Hydrogen exhibits oxidizing properties when reacting with. Interaction of halogens with simple substances

Lecture 29

Hydrogen. Water

Lecture plan:

Water. Chemical and physical properties

The role of hydrogen and water in nature

Hydrogen as a chemical element

Hydrogen is the only element in the periodic system of D. I. Mendeleev, the location of which is ambiguous. Its chemical symbol in the periodic table is recorded twice: in both IA and VIIA groups. This is explained by the fact that hydrogen has a number of properties that combine it with both alkali metals and halogens (Table 14).

Table 14

Comparison of the properties of hydrogen with the properties of alkali metals and halogens

In nature, hydrogen exists in the form of three isotopes with mass numbers 1, 2 and 3: protium 1 1 H, deuterium 2 1 D and tritium 3 1 T. The first two are stable isotopes, and the third is radioactive. The natural mixture of isotopes is dominated by protium. The quantitative ratios between the isotopes H: D: T are 1: 1.46 10 -5: 4.00 10 -15 .

Compounds of hydrogen isotopes differ in properties from each other. So, for example, the boiling and freezing points of light protium water (H 2 O), respectively, are - 100 o C and 0 o C, and deuterium (D 2 O) - 101.4 o C and 3.8 o C. The reaction rate with the participation of light water is higher than heavy water.

Hydrogen is the most common element in the Universe - it accounts for about 75% of the mass of the Universe or over 90% of all its atoms. Hydrogen is a part of water in its most important geological shell of the Earth - the hydrosphere.

Hydrogen forms, along with carbon, all organic substances, that is, it is part of the living shell of the Earth - the biosphere. In the earth's crust - the lithosphere - the mass content of hydrogen is only 0.88%, i.e., it occupies the 9th place among all elements. The air shell of the Earth - the atmosphere contains less than a millionth of the total volume attributable to molecular hydrogen. It is found only in the upper atmosphere.

Obtaining and using hydrogen

Hydrogen was first obtained in the 16th century by the medieval physician and alchemist Paracelsus, when an iron plate was immersed in sulfuric acid, and in 1766, the English chemist Henry Cavendish proved that hydrogen is obtained not only by the interaction of iron with sulfuric acid, but also of other metals with others. acids. Cavendish also described for the first time the properties of hydrogen.

IN laboratory hydrogen conditions are obtained:

1. Interaction of metals with acid:

Zn + 2HCl → ZnCl 2 + H 2

2. Interaction of alkali and alkaline earth metals with water

2Na + 2H 2 O → 2NaOH + H 2

Ca + 2H 2 O → Ca (OH) 2 + H 2

IN industry hydrogen is produced in the following ways:

1. Electrolysis of aqueous solutions of salts, acids and alkalis. The most commonly used salt solution is:

2NaCl + 2H 2 O →el. current H 2 + Cl 2 + NaOH

2. Recovery of water vapor by red-hot coke:

C + H 2 O → t CO + H 2

The resulting mixture of carbon monoxide and hydrogen is called water gas (synthesis gas), and is widely used for the synthesis of various chemical products (ammonia, methanol, etc.). To release hydrogen from water gas, carbon monoxide is converted into carbon dioxide when heated with water vapor:

CO + H 2 → t CO 2 + H 2

3. Methane heating in the presence of water vapor and oxygen. This method is currently the main one:

2CH 4 + O 2 + 2H 2 O → t 2CO 2 + 6H 2

Hydrogen is widely used for:

1. industrial synthesis of ammonia and hydrogen chloride;

2. obtaining methanol and synthetic liquid fuel as part of synthesis gas (2 volumes of hydrogen and 1 volume of CO);

3. hydrotreating and hydrocracking of oil fractions;

4. hydrogenation of liquid fats;

5. cutting and welding of metals;

6. obtaining tungsten, molybdenum and rhenium from their oxides;

7. space engines as fuel.

8. Thermonuclear reactors use hydrogen isotopes as fuel.

Physical and chemical properties of hydrogen

Hydrogen is a colorless, tasteless and odorless gas. Density at n.o. 0.09 g/l (14 times lighter than air). Hydrogen is poorly soluble in water (only 2 volumes of gas per 100 volumes of water), but it is well absorbed by d-metals - nickel, platinum, palladium (up to 900 volumes of hydrogen are dissolved in one volume of palladium).

In chemical reactions, hydrogen exhibits both reducing and oxidizing properties. Most often, hydrogen acts as a reducing agent.

