Description of hydrogen in chemistry. Physical and chemical properties of hydrogen

In the periodic table, it has its definite place of position, which reflects the properties manifested by it and speaks of its electronic structure. However, there is one special atom among all, which occupies two cells at once. It is located in two groups of elements that are completely opposite in terms of manifested properties. This is hydrogen. These features make it unique.

Hydrogen is not just an element, but also a simple substance, as well as a component of many complex compounds, a biogenic and organogenic element. Therefore, we will consider its characteristics and properties in more detail.

Hydrogen as a chemical element

Hydrogen is an element of the first group of the main subgroup, as well as the seventh group of the main subgroup in the first small period. This period consists of only two atoms: helium and the element we are considering. Let us describe the main features of the position of hydrogen in the periodic table.

1. The ordinal number of hydrogen is 1, the number of electrons is the same, respectively, the number of protons is the same. The atomic mass is 1.00795. There are three isotopes of this element with mass numbers 1, 2, 3. However, the properties of each of them are very different, since an increase in mass even by one for hydrogen is immediately double.
2. The fact that it contains only one electron on the outside allows it to successfully exhibit both oxidizing and reducing properties. In addition, after the release of an electron, it has a free orbital, which takes part in the formation chemical bonds by donor-acceptor mechanism.
3. Hydrogen is a powerful reducing agent. Therefore, its main place is considered the first group of the main subgroup, where it is headed by the most active metals - alkali.
4. However, when interacting with strong reducing agents, such as, for example, metals, it can also be an oxidizing agent, accepting an electron. These compounds are called hydrides. On this basis, he heads the subgroup of halogens, with which he is similar.
5. Due to its very small atomic mass, hydrogen is considered the lightest element. In addition, its density is also very low, so it is also the benchmark for lightness.

Thus, it is obvious that the hydrogen atom is completely unique, unlike all other elements. Consequently, its properties are also special, and the simple and complex substances formed are very important. Let's consider them further.

Simple substance

If we talk about this element as a molecule, then it must be said that it is diatomic. That is, hydrogen (a simple substance) is a gas. Its empirical formula will be written as H 2, and its graphic formula - through a single sigma-relationship H-H. The mechanism of bond formation between atoms is covalent non-polar.

1. Steam reforming of methane.
2. Coal gasification - the process involves heating coal to 1000 0 C, resulting in the formation of hydrogen and high-carbon coal.
3. Electrolysis. This method can only be used for aqueous solutions different salts, since the melts do not lead to the discharge of water at the cathode.

Laboratory methods for producing hydrogen:

1. Hydrolysis of metal hydrides.
2. The action of dilute acids on active metals and medium activity.
3. Interaction of alkali and alkaline earth metals with water.

To collect the generated hydrogen, the tube must be held upside down. After all, this gas cannot be collected in the same way as, for example, carbon dioxide. This is hydrogen, it is much lighter than air. Evaporates quickly, and explodes in large quantities when mixed with air. Therefore, the tube should be inverted. After filling it, it must be closed with a rubber stopper.

To check the purity of the collected hydrogen, you should bring a lighted match to the neck. If the cotton is dull and quiet, then the gas is clean, with minimal air impurities. If it is loud and whistling, it is dirty, with a large proportion of extraneous components.

Areas of use

When hydrogen burns, so much energy (heat) is released that this gas is considered the most profitable fuel. Moreover, it is environmentally friendly. However, to date, its application in this area is limited. This is due to the ill-conceived and unsolved problems of the synthesis of pure hydrogen, which would be suitable for use as fuel in reactors, engines and portable devices, as well as heating boilers in residential buildings.

After all, the methods of obtaining this gas are quite expensive, therefore, first it is necessary to develop a special synthesis method. One that will allow you to get a product in large quantities and at minimal cost.

There are several main areas in which the gas we are considering finds application.

1. Chemical syntheses. Hydrogenation produces soaps, margarines, and plastics. With the participation of hydrogen, methanol and ammonia, as well as other compounds, are synthesized.
2. V Food Industry- as an additive E949.
3. Aviation industry (rocketry, aircraft construction).
4. Power engineering.
5. Meteorology.
6. Environmentally friendly fuel.

