In the periodic system, hydrogen is located in two groups of elements that are absolutely opposite in their properties. This feature make it completely unique. Hydrogen is not only an element or substance, but also a integral part many complex compounds, organogenic and biogenic elements. Therefore, we consider its properties and characteristics in more detail.

The release of combustible gas during the interaction of metals and acids was observed as early as the 16th century, that is, during the formation of chemistry as a science. famous English scientist Henry Cavendish investigated the substance, starting in 1766, and gave it the name "combustible air". When burned, this gas produced water. Unfortunately, the scientist's adherence to the theory of phlogiston (hypothetical "hyperfine matter") prevented him from coming to the right conclusions.

The French chemist and naturalist A. Lavoisier, together with the engineer J. Meunier and with the help of special gasometers, in 1783 carried out the synthesis of water, and then its analysis by decomposing water vapor with red-hot iron. Thus, scientists were able to come to the right conclusions. They found that "combustible air" is not only part of the water, but can also be obtained from it.

In 1787, Lavoisier suggested that the studied gas is a simple substance and, accordingly, is among the primary chemical elements. He called it hydrogene (from the Greek words hydor - water + gennao - I give birth), that is, "giving birth to water."

The Russian name "hydrogen" was proposed in 1824 by the chemist M. Solovyov. The determination of the composition of water marked the end of the "phlogiston theory". At the turn of the 18th and 19th centuries, it was found that the hydrogen atom is very light (compared to the atoms of other elements) and its mass was taken as the main unit for comparing atomic masses, obtaining a value equal to 1.

Physical properties

Hydrogen is the lightest of all substances known to science (it is 14.4 times lighter than air), its density is 0.0899 g/l (1 atm, 0 °C). This material melts (solidifies) and boils (liquefies), respectively, at -259.1 ° C and -252.8 ° C (only helium has lower boiling and melting t °).

The critical temperature of hydrogen is extremely low (-240 °C). For this reason, its liquefaction is a rather complicated and costly process. critical pressure substances - 12.8 kgf / cm², and the critical density is 0.0312 g / cm³. Among all gases, hydrogen has the highest thermal conductivity: at 1 atm and 0 ° C, it is 0.174 W / (mxK).

The specific heat capacity of a substance under the same conditions is 14.208 kJ / (kgxK) or 3.394 cal / (gh ° C). This element is slightly soluble in water (about 0.0182 ml / g at 1 atm and 20 ° C), but well - in most metals (Ni, Pt, Pa and others), especially in palladium (about 850 volumes per volume of Pd ).

The latter property is associated with its ability to diffuse, while diffusion through a carbon alloy (for example, steel) can be accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (this process is called decarbonization). In the liquid state, the substance is very light (density - 0.0708 g / cm³ at t ° \u003d -253 ° C) and fluid (viscosity - 13.8 centigrade under the same conditions).

In many compounds, this element exhibits a +1 valency (oxidation state), similar to sodium and other alkali metals. It is usually considered as an analogue of these metals. Accordingly, he heads the I group of the Mendeleev system. In metal hydrides, the hydrogen ion exhibits a negative charge (the oxidation state is -1), that is, Na + H- has a structure similar to Na + Cl- chloride. In accordance with this and some other facts (the proximity physical properties element "H" and halogens, the ability to replace it with halogens in organic compounds) Hydrogene is classified as group VII of the Mendeleev system.

Under normal conditions, molecular hydrogen has low activity, directly combining only with the most active of non-metals (with fluorine and chlorine, with the latter - in the light). In turn, when heated, it interacts with many chemical elements.

Atomic hydrogen has an increased chemical activity (compared to molecular hydrogen). With oxygen, it forms water according to the formula:

Н₂ + ½О₂ = Н₂О,

releasing 285.937 kJ/mol of heat or 68.3174 kcal/mol (25°C, 1 atm). Under normal temperature conditions, the reaction proceeds rather slowly, and at t ° >= 550 ° С, it is uncontrolled. The explosive limits of a mixture of hydrogen + oxygen by volume are 4–94% H₂, and mixtures of hydrogen + air are 4–74% H₂ (a mixture of two volumes of H₂ and one volume of O₂ is called explosive gas).

