Properties and applications
noble gas
Each noble-gas element is situated in Group 18, which is on the far right of the periodic table. Conceptually, this group follows the most electropositive alkali metals (Group 1, whose atoms lose electrons to become positive ions) and lies immediately after the halogen elements (Group 17, whose atoms gain electrons to achieve the octet and become negative ions) in terms of periodic ordering.
Several important uses of the noble gases depend on their reluctance to react chemically. Their indifference toward oxygen, for example, confers utter nonflammability upon the noble gases. Although helium is not quite as buoyant as hydrogen, its incombustibility makes it a safer lifting gas for lighter-than-air craft. The noble gases—most often helium and argon, the least expensive—are used to provide protective, chemically unreactive environments for such operations as cutting, welding, and refining of metals such as aluminum (atmospheric oxygen and, in some cases, nitrogen or carbon dioxide, would react with the hot metal), as well as in electronics manufacturing. Besides helium and argon, other noble gases such as krypton and neon are widely used in industrial processes that require protective, nonreactive atmospheres.
The noble gases absorb and emit electromagnetic radiation in a much less complex way than do other substances. This behavior is used in discharge lamps and fluorescent lighting devices: If any noble gas is confined at low pressure in a glass tube and an electrical discharge is passed through it, the gas will glow. Neon produces the familiar orange-red color of advertising signs; xenon emits a beautiful blue color.
Oganesson is a transuranium element located at the end of Group 18 and is a synthetic noble gas. With atomic number 118, it was formerly known by the temporary name ununoctium. It is now officially called oganesson after Russian physicist Yuri Oganessian, who led the group of scientists that synthesized it.
Scientists believe that the electrons in oganesson move so fast—nearly as fast as light—that they behave differently from the electrons in lighter gases such as helium or neon. This “speed limit” effect, known as the relativistic effect, is attributed to its large atomic size and mass, which change its structure and properties. These changes would make oganesson solid at room temperature rather than a gas, and more reactive than its fellow group elements. It is believed to be the first noble gas to break the trend of being inert.
With a half-life (time required for half of the radioactive atoms to decay into a more stable form) of less than a millisecond, oganesson is one of the shortest-lived elements. Since only a few atoms of this highly radioactive element have been produced so far, it currently has no practical application outside of scientific research.
Noble gases have uses that are derived from their other chemical properties. The very low boiling points and melting points of the noble gases make them useful in the study of matter at extremely low temperatures. The low solubility of helium in fluids leads to its admixture with oxygen for breathing by deep-sea divers: Because helium does not dissolve in the blood, it does not form bubbles upon decompression (as nitrogen does, leading to the condition known as decompression sickness, or the bends). Xenon has been used as an anesthetic; although it is costly, it is nonflammable and readily eliminated from the body. Radon is highly radioactive; its only uses have been those that exploit this property (e.g., radiation therapy).
The applications of noble gases have expanded well beyond their conventional uses in lighting, inert chemical atmospheres, and specialized medical applications. Because of helium’s small atomic size and nonreactive nature, it is an ideal element for high-sensitivity leak detection systems in aerospace and vacuum technology. It is also extensively used in cryogenics for cooling superconducting magnets in magnetic resonance imaging (MRI) scanners and high-energy particle accelerators, because of its exceptionally low boiling point.
Neon powers the excimer lasers (ultraviolet chemical lasers, also called exciplex lasers) used in deep-ultraviolet (DUV) lithography to etch microchips. Because of its high atomic mass and ease of ionization, xenon is used as a propellant in ion thrusters for satellites and deep space probes, providing unparalleled fuel efficiency. Finally, radon is a critical element used in seismological studies to predict earthquakes, as it is sensitive to variations in pressure beneath Earth’s surface.
Only krypton, xenon, and radon are known to form stable compounds. The compounds of these noble gases are powerful oxidizing agents (substances that tend to remove electrons from others) and have potential value as reagents in the synthesis of other chemical compounds.