Chemical compounds of noble gases. Chemistry of inert gases Compounds of inert gases

SUB-GROUP VIIIA (HELIUM, NEON, ARGON, KRYPTON, XENON, RADON)

1. Characteristic oxidation states and the most important compounds. Xenon compounds are of the greatest importance. It is characterized by oxidation states +2 (XeF2), +4 (XeF4), +6 (XeF6, XeO3, XeOF4, Ba3XeO6), +8 (Na4XeO6 * 6H2O).

2. Natural resources. Noble gases are found predominantly in the atmosphere; their content is He - 5.24 * 10-4% (volume); Ne-1.8*10-3%; Ar - 0.93%, Kr-3*10-3%, Xe-0.39*10-4%.

Radon is formed from the radioactive decay of radium and is found in trace amounts in minerals containing uranium, as well as in some natural waters. Helium, which is a radioactive decay product of alpha-emitting elements, is sometimes found in significant amounts in natural gas and gas released from oil wells. In huge quantities, this element is found in the Sun and stars. It is the second most abundant (after hydrogen) of the elements of the cosmos.

3. Receipt. Noble gases are released along the way during the rectification of liquid air in order to obtain oxygen. Argon is also obtained during the synthesis of NH3 from the unreacted residue of the gas mixture (N2 with an admixture of Ar). Helium is extracted from natural gas by deep cooling (CH4 and other components of the gas mixture are liquefied, and He remains in a gaseous state). Ar and He are produced in large quantities, other noble gases are obtained much less, they are expensive.

4. Properties. Noble gases are colorless, gaseous substances at room temperature. The configuration of the outer electron layer of helium atoms 1s2 of the remaining elements of the subgroup VIIIA-ns2np8. The completeness of the electron shells explains the monoatomic nature of the molecules of noble gases, their very low polarizability, low melting points, boiling points, and chemical inertness.

The substances under consideration form solid solutions with each other at low temperatures (an exception is helium). Clathrate compounds of noble gases are known, in which their atoms are enclosed in voids in the crystal lattices of various substances. Such compounds - hydrates of noble gases - form ice (the most durable clathrate with xenon). The composition of the hydrates corresponds to the formula 8E*46H2O, or E*5.75H2O. Clathrates with phenol are known, for example Xe-3C6H5OH. Noble gas clathrates with hydroquinone C6H4(OH)2 are very strong. They are obtained by crystallizing hydroquinone under noble gas pressure (4 MPa). These clathrates are quite stable at room temperature. He and Ne do not form clathrates, since their atoms are too small and "escape" from the voids of the crystal lattices.

Helium has unique features. At 101 kPa, it does not crystallize (this requires a pressure exceeding 2.5 MPa at T = 1K). In addition, at T \u003d 2.19 K (at normal pressure), it passes into a low-temperature liquid modification of He (II), which has striking features of calm boiling, a huge ability to conduct heat and the absence of viscosity (superfluidity). The superfluidity of He (II) was "was discovered by P. L. Kapitsa (1938) and explained on the basis of quantum mechanical concepts by L. D. Landau (1941).

5. Connections. Possibility of existence of noble gas compounds (Kr and Xe fluorides). Compounds of krypton, xenon and radon are now known. Krypton compounds are few in number, they exist only for sharp temperature. Radon compounds should be the most numerous and durable, but their production and research is hindered very high alpha radioactivity Rn, since radiation destroys the substances formed by it. Therefore, there are few data on Rn compounds.

Xenon - directly interacts only with fluorine and some fluorides, such as PtF6. Xenon fluorides serve as starting materials for obtaining its other compounds.

When heated with fluorine at atmospheric pressure, mainly XeF4 is formed (mp 135°C). Under the action of an excess of fluorine at a pressure of 6 MPa, XeF6 is obtained (mp. 49 ° C). Acting on a mixture of Xe with F2 or CF4 with an electric discharge or ultraviolet radiation, XeF2 is synthesized (mp. 140 ° C).