Obviously, hydrogen is just as important as it is in nature. An even greater role is played by the various compounds formed by it.

Hydrogen compounds

These are complex substances containing hydrogen atoms. There are several main types of such substances.

1. Hydrogen halides. General formula- HHal. Of particular importance among them is hydrogen chloride. It is a gas that dissolves in water to form a hydrochloric acid solution. This acid is widely used in almost all chemical syntheses. And both organic and inorganic. Hydrogen chloride is a compound with the empirical formula HCL and is one of the largest in terms of production in our country every year. Hydrogen halides also include hydrogen iodide, hydrogen fluoride and hydrogen bromide. They all form the corresponding acids.
2. Volatile Almost all of them are quite poisonous gases. For example, hydrogen sulfide, methane, silane, phosphine and others. Moreover, it is very flammable.
3. Hydrides are compounds with metals. They belong to the class of salts.
4. Hydroxides: bases, acids and amphoteric compounds. They necessarily include hydrogen atoms, one or more. Example: NaOH, K 2, H 2 SO 4 and others.
5. Hydrogen hydroxide. This compound is better known as water. Another name for hydrogen oxide. The empirical formula looks like this - H 2 O.
6. Hydrogen peroxide. It is the strongest oxidizing agent, the formula of which is Н 2 О 2.
7. Numerous organic compounds: hydrocarbons, proteins, fats, lipids, vitamins, hormones, essential oils and others.

It is obvious that the variety of compounds of the element we are considering is very great. This once again confirms its high importance for nature and man, as well as for all living beings.

is the best solvent

As mentioned above, the common name for this substance is water. Consists of two hydrogen atoms and one oxygen, connected by covalent polar bonds. The water molecule is a dipole, which explains many of its properties. In particular, it is a universal solvent.

It is in the aquatic environment that almost all chemical processes take place. Internal reactions of plastic and energy exchange in living organisms are also carried out using hydrogen oxide.

Water is considered to be the most important substance on the planet. It is known that no living organism can live without it. On Earth, it is able to exist in three states of aggregation:

• liquid;
• gas (steam);
• solid (ice).

There are three types of water depending on the hydrogen isotope that is part of the molecule.

1. Lightweight or protium. Isotope c massive number 1. Formula - H 2 O. This is the usual form used by all organisms.
2. Deuterium or heavy, its formula is D 2 O. Contains the isotope 2 H.
3. Super heavy or tritium. The formula looks like T 3 O, the isotope is 3 N.

The reserves of fresh protium water on the planet are very important. Already now in many countries there is a lack of it. Methods are being developed for the treatment of salt water in order to obtain drinking water.

Hydrogen peroxide is a versatile remedy

This compound, as mentioned above, is an excellent oxidizing agent. However, with strong representatives it can behave as a restorer too. In addition, it has a pronounced bactericidal effect.

Another name for this compound is peroxide. It is in this form that it is used in medicine. A 3% solution of crystalline hydrate of the compound in question is a medical medicine that is used to treat small wounds in order to disinfect them. However, it has been proven that in this case, wound healing increases over time.

Hydrogen peroxide is also used in rocket fuel, in industry for disinfection and bleaching, as a foaming agent to obtain appropriate materials (foam, for example). In addition, peroxide helps clean aquariums, bleach hair, and whiten teeth. However, at the same time it damages the tissues, so it is not recommended by specialists for these purposes.

Hydrogen is the very first element in the Periodic Table of Chemical Elements, has an atomic number of 1 and a relative atomic mass of 1.0079. What are physical properties hydrogen?

Physical properties of hydrogen

Translated from Latin, hydrogen means "giving birth to water." Back in 1766, the English scientist G. Cavendish collected "combustible air" released by the action of acids on metals and began to study its properties. In 1787 A. Lavoisier defined this "combustible air" as a new chemical element, which is part of the water.

Rice. 1. A. Lavoisier.

Hydrogen has 2 stable isotopes - protium and deuterium, as well as radioactive - tritium, the amount of which on our planet is very small.

Hydrogen is the most abundant element in space. The sun and most stars have hydrogen as their primary element. Also, this gas is part of water, oil, natural gas... The total hydrogen content on Earth is 1%.

