Characteristics of s-elements

The block of s-elements includes 13 elements, common to which is the building up of the s-sublevel of the external energy level in their atoms.

Although hydrogen and helium are s-elements, due to the specificity of their properties, they should be considered separately. Hydrogen, sodium, potassium, magnesium, calcium are vital elements.

S-element compounds exhibit general patterns in properties due to the similarity electronic structure their atoms. All external electrons are valence and take part in the formation chemical bonds... Therefore, the maximum oxidation state of these elements in compounds is the number electrons in outer layer and, accordingly, is equal to the number of the group in which the given element... The oxidation state of s-element metals is always positive. Another feature is that after the separation of the electrons of the outer layer, an ion remains, which has a shell of a noble gas. When increasing serial number element, atomic radius, the ionization energy decreases (from 5.39 eV y Li to 3.83 eV y Fr), and the reducing activity of the elements increases.

The overwhelming majority of compounds of s-elements are colorless (in contrast to compounds of d-elements), since the transition of d-electrons from low energy levels to higher energy levels.

Compounds of elements of groups IA - IIA are typical salts, in an aqueous solution they almost completely dissociate into ions, are not susceptible to hydrolysis at the cation (except for the Be 2+ and Mg 2+ salts).

hydrogen hydride ionic covalent

Complexation is not typical for s-element ions. Crystalline complexes of s - elements with ligands H 2 O-crystalline hydrates are known from deep antiquity, for example: Na 2 B 4 O 7 10H 2 O-borax, KАl (SO 4) 2 12H 2 O-alum. Water molecules in crystalline hydrates are grouped around the cation, but sometimes they completely surround the anion as well. Due to the small charge of the ion and the large radius of the ion, alkali metals are least prone to the formation of complexes, including aqua complexes. As complexing agents in complex compounds lithium, beryllium and magnesium ions are of low stability.

Hydrogen. Chemical properties of hydrogen

Hydrogen is the lightest s-element. Its electronic configuration in the ground state is 1S 1. A hydrogen atom is made up of one proton and one electron. The peculiarity of hydrogen is that its valence electron is directly in the sphere of action atomic nucleus... Hydrogen does not have an intermediate electronic layer, so hydrogen cannot be considered an electronic analog of alkali metals.

Like alkali metals, hydrogen is a reducing agent and exhibits an oxidation state of +1. The spectra of hydrogen are similar to those of alkali metals. Hydrogen brings it closer to alkali metals by its ability to give hydrated positively charged H + ion in solutions.

Like a halogen, a hydrogen atom is missing one electron. This is the reason for the existence of the hydride ion H -.

In addition, like halogen atoms, hydrogen atoms are characterized by a high ionization energy (1312 kJ / mol). Thus, hydrogen occupies a special position in the Periodic Table of the Elements.

Hydrogen is the most abundant element in the universe, accounting for up to half the mass of the sun and most stars.

On the sun and other planets, hydrogen is in an atomic state, in the interstellar medium in the form of partially ionized diatomic molecules.

Hydrogen has three isotopes; protium 1 H, deuterium 2 D and tritium 3 T, with tritium being a radioactive isotope.

Hydrogen molecules are distinguished by high strength and low polarizability, small size and low mass, and high mobility. Therefore, hydrogen has very low melting (-259.2 o C) and boiling points (-252.8 o C). Because of high energy dissociation (436 kJ / mol) the decomposition of molecules into atoms occurs at temperatures above 2000 o C. Hydrogen is a colorless gas, odorless and tasteless. It has a low density - 8.99 · 10 -5 g / cm At very high pressures, hydrogen transforms into a metallic state. It is believed that on distant planets solar system- Jupiter and Saturn, hydrogen is in metal condition... There is an assumption that the composition the earth's core also includes metallic hydrogen, where it is at the ultra-high pressure created by the earth's mantle.

Chemical properties. At room temperature molecular hydrogen reacts only with fluorine, when irradiated with light - with chlorine and bromine, when heated with O 2, S, Se, N 2, C, I 2.

The reactions of hydrogen with oxygen and halogens proceed by a radical mechanism.

Interaction with chlorine is an example of an unbranched reaction when irradiated with light (photochemical activation), when heated (thermal activation).

Сl + H 2 = HCl + H (chain development)

H + Cl 2 = HCl + Cl

The explosion of an oxyhydrogen gas - a hydrogen-oxygen mixture - is an example of a branched chain process, when the initiation of a chain includes not one, but several stages:

H 2 + O 2 = 2OH

H + O 2 = OH + O

O + H 2 = OH + H

OH + H 2 = H 2 O + H

The explosive process can be avoided by working with pure hydrogen.

Since hydrogen is characterized by positive (+1) and negative (-1) oxidation states, hydrogen can exhibit both reducing and oxidizing properties.

The reducing properties of hydrogen are manifested when interacting with non-metals:

H 2 (g) + Cl 2 (g) = 2HCl (g),

2H 2 (g) + O 2 (g) = 2H 2 O (g),

These reactions proceed with the release a large number heat, which testifies to the high energy (strength) of the bonds H-Cl, H-O. Therefore, hydrogen exhibits reducing properties with respect to many oxides, halides, for example:

This is the basis for the use of hydrogen as a reducing agent for the production of simple substances from halide oxides.