All xenope fluorides react vigorously with water, subjecting being hydrolysis, which is usually accompanied by disproportionation. Hydrolysis of XeF4 in an acidic medium occurs according to the scheme 3Xe (+4) => Xe ° + 2Xe (+5) and in an alkaline medium as follows:

ZXe(+4) =>.Xe0+Xe(+8)

NH3

Structure

The molecule is polar, has the shape of a triangular pyramid with a nitrogen atom at the top, HNH = 107.3. The nitrogen atom is in the sp 3 hybrid state; Of the four nitrogen hybrid orbitals, three are involved in the formation of single N-H bonds, and the fourth bond is occupied by a lone electron pair.

Physical properties

NH 3 is a colorless gas, the smell is sharp, suffocating, poisonous, lighter than air.

air density \u003d MNH 3 / M medium air \u003d 17 / 29 \u003d 0.5862

t╟ boil. = -33.4C; tpl.= -78C.

Ammonia molecules are bound by weak hydrogen bonds.

Due to hydrogen bonds, ammonia has a relatively high boiling point. and tpl., as well as a high heat of vaporization, it is easily compressed.

Highly soluble in water: 750V NH 3 dissolves in 1V H 2 O (at t=20C and p=1 atm).

The good solubility of ammonia can be seen in the following experiment. A dry flask is filled with ammonia and closed with a stopper, into which a tube with a drawn end is inserted. The end of the tube is immersed in water and the flask is slightly heated. The volume of gas increases and some ammonia will come out of the tube. Then the heating is stopped and, due to the compression of the gas, some water will enter through the tube into the flask. In the very first drops of water, ammonia will dissolve, a vacuum will be created in the flask and water, under the influence of atmospheric pressure, will rise into the flask - the fountain will begin to beat.

Receipt

1. Industrial way

N 2 + 3H 2 \u003d 2NH 3

(p=1000 atm; t= 500C; kat = Fe + aluminosilicates; circulation principle).

2. Laboratory method. Heating of ammonium salts with alkalis.

2NH 4 Cl + Ca(OH) 2 t ═ CaCl 2 + 2NH 3 + 2H 2 O

(NH 4) 2 SO 4 + 2KOH═ t ═ K 2 SO 4 + 2NH 3 + 2Н 2 O

Ammonia can only be collected according to method (A), because it is lighter than air and very soluble in water.

Chemical properties

The formation of a covalent bond by the donor-acceptor mechanism.

1. Ammonia is a Lewis base. Its solution in water (ammonia water, ammonia) has an alkaline reaction (litmus - blue; phenolphthalein - raspberry) due to the formation of ammonium hydroxide.

NH 3 + H 2 O \u003d NH 4 OH \u003d NH 4 + + OH -

2. Ammonia reacts with acids to form ammonium salts.

NH 3 + HCl = NH 4 Cl

2NH 3 + H 2 SO 4 \u003d (NH 4) 2 SO 4

NH 3 + H 2 O + CO 2 \u003d NH 4 HCO 3

Ammonia - reducing agent (oxidized to N 2 O or NO)

1. Decomposition when heated

2NH 3 ═ t ═ N 2 + 3H 2

2. Combustion in oxygen

a) without catalyst

4NH 3 + 3O 2 \u003d 2N 2 + 6H 2 O

b) catalytic oxidation (kat = Pt)

4NH 3 + 5O 2 \u003d 4NO + 6H 2 O

3. Recovery of oxides of some metals

3CuO + 2NH 3 \u003d 3Cu + N 2 + 3H 2 O

In addition to NH3, two other hydrogen compounds of nitrogen are known - hydrazine N2H4 and hydronitrous acid HN3(there are a few more compounds of nitrogen with hydrogen, but they are not very stable and are practically not used)

Hydrazine is obtained by oxidation of ammonia in aqueous solution with sodium hypochlorite (Raschig method):

2NH3+NaOCl -> N2H3 + NaCl + H2O

Hydrazine - liquid, mp 2°C, bp. 114°C with an NH3-like odour. Poisonous, explosive. Often, not anhydrous hydrazine is used, but hydrazine - hydrate N2H4-H2O, so pl. - "52 ° C, bp 119 ° C. The N2H4 molecule consists of two NH2 groups,

Due to the presence of two lone pairs at the N atoms, hydrazine is capable of adding hydrogen ions; hydrazonium compounds are easily formed: hydroxide N2H5OH, chloride N2H5Cl, hydrosulfate N2H5HSO4, etc. Sometimes their formulas are written N2H4-H2O, N2H4-HC1, N2H4-H2S04, etc. and are called hydrazine hydrate, hydrochloric hydrazine, hydrazine sulfate, etc. e. Most hydrazonium salts are soluble in water.