This element is used to reduce most metals, since it takes oxygen from oxides:

Fe₃O₄ + 4H₂ = 3Fe + 4Н₂О,

CuO + H₂ = Cu + H₂O etc.

With different halogens, hydrogen forms hydrogen halides, for example:

H₂ + Cl₂ = 2HCl.

However, when reacting with fluorine, hydrogen explodes (this also happens in the dark, at -252 ° C), reacts with bromine and chlorine only when heated or illuminated, and with iodine - only when heated. When interacting with nitrogen, ammonia is formed, but only on a catalyst, at elevated pressures and temperatures:

ZN₂ + N₂ = 2NH₃.

When heated, hydrogen actively reacts with sulfur:

H₂ + S = H₂S (hydrogen sulfide),

and much more difficult - with tellurium or selenium. Hydrogen reacts with pure carbon without a catalyst, but at high temperatures:

2H₂ + C (amorphous) = CH₄ (methane).

This substance directly reacts with some of the metals (alkali, alkaline earth and others), forming hydrides, for example:

Н₂ + 2Li = 2LiH.

important practical value have interactions of hydrogen and carbon monoxide (II). In this case, depending on the pressure, temperature and catalyst, various organic compounds are formed: HCHO, CH₃OH, etc. Unsaturated hydrocarbons turn into saturated ones during the reaction, for example:

С n Н₂ n + Н₂ = С n Н₂ n ₊₂.

Hydrogen and its compounds play an exceptional role in chemistry. It determines the acidic properties of the so-called. protic acids, tends to form with different elements hydrogen bond, which has a significant effect on the properties of many inorganic and organic compounds.

Getting hydrogen

The main types of raw materials for industrial production of this element are petroleum refining gases, natural combustible and coke oven gases. It is also obtained from water through electrolysis (in places with affordable electricity). One of the most important methods for the production of material from natural gas the catalytic interaction of hydrocarbons, mainly methane, with water vapor (the so-called conversion) is considered. For example:

CH₄ + H₂O = CO + ZH₂.

Incomplete oxidation of hydrocarbons with oxygen:

CH₄ + ½O₂ \u003d CO + 2H₂.

Synthesized carbon monoxide (II) undergoes conversion:

CO + H₂O = CO₂ + H₂.

Hydrogen produced from natural gas is the cheapest.

For electrolysis of water, direct current is used, which is passed through a solution of NaOH or KOH (acids are not used to avoid corrosion of the equipment). Under laboratory conditions, the material is obtained by electrolysis of water or as a result of the reaction between hydrochloric acid and zinc. However, more often used ready-made factory material in cylinders.

From refinery gases and coke oven gas, this element is isolated by removing all other components of the gas mixture, since they are more easily liquefied during deep cooling.

This material began to be obtained industrially at the end of the 18th century. Then it was used to fill balloons. At the moment, hydrogen is widely used in industry, mainly in the chemical industry, for the production of ammonia.

Mass consumers of the substance are manufacturers of methyl and other alcohols, synthetic gasoline and many other products. They are obtained by synthesis from carbon monoxide (II) and hydrogen. Hydrogene is used to hydrogenate heavy and hard liquid fuel, fats, etc., for the synthesis of HCl, hydrotreating of petroleum products, as well as in cutting / welding of metals. Essential elements For nuclear energy are its isotopes - tritium and deuterium.

The biological role of hydrogen

About 10% of the mass of living organisms (on average) falls on this element. It is part of water and the most important groups of natural compounds, including proteins, nucleic acids, lipids, carbohydrates. What does it serve?

This material plays a decisive role: in maintaining the spatial structure of proteins (quaternary), in the implementation of the principle of complementarity nucleic acids(i.e., in the implementation and storage of genetic information), in general, in "recognition" at the molecular level.

The hydrogen ion H+ takes part in important dynamic reactions/processes in the body. Including: in biological oxidation, which provides living cells with energy, in biosynthesis reactions, in photosynthesis in plants, in bacterial photosynthesis and nitrogen fixation, in maintaining acid-base balance and homeostasis, in membrane transport processes. Along with carbon and oxygen, it forms the functional and structural basis of the phenomena of life.

