General characteristics of the elements of the IV-A group. Properties. General characteristics of the elements of the IV group of the main subgroup. Elements of the main subgroup of group 4

Metallic properties are enhanced, non-metallic properties are reduced. The outer layer has 4 electrons.

Chemical properties(carbon based)

Interact with metals:

4Al + 3C = Al 4 C 3 (reaction at high temperature)

Interact with non-metals:

2H 2 + C = CH 4

Interact with water:

C + H 2 O = CO + H 2

2Fe 2 O 3 + 3C = 3CO 2 + 4Fe

Interact with acids:

3C + 4HNO 3 = 3CO 2 + 4NO + 2H 2 O

Carbon. Characterization of carbon, based on its position in the periodic system, carbon allotropy, adsorption, distribution in nature, production, properties. The most important carbon compounds

Carbon (chemical symbol - C, Latin Carboneum) is a chemical element of the fourteenth group (according to the outdated classification - the main subgroup of the fourth group), the 2nd period of the periodic system of chemical elements. serial number 6, atomic mass - 12.0107.

Carbon exists in many allotropic modifications with very diverse physical properties. The variety of modifications is due to the ability of carbon to form chemical bonds of different types.

Natural carbon consists of two stable isotopes - 12C (98.93%) and 13C (1.07%) and one radioactive isotope 14C (β-emitter, Т½ = 5730 years), concentrated in the atmosphere and in the upper part of the earth's crust.

The main and well-studied allotropic modifications of carbon are diamond and graphite. Under normal conditions, only graphite is thermodynamically stable, while diamond and other forms are metastable. Liquid carbon exists only under a certain external pressure.

At pressures above 60 GPa, the formation of a very dense C III modification (the density is 15-20% higher than that of diamond) with metallic conductivity is assumed.

The crystalline modification of hexagonal carbon with a chain structure of molecules is called carbyne. Several forms of carbyne are known, differing in the number of atoms per unit cell.

Carbyne is a fine-crystalline black powder (density 1.9-2 g / cm³), has semiconducting properties. Made in artificial conditions from long chains of carbon atoms, stacked parallel to each other.

Carbyne is a linear polymer of carbon. In a carbyne molecule, carbon atoms are connected in chains alternately either by triple and single bonds (polyene structure), or permanently by double bonds (polycumulene structure). Carbyne has semiconducting properties, and under the influence of light, its conductivity is greatly increased. The first practical application is based on this property - in photocells.

The reaction of carbon with sulfur produces carbon disulfide CS2; CS and C3S2 are also known.

With most metals, carbon forms carbides, for example:

The reaction of carbon with water vapor is important in industry:

When heated, carbon reduces metal oxides to metals. This property is widely used in the metallurgical industry.

Graphite is used in the pencil industry, but mixed with clay to reduce its softness. Diamond, due to its exceptional hardness, is an indispensable abrasive material. In pharmacology and medicine, various carbon compounds are widely used - derivatives of carbonic acid and carboxylic acids, various heterocycles, polymers and other compounds. Carbon plays a huge role in human life. Its applications are as varied as the many-sided element itself. In particular, carbon is an integral component of steel (up to 2.14 wt%) and cast iron (more than 2.14 wt%)

Carbon is a part of atmospheric aerosols, as a result of which the regional climate can change, and the number of sunny days can decrease. Carbon enters the environment in the form of soot in the exhaust gases of vehicles, when coal is burned at thermal power plants, during open pit mining, underground gasification, coal concentrates production, etc. The concentration of carbon over combustion sources is 100-400 μg / m³, in large cities 2 , 4-15.9 mcg / m³, in rural areas 0.5-0.8 mcg / m³. With gas-aerosol emissions from nuclear power plants, (6-15) · 109 Bq / day 14СО2 enters the atmosphere.

The high content of carbon in atmospheric aerosols leads to an increase in the incidence of diseases in the population, especially in the upper respiratory tract and lungs. Occupational diseases are mainly anthracosis and dust bronchitis. In the air of the working area MPC, mg / m³: diamond 8.0, anthracite and coke 6.0, coal 10.0, carbon black and carbon dust 4.0; in the atmospheric air the maximum one-time 0.15, the daily average 0.05 mg / m³.

The most important connections. Carbon monoxide (II) (carbon monoxide) CO. Under normal conditions, it is a colorless, odorless and tasteless very poisonous gas. The toxicity is explained by the fact that it easily combines with blood hemoglobin.

Carbon monoxide (IV) CO2. Under normal conditions - a colorless gas with a slightly sour smell and taste, one and a half times heavier than air, does not burn and does not support combustion.
Carbonic acid H2CO3. Weak acid. Carbonic acid molecules exist only in solution.

