The noble gases occupy Group 18 of the periodic table. Their defining feature is a full outer electron shell, which makes them extremely unreactive under normal conditions. Ranging from helium (atomic number 2) to oganesson (118), these elements include some of the most and least abundant substances on Earth.
Properties of Noble Gases
Noble gases share several distinctive properties due to their filled valence electron shells. They have very low boiling points — helium has the lowest boiling point of any element at −268.93 °C (4.22 K). All noble gases are colorless, odorless, and tasteless under standard conditions, and they exist as monatomic gases rather than forming molecules. Their ionization energies are among the highest of all elements, reflecting the stability of their electron configurations.
The Noble Gases
Each noble gas has unique characteristics and applications:
Used in balloons, MRI machine coolant (liquid helium at 4.2 K), and deep-sea diving gas mixtures. The second most abundant element in the universe after hydrogen.
Used in neon signs, producing a distinctive orange-red glow when electrically excited. Also used in high-voltage indicators and lightning arresters.
The most abundant noble gas in Earth's atmosphere at 0.93% by volume. Widely used as a shield gas in welding and in incandescent and fluorescent lighting.
Used in fluorescent lamps, photographic flash equipment, and high-performance airport runway lights. Produces a brilliant white light.
Used in vehicle headlights (HID lamps), as a general anesthetic, and in ion propulsion systems for spacecraft. Can form compounds such as XeF₂, disproving early assumptions about noble gas inertness.
A radioactive gas produced by radium decay. Accumulates in buildings from soil and rock — the second leading cause of lung cancer after smoking. Radon testing is recommended for all homes.
A synthetic superheavy element. Theoretical calculations predict it may actually be a solid at room temperature, unlike all other noble gases, due to strong relativistic effects on its electron shell.
Noble Gas Compounds
For decades, noble gases were called "inert gases" because they were believed to be completely unreactive. This changed in 1962 when Neil Bartlett synthesized the first noble gas compound, xenon hexafluoroplatinate (XePtF₆). Since then, several xenon and krypton compounds have been produced, including XeF₂, XeF₄, XeF₆, and KrF₂. These discoveries proved that noble gases can form bonds when paired with highly electronegative elements like fluorine and oxygen, leading to the name change from "inert gases" to "noble gases."