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Xenon

From Academic Kids

iodinexenon
Kr
Xe  
Rn 
 
Image:Xe-TableImage.png
General
Name, Symbol, Number xenon, Xe, 54
Chemical series Noble gases
Group, Period, Block 18 (VIIIA), 5, p
Density, Hardness 5.9 kg/m3(273 K), NA
Appearance colorless
Atomic properties
Atomic weight 131.293 amu
Atomic radius (calc.) no data (108) pm
Covalent radius 130 pm
van der Waals radius 216 pm
Electron configuration [Kr]4d10 5s2 5p6
e- 's per energy level 2, 8, 18, 18, 8
Oxidation states (Oxide) 0, +2, +4, +6
(weak acid, rarely more than 0)
Crystal structure cubic face centered
Physical properties
State of matter gas (nonmagnetic)
Melting point 161.4 K (-169.1 ?F)
Boiling point 165.1 K (-162 ?F)
Heat of vaporization 12.636 kJ/mol
Heat of fusion 2.297 kJ/mol
Critical_pressure 5.84 MPa
Critical_temperature 61.9?F, 16.6?C
Vapor pressure NA
Speed of sound (in liquid) 1090 m/s
Miscellaneous
Electronegativity 2.6 (Pauling scale)
Specific heat capacity 158 J/(kg·K)
Electrical conductivity no data
Thermal conductivity 0.00569 W/(m·K)
1st ionization potential 1170.4 kJ/mol
2nd ionization potential 2046.4 kJ/mol
3rd ionization potential 3099.4 kJ/mol
Most stable isotopes
iso NA half-life DM DE DP
124Xe 0.1% 1,1 E17 y ε ε no data 124Te
126Xe 0.09% Xe is stable with 72 neutrons
127Xe {syn.} 36.4 d ε 0.662 127I
128Xe 1.91% Xe is stable with 74 neutrons
129Xe 26.4% Xe is stable with 75 neutrons
130Xe 4.1% Xe is stable with 76 neutrons
131Xe 21.29% Xe is stable with 77 neutrons
132Xe 26.9% Xe is stable with 78 neutrons
133Xe {syn.} 5.243 d Beta- 0.427 133Cs
134Xe 10.4% Xe is stable with 80 neutrons
136Xe 8.9% 2.36 E21 y Beta- no data 136Ba
SI units & STP are used except where noted.

Xenon is a chemical element in the periodic table that has the symbol Xe and atomic number 54. A colorless, very heavy, odorless noble gas, xenon occurs in the earth's atmosphere in trace amounts and was part of the first noble gas compound synthesized.

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Contents

Notable characteristics

Xenon is a member of the zero-valence elements that are called noble or inert gases. The word "inert" is no longer used to describe this chemical series since some zero valence elements do form compounds. In a gas filled tube, xenon emits a blue glow when the gas is excited by electrical discharge. Using tens of gigapascals of pressure, metallic xenon has been made. Xenon can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.

Applications

This gas is most widely and most famously used in light-emitting devices called Xenon flash lamps, which are used in photographic flashes, stroboscopic lamps, to excite the active medium in lasers which then generate coherent light, in bactericidal lamps (rarely), and in certain dermatological uses. Continuous, short-arc, high pressure xenon arc lamps have a color temperature closely approximating noon sunlight and are used in solar simulators, some projection systems, and other specialized uses. They are an excellent source of short wavelength ultraviolet light and they have intense emissions in the near infrared, which are used in some night vision systems. Other uses of Xenon:

  • Used as a general anaesthetic.
  • In nuclear energy applications it is used in bubble chambers, probes, and in other areas where a high molecular weight and inert nature is a desirable quality.
  • Perxenates are used as oxidizing agents in analytical chemistry.
  • The isotope Xe-133 is useful as a radioisotope.
  • Hyperpolarized MRI of the lungs and other tissues using 129Xe.[1] (http://imaging.med.virginia.edu/hyperpolarized/human.htm)
  • Preferred fuel for Ion propulsion because of high molecular weight, ease of ionization, store as a liquid at near room temperature (but at high pressure) yet easily converts back into a gas to fuel the engine, inert nature makes it environmentally friendly and less corrosive to ion engine then other fuels such a mercury or cesium. However, there is an emerging controversy over its possible future widespread use in the aerospace industry, as it is permanently lost to space, further decreasing the limited supply in the Earth's atmosphere.

