Compounds of noble gases, their production and properties. Chemical compounds of noble gases. Questions and tasks
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 gas mixture(N2 with Ar impurity). 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 of crystal lattices. 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).
Everything xenope fluorides react vigorously with water, subjecting being hydrolysis, which is usually accompanied by disproportionation. Hydrolysis of XeF4 in acidic environment occurs according to the scheme 3Xe (+4) => Xe ° + 2Xe (+5) and in an alkaline medium like this:
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). HN3-azide salts are usually highly explosive (only azides are non-explosive). alkali metals, with the exception of LiN3).
Noble gas compounds- a term that denotes chemical compounds that have in their composition an element from group 8 of the periodic table. Group 8 (previously called group 0) includes only noble (inert) gases.
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✪ Chemistry of noble gases - Artem Oganov
✪ Noble gases and their properties
✪ Prohibited chemical compounds - Artem Oganov
Subtitles
History
For a long time, scientists believed that the noble gases could not form compounds because there was no room for more electrons in their electron shells, which contain valence electrons. This means that they cannot accept more electrons, making chemical bonding impossible. However, in 1933, Linus Pauling suggested that heavy noble gases could react with fluorine or oxygen, since they have atoms with the highest electronegativity. His guess turned out to be correct, and noble gas compounds were later obtained.
The noble gas compound was first obtained by Canadian chemist Neil Bartlett in 1962 by reacting platinum hexafluoride with xenon. The compound was given the formula XePtF6 (which later turned out to be incorrect). Immediately after Bartlett's report, simple xenon fluorides were obtained in the same year. Since that time, the chemistry of noble gases has been actively developed.
Connection types
Enable connections
Compounds of noble gases, where the noble gases are included in the crystal or chemical lattice, without the formation of a chemical bond, are called inclusion compounds. These include, for example, hydrates of inert gases, clathrates of inert gases with chloroform, phenols, etc.
Noble gases can also form compounds with endohedral fullerenes when a noble gas atom is "pushed" inside a fullerene molecule.
Complex compounds
Recently (2000) it has been shown that xenon can complex with gold (eg (Sb 2 F 11) 2) as a ligand. Complex compounds were also obtained, where xenon difluoride acts as a ligand.
Chemical compounds
Behind last years several hundred chemical compounds of noble gases (that is, having at least one noble gas-element bond) have been obtained. These are predominantly xenon compounds, since lighter gases are more inert, and radon has significant radioactivity. For krypton, a little more than a dozen compounds are known (mainly krypton difluoride complexes), for radon, fluoride of unknown composition is known. For gases lighter than krypton, only compounds in a matrix of solid inert gases (for example, HArF) are known that decompose at cryogenic temperatures.
For xenon, compounds are known where there are Xe-F, Xe-O, Xe-N, Xe-B, Xe-C, Xe-Cl bonds. Almost all of them are fluorinated to one degree or another and decompose when heated.
The most studied noble gas compounds are xenon fluorides.
Xenon (II) fluoride, or xenon dnfluoride. This compound can be obtained by direct interaction of xenon and fluorine under illumination with a mercury arc lamp. It can also be obtained by the interaction of xenon with at a temperature of - 120 C:
Xenon difluoride consists of linear molecules. In the presence of alkalis, it hydrolyzes with the release of oxygen:
In addition to xenon difluoride, krypton difluoride and radon difluoride are also known.
Xenon (IV) fluoride, or xenon tetrafluoride. This compound is obtained by direct interaction of xenon and fluorine at a temperature of 400 °C:
(The parentheses on the right show the planar square structure of xenon tetrafluoride molecules.) This compound disproportionates in water to form the oxide and free xenon:
Fluoride or xenon hexafluoride. This compound is obtained by direct interaction of xenon with fluorine at a temperature of 300 °C and elevated pressure. It has the structure of a distorted octahedron. Xenon hexafluoride reacts with silica to form oxotetrafluoride
Argon, krypton and xenon also form clathrate compounds, or inclusion compounds. For example, xenon hydrate is a framework of water molecules with xenon atoms included in it. Water molecules are held in this framework by hydrogen bonds. If hydroquinone is crystallized from an aqueous solution of hydroquinone in an atmosphere of xenon, krypton or argon under pressure, clathrate compounds of the corresponding noble gases with hydroquinone are obtained.
DISTRIBUTION IN NATURE, PRODUCTION AND APPLICATIONS
Neon, argon, krypton and xenon exist only in atmospheric air (Table 16.20).
Helium is found not only in atmospheric air, but also in natural gas deposits. It is the second most abundant element in the Universe after hydrogen. Radon is found in trace amounts in the earth's atmosphere. This element is radioactive. Its most abundant isotope, radon-222, has a half-life of 3.823 days. This isotope is formed when
Table 16.20. The content of noble gases in the earth's atmosphere
The decay of radium:
It is estimated that every square mile (approximately 2.5 sq. km) of soil on Earth, in a layer six inches (about 15 cm) deep, contains approximately 1 g of radium.
