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37. INERT GASES.
The subgroup of inert gases includes elements: helium, neon, argon, krypton, xenon, radon.
Properties of the VIII-A elements of subgroup.
Element helium neon argon krypton xenon radon Property Order number of element 2 10 18 36 54 86 Relative atomic mass 4,003 20,180 39,948 83,80 131,29 222,018 Melting temperature, 0C - 272,15 - 248,6 - 189,4 - 157,2 - 111,8 - 71,0 Boiling temperature, 0C - 268,9 - 246,8 - 185,9 - 153,4 - 108,1 - 62,0 G/cm3 density 0,18
0,9 1,78 3,74
5,89 9,96 under normal conditions Oxidation levels 0 0 0 0, +2, +4 0, +2, +4, +6, +7 0
Properties and use of inert gases.
Properties: helium — light nonflammable gas, density of gaseous helium under normal conditions 0,178 kg/m3 (it is less only at gas of hydrogen (H)). Helium boiling temperature (with standard atmosphere pressure) about 4,2 To (or 268,93 °C, are the lowest temperature of boiling). With standard atmosphere pressure liquid helium does not manage to be turned into solid matter even at temperatures, near absolute zero (0K). With pressure about 3,76 MPas helium 2,0K melting temperature. The smallest pressure with which transition of liquid helium to solid state — 2,5mpa is observed (25 ат), helium melting temperature at the same time about 1,1 To (–272,1 °C).
In 100 ml of water at 20 °C 0,86 ml of helium are dissolved, in organic solvents its solubility is even less. Easy molecules of helium well pass (diffuse) through different materials (plastic, glass, some metals). For the liquid helium-4 cooled below-270,97 °C number of unusual effects is observed that gives the grounds to consider this liquid as special, so-called quantum, liquid. This liquid is usually designated as helium-II unlike liquid helium-I — the liquid existing at a little more high temperatures. Helium-I transition temperature in helium-II is equal to 2,186 K. This temperature is often called l-point. Liquid helium-II is capable to get quickly through the smallest openings and capillaries, without finding at the same time viscosity (so-called superflowability of liquid helium-II). Besides, helium-II films quickly move on surface of solid bodies therefore liquid quickly leaves that vessel in which it has been placed. This property of helium-II is called supercreep. The superflowability of helium-II is opened in 1938 by the Soviet physicist P. L. Kapitsey (The Nobel Prize on physics, 1978). The explanation for unique properties of helium-II is offered by other Soviet physicist L. D. Landau in 1941-1944 (The Nobel Prize on physics, 1962). Helium does not form any chemical compounds. However, in the rarefied ionized Gely it is possible to find rather steady diatomic ions of Ne2+.
History of opening and name: discovery of helium has begun since 1868 when at observation of solar eclipse astronomers Frenchman P. Zh. Zhansen and Englishman D. N. Lokyer independently have from each other found the yellow line in range of solar crown (she has received the name D3 line), which could not be attributed to any of elements known at that time. In 1871 Lokyer has explained its origin with presence in the Sun of new element. In 1895 Englishman U. Ramzay has emitted gas at which range there was same D3 line from natural radioactive ore of kleveit. Lokyer has named new element, reflecting history of its opening (Greek Helios — the sun). As Lokyer believed that the found metal element, he used the termination "lim" in the Latin name of element (corresponds to the Russian termination "y"), which is usually used in the name of metals. Thus, helium long before the opening on Earth has received name which the termination distinguishes it from names of other inert gases.
Stay in the nature: in free air the helium content very little also makes about 5,27·10-4% on volume. In crust of its 0,8·10–6%, in sea water — 4·10–10%. Oil and gelionosny natural gases in which the helium content reaches 2-3%, and in rare instances and 8-10% on volume are source of helium. But in space helium — element, the second for prevalence (after hydrogen (H)): 23% of space weight Receiving fall to its share: now helium is emitted from natural gelionosny gases, using method of deep cooling (helium is removed most difficultly than other gases). Fields of such gases are available in Russia, the USA, Canada and the Republic of South Africa. Gely contains also in some minerals (monazite, thorianite and others), at the same time from 1 kg of mineral when heating it is possible to allocate up to 10 l of helium.
Application: helium is used for creation of the inert and protective atmosphere when welding, cutting and melting of metals, when pumping rocket fuel, for filling of airships and aerostats as component of the environment of helium lasers. Liquid helium, the coldest liquid on Earth — the unique coolant in experimental physics allowing to use cryogenic temperatures in scientific research (for example, when studying electric superconductivity). Thanks to the fact that we will very badly dissolve helium in blood it is used as component of the artificial air given for breath to divers. Replacement of nitrogen (N) by helium prevents lacunar disease (at inhalation of usual air nitrogen under positive pressure is dissolved in blood, and then it is allocated from it in the form of the bubbles corking small vessels).
Neon — monatomic gas without color and smell.
Svoystva:temperatura of neon boiling (with standard atmosphere pressure) –245,9 °C, temperature of melting is –248,6 °C. Critical temperature is –228,8 °C, critical pressure is 2,65 MPas. Density under normal conditions 1,444 kg/m3. In 100 ml of water at 20 °C about 10 ml of neon are dissolved. Neon forms with water connection of inclusion (clathrate) of structure Ne · 6H2O. Neon does not form chemical compounds. The so-called excimer molecules Ne2 and NeF containing neon are known. On transitions of these molecules from metastable state in untied laser radiation is generated. Opening history: neon was discovered in 1898 by the English scientific U. Ramzay and M. Travers at spectral research of the remains of slowly evaporating liquid air.
The name comes from the Greek neos — new and confirms joy of the researchers who have found in air except argon (Ar), and other inert gases. There is legend according to which the name to new element was given by the twelve-year-old son Ramzaya: having seen the unusual bright red radiation emitted by substance in tube for carrying out the spectral analysis he joyfully has cried: "New! New!". Stay in the nature: content of neon in free air makes 1,82·10–3% on the volume (the general stocks of 7,8·1014 m3). 1 m3 of air contains about 18,2 cm3 of neon. Crust contains 7·10–9% of neon, in sea water — 2·10–8%. Receiving: in the industry neon is received as by-product at large-scale division of liquid air into oxygen (O) and nitrogen (N).
Application: neon is applied to filling of gas-discharge tubes, alarm lamps of the radio engineering equipment, indicator lights, in the equipment of low temperatures. Mix of neon and helium (He) use as actuation medium in gas lasers. The tubes filled with mix of neon and nitrogen (N) (the so-called neon tubes containing about 10 volume % of neon) at transmission through them electric discharge let out red luminescence.
Information on argon, xenon, krypton, radon.
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