periodic table argon product definition chemistry

A century later, in 1895, Lord Rayleigh discovered that samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. Before them, in 1784, the English chemist and physicist Henry Cavendish had discovered that air contains a small proportion of a substance less reactive than nitrogen. No chemical analysis was possible at the time, but helium was later found to be a noble gas. Pierre Janssen and Joseph Norman Lockyer had discovered a new element on 18 August 1868 while looking at the chromosphere of the Sun, and named it helium after the Greek word for the Sun, ἥλιος ( hḗlios). Helium was first detected in the Sun due to its characteristic spectral lines. Rare gases is another term that was used, but this is also inaccurate because argon forms a fairly considerable part (0.94% by volume, 1.3% by mass) of the Earth's atmosphere due to decay of radioactive potassium-40. The noble gases have also been referred to as inert gases, but this label is deprecated as many noble gas compounds are now known. The name makes an analogy to the term ' noble metals', which also have low reactivity. Noble gas is translated from the German noun Edelgas, first used in 1900 by Hugo Erdmann to indicate their extremely low level of reactivity. In the rest of this article, the term 'noble gas' should be understood not to include oganesson unless it is specifically mentioned.

IUPAC uses the term 'noble gas' interchangeably with 'group 18' and thus includes oganesson however, due to relativistic effects, oganesson is predicted to be a solid under standard conditions and reactive enough not to qualify functionally as 'noble'. The seventh member of group 18 is oganesson (Og), an unstable synthetic element whose chemistry is still uncertain because only five very short-lived atoms have ever been synthesized (as of 2020 ). Radon is usually isolated from the radioactive decay of dissolved radium, thorium, or uranium compounds. Helium is also a byproduct of the mining of natural gas. Industrial quantities of the noble gases, except for radon, are obtained by separating them from air using the methods of liquefaction of gases and fractional distillation. Helium and neon are also used as refrigerants due to their low boiling points. After the risks caused by the flammability of hydrogen became apparent in the Hindenburg disaster, hydrogen was replaced with helium in blimps and balloons. For example, argon is used as a shielding gas in welding and as a filler gas in incandescent light bulbs. The inertness of noble gases makes them useful whenever chemical reactions are not wanted. For the same reason, noble gas atoms are small, and the only intermolecular force between them is the very weak London dispersion force, so their boiling points are all cryogenic, below 165 K (−108 ☌ −163 ☏). Only a few hundred noble gas compounds are known to exist. The inertness of noble gases results from their electron configuration: Their outer shell of valence electrons is 'full', giving them little tendency to participate in chemical reactions. Under standard conditions, these chemical elements are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points. The noble gases (historically also the inert gases, sometimes referred to as aerogens ) are the naturally occurring members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn).

Periodic table argon product definition chemistry