Xenon in the context of "Alpha Andromedae"

An inert gas is a gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds. Though inert gases have a variety of applications, they are generally used to prevent unwanted chemical reactions with the oxygen (oxidation) and moisture (hydrolysis) in the air from degrading a sample. Generally, nitrogen, carbon dioxide, and all noble gases except oganesson (helium, neon, argon, krypton, xenon, and radon) are considered inert gases. The term inert gas is context-dependent because several of the inert gases, including nitrogen and carbon dioxide, can be made to react under certain conditions.

Purified argon gas is the most commonly used inert gas due to its high natural abundance (78.3% N₂, 1% Ar in air) and low relative cost.

The noble gases (historically the inert gases, sometimes referred to as aerogens) are the members of group 18 of the periodic table: helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn) and, in some cases, oganesson (Og). Under standard conditions, the first six of these elements are odorless, colorless, monatomic gases with very low chemical reactivity and cryogenic boiling points. The properties of oganesson are uncertain.

The intermolecular force between noble gas atoms is the very weak London dispersion force, so their boiling points are all cryogenic, below 165 K (−108 °C; −163 °F).

Neon is a chemical element; it has symbol Ne and atomic number 10. It is the second noble gas in the periodic table. Neon is a colorless, odorless, inert monatomic gas under standard conditions, with approximately two-thirds the density of air.

Neon was discovered in 1898 alongside krypton and xenon, identified as one of the three remaining rare inert elements in dry air after the removal of nitrogen, oxygen, argon, and carbon dioxide. Its discovery was marked by the distinctive bright red emission spectrum it exhibited, leading to its immediate recognition as a new element. The name neon originates from the Greek word νέον, a neuter singular form of νέος (neos), meaning 'new'. Neon is a chemically inert gas; although neon compounds do exist, they are primarily ionic molecules or fragile molecules held together by van der Waals forces.

In physics and chemistry, "monatomic" is a combination of the words "mono" and "atomic", and means "single atom". It is usually applied to gases: a monatomic gas is a gas in which atoms are not bound to each other. Examples at standard conditions of temperature and pressure include all the noble gases (helium, neon, argon, krypton, xenon, and radon), though all chemical elements will be monatomic in the gas phase at sufficiently high temperature (or very low pressure). The thermodynamic behavior of a monatomic gas is much simpler when compared to polyatomic gases because it is free of any rotational or vibrational energy.

Sir William Ramsay KCB FRS FRSE (/ˈræmzi/; 2 October 1852 – 23 July 1916) was a Scottish chemist who discovered the noble gases and received the Nobel Prize in Chemistry in 1904 "in recognition of his services in the discovery of the inert gaseous elements in air" along with his collaborator, John William Strutt, 3rd Baron Rayleigh, who received the Nobel Prize in Physics that same year for their discovery of argon. After the two men identified argon, Ramsay investigated other atmospheric gases. His work in isolating argon, helium, neon, krypton, and xenon led to the development of a new section of the periodic table.

A plasma ball, plasma globe, or plasma lamp is a clear glass container filled with noble gases, usually a mixture of neon, krypton, and xenon, that has a high-voltage electrode in the center of the container. When voltage is applied, a plasma is formed within the container. Plasma filaments extend from the inner electrode to the outer glass insulator, giving the appearance of multiple constant beams of colored light. Plasma balls were popular as novelty items in the 1980s.

The plasma lamp was invented by Nikola Tesla, during his experimentation with high-frequency currents in an evacuated glass tube for the purpose of studying high voltage phenomena. Tesla called his invention an "inert gas discharge tube". The modern plasma lamp design was developed by James Falk and MIT student Bill Parker.

Gas-discharge lamps are a family of artificial light sources that generate light by sending an electric discharge through an ionized gas, a plasma.

Typically, such lamps use anoble gas (argon, neon, krypton, and xenon) or a mixture of these gases. Some include additional substances, such as mercury, sodium, and metal halides, which are vaporized during start-up to become part of the gas mixture.