Let's compare the strength of the base formed in an aqueous solution of NH3, NH2OH and N2H4.

In terms of stability, N2H4 is significantly inferior to NНз, since the N-N bond is not very strong. Hydrazine burns in air:

N2H4 (l) + O2 (g) = n2 (g) + 2H2O (g);

In solutions, hydrazine is usually also oxidized to N2. Hydrazine can be reduced (to NH3) only with strong reducing agents, for example, Sn2+, Ti3+, Zn:

N2H4 + Zn + 4HC1 => 2NH4C1 + ZnCl2

Nitrous acid HN3 is obtained by the action of H2SO4 on sodium azide NaNs, which is synthesized by the reaction;

2NaNH2 + N2O -> NaNa + NaOH + NHa

HN3 - liquid, m.p. -80 °C, bp 37 ° C, with a pungent odor. It explodes very easily with great force, its dilute aqueous solutions are not explosive.

You can also represent the structure of HN3 by superimposing valence schemes

H-N=N=N and h-n-n=n°!

HN3 is a weak acid (K = 10-5). Salts of HN3-azides are usually highly explosive (only alkali metal azides are non-explosive, with the exception of LiN3).

Tsaregorodtsev Alexander

Compounds of noble gases are one of the most interesting topics in organic and inorganic chemistry, the discovery of the properties of their compounds turned the idea of ​​​​all scientists of the 20th century upside down, because at that time the existence of such substances was considered impossible, and now it is perceived as something normal, then, which has already been explained.

Xenon is a noble gas that is the easiest to form bonds with other chemicals. Mankind has harnessed its compounds, and they are already being applied in our lives.

The presented work may arouse the interest of the general public in this topic.

Download:

Preview:

Municipal Autonomous General Educational Institution

"Secondary school No. 5 with in-depth study of chemistry and biology"

Educational research work within

V Mendeleev readings

Subject: Noble gas compounds

Completed by: Tsaregorodtsev
Alexander, 9th grade student

Leader: Grigorieva

Natalya Gennadievna, chemistry teacher

Staraya Russa

2017

Introduction

Inert gases are non-metals that are in group VIII-a. They were discovered at the end of the 19th century and were considered superfluous in the Periodic Table, but the noble gases took their place in it.
Due to the filled last energy level, for a long time it was believed that these substances could not form bonds, because. and after the discovery of their molecular compounds, many scientists were shocked and could not believe it, because it did not succumb to the laws of chemistry that existed at that time.
Unsuccessful attempts to form compounds of noble gases adversely affected the enthusiasm of scientists, but this did not prevent the development of this industry.
I will try to arouse the interest of those present in the audience to whom I present my work.

The purpose of my work: to study the history of the creation and properties of inorganic xenon compounds.

Tasks :

1. Familiarize yourself with the history of the production of noble gas compounds
2. Get acquainted with the properties of fluorine and oxygen compounds
3. Communicate the results of my work to students

History reference

Xenon was discovered in 1898, and immediately a few years later, its hydrates were obtained, as well as xenon and krypton, all of which were called clathrates.
In 1916, Kessel, based on the values ​​of the degrees of ionization of inert gases, predicted the formation of their direct chemical compounds.
Most scientists of the 1st quarter of the 20th century believed that noble gases are in the zero group of the Periodic system and have a valence of 0, but in 1924 A. von Antropov, contrary to the opinions of other chemists, assigned these elements to the eighth group, from which it followed that the highest valence in their compounds - 8. He also predicted that they should form bonds with halogens, that is, non-metals of group VII-a.
In 1933, Pauling predicted the formulas for possible compounds of krypton and xenon: stable krypton and xenon hexafluoride (KrF 6 and XeF 6 ), unstable xenon octafluoride (XeF 8 ) and xenon acid (H 4 Xeo 6 ). In the same year, G. Oddo tried to synthesize xenon and fluorine by passing an electric current, but could not clean the resulting substance from the corrosion products of the vessel in which this reaction was carried out. From that moment on, scientists lost interest in this topic, and until the 60s, almost no one was engaged in this.
Direct evidence that noble gas compounds are possible came from the British scientist Neil Bartlett's synthesis of dioxygenyl hexafluoroplatinate (O 2). Platinum hexafluoride has a widow's oxidation capacity greater than that of fluorine. On March 23, 1962, Neil Bartlett synthesized xenon and platinum hexafluoride, and he got what he wanted: the first noble gas compound in existence, the yellow solid Xe. After that, all the forces of scientists of that time were thrown into the creation of xenon fluoride compounds.

