Inert gases (noble gases) - elements forming the 18th group of PS (in the short-period variant - the main subgroup of the 8th group): helium He (atomic number 2), neon Ne (Z = 10), argon Ar (Z = 18), krypton Kr (Z = 36), xenon Xe (Z = 54) and radon Rn (Z = 86). Inert gases are constantly present in the air (1 m3 of air contains about 9.4 liters, mainly Ar). The composition of the air has been analyzed by scientists since the second half of the 18th century. However, it has not been possible to detect inert gases for a long time. Because of their chemical passivity, they did not show themselves in the usual reactions and slipped out of sight of the researchers. It was only after the discovery of spectral analysis that helium and argon were discovered, and then other inert gases were discovered. At the beginning of the 20th-century mankind was surprised to learn that the air, so familiar and seemed to be studied, contains 6 previously unknown elements.
The inert gases are dissolved in water and contained in some rocks. Helium is sometimes a part of underground gases. Such gases are its only industrial source. Neon, argon, krypton, and xenon are extracted from the air in the process of its separation into nitrogen and oxygen.
The source of Rn is uranium, radium and other radioactive elements. Although all inert gases, except radon, are stable, their origin is largely related to radioactivity. Thus, helium nuclei, otherwise called ɑ-particles, are constantly formed as a result of radioactive decay of uranium or thorium. Argon-40, which prevails in the natural mixture of argon isotopes, arises from the radioactive decay of the potassium-40 isotope. Finally, the origin of most of the Earth's Xe resources is probably due to the spontaneous fission of uranium nuclei.
All inert gases have neither color nor odor. The outer electron shells of their atoms contain the maximum possible number of electrons for the corresponding outer shells: 2 for helium and 8 for each of the others. Such shells are highly resistant. Firstly, the chemical passivity of inert gases in relation to other elements is related to this. And secondly, the inability of their atoms to bind to each other, so that their molecules are unit automatic. Inert gases, especially light ones, are difficult to transfer to a liquid state. Let's try to understand. Why is it so? Other gas molecules are either permanent dipoles, such as HCl or easily become dipoles (Cl2). In the case of permanent dipoles, the "centers of gravity" of positive and negative charges do not always coincide with each other. The formation of a dipole in Cl2 molecules is associated with the displacement of "centers of gravity" of charges relative to each other under the influence of external forces, in particular under the influence of electric fields of neighboring molecules. Thus, both in HCl molecules and Cl2 molecules there are forces of electrostatic attraction between the dipoles of different names. At certain low temperatures, these forces are sufficient to keep the molecules close to each other. In the case of inert gas atoms, the arrangement of electrons around the nuclei is strictly spherical. Therefore, neighboring atoms cannot cause displacement of "centers of gravity" of electric charges in their atoms and lead to the formation of "induced" dipole, as in chlorine molecules. Thus, there are neither constant nor induced dipoles in the inert gas atoms. And if so, there are practically no attraction forces between them under normal conditions. However, due to the constant fluctuations of atoms, the "centers" of charges may shift to different sides of the atom for a moment. The electrostatic gravitational forces occurring during the formation of this instantaneous dipole are very small, but at very low temperatures they are sufficient to condense these gases.
For a long time, attempts to obtain conventional inert gas chemicals have failed. The Canadian scientist N. Bartlett, who in 1962 reported the synthesis of xenon compound with platinum hexafluoride PtF6, has managed to put an end to the idea of absolute chemical inertia of inert gases. The obtained xenon compound was composed of Xe[PtF6]. In the following years, a large number of other compounds of radon, xenon, and krypton were also synthesized.