In our Everyday life there are things 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?

Image source: pixabay.com

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 the water should 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 - a fuel as a source of combustion (for example, a sheet of paper, a piece of wood, etc.) and an oxidizing agent (the oxygen contained in the earth's atmosphere is the main oxidizing agent). We also need the heat necessary to reach the ignition temperature of the substance in order to start the combustion process.

Image source auclip.ru

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

The structure of the chemical composition of water

Image source: water-service.com.ua

Water is made up of two hydrogen atoms and one oxygen atom. Her chemical formula H2O. It is now interesting to note that the two constituent elements of water are indeed flammable substances.

Why is hydrogen flammable?

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

Image source: myshared.ru

When hydrogen is burned, a large amount of energy is released, so it is often used in liquefied form to launch spacecraft into space.

Oxygen supports combustion

As mentioned earlier, any combustion requires an oxidizer. There are many chemical oxidizing agents, including oxygen, ozone, hydrogen peroxide, fluorine, etc. Oxygen is the main oxidizing agent 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 necessary to sustain the fire.

Water puts out the fire

Water can extinguish fire for a number of reasons, one of which is that it is a non-flammable liquid, despite being composed of two elements that can individually create a fiery hell.

Water is the most common means of extinguishing fires. 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 common oxidizing agent on Earth, it quickly combines with hydrogen atoms, releasing large amounts of light and heat, and water molecules are formed. Here's how it goes:

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

Hydrogen H is the most common element in the Universe (about 75% by mass), on Earth it is the ninth most common element. The most important natural hydrogen compound is water.
Hydrogen ranks first in the periodic table (Z = 1). It has the simplest structure of an atom: the nucleus of an atom is 1 proton, surrounded by an electron cloud consisting of 1 electron.
Under some conditions, hydrogen exhibits metallic properties (donates an electron), in others - non-metallic (accepts an electron).
Hydrogen isotopes are found in nature: 1H - protium (the nucleus consists of one proton), 2H - deuterium (D - the nucleus consists of one proton and one neutron), 3H - tritium (T - the nucleus consists of one proton and two neutrons).

The simple substance hydrogen

The hydrogen molecule consists of two atoms linked by a non-polar covalent bond.
physical properties. Hydrogen is a colorless, non-toxic, odorless and tasteless gas. The hydrogen molecule is not polar. Therefore, the forces of intermolecular interaction in gaseous hydrogen are small. This manifests itself in low temperatures boiling (-252.6 0С) and melting (-259.2 0С).
Hydrogen is lighter than air, D (in air) = 0.069; slightly soluble in water (2 volumes of H2 dissolve in 100 volumes of H2O). Therefore, hydrogen, when produced in the laboratory, can be collected by air or water displacement methods.

Getting hydrogen

In the laboratory:

1. Action of dilute acids on metals:
Zn +2HCl → ZnCl 2 +H 2

2. Interaction of alkaline and sh-z metals with water:
Ca + 2H 2 O → Ca (OH) 2 + H 2

3. Hydrolysis of hydrides: metal hydrides are easily decomposed by water with the formation of the corresponding alkali and hydrogen:
NaH + H 2 O → NaOH + H 2
CaH 2 + 2H 2 O \u003d Ca (OH) 2 + 2H 2

4. The action of alkalis on zinc or aluminum or silicon:
2Al + 2NaOH + 6H 2 O → 2Na + 3H 2
Zn + 2KOH + 2H 2 O → K 2 + H 2
Si + 2NaOH + H 2 O → Na 2 SiO 3 + 2H 2

5. Water electrolysis. To increase the electrical conductivity of water, an electrolyte is added to it, for example, NaOH, H 2 SO 4 or Na 2 SO 4. At the cathode, 2 volumes of hydrogen are formed, at the anode - 1 volume of oxygen.
2H 2 O → 2H 2 + O 2

Industrial production of hydrogen

1. Conversion of methane with steam, Ni 800 °C (cheapest):
CH 4 + H 2 O → CO + 3 H 2
CO + H 2 O → CO 2 + H 2

In total:
CH 4 + 2 H 2 O → 4 H 2 + CO 2

2. Water vapor through hot coke at 1000 o C:
C + H 2 O → CO + H 2
CO + H 2 O → CO 2 + H 2

The resulting carbon monoxide (IV) is absorbed by water, in this way 50% of industrial hydrogen is obtained.

