	7,42
Content in the earth's crust, at. %	0,15	20,0	2∙10 –4	7∙10 – 4	1,6∙10 – 4

Secondary periodicity (non-monotonic change in the properties of elements in groups) is due to the nature of the penetration of external electrons to the nucleus. Thus, the non-monotonicity of the change in atomic radii on going from silicon to germanium and from tin to lead is due to the penetration of s electrons under the 3d 10 electron shield in germanium, respectively, and the double shield of 4f 14 and 5d 10 electrons in lead. Since the penetrating power decreases in the series s> p> d, the internal periodicity in the change in properties is most clearly manifested in the properties of elements determined by s-electrons. Therefore, it is most typical for compounds of the elements of the A-groups of the periodic table, corresponding to the highest oxidation state of the elements.

Carbon differs significantly from other p-elements of the group by its high value of ionization energy.

Carbon and silicon have polymorphic modifications with different crystal lattice structures. Germanium belongs to metals, silvery-white in color with a yellowish tint, but has a diamond-like atomic crystal lattice with strong covalent bonds. Tin has two polymorphic modifications: a metal modification with a metal crystal lattice and a metal bond; non-metallic modification with an atomic crystal lattice, which is stable at temperatures below 13.8 C. Lead is a dark gray metal with a metallic face-centered cubic crystal lattice. A change in the structure of simple substances in the germanium – tin – lead series corresponds to a change in their physical properties. So germanium and non-metallic tin are semiconductors, metallic tin and lead are conductors. The change in the type of chemical bond from predominantly covalent to metallic is accompanied by a decrease in the hardness of simple substances. So, germanium is quite hard, while lead is easily rolled into thin sheets.

Compounds of elements with hydrogen have the formula EN 4: CH 4 - methane, SiH 4 - silane, GeH 4 - german, SnH 4 - stannane, PbH 4 - plumbane. They are insoluble in water. From top to bottom, in the series of hydrogen compounds, their stability decreases (plumban is so unstable that its existence can only be judged by indirect signs).

Compounds of elements with oxygen have the general formulas: EO and EO 2. The oxides CO and SiO are non-salt-forming; GeO, SnO, PbO - amphoteric oxides; CO 2, SiO 2 GeO 2 - acidic, SnO 2, PbO 2 - amphoteric. With an increase in the oxidation state, the acidic properties of the oxides increase, the basic properties weaken. The properties of the corresponding hydroxides change similarly.

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The IVA group contains the most important elements, without which there would be neither us, nor the Earth on which we live. This carbon is the basis of all organic life, and silicon is the "monarch" of the mineral kingdom.

If carbon and silicon are typical non-metals, and tin and lead are metals, then germanium occupies an intermediate position. Some textbooks classify it as a non-metal, while others refer to it as a metal. It is silvery white in color and looks like a metal, but has a diamond-like crystal lattice and is a semiconductor, like silicon.

From carbon to lead (with a decrease in non-metallic properties):

w decreases the stability of the negative oxidation state (-4)

w decreases the stability of the highest positive oxidation state (+4)

w increased stability of low positive oxidation state (+2)

Carbon is the main constituent of all organisms. In nature, there are both simple substances formed by carbon (diamond, graphite) and compounds (carbon dioxide, various carbonates, methane and other hydrocarbons in the composition of natural gas and oil). The mass fraction of carbon in coal reaches 97%.
A carbon atom in the ground state can form two covalent bonds by the exchange mechanism, but such compounds are not formed under normal conditions. A carbon atom, passing into an excited state, uses all four valence electrons.
Carbon forms quite a few allotropic modifications (see Figure 16.2). These are diamond, graphite, carbyne, and various fullerenes.