Rice. 2. Formula of hydrogen.

The atom of this substance includes a nucleus and one electron. When an electron is lost from hydrogen, it forms a positively charged ion, that is, it exhibits metallic properties. But also a hydrogen atom is capable of not only losing, but also attaching an electron. In this it is very similar to halogens. Therefore, hydrogen in the Periodic Table belongs to both I and VII groups. The non-metallic properties of hydrogen are more pronounced in it.

A hydrogen molecule consists of two atoms linked by a covalent bond

Under normal conditions, hydrogen is a colorless gaseous element that is odorless and tasteless. It is 14 times lighter than air, and its boiling point is -252.8 degrees Celsius.

Table "Physical properties of hydrogen"

In addition to its physical properties, hydrogen also possesses a number of chemical properties. When heated or under the action of catalysts, hydrogen reacts with metals and non-metals, sulfur, selenium, tellurium, and can also reduce oxides of many metals.

Hydrogen production

Of the industrial methods for producing hydrogen (except for the electrolysis of aqueous solutions of salts), the following should be noted:

• passing water vapor through hot coal at a temperature of 1000 degrees:

• conversion of methane with water vapor at a temperature of 900 degrees:

CH 4 + 2H 2 O = CO 2 + 4H 2

The history of the discovery of hydrogen

If it is the most abundant chemical element on Earth, then hydrogen is the most abundant element in the entire universe. Our (and other stars) are about half hydrogen, and as for interstellar gas, it is 90% hydrogen atoms. This chemical element also occupies a significant place on Earth, because, together with oxygen, it is part of water, and its very name "hydrogen" comes from two ancient Greek words: "water" and "give birth." In addition to water, hydrogen is present in most organic matter and cells, without it, as well as without oxygen, Life itself would be inconceivable.

The history of the discovery of hydrogen

The first scientist to notice hydrogen was the great alchemist and healer of the Middle Ages, Theophrastus Paracelsus. In his alchemical experiments, in the hope of finding the "philosopher's stone" mixing with acids Paracelsus received a previously unknown combustible gas. True, it was not possible to separate this gas from the air.

Only a century and a half after Paracelsus, the French chemist Lemery managed to separate hydrogen from air and prove its flammability. True, Lemery did not understand that the gas he received was pure hydrogen. In parallel, the Russian scientist Lomonosov was engaged in similar chemical experiments, but the real breakthrough in the study of hydrogen was made by the English chemist Henry Cavendish, who is rightfully considered the discoverer of hydrogen.

In 1766, Cavendish managed to obtain pure hydrogen, which he called "combustible air." After another 20 years, the talented French chemist Antoine Lavoisier was able to synthesize water and extract from it this very "combustible air" - hydrogen. And by the way, it was Lavoisier who offered hydrogen its name - "Hydrogenium", aka "hydrogen".

Antoine Lavoisier with his wife, who helped him conduct chemical experiments, including the synthesis of hydrogen.

The arrangement of chemical elements in the periodic table of Mendeleev is based on their atomic weight, calculated relative to the atomic weight of hydrogen. That is, in other words, hydrogen and its atomic weight is the cornerstone of the periodic table, the fulcrum on the basis of which the great chemist created his system. Therefore, it is not surprising that hydrogen occupies the honorable first place in the periodic table.

In addition, hydrogen has the following characteristics:

• The atomic mass of hydrogen is 1.00795.
• Hydrogen has three isotopes, each of which has individual properties.
• Hydrogen is a light element with low density.
• Hydrogen has reducing and oxidizing properties.
• Entering with metals, hydrogen takes their electron and becomes an oxidizing agent. These compounds are called hydrates.

Hydrogen is a gas, its molecule consists of two atoms.

This is how a hydrogen molecule looks schematically.

Molecular hydrogen formed from such diatomic molecules explodes when a burning match is brought up. The hydrogen molecule in the explosion breaks down into atoms, which turn into helium nuclei. This is exactly how it happens on the Sun and other stars - due to the constant disintegration of hydrogen molecules, our star burns and warms us with its heat.