Atomic hydrogen is an even stronger reducing agent. It is formed from molecular in electronic discharge under low pressure conditions.

Hydrogen has a high reducing activity at the moment of release during the interaction of a metal with an acid. This hydrogen reduces CrCl 3 to CrCl 2:

2CrCl 3 + 2HCl + 2Zn = 2CrCl 2 + 2ZnCl 2 + H 2 ^

The interaction of hydrogen with nitrogen oxide (II) is important:

2NO + 2H 2 = N 2 + H 2 O

Used in purification systems for nitric acid production.

As an oxidizing agent, hydrogen interacts with active metals:

In this case, hydrogen behaves like a halogen, forming analogous to halides hydrides.

Group I s-element hydrides have an ionic structure of the NaCl type. Chemically, ionic hydrides behave like basic compounds.

Covalent hydrides are less electronegative than hydrogen itself of non-metallic elements, for example, hydrides of the composition SiH 4, BH 3, CH 4. By their chemical nature, nonmetal hydrides are acidic compounds.

A characteristic feature of hydrolysis of hydrides is the evolution of hydrogen; the reaction proceeds according to a redox mechanism.

Basic hydride

Acid hydride

Due to the evolution of hydrogen, hydrolysis proceeds completely and irreversibly (? Н<0, ?S>0). In this case, basic hydrides form an alkali, and acidic acid.

Standard potential of system B. Consequently, the H ion is a strong reducing agent.

In the laboratory, hydrogen is produced by the interaction of zinc with 20% sulfuric acid in the Kipp apparatus.

Technical zinc often contains small impurities of arsenic and antimony, which are reduced by hydrogen at the time of release to poisonous gases: arsine SbH 3 and stubin SbH Such hydrogen can be poisoned. With chemically pure zinc, the reaction proceeds slowly due to overvoltage and a good current of hydrogen cannot be obtained. The rate of this reaction is increased by the addition of crystals copper sulfate, the reaction is accelerated due to the formation of a galvanic pair of Cu-Zn.

Pure hydrogen is formed by the action of alkali on silicon or aluminum when heated:

In industry, pure hydrogen is obtained by electrolysis of water containing electrolytes (Na 2 SO 4, Ba (OH) 2).

A large amount of hydrogen is formed as a by-product in the electrolysis of an aqueous solution of sodium chloride with a diaphragm separating the cathode and anode space,

The largest amount of hydrogen is obtained by gasification solid fuel(anthracite) with superheated steam:

Or conversion natural gas(methane) with superheated steam:

The resulting mixture (synthesis gas) is used in the production of many organic compounds... The hydrogen yield can be increased by passing synthesis gas over the catalyst, whereby CO is converted to CO 2.

Application. A large amount of hydrogen is consumed in the synthesis of ammonia. For the production of hydrogen chloride and hydrochloric acid, for the hydrogenation of vegetable fats, for the reduction of metals (Mo, W, Fe) from oxides. The hydrogen-oxygen flame is used for welding, cutting and melting metals.

Liquid hydrogen is used as propellant. Hydrogen fuel is environmentally friendly and more energy intensive than gasoline, so in the future it may replace petroleum products. Several hundred cars are already running on hydrogen in the world. The problems of hydrogen energy are associated with the storage and transportation of hydrogen. Hydrogen storing in underground tankers in liquid state under a pressure of 100 atm. Shipping large quantities liquid hydrogen is a serious hazard.

DEFINITION

Hydrogen- the first element of the Periodic Table chemical elements DI. Mendeleev. Symbol - N.

Atomic mass - 1 amu The hydrogen molecule is diatomic - Н 2.

The electronic configuration of the hydrogen atom is 1s 1. Hydrogen belongs to the s-element family. In its compounds, it exhibits oxidation states -1, 0, +1. Natural hydrogen consists of two stable isotopes - protium 1 H (99.98%) and deuterium 2 H (D) (0.015%) - and radioactive isotope tritium 3 H (T) (trace amounts, half-life - 12.5 years).

Chemical properties of hydrogen

Under normal conditions, molecular hydrogen exhibits a relatively low reactivity, which is explained by the high strength of bonds in the molecule. When heated, it interacts with almost all simple substances formed by elements of the main subgroups (except for noble gases, B, Si, P, Al). In chemical reactions, it can act both as a reducing agent (more often) and as an oxidizing agent (less often).

Hydrogen exhibits reducing agent properties(Н 2 0 -2е → 2Н +) in the following reactions:

1. Reactions of interaction with simple substances - non-metals. Hydrogen reacts with halogens, moreover, the reaction of interaction with fluorine under normal conditions, in the dark, with an explosion, with chlorine - under illumination (or UV irradiation) by a chain mechanism, with bromine and iodine only when heated; oxygen(a mixture of oxygen and hydrogen in a volume ratio of 2: 1 is called "oxyhydrogen gas"), gray, nitrogen and carbon:

H 2 + Hal 2 = 2HHal;

2H 2 + O 2 = 2H 2 O + Q (t);

H 2 + S = H 2 S (t = 150 - 300C);

3H 2 + N 2 ↔ 2NH 3 (t = 500C, p, kat = Fe, Pt);

2H 2 + C ↔ CH 4 (t, p, kat).