Xenon fluoride compounds and their properties

The first molecular compound was xenon hexafluorideplatinate with the formula XePtF 6 . It is a solid, yellow on the outside and brick red on the inside; when heated to 115°C, it becomes glassy in appearance, when heated to 165°C, it begins to decompose with the release of XeF 4 .

It can also be obtained by reacting xenon and fluorine peroxide:

And also during the interaction of xenon and oxygen fluoride under high temperature and pressure:

XeF2 are colorless crystals, soluble in water. In solution, it exhibits very strong oxidizing properties, but they do not exceed the ability of fluorine. The strongest connection.

1. When interacting with alkalis, xenon is restored:

2. You can restore xenon from this fluoride by interacting with hydrogen:

3. When xenon difluoride is sublimated, xenon tetrafluoride and xenon itself are obtained:

Xenon(IV) fluoride XeF4was obtained in the same way as difluoride, but at a temperature of 400 ° C:

XEF 4 - These are white crystals, it is a strong oxidizing agent. The following can be said about the properties of this substance.

1. It is a strong fluorinating agent, that is, when interacting with other substances, it is able to transfer fluorine molecules to them:

2. When interacting with water, xenon tetrafluoride forms xenon oxide (III):

3.Recovered to xenon when interacting with hydrogen:

Xenon(VI) fluoride XeF 6 formed at even higher temperature and at elevated pressure:

XEF 6 they are pale greenish crystals, also having strong oxidizing properties.

1. Like xenon (IV) fluoride, it is a fluorinating agent:

2. Hydrolysis forms xenonic acid

Oxygen compounds of xenon and their properties
Xenon(III) oxide XeO 3 - it is a white, non-volatile, explosive substance, highly soluble in water. It is obtained by hydrolysis of xenon (IV) fluoride:

1. Under the action of ozone on an alkaline solution, it forms a salt of xenonic acid, in which xenon has an oxidation state of +8:

2. When the xenon salt interacts with concentrated sulfuric acid, it formsxenon(IV) oxide:

Xeo 4 - at temperatures below -36 ° C, yellow crystals, at temperatures above - a colorless explosive gas, decomposing at a temperature of 0 ° C:

As a result, it turns out that xenon fluorides are white or colorless crystals that dissolve in water, have strong oxidizing properties and chemical activity, and oxides easily release thermal energy and, as a result, they are explosive.

Application and potential

Because of their properties, xenon compounds can be used:

• For the production of rocket fuel
• For the production of medicines and medical equipment
• For the production of explosives
• As strong oxidizing agents in organic and inorganic chemistry
• As a way to transport reactive fluorine

Conclusion

Compounds of noble gases are one of the most interesting topics in organic and inorganic chemistry, the discovery of the properties of their compounds turned the idea of ​​​​all scientists of the 20th century upside down, because at that time the existence of such substances was considered impossible, and now it is perceived as something normal, then, which has already been explained.

Xenon is a noble gas that is the easiest to form bonds with other chemicals. Mankind has harnessed its compounds, and they are already being applied in our lives.

I believe that I have fully achieved the goal of my research: I have revealed the topic as accurately as possible, the content of the work is fully consistent with its topic, the history of the creation and properties of inorganic xenon compounds has been studied.