3. By heating methane to 350°C in the presence of an iron or nickel catalyst:
CH 4 → C + 2H 2

4. Electrolysis of aqueous solutions of KCl or NaCl as a by-product:
2H 2 O + 2NaCl → Cl 2 + H 2 + 2NaOH

Chemical properties of hydrogen

• In compounds, hydrogen is always monovalent. It has an oxidation state of +1, but in metal hydrides it is -1.
• The hydrogen molecule consists of two atoms. The emergence of a bond between them is explained by the formation of a generalized pair of electrons H: H or H 2
• Due to this generalization of electrons, the H 2 molecule is more energetically stable than its individual atoms. To break a molecule into atoms in 1 mole of hydrogen, it is necessary to expend an energy of 436 kJ: H 2 \u003d 2H, ∆H ° \u003d 436 kJ / mol
• This explains the relatively low activity of molecular hydrogen at ordinary temperature.
• With many non-metals, hydrogen forms gaseous compounds such as RN 4, RN 3, RN 2, RN.

1) Forms hydrogen halides with halogens:
H 2 + Cl 2 → 2HCl.
At the same time, it explodes with fluorine, reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated.

2) With oxygen:
2H 2 + O 2 → 2H 2 O
with heat release. At ordinary temperatures, the reaction proceeds slowly, above 550 ° C - with an explosion. A mixture of 2 volumes of H 2 and 1 volume of O 2 is called explosive gas.

3) When heated, it reacts vigorously with sulfur (much more difficult with selenium and tellurium):
H 2 + S → H 2 S (hydrogen sulfide),

4) With nitrogen with the formation of ammonia only on the catalyst and at elevated temperatures and pressures:
ZN 2 + N 2 → 2NH 3

5) With carbon at high temperatures:
2H 2 + C → CH 4 (methane)

6) Forms hydrides with alkali and alkaline earth metals (hydrogen is an oxidizing agent):
H 2 + 2Li → 2LiH
in metal hydrides, the hydrogen ion is negatively charged (oxidation state -1), that is, the hydride Na + H - is built like chloride Na + Cl -

So complex substances:

7) With metal oxides (used to restore metals):
CuO + H 2 → Cu + H 2 O
Fe 3 O 4 + 4H 2 → 3Fe + 4H 2 O

8) with carbon monoxide (II):
CO + 2H 2 → CH 3 OH
Synthesis - gas (a mixture of hydrogen and carbon monoxide) is of great practical importance, because, depending on temperature, pressure and catalyst, various organic compounds are formed, for example, HCHO, CH 3 OH and others.

9) Unsaturated hydrocarbons react with hydrogen, turning into saturated:
C n H 2n + H 2 → C n H 2n+2.

§3. Reaction equation and how to write it

Interaction hydrogen With oxygen, as Sir Henry Cavendish established, leads to the formation of water. Let's get on with it simple example learn how to compose equations of chemical reactions.
What comes from hydrogen And oxygen, we already know:

H 2 + O 2 → H 2 O

Now we take into account that the atoms of chemical elements in chemical reactions do not disappear and do not appear from nothing, do not turn into each other, but combine in new combinations to form new molecules. So in the equation chemical reaction there should be the same number of atoms of each kind before reactions ( left from the equal sign) and after the end of the reaction ( on right from the equal sign), like this:

2H 2 + O 2 \u003d 2H 2 O

That's what it is reaction equation - conditional record of an ongoing chemical reaction using formulas of substances and coefficients.

This means that in the above reaction two moles hydrogen should react with by one mole oxygen, and the result will be two moles water.

Interaction hydrogen With oxygen- not a simple process at all. It leads to a change in the oxidation states of these elements. To select coefficients in such equations, one usually uses the method " electronic balance".