2. Reactions of interaction with complex substances... Hydrogen reacts with oxides of low-activity metals, and it is able to reduce only metals standing in the row of activity to the right of zinc:

CuO + H 2 = Cu + H 2 O (t);

Fe 2 O 3 + 3H 2 = 2Fe + 3H 2 O (t);

WO 3 + 3H 2 = W + 3H 2 O (t).

Hydrogen reacts with oxides of non-metals:

H 2 + CO 2 ↔ CO + H 2 O (t);

2H 2 + CO ↔ CH 3 OH (t = 300C, p = 250 - 300 atm., Kat = ZnO, Cr 2 O 3).

Hydrogen enters into hydrogenation reactions with organic compounds of the class of cycloalkanes, alkenes, arenes, aldehydes and ketones, etc. All these reactions are carried out under heating, under pressure, platinum or nickel are used as catalysts:

CH 2 = CH 2 + H 2 ↔ CH 3 -CH 3;

C 6 H 6 + 3H 2 ↔ C 6 H 12;

C 3 H 6 + H 2 ↔ C 3 H 8;

CH 3 CHO + H 2 ↔ CH 3 —CH 2 —OH;

CH 3 -CO-CH 3 + H 2 ↔ CH 3 -CH (OH) -CH 3.

Hydrogen as an oxidizing agent(Н 2 + 2е → 2Н -) acts in reactions of interaction with alkali and alkaline earth metals. In this case, hydrides are formed - crystalline ionic compounds in which hydrogen exhibits an oxidation state of -1.

2Na + H 2 ↔ 2NaH (t, p).

Ca + H 2 ↔ CaH 2 (t, p).

Physical properties of hydrogen

Hydrogen is a light, colorless gas, odorless, density at normal conditions. - 0.09 g / l, 14.5 times lighter than air, bale t = -252.8C, t pl = - 259.2C. Hydrogen is poorly soluble in water and organic solvents, well soluble in some metals: nickel, palladium, platinum.

According to modern cosmochemistry, hydrogen is the most abundant element in the Universe. The main form of existence of hydrogen in outer space- individual atoms. In terms of abundance on Earth, hydrogen ranks 9th among all elements. The main amount of hydrogen on Earth is in a bound state - in the composition of water, oil, natural gas, coal, etc. In the form of a simple substance, hydrogen is rare - in the composition of volcanic gases.

Hydrogen production

There are laboratory and industrial methods for producing hydrogen. Laboratory methods include the interaction of metals with acids (1), as well as the interaction of aluminum with aqueous solutions of alkalis (2). Among the industrial methods for producing hydrogen, electrolysis plays an important role. aqueous solutions alkalis and salts (3) and methane conversion (4):

Zn + 2HCl = ZnCl 2 + H 2 (1);

2Al + 2NaOH + 6H 2 O = 2Na +3 H 2 (2);

2NaCl + 2H 2 O = H 2 + Cl 2 + 2NaOH (3);

CH 4 + H 2 O ↔ CO + H 2 (4).

Examples of problem solving

EXAMPLE 1

Exercise	When 23.8 g of metallic tin reacted with an excess of hydrochloric acid, hydrogen was liberated in an amount sufficient to obtain 12.8 g of metallic copper. Determine the oxidation state of tin in the resulting compound.
Solution	Based on the electronic structure of the tin atom (… 5s 2 5p 2), it can be concluded that tin is characterized by two oxidation states - +2, +4. Based on this, we will compose the equations of possible reactions: Sn + 2HCl = H 2 + SnCl 2 (1); Sn + 4HCl = 2H 2 + SnCl 4 (2); CuO + H 2 = Cu + H 2 O (3). Let's find the amount of copper substance: v (Cu) = m (Cu) / M (Cu) = 12.8 / 64 = 0.2 mol. According to equation 3, the amount of substance hydrogen: v (H 2) = v (Cu) = 0.2 mol. Knowing the mass of tin, we find its amount of substance: v (Sn) = m (Sn) / M (Sn) = 23.8 / 119 = 0.2 mol. Let us compare the amounts of the substance of tin and hydrogen according to equations 1 and 2 and according to the condition of the problem: v 1 (Sn): v 1 (H 2) = 1: 1 (equation 1); v 2 (Sn): v 2 (H 2) = 1: 2 (equation 2); v (Sn): v (H 2) = 0.2: 0.2 = 1: 1 (problem condition). Therefore, tin reacts with hydrochloric acid according to equation 1 and the oxidation state of tin is +2.
Answer	The oxidation state of tin is +2.