Bibliography

1. Kuzmenko N.E. “A short course in chemistry. A guide for applicants to universities ”/ / Higher School Publishing House, 2002, p. 267

2. Pushlenkov M.F. “Compounds of noble gases”//Atomizdat, 1965

3. Fremantle M. "Chemistry in action" Part 2 / / Mir publishing house, 1998, pp. 290-291

4. Internet resources

http://him.1september.ru/article.php?ID=200701901
http://rudocs.exdat.com/docs/index-160337.html
https://en.wikipedia.org/wiki/Xenon_fluoride(II)
https://ru.wikipedia.org/wiki/Xenon_fluoride(IV)
https://en.wikipedia.org/wiki/Xenon_fluoride(VI)
http://edu.sernam.ru/book_act_chem2.php?id=96
http://chemistry.ru/course/content/chapter8/section/paragraph2/subparagraph7.html#.WLMQ5FPyjGg

Preview:

To use the preview of presentations, create a Google account (account) and sign in: https://accounts.google.com

Slides captions:

Fluorine and oxygen compounds of noble gases. Xenon compounds Completed by: Tsaregorodtsev Alexander, student 9th grade, secondary school No. 5 Head: Natalya Gennadievna Grigorieva, chemistry teacher

Introduction Inert gases are non-metals that are in the VIII - a group. They were discovered at the end of the 19th century and were considered superfluous in the Periodic Table, but the noble gases took their place in it. Due to the filled last energy level, for a long time it was believed that these substances could not form bonds, and after the discovery of their molecular compounds, many scientists were shocked and could not believe this, because it did not succumb to the laws of chemistry that existed at that time. Unsuccessful attempts to form compounds of noble gases adversely affected the enthusiasm of scientists, but this did not prevent the development of this industry. I will try to arouse the interest of those present in the audience to whom I present my work.

Goals and objectives The purpose of the work: to study the history of the creation and properties of inorganic xenon compounds. Objectives: 1. Get acquainted with the history of obtaining noble gas compounds 2. Understand why the formation of these compounds is possible 3. Get acquainted with the properties of fluorine and oxygen compounds 4. Communicate the results of my work to peers

History of creation All attempts to obtain these compounds were unsuccessful, scientists could only guess what their formulas and approximate properties would look like. The most productive chemist in this field was Neil Bartlett. His main merit is the preparation of xenon hexafluoroplatinate Xe [PtF 6 ].

Xenon fluorides Xenon(II) fluoride Xenon(IV) fluoride Xenon(VI) fluoride

Xenon oxides Xenon (VI) oxide Xenon (VIII) oxide EXPLOSIVE!!!

The use of xenon compounds For the production of rocket fuel For the creation of medicines and medical equipment For the production of explosives As a method of transporting fluorine As oxidizing agents in organic and inorganic chemistry

Conclusion Compounds of noble gases are one of the most interesting topics in organic and inorganic chemistry, the discovery of the properties of their compounds turned the view of all scientists of the 20th century upside down, because at that time the existence of such substances was considered impossible, and now it is perceived as something normal, then which has already been explained.

Thank you for your attention!

The year was 1896. The first stage of experiments has just been completed in the laboratories of Ramsay and his followers, announcing the complete chemical inactivity of argon and helium. Against this background, the report of the French physicist Villar about the crystalline compound of argon with water of the composition Ar · 6H2O obtained by him, resembling compressed snow, sounded like a sharp dissonance. Moreover, it was obtained very simply and under unexpected conditions: Villard strongly compressed over ice at moderately low temperatures.

Generally speaking, a similar chlorine hydrate Cl2 6H2O, obtained under similar conditions, was reported as early as the beginning of the 19th century; later, hydrates of a large number of gases and easily volatile substances became known. But there were usual ones for a chemist, but here it was about a compound of inert argon! Villard's message seemed implausible and was simply brushed aside; there were not even hunters to check it.

They remembered Villar's discovery 29 years later, when R. Farkran reported on the hexahydrates of krypton and xenon obtained by him when these gases came into contact with ice under pressure. Ten years later, B. A. Nikitin obtained hexahydrates of all - except - inert gases, and then compounds consisting of an inert gas atom and three (in the case of radon - two) molecules of phenol, toluene or n-chlorophenol. Later, compounds withβ -hydroquinone, as well as ternary compounds of krypton or xenon, seventeen water molecules and one molecule of acetone, chloroform or carbon tetrachloride. The structure of these compounds was established only in the 1940s. By this time, a large number of so-called inclusion compounds had already been identified; they occupy an intermediate position between truly chemical Compounds and interstitial solid solutions.

