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The noble gases (often mistakenly referred to as inert gases) are a group of chemical elements with...

The noble gases (often mistakenly referred to as inert gases) are a group of chemical elements with very similar properties: under standard conditions, they are all odorless, colorless, monatomic gases, with a 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). For the first six periods of the periodic table, the noble gases are exactly the members of group 18 of the periodic table. However, this no longer holds in the seventh period (due to relativistic effects): The next member of group 18, ununoctium, is probably not a noble gas. Instead, group 14 member ununquadium exhibits noble-gas-like properties. The properties of the noble gases can be well explained by modern theories of atomic structure: their outer shell of valence electrons is considered to be "full", giving them little tendency to participate in chemical reactions, and only a few hundred noble gas compounds have been prepared. The melting and boiling points for each noble gas are close together, differing by less than 10 °C (18 °F); consequently, they are liquids only over a small temperature