1. Interaction with non-metals. Hydrogen forms volatile hydrogen compounds with non-metals (see lecture 25).

With halogens the reaction rate and flow conditions change from fluorine to iodine: hydrogen reacts with fluorine with an explosion even in the dark, with chlorine the reaction proceeds quite calmly with little light exposure, with bromine and iodine the reactions are reversible and proceed only when heated:

H 2 + F 2 → 2HF

H 2 + Cl 2 → hν 2HCl

H 2 + I 2 → t 2HI

With oxygen and sulfuric hydrogen reacts with slight heating. A 1:2 mixture of oxygen and hydrogen is called explosive gas:

H 2 + O 2 → t H 2 O

H 2 + S → t H 2 S

With nitrogen, phosphorus and carbon the reaction occurs under heating, elevated pressure and in the presence of a catalyst. Reactions are reversible:

3H 2 + N 2 → cat., p, t2NH 3

2H 2 + 3P → cat., p, t3PH 3

H 2 + C → cat., p, t CH 4

2. Interaction with complex substances. At high temperatures, hydrogen reduces metals from their oxides:

CuO + H 2 → t Cu + H 2 O

3. At interaction with alkali and alkaline earth metals Hydrogen exhibits oxidizing properties:

2Na + H 2 → 2NaH

Ca + H 2 → CaH 2

4. Interaction with organic substances. Hydrogen actively interacts with many organic substances, such reactions are called hydrogenation reactions. Similar reactions will be considered in more detail in Part III of the collection "Organic Chemistry".

Hydrogen H is a chemical element, one of the most common in our Universe. The mass of hydrogen as an element in the composition of substances is 75% of the total content of atoms of another type. It is included in the most important and vital connection on the planet - water. A distinctive feature of hydrogen is also that it is the first element in the periodic system of chemical elements of D. I. Mendeleev.

Discovery and exploration

The first references to hydrogen in the writings of Paracelsus date back to the sixteenth century. But its isolation from the gas mixture of air and the study of combustible properties were already made in the seventeenth century by the scientist Lemery. Hydrogen was thoroughly studied by an English chemist, physicist and naturalist who experimentally proved that the mass of hydrogen is the smallest in comparison with other gases. In the subsequent stages of the development of science, many scientists worked with him, in particular Lavoisier, who called him "giving birth to water."

Characteristic according to the position in the PSCE

The element that opens the periodic table of D. I. Mendeleev is hydrogen. The physical and chemical properties of the atom show some duality, since the hydrogen is simultaneously assigned to the first group, the main subgroup, if it behaves like a metal and gives up a single electron in the process of a chemical reaction, and to the seventh - in the case of complete filling of the valence shell, that is, reception negative particle, which characterizes it as similar to halogens.

Features of the electronic structure of the element

The properties of the complex substances in which it is included, and the simplest substance H 2 are primarily determined by the electronic configuration of the hydrogen. The particle has one electron with Z= (-1), which rotates in its orbit around the nucleus, containing one proton with unit mass and positive charge (+1). Its electronic configuration is written as 1s 1, which means the presence of one negative particle in the very first and only s-orbital for the hydrogen.

When an electron is detached or given away, and an atom of this element has such a property that it is related to metals, a cation is obtained. In fact, the hydrogen ion is a positive elementary particle. Therefore, a hydrogen devoid of an electron is simply called a proton.

Physical properties

Briefly describing hydrogen, it is a colorless, slightly soluble gas with a relative atomic mass of 2, 14.5 times lighter than air, with a liquefaction temperature of -252.8 degrees Celsius.

It can be easily seen from experience that H2 is the lightest. To do this, it is enough to fill three balls with various substances - hydrogen, carbon dioxide, ordinary air - and simultaneously release them from your hand. The one that is filled with CO 2 will reach the ground faster than anyone, after which it will fall inflated with an air mixture, and the one containing H 2 will rise to the ceiling.

The small mass and size of hydrogen particles justify its ability to penetrate through various substances. On the example of the same ball, this is easy to verify, in a couple of days it will deflate itself, since the gas will simply pass through the rubber. Also, hydrogen can accumulate in the structure of some metals (palladium or platinum), and evaporate from it when the temperature rises.

The property of low solubility of hydrogen is used in laboratory practice to isolate it by the method of hydrogen displacement (the table below contains the main parameters) determine the scope of its application and methods of production.