It turned out that the above are clathrate compounds - a kind of "lattice" inclusion compounds. Their name comes from the Latin clatratus, which means enclosed, enclosed. Clathrates are formed as follows: a neutral molecule of an inert gas (another molecule can take its place, for example, Cl2, H2S, SO2, CO2, CH4) is tightly surrounded, as if taken in pincers by polar molecules - water, phenol, hydroquinone, etc., which are connected to each other by hydrogen bonds. Clathrates arise in those cases when, during the crystallization of a solvent, its molecules form openwork structures with voids capable of containing foreign molecules. The main condition necessary for the existence of a stable clathrate compound is the most complete coincidence of the spatial dimensions of the cavity formed between the adherent “host” molecules and the dimensions of the “guest” molecule that has penetrated into the cavity.

If the "guest" is small (say, a neon molecule), it is difficult to fix in the cavity and necessarily with the assistance of low temperature and high pressure, which prevent the escape of the "guest" and often contribute to the compression of the cavity. It is also difficult for an overly bulky molecule; in this case, increased pressure is also needed to “push” it into the cavity.

Formally, clathrates can be attributed to chemical compounds, since most of them have a strictly constant composition. But these are compounds of the molecular type, arising due to the van der Waals forces of contraction of molecules. it is absent in clathrates, since during their formation there is no pairing of valence electrons and the corresponding spatial redistribution of the electron density in the molecule.

The van der Waals forces themselves are very small, but the binding energy in a clathrate molecule may turn out to be not so small (on the order of 5-10 kcal / mol) due to the close proximity of the included molecule to the molecules of the including, since the van der Waals forces increase sharply as the molecules approach each other, B In general, clathrates are low-resistant compounds; when heated and dissolved, they quickly decompose into their constituent components.

A major contribution to the study of inert gas clathrates was made by the Soviet chemist B. A. Nikitin. During 1936-1952. he synthesized and studied these compounds, guided by the principle of V. G. Khlopin about isomorphic co-crystallization of molecules similar in size and structure. Nikitin found that at low temperatures they form isomorphic crystals with volatile hydrides - hydrogen sulfide, hydrogen halide, methane, as well as with sulfur and carbon dioxide. Nikitin found that the clathrates of inert gases are the more stable and easier to form, the higher their molecular weights. This is consistent with the general regularity of the action of van der Waals forces. Radon hydrate (if we ignore the rapid radioactive decay of radon) is much more stable than neon hydrate, and phenolates are stronger than the corresponding hydrates. That is why deuterated hydrates are stronger than ordinary ones.

If the experimenters had significant amounts of radon at their disposal, it would be possible to observe the instantaneous formation of a precipitate of Rn(H2O)6 when passing radon over ice at ordinary pressure. In order to obtain xenon hydrate at 0°, it is sufficient to apply a pressure somewhat greater than atmospheric pressure. With thistemperature has to be compressed to 14.5, to 150, and almost to 300 at. It can be expected that helium hydrate can be obtained under a pressure of several thousand atmospheres.

Clathrates can be used as convenient forms for storing inert gases, as well as for their separation. Having subjected sulfur dioxide hydrate to recrystallization in an atmosphere from a mixture of inert gases, Nikitin found all that did not decompose in the precipitate, which was an isomorphic mixture of SO2 6H2O and Rn 6H2O; same, and were preserved in the gas phase. In a similar way, argon can be almost completely precipitated and separated from the remaining neon and helium gases.

With the help of inert gas clathrates, it is possible to solve some research problems. These include, for example, the identification of the nature of the connection in the studied compound. If it forms mixed crystals with a heavy inert gas, then it should be attributed to the molecular type (inclusion compound); the opposite indicates the presence of a connection of a different type.

The main subgroup of the eighth group of the periodic system is the noble gases - helium, neon, argon, krypton, xenon and radon. These elements are characterized by very low chemical activity, which gave reason to call them noble or inert gases. They only with difficulty form compounds with other elements or substances; chemical compounds of helium, neon and argon have not been obtained. Atoms of noble gases are not combined into molecules, in other words, their molecules are monatomic.

The noble gases complete each period of the system of elements. In addition to helium, all of them have eight electrons in the outer electron layer of the atom, forming a very stable system. The electron shell of helium, which consists of two electrons, is also stable. Therefore, noble gas atoms are characterized by high ionization energies and, as a rule, negative electron affinity energies.

