History, Occurrence, and Uses
Xenon was discovered by Ramsay and Travers in 1898 while purifying krypton by fractional distillation. The name is from the Greek word zenos meaning “Stranger.”
Xenon occurs in the atmosphere at trace concentrations. It also occurs in gases from certain mineral springs. Xenon also is a fission product of uranium, plutonium, and thorium isotopes induced by neutron bombardment. The radioactive fission product, xenon-135, has a very high thermal neutron crosssection. The element has been detected in Mars’ atmosphere.
Xenon is a filling gas for light bulbs in high-intensity lamps and in flash lamps for photography. It forms a beautiful blue glow under vacuum in an electric discharge tube. It also is used in lamps that excite ruby lasers to produce coherent light. Xenon gas is a filler in proportional radiation counters and liquid xenon bubble chambers. Xenon is an anesthetic gas in surgery.
Radioactive xenon is a biological tracer.
Xenon is recovered from air by liquefaction and fractional distillation. Usually it is obtained as a by-product of making other noble gases. It is collected in the liquid oxygen fraction along with krypton, acetylene, and other hydrocarbons that may be present in air. The xenon fraction is flash vaporized. Hydrocarbons present are separated by burning over a catalyst. Xenon is absorbed on silica gel at low temperatures. Finally, it is separated from krypton by selective absorption and desorption from charcoal.
Although xenon has the stable octet configuration and is thought to be as inert as other noble gases, several xenon compounds have been prepared. The first xenon compound synthesized by N. Bartlett in 1962 was a red solid, XePtF6, made by the reaction of xenon with platinum hexafluoride undergoing the following oxidation sequence.
Xe + 2PtF6 −−−→ [XeF+] [PtF6–] + PtF5 −−−→ [XeF+] [PtF11–]
Xenon forms three binary fluorides, XeF2, XeF4, and XeF6. Fluorine is the only element with which xenon reacts directly forming XeF2. Reactions occur with excess xenon under pressure:
Xe + F2 → XeF2 −−−→ XeF4 −−−→ XeF6
Bartlett prepared xenon difluoride by the reaction of xenon with silver fluoride in hydrofluoric acid in the presence of boron trifluoride:
2AgF2 + 2BF3 + Xe → XeF2 + 2AgBF4
Xenon tetrafluoride also can be prepared by oxidizing xenon with dioxygen difluoride, O2F2, or by photolysis of xenon-fluorine mixture.
All other compounds of xenon are made from xenon fluorides.
Compounds in oxidation states +2, +4, +6, and +8 are well known. The tetrafluoride and hexafluoride are readily hydrolyzed by water forming xenon trioxide, XeO3, and the xenon tetraoxide, XeO4, both of which are dangerously explosive. While the trioxide XeO3 is a colorless crystalline solid, stable in solution, the tetraoxide XeO4 is a colorless unstable gas.
The oxyfluoride, XeOF4 is a stable colorless liquid produced by the reaction of xenon hexafluoride with sodium nitrate:
XeF6 + NaNO3 → XeOF4 + FNO2 + NaF
The oxodifluoride, XeOF2, dioxodifluoride, XeO2F2 and the trioxodifluoride, XeO3F2 all are unstable.
Xenon also forms many fluoroanions and their salts, mostly prepared from xenon tetrafluoride and hexafluoride. Such compounds include Na+XeF5¯ and Cs+XeF7¯ formed by reactions of xenon fluorides with sodium fluoride or cesium fluoride. The dicesium xenon octafluoride, Cs2XeF8, is a stable yellow solid that decomposes above 400°C.
Krypton, neon, and xenon are rare atmospheric gases. Each is odorless, colorless, tasteless, nontoxic, monatomic, and chemically inert.
All three together constitute less than 0.002
percent of the atmosphere with approximate
concentrations in the atmosphere of 18 ppm for
neon, 1.1 ppm for krypton, and 0.09 ppm for
xenon. Few users of the three gases need them
in bulk quantities, and the three are shipped
most often in single cylinders and glass liter
flasks.
Radon, a radioactive rare gas, is not treated in
this book because it has little or no practical
application at present. It is the heaviest gas
known (density at 70°F and 1 atm, 0.61 Ib/ft3; at
21.1°C and 1 atm, 9.8 kg/m3.
Among the rare gases, neon, krypton, and xenon in particular ionize at lower voltages than
other gases, and the brilliant, distinctive light
they emit while conducting electricity in the
ionized state accounts for one of their primary
uses. Their characteristic colors as ionized conductors are red for neon, yellow-green for
krypton, and blue to green for xenon. Similarly,
argon and helium are also used for this purpose
and emit red or blue for argon and yellow for
helium. These latter two gases are treated in
separate monographs.