Isotopic composition

Like many other representatives of the periodic system of chemical elements, hydrogen has several natural isotopes, that is, atoms with the same number of protons in the nucleus, but a different number of neutrons - particles with zero charge and unit mass. Examples of atoms that have a similar property are oxygen, carbon, chlorine, bromine and others, including radioactive ones.

The physical properties of hydrogen 1 H, the most common of the representatives of this group, differ significantly from the same characteristics of its counterparts. In particular, the characteristics of the substances in which they are included differ. So, there is ordinary and deuterated water, containing in its composition, instead of a hydrogen atom with a single proton, deuterium 2 H - its isotope with two elementary particles: positive and uncharged. This isotope is twice as heavy as ordinary hydrogen, which explains the fundamental difference in the properties of the compounds they make up. In nature, deuterium is 3200 times rarer than hydrogen. The third representative is tritium 3 H, in the nucleus it has two neutrons and one proton.

Methods for obtaining and isolating

Laboratory and industrial methods are very different. So, in small quantities, gas is obtained mainly through reactions in which minerals are involved, and large-scale production uses organic synthesis to a greater extent.

The following chemical interactions are used in the laboratory:

In industrial interests, gas is obtained by such methods as:

1. Thermal decomposition of methane in the presence of a catalyst to its constituent simple substances (350 degrees reaches the value of such an indicator as temperature) - hydrogen H 2 and carbon C.
2. Passing vaporous water through coke at 1000 degrees Celsius with the formation of carbon dioxide CO 2 and H 2 (the most common method).
3. Conversion of gaseous methane on a nickel catalyst at a temperature reaching 800 degrees.
4. Hydrogen is a by-product in the electrolysis of aqueous solutions of potassium or sodium chlorides.

Chemical interactions: general provisions

The physical properties of hydrogen largely explain its behavior in reaction processes with one or another compound. The valency of the hydrogen is 1, since it is located in the first group in the periodic table, and the degree of oxidation shows a different one. In all compounds, except for hydrides, hydrogen in s.o. = (1+), in molecules like XH, XH 2, XH 3 - (1-).

The hydrogen gas molecule, formed by creating a generalized electron pair, consists of two atoms and is quite stable energetically, which is why under normal conditions it is somewhat inert and enters into reactions when normal conditions change. Depending on the degree of oxidation of hydrogen in the composition of other substances, it can act both as an oxidizing agent and a reducing agent.

Substances with which hydrogen reacts and forms

Elemental interactions to form complex substances (often at elevated temperatures):

1. Alkaline and alkaline earth metal + hydrogen = hydride.
2. Halogen + H 2 = hydrogen halide.
3. Sulfur + hydrogen = hydrogen sulfide.
4. Oxygen + H 2 = water.
5. Carbon + hydrogen = methane.
6. Nitrogen + H 2 = ammonia.

Interaction with complex substances:

1. Obtaining synthesis gas from carbon monoxide and hydrogen.
2. Recovery of metals from their oxides with H 2 .
3. Hydrogen saturation of unsaturated aliphatic hydrocarbons.

hydrogen bond

The physical properties of hydrogen are such that, when combined with an electronegative element, it allows it to form a special type of bond with the same atom from neighboring molecules that have unshared electron pairs (for example, oxygen, nitrogen and fluorine). The clearest example on which it is better to consider such a phenomenon is water. It can be said that it is stitched with hydrogen bonds, which are weaker than covalent or ionic ones, but due to the fact that there are many of them, they have a significant effect on the properties of the substance. Essentially, hydrogen bonding is an electrostatic interaction that binds water molecules into dimers and polymers, giving rise to its high boiling point.

Hydrogen in the composition of mineral compounds

All contain a proton - a cation of an atom such as hydrogen. A substance whose acid residue has an oxidation state greater than (-1) is called a polybasic compound. It contains several hydrogen atoms, which makes dissociation in aqueous solutions multi-stage. Each subsequent proton breaks away from the rest of the acid more and more difficult. According to the quantitative content of hydrogens in the medium, its acidity is determined.

Application in human activities

Cylinders with a substance, as well as containers with other liquefied gases, such as oxygen, have a specific appearance. They are painted dark green with a bright red "Hydrogen" lettering. Gas is pumped into a cylinder under a pressure of about 150 atmospheres. The physical properties of hydrogen, in particular the lightness of the gaseous state of aggregation, are used to fill balloons, balloons, etc. mixed with helium.

