General and inorganic chemistry

Lecture 6. Hydrogen and oxygen. Water. Hydrogen peroxide.

Hydrogen

The hydrogen atom is the simplest object of chemistry. Strictly speaking, its ion - proton - is even simpler. First described in 1766 by Cavendish. The name is from the Greek. “Hydro genes” - generates water.

The radius of the hydrogen atom is about 0.5 * 10-10 m, and its ion (proton) is 1.2 * 10-15 m.Or from 50 pm to 1.2 * 10-3 pm or from 50 meters (SCA diagonal ) up to 1 mm.

The next 1s element, lithium, changes only from 155 pm to 68 pm for Li +. This difference in the size of an atom and its cation (5 orders of magnitude) is unique.

Due to the small size of the proton, an exchange hydrogen bond, primarily between the atoms of oxygen, nitrogen and fluorine. The strength of hydrogen bonds is 10-40 kJ / mol, which is much less than the breaking energy of most ordinary bonds (100-150 kJ / mol in organic molecules), but more than the average kinetic energy of thermal motion at 370 C (4 kJ / mol). As a result, in a living organism, hydrogen bonds are reversibly broken, ensuring the course of vital processes.

Hydrogen melts at 14 K, boils at 20.3 K (pressure 1 atm), the density of liquid hydrogen is only 71 g / l (14 times lighter than water).

In a rarefied interstellar medium, excited hydrogen atoms were found with transitions up to n 733 → 732 with a wavelength of 18 m, which corresponds to a Bohr radius (r \u003d n2 * 0.5 * 10-10 m) of the order of 0.1 mm (!).

The most common element in space (88.6% of atoms, 11.3% of atoms are helium, and only 0.1% are atoms of all other elements).

4 H → 4 He + 26.7 MeV 1 eV \u003d 96.48 kJ / mol

Since protons have a spin of 1/2, there are three variants of hydrogen molecules:

orthohydrogen o-H2 with parallel nuclear spins, parahydrogen p-H2 with antiparallelspins and normal n-H2 - a mixture of 75% ortho-hydrogen and 25% para-hydrogen. The transformation o-H2 → p-H2 releases 1418 J / mol.

Properties of ortho- and parahydrogen

Since the atomic mass of hydrogen is the lowest possible, its isotopes - deuterium D (2 H) and tritium T (3 H) differ significantly from protium 1 H in physical and chemical properties. For example, the replacement of one of the hydrogens in an organic compound with deuterium is noticeably reflected in its vibrational (infrared) spectrum, which makes it possible to establish the structure of complex molecules. Such substitutions ("the method of tagged atoms") are also used to establish the mechanisms of complex

chemical and biochemical processes. The tracer method is especially sensitive when radioactive tritium is used instead of protium (β-decay, half-life 12.5 years).

Properties of protium and deuterium

					Density, g / l (20 K)
The main method hydrogen productionin industry - methane conversion
or hydration of coal at 800-11000 C (catalyst):
CH4 + H2 O \u003d CO + 3 H2				above 10000 С
"Water gas": C + H2 O \u003d CO + H2
Then CO conversion: CO + H2 O \u003d CO2 + H2						4000 C, cobalt oxides

Total: C + 2 H2 O \u003d CO2 + 2 H2

Other sources of hydrogen.

Coke oven gas: about 55% hydrogen, 25% methane, up to 2% heavy hydrocarbons, 4-6% CO, 2% CO2, 10-12% nitrogen.

Hydrogen as a combustion product:

Si + Ca (OH) 2 + 2 NaOH \u003d Na2 SiO3 + CaO + 2 H2

Up to 370 liters of hydrogen is released per 1 kg of pyrotechnic mixture.

Hydrogen in the form of a simple substance is used for the production of ammonia and the hydrogenation (hardening) of vegetable fats, for the reduction of certain metal oxides (molybdenum, tungsten), for the production of hydrides (LiH, CaH2,

LiAlH4).

The enthalpy of reaction: H. + H. \u003d H2 is -436 kJ / mol, therefore atomic hydrogen is used to obtain a high-temperature reduction "flame" ("Langmuir burner"). A stream of hydrogen in an electric arc is atomized at 35,000 C by 30%, then, during the recombination of atoms, it is possible to reach 50,000 C.

Liquefied hydrogen is used as a fuel in rockets (see oxygen). Promising environmentally friendly fuel for land transport; experiments on the use of metal hydride hydrogen accumulators are underway. For example, LaNi5 alloy can absorb 1.5-2 times more hydrogen than it contains in the same volume (as the alloy volume) of liquid hydrogen.

Oxygen

According to the generally accepted data, oxygen was discovered in 1774 by J. Priestley and independently by K. Scheele. The story of the discovery of oxygen is a good example of the influence of paradigms on the advancement of science (see Appendix 1).

It appears that oxygen was actually discovered much earlier than the official date. In 1620 anyone could ride on the Thames (in the Thames) in a submarine designed by Cornelius van Drebbel. The boat moved underwater thanks to the efforts of a dozen rowers. According to numerous eyewitnesses, the inventor of the submarine successfully solved the breathing problem by “refreshing” the air in it by chemical means. Robert Boyle wrote in 1661: “... In addition to the mechanical structure of the boat, the inventor had a chemical solution (liquor), which he

considered the main secret of scuba diving. And when from time to time he became convinced that the breathable part of the air had already been consumed and made it difficult for the people in the boat to breathe, he could, by opening the vessel filled with this solution, quickly replenish the air with such a content of vital parts that would make it again suitable for breathing for a sufficiently long time. "

A healthy person in a calm state pumps about 7200 liters of air through his lungs per day, taking 720 liters of oxygen irretrievably. In a closed room with a volume of 6 m3, a person can hold out without ventilation for up to 12 hours, and with physical work 3-4 hours. The main cause of difficulty breathing is not a lack of oxygen, but accumulation of carbon dioxidefrom 0.3 to 2.5%.

For a long time, the main method for producing oxygen was the "barium" cycle (obtaining oxygen by the Brin method):

BaSO4 -t- → BaO + SO3;

5000 C -\u003e

BaO + 0.5 O2 \u003d\u003d\u003d\u003d\u003d\u003d BaO2<- 7000 C

Drebbel's secret solution could be a hydrogen peroxide solution: BaO2 + H2 SO4 \u003d BaSO4 ↓ + H2 O2

Oxygen production during the combustion of pyro-mixture: NaClO3 \u003d NaCl + 1.5 O2 + 50.5 kJ

The mixture contains up to 80% NaClO3, up to 10% iron powder, 4% barium peroxide and glass wool.

The oxygen molecule is paramagnetic (practically biradical), therefore its activity is high. Organic substances are oxidized in air through the stage of peroxide formation.

Oxygen melts at 54.8 K, boils at 90.2 K.

Allotropic modification of the element oxygen - the substance ozone O3. The biological ozone protection of the Earth is extremely important. At an altitude of 20-25 km, a balance is established:

UV<280 нм		UV 280-320nm
O2 ----\u003e 2 O *	O * + O2 + M -\u003e O3	O3 -------	\u003e O2 + O
	(M - N2, Ar)

In 1974, it was discovered that atomic chlorine, which is formed from freons at an altitude of more than 25 km, catalyzes the decay of ozone, as if replacing the "ozone" ultraviolet light. This UV is capable of causing skin cancer (in the United States, up to 600 thousand cases a year). The ban on freons in aerosol cans has been in effect in the United States since 1978.

Since 1990, the list of prohibited substances (in 92 countries) includes CH3 CCl3, CCl4, chlorobromohydrocarbons - their production is curtailed by 2000.

Combustion of hydrogen in oxygen

The reaction is very complex (the diagram in Lecture 3), so a long study was required before the start of practical application.

On July 21, 1969 the first earthling - N. Armstrong walked on the Moon. The Saturn 5 rocket (designed by Wernher von Braun) consists of three stages. The first contains kerosene and oxygen, the second and the third contain liquid hydrogen and oxygen. A total of 468 tons of liquid O2 and H2. 13 successful launches were made.

Since April 1981, the US has been flying the Space Shuttle: 713 tons of liquid O2 and H2, as well as two solid-fuel boosters of 590 tons each (the total mass of solid fuel is 987 tons). The first 40 km climb to the TTU, from 40 to 113 km the engines run on hydrogen and oxygen.