History

Xenon (Greek xenon meaning "stranger") was discovered in England by William Ramsay and Morris Travers in 1898 in the residue left over from evaporating components of liquid air.

Occurrence

Xenon is a trace gas in Earth's atmosphere, occurring in one part in twenty million. The element is obtained commercially through extraction from the residues of liquefied air. This noble gas is naturally found in gases emitted from some mineral springs. Xe-133 and Xe-135 are synthesized by neutron irradiation within air-cooled nuclear reactors.

Missing image
Xenon_tetrafluoride.gif
XeF4 crystals. 1962.

Compounds

Before 1962, xenon and the other noble gases were generally considered to be chemically inert and not able to form compounds. Evidence since this time has been mounting that xenon, along with other noble gases, do in fact form compounds. Some of the xenon compounds are xenon difluoride, tetrafluoride, hexafluoride, hydrate, and deuterate, as well as sodium perxenate. The highly explosive compound xenon trioxide has also been made. There are at least 80 xenon compounds in which fluorine or oxygen is bonded to xenon. Some compounds of xenon are colored but most are colorless.

Isotopes

Naturally occurring xenon is made of seven stable and two slightly radioactive isotopes. Beyond these stable forms, there are 20 unstable isotopes that have been studied. Xe-129 is produced by beta decay of I-129 (half-life: 16 million years); Xe-131m, Xe-133, Xe-133m, and Xe-135 are some of the fission products of both U-235 and Pu-239, and therefore used as indicators of nuclear explosions.

Relatively high concentrations of radioactive xenon isotopes are also found emanating from nuclear reactors due to the release of this fission gas from cracked fuel rods or fissioning of uranium in cooling water. The concentrations of these isotopes are still usually low compared to naturally occurring radioactive noble gases such as Rn-222.

Because xenon is a tracer for two parent isotopes, Xe isotope ratios in meteorites are a powerful tool for studying the formation of the solar system. The I-Xe method of dating gives the time elapsed between nucleosynthesis and the condensation of a solid object from the solar nebula. Xenon isotopes are also a powerful tool for understanding terrestrial differentiation. Excess Xe-129 found in carbon dioxide well gases from New Mexico was believed to be from the decay of mantle-derived gases soon after Earth's formation.

Precautions

The gas can be safely kept in normal sealed glass containers at standard temperature and pressure. Xenon is non-toxic, but many of its compounds are toxic due to their strong oxidative properties.

Because xenon is heavier than air, the speed of sound in xenon is slower than that in air, and when inhaled, lowers the resonant frequencies of the vocal tract. This produces a characteristic lowered voice analogous to that caused by inhalation of helium. For several reasons, the inhalation of xenon is more dangerous than the inhalation of helium. First, xenon has poorly understood anaesthetic effects, similar to those of nitrous oxide. Inhalation can cause mild-to-moderate, short-lasting effects, including a pounding sensation associated with light and sound.

A myth exists that xenon is too heavy for the lungs to expel unassisted, and that after inhaling xenon, it is necessary to bend over completely at the waist to allow the excess gas to "spill" out of the body. In fact, the lungs mix gases very effectively and rapidly, so that a heavy gas would be purged from the lungs within a breath or two (in fact, carbon dioxide, which the lungs are designed to exhaust from the body, is quite heavy). There is a danger associated with any heavy gas in large quantities: it may sit invisibly in a container, and if a person enters a container filled with an odorless, colorless gas, they may find themselves breathing it unknowingly. Xenon is rarely used in large enough quantities for this to be a concern.

Because of the dangers associated with xenon inhalation, many universities no longer allow the practice as a general chemistry demonstration. Xenon is in any case quite expensive. The gas sulfur hexafluoride is generally used as a replacement.

References

  • Los Alamos National Laboratory – Xenon (http://periodic.lanl.gov/elements/54.html)
  • Thermophysical properties of neon, argon, krypton, and xenon / V. A. Rabinovich ... Theodore B. Selover, English-language edition ed.

Washington [u.a.] Hemisphere Publ. Corp. [u.a.] , 1988. - XVIII (National standard reference data service of the USSR ; 10)

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