Hydrogen, the physical and chemical properties of which people learned to use many years ago, is currently used in many industries. Most of it goes to the production of ammonia. Also, hydrogen is involved in (hafnium, germanium, gallium, silicon, molybdenum, tungsten, zirconium and others) from oxides, acting in the reaction as a reducing agent, hydrocyanic and hydrochloric acids, as well as artificial liquid fuel. The food industry uses it to convert vegetable oils into solid fats.

We determined the chemical properties and use of hydrogen in various processes of hydrogenation and hydrogenation of fats, coals, hydrocarbons, oils and fuel oil. With the help of it, precious stones, incandescent lamps are produced, metal products are forged and welded under the influence of an oxygen-hydrogen flame.

Let's take a look at what hydrogen is. The chemical properties and production of this non-metal are studied in the course of inorganic chemistry at school. It is this element that heads the periodic system of Mendeleev, and therefore deserves a detailed description.

Brief information about opening an element

Before considering the physical and chemical properties of hydrogen, let's find out how this important element was found.

Chemists who worked in the sixteenth and seventeenth centuries repeatedly mentioned in their writings the combustible gas that is released when acids are exposed to active metals. In the second half of the eighteenth century, G. Cavendish managed to collect and analyze this gas, giving it the name "combustible gas".

The physical and chemical properties of hydrogen at that time were not studied. Only at the end of the eighteenth century, A. Lavoisier managed to establish by analysis that this gas can be obtained by analyzing water. A little later, he began to call the new element hydrogene, which means "giving birth to water." Hydrogen owes its modern Russian name to M.F. Solovyov.

Being in nature

The chemical properties of hydrogen can only be analyzed based on its abundance in nature. This element is present in the hydro- and lithosphere, and is also part of minerals: natural and associated gas, peat, oil, coal, oil shale. It is difficult to imagine an adult who would not know that hydrogen is an integral part of water.

In addition, this non-metal is found in animal organisms in the form of nucleic acids, proteins, carbohydrates, and fats. On our planet, this element is found in free form quite rarely, perhaps only in natural and volcanic gas.

In the form of plasma, hydrogen makes up about half the mass of stars and the Sun, and is also part of the interstellar gas. For example, in free form, as well as in the form of methane, ammonia, this non-metal is present in comets and even some planets.

Physical properties

Before considering the chemical properties of hydrogen, we note that under normal conditions it is a gaseous substance lighter than air, having several isotopic forms. It is almost insoluble in water and has a high thermal conductivity. Protium, which has a mass number of 1, is considered its lightest form. Tritium, which has radioactive properties, is formed in nature from atmospheric nitrogen when neurons expose it to UV rays.

Features of the structure of the molecule

To consider the chemical properties of hydrogen, the reactions characteristic of it, let us dwell on the features of its structure. This diatomic molecule has a covalent non-polar chemical bond. The formation of atomic hydrogen is possible when active metals interact with acid solutions. But in this form, this non-metal is able to exist only for a short time period, almost immediately it recombines into a molecular form.

Chemical properties

Consider the chemical properties of hydrogen. In most of the compounds that this chemical element forms, it exhibits an oxidation state of +1, which makes it similar to active (alkali) metals. The main chemical properties of hydrogen, characterizing it as a metal:

• interaction with oxygen to form water;
• reaction with halogens, accompanied by the formation of hydrogen halide;
• production of hydrogen sulfide when combined with sulfur.

Below is the reaction equation that characterizes the chemical properties of hydrogen. We draw attention to the fact that as a non-metal (with an oxidation state of -1), it acts only in the reaction with active metals, forming the corresponding hydrides with them.

Hydrogen at ordinary temperature does not actively interact with other substances, so most of the reactions are carried out only after preheating.

Let us dwell in more detail on some chemical interactions of the element that heads the periodic system of chemical elements of Mendeleev.

The reaction of water formation is accompanied by the release of 285.937 kJ of energy. At elevated temperatures (more than 550 degrees Celsius), this process is accompanied by a strong explosion.

Among those chemical properties of gaseous hydrogen that have found significant application in industry, its interaction with metal oxides is of interest. It is by catalytic hydrogenation in modern industry that metal oxides are processed, for example, pure metal is isolated from iron scale (mixed iron oxide). This method allows for efficient processing of scrap metal.

The synthesis of ammonia, which involves the interaction of hydrogen with atmospheric nitrogen, is also in demand in the modern chemical industry. Among the conditions for the occurrence of this chemical interaction, we note pressure and temperature.