EXAMPLE 2

Exercise	The gas released by the action of 2.0 g of zinc in 18.7 ml of 14.6% hydrochloric acid (solution density 1.07 g / ml) was passed by heating over 4.0 g of copper (II) oxide. What is the mass of the resulting solid mixture?
Solution	When zinc acts on hydrochloric acid hydrogen is released: Zn + 2HCl = ZnCl 2 + H 2 (1), which, when heated, reduces copper (II) oxide to copper (2): CuO + H 2 = Cu + H 2 O. Let's find the amount of substances in the first reaction: m (solution HCl) = 18.7. 1.07 = 20.0 g; m (HCl) = 20.0. 0.146 = 2.92 g; v (HCl) = 2.92 / 36.5 = 0.08 mol; v (Zn) = 2.0 / 65 = 0.031 mol. Zinc is in short supply, so the amount of released hydrogen is equal to: v (H 2) = v (Zn) = 0.031 mol. In the second reaction, hydrogen is in short supply, because: v (CuO) = 4.0 / 80 = 0.05 mol. As a result of the reaction, 0.031 mol of CuO will turn into 0.031 mol of Cu, and the weight loss will be: m (CuO) - m (Cu) = 0.031 × 80 - 0.031 × 64 = 0.50 g. The mass of the solid mixture of CuO with Cu after passing hydrogen will be: 4.0-0.5 = 3.5 g.
Answer	The mass of the solid mixture of CuO and Cu is 3.5 g.

Hydrogen in the periodic table is at number one, in I and VII groups straightaway. The symbol for hydrogen is H (Latin Hydrogenium). It is a very light, colorless and odorless gas. There are three isotopes of hydrogen: 1H - protium, 2H - deuterium, and 3H - tritium (radioactive). Air or oxygen in reaction with simple hydrogen H₂ is highly flammable and also explosive. Hydrogen does not emit toxic products. It is soluble in ethanol and a number of metals (this is especially true for the side subgroup).

The prevalence of hydrogen on Earth

Like oxygen, hydrogen is essential. But, unlike oxygen, hydrogen is almost all in bound form with other substances. In a free state, it is found only in the atmosphere, but its amount there is extremely negligible. Hydrogen is a part of almost all organic compounds and living organisms. Most often it occurs in the form of an oxide - water.

Physicochemical properties

Hydrogen is inactive, and when heated or in the presence of catalysts, it reacts with almost all simple and complex chemical elements.

Reaction of hydrogen with simple chemical elements

At elevated temperatures, hydrogen reacts with oxygen, sulfur, chlorine and nitrogen. you will learn what experiments with gases can be done at home.

Experience of interaction of hydrogen with oxygen in laboratory conditions

Let's take pure hydrogen, which enters through the gas outlet pipe, and set it on fire. It will burn with a barely noticeable flame. If you place a hydrogen tube in a vessel, it will continue to burn, and water droplets will form on the walls. It was oxygen that reacted with hydrogen:

2Н₂ + О₂ = 2Н₂О + Q

When hydrogen burns, a lot of thermal energy is generated. The temperature of the combination of oxygen and hydrogen reaches 2000 ° C. Oxygen oxidized hydrogen, so this reaction is called an oxidation reaction.

Under normal conditions (without heating), the reaction is slow. And at temperatures above 550 ° C, an explosion occurs (the so-called detonating gas is formed). Previously, hydrogen was often used in balloons, but due to the formation of oxyhydrogen gas there have been many disasters. The integrity of the ball was broken, and an explosion took place: hydrogen reacted with oxygen. Therefore, helium is now used, which is periodically heated with a flame.

Chlorine interacts with hydrogen and forms hydrogen chloride (only in the presence of light and heat). The chemical reaction of hydrogen and chlorine looks like this:

Н₂ + Cl₂ = 2HCl

An interesting fact: the reaction of fluorine with hydrogen causes an explosion even at dark and temperatures below 0 ° C.

The interaction of nitrogen with hydrogen can only occur when heated and in the presence of a catalyst. This reaction produces ammonia. Reaction equation:

ЗН₂ + N₂ = 2NН₃

The reaction of sulfur and hydrogen occurs with the formation of a gas - hydrogen sulfide. As a result, you can smell rotten eggs:

Н₂ + S = H₂S

In metals, hydrogen not only dissolves, but can also react with them. As a result, compounds are formed, which are called hydrides. Some hydrides are used as fuel in rockets. Also, with their help, nuclear energy is obtained.

Reaction with complex chemical elements

For example, hydrogen with copper oxide. Take a tube of hydrogen and pass it through the copper oxide powder. The whole reaction takes place when heated. Black copper powder will turn brownish red (plain copper color). Droplets of liquid will also appear on the unheated areas of the flask - this is formed.

Chemical reaction:

CuO + H₂ = Cu + H₂O

As you can see, hydrogen reacted with oxide and reduced copper.

Reductive reactions

If a substance takes away oxide during the reaction, it is a reducing agent. Using the example of the reaction of copper oxide with, we see that hydrogen was a reducing agent. It also reacts with some other oxides such as HgO, MoO₃ and PbO. In any reaction, if one of the elements is an oxidizing agent, the other will be a reducing agent.

All hydrogen compounds

Hydrogen compounds with non-metals- very volatile and poisonous gases(for example, hydrogen sulfide, silane, methane).

Hydrogen halides- Hydrogen chloride is used most of all. When dissolved, it forms hydrochloric acid. This group also includes: hydrogen fluoride, hydrogen iodide and hydrogen bromide. All of these compounds result in the corresponding acids.

Hydrogen peroxide (chemical formulaН₂О₂) exhibits strong oxidizing properties.

Hydrogen hydroxides or water H₂O.

Hydrides are compounds with metals.

Hydroxides- these are acids, bases and other compounds, which include hydrogen.