Noble gases are obtained from liquid air by fractional distillation followed by absorption with activated carbon.
Applications
The density of helium is twice that of hydrogen. However, it is much safer than hydrogen and is therefore used to fill balloons and meteorological probes; in addition, it is used in space technology.
A mixture of 80% helium and 20% oxygen is used as artificial breathing atmosphere for divers. The advantage of such an atmosphere is that helium has a much lower solubility in the blood than nitrogen, and therefore the use of an artificial atmosphere can save divers from "caisson disease" (boiling of blood due to the release of nitrogen dissolved in it during a rapid rise from great depths). Helium and argon serve to create an inert atmosphere during welding. In addition, helium is used to create a protective atmosphere when growing ultrapure germanium and silicon crystals.
Argon is used to fill electric lamps and various types of fluorescent tubes and photomultipliers.
Thanks to the completion of the external electronic level noble gases are chemically inert. Until 1962, it was believed that they did not form chemical compounds at all. In the Brief Chemical Encyclopedia (M., 1963, v. 2) it is written: “Compounds with ionic and covalent bonds inert gases do not give. By this time, some compounds of the clathrate type had been obtained, in which a noble gas atom is mechanically held in a framework formed by molecules of another substance. For example, under strong compression of argon over supercooled water, the crystal hydrate Ar 6H 2 0 was isolated. At the same time, all attempts to force noble gases to react even with the most energetic oxidizing agents (such as fluorine) ended in vain. And although theorists led by Linus Pauling predicted that the molecules of fluorides and xenon oxides could be stable, the experimenters said: "This cannot be."
Throughout this book, we try to emphasize two important ideas:
- 1) there are no immutable truths in science;
- 2) in chemistry, ABSOLUTELY EVERYTHING is possible, even what seems impossible or ridiculous for decades.
These ideas were perfectly confirmed by the Canadian chemist Neil Bartlett, when in 1962 he received the first chemical compound of xenon. That's how it was.
In one of the experiments with platinum hexafluoride PtF 6 Bartlett obtained red crystals, which, according to the results of chemical analysis, had the formula 0 2 PtF 6 and consisted of 0 2 and PtF 6 ions. This meant that PtF 6 is such a strong oxidizing agent that it takes electrons even from molecular oxygen! Bartlett decided to oxidize another spectacular substance and realized that it was even easier to take electrons from xenon than from oxygen (ionization potentials 0 2 12.2 eV and Xe 12.1 eV). He placed platinum hexafluoride in a vessel, launched a precisely measured amount of xenon into it, and a few hours later received xenon hexafluoroplatinate.
Immediately following this reaction, Bartlett carried out the reaction of xenon with fluorine. It turned out that when heated in a glass vessel, xenon reacts with fluorine, and a mixture of fluorides is formed.
Xenon fluoride^ II) XeF 2 is formed under the action of daylight on a mixture of xenon with fluorine at ordinary temperature
or during the interaction of xenon and F 2 0 2 at -120 ° C.
Colorless XeF 2 crystals are soluble in water. The XeF 2 molecule is linear. A solution of XeF 2 in water is a very strong oxidizing agent, especially in an acidic environment. In an alkaline environment, XeF 2 is hydrolyzed:
Xenon fluoride(H) XeF 4 is formed by heating a mixture of xenon with fluorine to 400 °C.
XeF 4 forms colorless crystals. The XeF 4 molecule is a square with a xenon atom in the center. XeF 4 is a very strong oxidizing agent and is used as a fluorinating agent.
When interacting with water, XeF 4 disproportionates.
Xenon Fluoride(Ch1) XeF 6 is formed from the elements when heated and pressurized with fluorine.
XeF 6 - colorless crystals. The XeF 6 molecule is a distorted octahedron with a xenon atom in the center. Like other xenon fluorides, XeF 6 is a very strong oxidizing agent and can be used as a fluorinating agent.
XeF 6 is partially decomposed by water:
xenon oxide(U I) Xe0 3 is formed during the hydrolysis of XeF 4 (see above). It is a white, non-volatile, highly explosive substance, highly soluble in water, and the solution has a slightly acidic reaction due to the following reactions:
Under the action of ozone on an alkaline solution of Xe0 3, a salt of xenonic acid is formed, in which xenon has an oxidation state of +8.
Xenon oxide (U1N) XeO 4 can be obtained by reacting barium perxenate with anhydrous sulfuric acid at low temperatures.
Xe0 4 is a colorless gas, highly explosive and decomposes at temperatures above 0 °C.