Conclusion

It is hydrogen that is an inactive chemical substance under normal conditions. As the temperature rises, its activity increases significantly. This substance is in demand in organic synthesis. For example, by hydrogenation, ketones can be reduced to secondary alcohols, and aldehydes can be converted to primary alcohols. In addition, by hydrogenation, unsaturated hydrocarbons of the ethylene and acetylene classes can be converted into saturated compounds of the methane series. Hydrogen is rightly considered a simple substance in demand in modern chemical production.

In the periodic system, hydrogen is located in two groups of elements that are absolutely opposite in their properties. This feature makes it completely unique. Hydrogen is not just an element or substance, but also a component of many complex compounds, an organogenic and biogenic element. 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. The famous English scientist Henry Cavendish studied 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 using special gasometers in 1783, synthesized water, and then analyzed it 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. The critical pressure of a substance is 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 closeness of the physical properties of the element "H" and halogens, the ability to replace it with halogens in organic compounds), Hydrogene is assigned to 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.

Of no small practical importance are the 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 tend to form hydrogen bonds with different elements, which have a significant effect on the properties of many inorganic and organic compounds.

Getting hydrogen

The main types of raw materials for the industrial production of this element are refinery 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 producing material from natural gas is the catalytic interaction of hydrocarbons, mainly methane, with water vapor (the so-called conversion). 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 for the hydrogenation of heavy and solid liquid fuels, fats, etc., for the synthesis of HCl, hydrotreating of petroleum products, as well as in cutting / welding of metals. The most important 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 implementing the principle of complementarity of 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.

distribution in nature. V. is widely distributed in nature, its content in the earth's crust (the lithosphere and hydrosphere) is 1% by mass and 16% by the number of atoms. V. is a part of the most common substance on Earth - water (11.19% of V. by mass), in the composition of compounds that make up coals, oil, natural gases, clay, as well as animal and plant organisms (i.e., in the composition proteins, nucleic acids, fats, carbohydrates, etc.). In the free state, V. is extremely rare; it is found in small quantities in volcanic and other natural gases. Negligible amounts of free V. (0.0001% by number of atoms) are present in the atmosphere. In the near-Earth space, V. in the form of a stream of protons forms the internal (“proton”) radiation belt of the Earth. In space, V. is the most common element. In the form of plasma, it makes up about half the mass of the Sun and most stars, the main part of the gases of the interstellar medium and gaseous nebulae. V. is present in the atmosphere of a number of planets and in comets in the form of free H2, methane CH4, ammonia NH3, water H2O, radicals such as CH, NH, OH, SiH, PH, etc. In the form of a stream of protons, V. is part of the corpuscular radiation of the Sun and cosmic rays.

Isotopes, atom and molecule. Ordinary V. consists of a mixture of two stable isotopes: light V., or protium (1H), and heavy V., or deuterium (2H, or D). In natural compounds of V., there are on average 6,800 1H atoms per 1 2H atom. A radioactive isotope has been artificially obtained - superheavy B., or tritium (3H, or T), with soft β-radiation and a half-life T1 / 2 = 12.262 years. In nature, tritium is formed, for example, from atmospheric nitrogen under the action of cosmic ray neutrons; it is negligible in the atmosphere (4-10-15% of the total number of atoms of air). An extremely unstable 4H isotope has been obtained. The mass numbers of the isotopes 1H, 2H, 3H and 4H, respectively 1,2, 3 and 4, indicate that the nucleus of the protium atom contains only 1 proton, deuterium - 1 proton and 1 neutron, tritium - 1 proton and 2 neutrons, 4H - 1 proton and 3 neutrons. The large difference in the masses of isotopes of hydrogen causes a more noticeable difference in their physical and chemical properties than in the case of isotopes of other elements.

The atom V. has the simplest structure among the atoms of all other elements: it consists of a nucleus and one electron. The binding energy of an electron with a nucleus (ionization potential) is 13.595 eV. The neutral atom V. can also attach a second electron, forming a negative ion H-; in this case, the binding energy of the second electron with the neutral atom (electron affinity) is 0.78 eV. Quantum mechanics makes it possible to calculate all possible energy levels of the atom, and, consequently, to give a complete interpretation of its atomic spectrum. The V atom is used as a model atom in quantum mechanical calculations of the energy levels of other, more complex atoms. The B. H2 molecule consists of two atoms connected by a covalent chemical bond. The energy of dissociation (i.e., decay into atoms) is 4.776 eV (1 eV = 1.60210-10-19 J). The interatomic distance at the equilibrium position of the nuclei is 0.7414-Å. At high temperatures, molecular V. dissociates into atoms (the degree of dissociation at 2000°C is 0.0013; at 5000°C it is 0.95). Atomic V. is also formed in various chemical reactions (for example, by the action of Zn on hydrochloric acid). However, the existence of V. in the atomic state lasts only a short time, the atoms recombine into H2 molecules.