May 15, 1987 the first launch of Energia, November 15, 1988 the first and only flight of the Buran. The starting weight is 2400 tons, the mass of fuel (kerosene in

side compartments, liquid O2 and H2) 2000 t. Engine power 125000 MW, payload 105 t.

The combustion was not always manageable and successful.

In 1936, the world's largest hydrogen airship LZ-129 "Hindenburg" was built. The volume is 200,000 m3, the length is about 250 m, the diameter is 41.2 m. The speed is 135 km / h thanks to 4 engines of 1100 hp each, the payload is 88 tons. The airship made 37 flights across the Atlantic and carried more than 3 thousand passengers.

On May 6, 1937, when docking in the United States, the airship exploded and burned down. One of the possible reasons is sabotage.

On January 28, 1986, at the 74th second of the flight, the Challenger exploded with seven cosmonauts - the 25th flight of the Shuttle system. The reason is a defect in the solid fuel accelerator.

Demonstration:

detonating gas explosion (mixture of hydrogen and oxygen)

Fuel cells

A technically important variant of this combustion reaction is to split the process into two:

hydrogen electrooxidation (anode): 2 H2 + 4 OH– - 4 e– \u003d 4 H2 O

oxygen electroreduction (cathode): O2 + 2 H2 O + 4 e– \u003d 4 OH–

The system in which such "combustion" is carried out - fuel cell... The efficiency is much higher than that of thermal power plants, since there is no

special stage of heat generation. Maximum efficiency \u003d ∆ G / ∆ H; for the combustion of hydrogen, 94% is obtained.

The effect has been known since 1839, but the first practically working fuel cells have been implemented.

at the end of the 20th century in space (Gemini, Apollo, Shuttle - USA, Buran - USSR).

Fuel Cell Prospects [17]

A spokesman for Ballard Power Systems, speaking at a scientific conference in Washington, DC, stressed that a fuel cell engine will become commercially viable when it meets four main criteria: reduced energy costs, increased durability, reduced plant size and the ability to quickly start in cold weather. ... The cost of one kilowatt of energy generated by the fuel cell plant should be reduced to $ 30. For comparison, in 2004 the same figure was $ 103, and in 2005 it is expected to reach $ 80. To achieve this price, it is necessary to produce at least 500 thousand engines per year. European scientists are more cautious in their forecasts and believe that the commercial use of fuel hydrogen cells in the automotive industry will not begin until 2020.

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen consists of hydrogen atoms. Simple substance hydrogenconsists of hydrogen molecules.

a) Chemical element hydrogen

In the natural series of elements, the ordinal number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.

Hydrogen is one of the most abundant elements on Earth. The molar fraction of hydrogen atoms in the atmosphere, hydrosphere and lithosphere of the Earth (all together this is called the earth's crust) is 0.17. It is found in water, many minerals, oil, natural gas, plants and animals. The human body contains on average about 7 kilograms of hydrogen.

There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen - deuterium (D),
c) superheavy hydrogen - tritium (T).

Tritium is an unstable (radioactive) isotope; therefore, it practically does not occur in nature. Deuterium is stable, but very little of it: w D \u003d 0.015% (of the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 D (1.00794 D).

b) Hydrogen atom

From the previous sections of the chemistry course, you already know the following characteristics of the hydrogen atom:

The valence capabilities of the hydrogen atom are determined by the presence of one electron in a single valence orbital. A high ionization energy makes a hydrogen atom not prone to give up an electron, and a not too high energy of affinity for an electron leads to a slight tendency to accept it. Consequently, in chemical systems the formation of the H cation is impossible, and the compounds with the H anion are not very stable. Thus, for the hydrogen atom, the most characteristic is the formation of a covalent bond with other atoms due to its one unpaired electron. And in the case of the formation of an anion, and in the case of the formation of a covalent bond, the hydrogen atom is monovalent.
In a simple substance, the oxidation state of hydrogen atoms is zero, in most compounds, hydrogen exhibits an oxidation state of + I, and only in hydrides of the least electronegative elements of hydrogen has an oxidation state of –I.
Information on the valence capabilities of the hydrogen atom is given in table 28. The valence state of the hydrogen atom bound by one covalent bond to any atom is indicated in the table by the symbol "H-".

Table 28.The valence capabilities of the hydrogen atom

Valence state				Examples of chemicals
			I 0 –I	HCl, H 2 O, H 2 S, NH 3, CH 4, C 2 H 6, NH 4 Cl, H 2 SO 4, NaHCO 3, KOH H 2 B 2 H 6, SiH 4, GeH 4
				NaH, KH, CaH 2, BaH 2

c) Hydrogen molecule

The diatomic hydrogen molecule H 2 is formed when hydrogen atoms are bound by the only covalent bond possible for them. The bond is formed by the exchange mechanism. By the way the electron clouds overlap, this is the s-bond (Fig.10.1 and). Since the atoms are the same, the bond is non-polar.

Interatomic distance (more precisely, the equilibrium interatomic distance, because the atoms vibrate) in a hydrogen molecule r(H – H) \u003d 0.74 A (fig.10.1 in), which is much less than the sum of the orbital radii (1.06 A). Consequently, the electron clouds of the bonded atoms overlap deeply (Fig.10.1 b), and the bond in the hydrogen molecule is strong. This is evidenced by the rather large value of the binding energy (454 kJ / mol).
If we characterize the shape of the molecule by the boundary surface (similar to the boundary surface of the electron cloud), then we can say that the hydrogen molecule has the shape of a slightly deformed (elongated) sphere (Fig.10.1 r).

d) Hydrogen (substance)

Under normal conditions, hydrogen is a colorless and odorless gas. In small quantities, it is non-toxic. Solid hydrogen melts at 14 K (–259 ° C), and liquid hydrogen boils at 20 K (–253 ° C). Low melting and boiling points, a very small temperature range for the existence of liquid hydrogen (only 6 ° C), as well as small values \u200b\u200bof molar heats of fusion (0.117 kJ / mol) and vaporization (0.903 kJ / mol) indicate that intermolecular bonds in hydrogen very weak.
The density of hydrogen r (H 2) \u003d (2 g / mol) :( 22.4 l / mol) \u003d 0.0893 g / l. For comparison: the average density of air is 1.29 g / l. That is, hydrogen is 14.5 times lighter than air. It is practically insoluble in water.
At room temperature, hydrogen is inactive, but when heated it reacts with many substances. In these reactions, hydrogen atoms can both increase and decrease their oxidation state: Н 2 + 2 e - \u003d 2Н -I, Н 2 - 2 e - \u003d 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or with calcium: 2Na + H 2 \u003d 2NaH, ( t) Ca + H 2 \u003d CaH 2. ( t)
But the reducing properties of hydrogen are more characteristic: O 2 + 2H 2 \u003d 2H 2 O, ( t)
CuO + H 2 \u003d Cu + H 2 O. ( t)
When heated, hydrogen is oxidized not only by oxygen, but also by some other non-metals, for example, fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is obtained as a result of the reaction

Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.

Iron, aluminum and some other metals can be used instead of zinc, and some other dilute acids can be used instead of sulfuric acid. The resulting hydrogen is collected in a test tube by the displacement method (see Fig.10.2 b) or simply into an inverted flask (fig.10.2 and).

In industry, hydrogen is obtained in large quantities from natural gas (mainly methane) by interacting with water vapor at 800 ° C in the presence of a nickel catalyst:

CH 4 + 2H 2 O \u003d 4H 2 + CO 2 ( t, Ni)

or coal is treated at high temperature with water vapor:

2H 2 O + C \u003d 2H 2 + CO 2. ( t)

Pure hydrogen is obtained from water by decomposing it with electric current (subjecting it to electrolysis):

2H 2 O \u003d 2H 2 + O 2 (electrolysis).

e) Hydrogen compounds

Hydrides (binary compounds containing hydrogen) are divided into two main types:
a) volatile (molecular) hydrides,
b) salt-like (ionic) hydrides.
Elements IVA - VIIA of groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:

B 2 H 6; CH 4; NH 3; H 2 O; HF
SiH 4; PH 3; H 2 S; HCl
AsH 3; H 2 Se; HBr
H 2 Te; HI
With the exception of water, all these compounds at room temperature are gaseous substances, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also found in more complex hydrides. For example, carbon forms compounds with general formulas C n H 2 n+2, C n H 2 n , C n H 2 n–2 and others, where n can be very large (these compounds are studied by organic chemistry).
Ionic hydrides include hydrides of alkali, alkaline earth elements and magnesium. Crystals of these hydrides consist of H anions and metal cations in the highest oxidation state Me or Me 2 (depending on the group of the system of elements).