In inorganic substances, the oxidation state of carbon is + II and + IV. With these oxidation states of carbon, there are two oxides.
Carbon monoxide (II) is a colorless poisonous gas, odorless. The trivial name is carbon monoxide. Formed by incomplete combustion of carbonaceous fuel. For the electronic structure of its molecule, see page 121. According to the chemical properties of CO, a non-salt-forming oxide, when heated, exhibits reducing properties (it reduces many oxides of not very active metals to metal).
Carbon monoxide (IV) is a colorless, odorless gas. The trivial name is carbon dioxide. Acidic oxide. It is slightly soluble in water (physically), partially reacts with it, forming carbonic acid H2CO3 (molecules of this substance exist only in very dilute aqueous solutions).
Carbonic acid is a very weak, dibasic acid, forms two series of salts (carbonates and bicarbonates). Most carbonates are insoluble in water. Of bicarbonates, only alkali metal and ammonium bicarbonates exist as individual substances. Both the carbonate ion and the bicarbonate ion are base particles; therefore, both carbonates and bicarbonates in aqueous solutions undergo hydrolysis at the anion.
Of the carbonates, the most important are sodium carbonate Na2CO3 (soda, soda ash, washing soda), sodium bicarbonate NaHCO3 (baking soda, baking soda), potassium carbonate K2CO3 (potash) and calcium carbonate CaCO3 (chalk, marble, limestone).
Qualitative reaction to the presence of carbon dioxide in the gas mixture: the formation of a calcium carbonate precipitate when the test gas is passed through lime water (saturated solution of calcium hydroxide) and the subsequent dissolution of the precipitate with further gas passing. Proceeding reactions:

Ca2 + 2OH + CO2 = CaCO3 + H2O;
CaCO3 + CO2 + H2O = Ca2 + 2HCO3.

In pharmacology and medicine, various carbon compounds are widely used - derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers and other compounds. Thus, carbolene (activated carbon) is used to absorb and remove various toxins from the body; graphite (in the form of ointments) - for the treatment of skin diseases; radioactive isotopes of carbon - for scientific research (radiocarbon analysis).

Carbon is the basis of all organic matter. Any living organism is made up largely of carbon. Carbon is the basis of life. The carbon source for living organisms is usually CO 2 from the atmosphere or water. As a result of photosynthesis, it enters biological food chains, in which living things eat each other or each other's remains and thereby extract carbon to build their own bodies. The biological carbon cycle ends with either oxidation and re-entry into the atmosphere, or disposal in the form of coal or oil.

Analytical reactions of carbonate ion CO 3 2-

Carbonates are salts of an unstable, very weak carbonic acid H 2 CO 3, which is unstable in a free state in aqueous solutions and decomposes with the release of CO 2: H 2 CO 3 - CO 2 + H 2 O

Carbonates of ammonium, sodium, rubidium, cesium are soluble in water. Lithium carbonate is slightly soluble in water. Carbonates of other metals are slightly soluble in water. Hydrocarbonates dissolve in water. Carbonate - ions in aqueous solutions are colorless and undergo hydrolysis. Aqueous solutions of alkali metal bicarbonates do not stain when a drop of phenolphthalein solution is added to them, which makes it possible to distinguish carbonate solutions from bicarbonate solutions (pharmacopoeial test).

1.Reaction with barium chloride.

Ва 2+ + СОЗ 2 - -> ВаСО 3 (white fine crystalline)

Similar precipitates of carbonates are produced by cations of calcium (CaCO 3) and strontium (SrCO 3). The precipitate dissolves in mineral acids and acetic acid. In the H 2 SO 4 solution, a white precipitate of BaSO 4 is formed.

A solution of HC1 is slowly added dropwise to the precipitate until the precipitate is completely dissolved: BaCO3 + 2 HC1 -> BaC1 2 + CO 2 + H 2 O

2. Reaction with magnesium sulfate (pharmacopoeial).

Mg 2+ + СОЗ 2 - -> MgCO 3 (white)

Bicarbonate - ion HCO 3 - forms a precipitate of MgCO 3 with magnesium sulfate only when boiling: Mg 2+ + 2 HCO3- -> MgCO 3 + CO 2 + H 2 O

The precipitate MgCO 3 dissolves in acids.

3. Reaction with mineral acids (pharmacopoeial).

CO 3 2- + 2 H 3 O = H 2 CO 3 + 2H 2 O

HCO 3 - + H 3 O + = H 2 CO 3 + 2H 2 O

H 2 CO 3 - CO 2 + H 2 O

The evolved gaseous CO 2 is detected by the turbidity of baritone or lime water in the device for detecting gases, gas bubbles (CO 2), in the test tube - the receiver - the turbidity of the solution.

4. Reaction with uranyl hexacyanoferrate (II).

2CO 3 2 - + (UО 2) 2 (brown) -> 2 UO 2 CO 3 (colorless) + 4 -

A brown solution of uranyl hexacyanoferrate (II) is obtained by mixing a solution of uranyl acetate (CH 3 COO) 2 UO 2 with a solution of potassium hexacyanoferrate (II):

2 (CH 3 COO) 2 GO 2 + K 4 -> (UO 2) 2 + 4 CH 3 COOK

To the resulting solution is added dropwise a solution of Na 2 CO 3 or K 2 CO 3 with stirring until the brown color disappears.

