The noble gases are unreactive gases. Apart from helium and neon, the noble gases are denser than air.
|Relative atomic mass:||4||20||40||84||131|
|Boiling point (°C):||-268.95||-246.15||-186.15||-153.15||-108.15|
|Electronic configuration:||1s2||1s22s22p6||1s22s22p6 3s23p6||3d104s24p6||4d105s25p6|
|Major industrial applications:||
|Discoverers:||Pierre Janssen (1868)||William Ramsay (1898)|
Argon is the third most abundant gas in the atmosphere, after nitrogen and oxygen, at 9340 parts per million or 0.934%. The other noble gases are found in very much smaller proportions in the Earth's atmosphere (see table below). However, helium is the second most abundant element in the universe after hydrogen. About 7.2% of all the atoms in the universe are helium atoms, and they form about 23% of the mass of the universe. Helium is also the second most abundant element in the sun.
Helium is formed in the Earth's crust as a result of radioactive decay (alpha particles are helium nuclei) and it can become trapped in natural gas fields. Some sources of natural gas may contain as much as 7% helium. The main sources of helium are gas fields in the US, Algeria, Russia, Poland and the Middle East. The other noble gases are obtained from liquefied air using fractional distillation.