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The noble gases (historically also referred to as inert gases or rare gases) are the members of group 18 in the periodic table. They are helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and the radioactive radon (Rn) as well as oganesson (Og), though the latter's properties are still debated.
Elements in the noble gas group
Neon, atomic number 10, is the second element of the group. It does not form any compounds and it's considered truly inert. When placed in an electrical field, it exhibits a red to red-orange glow.
Argon, atomic number 18, is a gas heavier than air, which makes up 0.934% of Earth's atmosphere, being the third most abundant gas in the atmosphere. As such, the usage of the former name for this group, the rare gases, has been largely discontinued. When placed in an electrical field, it exhibits a purple/lilac glow.
Krypton, atomic number 36, is a heavy monoatomic gas, commonly used in gas discharge lamps. When placed in an electrical field, it exhibits a white glow.
Xenon, atomic number 54, is the heaviest stable gaseous element. When placed in an electrical field, it exhibits a light blue glow.
Radon, atomic number 86, is a radioactive gas, with its main isotope 222Rn having a half life of 3.8235 days. When placed in an electrical field, it exhibits a red glow (some sources also say green).
Oganesson, atomic number 118, first synthesized in 2002, is heaviest element in the group, a radioactive element with the longest half life of 0.7 miliseconds (294Og). Due to relativistic effects, it's theorized it will have properties slightly different to the elements above it.
The first three elements do not form true chemical compounds at standard conditions, while neon will not form any detectable compounds in any conditions. Krypton will react with fluorine, as does radon, while xenon will react with fluorine and can also form oxides.
The first six members of this group are, under standard conditions, odorless, colorless, monatomic gases with very low chemical reactivity.
Since they're non-reactive, noble gases do not pose significant hazard to health, though they can pose an asphyxiation hazard in closed environments. Xenon has been shown to have anesthetic properties in high concentrations. Radon, being very radioactive, is extremely harmful.