|
( Noble gas)
The noble gases are the non-metal, chemically inert elements in group 18 of the periodic table. Chemically, the noble gases are very stable due to having the maximum number of valence electrons their outer shell can hold. Noble gases rarely react with other elements since they are already stable. Under normal conditions, they occur as odorless, colorless, monatomic gases. Each of them has its melting and boiling point close together, so that only a small temperature range exists for each noble gas in which it is a liquid. Noble gases have numerous important applications in lighting, welding and space technology. The six known noble gases are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) and radon (Rn). The synthetic elements ununquadium (Uuq)[1] and/or ununoctium (Uuo) may also turn out to be noble gases. "Noble gas" is the translation of the German Edelgas, which was in use as early as 1898 by Hugo Erdmann.[2] This refers to the extremely low level of reactivity under normal conditions. The noble gases have also been referred to as inert gases, but these terms are not strictly accurate because several of them do take part in chemical reactions. Another old term is rare gases, although argon forms a fairly considerable part (0.93% by volume, 1.29% by mass) of the Earth's atmosphere.[3] The existence of noble gases was not known until after the advent of the periodic table. In the late nineteenth century, Lord Rayleigh discovered that some samples of nitrogen from the air were of a different density than nitrogen resulting from chemical reactions. Along with scientist William Ramsay, Lord Rayleigh theorized that the nitrogen extracted from air was associated with another gas, argon. With this discovery, they realized that a whole class of gases was missing from the periodic table. Eventually, all the known noble gases except for helium were discovered in the air, with argon being much more common than the others, and the table was completed. Helium was detected spectrographically in the Sun in 1868. The isolation of helium on Earth had to wait until 1895. Under standard conditions, the noble gases all occur as monatomic gases.[4][5]
|
Noble gas Subcategories
Noble gas Articles
|
|