5. Separate discovery of carbonate - ions and bicarbonate - ions by reactions with calcium cations and ammonia.

If carbonate - ions and bicarbonate - ions are simultaneously present in the solution, then each of them can be opened separately.

To do this, first, an excess of CaCl 2 solution is added to the analyzed solution. In this case, СОz 2 - are precipitated in the form of CaCO 3:

COz 2 - + Ca 2+ = CaCO 3

Bicarbonate - ions remain in solution, as Ca (HCO 3) 2 solutions in water. The precipitate is separated from the solution and an ammonia solution is added to the latter. HCO 2 - -anions with ammonia and calcium cations again give a precipitate of CaCO 3: HCO 3 - + Ca 2+ + NH 3 -> CaCO 3 + NH 4 +

6. Other reactions of carbonate - ion.

Carbonate ions, upon reaction with iron (III) chloride FeCl 3, form a brown precipitate Fe (OH) CO 3, with silver nitrate - a white precipitate of silver carbonate Ag 2 CO3, soluble in HbTO3 and decomposing upon boiling in water to a dark precipitate Ag 2 O iCO 2: Ag 2 CO 3 -> Ag 2 O + CO 2

Analytical reactions of acetate - ion CH 3 COO "

Acetate - ion CH 3 COO - - anion of weak monobasic acetic acid CH 3 COOH: colorless in aqueous solutions, subject to hydrolysis, does not have redox properties; rather effective ligand and forms stable acetate complexes with cations of many metals. When reacting with alcohols in an acidic medium, it gives esters.

Acetates of ammonium, alkali and most other metals are readily soluble in water. Silver acetates CH 3 COOAg and mercury (I) are less soluble in water than acetates of other metals.

1.Reaction with iron (III) chloride (pharmacopoeial).

At pH = 5-8 acetate - ion with Fe (III) cations forms a soluble dark red (strong tea color) acetate or iron (III) oxyacetate.

In aqueous solution, it is partially hydrolyzed; acidification of the solution with mineral acids suppresses hydrolysis and leads to the disappearance of the red color of the solution.

3 CH3COOH + Fe -> (CH 3 COO) 3 Fe + 3 H +

When boiling, a red-brown precipitate of basic iron (III) acetate precipitates from the solution:

(CH 3 COO) 3 Fe + 2 H 2 O<- Fe(OH) 2 CH 3 COO + 2 СН 3 СООН

Depending on the ratios of the concentrations of iron (III) and acetate ions, the composition of the sediment can change and respond, for example, to the formulas: Fe OH (CH 3 COO) 2, Fe 3 (OH) 2 O 3 (CH 3 COO), Fe 3 O (OH) (CH 3 COO) 6 or Fe 3 (OH) 2 (CH 3 COO) 7.

The reaction is interfered with by the anions CO 3 2 -, SO 3 "-, PO 4 3 -, 4, which form precipitates with iron (III), as well as SCN- anions (giving red complexes with Fe 3+ cations), iodide is the G ion, oxidized to iodine 1 2, which gives the solution a yellow color.

2. Reaction with sulfuric acid.

Acetate - an ion in a strongly acidic medium turns into weak acetic acid, the vapors of which have a characteristic vinegar smell:

CH 3 COO- + H +<- СН 3 СООН

The reaction is interfered with by the anions NO 2 \ S 2 -, SO 3 2 -, S 2 O 3 2 -, which also emit gaseous products with a characteristic odor in a concentrated H 2 SO4 environment.

3. Reaction of ethyl acetate formation (pharmacopoeial).

The reaction is carried out in a sulfuric acid medium. With ethanol:

CH 3 COO- + H + - CH 3 COOH CH 3 COOH + C 2 H 5 OH = CH 3 COOC 2 H 4 + H 2 O

Released ethyl acetate is detected by its characteristic pleasant odor. Silver salts catalyze this reaction, therefore it is recommended to add a small amount of AgNO 3 during this reaction.

Similarly, when reacting with amyl alcohol С 5 НцОН, a pleasant smelling amyl acetate СН 3 СООС 5 Н (- pearl) is also formed. A characteristic smell of ethyl acetate is felt, which intensifies with careful heating of the mixture.