Phosgene COCl2. Colorless gas with a characteristic odor, tboil = 8оС, tmelt = -118оС. Very poisonous. Let's slightly dissolve in water. Reactive. Used in organic syntheses.

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 included in the 4th group, to study their basic properties, to consider their biochemical role and the use of basic compounds of elements.

Developing: to develop the skills of writing and speaking, thinking, the ability to use the knowledge gained to solve various tasks.

Educational: foster a sense of the need to learn new things.

During the classes

Repetition of the passed topic:

How many elements are non-metals? Indicate their place in the PSKhE?

What elements are organogenic?

Indicate the state of aggregation of all non-metals.

How many atoms are nonmetal molecules made of?

What oxides are called non-salt-forming? Write the 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

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

Learning new material.

Group 4 includes p-elements: carbon, silicon, germanium, tin and lead. Differing in the number of energy levels, unexcited atoms have 4 electrons each 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 external 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. Nevertheless, carbon and silicon differ significantly in properties from other elements. These are typical non-metals. Germanium has metallic features, while in tin and lead they prevail over non-metallic ones.

In nature carbon occurs 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 constituent of organic matter. Coal, peat, oil, wood and natural gas are generally considered combustible materials used as fuels.

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 - fine-crystalline black powder, first synthesized in the 60s by Soviet chemists, 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. 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 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

Under the influence of 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:

CaC 2 + HCl = CaCl 2 + C 2 H 2

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

Of great practical importance is 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:

CaC 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 a high temperature. Under laboratory conditions, CO is obtained by the action of concentrated sulfuric acid on formic acid when heated (sulfuric acid takes away water):

NSOOH =H 2 O+ CO

Carbon monoxide (CO 2) is carbon dioxide. In an atmosphere of carbon dioxide, there is little 0.03% by volume, or 0.04% by weight. Volcanoes and hot springs supply the atmosphere, and, finally, man 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 sunlight well in the infrared region of the spectrum. Thus, carbon dioxide creates Greenhouse effect and regulates the global temperature.

Under 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 non-combustion property of carbon dioxide 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 effervescent drinks.

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

The most important reaction to carbonate - ion is the action of dilute mineral acids - hydrochloric or sulfuric. At the same time, bubbles of carbon dioxide are released 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 is found in the form of sand or quartz. In very pure form, silicon oxide occurs in the form of 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 reduction of silicon tetrachloride with zinc vapor:

SiCl 4 + 2 Zn = Si + 2 ZnCl 2

Physical properties. Crystalline silicon is a brittle dark gray substance with a steel sheen. The structure of silicon is similar to that of diamond. Silicon is used as a semiconductor. The so-called solar batteries are made from it, converting 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 is chemically quite inert under normal conditions. 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) do not affect 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

Grinding stones 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 acted upon with hydrochloric acid, the simplest hydrogen silicon compound is obtained silane -SiH 4 :

Mg 2 Si+ 4NSl = 2 MdCl 2 + SiH 4

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

Silicon compounds. Silica- solid refractory substance. In nature, it is distributed in two types 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 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 water soluble. They are called soluble glass and their solution - liquid glass.

Tasks for consolidation.

2. To add possible reaction equations, to solve the problem.

Crossword.

NSabout vertical: 1. Carbonic acid salt.

Horizontally: 1. The hardest natural substance on Earth. 2. Building material. 3. The substance used to make the dough. 4. Compounds of silicon with metals. 5. Element of the main subgroup 1V of group PS of chemical elements. 6. Hydrogen-containing carbonic acid salts. 7. Natural compound of silicon.

Homework: pp. 210 - 229.

IV group main subgroup

Application

Germanium is widely used as a semiconductor. Almost half of the tin produced is used to make tin, the main consumer of which is the production of canned food. A significant amount of tin is consumed to obtain alloys - bronze (copper + 10 - 20% Sn). Tin (IV) oxide is used for the manufacture of semiconductor sensors. Chemical semiconductor sensors are sensitive elements based on SnO 2, In 2 O 3, ZnO, TiO, which convert the energy of a chemical process into electrical energy. The interaction of the detected gas (O 2, CO, NO 2) with the sensitive material of the sensor causes a reversible change in its electrical conductivity, which is recorded by an electronic device.

Elements IV (14 according to the new YUPAC nomenclature) of the main subgroup include: carbon C, silicon Si, germanium Ge, tin Sn, lead Pb.

In the ground state, atoms of pnictogens have an electronic configuration of the external energy level -… ns 2 np 2, where n is the principal quantum number (period number). The following oxidation states are characteristic for the atoms of Group IV elements of the main subgroup: for carbon - (–4, 0, +2, +4); for silicon - (–4, 0, (+2), +4); for germanium - ((–4), 0, +2, +4); for tin - (0, +2, +4), for lead - (0, +2, +4).

