Xenon,  54Xe
Xenon discharge tube.jpg
A xenon-filled discharge tube glowing light blue
Appearancecolorless gas, exhibiting a blue glow when placed in an electric field
Standard atomic weight Ar, std(Xe)131.293(6)[3]
Xenon in the periodic table
CaesiumBariumLanthanumCeriumPraseodymiumNeodymiumPromethiumSamariumEuropiumGadoliniumTerbiumDysprosiumHolmiumErbiumThuliumYtterbiumLutetiumHafniumTantalumTungstenRheniumOsmiumIridiumPlatinumGoldMercury (element)ThalliumLeadBismuthPoloniumAstatineRadon


Atomic number (Z)54
Groupgroup 18 (noble gases)
Periodperiod 5
Element category  Noble gas
Electron configuration[Kr] 4d10 5s2 5p6
Electrons per shell
2, 8, 18, 18, 8
Physical properties
Phase at STPgas
Melting point161.40 K ​(−111.75 °C, ​−169.15 °F)
Boiling point165.051 K ​(−108.099 °C, ​−162.578 °F)
Density (at STP)5.894 g/L
when liquid (at b.p.)2.942 g/cm3[4]
Triple point161.405 K, ​81.77 kPa[5]
Critical point289.733 K, 5.842 MPa[5]
Heat of fusion2.27 kJ/mol
Heat of vaporization12.64 kJ/mol
Molar heat capacity21.01[6] J/(mol·K)
Vapor pressure
P (Pa)1101001 k10 k100 k
at T (K)8392103117137165
Atomic properties
Oxidation states0, +1, +2, +4, +6, +8 (rarely more than 0; a weakly acidic oxide)
ElectronegativityPauling scale: 2.6
Ionization energies
  • 1st: 1170.4 kJ/mol
  • 2nd: 2046.4 kJ/mol
  • 3rd: 3099.4 kJ/mol
Covalent radius140±9 pm
Van der Waals radius216 pm
Color lines in a spectral range
Spectral lines of xenon
Other properties
Natural occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for xenon
Speed of soundgas: 178 m·s−1
liquid: 1090 m/s
Thermal conductivity5.65×10−3 W/(m·K)
Magnetic orderingdiamagnetic[7]
Magnetic susceptibility−43.9·10−6 cm3/mol (298 K)[8]
CAS Number7440-63-3
Discovery and first isolationWilliam Ramsay and Morris Travers (1898)
Main isotopes of xenon
Iso­topeAbun­danceHalf-life (t1/2)Decay modePro­duct
124Xe0.095%1.8×1022 y[9]εε124Te
125Xesyn16.9 hε125I
127Xesyn36.345 dε127I
133Xesyn5.247 dβ133Cs
135Xesyn9.14 hβ135Cs
136Xe8.857%2.165×1021 y[10]ββ136Ba
| references

Xenon is a chemical element with the symbol Xe and atomic number 54. It is a colorless, dense, odorless noble gas found in Earth's atmosphere in trace amounts.[11] Although generally unreactive, xenon can undergo a few chemical reactions such as the formation of xenon hexafluoroplatinate, the first noble gas compound to be synthesized.[12][13][14]

Xenon is used in flash lamps[15] and arc lamps,[16] and as a general anesthetic.[17] The first excimer laser design used a xenon dimer molecule (Xe2) as the lasing medium,[18] and the earliest laser designs used xenon flash lamps as pumps.[19] Xenon is used to search for hypothetical weakly interacting massive particles[20] and as the propellant for ion thrusters in spacecraft.[21]

Naturally occurring xenon consists of seven stable isotopes and two long-lived radioactive isotopes. More than 40 unstable xenon isotopes undergo radioactive decay, and the isotope ratios of xenon are an important tool for studying the early history of the Solar System.[22] Radioactive xenon-135 is produced by beta decay from iodine-135 (a product of nuclear fission), and is the most significant (and unwanted) neutron absorber in nuclear reactors.[23]


Xenon was discovered in England by the Scottish chemist William Ramsay and English chemist Morris Travers in September 1898,[24] shortly after their discovery of the elements krypton and neon. They found xenon in the residue left over from evaporating components of liquid air.[25][26] Ramsay suggested the name xenon for this gas from the Greek word ξένον xénon, neuter singular form of ξένος xénos, meaning 'foreign(er)', 'strange(r)', or 'guest'.[27][28] In 1902, Ramsay estimated the proportion of xenon in the Earth's atmosphere to be one part in 20 million.[29]

During the 1930s, American engineer Harold Edgerton began exploring strobe light technology for high speed photography. This led him to the invention of the xenon flash lamp in which light is generated by passing brief electric current through a tube filled with xenon gas. In 1934, Edgerton was able to generate flashes as brief as one microsecond with this method.[15][30][31]

In 1939, American physician Albert R. Behnke Jr. began exploring the causes of "drunkenness" in deep-sea divers. He tested the effects of varying the breathing mixtures on his subjects, and discovered that this caused the divers to perceive a change in depth. From his results, he deduced that xenon gas could serve as an anesthetic. Although Russian toxicologist Nikolay V. Lazarev apparently studied xenon anesthesia in 1941, the first published report confirming xenon anesthesia was in 1946 by American medical researcher John H. Lawrence, who experimented on mice. Xenon was first used as a surgical anesthetic in 1951 by American anesthesiologist Stuart C. Cullen, who successfully used it with two patients.[32]

An acrylic cube specially prepared for element collectors containing liquefied xenon

Xenon and the other noble gases were for a long time considered to be completely chemically inert and not able to form compounds. However, while teaching at the University of British Columbia, Neil Bartlett discovered that the gas platinum hexafluoride (PtF6) was a powerful oxidizing agent that could oxidize oxygen gas (O2) to form dioxygenyl hexafluoroplatinate (O+
).[33] Since O2 and xenon have almost the same first ionization potential, Bartlett realized that platinum hexafluoride might also be able to oxidize xenon. On March 23, 1962, he mixed the two gases and produced the first known compound of a noble gas, xenon hexafluoroplatinate.[34][14]

Bartlett thought its composition to be Xe+[PtF6], but later work revealed that it was probably a mixture of various xenon-containing salts.[35][36][37] Since then, many other xenon compounds have been discovered,[38] in addition to some compounds of the noble gases argon, krypton, and radon, including argon fluorohydride (HArF),[39] krypton difluoride (KrF2),[40][41] and radon fluoride.[42] By 1971, more than 80 xenon compounds were known.[43][44]

In November 1989, IBM scientists demonstrated a technology capable of manipulating individual atoms. The program, called IBM in atoms, used a scanning tunneling microscope to arrange 35 individual xenon atoms on a substrate of chilled crystal of nickel to spell out the three letter company initialism. It was the first time atoms had been precisely positioned on a flat surface.[45]

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