Analytical reactions of tartrate - ion POC - CH (OH) - CH (OH) - COMPOSITION. Tartrate ion - the anion of a weak dibasic tartaric acid:

NO-CH-COOH

HO-CH-COOH

Tartrate - the ion is highly soluble in water. In aqueous solutions, tartrate ions are colorless, undergo hydrolysis, are prone to complexation, giving stable tartrate complexes with cations of many metals. Tartaric acid forms two rows of salts - medium tartrates containing two charged tartrate - the COCH (OH) CH (OH) COO - ion, and acidic tartrates - hydrotartrates containing a singly charged hydrotartrate - HOOOCH (OH) CH (OH) COO - ion. Potassium hydrogen tartrate (-tartar) KNS 4 H 4 O 6 is practically not a solution in water, which is used to open potassium cations. Medium calcium salt is also slightly soluble in water. Medium potassium salt K 2 C 4 H 4 O 6 is well soluble in water.

I. Reaction with potassium chloride (pharmacopoeial).

С 4 Н 4 О 6 2 - + К + + Н + -> KNS 4 Н 4 О 6 1 (white)

2. Reaction with resorcinol in an acidic medium (pharmacopoeial).

Tartrates when heated with resorcinol meta - C 6 H 4 (OH) 2 in concentrated sulfuric acid form reaction products of cherry red color.

14) Reactions with the ammonia complex of silver. A black precipitate of metallic silver falls out.

15) Reaction with iron (II) sulfate and hydrogen peroxide.

The addition of a dilute aqueous solution of FeSO 4 and H 2 O 2 to a solution containing tartrates. leads to the formation of an unstable iron complex of a crinkled color. Subsequent treatment with an alkali solution of NaOH leads to the formation of a blue complex.

Analytical reactions of oxalate ion С 2 О 4 2-

Oxalate - ion С 2 О 4 2 - - anion of dibasic oxalic acid Н 2 С 2 О 4 of medium strength, relatively well soluble in water. Oxalate - ion in aqueous solutions is colorless, partially hydrolyzed, strong reducing agent, effective ligand - forms stable oxalate complexes with cations of many metals. Oxalates of alkali metals, magnesium and ammonium dissolve in water, while other metals are slightly soluble in water.

1Reaction with barium chloride Ва 2+ + С 2 О 4 2- = ВаС 2 О 4 (white) The precipitate dissolves in mineral acids and in acetic acid (during boiling). 2. Reaction with calcium chloride (pharmacopoeial): Ca 2+ + C 2 O 4 2 - = CaC 2 O 4 (white)

The precipitate dissolves in mineral acids, but does not dissolve in acetic acid.

3. Reaction with silver nitrate.

2 Ag + + С 2 О 4 2 - -> Ag2C2O 4. |. (Curd) Test for solubility. The sediment is divided into 3 parts:

a). In the first test tube with the precipitate, add dropwise with stirring a solution of HNO 3 until the precipitate dissolves;

b). A concentrated ammonia solution is added dropwise to the second test tube with the precipitate with stirring until the precipitate dissolves; v). Add 4-5 drops of HC1 solution to the third test tube with sediment; a white precipitate of silver chloride remains in the test tube:

Ag 2 C 2 O 4 + 2 HC1 -> 2 AC1 (white) + H 2 C 2 O 4

4. Reaction with potassium permanganate. Oxalate ions with KMnO 4 in an acidic medium are oxidized with the release of CO 2; the KMnO 4 solution is discolored due to the reduction of manganese (VII) to manganese (II):

5 C 2 O 4 2 - + 2 MnO 4 "+ 16 H + -> 10 CO 2 + 2 Mn 2+ + 8 H 2 O

Diluted solution of KMnO 4. The latter is discolored; there is a release of gas bubbles - CO 2.

38 Elements of group VA

General characteristics of VA group of the Periodic system. in the form of s x p y is the electronic configuration of the external energy level of the elements of the VA group.

