Any of the six inert gaseous elements of group 0 in the periodic table. The inert, or noble gases are helium, neon, argon, krypton, xenon and radon. They have a filled outer p shell in their electronic structure and thus are considered as having a valence number of zero. Originally, it was thought that the noble gases were unreactive or inert. However in recent years scientists have been able to react krypton, xenon and radon with other elements, but only under extreme conditions such as high pressures, high temperatures and strong electrical fields.
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