Xenon
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| Name, Symbol, Number | xenon, Xe, 54 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | noble gases | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group, Period, Block | 18, 5, p | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | colorless | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Standard atomic weight | 131.293(6) g·mol−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electron configuration | [Kr] 4d10 5s2 5p6 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electrons per shell | 2, 8, 18, 18, 8 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Physical properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Phase | gas | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Density | (0 °C, 101.325 kPa) 5.894 g/L | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Melting point | 161.4 K (-111.7 °C, -169.1 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Boiling point | 165.03 K (-108.12 °C, -162.62 °F) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Triple point | 161.405 K, 81.6 kPa[1] | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Critical point | 289.77 K, 5.841 MPa | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat of fusion | 2.27 kJ·mol−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat of vaporization | 12.64 kJ·mol−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Heat capacity | (25 °C) 20.786 J·mol−1·K−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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| Atomic properties | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Crystal structure | cubic face centered | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Oxidation states | 0, +1, +2, +4, +6, +8 (rarely more than 0) (weakly acidic oxide) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Electronegativity | 2.6 (scale Pauling) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Ionization energies | 1st: 1170.4 kJ/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 2nd: 2046.4 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 3rd: 3099.4 kJ/mol | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Atomic radius (calc.) | 108 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Covalent radius | 130 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Van der Waals radius | 216 pm | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Miscellaneous | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Magnetic ordering | nonmagnetic | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Thermal conductivity | (300 K) 5.65 m W·m−1·K−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Speed of sound | (liquid) 1090 m/s | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| CAS registry number | 7440-63-3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Xenon (IPA: /ˈzɛnɒn, ˈziːnɒn/) is a chemical element that has the symbol Xe and atomic number 54. A colorless, heavy, odorless noble gas, xenon occurs in the earth's atmosphere in trace amounts and was part of the first noble gas compound synthesized.[2][3] It has many uses such as Xenon lamps, IMAX film projection systems and as a general anesthetic.
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[edit] Notable characteristics
Xenon is a member of the zero-valence elements that are called noble or inert gases. In a gas filled tube, xenon emits a blue glow when the gas is excited by electrical discharge. Using gigapascals of pressure, xenon has been forced into a metallic phase.[4] Although nearly inert, xenon can be oxidized by powerful oxidizing agents, and at least 80 compounds of this noble gas have been synthesized. Xenon can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.
[edit] Applications
This gas is most widely and most famously used in light-emitting devices called xenon flash lamps, which are used in photographic flashes and stroboscopic lamps, to excite the active medium in lasers which then generate coherent light, to produce laser power for inertial confinement fusion, 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, typical 35mm and IMAX film projection systems, automotive HID headlights and other specialized uses. They are an excellent source of short wavelength ultraviolet radiation and they have intense emissions in the near infrared, which are used in some night vision systems. Other uses of xenon:
- Has been used as a general anesthetic, though it is expensive. Even so, anesthesia machines that can deliver xenon are about to appear on the European market. [5] Two kinds of mechanism have been proposed. The first one involves the inhibition of the calcium ATPase pump in synaptic plasma membranes,[6] which results from a conformational change when xenon binds to nonpolar sites inside the protein.[7] The second mechanism focuses on the non-specific interactions between the anesthetic and the lipid membrane.[8]
- 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 133Xe is useful as a radioisotope.
- Hyperpolarized MRI of the lungs and other tissues using 129Xe.[9]
- Preferred fuel for Ion propulsion because of high atomic 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 an ion engine than other fuels such as mercury or caesium. Europe's SMART-1 spacecraft utilized xenon in its engines.[10]
- Xenon is used in protein crystallography. Applied at high pressure (~600 psi) to a protein crystal, xenon atoms bind in predominantly hydrophobic cavities, often creating a high quality, isomorphous, heavy-atom derivative.[11]
- Xenon difluoride is used as an etchant for silicon, particularly in the production of microelectromechanical systems, or MEMS[12].
[edit] History
Xenon (from Greek ξένον meaning "strange one" or "stranger") was discovered in England by William Ramsay and Morris Travers on July 12, 1898, shortly after their discovery of the elements krypton and neon. They found it in the residue left over from evaporating components of liquid air.[13]
[edit] Occurrence
Xenon is a trace gas in Earth's atmosphere, occurring in one part in twenty million.[14] 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. Radioactive species of xenon, for example 133Xe and 135Xe are produced by neutron irradiation of fissionable material within nuclear reactors. Like the noble gas krypton, xenon can also be extracted by fractional distillation or liquefaction of liquid air and by selective adsorption on activated carbon.[15]
[edit] Compounds
Xenon and the other noble gases had for a long time been considered to be completely chemically inert and not able to form compounds. However, in 1962 at the University of British Columbia, the first xenon compound, xenon hexafluoroplatinate, was synthesized by Neil Bartlett.[16] Now, many compounds of xenon are known, including xenon difluoride, xenon tetrafluoride, xenon hexafluoride, xenon tetroxide, xenon hydrate, xenon deuterate, and sodium perxenate. A 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.
Recently at the University of Helsinki in Finland, a group of scientists (M. Räsänen et al.) prepared HXeH, HXeOH, and HXeCCH (xenon dihydride, xenon hydride-hydroxide, and hydroxenoacetylene). They are stable up to 40K.[17]
[edit] Isotopes
Naturally occurring xenon is made of nine stable isotopes. (124Xe, 134Xe and 136Xe are predicted to undergo double beta decay, but this has never been observed, so they are considered to be stable.)[18][19] Beyond these stable forms, there are over 40 unstable isotopes that have been studied. 129Xe is produced by beta decay of 129I (half-life: 16 million years); 131mXe, 133Xe, 133mXe, and 135Xe are some of the fission products of both 235U and 239Pu, and therefore used as indicators of nuclear explosions.
The artificial isotope 135Xe is of considerable significance in the operation of nuclear fission reactors. 135Xe has a huge cross section for thermal neutrons, 2.65x106 barns, so it acts as a neutron absorber or "poison" that can slow or stop the chain reaction after a period of operation. This was discovered in the earliest nuclear reactors built by the American Manhattan Project for plutonium production. Fortunately the designers had made provisions in the design to increase the reactor's reactivity (the number of neutrons per fission that go on to fission other atoms of nuclear fuel).
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 222Rn.
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 129Xe 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.[20]
[edit] 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.
The speed of sound in xenon is slower than that in air (due to the slower average speed of the heavy xenon atoms compared to nitrogen and oxygen molecules), so xenon lowers the resonant frequencies of the vocal tract when inhaled. This produces a characteristic lowered voice pitch, opposite the high-pitched voice caused by inhalation of helium. Like helium, xenon does not satisfy the body's need for oxygen and is a simple asphyxiant; consequently, many universities no longer allow the voice stunt as a general chemistry demonstration. As xenon is expensive, the gas sulfur hexafluoride, which is similar to xenon in molecular weight (146 vs 131), is generally used in this stunt, although it too is an asphyxiant.
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, such that xenon would be purged from the lungs within a breath or two. There is, however, 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, though the potential for danger exists any time a tank or container of xenon is kept in an unventilated space.