When water is formed from hydrogen and oxygen, this means that hydrogen changed its oxidation state from 0 before +I, A oxygen- from 0 before −II. At the same time, several (n) electrons:

Hydrogen donating electrons serves here reducing agent, and oxygen accepting electrons - oxidizing agent.

Oxidizing and reducing agents

Now let's see how the processes of giving and receiving electrons look like separately. Hydrogen, having met with the "robber" - oxygen, loses all its property - two electrons, and its oxidation state becomes equal to +I:

H 2 0 − 2 e− = 2Н + I

Happened oxidation half-reaction equation hydrogen.

And the bandit oxygen About 2, having taken the last electrons from the unfortunate hydrogen, is very pleased with his new oxidation state -II:

O 2 + 4 e− = 2O − II

This reduction half-reaction equation oxygen.

It remains to add that both the "bandit" and his "victim" have lost their chemical identity and from simple substances - gases with diatomic molecules H 2 And About 2 turned into components of a new chemical substance - water H 2 O.

Further, we will argue as follows: how many electrons the reductant gave to the oxidizing bandit, that is how much he received. The number of electrons donated by the reducing agent must be equal to the number of electrons accepted by the oxidizing agent..

So you need equalize the number of electrons in the first and second half-reactions. In chemistry, the following conditional form of writing the equations of half-reactions is accepted:

	2 H 2 0 − 2 e− = 2Н + I
	1 O 2 0 + 4 e− = 2O − II

Here, the numbers 2 and 1 to the left of the curly bracket are factors that will help ensure that the number of given and received electrons is equal. We take into account that in the equations of half-reactions 2 electrons are given away, and 4 are accepted. To equalize the number of received and given electrons, the least common multiple and additional factors are found. In our case, the least common multiple is 4. Additional factors will be 2 for hydrogen (4: 2 = 2), and for oxygen - 1 (4: 4 = 1)
The resulting multipliers will serve as the coefficients of the future reaction equation:

2H 2 0 + O 2 0 \u003d 2H 2 + I O -II

Hydrogen oxidized not only when meeting oxygen. Approximately the same effect on hydrogen and fluorine F2, halogen and the famous "robber", and seemingly harmless nitrogen N 2:

H 2 0 + F 2 0 = 2H + I F −I

3H 2 0 + N 2 0 \u003d 2N -III H 3 + I

This results in hydrogen fluoride HF or ammonia NH3.

In both compounds, the oxidation state hydrogen becomes equal +I, because he gets partners in the molecule "greedy" for someone else's electronic good, with high electronegativity - fluorine F And nitrogen N. At nitrogen the value of electronegativity is considered equal to three conventional units, and y fluorine in general, the highest electronegativity among all chemical elements is four units. So it's no wonder they leave the poor hydrogen atom without any electronic environment.

But hydrogen maybe restore- accept electrons. This happens if alkali metals or calcium, in which the electronegativity is less than that of hydrogen, participate in the reaction with it.

10.1 Hydrogen

The name "hydrogen" refers to both a chemical element and a simple substance. Element hydrogen is made up of hydrogen atoms. simple substance hydrogen is made up of hydrogen molecules.

A) Chemical element hydrogen

In the natural series of elements, the serial 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 (collectively, this is called the earth's crust) is 0.17. It is found in water, many minerals, oil, natural gas, plants and animals. The average human body contains 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, so it practically does not occur in nature. Deuterium is stable, but there is very little of it: w D = 0.015% (of the mass of all terrestrial hydrogen). Therefore, the atomic mass of hydrogen differs very little from 1 Dn (1.00794 Dn).

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 a hydrogen atom are determined by the presence of one electron in a single valence orbital. A large ionization energy makes the hydrogen atom not prone to donate an electron, and not too high an electron affinity leads to a slight tendency to accept it. Consequently, in chemical systems, the formation of the H cation is impossible, and compounds with the H anion are not very stable. Thus, the formation of a covalent bond with other atoms due to its one unpaired electron is most characteristic of the hydrogen atom. Both 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 in hydrogen is an oxidation state of –I.
Information about the valence capabilities of the hydrogen atom is given in table 28. The valence state of a hydrogen atom connected by one covalent bond with any atom is indicated in the table by the symbol "H-".