In table. 38 shows some of the properties of noble gases, as well as their content in the air. It can be seen that the liquefaction and solidification temperatures of noble gases are the lower, the lower their atomic masses or serial numbers: the lowest liquefaction temperature for helium, the highest for radon.

Table 38. Some properties of noble gases and their content in the air

Until the end of the 19th century, it was believed that air consisted only of oxygen and nitrogen. But in 1894, the English physicist J. Rayleigh found that the density of nitrogen obtained from air (1.2572 ) is somewhat greater than the density of nitrogen obtained from its compounds (1.2505 ). Chemistry professor W. Ramsay suggested that the difference in density is caused by the presence of some heavier gas in atmospheric nitrogen. By binding nitrogen with red-hot magnesium (Ramsay) or by causing it to combine with oxygen (Rayleigh) by an electric discharge, both scientists isolated small amounts of a chemically inert gas from atmospheric nitrogen. Thus, an element unknown until that time, called argon, was discovered. Following argon, helium, neon, krypton and xenon, contained in the air in negligible amounts, were isolated. The last element of the subgroup - radon - was discovered in the study of radioactive transformations.

It should be noted that the existence of noble gases was predicted back in 1883, i.e. 11 years before the discovery of argon, by the Russian scientist II A. Morozov (1854-1946), who was imprisoned in 1882 for participating in the revolutionary movement by the tsarist government to the Shlisselburg fortress. N. A. Morozov correctly determined the place of noble gases in the periodic system, put forward ideas about the complex structure of the atom, about the possibility of synthesizing elements and using intra-atomic energy. N. A. Morozov was released from prison in 1905, and his remarkable foresight became known only in 1907 after the publication of his book Periodic Systems of the Structure of Matter, written in solitary confinement.

In 1926 N. A. Morozov was elected an honorary member of the USSR Academy of Sciences.

For a long time it was believed that atoms of noble gases were generally incapable of forming chemical bonds with atoms of other elements. Only relatively unstable molecular compounds of noble gases were known - for example, hydrates, formed by the action of compressed noble gases on crystallizing supercooled water. These hydrates belong to the clathrate type (see § 72); valence bonds do not arise in the formation of such compounds.

The formation of clathrates with water is favored by the presence of numerous cavities in the crystal structure of ice (see § 70).

However, during the last decades it has been established that krypton, xenon and radon are able to combine with other elements and, above all, with fluorine. So, by direct interaction of noble gases with fluorine (when heated or in an electric discharge), fluorides and are obtained. All of them are crystals that are stable under normal conditions. Xenon derivatives were also obtained in the degree of oxidation - hexafluoride, trioxide, hydroxide. The last two compounds exhibit acidic properties; so, reacting with alkalis, they form salts of xenonic acid, for example:.

The noble gases have an electronic configuration of n s 2n p 6 (for helium 1 s 2) and constitute the VIIIA subgroup. As the atomic number increases, the atomic radii and their polarizability increase. This leads to an increase in intermolecular interactions, to an increase in the melting and boiling points, to an increase in the solubility of gases in water and other solvents. For noble gases, the following groups of compounds are known: molecular ions, inclusion compounds, and valence compounds.

The noble gas molecule E 2 cannot exist - (s) 2 (s *) 2. But if one electron is removed, then the filling of the upper loosening orbital is only half - (s) 2 (s *) 1 is the energy basis of existence molecular ions noble gases E 2 + .

Inclusion compounds, or clathrates, are known only in the solid state. In the series He – Rn, the stability of clathrates increases. For example, hydrates of the E. 6H 2 O type are formed at high pressures and low temperatures. At 0 0 С hydrates Xe, Kr, Ar and Ne are stable at pressures ~1.1, respectively. 10 5 , 1.5 . 106, 1.5. 107, 3. 10 7 Pa. Clathrate compounds are used for the separation and storage of noble gases. Kr and Xe are obtained by distillation of liquid air.

Compounds with valence bonds E(II), E(IV), E(VI), E(VIII) are well studied on the example of Kr and Xe fluorides obtained according to the scheme:

Chemical bonding in noble gas compounds cannot be described from the standpoint of MHS, since, in accordance with this method, bonds must be formed by d- orbitals. However, the excitation of the Xe atom from the state 5 s 2 5p 6 in 5s 2 5p 5 6s 1 or 5 s 2 5p 5 5d 1 requires 795 or 963 kJ. mol –1, and excitation 5 s 2 5p 4 5d 2 and 5 s 2 5p 4 5d 1 6s 1 - 1758 and 1926 kJ mol -1 , which is not compensated by the bond formation energy.