LiH
NaH	MgH 2
KH	CaH 2
RbH	SrH 2
CsH	BaH 2

Both ionic and almost all molecular hydrides (except for H 2 O and HF) are reducing agents, but ionic hydrides exhibit reducing properties much stronger than molecular ones.
In addition to hydrides, hydrogen is part of hydroxides and some salts. You will become familiar with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of hydrogen produced in the industry are plants for the production of ammonia and nitrogen fertilizers, where ammonia is obtained directly from nitrogen and hydrogen:

N 2 + 3H 2 2NH 3 ( R, t, Pt - catalyst).

In large quantities, hydrogen is used to obtain methyl alcohol (methanol) by the reaction 2H 2 + CO \u003d CH 3 OH ( t, ZnO - catalyst), as well as in the production of hydrogen chloride, which is obtained directly from chlorine and hydrogen:

H 2 + Cl 2 \u003d 2HCl.

Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O.

1. What particles are the nuclei of a) protium, b) deuterium, c) tritium?
2. Compare the ionization energy of a hydrogen atom with the ionization energy of atoms of other elements. Which element is hydrogen closest to by this characteristic?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the oxidation state of hydrogen in the compounds: a) BeH 2, CH 4, NH 3, H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest molecular, structural and spatial formula of hydrogen. Which one is most commonly used?
6. It is often said: "Hydrogen is lighter than air." What does this mean? When can this expression be taken literally, and when not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values \u200b\u200bof the corresponding specific quantities.
9. For each of the four reactions that illustrate the basic chemical properties of hydrogen, draw up an electronic balance. Note oxidants and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in a laboratory way.
11. Determine the mass and volume of hydrogen that can be obtained from a 30 m 3 mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions occurring in the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The following reaction schemes illustrate the main chemical properties of ionic hydrides:

a) MH + O 2 MOH ( t); b) MH + Cl 2 MCl + HCl ( t);
c) MH + H 2 O MOH + H 2; d) MH + HCl (p) MCl + H 2
Here M is lithium, sodium, potassium, rubidium or cesium. Write the equations of the corresponding reactions in case M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electronic balance method, construct the equations of the following reactions, illustrating the reducing properties of some molecular hydrides:
a) HI + Cl 2 HCl + I 2 ( t); b) NH 3 + O 2 H 2 O + N 2 ( t); c) CH 4 + O 2 H 2 O + CO 2 ( t).

10.2 Oxygen

As in the case of hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. In addition to a simple substance " oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). These are allotropic modifications of oxygen. The substance oxygen consists of oxygen molecules O 2, and the substance ozone consists of molecules of ozone O 3.

a) Chemical element oxygen

In the natural series of elements, the ordinal number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on Earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) is an integral part of air. The volume fraction of oxygen in the air is 21%. Oxygen (an element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most abundant. Therefore, the atomic mass of oxygen is close to 16 D (15.9994 D).

b) Oxygen atom

You know the following characteristics of the oxygen atom.

Table 29. Oxygen atom valence

Valence state				Examples of chemicals
				Al 2 O 3, Fe 2 O 3, Cr 2 O 3 *
			–II –I 0 + I + II	H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 O 2 ** O 2 F 2 OF 2
				NaOH, KOH, Ca (OH) 2, Ba (OH) 2 Na 2 O 2, K 2 O 2, CaO 2, BaO 2
				Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3

* These oxides can also be considered ionic compounds.
** Oxygen atoms in a molecule are not in a given valence state; this is just an example of a substance with an oxidation state of oxygen atoms equal to zero
The high ionization energy (like hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice that of hydrogen), which provides a greater tendency for the oxygen atom to attach electrons and the ability to form O 2A anions. But the energy of electron affinity for the oxygen atom is still lower than that of halogen atoms and even other elements of group VIA. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements, the atoms of which donate electrons very easily.
By socializing two unpaired electrons, an oxygen atom can form two covalent bonds. Due to the impossibility of excitation, two lone pairs of electrons can only enter into donor-acceptor interaction. Thus, disregarding the multiplicity of the bond and hybridization, the oxygen atom can be in one of five valence states (Table 29).
The most characteristic of the oxygen atom is the valence state with W k \u003d 2, that is, the formation of two covalent bonds due to two unpaired electrons.
The very high electronegativity of the oxygen atom (higher - only for fluorine) leads to the fact that in most of its compounds oxygen has an oxidation state of –II. There are substances in which oxygen exhibits other values \u200b\u200bof the oxidation state, some of which are shown in Table 29 as examples, and the comparative stability is shown in Fig. 10.3.

c) Oxygen molecule

It has been experimentally established that a diatomic oxygen molecule O 2 contains two unpaired electrons. Using the method of valence bonds, such an electronic structure of this molecule cannot be explained. Nevertheless, the bond in the oxygen molecule is close in properties to covalent. The oxygen molecule is non-polar. Interatomic distance ( r o – o \u003d 1.21 A \u003d 121 nm) is less than the distance between atoms bound by a simple bond. The molar binding energy is quite high and amounts to 498 kJ / mol.

d) Oxygen (substance)

Under normal conditions oxygen is a colorless and odorless gas. Solid oxygen melts at 55 K (–218 ° C), and liquid oxygen boils at 90 K (–183 ° C).
Intermolecular bonds in solid and liquid oxygen are somewhat stronger than in hydrogen, as evidenced by the wider temperature range of existence of liquid oxygen (36 ° C) and higher molar heats of fusion (0.446 kJ / mol) and vaporization (6, 83 kJ / mol).
Oxygen is slightly soluble in water: at 0 ° C, only 5 volumes of oxygen (gas!) Dissolve in 100 volumes of water (liquid!).
The high tendency of oxygen atoms to attach electrons and high electronegativity lead to the fact that oxygen exhibits only oxidizing properties. These properties are especially pronounced at high temperatures.
Oxygen reacts with many metals: 2Ca + O 2 \u003d 2CaO, 3Fe + 2O 2 \u003d Fe 3 O 4 ( t);
non-metals: C + O 2 \u003d CO 2, P 4 + 5O 2 \u003d P 4 O 10,
and complex substances: CH 4 + 2O 2 \u003d CO 2 + 2H 2 O, 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2.

Most often, as a result of such reactions, various oxides are obtained (see Chapter II § 5), but active alkali metals, for example sodium, are converted into peroxides by combustion:

2Na + O 2 \u003d Na 2 O 2.

Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter, placed in oxygen, flares up. It is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory, by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 \u003d 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 \u003d 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 \u003d 2H 2 O + O 2 (MnO 2 is a catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocketry, liquid oxygen is used as an oxidizer.
Oxygen is of great importance for maintaining the life of plants, animals and humans. Under normal conditions, a person has enough oxygen to breathe. But in conditions when there is not enough air, or it is absent altogether (in airplanes, during diving work, in spaceships, etc.), special gas mixtures containing oxygen are prepared for breathing. Oxygen is also used in medicine for diseases that cause breathing difficulties.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has an angular structure in between two structures, represented by the following formulas:

Ozone is a dark blue gas with a pungent odor. Due to its strong oxidative activity, it is poisonous. Ozone is one and a half times "heavier" than oxygen and is slightly more soluble in water than oxygen.
Ozone is formed in the atmosphere from oxygen during lightning electrical discharges:

3O 2 \u003d 2O 3 ().

At normal temperatures, ozone is slowly converted to oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" of the earth's atmosphere, protecting all life on earth from the harmful effects of solar radiation.
In some cities, ozone is used instead of chlorine to disinfect (decontaminate) drinking water.