Table 28Valence possibilities 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 H2 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. Communication is formed by the exchange mechanism. According to the way electron clouds overlap, this is an s-bond (Fig. 10.1 A). Since the atoms are the same, the bond is non-polar.

Interatomic distance (more precisely, the equilibrium interatomic distance, because atoms vibrate) in a hydrogen molecule r(H-H) = 0.74 A (Fig. 10.1 V), which is much less than the sum of orbital radii (1.06 A). Consequently, the electron clouds of bonding atoms overlap deeply (Fig. 10.1 b), and the bond in the hydrogen molecule is strong. Quite talking about the same great importance 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) ball (Fig. 10.1 G).

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), while liquid hydrogen boils at 20 K (–253°C). Low melting and boiling points, a very small temperature interval for the existence of liquid hydrogen (only 6 °C), as well as small molar heats of melting (0.117 kJ/mol) and vaporization (0.903 kJ/mol) indicate that intermolecular bonds in hydrogen very weak.
Hydrogen density r (H 2) \u003d (2 g / mol): (22.4 l / mol) \u003d 0.0893 g / l. For comparison: the average air density 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: H 2 + 2 e- \u003d 2H -I, H 2 - 2 e- \u003d 2H + I.
In the first case, hydrogen is an oxidizing agent, for example, in reactions with sodium or calcium: 2Na + H 2 = 2NaH, ( t) Ca + H 2 = CaH 2 . ( t)
But the reducing properties are more characteristic of hydrogen: 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, such as fluorine, chlorine, sulfur, and even nitrogen.
In the laboratory, hydrogen is produced by 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 method of water displacement (see Fig. 10.2 b) or simply into an inverted flask (Fig. 10.2 A).

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 treated at high temperature with water vapor coal:

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

Pure hydrogen is obtained from water by decomposing it with an electric current (subjecting 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 groups and boron form molecular hydrides. Of these, only hydrides of elements that form non-metals are stable:

B 2 H 6 ; CH 4 ; NH3; H2O; HF
SiH 4 ;PH 3 ; H2S; HCl
AsH 3 ; H2Se; HBr
H2Te; HI
With the exception of water, all of these compounds are gaseous substances at room temperature, hence their name - "volatile hydrides".
Some of the elements that form non-metals are also included in more complex hydrides. For example, carbon forms compounds with the general formulas C n H2 n+2 , C n H2 n, C n H2 n-2 and others, where n can be very large (organic chemistry studies these compounds).
Ionic hydrides include alkali, alkaline earth and magnesium hydrides. The crystals of these hydrides consist of H anions and metal cations in the highest oxidation state of Me or Me 2 (depending on the group of the system of elements).

LiH
NaH	MgH2
KH	CaH2
RbH	SrH 2
CSH	BaH2

Both ionic and almost all molecular hydrides (except 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 a part of hydroxides and some salts. You will get acquainted with the properties of these more complex hydrogen compounds in the following chapters.
The main consumers of hydrogen produced in 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 is the catalyst).

Hydrogen is used in large quantities to produce methyl alcohol (methanol) by the reaction 2H 2 + CO = 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 = 2Fe + 3H 2 O.

1. What particles do the nuclei of a) protium, b) deuterium, c) tritium consist of?
2. Compare the ionization energy of a hydrogen atom with the ionization energy of atoms of other elements. Which element is closest to hydrogen in this characteristic?
3. Do the same for the electron affinity energy
4. Compare the direction of polarization of the covalent bond and the degree of oxidation 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 the most commonly used?
6. They often say: "Hydrogen is lighter than air." What is meant by this? In what cases can this expression be taken literally, and in what cases 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 ​​of the corresponding specific quantities.
9. For each of the four reactions illustrating the main Chemical properties hydrogen, make an electronic balance. List the oxidizing 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 30 m 3 of a 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 that take place during the interaction of hydrogen a) with fluorine, b) with sulfur.
13. The reaction schemes below illustrate the basic 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. Make up the equations of the corresponding reactions if M is sodium. Illustrate the chemical properties of calcium hydride with reaction equations.
14. Using the electron balance method, write the equations for 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 with hydrogen, the word "oxygen" is the name of both a chemical element and a simple substance. Except simple substance" oxygen"(dioxygen) the chemical element oxygen forms another simple substance called " ozone"(trioxygen). This allotropic modifications oxygen. The substance oxygen consists of oxygen molecules O 2 , and the substance ozone consists of ozone molecules O 3 .