Arsenic and antimony have different allotropic modifications: both with molecular and metal crystal lattices. However, based on a comparison of the stability of cationic forms (As 3+, Sb 3+), arsenic is referred to as non-metals, and antimony to metals.

oxidation states stable for group VA elements

From nitrogen to bismuth (with a decrease in non-metallic properties):

w decreases the stability of the negative oxidation state (-3) (m. properties of hydrogen compounds)

w decreases the stability of the highest positive oxidation state (+5)

w increased stability of low positive oxidation state (+3)

Element	C	Si	Ge	Sn	Pb
Serial number	6	14	32	50	82
Atomic mass (relative)	12,011	28,0855	72,59	118,69	207,2
Density (n.u.), g / cm 3	2,25	2,33	5,323	7,31	11,34
t pl, ° C	3550	1412	273	231	327,5
bale t, ° C	4827	2355	2830	2600	1749
Ionization energy, kJ / mol	1085,7	786,5	762,1	708,6	715,2
Electronic formula	2s 2 2p 2	3s 2 3p 2	3d 10 4s 2 4p 2	4d 10 5s 2 5p 2	4f 14 5d 10 6s 2 6p 2
Electronegativity (Polling)	2,55	1,9	2,01	1,96	2,33

Electronic formulas of inert gases:

• He - 1s 2;
• Ne - 1s 2 2s 2 2p 6;
• Ar - 1s 2 2s 2 2p 6 3s 2 3p 6;
• Kr - 3d 10 4s 2 4p 6;
• Xe - 4d 10 5s 2 5p 6;

Rice. The structure of the carbon atom.

Group 14 (group IVa according to the old classification) of the periodic table of chemical elements of D.I. Mendeleev includes 5 elements: carbon, silicon, germanium, tin, lead (see table above). Carbon and silicon are non-metals, germanium is a substance with metallic properties, tin and lead are typical metals.

The most common element of group 14 (IVa) in the earth's crust is silicon (the second most abundant element after oxygen on Earth) (27.6% by mass), followed by: carbon (0.1%), lead (0.0014%) , tin (0.00022%), germanium (0.00018%).

Silicon, unlike carbon, is not found in free form in nature; it can only be found in bound form:

• SiO 2 - silica, found in the form of quartz (included in many rocks, sand, clay) and its varieties (agate, amethyst, rock crystal, jasper, etc.);
• silicates rich in silicon: talc, asbestos;
• aluminosilicates: feldspar, mica, kaolin.

Germanium, tin and lead are also not found in free form in nature, but are part of some minerals:

• germanium: (Cu 3 (Fe, Ge) S 4) - the mineral germanite;
• tin: SnO 2 - cassiterite;
• lead: PbS - galena; PbSO 4 - anglesite; PbCO 3 - cerussite.

All elements of the 14 (IVa) group in an unexcited state at the external energy level have two unpaired p-electrons (valence is 2, for example, CO). Upon transition to an excited state (the process requires energy consumption), one paired s-electron of the external level "jumps" to a free p-orbital, thus forming 4 "lonely" electrons (one at the s-sublevel and three at the p-sublevel) , which expands the valence capabilities of the elements (valence is 4: for example, CO 2).

Rice. The transition of a carbon atom to an excited state.

For the above reason, elements of group 14 (IVa) can exhibit oxidation states: +4; +2; 0; -4.

Since more and more energy is required to "jump" an electron from the s-sublevel to the p-sublevel in the row from carbon to lead (much less energy is required to excite a carbon atom than to excite a lead atom), carbon enters compounds in which it exhibits a valency of four; and lead is two.

The same can be said about the oxidation states: in the series from carbon to lead, the manifestation of the +4 and -4 oxidation states decreases, and the +2 oxidation state increases.

Since carbon and silicon are non-metals, they can exhibit both positive and negative oxidation states, depending on the compound (in compounds with more electronegative elements, C and Si donate electrons, and are obtained in compounds with less electronegative elements):

C +2 O, C +4 O 2, Si +4 Cl 4 C -4 H 4, Mg 2 Si -4

Ge, Sn, Pb, like metals in compounds, always donate their electrons:

Ge +4 Cl 4, Sn +4 Br 4, Pb +2 Cl 2

The elements of the carbon group form the following compounds:

• unstable volatile hydrogen compounds(general formula EH 4), of which only methane CH 4 is a stable compound.
• non-salt-forming oxides- lower oxides CO and SiO;
• acid oxides- higher oxides CO 2 and SiO 2 - they correspond to hydroxides, which are weak acids: H 2 CO 3 (carbonic acid), H 2 SiO 3 (silicic acid);
• amphoteric oxides- GeO, SnO, PbO and GeO 2, SnO 2, PbO 2 - the latter correspond to hydroxides (IV) of germanium Ge (OH) 4, strontium Sn (OH) 4, lead Pb (OH) 4;

Key words of the abstract: carbon, silicon, elements of IVA-group, properties of elements, diamond, graphite, carbyne, fullerene.