The stability of compounds with the highest oxidation state +4 is maximum for silicon and decreases in the Ge - Sn - Pb series. This is explained by the fact that the energy consumption for the transfer of an electron from the s to the p sublevel is not compensated by the energy of the formed chemical bonds. The stability of compounds with an oxidation state of +2 increases.

Table 1 shows the main properties of the IV (14) group of the main subgroup.

In group IV, the main subgroup, from top to bottom, the orbital radius increases. The nonuniform change in the radius on going from Si to Ge and from Sn to Pb is due to the effects of d and f compression. Electrons of the 3d and 4f sublevels weakly screen the charge of atomic nuclei. This leads to the contraction of the electron shells of germanium and lead due to an increase in the effective charge of the nucleus.

In group IV, the main subgroup from top to bottom, the effective charge of the nucleus increases, the orbital radius also increases, the ionization energy decreases, and the reducing properties of atoms increase.

Carbon differs from other atoms of Group IV elements of the main subgroup by its high ionization energy.

The carbon atom has no free d-orbitals, the valence electrons of the carbon atom (... 2s 2 2p 2) are weakly screened from the action of the nucleus, which explains the small radius of the carbon atom and high values ​​of ionization and electronegativity.

In group IV, the main subgroup from top to bottom, the effective charge of the nucleus increases, the orbital radius increases, the energy of electron affinity decreases, and the oxidizing properties of atoms decrease.

The electron affinity energy of a carbon atom is less than that of a silicon atom, which is due to the small radius of the carbon atom and strong electron-electron repulsion when an electron is attached to the atom.

In group IV, the main subgroup from top to bottom, the ionization energy decreases, the electron affinity energy decreases, and electronegativity decreases.

With a change in the ionization energy, the properties of Group IV elements of the main subgroup change from typical non-metals to metals. Carbon and silicon are typical non-metals, germanium is a metalloid with characteristic metallic properties, tin, lead is a metal.

In group IV, the main subgroup, from top to bottom, the melting and boiling points decrease.

The decrease in the melting temperature is due to an increase in the proportion of the metal bond.

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, exhibits non-metallic properties. However, at elevated temperatures, germanium acquires characteristic metallic properties such as plasticity and high electrical conductivity.

The atoms of carbon, silicon, germanium, tin and lead in the ground state have a similar structure of the outer electron layer and belong to p-elements:

Si 3s23p23d0

Ge 3d104s24p24d0

Sn 4d105s25p25d0

Pb 4f145d106s26p26d0

However, only germanium, tin and lead are full 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 - 4, the main valences of all elements II and IV. Starting with silicon, p-elements of group IV have vacant d-orbitals. This determines the possibility of bond formation by the donor-acceptor mechanism and leads to an increase in the valence in coordination compounds to VI. Due to the absence of a d-sublevel at a carbon atom, its valence in compounds cannot exceed IV, and carbon, unlike Si, Ge, Sn, and Pb, is not capable of forming complex compounds. This circumstance, as well as the smallest atomic size 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 values ​​of electronegativity, all elements have characteristic oxidation states of -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 oxidation state +2 increases.

General characteristics of the fourth group of the main subgroup:

a) properties of elements in terms of atomic structure;

b) oxidation state;

c) properties of oxides;

d) properties of hydroxides;

e) hydrogen compounds.

a) Carbon (C), silicon (Si), germanium (Ge), tin (Sn), lead (Pb) - elements of the 4th group of the main subgroup of the PSE. On the outer electron layer, the atoms of these elements have 4 electrons: ns2np2. In a subgroup, with an increase in the ordinal number of an element, the atomic radius increases, the non-metallic properties weaken, and the metallic ones intensify: 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.

c) Higher oxides of carbon and silicon (CO2, Si02) have acidic properties, oxides of other 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 and 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 is a strong compound, silane SiH4 is a less strong compound.

Diagrams 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 radius of the atom, then it is more characteristic of the ability to donate electrons than 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. The density of germanium in the solid state is 5.327 g / cm3, in the liquid -5.557 g / cm3.

Tin is a malleable, lightweight metal of 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.

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

In an unexcited state, the elements of this subgroup exhibit a valency equal to 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 the electrons of the outer layer become unpaired, and the valence increases to 4.

The energy expended for the transition of an electron is more than compensated for 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 an increase in the nuclear charge. For carbon, silicon and germanium, the most typical oxidation state is +4, for lead - +2. The oxidation state -4 in the C - Pb sequence is becoming less and less characteristic.

The 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 in lead hydrates. The strength of hydrogen compounds RH 4 decreases from carbon to lead: CH 4 is a strong substance, and PbH 4 is not isolated in free form.

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