Draw the structural formulas of the following substances: OF 2, H 2 O, H 2 O 2, H 3 PO 4, (H 3 O) 2 SO 4, BaO, BaO 2, Ba (OH) 2. Name these substances. Describe the valence states of oxygen atoms in these compounds.
Determine the valence and oxidation state of each of the oxygen atoms.
2. Make the equations of combustion reactions in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (selenium atoms are oxidized to the oxidation state + IV, the atoms of other elements - to the highest oxidation state). What classes of oxides are the products of these reactions?
3. How many liters of ozone can be obtained (under normal conditions) a) from 9 liters of oxygen, b) from 8 g of oxygen?

Water is the most abundant substance in the earth's crust. The mass of the earth's water is estimated at 10 18 tons. Water is the basis of the hydrosphere of our planet, in addition, it is contained in the atmosphere, in the form of ice forms the polar caps of the Earth and high-altitude glaciers, and is also part of various rocks. The mass fraction of water in the human body is about 70%.
Water is the only substance that in all three states of aggregation has its own special names.

The electronic structure of a water molecule (Fig.10.4 and) we studied in detail earlier (see § 7.10).
Due to the polarity of the O – H bonds and the angular shape, the water molecule is electric dipole.

To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole "or simply " dipole moment ".

In chemistry, the dipole moment is measured in Debyes: 1 D \u003d 3.34. 10-30 Cl. m

In a water molecule there are two polar covalent bonds, that is, two electric dipoles, each of which has its own dipole moment (and). The total dipole moment of the molecule is equal to the vector sum of these two moments (Fig.10.5):

(H 2 O) \u003d ,

where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic O - H distances in the molecule. Because q 1 = q 2 = q, a, then

The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.

Table 30.Dipole moments of some polar molecules

Molecule		Molecule		Molecule

Given the dipole nature of the water molecule, it is often schematically depicted as follows:
Pure water is a colorless liquid, tasteless and odorless. Some of the main physical characteristics of water are given in the table.

Table 31.Some physical characteristics of water

Large values \u200b\u200bof molar heats of fusion and vaporization (an order of magnitude higher than those of hydrogen and oxygen) indicate that water molecules, both in solid and in liquid matter, are quite tightly bound together. These connections are called " hydrogen bonds ".

ELECTRIC DIPOLE, DIPOLE MOMENT, BONDING POLARITY, MOLECULE POLARITY.
How many valence electrons of an oxygen atom take part in the formation of bonds in a water molecule?
2.When overlapping of which orbitals are bonds formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in the hydrogen peroxide molecule H 2 O 2. What can you say about the spatial structure of this molecule?
4. The interatomic distances in the HF, HCl and HBr molecules are 0.92, respectively; 1.28 and 1.41. Using the dipole moment table, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. The interatomic distances S - H in the hydrogen sulfide molecule are 1.34, and the angle between the bonds is 92 °. Determine the values \u200b\u200bof the partial charges on the sulfur and hydrogen atoms. What can you say about hybridization of the valence orbitals of the sulfur atom?

10.4. Hydrogen bond

As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), the hydrogen atom in the water molecule has a large positive partial charge ( q h \u003d 0.33 e), and the oxygen atom has an even larger negative partial charge ( q h \u003d -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons of the oxygen atom. As a result of these interactions between molecules, a special type of intermolecular bonds arises - a hydrogen bond.
In the case of water, hydrogen bonding can be schematically represented as follows:

In the last structural formula, three dots (dotted line, not electrons!) Show the hydrogen bond.

The hydrogen bond exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar N – E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) the molecule contains an atom E with a large negative partial charge and a lone pair of electrons.
The element E can be fluorine, oxygen and nitrogen. Hydrogen bonds are much weaker if E is chlorine or sulfur.
Examples of substances with a hydrogen bond between molecules: hydrogen fluoride, solid or liquid ammonia, ethyl alcohol and many others.

In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds in rather long chains, and three-dimensional networks are formed in liquid and solid ammonia.
In terms of strength, a hydrogen bond is intermediate between a chemical bond and other types of intermolecular bonds. The molar energy of a hydrogen bond usually ranges from 5 to 50 kJ / mol.
In solid water (that is, in ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). This structure makes ice "looser" in comparison with liquid water, where some of the hydrogen bonds are broken, and the molecules are able to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in a solid state has a lower density than in a liquid state. Water reaches its maximum density at 4 ° С - at this temperature, a lot of hydrogen bonds break, and thermal expansion does not have a very strong effect on the density.
Hydrogen bonds are very important in our life. Let's imagine for a moment that hydrogen bonds have ceased to form. Here are some of the consequences:

• water at room temperature would become gaseous, since its boiling point would drop to about –80 ° C;
• all reservoirs would freeze from the bottom, since the density of ice would be greater than the density of liquid water;
• the double helix of DNA would cease to exist and much more.

The examples given are enough to understand that in this case, nature on our planet would become completely different.

HYDROGEN BONDING, THE CONDITIONS OF ITS FORMATION.
The formula of ethyl alcohol is CH 3 –CH 2 –O – H. Between what atoms of different molecules of this substance are hydrogen bonds formed? Draw up structural formulas to illustrate their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with the help of structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). \u003d 2H 2 O.
Both of these reactions occur in water constantly and at an equal rate, therefore, there is an equilibrium in water: 2H 2 O AH 3 O + OH.
This balance is called equilibrium of autoprotolysiswater.

The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis is enhanced, but at room temperature the equilibrium is shifted to the left, that is, the concentration of H 3 O and OH ions is negligible. What are they equal to?
According to the law of the acting masses

But due to the fact that the number of reacted water molecules is insignificant in comparison with the total number of water molecules, it can be assumed that the water concentration during auto-protolysis practically does not change, and 2 \u003d const Such a low concentration of oppositely charged ions in pure water explains why this liquid, although poorly, still conducts an electric current.

AUTOPROTOLYSIS OF WATER, CONSTANT OF AUTOPROTOLYSIS (IONIC PRODUCTION) OF WATER.
The ionic product of liquid ammonia (boiling point –33 ° C) is 2 · 10 –28. Make an equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. Which of the substances is more conductive, water or liquid ammonia?

1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).

The purpose of the lesson. In this lesson, you will learn about perhaps the most important chemical elements for life on earth - hydrogen and oxygen, learn about their chemical properties, as well as the physical properties of simple substances they form, learn more about the role of oxygen and hydrogen in nature and life human.

Hydrogen - the most common element in the universe. Oxygen - the most abundant element on Earth. Together they form water, a substance that makes up more than half the mass of the human body. Oxygen is a gas that we need for breathing, and without water we could not live even a few days, so oxygen and hydrogen can undoubtedly be considered the most important chemical elements necessary for life.

The structure of hydrogen and oxygen atoms

Thus, hydrogen exhibits non-metallic properties. In nature, hydrogen occurs in the form of three isotopes, protium, deuterium and tritium, the isotopes of hydrogen are very different from each other in physical properties, so they are even assigned individual symbols.

If you do not remember or do not know what isotopes are, work with the materials of the electronic educational resource "Isotopes as varieties of atoms of one chemical element." In it you will learn how the isotopes of one element differ from each other, which leads to the presence of several isotopes in one element, and also get acquainted with the isotopes of several elements.

Thus, the possible oxidation states of oxygen are limited to values \u200b\u200bfrom –2 to +2. If oxygen accepts two electrons (becoming an anion) or forms two covalent bonds with less electronegative elements, it goes into the –2 oxidation state. If oxygen forms one bond with another oxygen atom, and the second bond with an atom of a less electronegative element, it goes into the –1 oxidation state. By forming two covalent bonds with fluorine (the only element with a higher electronegativity value), oxygen goes into the +2 oxidation state. Forming one bond with another oxygen atom, and the second with a fluorine atom - +1. Finally, if oxygen forms one bond with a less electronegative atom and another bond with fluorine, it will be in the 0 oxidation state.

Physical properties of hydrogen and oxygen, oxygen allotropy

Hydrogen - a colorless, odorless and tasteless gas. Very light (14.5 times lighter than air). The temperature of hydrogen liquefaction - -252.8 ° C - is almost the lowest among all gases (second only to helium). Liquid and solid hydrogen are very light colorless substances.

Oxygen - a colorless, odorless and tasteless gas, slightly heavier than air. At -182.9 ° C it turns into a heavy blue liquid, at -218 ° C it solidifies with the formation of blue crystals. Oxygen molecules are paramagnetic, meaning oxygen is attracted by a magnet. Oxygen is poorly soluble in water.