Physical properties of hydrogen

Hydrogen has the following physical properties:

• The boiling point of hydrogen is 252.76 ° C;
• And at a temperature of 259.14 ° C, it already begins to melt.
• Hydrogen dissolves slightly in water.
• Pure hydrogen is a highly dangerous explosive and flammable substance.
• Hydrogen is 14.5 times lighter than air.

Chemical properties of hydrogen

Since hydrogen can be in different situations both an oxidizing agent and a reducing agent, it is used to carry out reactions and syntheses.

Oxidizing properties hydrogen interacts with active (usually alkali and alkaline earth) metals, the result of these interactions is the formation of hydrides - salt-like compounds. However, hydrides are also formed during the reactions of hydrogen with low-activity metals.

The reducing properties of hydrogen have the ability to reduce metals to simple substances from their oxides, in industry this is called hydrogenothermy.

How to get hydrogen?

Among the industrial means for producing hydrogen are:

• coal gasification,
• steam reforming of methane,
• electrolysis.

In the laboratory, hydrogen can be obtained:

• during hydrolysis of metal hydrides,
• when reacting with water of alkali and alkaline earth metals,
• when diluted acids interact with active metals.

Application of hydrogen

Since hydrogen is 14 times lighter than air, in the old days it was filled Balloons and airships. But after a series of disasters that happened to airships, the designers had to look for a replacement for hydrogen (recall that pure hydrogen is an explosive substance, and the slightest spark was enough to cause an explosion).

The explosion of the Hindenburg airship in 1937, the cause of the explosion was the ignition of hydrogen (due to a short circuit), on which this huge airship flew.

Therefore, for such aircraft, instead of hydrogen, they began to use helium, which is also lighter than air, obtaining helium is more laborious, but it is not as explosive as hydrogen.

Also, hydrogen is used for cleaning different types fuels, especially based on oil and petroleum products.

Hydrogen video

And in conclusion, an educational video on the topic of our article.

Starting to consider the chemical and physical properties of hydrogen, it should be noted that in its usual state, this chemical element is in a gaseous form. The colorless hydrogen gas is odorless and tasteless. For the first time, this chemical element was called hydrogen after the scientist A. Lavoisier conducted experiments with water, according to the results of which, world science I learned that water is a multicomponent liquid, which contains Hydrogen. This event happened in 1787, but long before that date hydrogen was known to scientists as "combustible gas".

Hydrogen in nature

According to scientists, hydrogen is contained in earth crust and in water (approximately 11.2% of the total volume of water). This gas is part of many minerals that mankind has been extracting from the bowels of the earth for centuries. The properties of hydrogen are partially characteristic of oil, natural gases and clay, for organisms of animals and plants. But in its pure form, that is, not combined with other chemical elements of the periodic table, this gas is extremely rare in nature. This gas can be released to the surface of the earth during volcanic eruptions. Free hydrogen is present in trace amounts in the atmosphere.

Chemical properties of hydrogen

Insofar as Chemical properties hydrogen is not uniform, then this chemical element belongs to both the I group of the Mendeleev system and the VII group of the system. Being a representative of the first group, hydrogen is, in fact, an alkali metal, which has an oxidation state of +1 in most of the compounds to which it belongs. The same valence is characteristic of sodium and other alkali metals. Due to these chemical properties, hydrogen is considered to be an element similar to these metals.

If it comes about metal hydrides, then the hydrogen ion has a negative valence - its oxidation state is -1. Na + H- is built according to the same scheme as Na + Cl- chloride. This fact is the reason for attributing hydrogen to the VII group of the Mendeleev system. Hydrogen, being in the state of a molecule, provided that it stays in an ordinary environment, is inactive, and can combine exclusively with non-metals, which are more active for it. These metals include fluorine, in the presence of light, hydrogen combines with chlorine. If hydrogen is heated, it becomes more active, reacting with many elements. periodic system Mendeleev.

Atomic hydrogen exhibits more active chemical properties than molecular hydrogen. Oxygen molecules with form water - H2 + 1 / 2O2 = H2O. When hydrogen interacts with halogens, hydrogen halides H2 + Cl2 = 2HCl are formed, and hydrogen enters into this reaction in the absence of light and at sufficiently high negative temperatures - up to - 252 ° С. The chemical properties of hydrogen make it possible to use it for the reduction of many metals, since, when reacting, hydrogen absorbs oxygen from metal oxides, for example, CuO + H2 = Cu + H2O. Hydrogen participates in the formation of ammonia, interacting with nitrogen in the reaction 3H2 + N2 = 2NH3, but on condition that a catalyst is used, and the temperature and pressure are increased.