Organic compounds: proteins, fats, lipids, hormones and others.

Liquid

Hydrogen(lat. Hydrogenium; denoted by the symbol H) - the first element periodic system elements. Widely distributed in nature. The cation (and nucleus) of the most abundant hydrogen isotope, 1 H, is the proton. The properties of the 1 H nucleus make it possible to widely use NMR spectroscopy in analysis. organic matter.

Three isotopes of hydrogen have their own names: 1 H - protium (H), 2 H - deuterium (D) and 3 H - tritium (radioactive) (T).

Simple substance hydrogen - H 2 - light colorless gas. It is flammable and explosive when mixed with air or oxygen. Non-toxic. Let's dissolve in ethanol and a number of metals: iron, nickel, palladium, platinum.

History

The release of combustible gas during the interaction of acids and metals was observed in the XVI and XVII centuries at the dawn of the formation of chemistry as a science. Mikhail Vasilyevich Lomonosov also directly pointed to its separation, but already definitely realizing that it was not phlogiston. The English physicist and chemist Henry Cavendish investigated this gas in 1766 and called it "combustible air." When burned, the "combustible air" produced water, but Cavendish's adherence to the phlogiston theory prevented him from drawing the correct conclusions. The French chemist Antoine Lavoisier, together with the engineer J. Meunier, using special gas meters, in 1783 synthesized water, and then analyzed it, decomposing water vapor with hot iron. Thus, he established that "combustible air" is part of water and can be obtained from it.

origin of name

Lavoisier gave hydrogen the name hydrogène - "giving birth to water." Russian name"Hydrogen" was proposed by the chemist M.F.

Prevalence

Hydrogen is the most abundant element in the universe. It accounts for about 92% of all atoms (8% are helium atoms, the share of all other elements taken together is less than 0.1%). Thus, hydrogen is the main component stars and interstellar gas. Under conditions of stellar temperatures (for example, the surface temperature of the Sun is ~ 6000 ° C), hydrogen exists in the form of plasma; in interstellar space, this element exists in the form of individual molecules, atoms and ions and can form molecular clouds that differ significantly in size, density and temperature.

Earth's crust and living organisms

Mass fraction of hydrogen in earth crust is 1% - this is the tenth most common element. However, its role in nature is determined not by mass, but by the number of atoms, the proportion of which among other elements is 17% (second place after oxygen, the proportion of atoms of which is ~ 52%). Therefore, the value of hydrogen in chemical processes occurring on Earth is almost as great as oxygen. Unlike oxygen, which exists on Earth in both bound and free states, practically all hydrogen on Earth is in the form of compounds; only a very small amount of hydrogen in the form of a simple substance is contained in the atmosphere (0.00005% by volume).

Hydrogen is a part of almost all organic substances and is present in all living cells. In living cells, hydrogen accounts for almost 50% of the number of atoms.

Receiving

Industrial methods of obtaining simple substances depend on the form in which the corresponding element is found in nature, that is, what can be the raw materials for its production. So, oxygen available in a free state is obtained physically- release from liquid air. Almost all hydrogen is in the form of compounds, therefore, to obtain it, they use chemical methods... In particular, decomposition reactions can be used. One of the methods for producing hydrogen is the reaction of water decomposition by electric current.

Basic industrial way hydrogen production - reaction of methane with water, which is a part of natural gas. It is carried out at high temperature(it is easy to make sure that when methane is passed even through boiling water, no reaction occurs):

CH 4 + 2H 2 O = CO 2 + 4H 2 −165 kJ

In the laboratory, to obtain simple substances, they do not necessarily use natural raw materials, but select those starting materials from which it is easier to isolate the required substance. For example, in a laboratory, oxygen is not obtained from the air. The same applies to the production of hydrogen. One of the laboratory methods for producing hydrogen, which is sometimes used in industry, is the decomposition of water with an electric current.

Usually in the laboratory, hydrogen is produced by the interaction of zinc with hydrochloric acid.

In industry

1.Electrolysis of aqueous solutions of salts:

2NaCl + 2H 2 O → H 2 + 2NaOH + Cl 2

2.Passage of water vapor over red-hot coke at a temperature of about 1000 ° C:

H 2 O + C? H 2 + CO

3.From natural gas.

Steam conversion:

CH 4 + H 2 O? CO + 3H 2 (1000 ° C)

Catalytic oxidation with oxygen:

2CH 4 + O 2? 2CO + 4H 2

4. Cracking and reforming of hydrocarbons in the process of oil refining.

In the laboratory

1.The action of dilute acids on metals. To carry out such a reaction, zinc and dilute hydrochloric acid are most often used:

Zn + 2HCl → ZnCl 2 + H 2

2.Interaction of calcium with water:

Ca + 2H 2 O → Ca (OH) 2 + H 2

3.Hydrolysis of hydrides:

NaH + H 2 O → NaOH + H 2

4.The action of alkalis on zinc or aluminum:

2Al + 2NaOH + 6H 2 O → 2Na + 3H 2

Zn + 2KOH + 2H 2 O → K 2 + H 2

5.By electrolysis. During the electrolysis of aqueous solutions of alkalis or acids, hydrogen is evolved at the cathode, for example:

2H 3 O + + 2e - → H 2 + 2H 2 O

Physical properties

Hydrogen can exist in two forms (modifications) - in the form of ortho- and para-hydrogen. Orthohydrogen molecule o-H 2 (m.p. -259.10 ° C, bp. -252.56 ° C) nuclear spins are directed in the same way (parallel), p-H 2 (m.p. -259.32 ° C, bp. -252.89 ° C) - opposite to each other (antiparallel). Equilibrium mixture o-H 2 and p-H 2 at a given temperature is called equilibrium hydrogen e-H 2.

