Xenon
2007 Schools Wikipedia Selection. Related subjects: Chemical elements
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| General | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Name, Symbol, Number | xenon, Xe, 54 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Chemical series | noble gases | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Group, Period, Block | 18, 5, p | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Appearance | colorless |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Atomic mass | 131.293 (6) g/mol | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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) |
||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 (Pauling scale) | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 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 mW·m−1·K−1 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Speed of sound | (liquid) 1090 m/s | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| CAS registry number | 7440-63-3 | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| Selected isotopes | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| References | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Xenon ( IPA: /ˈzɛnɒn, ˈziːnɒn/) is a chemical element in the periodic table 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.
Notable characteristics
Xenon is a member of the zero- valence elements that are called noble or inert gases, however, "inert" is not a completely accurate description of this chemical series since some noble gas compounds have been synthesized. In a gas filled tube, xenon emits a blue glow when the gas is excited by electrical discharge. Using tens of gigapascals of pressure, xenon has been forced into a metallic phase. 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, 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 colour temperature closely approximating noon sunlight and are used in solar simulators, some projection systems, automotive HID headlights 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:
- Has been used as a general anaesthetic, though the cost is prohibitive.
- 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.
- 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 an ion engine than other fuels such as mercury or cesium. Europe's SMART-1 spacecraft utilized Xenon in its engines.
- Is commonly 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.
History
Xenon ( Greek ξένος meaning "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.
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.
Extraction
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.
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. 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 40 K.
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.
The artificial isotope Xe-135 is of considerable significance in the operation of nuclear fission reactors. Xe-135 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 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 denser 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 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.