Unlike hydrogen, which forms molecules of only one type, oxygen exhibits allotropy and forms molecules of two types, that is, the element oxygen forms two simple substances: oxygen and ozone.

Chemical properties and production of simple substances

Hydrogen.

The bond in the hydrogen molecule is single, but it is one of the strongest single bonds in nature, and it takes a lot of energy to break it, for this reason hydrogen is very inactive at room temperature, however, when the temperature rises (or in the presence of a catalyst), hydrogen easily interacts with many simple and complex substances.

From a chemical point of view, hydrogen is a typical non-metal. That is, it is capable of interacting with active metals to form hydrides, in which it exhibits an oxidation state of –1. With some metals (lithium, calcium), the interaction proceeds even at room temperature, but rather slowly, therefore, heating is used in the synthesis of hydrides:

,

.

The formation of hydrides by direct interaction of simple substances is possible only for active metals. Already aluminum does not interact with hydrogen directly, its hydride is obtained by exchange reactions.

Hydrogen also reacts with non-metals only when heated. Exceptions are chlorine and bromine halogens, the reaction with which can be induced by light:

.

The reaction with fluorine also does not require heating; it proceeds explosively even with strong cooling and in absolute darkness.

The reaction with oxygen proceeds according to a branched chain mechanism, so the reaction rate increases rapidly, and in a mixture of oxygen with hydrogen in a ratio of 1: 2, the reaction proceeds with an explosion (such a mixture is called "detonating gas"):

.

The reaction with sulfur proceeds much more calmly, with practically no heat release:

.

Reactions with nitrogen and iodine are reversible:

,

.

This circumstance greatly complicates the production of ammonia in industry: the process requires the use of increased pressure to mix the equilibrium towards the formation of ammonia. Hydrogen iodide is not obtained by direct synthesis, since there are several much more convenient methods for its synthesis.

Hydrogen does not react directly with low-active non-metals (), although its compounds with them are known.

In reactions with complex substances, hydrogen in most cases acts as a reducing agent. In solutions, hydrogen can reduce low-activity metals (located after hydrogen in a series of voltages) from their salts:

When heated, hydrogen can reduce many metals from their oxides. Moreover, the more active the metal, the more difficult it is to restore it and the higher the temperature is needed for this:

.

Metals more active than zinc are practically impossible to reduce with hydrogen.

Hydrogen in the laboratory is obtained by the interaction of metals with strong acids. The most commonly used are zinc and hydrochloric acid:

Less commonly used electrolysis of water in the presence of strong electrolytes:

In industry, hydrogen is obtained as a by-product in the production of caustic soda by electrolysis of sodium chloride solution:

In addition, hydrogen is obtained from oil refining.

Hydrogen production by photolysis of water is one of the most promising methods in the future; however, at present, the industrial application of this method is difficult.

Work with the materials of electronic educational resources. Laboratory work "Obtaining and properties of hydrogen" and Laboratory work "Reducing properties of hydrogen". Learn the principle of the Kipp apparatus and the Kiryushkin apparatus. Think, in which cases it is more convenient to use the Kipp apparatus, and in which - Kiryushkin. What properties does hydrogen show in reactions?

Oxygen.

The bond in the oxygen molecule is double and very strong. Therefore, oxygen is rather inactive at room temperature. When heated, however, it begins to exhibit strong oxidizing properties.

Oxygen reacts without heating with active metals (alkaline, alkaline earth and some lanthanides):

When heated, oxygen interacts with most metals to form oxides:

,

,

.

Silver and less active metals are not oxidized by oxygen.

Oxygen also reacts with most non-metals to form oxides:

,

,

.

Interaction with nitrogen occurs only at very high temperatures, around 2000 ° C.

Oxygen does not react with chlorine, bromine and iodine, although many of their oxides can be obtained indirectly.

The interaction of oxygen with fluorine can be carried out by passing an electric discharge through a mixture of gases:

.

Oxygen (II) fluoride is an unstable compound, easily decomposes and is a very strong oxidizing agent.

In solutions, oxygen is a strong, albeit slow, oxidizing agent. As a rule, oxygen promotes the transition of metals to higher oxidation states:

The presence of oxygen often makes it possible to dissolve in acids metals located immediately behind hydrogen in a series of voltages:

When heated, oxygen can oxidize lower metal oxides:

.

Oxygen is not produced in industry by chemical methods; it is obtained from air by distillation.

The laboratory uses the decomposition reactions of oxygen-rich compounds - nitrates, chlorates, permanganates when heated:

Oxygen can also be obtained by catalytic decomposition of hydrogen peroxide:

In addition, the above water electrolysis reaction can be used to generate oxygen.

Work with the materials of the electronic educational resource. Laboratory work "Obtaining oxygen and its properties."

What is the name of the oxygen collection method used in laboratory work? What other ways of collecting gases are there, and which ones are suitable for collecting oxygen?

Task 1. Watch the video "Decomposition of potassium permanganate on heating."

Answer the questions:

1. 1. Which of the solid reaction products is soluble in water?
   2. What color is potassium permanganate solution?
   3. What is the color of the potassium manganate solution?

Write down the equations of the reactions taking place. Equalize them using the electronic balance method.

Discuss the assignment with the teacher in or in the video room.

Ozone.

The ozone molecule is triatomic and the bonds in it are less strong than in the oxygen molecule, which leads to a greater chemical activity of ozone: ozone easily oxidizes many substances in solutions or in dry form without heating:

Ozone is able to easily oxidize nitrogen oxide (IV) to nitrogen oxide (V), and sulfur oxide (IV) to sulfur oxide (VI) without a catalyst:

Ozone gradually decomposes to form oxygen:

To obtain ozone, special devices are used - ozonizers, in which a glow discharge is passed through oxygen.

In the laboratory, to obtain small amounts of ozone, sometimes the decomposition reactions of peroxo compounds and some higher oxides are used when heated:

Work with the materials of the electronic educational resource. Laboratory work "Obtaining ozone and studying its properties."

Explain why the indigo solution is discolored. Write down the equations for the reactions that occur when solutions of lead nitrate and sodium sulfide are mixed and when ozonized air is passed through the resulting suspension. For the ion exchange reaction, write the ionic equations. For a redox reaction, draw up an electronic balance.

Discuss the assignment with the teacher in or in the video room.

Chemical properties of water

For a better acquaintance with the physical properties of water and its significance, work with the materials of the electronic educational resources "Anomalous properties of water" and "Water is the most important liquid on Earth."

Water is of great importance for all living organisms - in fact, many living organisms are more than half water. Water is one of the most versatile solvents (at high temperatures and pressures, its capabilities as a solvent increase significantly). From a chemical point of view, water is hydrogen oxide, while in an aqueous solution it dissociates (albeit to a very small extent) into hydrogen cations and hydroxide anions:

.

Water interacts with many metals. With active (alkaline, alkaline earth and some lanthanides) water reacts without heating:

Interaction with less active occurs when heated.

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen consists of hydrogen atoms. Simple substance hydrogenconsists of hydrogen molecules.

a) Chemical element hydrogen

In the natural series of elements, the ordinal number of hydrogen is 1. In the system of elements, hydrogen is in the first period in the IA or VIIA group.

Hydrogen is one of the most abundant elements on Earth. The molar fraction of hydrogen atoms in the atmosphere, hydrosphere and lithosphere of the Earth (all together this is called the earth's crust) is 0.17. It is found in water, many minerals, oil, natural gas, plants and animals. The human body contains on average about 7 kilograms of hydrogen.

There are three isotopes of hydrogen:
a) light hydrogen - protium,
b) heavy hydrogen - deuterium (D),
c) superheavy hydrogen - tritium (T).

