Xenon

Xenon
Name	Xenon
Number	54
Category	Noble gas
Group	18
Appearance	Colorless gas, exhibiting a blue glow when placed in a high-voltage electric field
Standard atomic weight	131.293(6)
Electron configuration	[Kr] 4d10 5s2 5p6
Phase	Gas
Melting point	161.40 K
Boiling point	165.051 K
Density	5.894 g/L
Triple point	161.405 K, 81.77 kPa
Critical point	289.733 K, 5.842 MPa
Heat of fusion	2.27 kJ/mol
Heat of vaporization	12.64 kJ/mol
Molar heat capacity	21.01 J/(mol·K)
Atomic radius	108 pm
Covalent radius	140±9 pm
Van der Waals radius	216 pm
Crystal structure	Face-centered cubic
Thermal conductivity	5.65×10−3 W/(m·K)
Magnetic ordering	Diamagnetic
CAS number	7440-63-3
Isotopes link	Isotopes of xenon

Xenon. It is a heavy, colorless, dense noble gas found in trace amounts in the Earth's atmosphere. Discovered in 1898 by William Ramsay and Morris Travers, it is notable for its relative reactivity among the noble gases, forming a variety of chemical compounds. Its unique properties, including its ability to produce intense light when electrically excited, have led to applications ranging from specialized lighting to medical imaging and propulsion.

Properties

Under standard conditions, it exists as a monatomic gas and is the heaviest of the stable noble gases found in significant quantities. It exhibits a brilliant blue or lavender glow when placed in a discharge tube, a property utilized in flash lamps and certain laser systems. Unlike lighter noble gases like helium or neon, it has a high atomic mass and density, making it useful in applications requiring a heavy, inert atmosphere. Its ionization energy is relatively low compared to other noble gases, which contributes to its unexpected chemical reactivity. Spectroscopic studies of its emission lines have been historically important, with the definition of the International System of Units for length once being based on a specific emission line from an excited atom.

History

The element was isolated in July 1898 by the Scottish chemist William Ramsay and his English colleague Morris Travers at University College London. They discovered it as a residual component left after repeatedly fractionating liquefied air to isolate krypton and argon. The name derives from the Greek word *xenos*, meaning "stranger," reflecting its elusive nature. For decades, it and other noble gases were considered completely inert, a concept challenged in 1962 when Neil Bartlett created the first noble gas compound, xenon hexafluoroplatinate. This groundbreaking work at the University of British Columbia fundamentally altered chemical bonding theory and opened the field of noble gas chemistry.

Occurrence and production

It is exceptionally rare in the Solar System and on Earth, present in the atmosphere at a concentration of approximately 0.087 parts per million by volume. It is obtained commercially as a byproduct of the industrial separation of air into oxygen and nitrogen using large-scale cryogenic air separation plants, primarily operated by companies like Linde plc and Air Products. During this process, the rare components of liquid air, including krypton and neon, are collected and further purified. Trace amounts of various isotopes of xenon, such as Xe-129 and Xe-136, are produced in nuclear reactors and are studied in fields like neutrino physics.

Compounds

Despite being a noble gas, it forms a diverse array of chemical compounds, primarily with highly electronegative elements like fluorine and oxygen. The most common and stable compounds are the fluorides, including xenon difluoride, xenon tetrafluoride, and xenon hexafluoride. Under specific conditions, it can also form oxides like xenon trioxide and the explosive xenon tetroxide. The synthesis of xenon hexafluoroplatinate by Neil Bartlett proved that noble gases could participate in chemical reactions. Research into its chemistry continues at institutions like the Argonne National Laboratory, exploring compounds with elements such as carbon and even gold.

Applications

Its primary use is in high-intensity lighting, where it fills flash lamps used in photography, strobe lights, and lighthouses. It is the gas of choice in ion thrusters for spacecraft propulsion, such as those on NASA's Deep Space 1 and DAWN missions, due to its high atomic mass and inertness. In medicine, the stable isotope Xe-129 is used as a contrast agent in hyperpolarized Magnetic Resonance Imaging to study lung ventilation. It also serves as a general anesthetic, marketed under names like Xenleta, and is used in specialized laser systems, including excimer lasers for photolithography in semiconductor manufacturing.

Biological role and hazards

The element has no known biological role and is not essential for any life processes. As a simple asphyxiant, it can displace oxygen in confined spaces, posing a risk of hypoxia. When used as an anesthetic, it has minimal side effects and is rapidly eliminated from the body, but it can increase cerebral blood flow. Its radioactive isotope Xe-133 is used in nuclear medicine for ventilation scintigraphy to image the lungs. Environmental release of certain isotopes can occur from nuclear fuel reprocessing plants, such as Sellafield, and is monitored as part of Comprehensive Nuclear-Test-Ban Treaty verification regimes.

Category:Noble gases Category:Chemical elements