Colorless, odorless gas or liquid. Gas
(at STP) has d 5.8971 g/L (air = 1.29 g/L), dielectric
constant 1.0012 (25C) (1 atm); liquid has bp
108.12C (1 mm Hg), d (at bp) of 1.987 g/cc; liquefaction
temp106.9C.Chemically unreactive but
not completely inert. Noncombustible.
Xenon has a relatively high atomic weight and is about 4.5 times heavier than air. It is colorless,tasteless, and odorless. Its critical temperature is comparatively high at 16.6°C, which isfar above oxygen (–188°C). This means that xenon will boil away from commercial fractionaldistillation of liquid oxygen.
Xenon’s melting point is –111.79°C, its boiling point is –108.12°C, and its density is0.005887g/cm3.
There are 46 isotopes of xenon. Nine of these are stable. Two of the stableisotopes are radioactive, but with half-lives long enough to be considered stable.They are Xe-124 (1.1×10+17years) and Xe-136 (3.6×10+20 years). The 47 manmadeartificial radioactive isotopes have half-lives ranging from 150 nanoseconds to11.9 days.
The word “xenon” is derived from the Greek word xenon, meaning
“stranger.”
Xenon is found in trace amounts in the atmosphere. It makes up just 0.086 ppm by volumeof air. Xenon is the rarest of the noble gases. For every thousand-million atoms of air, thereare only 87 atoms of xenon. Even so, it is recovered in commercial amounts by boiling off thexenon from fractional distillation of liquid air. Small amounts of xenon have been found insome minerals and meteorites, but not in amounts great enough to exploit.
Xenon is noncombustible, and even though it is considered inert, it will combine with afew elements (i.e., oxygen, fluorine, and platinum). Xenon is the only member of group 18that exhibits all of the even valence states of +2, +4, +6, and +8. It has similar oxidation stateseven though most periodic tables list a single oxidation state of zero.
Xenon was discovered by William Ramsay and Morris Travers in July 1898 at University College London. They had already extracted neon, argon, and krypton from liquid air, and wondered if it contained other gases. The wealthy industrialist Ludwig Mond gave them a new liquid-air machine and they used it to extract more of the rare gas krypton. By repeatedly distilling this, they eventually isolated a heavier gas, and when they examined this in a vacuum tube it gave a beautiful blue glow. They realised it was yet another member of the ‘inert’ group of gaseous elements as they were then known because of their lack of chemical reactivity. They called the new gas xenon. It was this gas which Neil Bartlett eventually showed was not inert by making a fluorine derivative in 1962. So far more than 100 xenon compounds have been made.The element is available in sealed glass containers for about $20/L of gas at standard pressure. Xenon is not toxic, but its compounds are highly toxic because of their strong oxidizing characteristics.
When excited electrically, xenon (sometimes mixed with krypton) produces a brilliantwhite flash of light that makes it useful as the gas in strobe lights. The flash used in photog-raphy can repeatedly be used to provide a well-balanced light for illumination. The xenon inflash tubes is not consumed and can be flashed over and over again.
Xenon lamps are also used as an antiseptic to kill bacteria, to power lasers, and as tracers.Because of its high atomic mass, xenon ions are preferred as fuel for ion engines to powerspacecraft in deep space.
Luminescent tubes, flash lamps in photography,
fluorimetry, lasers, tracer studies, anesthesia.
Neon, krypton, and xenon are used principally
to fill lamp bulbs and tubes. The electronics
industry uses them singly or in mixtures in many
types of gas-filled electron tubes (among them, voltage regulator tubes, starter tubes, phototubes, counter tubes, T.R. tubes, xenon thryatron tubes, halfwave xenon rectifier tubes, and
Geiger-Muller tubes). Large quantities of neon
(as well as of atmospheric helium and specially
purified argon) are used as fill gases in illuminated signs. Small quantities of krypton and
xenon are used for special effects.
In the lamp industry, the three gases serve as
fill gas in specialty lamps, neon glow lamps,
100-watt fluorescent lamps, ultraviolet sterilizing lamps, and very high-output lamps. The
three gases have additional applications in the
atomic energy field as fill gas for ionization
chambers, bubble chambers, gaseous scintillation counters, and other detection and measurement devices.
xenon: Symbol Xe. A colourless odourless gas belonging to group 18 of the periodic table (see noble gases); a.n. 54; r.a.m. 131.30; d. 5.887 g dm–3; m.p. –111.9°C; b.p. –107.1°C. It is present in the atmosphere (0.00087%) from which it is extracted by distillation of liquid air. There are nine natural isotopes with mass numbers 124, 126, 128–132, 134, and 136. Seven radioactive isotopes are also known. The element is used in Ûuorescent lamps and bubble chambers. Liquid xenon in a supercritical state at high temperatures is used as a solvent for infrared spectroscopy and for chemical reactions. The compound Xe+PtF6– was the Ürst noblegas compound to be synthesized. Several other compounds of xenon are known, including XeF2, XeF4, XeSiF6, XeO2F2, and XeO3. Recently, compounds have been isolated that contain xenon–carbon bonds, such as [C6H5Xe][B(C6H5)3F] (pentafluorophenylxenon fluoroborate), which is stable under normal conditions. The element was discovered in 1898 by Ramsey and Travers.