Physical and chemical properties. V. - the lightest of all known substances (14.4 times lighter than air), density 0.0899 g / l at 0 ° C and 1 atm. V. boils (liquefies) and melts (solidifies) at -252.6°C and -259.1°C, respectively (only helium has lower melting and boiling points). The critical temperature of V. is very low (-240 ° C), so its liquefaction is associated with great difficulties; critical pressure 12.8 kgf/cm2 (12.8 atm), critical density 0.0312 g/cm3. Of all gases, V. has the highest thermal conductivity, equal to 0.174 W / (m-K) at 0 ° C and 1 atm, i.e. 4.16-0-4 cal / (s-cm- ° C). The specific heat capacity of V. at 0 ° C and 1 atm Cp 14.208-103 j / (kg-K), i.e. 3.394 cal / (g- ° C). V. slightly soluble in water (0.0182 ml / g at 20 ° C and 1 atm), but well - in many metals (Ni, Pt, Pd, etc.), especially in palladium (850 volumes per 1 volume of Pd) . V.'s solubility in metals is associated with its ability to diffuse through them; diffusion through a carbonaceous alloy (for example, steel) is sometimes accompanied by the destruction of the alloy due to the interaction of steel with carbon (the so-called decarbonization). Liquid water is very light (density at -253°C 0.0708 g/cm3) and fluid (viscosity at -253°C 13.8 centigrade).

In most compounds, V. exhibits a valency (more precisely, an oxidation state) of +1, like sodium and other alkali metals; usually he is considered as an analogue of these metals, heading 1 gr. Mendeleev's systems. However, in metal hydrides, the B. ion is negatively charged (oxidation state -1), that is, the Na + H- hydride is built like Na + Cl- chloride. This and some other facts (the closeness of the physical properties of V. and halogens, the ability of halogens to replace V. in organic compounds) give reason to attribute V. also to group VII of the periodic system (for more details, see the Periodic system of elements). Under normal conditions, molecular V. is relatively inactive, combining directly with only the most active of the nonmetals (with fluorine, and in the light with chlorine). However, when heated, it reacts with many elements. Atomic V. has increased chemical activity compared to molecular V.. V. forms water with oxygen: H2 + 1 / 2O2 = H2O with the release of 285.937-103 J / mol, i.e. 68.3174 kcal / mol of heat (at 25 ° C and 1 atm). At ordinary temperatures, the reaction proceeds extremely slowly, above 550 ° C - with an explosion. The explosive limits of the hydrogen-oxygen mixture are (by volume) from 4 to 94% H2, and the hydrogen-air mixture is from 4 to 74% H2 (a mixture of 2 volumes of H2 and 1 volume of O2 is called explosive gas). V. is used to reduce many metals, as it takes away oxygen from their oxides:

CuO + H2 \u003d Cu + H2O,
Fe3O4 + 4H2 = 3Fe + 4H2O, etc.
V. forms hydrogen halides with halogens, for example:
H2 + Cl2 = 2HCl.

At the same time, it explodes with fluorine (even in the dark and at -252°C), reacts with chlorine and bromine only when illuminated or heated, and with iodine only when heated. V. interacts with nitrogen to form ammonia: 3H2 + N2 = 2NH3 only on a catalyst and at elevated temperatures and pressures. When heated, V. reacts vigorously with sulfur: H2 + S = H2S (hydrogen sulfide), much more difficult with selenium and tellurium. V. can react with pure carbon without a catalyst only at high temperatures: 2H2 + C (amorphous) = CH4 (methane). V. directly reacts with some metals (alkali, alkaline earth, etc.), forming hydrides: H2 + 2Li = 2LiH. Of great practical importance are the reactions of carbon monoxide with carbon monoxide, in which, depending on the temperature, pressure, and catalyst, various organic compounds are formed, such as HCHO, CH3OH, and others (see Carbon monoxide). Unsaturated hydrocarbons react with hydrogen, becoming saturated, for example: CnH2n + H2 = CnH2n+2 (see Hydrogenation).