The term "noble" was coined by the German chemist Hugo Erdmann because these elements are particularly non-reactive; noble gases are nonflammable under normal conditions. They were also thought to have zero valence because chemists believed that these elements were not able to combine with other elements. This was eventually disproved by later scientists who discovered compounds using xenon with oxygen as well as krypton and fluorine; however, helium, neon and argon have no known compounds as of 2011.
Noble gases are odorless, colorless and tasteless. According to the Royal Society of Chemistry, these gases boil at particularly low temperatures because of the few dispersion forces between their atoms. Helium has the lowest boiling point. Going down the list of the noble gases from top to bottom, the corresponding atomic radius of each gas increases.
The noble gases can be readily found in the upper layer of the atmosphere, although in limited quantities. Helium can also be found in natural gas wells due to radioactive reactions and decay. Argon is found in the earth as a result of the decay of potassium compounds. Scientists have noted that the amount of xenon is unexpectedly small in the atmosphere compared to the amounts of other noble gases; this phenomenon is known as the "missing xenon problem."
The noble gases have everyday uses. Helium is used to inflate balloons. The Royal Society of Chemistry notes that helium is also used by divers to dilute the oxygen in their tanks. Argon is used as an inert atmospheric gas for high temperature metallurgy; it is also used to fill discharge tubes. Neon lamps are made by removing the air from glass tubes and replacing the air with neon gas or another noble gas. Ionization of the gas results in the bright colors characteristic of these lights.