Noble Gases: Properties, History, and Chemistry

Group 18 membership and elements

Group 18 of the periodic table is the noble gases: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn), and (historically/optionally) oganesson (Og). Under standard conditions, the first six are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points. Their “inertness” comes from having a full valence electron shell, which makes them energetically unlikely to gain, lose, or share electrons; only a few hundred noble-gas compounds are known, and helium and neon form essentially no neutral compounds under normal conditions. Physically, noble gases have weak intermolecular (London dispersion/van der Waals) forces, leading to low melting/boiling points that increase down the group. They also show systematic trends in properties such as atomic radius, ionization energy, and solubility, and they are nearly ideal gases under standard conditions. Chemically, their electron configurations follow a pattern with full outer shells (He: 2; others: 8 valence electrons), which explains their stability and the “noble gas notation” used to write electron configurations compactly. Oganesson’s chemistry and physical state are uncertain due to its extreme instability and relativistic effects. In applications and Earth sciences, noble gases are valuable because they resist reactions and can be traced via isotopic signatures. Industrially, they are used for shielding (argon), buoyancy (helium), and refrigeration (helium/neon), while radon is used in radiotherapy. In geology, isotopic ratios of noble gases (e.g., helium, neon, argon, krypton, xenon) help reconstruct Earth’s degassing history and distinguish sources across geological reservoirs; careful sampling and high-precision mass spectrometry are required to avoid atmospheric contamination and resolve closely spaced isotopes.

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Standard physical state and basic reactivity

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