A vigorous reaction occurs when hydrogen interacts with sulfur in the reaction H2 + S = H2S, the result of which is hydrogen sulfide. The interaction of hydrogen with tellurium and selenium is slightly less active. If there is no catalyst, then it reacts with pure carbon, hydrogen only under the condition that high temperatures are created. 2H2 + C (amorphous) = CH4 (methane). In the process of hydrogen activity with some alkali and other metals, hydrides are obtained, for example, H2 + 2Li = 2LiH.

Physical properties of hydrogen

Hydrogen is a very light chemical. At least scientists say that on this moment, there is no lighter substance than hydrogen. Its mass is 14.4 times lighter than air, its density is 0.0899 g / l at 0 ° C. At temperatures of -259.1 ° C, hydrogen is capable of melting - this is a very critical temperature that is not typical for the transformation of most chemical compounds from one state to another. Only such an element as helium exceeds the physical properties of hydrogen in this regard. Liquefaction of hydrogen is difficult, since its critical temperature is (-240 ° C). Hydrogen is the most heat-producing gas known to mankind. All of the properties described above are the most significant physical properties of hydrogen that are used by humans for specific purposes. Also, these properties are the most relevant for modern science.

Structure and physical properties of hydrogen Hydrogen is a diatomic gas H2. It is colorless and odorless. It is the lightest gas. Due to this property, it was used in balloons, airships and similar devices, however, the widespread use of hydrogen for these purposes is hindered by its explosiveness in a mixture with air.

Hydrogen molecules are non-polar and very small, so there is little interaction between them. In this regard, it has very low melting (-259 ° C) and boiling points (-253 ° C). Hydrogen is practically insoluble in water.

Hydrogen has 3 isotopes: ordinary 1H, deuterium 2H or D, and radioactive tritium 3H or T. Heavy isotopes of hydrogen are unique in that they are 2 or even 3 times heavier than ordinary hydrogen! That is why replacing ordinary hydrogen with deuterium or tritium noticeably affects the properties of the substance (for example, the boiling points of ordinary hydrogen H2 and deuterium D2 differ by 3.2 degrees). Interaction of hydrogen with simple substances Hydrogen is a non-metal of medium electronegativity. Therefore, both oxidizing and reducing properties are inherent in it.

The oxidizing properties of hydrogen are manifested in reactions with typical metals - elements of the main subgroups of groups I-II of the periodic table. The most active metals (alkali and alkaline earth) when heated with hydrogen give hydrides - solid salt-like substances containing a hydride ion H- in the crystal lattice. 2Na + H2 = 2NaH ; Ca + H2 = CaH2 The reducing properties of hydrogen appear in reactions with more typical non-metals than hydrogen: 1) Interaction with halogens H2 + F2 = 2HF

The interaction with fluorine analogs - chlorine, bromine, iodine - proceeds in a similar way. As the activity of the halogen decreases, the intensity of the reaction decreases. The reaction with fluorine occurs explosively under normal conditions, illumination or heating is required for the reaction with chlorine, and the reaction with iodine proceeds only with strong heating and is reversible. 2) Interaction with oxygen 2H2 + O2 = 2H2O The reaction proceeds with a large release of heat, sometimes with an explosion. 3) Interaction with sulfur H2 + S = H2S Sulfur is a much less active non-metal than oxygen, and the interaction with hydrogen proceeds calmly. 4) Interaction with nitrogen 3H2 + N2↔ 2NH3 The reaction is reversible, proceeds to a noticeable extent only in the presence of a catalyst, under heating and under pressure. The product is called ammonia. 5) Interaction with carbonС + 2Н2↔ СН4 The reaction takes place in an electric arc or at very high temperatures. Other hydrocarbons are also formed as by-products. 3. Interaction of hydrogen with complex substances Hydrogen also exhibits reducing properties in reactions with complex substances: 1) Reduction of metal oxides standing in the electrochemical series of voltages to the right of aluminum, as well as nonmetal oxides: Fe2O3 + 2H2 2Fe + 3H2O ; CuO + H2 Cu + H2O Hydrogen is used as a reducing agent for the extraction of metals from oxide ores. Reactions proceed when heated. 2) Attachment to organic unsaturated substances; С2Н4 + Н2 (t; p) → С2Н6 The reactions proceed in the presence of a catalyst and under pressure. We will not touch on other hydrogen reactions for now. 4. Obtaining hydrogen In industry, hydrogen is produced by processing hydrocarbon raw materials - natural and associated gas, coke, etc. Laboratory methods for producing hydrogen:

1) Interaction of metals standing in the electrochemical series of metal voltages to the left of hydrogen with acids. Li K Ba Sr Ca Na Mg Al Mn Zn Cr Fe Cd Co Ni Sn Pb (H2) Cu Hg Ag Pt Mg + 2HCl = MgCl2 + H22) Interaction of metals in the electrochemical series of metal voltages to the left of magnesium, with cold water... This also produces alkali.

2Na + 2H2O = 2NaOH + H2 A metal located in the electrochemical series of metal voltages to the left of manganese is capable of displacing hydrogen from water under certain conditions (magnesium - from hot water, aluminum - provided that the oxide film is removed from the surface).

Mg + 2H2O Mg (OH) 2 + H2

A metal located in the electrochemical series of metal voltages to the left of cobalt is capable of displacing hydrogen from water vapor. This also produces an oxide.

3Fe + 4H2O vapor Fe3O4 + 4H23) Interaction of metals, hydroxides of which are amphoteric, with alkali solutions.

Metals, hydroxides of which are amphoteric, displace hydrogen from alkali solutions. You need to know 2 such metals - aluminum and zinc:

2Al + 2NaOH + 6H2O = 2Na + + 3H2

Zn + 2KOH + 2H2O = K2 + H2

In this case, complex salts are formed - hydroxoaluminates and hydroxozincates.

All the methods listed so far are based on the same process - the oxidation of a metal with a hydrogen atom in the +1 oxidation state:

М0 + nН + = Мn + + n / 2 H2

4) Interaction of hydrides of active metals with water:

CaH2 + 2H2O = Ca (OH) 2 + 2H2

This process is based on the interaction of hydrogen in the -1 oxidation state with hydrogen in the +1 oxidation state:

5) Electrolysis of aqueous solutions of alkalis, acids, some salts:

2H2O 2H2 + O2

5. Hydrogen compounds In this table, on the left, a light shadow highlights the cells of elements that form ionic compounds with hydrogen - hydrides. These substances contain a hydride ion H-. They are solid, colorless, salt-like substances and react with water to produce hydrogen.

Elements of the main subgroups IV-VII groups form compounds of molecular structure with hydrogen. They are sometimes also called hydrides, but this is incorrect. They do not contain a hydride ion, they consist of molecules. As a rule, the simplest hydrogen compounds of these elements are colorless gases. The exceptions are water, which is a liquid, and hydrogen fluoride, which is gaseous at room temperature, but liquid under normal conditions.

Dark cells mark elements that form compounds with hydrogen and exhibit acidic properties.

Dark cells with a cross indicate elements that form compounds with hydrogen and exhibit basic properties.

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29). general characteristics properties of elements of the main subgroup 7gr. Chlorine. Lore properties. Hydrochloric acid. The subgroup of halogens includes fluorine, chlorine, bromine, iodine and astatine (astatine is a radioactive element, little studied). These are p-elements of the VII group of the periodic system of D.I. Mendeleev. At the external energy level, their atoms each have 7 electrons ns2np5. This explains the commonality of their properties.

They easily attach one electron at a time, exhibiting an oxidation state of -1. Halogens have this oxidation state in compounds with hydrogen and metals.

However, halogen atoms, in addition to fluorine, can also exhibit positive oxidation states: +1, +3, +5, +7. Possible values ​​of the oxidation degrees are explained by the electronic structure, which for fluorine atoms can be represented by the diagram

Being the most electronegative element, fluorine can only accept one electron per 2p sublevel. It has one unpaired electron, so fluorine is only monovalent and the oxidation state is always -1.