Hydrogen modifications can be separated by adsorption on active carbon at liquid nitrogen temperature. With very low temperatures the balance between orthohydrogen and parahydrogen is almost entirely shifted towards the latter. At 80 K, the ratio of forms is approximately 1: 1. Desorbed parahydrogen on heating is converted into orthohydrogen until a mixture equilibrium at room temperature is formed (ortho-pair: 75:25). Without a catalyst, the transformation occurs slowly (under conditions of the interstellar medium - with characteristic times up to cosmological), which makes it possible to study the properties of individual modifications.

Hydrogen is the lightest gas; it is 14.5 times lighter than air. Obviously, the smaller the mass of the molecules, the higher their speed at the same temperature. As the lightest, hydrogen molecules move faster than molecules any other gas and thus more quickly can transfer heat from one body to another. It follows that hydrogen has the highest thermal conductivity among gaseous substances... Its thermal conductivity is about seven times higher than the thermal conductivity of air.

The hydrogen molecule is diatomic - Н 2. Under normal conditions, it is a colorless, odorless and tasteless gas. Density 0.08987 g / l (n.o.), boiling point −252.76 ° C, specific heat combustion 120.9 × 10 6 J / kg, slightly soluble in water - 18.8 ml / l. Hydrogen is readily soluble in many metals (Ni, Pt, Pd, etc.), especially in palladium (850 volumes per 1 volume of Pd). The solubility of hydrogen in metals is associated with its ability to diffuse through them; diffusion through a carbonaceous alloy (eg steel) is sometimes accompanied by the destruction of the alloy due to the interaction of hydrogen with carbon (so-called decarbonization). Practically insoluble in silver.

Liquid hydrogen exists in a very narrow temperature range from -252.76 to -259.2 ° C. It is a colorless liquid, very light (density at -253 ° C 0.0708 g / cm 3) and fluid (viscosity at -253 ° C 13.8 cpoise). The critical parameters of hydrogen are very low: the temperature is −240.2 ° C and the pressure is 12.8 atm. This explains the difficulties in liquefying hydrogen. In the liquid state, equilibrium hydrogen consists of 99.79% para-H 2, 0.21% ortho-H 2.

Solid hydrogen, melting point −259.2 ° C, density 0.0807 g / cm 3 (at −262 ° C) - snow-like mass, crystals of hexagonal system, space group P6 / mmc, cell parameters a=3,75 c= 6.12. At high pressure, hydrogen transforms into a metallic state.

Isotopes

Hydrogen is found in the form of three isotopes that have individual names: 1 H - protium (H), 2 H - deuterium (D), 3 H - tritium (radioactive) (T).

Protium and deuterium are stable isotopes with mass numbers 1 and 2. Their content in nature is, respectively, 99.9885 ± 0.0070% and 0.0115 ± 0.0070%. This ratio may vary slightly depending on the source and method of producing hydrogen.

The hydrogen isotope 3 H (tritium) is unstable. Its half-life is 12.32 years. Tritium is found in nature in very small quantities.

The literature also contains data on hydrogen isotopes with mass numbers 4–7 and half-lives of 10–22–10–23 s.

Natural hydrogen consists of H 2 and HD (hydrogen deuteride) molecules in a ratio of 3200: 1. The content of pure deuterium hydrogen D 2 is even less. The ratio of the concentrations of HD and D 2 is approximately 6400: 1.

Of all the isotopes of chemical elements, the physical and chemical properties of hydrogen isotopes differ from each other the most. This is due to the largest relative change in atomic masses.

	Temperature melting, K	Temperature boiling, K	Triple point, K / kPa	Critical point, K / kPa	Density liquid / gas, kg / m³

Deuterium and tritium also have ortho and para modifications: p-D 2, o-D 2, p-T 2, o-T 2. Heteroisotopic hydrogen (HD, HT, DT) have no ortho and para modifications.

Chemical properties

Fraction of dissociated hydrogen molecules

The hydrogen molecules H 2 are quite strong, and a lot of energy must be expended in order for hydrogen to react:

H 2 = 2H - 432 kJ

Therefore, at ordinary temperatures, hydrogen reacts only with very active metals, for example with calcium, forming calcium hydride:

Ca + H 2 = CaH 2

and with the only non-metal - fluorine, forming hydrogen fluoride:

With most metals and non-metals, hydrogen reacts at elevated temperatures or under other influences, for example, under lighting:

О 2 + 2Н 2 = 2Н 2 О

It can "take" oxygen from some oxides, for example:

CuO + H 2 = Cu + H 2 O

The written equation reflects the reducing properties of hydrogen.