A colorless odorless
monatomic element of the rare-gas group.
It occurs in trace amounts in air. Xenon is
used in electron tubes and strobe lighting.
Symbol: Xe; m.p. –111.9°C; b.p.
–107.1°C; d. 5.8971 (0°C) kg m–3; p.n. 54;
r.a.m. 131.29.
Xenon is an inert gas that is nonflammable and nonexplosive.The outer shell of xenon is complete thus it is not ahighly reactive compound neither seeking, nor donatingelectrons to biological molecules. Despite its “inert” status,xenon has been shown to interact with biological moleculesby forming an induced dipole in the presence of a cationicsite. An induced dipole could also result from an interactionwith another fleeting dipole formed at the proposedbinding site to form an induced dipole-induced dipole orLondon dispersion force.The mechanism of xenon anesthesiaand the site of action are still unknown.
As a noble gas that is mostly inert, xenon is nontoxic and noncombustible. Some of itscompounds are toxic and potentially explosive, but there is little chance of coming into contactwith them on a day-to-day basis.
Xenon, another gas occurring in the air to theextent of 1 part in 11 million, is the heaviestof the rare gases. When atomic reactors are operated at high power, xenon tends to buildup as a reaction product, poisoning the fuel andreducing the reactivity. Xenon lamps for militaryuse give a clear white light known as sunlightplus north-sky light. This color does notchange with the voltage, and thus the lampsrequire no voltage regulators. Xenon is a mildanesthetic; the accumulation from air helps toinduce natural sleep, but it cannot be used insurgery since the quantity needed producesasphyxiation.
Gaseous neon, krypton, and xenon are noncorrosive and inert, so they may be contained in
systems constructed of any common metals designed to withstand safely the pressures involved. At the temperatures encountered with
liquid neon, krypton, and xenon, ordinary carbon steels and most alloy steels lose their ductility and are considered unsafe for use with
these cryogenic liquids. Satisfactory materials
for use with liquid neon, krypton, and xenon
include austenitic stainless steel (for example
types 304 and 316) and other nickel-chromium
alloys, copper, Monel, brass, and aluminum.
An inert gas that acts as
a simple asphyxiant. For a dscussion of
toxicity effects, see ARGON. A common air
contaminant.
Neon, krypton, and xenon are nontoxic and
largely inert. They can act as simple asphyxiants
by displacing air, thereby diluting the concentration of oxygen below levels necessary to support life. Inhalation in excessive concentrations
can result in dizziness, nausea, vomiting, loss of
consciousness, and death. Death may result
from errors in judgment, confusion, or loss of
consciousness, which prevents self-rescue. At
low-oxygen concentrations, unconsciousness
and death may occur in seconds without warning.
Gaseous neon, krypton, and xenon must be handled with all the precautions necessary for
safety with any nonflammable, nontoxic compressed gas.
All precautions necessary for the safe handling of any gas liquefied at very low temperatures must be observed with liquid neon, krypton, and xenon. Extensive tissue damage or
bums can result from exposure to liquid neon,
krypton, or xenon or their cold vapors.
CGA P-l, Safe Handling of Compressed
Gases in Containers, provides basic guidelines
and requirements for the safe handling and storage of compressed gas cylinders. Also
refer to CGA P-12, Safe Handling of Cryogenic
Liquids, for information concerning safe handling of neon, krypton, and xenon in liquid form. Another useful reference concerning inert
gases is CGA P-14, Accident Prevention in
Oxygen-Rich and Oxygen-Deficient Atmospheres.
When disposal becomes necessary, vent neon,
krypton, and xenon gas slowly to a
well-ventilated outdoor location remote from
personnel work areas and building air intakes.
Do not dispose of any residual neon, krypton,
and xenon in compressed gas cylinders. Return
cylinders to the supplier with residual pressure,
the cylinder valve tightly closed, and the valve
caps in place.
Allow liquid neon, krypton, and xenon to
evaporate in well-ventilated outdoor locations
that are remote from work areas.
Neon, krypton, and xenon are available in various grades for industrial, medical, and advanced
technology uses. Neon is available with a minimum purity ranging from 75 mole percent to
99.999 mole percent. Krypton and xenon are
each available with a minimum purity ranging
from 99.95 mole percent to 99.997 mole percent.
