2) Describe of Xenon properties. Distribution in nature, production technology, physico-chemical characteristics.

Xenon is a chemical element with symbol Xe and atomic number 54. It is a colorless, dense, odorless noble gas found in the Earth's atmosphere in trace amounts. Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized. Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe₂) as the lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft. Naturally occurring xenon consists of eight stable isotopes. More than 40 unstable xenon isotopes undergo radioactive decay, and the isotope ratios of xenon are an important tool for studying the early history of the Solar System. Radioactive xenon -135 is produced by beta decay from iodine -135 (a product of nuclear fission), and is the most significant neutron absorber in nuclear reactors.

Characteristics. Xenon has atomic number 54; that is, its nucleus contains 54 protons. At standard temperature and pressure, pure xenon gas has a density of 5.761 kg/m³, about 4.5 times the density of the Earth's atmosphere at sea level, 1.217 kg/m³. As a liquid, xenon has a density of up to 3.100 g/mL, with the density maximum occurring at the triple point. Liquid xenon has a high polarizability due to its large atomic volume, and thus is an excellent solvent. It can dissolve hydrocarbons, biological molecules, and even water. Under the same conditions, the density of solid xenon, 3.640 g/cm³, is greater than the average density of granite, 2.75 g/cm³. Under gigapascals of pressure, xenon forms a metallic phase. Solid xenon changes from face-centered cubic (fcc) to hexagonal close packed (hcp) crystal phase under pressure and begins to turn metallic at about 140 GPa, with no noticeable volume change in the hcp phase. It is completely metallic at 155 GPa. When metallized, xenon looks sky blue because it absorbs red light and transmits other visible frequencies. Such behavior is unusual for a metal and is explained by the relatively small width of the electron bands in that state. Liquid or solid xenon nanoparticles can be formed at room temperature by implanting Xe⁺ ions into a solid matrix. Many solids have lattice constants smaller than solid Xe. This results in compression of the implanted Xe to pressures that may be sufficient for its liquefaction or solidification. Xenon is a member of the zero-valence elements that are called noble or inert gases. It is inert to most common chemical reactions (such as combustion, for example) because the outer valence shell contains eight electrons. This produces a stable, minimum energy configuration in which the outer electrons are tightly bound. In a gas-filled tube, xenon emits a blue or lavenderish glow when excited by electrical discharge. Xenon emits a band of emission lines that span the visual spectrum, but the most intense lines occur in the region of blue light, producing the coloration.

Occurrence and production. Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L), or approximately 1 part per 11.5 million. It is also found as a component of gases emitted from some mineral springs. Xenon is obtained commercially as a by-product of the separation of air into oxygen and nitrogen. After this separation, generally performed by fractional distillation in a double-column plant, the liquid oxygen produced will contain small quantities of krypton and xenon. By additional fractional distillation, the liquid oxygen may be enriched to contain 0.1–0.2% of a krypton/xenon mixture, which is extracted either by absorption onto silica gel or by distillation. Finally, the krypton/xenon mixture may be separated into krypton and xenon by further distillation. Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m³. Because of its scarcity, xenon is much more expensive than the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10 €/L for xenon, 1 €/L for krypton, and 0.20 €/L for neon, while the much more plentiful argon costs less than a cent per liter.

Preparation of xenon. The main source of industrial production of xenon is air, where in 1000 m³ contains 86 cm³ of xenonIn industry, xenon is produced as a by-product of air separation into oxygen and nitrogen. After such separation, which is usually carried out by rectification, the resulting liquid oxygen contains small amounts of krypton and xenon. Further rectification enriches liquid oxygen to a content of 0.1-0.2% of the kryptonoxenone mixture, which is separated by adsorption onto silica gel or by distillation. As a conclusion, the xenon-krypton concentrate can be separated by distillation into krypton and xenon. To produce pure xenon, a krypton-xenon concentrate is used which undergoes cryogenic rectification at gas separation plants, which ensure the production of high purity xenon (99.999%). Because of its low prevalence, xenon is much more expensive than lighter inert gases. Separation of argon, krypton and xenon. The separation of these gases is not particularly difficult. For this, columns with activated carbon or molecular sieves can be used. Glukauf used gas chromatography on activated carbon to determine krypton and xenon as early as 1956. A number of works were devoted to the determination of Kr and Xe in gaseous products of radioactive decay.