Xe

Xe is a chemical element with the symbol Xe and atomic number 54. It is a noble gas in group 18 of the periodic table, existing as a colorless, odorless, monoatomic gas at standard conditions. Xenon is relatively heavy for a gas, with a density around 5.9 g/L and a boiling point of −108.1°C. It occurs in trace amounts in the Earth's atmosphere, about 0.087 parts per million by volume, and is collected by fractional distillation of liquid air.

Xenon is highly unreactive due to its closed-shell electron configuration, making it one of the least reactive elements. Nevertheless, it can form a small number of compounds under specific conditions, notably fluorides such as XeF2, XeF4, and XeF6, and oxides like XeO3. The first noble-gas compound discovered was xenon hexafluoroplatinate, reported in 1962, which demonstrated that inert gases can participate in chemistry under the right conditions. Xenon compounds are typically used in specialized chemical synthesis and Lighting and electronics applications.

In industry and technology, xenon has several important uses. It is employed in high-intensity discharge lamps, arc lamps, and some projection and flash lamps due to its bright, efficient light. Xenon is also used as a propellant in certain ion-thrust propulsion systems for spacecraft. Historically, xenon has been explored for anesthesia, but its high cost and rarity limit widespread use. Some xenon isotopes are used in medical imaging: 133Xe in ventilation imaging and hyperpolarized 129Xe in magnetic resonance imaging of the lungs.

Xenon has multiple isotopes, including several stable forms and radioactive varieties produced by fission. It was discovered in 1898 by William Ramsay and Morris Travers and named from the Greek xenos, meaning strange or foreign, reflecting its unexpected properties as a noble gas.