Of the compounds of other noble gases, KrF 2 , KrF 4 , RnF 2 , RnF 4 , RnF 6 , Rn0 3 are known. It is believed that similar compounds of helium, neon and argon are unlikely to ever be obtained in the form of individual substances.
Above we stated that in chemistry "everything is possible". Let us therefore report that compounds of helium, neon and argon exist in the form of so-called excimer molecules, i.e. molecules in which the excited electronic states are stable and the ground state is unstable. For example, upon electrical excitation of a mixture of argon and chlorine, a gas-phase reaction can proceed with the formation of an excimer ArCl molecule.
Similarly, in the reactions of excited noble gas atoms, a whole set of diatomic molecules can be obtained, such as He 2, HeNe, Ne 2, NeCl, NeF, HeCl, ArF, etc. All these molecules are unstable and cannot be isolated as individual substances, however, they can be registered and their structure studied using spectroscopic methods. Moreover, electronic transitions in excimer molecules are used to generate UV radiation in high-power excimer UV lasers.
Due to the completeness of the outer electronic level, noble gases are extremely chemically inert. Until 1962, it was believed that they did not form chemical compounds at all. By this time, some compounds of the clathrate type had been obtained, in which the atom of a noble gas is mechanically (without the formation of chemical bonds) held in a framework formed by the molecules of another substance. For example, under strong compression of argon over supercooled water, the crystal hydrate Ar 6H20 was isolated. At the same time, all attempts to force the noble gases to react even with the most energetic oxidizing agents (such as fluorine) ended in vain. The first chemical compound in which the noble gas atom forms chemical bonds with other elements, received in 1962 by N. Bartlett. In one of his experiments with sycamore hexafluoride PtF*, Bartlett obtained red crystals, which, according to the results of chemical analysis, had the formula 02PtF6 and consisted of C>2* and PtF6~ ions. This meant that PtFfi is such a strong oxidizing agent that it takes electrons even from oxygen. Bartlett decided to oxidize another spectacular substance and realized that it was even easier to take electrons from xenon than from oxygen (ionization potentials: 12.2 eV for O * and 12.1 eV for Xe). He placed platinum hexafluoride in a vessel, launched an accurately measured amount of xenon into it, and after a few hours received xenon hexafluoroplatinate: Soon Bartlett also carried out the reaction of xenon with fluorine. It turned out that xenon reacts well with fgor when heated in a glass vessel, and a mixture of fluorides is formed. Xenon (II) fluoride XeF2 is formed under the action of daylight on a mixture of xenon with fluorine at ordinary temperature: or by the interaction of xenon and F202 at -120 ° C: XeF2 are colorless crystals soluble in water. The XeF2 molecule is linear. A solution of XeF2 in water is a very strong oxidizing agent, especially in an acidic environment, where it is able to oxidize bromine and manganese to their the highest degree oxidation (+7). In an alkaline environment, XeF2 is hydrolyzed according to the equation: Xenon (IV) fluoride XeF4 is formed by heating a mixture of xenon with fluorine to 40°C: XeF* is colorless crystals. The XeF4 molecule is a "square" with a xenon atom in the center. XeF4 is a very strong oxidizing agent, used as a fluorinating agent: When interacting with water, XeF4 disproportionates: Xenon (VI) fluoride XeF6 is formed from elements during heating and high fluorine pressure: XeFe - colorless crystals. The XeF' molecule is a distorted octahedron with a xenon atom in the center. Like other xenon fluorides, XeF6 is a very strong oxidizing agent, it can be used as a fluorinating agent: XeF6 partially decomposes with water: Xenon (VI) oxide Xe03 is formed during the hydrolysis of XeF4 (see above). It is a white, non-volatile, highly explosive substance, highly soluble in water, and the solution has a slightly acidic environment due to the reaction: Under the action of ozone on an alkaline solution of XO3, a salt of xenonic acid is formed, in which xenon has an oxidation state of 4-8: Xenon oxide (VIII ) Xe04 can be obtained by reacting barium perkssnate with anhydrous sulfuric acid at low temperatures: Xe04 is a colorless gas that is very explosive and decomposes at temperatures above 0 ° C: Of the compounds of other noble gases, KrF2, KtF4, RnF2, RnF4, RnF6, Rn03. It is believed that similar compounds of helium, neon and argon are unlikely to ever be obtained in the form of individual substances. Nevertheless, chemical compounds of helium, neon, and argon exist in the form of so-called excimer molecules, i.e., molecules in which excited electronic states are stable and the ground state is unstable. For example, with electrical excitation of a mixture of argon and chlorine, a gas-phase reaction is possible with the formation of the excimer ArCl molecule. Similarly, reactions of excited atoms of noble gases can produce a whole set of diatomic molecules, such as Her, Ne2, NeF, etc. All these molecules are unstable and cannot be isolated as individual substances, but they can be registered and the structure of their molecules studied using spectroscopic methods.
