What are noble gases and how many are there?

The noble gases are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with very low chemical reactivity. The six noble gases that occur naturally are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn).

Noble gas is translated from the German noun Edelgas, first used in 1898 by Hugo Erdmann[3] to indicate their extremely low level of reactivity. The name makes an analogy to the term "noble metals", which also have low reactivity. The noble gases have also been referred to as inert gases, but this label is now deprecated as many noble gas compounds are now known.[4] Rare gases is another term that was used,[5] 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.[

https://en.wikipedia.org/wiki/Noble_gas

'Noble gases' is one of the most common names for the elements in the rightmost group of the periodic table of the elements. They are also sometimes called 'inert gases'. For a number of complicated reasons, these elements have one important chemical property: they are extremely un-reactive. One consequence of this was that the noble gases were isolated and characterised only relatively late.

The first person to actually isolate and note the presence of these noble gases was Henry Cavendish (1731-1810: chemistry bigwig and discoverer of hydrogen) in 1785. He removed all the nitrogen and oxygen chemically from a receptacle contining air. The nitrogen was oxidised to NO2 by electric discharges and absorbed by a sodium hydroxide solution. Remaining oxygen was removed from the mixture by a special adsorber. 1/120 of the gas volume remained unreacted in the receptacle. As we know today, this must have been mainly argon (99.8%) and traces (0.2%) of other noble gases. The second person to isolate a noble gas, but without characterising it, was mineralogist William Francis Hillebrand (1853-1925) who noted the formation of a gas while dissolving uranium containing minerals in acid. We know today this must have been helium.

http://www.bbc.co.uk/dna/h2g2/A2342189

"There is a possible seventh noble gas element. Ununoctium exhibits noble-gas-like properties, but it's all a bit iffy over a decade after its discovery. It has some odd relativistic properties that the other six noble gases don't exhibit, and it may not even be a gas at all! So a proposed seventh track between "Radon" and "Group Zero" was put on hold. It was briefly considered for addition as a bonus but it was decided that it would spoil the continuity of the album. Besides, it was a demo, not finished to the same standard as the others. Ergo it was deep-sixed."

http://www.mikedickson.org.uk/noblegases/index.html


"...although ununoctium is a member of Group 18, it may possibly not be a noble gas, unlike all the other Group 18 elements. It was formerly thought to be a gas but is now predicted to be a solid under normal conditions due to relativistic effects..."
"...It is thought that similarly, ununoctium has a closed outer valence shell in which its valence electrons are arranged in a 7s27p6 configuration.

Consequently, some expect ununoctium to have similar physical and chemical properties to other members of its group, most closely resembling the noble gas above it in the periodic table, radon.Following the periodic trend, ununoctium would be expected to be slightly more reactive than radon. However, theoretical calculations have shown that it could be quite reactive, so that it can probably not be considered a noble gas."

https://en.wikipedia.org/wiki/Ununoctium