Xenon – facts and properties

Position in the periodic table

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Occurrence and extraction

Xenon is one of the rarest gases in air. Roughly one in eleven million particles in the atmosphere is a xenon atom. It is therefore obtained only as a by-product of air liquefaction, in which air is separated into its components by distillation. Oxygen, nitrogen and argon are produced in large amounts, xenon only in small ones. That makes it expensive.

Xenon was discovered in 1898 by the British chemists William Ramsay and Morris Travers. They let liquid air evaporate and examined the heaviest residue, which was the last to remain. In its spectrum they found new lines and recognised another noble gas. They named it xenon, from the Greek xenos, the stranger. Shortly before, they had found krypton and neon in the same way.

Properties and reactions

Xenon is in period 5 and group 18, below krypton and above radon. In the period, iodine lies to its left. Its electron configuration is [Kr] 4d¹⁰ 5s² 5p⁶ and its electronegativity is 2.6. The element has 8 valence electrons, so the outer shell is full. The density is 5.89 g/L, the melting point -111.79 °C and the boiling point -108.12 °C. Xenon is a monatomic gas and does not conduct electricity unless it is ionised.

Thanks to the full outer shell, xenon hardly reacts. Because its atoms are large and the outer electrons are loosely held, however, it is the most reactive of the stable noble gases. In 1962 the chemist Neil Bartlett made the first noble gas compound, using platinum hexafluoride. Soon afterwards the xenon fluorides XeF₂, XeF₄ and XeF₆ were made by reacting xenon with fluorine. This discovery disproved the belief that noble gases form no compounds. Xenon oxides are also known, and xenon trioxide is explosive. Fluorine is the most reactive nonmetal, which is why it can bond even to xenon.

Xenon is not toxic. In large amounts, however, it displaces oxygen from the air we breathe and can cause suffocation. In high concentrations it acts as an anaesthetic, which is the basis of its medical use.

Uses in everyday life and technology

When an electric current passes through xenon, the gas gives off a bright, bluish-white light that resembles daylight. This is used in xenon arc lamps for film projectors and searchlights, and in flash tubes for camera flashes and strobe lights. Xenon headlamps in cars give white light but are increasingly being replaced by LEDs.

Space probes use xenon as propellant in ion thrusters. Xenon atoms are electrically charged and strongly accelerated by an electric field. The thrust is small, but the drive is very economical and can run for months. The Dawn probe travelled in this way to the asteroid Vesta and the dwarf planet Ceres. Xenon is suited to this because it is heavy, non-toxic and unreactive.

In medicine, xenon serves as an anaesthetic gas. It acts quickly and is gentle on the circulation, but it is so expensive that it is rarely used. For imaging the lungs in magnetic resonance scans, xenon-129 is also used, whose atomic nuclei have first been aligned with laser light.

In chemistry, xenon difluoride is a reagent that transfers fluorine, and it is used to etch silicon in microtechnology.

Quick question

Noble gases have very high ionization energies, so they never react - why does that still not hold for xenon (Xe)?

FAQ