Tritium is an unstable (radioactive) isotope; therefore, it practically does not occur in nature. Deuterium is stable, but very little of it: w D \u003d 0.015% (of the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 D (1.00794 D).

b) Hydrogen atom

From the previous sections of the chemistry course, you already know the following characteristics of the hydrogen atom:

The valence capabilities of the hydrogen atom are determined by the presence of one electron in a single valence orbital. A high ionization energy makes a hydrogen atom not prone to give up an electron, and a not too high energy of affinity for an electron leads to a slight tendency to accept it. Consequently, in chemical systems the formation of the H cation is impossible, and the compounds with the H anion are not very stable. Thus, for the hydrogen atom, the most characteristic is the formation of a covalent bond with other atoms due to its one unpaired electron. And in the case of the formation of an anion, and in the case of the formation of a covalent bond, the hydrogen atom is monovalent.
In a simple substance, the oxidation state of hydrogen atoms is zero, in most compounds, hydrogen exhibits an oxidation state of + I, and only in hydrides of the least electronegative elements of hydrogen has an oxidation state of –I.
Information on the valence capabilities of the hydrogen atom is given in table 28. The valence state of the hydrogen atom bound by one covalent bond to any atom is indicated in the table by the symbol "H-".

Table 28.The valence capabilities of the hydrogen atom

Valence state				Examples of chemicals
			I 0 –I	HCl, H 2 O, H 2 S, NH 3, CH 4, C 2 H 6, NH 4 Cl, H 2 SO 4, NaHCO 3, KOH H 2 B 2 H 6, SiH 4, GeH 4
				NaH, KH, CaH 2, BaH 2

c) Hydrogen molecule

The diatomic hydrogen molecule H 2 is formed when hydrogen atoms are bound by the only covalent bond possible for them. The bond is formed by the exchange mechanism. By the way the electron clouds overlap, this is the s-bond (Fig.10.1 and). Since the atoms are the same, the bond is non-polar.

Interatomic distance (more precisely, the equilibrium interatomic distance, because the atoms vibrate) in a hydrogen molecule r(H – H) \u003d 0.74 A (fig.10.1 in), which is much less than the sum of the orbital radii (1.06 A). Consequently, the electron clouds of the bonded atoms overlap deeply (Fig.10.1 b), and the bond in the hydrogen molecule is strong. This is evidenced by the rather large value of the binding energy (454 kJ / mol).
If we characterize the shape of the molecule by the boundary surface (similar to the boundary surface of the electron cloud), then we can say that the hydrogen molecule has the shape of a slightly deformed (elongated) sphere (Fig.10.1 r).

d) Hydrogen (substance)

Under normal conditions, hydrogen is a colorless and odorless gas. In small quantities, it is non-toxic. Solid hydrogen melts at 14 K (–259 ° C), and liquid hydrogen boils at 20 K (–253 ° C). Low melting and boiling points, a very small temperature range for the existence of liquid hydrogen (only 6 ° C), as well as small values \u200b\u200bof molar heats of fusion (0.117 kJ / mol) and vaporization (0.903 kJ / mol) indicate that intermolecular bonds in hydrogen very weak.
The density of hydrogen r (H 2) \u003d (2 g / mol) :( 22.4 l / mol) \u003d 0.0893 g / l. For comparison: the average density of air is 1.29 g / l. That is, hydrogen is 14.5 times lighter than air. It is practically insoluble in water.
At room temperature, hydrogen is inactive, but when heated it reacts with many substances. In these reactions, hydrogen atoms can both increase and decrease their oxidation state: Н 2 + 2 e - \u003d 2Н -I, Н 2 - 2 e - \u003d 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or with calcium: 2Na + H 2 \u003d 2NaH, ( t) Ca + H 2 \u003d CaH 2. ( t)
But the reducing properties of hydrogen are more characteristic: O 2 + 2H 2 \u003d 2H 2 O, ( t)
CuO + H 2 \u003d Cu + H 2 O. ( t)
When heated, hydrogen is oxidized not only by oxygen, but also by some other non-metals, for example, fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is obtained as a result of the reaction

Zn + H 2 SO 4 \u003d ZnSO 4 + H 2.

Iron, aluminum and some other metals can be used instead of zinc, and some other dilute acids can be used instead of sulfuric acid. The resulting hydrogen is collected in a test tube by the displacement method (see Fig.10.2 b) or simply into an inverted flask (fig.10.2 and).

In industry, hydrogen is obtained in large quantities from natural gas (mainly methane) by interacting with water vapor at 800 ° C in the presence of a nickel catalyst:

CH 4 + 2H 2 O \u003d 4H 2 + CO 2 ( t, Ni)

or coal is treated at high temperature with water vapor:

2H 2 O + C \u003d 2H 2 + CO 2. ( t)

Pure hydrogen is obtained from water by decomposing it with electric current (subjecting it to electrolysis):

2H 2 O \u003d 2H 2 + O 2 (electrolysis).

e) Hydrogen compounds

Hydrides (binary compounds containing hydrogen) are divided into two main types:
a) volatile (molecular) hydrides,
b) salt-like (ionic) hydrides.
Elements IVA - VIIA of groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:

B 2 H 6; CH 4; NH 3; H 2 O; HF
SiH 4; PH 3; H 2 S; HCl
AsH 3; H 2 Se; HBr
H 2 Te; HI
With the exception of water, all these compounds at room temperature are gaseous substances, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also found in more complex hydrides. For example, carbon forms compounds with general formulas C n H 2 n+2, C n H 2 n , C n H 2 n–2 and others, where n can be very large (these compounds are studied by organic chemistry).
Ionic hydrides include hydrides of alkali, alkaline earth elements and magnesium. Crystals of these hydrides consist of H anions and metal cations in the highest oxidation state Me or Me 2 (depending on the group of the system of elements).

LiH
NaH	MgH 2
KH	CaH 2
RbH	SrH 2
CsH	BaH 2

Both ionic and almost all molecular hydrides (except for H 2 O and HF) are reducing agents, but ionic hydrides exhibit reducing properties much stronger than molecular ones.
In addition to hydrides, hydrogen is part of hydroxides and some salts. You will become familiar with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of hydrogen produced in the industry are plants for the production of ammonia and nitrogen fertilizers, where ammonia is obtained directly from nitrogen and hydrogen:

N 2 + 3H 2 2NH 3 ( R, t, Pt - catalyst).

In large quantities, hydrogen is used to obtain methyl alcohol (methanol) by the reaction 2H 2 + CO \u003d CH 3 OH ( t, ZnO - catalyst), as well as in the production of hydrogen chloride, which is obtained directly from chlorine and hydrogen:

H 2 + Cl 2 \u003d 2HCl.

Sometimes hydrogen is used in metallurgy as a reducing agent in the production of pure metals, for example: Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O.

1. What particles are the nuclei of a) protium, b) deuterium, c) tritium?
2. Compare the ionization energy of a hydrogen atom with the ionization energy of atoms of other elements. Which element is hydrogen closest to by this characteristic?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the oxidation state of hydrogen in the compounds: a) BeH 2, CH 4, NH 3, H 2 O, HF; b) CH 4, SiH 4, GeH 4.
5. Write down the simplest molecular, structural and spatial formula of hydrogen. Which one is most commonly used?
6. It is often said: "Hydrogen is lighter than air." What does this mean? When can this expression be taken literally, and when not?
7. Make the structural formulas of potassium and calcium hydrides, as well as ammonia, hydrogen sulfide and hydrogen bromide.
8. Knowing the molar heats of fusion and vaporization of hydrogen, determine the values \u200b\u200bof the corresponding specific quantities.
9. For each of the four reactions that illustrate the basic chemical properties of hydrogen, draw up an electronic balance. Note oxidants and reducing agents.
10. Determine the mass of zinc required to obtain 4.48 liters of hydrogen in a laboratory way.
11. Determine the mass and volume of hydrogen that can be obtained from a 30 m 3 mixture of methane and water vapor, taken in a volume ratio of 1: 2, with a yield of 80%.
12. Make up the equations of the reactions occurring in the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The following reaction schemes illustrate the main chemical properties of ionic hydrides:

a) MH + O 2 MOH ( t); b) MH + Cl 2 MCl + HCl ( t);
c) MH + H 2 O MOH + H 2; d) MH + HCl (p) MCl + H 2
Here M is lithium, sodium, potassium, rubidium or cesium. Write the equations of the corresponding reactions in case M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electronic balance method, construct the equations of the following reactions, illustrating the reducing properties of some molecular hydrides:
a) HI + Cl 2 HCl + I 2 ( t); b) NH 3 + O 2 H 2 O + N 2 ( t); c) CH 4 + O 2 H 2 O + CO 2 ( t).