The electronic structure of the chlorine atom is expressed by the scheme: The chlorine atom has one unpaired electron on the 3p-sublevel and in the usual (unexcited) state, chlorine is monovalent. But since chlorine is in the third period, then it has five more orbitals of the 3d-sublevel, in which 10 electrons can be accommodated.

Fluorine has no free orbitals, which means that at chemical reactions there is no separation of paired electrons in the atom. Therefore, when considering the properties of halogens, it is always necessary to take into account the characteristics of fluorine and compounds.

Aqueous solutions of hydrogen compounds of halogens are acids: HF - hydrofluoric (hydrofluoric), HCl - hydrochloric (hydrochloric), HBr - hydrogen bromide, HI - hydriodic.

Chlorine (Latin Chlorum), Cl, chemical element of group VII of Mendeleev's periodic system, atomic number 17, atomic mass 35,453; belongs to the halogen family. Under normal conditions (0 ° C, 0.1 MN / m2, or 1 kgf / cm2) yellow-green gas with a sharp irritating odor. Natural chlorine consists of two stable isotopes: 35Cl (75.77%) and 37Cl (24.23%).

Chlorine chemical properties. External electronic configuration atom Cl 3s2Зр5. In accordance with this, Chlorine in compounds exhibits oxidation states -1, + 1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.99 Å, the ionic radius of Cl is 1.82 Å, the affinity of the Chlorine atom to the electron is 3.65 eV, and the ionization energy is 12.97 eV.

Chemically, Chlorine is very active, it combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except carbon, nitrogen, oxygen, inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and joins unsaturated compounds. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals; it is displaced by fluorine from chlorine compounds with these elements. Alkali metals in the presence of traces of moisture, they interact with Chlorine with ignition, most metals react with dry Chlorine only when heated Phosphorus ignites in an atmosphere of Chlorine, forming РCl3, and with further chlorination - РСl5; sulfur with Chlorine when heated gives S2Cl2, SCl2 and other SnClm. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with Chlorine. A mixture of chlorine with hydrogen burns with a colorless or yellow-green flame with the formation of hydrogen chloride (this chain reaction). Chlorine forms oxides with oxygen: Cl2O, ClO2, Cl2O6, Cl2O7, Cl2O8, as well as hypochlorites (hypochlorous acid salts), chlorites, chlorates and perchlorates. All oxygenated chlorine compounds form explosive mixtures with easily oxidizable substances. Chlorine in water is hydrolyzed, forming hypochlorous and hydrochloric acids: Cl2 + Н2О = НClО + НCl. When chlorinating aqueous solutions of alkalis in cold conditions, hypochlorites and chlorides are formed: 2NaOH + Cl2 = NaClO + NaCl + H2O, and when heated, chlorates. By chlorination of dry calcium hydroxide, bleach is obtained. When ammonia interacts with Chlorine, nitrogen trichloride is formed. In the chlorination of organic compounds, Chlorine either replaces hydrogen or is added via multiple bonds, forming various chlorine-containing organic compounds. Chlorine forms interhalogen compounds with other halogens. Fluorides ClF, ClF3, ClF3 are very reactive; for example, glass wool ignites spontaneously in a ClF3 atmosphere. Known compounds of chlorine with oxygen and fluorine - Chlorine oxyfluorides: ClO3F, ClO2F3, ClOF, ClOF3 and fluorine perchlorate FClO4. Hydrochloric acid (hydrochloric acid, hydrochloric acid, hydrogen chloride) - HCl, a solution of hydrogen chloride in water; strong monobasic acid. Colorless (technical hydrochloric acid is yellowish due to impurities of Fe, Cl2, etc.), "fuming" in the air, caustic liquid. The maximum concentration at 20 ° C is 38% by weight. Salts of hydrochloric acid are called chlorides.

Interaction with strong oxidants (potassium permanganate, manganese dioxide) with the release of chlorine gas:

Interaction with ammonia with the formation of thick white smoke, consisting of the smallest crystals of ammonium chloride:

Qualitative response to hydrochloric acid and its salt is its interaction with silver nitrate, in which a ferrous precipitate of silver chloride is formed, insoluble in nitric acid:

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