N 2 + 3H 2 → 2NH 3

Forms hydrogen halides with halogens:

F 2 + H 2 → 2HF, the reaction proceeds with an explosion in the dark and at any temperature,

Cl 2 + H 2 → 2HCl, the reaction proceeds with an explosion, only in the light.

Reacts with soot under strong heating:

C + 2H 2 → CH 4

Interaction with alkali and alkaline earth metals

When interacting with active metals, hydrogen forms hydrides:

2Na + H 2 → 2NaH

Ca + H 2 → CaH 2

Mg + H 2 → MgH 2

Hydrides- salty, solid substances, easily hydrolyzed:

CaH 2 + 2H 2 O → Ca (OH) 2 + 2H 2

Interaction with metal oxides (usually d-elements)

Oxides are reduced to metals:

CuO + H 2 → Cu + H 2 O

Fe 2 O 3 + 3H 2 → 2Fe + 3H 2 O

WO 3 + 3H 2 → W + 3H 2 O

Hydrogenation of organic compounds

Molecular hydrogen is widely used in organic synthesis for the reduction of organic compounds. These processes are called hydrogenation reactions... These reactions are carried out in the presence of a catalyst at high blood pressure and temperature. The catalyst can be either homogeneous (e.g. Wilkinson's catalyst) or heterogeneous (e.g. Raney nickel, palladium-carbon).

So, in particular, during the catalytic hydrogenation of unsaturated compounds such as alkenes and alkynes, saturated compounds are formed - alkanes.

Hydrogen Geochemistry

Free hydrogen H 2 is relatively rare in terrestrial gases, but in the form of water it plays an extremely important role in geochemical processes.

Hydrogen can be part of minerals in the form of ammonium ion, hydroxyl ion and crystal water.

In the atmosphere, hydrogen is continuously formed as a result of the decomposition of water solar radiation... Having a small mass, hydrogen molecules have a high speed of diffusion movement (it is close to the second cosmic speed) and, falling into the upper layers of the atmosphere, can fly into space.

Features of treatment

When mixed with air, hydrogen forms an explosive mixture - the so-called explosive gas. This gas is most explosive when the volumetric ratio of hydrogen and oxygen is 2: 1, or hydrogen and air is approximately 2: 5, since the air contains about 21% oxygen. Also hydrogen is fire hazardous. Liquid hydrogen can cause severe frostbite if it comes into contact with the skin.

Explosive concentrations of hydrogen with oxygen arise from 4% to 96% by volume. When mixed with air from 4% to 75 (74)% by volume.

Economy

The cost of hydrogen for large-scale wholesale supplies fluctuates in the range of $ 2-5 per kg.

Application

Atomic hydrogen is used for atomic hydrogen welding.

Chemical industry

• In the production of ammonia, methanol, soap and plastics
• In the production of margarine from liquid vegetable oils
• Registered as food additive E949(packing gas)

Food industry

Aviation industry

Hydrogen is very light and always rises up in the air. Once airships and Balloons filled with hydrogen. But in the 30s. XX century there were several disasters, during which the airships exploded and burned. Nowadays, airships are filled with helium, despite its significantly higher cost.

Fuel

Hydrogen is used as propellant.

Research is underway on the use of hydrogen as a fuel for cars and trucks. Hydrogen engines don't pollute environment and emit only water vapor.

Hydrogen-oxygen fuel cells use hydrogen to directly convert energy chemical reaction into electric.

"Liquid hydrogen"("LH") is a liquid aggregate state of hydrogen, with a low specific gravity of 0.07 g / cm³ and cryogenic properties with a freezing point of 14.01 K (−259.14 ° C) and a boiling point of 20.28 K (−252.87 ° C). It is a colorless, odorless liquid which, when mixed with air, is classified as explosive with a flammability range of 4-75%. The spin ratio of isomers in liquid hydrogen is: 99.79% - parahydrogen; 0.21% - orthohydrogen. The expansion coefficient of hydrogen when changing the state of aggregation to gaseous is 848: 1 at 20 ° C.

As with any gas, the liquefaction of hydrogen leads to a decrease in its volume. After liquefaction, "LH" is stored in thermally insulated containers under pressure. Liquid hydrogen (rus. Liquid hydrogen, LH2, LH 2) is actively used in industry, as a form of gas storage, and in the space industry, as a rocket fuel.

History

The first documented use of artificial cooling in 1756 was carried out by the English scientist William Cullen, Gaspard Monge was the first to obtain the liquid state of sulfur oxide in 1784, Michael Faraday was the first to obtain liquefied ammonia, the American inventor Oliver Evans was the first to develop a refrigeration compressor in 1805, Jacob Perkins was the first to patent a cooling machine in 1834, and John Gorey was the first U.S. patent to patent an air conditioner in 1851. Werner Siemens proposed the concept of regenerative cooling in 1857, Karl Linde patented equipment for producing liquid air using the cascade Joule-Thomson expansion effect and regenerative cooling in 1876. In 1885, the Polish physicist and chemist Sigmund Wrobblewski published a critical temperature of 33 K for hydrogen and a critical pressure of 13.3 atm. and a boiling point at 23 K. Hydrogen was first liquefied by James Dewar in 1898 using regenerative refrigeration and his invention, the Dewar vessel. The first synthesis of the stable isomer of liquid hydrogen - parahydrogen - was carried out by Paul Hartek and Karl Bonhoeffer in 1929.