10.2 Oxygen

As in the case of hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. In addition to a simple substance " oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). These are allotropic modifications of oxygen. The substance oxygen consists of oxygen molecules O 2, and the substance ozone consists of molecules of ozone O 3.

a) Chemical element oxygen

In the natural series of elements, the ordinal number of oxygen is 8. In the system of elements, oxygen is in the second period in the VIA group.
Oxygen is the most abundant element on Earth. In the earth's crust, every second atom is an oxygen atom, that is, the molar fraction of oxygen in the atmosphere, hydrosphere and lithosphere of the Earth is about 50%. Oxygen (substance) is an integral part of air. The volume fraction of oxygen in the air is 21%. Oxygen (an element) is a part of water, many minerals, as well as plants and animals. The human body contains an average of 43 kg of oxygen.
Natural oxygen consists of three isotopes (16 O, 17 O and 18 O), of which the lightest isotope 16 O is the most abundant. Therefore, the atomic mass of oxygen is close to 16 D (15.9994 D).

b) Oxygen atom

You know the following characteristics of the oxygen atom.

Table 29. Oxygen atom valence

Valence state				Examples of chemicals
				Al 2 O 3, Fe 2 O 3, Cr 2 O 3 *
			–II –I 0 + I + II	H 2 O, SO 2, SO 3, CO 2, SiO 2, H 2 SO 4, HNO 2, HClO 4, COCl 2, H 2 O 2 O 2 ** O 2 F 2 OF 2
				NaOH, KOH, Ca (OH) 2, Ba (OH) 2 Na 2 O 2, K 2 O 2, CaO 2, BaO 2
				Li 2 O, Na 2 O, MgO, CaO, BaO, FeO, La 2 O 3

* These oxides can also be considered ionic compounds.
** Oxygen atoms in a molecule are not in a given valence state; this is just an example of a substance with an oxidation state of oxygen atoms equal to zero
The high ionization energy (like hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice that of hydrogen), which provides a greater tendency for the oxygen atom to attach electrons and the ability to form O 2A anions. But the energy of electron affinity for the oxygen atom is still lower than that of halogen atoms and even other elements of group VIA. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements, the atoms of which donate electrons very easily.
By socializing two unpaired electrons, an oxygen atom can form two covalent bonds. Due to the impossibility of excitation, two lone pairs of electrons can only enter into donor-acceptor interaction. Thus, disregarding the multiplicity of the bond and hybridization, the oxygen atom can be in one of five valence states (Table 29).
The most characteristic of the oxygen atom is the valence state with W k \u003d 2, that is, the formation of two covalent bonds due to two unpaired electrons.
The very high electronegativity of the oxygen atom (higher - only for fluorine) leads to the fact that in most of its compounds oxygen has an oxidation state of –II. There are substances in which oxygen exhibits other values \u200b\u200bof the oxidation state, some of which are shown in Table 29 as examples, and the comparative stability is shown in Fig. 10.3.

c) Oxygen molecule

It has been experimentally established that a diatomic oxygen molecule O 2 contains two unpaired electrons. Using the method of valence bonds, such an electronic structure of this molecule cannot be explained. Nevertheless, the bond in the oxygen molecule is close in properties to covalent. The oxygen molecule is non-polar. Interatomic distance ( r o – o \u003d 1.21 A \u003d 121 nm) is less than the distance between atoms bound by a simple bond. The molar binding energy is quite high and amounts to 498 kJ / mol.

d) Oxygen (substance)

Under normal conditions oxygen is a colorless and odorless gas. Solid oxygen melts at 55 K (–218 ° C), and liquid oxygen boils at 90 K (–183 ° C).
Intermolecular bonds in solid and liquid oxygen are somewhat stronger than in hydrogen, as evidenced by the wider temperature range of existence of liquid oxygen (36 ° C) and higher molar heats of fusion (0.446 kJ / mol) and vaporization (6, 83 kJ / mol).
Oxygen is slightly soluble in water: at 0 ° C, only 5 volumes of oxygen (gas!) Dissolve in 100 volumes of water (liquid!).
The high tendency of oxygen atoms to attach electrons and high electronegativity lead to the fact that oxygen exhibits only oxidizing properties. These properties are especially pronounced at high temperatures.
Oxygen reacts with many metals: 2Ca + O 2 \u003d 2CaO, 3Fe + 2O 2 \u003d Fe 3 O 4 ( t);
non-metals: C + O 2 \u003d CO 2, P 4 + 5O 2 \u003d P 4 O 10,
and complex substances: CH 4 + 2O 2 \u003d CO 2 + 2H 2 O, 2H 2 S + 3O 2 \u003d 2H 2 O + 2SO 2.

Most often, as a result of such reactions, various oxides are obtained (see Chapter II § 5), but active alkali metals, for example sodium, are converted into peroxides by combustion:

2Na + O 2 \u003d Na 2 O 2.

Structural formula of the resulting sodium peroxide (Na) 2 (O-O).
A smoldering splinter, placed in oxygen, flares up. It is a convenient and easy way to detect pure oxygen.
In industry, oxygen is obtained from air by rectification (complex distillation), and in the laboratory, by subjecting some oxygen-containing compounds to thermal decomposition, for example:
2KMnO 4 \u003d K 2 MnO 4 + MnO 2 + O 2 (200 ° C);
2KClO 3 \u003d 2KCl + 3O 2 (150 ° C, MnO 2 - catalyst);
2KNO 3 \u003d 2KNO 2 + 3O 2 (400 ° C)
and, in addition, by catalytic decomposition of hydrogen peroxide at room temperature: 2H 2 O 2 \u003d 2H 2 O + O 2 (MnO 2 is a catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocketry, liquid oxygen is used as an oxidizer.
Oxygen is of great importance for maintaining the life of plants, animals and humans. Under normal conditions, a person has enough oxygen to breathe. But in conditions when there is not enough air, or it is absent altogether (in airplanes, during diving work, in spaceships, etc.), special gas mixtures containing oxygen are prepared for breathing. Oxygen is also used in medicine for diseases that cause breathing difficulties.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has an angular structure in between two structures, represented by the following formulas:

Ozone is a dark blue gas with a pungent odor. Due to its strong oxidative activity, it is poisonous. Ozone is one and a half times "heavier" than oxygen and is slightly more soluble in water than oxygen.
Ozone is formed in the atmosphere from oxygen during lightning electrical discharges:

3O 2 \u003d 2O 3 ().

At normal temperatures, ozone is slowly converted to oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" of the earth's atmosphere, protecting all life on earth from the harmful effects of solar radiation.
In some cities, ozone is used instead of chlorine to disinfect (decontaminate) drinking water.

Draw the structural formulas of the following substances: OF 2, H 2 O, H 2 O 2, H 3 PO 4, (H 3 O) 2 SO 4, BaO, BaO 2, Ba (OH) 2. Name these substances. Describe the valence states of oxygen atoms in these compounds.
Determine the valence and oxidation state of each of the oxygen atoms.
2. Make the equations of combustion reactions in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (selenium atoms are oxidized to the oxidation state + IV, the atoms of other elements - to the highest oxidation state). What classes of oxides are the products of these reactions?
3. How many liters of ozone can be obtained (under normal conditions) a) from 9 liters of oxygen, b) from 8 g of oxygen?

Water is the most abundant substance in the earth's crust. The mass of the earth's water is estimated at 10 18 tons. Water is the basis of the hydrosphere of our planet, in addition, it is contained in the atmosphere, in the form of ice forms the polar caps of the Earth and high-altitude glaciers, and is also part of various rocks. The mass fraction of water in the human body is about 70%.
Water is the only substance that in all three states of aggregation has its own special names.

The electronic structure of a water molecule (Fig.10.4 and) we studied in detail earlier (see § 7.10).
Due to the polarity of the O – H bonds and the angular shape, the water molecule is electric dipole.

To characterize the polarity of an electric dipole, a physical quantity called " electric moment of an electric dipole "or simply " dipole moment ".

In chemistry, the dipole moment is measured in Debyes: 1 D \u003d 3.34. 10-30 Cl. m

In a water molecule there are two polar covalent bonds, that is, two electric dipoles, each of which has its own dipole moment (and). The total dipole moment of the molecule is equal to the vector sum of these two moments (Fig.10.5):

(H 2 O) \u003d ,

where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic O - H distances in the molecule. Because q 1 = q 2 = q, a, then

The experimentally determined dipole moments of the water molecule and some other molecules are given in the table.