Within the framework of the MMO, the structure of XeF 2 is explained by a scheme of three orbitals - one from Xe and two from fluorine atoms:

Xenon tetrafluoride is a strong oxidizing agent:

Pt + XeF 4 + 2HF = H 2 + Xe,

4KI + XeF 4 = Xe + 2I 2 + 4KF.

When heated and hydrolyzed, xenon fluorides disproportionate:

2XeF 2 = XeF 4 + Xe

3XeF 4 = 2XeF 6 + Xe

6XeF 4 + 12H 2 O = 2XeO 3 + 4Xe + 3O 2 + 24HF.

For hexavalent Xe, XeF 6 fluoride, XeO 3 oxide, XeOF 4 and XeO 2 F 2 oxofluorides, Xe(OH) 6 hydroxide, and complex ions of the XeO 4 2– and XeO 6 6– types are known.

XeO 3 is highly soluble in water and forms a strong acid:

XeO 3 + H 2 O⇆ H 2 XeO 4 ® H + + HxeO 4 ¯.

Hexafluoride is very active, reacts with quartz:

2XeF 6 + SiO 2 \u003d 2XeOF 4 + SiF 4.

Xe(VI) derivatives are strong oxidizing agents, for example:

Xe(OH) 6 + 6KI + 6HCl = Xe + 3I 2 + 6KCl + 6H 2 O.

For Xe(VIII), in addition, XeF 8 , XeO 4 , XeOF 6 , XeO 6 4– are known.

Under normal conditions, XeO 4 slowly decomposes:

3XeO 4 \u003d Xe + 2XeO 3 + 3O 2.

As the oxidation state of xenon increases, the stability of binary and salt-like compounds decreases, while that of anionic complexes increases.

For krypton, only KrF 2 , KrF 4 , unstable kryptonic acid KrO 3 · H 2 O and its salt BaKrO 4 .

Helium is used in low-temperature processes to create an inert atmosphere in laboratory apparatus, in welding and in gas-filled electric lamps, neon in gas-discharge tubes.

Noble gas compounds are used as strong oxidizing agents. Fluorine and xenon are stored in the form of xenon fluorides.

Questions for self-examination

I. 1) The place of hydrogen in the periodic system.

2) Classification of hydrogen compounds.

II. one) s - Elements: oxidation states, changes in ionization radii and energies, acid-base and reducing properties of compounds.

2) Connections s- elements:

a) hydrides s- elements (nature of connection, properties);

b) compounds with oxygen; hydroxides.

III. 1) What determines the valence possibilities R-elements?

2) How does the stability of higher and lower oxidation states in subgroups change with increasing Z?

IV. Analyzing the change in T pl. oxides, answer the following questions:

1) Why does the melting point rise sharply when going from CO 2 to SiO 2?

2) Why is PbO 2 thermally less stable than other oxides of the IVA subgroup?

V. The binding energy in hydrogen and halogen molecules is characterized by the following values:

1) What explains the significantly higher binding energy in H2?

2) Why does the binding energy in Г 2 first increase with Z and then decrease?

VI. How and why do the acid-base properties of oxygen-free (H n E) and oxygen-containing E (OH) n, H n EO m compounds change R- elements in period and group?

VII. Hydrogen compounds R- elements:

1) Communication, periodicity of properties, stability.

2) Tendency to form H-bonds.

3) Feature of the chemical bond in B 2 H 6 (MMO).

VIII. oxides R- elements. Communication and properties.

IX. Connections R- elements - semiconductors.

1) Factors that determine the band gap.

2) Elementary semiconductors and compounds with semiconductor properties. Their place in the periodic table.

X. Diamond-like compounds. The position of the elements that form them in the periodic system. Communication and properties.

XI. 1) Compounds of noble gases and methods for their production.

2) Give the MO scheme for XeF 2.

3) Write the equation for the reaction of disproportionation XeF 2 , XeF 4 .

experimental part