Elements of group IV are carbon, silicon, germanium, tin and lead... Let's take a closer look at the properties of carbon and silicon. The table lists the most important characteristics of these elements.

In almost all of its compounds, carbon and silicon tetravalent , their atoms are in an excited state. The configuration of the valence layer of a carbon atom changes upon excitation of the atom:

The configuration of the valence layer of a silicon atom changes in a similar way:

At the outer energy level of carbon and silicon atoms, there are 4 unpaired electrons. The radius of the silicon atom is larger; its valence layer contains vacant 3 d–Orbitals, this causes differences in the nature of the bonds that form silicon atoms.

The oxidation states of carbon vary in the range from –4 to +4.

A characteristic feature of carbon is its ability to form chains: carbon atoms combine with each other and form stable compounds. Similar silicon compounds are unstable. The ability of carbon to chain formation determines the existence of a huge number organic compounds .

TO inorganic compounds carbon includes its oxides, carbonic acid, carbonates and hydrocarbonates, carbides. The rest of the carbon compounds are organic.

The carbon element is characterized by allotropy, its allotropic modifications are diamond, graphite, carbyne, fullerene... Other allotropic modifications of carbon are now known.

Coal and soot can be seen as amorphous varieties of graphite.

Silicon forms a simple substance - crystalline silicon... There is amorphous silicon - white powder (no impurities).

The properties of diamond, graphite and crystalline silicon are given in the table.

The reason for the obvious differences in the physical properties of graphite and diamond is due to different crystal lattice structure ... In a diamond crystal, each carbon atom (excluding those on the surface of the crystal) forms four equivalent strong bonds with neighboring carbon atoms. These bonds are directed towards the vertices of the tetrahedron (as in the CH 4 molecule). Thus, in a diamond crystal, each carbon atom is surrounded by four of the same atoms located at the vertices of a tetrahedron. The symmetry and strength of C – C bonds in a diamond crystal provide exceptional strength and the absence of electronic conductivity.

V crystal graphite each carbon atom forms three strong equivalent bonds with adjacent carbon atoms in the same plane at an angle of 120 °. In this plane, a layer is formed, consisting of flat six-membered rings.

In addition, each carbon atom has one unpaired electron... These electrons form a common electronic system. The connection between the layers is carried out due to relatively weak intermolecular forces. The layers are located relative to each other in such a way that the carbon atom of one layer is above the center of the hexagon of the other layer. The length of the C – C bond inside the layer is 0.142 nm, the distance between the layers is 0.335 nm. As a result, the bonds between the layers are much weaker than the bonds between atoms within the layer. This causes graphite properties: It is soft, easy to exfoliate, has a gray color and a metallic luster, is electrically conductive and chemically more reactive than diamond. Models of crystal lattices of diamond and graphite are shown in the figure.

Is it possible to turn graphite into diamond? This process can be carried out under severe conditions - at a pressure of about 5000 MPa and at a temperature of 1500 ° C to 3000 ° C for several hours in the presence of catalysts (Ni). The bulk of the products are small crystals (from 1 to several mm) and diamond dust.

Carbin- allotropic modification of carbon, in which carbon atoms form linear chains of the type:

–С≡С – С≡С – С≡С–(α-carbyne, polyyne) or = C = C = C = C = C = C =(β-carbyne, polyene)

The distance between these chains is less than between the graphite layers due to the stronger intermolecular interaction.

Carbyne is a black powder and is a semiconductor. It is chemically more reactive than graphite.

Fullerene- allotropic modification of carbon formed by C 60, C 70 or C 84 molecules. On the spherical surface of the C 60 molecule, carbon atoms are located at the vertices of 20 regular hexagons and 12 regular pentagons. All fullerenes are closed structures of carbon atoms. Fullerene crystals are substances with a molecular structure.

Silicon. There is only one stable allotropic modification of silicon, the crystal lattice of which is similar to that of diamond. Silicon - solid, refractory ( t° pl = 1412 ° C), a very fragile substance of dark gray color with a metallic luster, under standard conditions it is a semiconductor.