Table 30.Dipole moments of some polar molecules

Molecule		Molecule		Molecule

Given the dipole nature of the water molecule, it is often schematically depicted as follows:
Pure water is a colorless liquid, tasteless and odorless. Some of the main physical characteristics of water are given in the table.

Table 31.Some physical characteristics of water

Large values \u200b\u200bof molar heats of fusion and vaporization (an order of magnitude higher than those of hydrogen and oxygen) indicate that water molecules, both in solid and in liquid matter, are quite tightly bound together. These connections are called " hydrogen bonds ".

ELECTRIC DIPOLE, DIPOLE MOMENT, BONDING POLARITY, MOLECULE POLARITY.
How many valence electrons of an oxygen atom take part in the formation of bonds in a water molecule?
2.When overlapping of which orbitals are bonds formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in the hydrogen peroxide molecule H 2 O 2. What can you say about the spatial structure of this molecule?
4. The interatomic distances in the HF, HCl and HBr molecules are 0.92, respectively; 1.28 and 1.41. Using the dipole moment table, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. The interatomic distances S - H in the hydrogen sulfide molecule are 1.34, and the angle between the bonds is 92 °. Determine the values \u200b\u200bof the partial charges on the sulfur and hydrogen atoms. What can you say about hybridization of the valence orbitals of the sulfur atom?

10.4. Hydrogen bond

As you already know, due to the significant difference in the electronegativity of hydrogen and oxygen (2.10 and 3.50), the hydrogen atom in the water molecule has a large positive partial charge ( q h \u003d 0.33 e), and the oxygen atom has an even larger negative partial charge ( q h \u003d -0.66 e). Recall also that the oxygen atom has two lone pairs of electrons per sp 3-hybrid AO. The hydrogen atom of one water molecule is attracted to the oxygen atom of another molecule, and, in addition, the half-empty 1s-AO of the hydrogen atom partially accepts a pair of electrons of the oxygen atom. As a result of these interactions between molecules, a special type of intermolecular bonds arises - a hydrogen bond.
In the case of water, hydrogen bonding can be schematically represented as follows:

In the last structural formula, three dots (dotted line, not electrons!) Show the hydrogen bond.

The hydrogen bond exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar N – E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) the molecule contains an atom E with a large negative partial charge and a lone pair of electrons.
The element E can be fluorine, oxygen and nitrogen. Hydrogen bonds are much weaker if E is chlorine or sulfur.
Examples of substances with a hydrogen bond between molecules: hydrogen fluoride, solid or liquid ammonia, ethyl alcohol and many others.

In liquid hydrogen fluoride, its molecules are linked by hydrogen bonds in rather long chains, and three-dimensional networks are formed in liquid and solid ammonia.
In terms of strength, a hydrogen bond is intermediate between a chemical bond and other types of intermolecular bonds. The molar energy of a hydrogen bond usually ranges from 5 to 50 kJ / mol.
In solid water (that is, in ice crystals), all hydrogen atoms are hydrogen bonded to oxygen atoms, with each oxygen atom forming two hydrogen bonds (using both lone pairs of electrons). This structure makes ice "looser" in comparison with liquid water, where some of the hydrogen bonds are broken, and the molecules are able to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in a solid state has a lower density than in a liquid state. Water reaches its maximum density at 4 ° С - at this temperature, a lot of hydrogen bonds break, and thermal expansion does not have a very strong effect on the density.
Hydrogen bonds are very important in our life. Let's imagine for a moment that hydrogen bonds have ceased to form. Here are some of the consequences:

• water at room temperature would become gaseous, since its boiling point would drop to about –80 ° C;
• all reservoirs would freeze from the bottom, since the density of ice would be greater than the density of liquid water;
• the double helix of DNA would cease to exist and much more.

The examples given are enough to understand that in this case, nature on our planet would become completely different.

HYDROGEN BONDING, THE CONDITIONS OF ITS FORMATION.
The formula of ethyl alcohol is CH 3 –CH 2 –O – H. Between what atoms of different molecules of this substance are hydrogen bonds formed? Draw up structural formulas to illustrate their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with the help of structural formulas how hydrogen bonds are formed in an aqueous solution of a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). \u003d 2H 2 O.
Both of these reactions occur in water constantly and at an equal rate, therefore, there is an equilibrium in water: 2H 2 O AH 3 O + OH.
This balance is called equilibrium of autoprotolysiswater.

The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis is enhanced, but at room temperature the equilibrium is shifted to the left, that is, the concentration of H 3 O and OH ions is negligible. What are they equal to?
According to the law of the acting masses

But due to the fact that the number of reacted water molecules is insignificant in comparison with the total number of water molecules, it can be assumed that the water concentration during auto-protolysis practically does not change, and 2 \u003d const Such a low concentration of oppositely charged ions in pure water explains why this liquid, although poorly, still conducts an electric current.

AUTOPROTOLYSIS OF WATER, CONSTANT OF AUTOPROTOLYSIS (IONIC PRODUCTION) OF WATER.
The ionic product of liquid ammonia (boiling point –33 ° C) is 2 · 10 –28. Make an equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. Which of the substances is more conductive, water or liquid ammonia?

1. Obtaining hydrogen and its combustion (reducing properties).
2. Obtaining oxygen and combustion of substances in it (oxidizing properties).

There are things in our daily life that are so common that almost everyone knows about them. For example, everyone knows that water is a liquid, it is easily accessible and does not burn, therefore, it can extinguish fire. But have you ever wondered why this is so?

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Water is made up of hydrogen and oxygen atoms. Both of these elements support combustion. So, based on general logic (not scientific), it follows that water must also burn, right? However, this does not happen.

When does combustion occur?

Combustion is a chemical process in which molecules and atoms combine to release energy in the form of heat and light. To burn something, you need two things - fuel as a source of combustion (for example, a sheet of paper, a piece of wood, etc.) and an oxidizer (oxygen in the earth's atmosphere is the main oxidant). We also need the heat needed to reach the ignition temperature of the substance in order for the combustion process to begin.

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For example, consider the process of burning paper using matches. In this case, paper will be the fuel, the gaseous oxygen contained in the air will act as an oxidizing agent, and the ignition temperature will be reached due to a burning match.

The structure of the chemical composition of water

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Water is made up of two hydrogen atoms and one oxygen atom. Its chemical formula is H2O. Now it is interesting to note that the two constituents of water are indeed highly flammable.

Why is hydrogen a flammable substance?

Hydrogen atoms have only one electron and therefore easily bind with other elements. As a rule, hydrogen occurs naturally in the form of a gas, the molecules of which consist of two atoms. This gas is highly reactive and oxidizes rapidly in the presence of an oxidizing agent, making it flammable.

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When hydrogen burns, a large amount of energy is released, so it is often used in liquefied form for launching spacecraft into space.

Oxygen supports combustion

As mentioned earlier, an oxidizing agent is required for any combustion. There are many chemical oxidants, including oxygen, ozone, hydrogen peroxide, fluorine, etc. Oxygen is the main oxidant that is found in excess in the Earth's atmosphere. It is generally the main oxidizing agent in most fires. That is why a constant supply of oxygen is required to maintain a fire.

Water extinguishes fire

Water can extinguish fire for a number of reasons, one of which is that it is a non-combustible liquid, despite the fact that it consists of two elements that can individually create a fiery hell.

Water is the most common fire extinguishing agent. Image source: pixabay.com

As we said earlier, hydrogen is highly flammable, all it takes is an oxidizing agent and an ignition temperature to start the reaction. Since oxygen is the most abundant oxidizing agent on Earth, it quickly combines with hydrogen atoms, releasing large amounts of light and heat, thus forming water molecules. This is how it works:

Note that a mixture of hydrogen with a small volume of oxygen or air is explosive and is called an oxyhydrogen gas, it burns extremely quickly with a loud pop, which is perceived as an explosion. The Hindenburg airship disaster in 1937 in New Jersey claimed dozens of lives as a result of the ignition of hydrogen that filled the airship shell. The flammability of hydrogen and its explosiveness in combination with oxygen is the main reason why we do not receive water chemically in laboratories.