a) The chemical element oxygen

In the natural series of elements, the serial 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) - component air. The volume fraction of oxygen in the air is 21%. Oxygen (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 common. Therefore, the atomic mass of oxygen is close to 16 Dn (15.9994 Dn).

b) Oxygen atom

You know the following characteristics of the oxygen atom.

Table 29Valence possibilities of the oxygen atom

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 O2** 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 as ionic compounds.
** The oxygen atoms in the molecule are not in the 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 that of hydrogen) excludes the formation of a simple cation from the oxygen atom. The electron affinity energy is quite high (almost twice as high as that of hydrogen), which provides a greater propensity for the oxygen atom to attach electrons and the ability to form O 2A anions. But the electron affinity energy of the oxygen atom is still less than that of halogen atoms and even other elements of the VIA group. Therefore, oxygen anions ( oxide ions) exist only in compounds of oxygen with elements whose atoms donate electrons very easily.
By sharing two unpaired electrons, an oxygen atom can form two covalent bonds. Two lone pairs of electrons, due to the impossibility of excitation, can only enter into a donor-acceptor interaction. Thus, without taking into account the multiplicity of bonds and hybridization, the oxygen atom can be in one of the 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 (only fluorine is higher) 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 ​​of the oxidation state, some of them are given in table 29 as examples, and the comparative stability is shown in fig. 10.3.

c) Oxygen molecule

It has been experimentally established that the 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 the covalent bond. The oxygen molecule is non-polar. Interatomic distance ( r o–o = 1.21 A = 121 nm) is less than the distance between atoms connected by a single bond. The molar binding energy is rather 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), while 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 larger temperature interval for the existence of liquid oxygen (36 ° C) and the molar heats of melting (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 propensity 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 = 2CaO, 3Fe + 2O 2 = 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 Ch. II § 5), but active alkali metals, such as sodium, when burned, turn into peroxides:

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. This 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 = 2H 2 O + O 2 (MnO 2 -catalyst).
Pure oxygen is used in industry to intensify those processes in which oxidation occurs and to create a high-temperature flame. In rocket technology, liquid oxygen is used as an oxidizing agent.
Oxygen plays an important role in maintaining the life of plants, animals and humans. Under normal conditions, a person needs enough oxygen to breathe in the air. But in conditions where there is not enough air, or it is completely absent (in airplanes, during diving, in spaceships etc.), special gas mixtures containing oxygen are prepared for breathing. Oxygen is also used in medicine for diseases that cause difficulty in breathing.

e) Ozone and its molecules

Ozone O 3 is the second allotropic modification of oxygen.
The triatomic ozone molecule has a corner structure midway between the 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 somewhat more than oxygen, soluble in water.
Ozone is formed in the atmosphere from oxygen during lightning electrical discharges:

3O 2 \u003d 2O 3 ().

At ordinary temperatures, ozone slowly turns into oxygen, and when heated, this process proceeds with an explosion.
Ozone is contained in the so-called "ozone layer" earth's atmosphere protecting all life on Earth from harmful effects 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 the oxygen atoms in these compounds.
Determine the valency and oxidation state of each of the oxygen atoms.
2. Make the equations for the reactions of combustion in oxygen of lithium, magnesium, aluminum, silicon, red phosphorus and selenium (the atoms of selenium are oxidized to the oxidation state + IV, the atoms of the remaining elements to the highest oxidation state). What classes of oxides do the products of these reactions belong to?
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 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 it forms the polar caps of the Earth and high-mountain 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 has its own special names in all three states of aggregation.

The electronic structure of the water molecule (Fig. 10.4 A) we have 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 = 3.34. 10–30 C. 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 a molecule is equal to the vector sum of these two moments (Fig. 10.5):

(H 2 O) = ,

Where q 1 and q 2 - partial charges (+) on hydrogen atoms, and and - interatomic distances O - H 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 30Dipole 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 without taste or smell. Some basic physical characteristics of water are given in the table.