Spin isomers of hydrogen

Hydrogen at room temperature consists mainly of the spin isomer, orthohydrogen. After production, liquid hydrogen is in a metastable state and must be converted to a parahydrogenic form in order to avoid the explosive exothermic reaction that occurs when it changes at low temperatures. Conversion to the parahydrogen phase is usually carried out using catalysts such as iron oxide, chromium oxide, Activated carbon platinum-coated asbestos, rare earth metals or by using uranium or nickel additives.

Usage

Liquid hydrogen can be used as a form of fuel storage for engines internal combustion and fuel cells. Various submarines (projects 212A and 214, Germany) and hydrogen transport concepts have been created using this aggregate form of hydrogen (see for example "DeepC" or "BMW H2R"). Due to the proximity of the structures, the creators of the equipment on "ZhV" can use or only modify systems using liquefied natural gas ("LNG"). However, due to the lower bulk energy density, combustion requires a higher volume of hydrogen than natural gas. If liquid hydrogen is used instead of "LNG" in piston engines, usually a more bulky fuel system is required. With direct injection, the increased intake losses reduce the cylinder filling.

Liquid hydrogen is also used to cool neutrons in neutron scattering experiments. The masses of the neutron and the hydrogen nucleus are practically equal; therefore, the exchange of energy in an elastic collision is most effective.

Advantages

The advantage of using hydrogen is the "zero emission" of its use. The product of its interaction with air is water.

Obstacles

One liter of "ZhV" weighs only 0.07 kg. That is, its specific gravity is 70.99 g / l at 20 K. Liquid hydrogen requires cryogenic storage technology, such as special thermally insulated containers, and requires special handling, which is typical for all cryogenic materials. It is close in this respect to liquid oxygen, but requires more caution due to the fire hazard. Even with thermally insulated containers, it is difficult to keep it at the low temperature required to keep it liquid (it usually evaporates at a rate of 1% per day). When handling it, you must also follow the usual safety precautions when working with hydrogen - it is cold enough to liquefy air, which is explosive.

Rocket fuel

Liquid hydrogen is a common ingredient rocket fuels which is used for jet acceleration of launch vehicles and spacecraft... Most liquid rocket engines hydrogen, it is first used for regenerative cooling of the nozzle and other parts of the engine, before it is mixed with an oxidizer and burned to obtain thrust. Used modern H 2 / O 2 engines consume a re-enriched fuel mixture, which results in some unburned hydrogen in the exhaust. In addition to increasing the specific impulse of the engine by reducing the molecular weight, it further reduces the erosion of the nozzle and combustion chamber.

Such obstacles to the use of "LH" in other areas, such as cryogenic nature and low density, are also a limiting factor for use in this case. For 2009, there is only one launch vehicle (LV "Delta-4"), which is entirely a hydrogen rocket. Basically, "ZhV" is used either on upper steps rockets, or on blocks, which perform a significant part of the work on the output of the payload into space in a vacuum. As one of the measures to increase the density of this type of fuel, there are proposals to use slushy hydrogen, that is, the semi-frozen form of "ZhV".

§3. The reaction equation and how to compose it

Interaction hydrogen with oxygen as it was established by Sir Henry Cavendish, leads to the formation of water. Let's get on with it simple example learn to compose chemical reaction equations.
What comes out of hydrogen and oxygen, we already know:

H 2 + O 2 → H 2 O

Now let's take into account that the atoms of chemical elements in chemical reactions do not disappear and do not appear out of nothing, do not turn into each other, but connect in new combinations forming new molecules. This means that in the equation of the chemical reaction of atoms of each type there should be the same number 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 = 2H 2 O

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

This means that in the given reaction two praying hydrogen should react with one pray oxygen, and the result will be two praying water.

Interaction hydrogen with oxygen is not an easy process at all. It leads to a change in the oxidation states of these elements. To select the coefficients in such equations, usually use 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... In this case, several (n) electrons:

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

Oxidizing and reducing agents

Let us now see what 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 + I:

H 2 0 - 2 e- = 2H + I

Happened oxidation half-reaction equation hydrogen.

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

O 2 + 4 e- = 2O −II

it recovery half-reaction equation oxygen.

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

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

So it is necessary 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 adopted:

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

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

2H 2 0 + O 2 0 = 2H 2 + I O −II

Hydrogen oxidizes not only when meeting with oxygen... About the same effect on hydrogen and fluorine F 2, halogen and famous "robber", and seemingly harmless nitrogen N 2:

H 2 0 + F 2 0 = 2H + I F −I

3H 2 0 + N 2 0 = 2N −III H 3 + I

Thus it turns out hydrogen fluoride HF or ammonia NH 3.

In both compounds, the oxidation state is hydrogen becomes equal + I, because partners in a molecule he gets "greedy" for someone else's electronic good, with high electronegativity - fluorine F and nitrogen N... Have nitrogen the value of electronegativity is considered equal to three arbitrary units, and in fluorine in general, the highest electronegativity among all chemical elements is four units. So it is not surprising for them to leave the poor thing, a hydrogen atom, without any electronic environment.

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