Table 31Some physical characteristics of water

The large values ​​of the molar heats of melting and vaporization (an order of magnitude greater than those of hydrogen and oxygen) indicate that water molecules, both in solid and liquid substances, are quite strongly bonded to each other. These connections are called hydrogen bonds".

ELECTRIC DIPOLE, DIPOLE MOMENT, COMMUNICATION 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 which orbitals, bonds are formed between hydrogen and oxygen in a water molecule?
3. Make a diagram of the formation of bonds in a molecule of hydrogen peroxide H 2 O 2. What can you say about the spatial structure of this molecule?
4. Interatomic distances in HF, HCl and HBr molecules are equal, respectively, to 0.92; 1.28 and 1.41. Using the table of dipole moments, calculate and compare the partial charges on the hydrogen atoms in these molecules.
5. Interatomic distances S - H in a hydrogen sulfide molecule are equal to 1.34, and the angle between bonds is 92 °. Determine the values ​​of partial charges on sulfur and hydrogen atoms. What can you say about the 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 acquires a large positive partial charge ( q h = 0.33 e), and the oxygen atom has an even larger negative partial charge ( q h = -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 from the oxygen atom. As a result of these interactions between molecules, special kind intermolecular bonds - hydrogen bond.
In the case of water, hydrogen bond formation can be schematically represented as follows:

In the last structural formula, three dots (dashed stroke, not electrons!) Show a hydrogen bond.

Hydrogen bonding exists not only between water molecules. It is formed if two conditions are met:
1) there is a strongly polar H–E bond in the molecule (E is the symbol of an atom of a sufficiently electronegative element),
2) in the molecule there is an atom E with a large negative partial charge and an unshared pair of electrons.
As 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 into rather long chains, while in liquid and solid ammonia, three-dimensional networks are formed.
The strength of the hydrogen bond is intermediate between chemical bond and other types of intermolecular bonds. The molar energy of the hydrogen bond usually lies in the range from 5 to 50 kJ/mol.
In solid water (that is, 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). Such a structure makes ice more "loose" compared to liquid water, where some of the hydrogen bonds are broken, and the molecules get the opportunity to "pack" somewhat more densely. This feature of the structure of ice explains why, unlike most other substances, water in the solid state has a lower density than in the liquid state. Water reaches its maximum density at 4 ° C - at this temperature, quite a lot of hydrogen bonds are broken, and thermal expansion does not yet have a very strong effect on density.
Hydrogen bonds are very important in our life. Imagine for a moment that hydrogen bonds have ceased to form. Here are some consequences:

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

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

HYDROGEN BOND, 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? Make structural formulas illustrating their formation.
2. Hydrogen bonds exist not only in individual substances, but also in solutions. Show with structural formulas how hydrogen bonds are formed aqueous solution a) ammonia, b) hydrogen fluoride, c) ethanol (ethyl alcohol). \u003d 2H 2 O.
Both of these reactions proceed in water constantly and at the same rate, therefore, there is an equilibrium in water: 2H 2 O AN 3 O + OH.
This balance is called autoprotolysis equilibrium water.

The direct reaction of this reversible process is endothermic, therefore, when heated, autoprotolysis increases, while at room temperature, the equilibrium is shifted to the left, that is, the concentrations of H 3 O and OH ions are negligible. What are they equal to?
According to the law of mass action

But due to the fact that the number of reacted water molecules is insignificant compared to the total number of water molecules, we can assume that the water concentration during autoprotolysis practically does not change, and 2 = const Such a low concentration of oppositely charged ions in clean water explains why this liquid, although bad, still conducts electricity.

AUTOPROTOLYSIS OF WATER, AUTOPROTOLYSIS CONSTANT (IONIC PRODUCT) OF WATER.
The ionic product of liquid ammonia (boiling point -33 ° C) is 2 10 -28. Write an equation for the autoprotolysis of ammonia. Determine the concentration of ammonium ions in pure liquid ammonia. The electrical conductivity of which of the substances is greater, water or liquid ammonia?

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