Xenon
Naturally occurring xenon consists of eight stable isotopes. There are also over 40 unstable isotopes that undergo radioactive decay. The isotope ratios of xenon are an important tool for studying the early history of the Solar System. Radioactive xenon-135 is produced from iodine-135 as a result of nuclear fission, and it acts as the most significant neutron absorber in nuclear reactors.
Xenon is used in flash lamps and arc lamps, and as a general anesthetic. The first excimer laser design used a xenon dimer molecule (Xe2) as its lasing medium, and the earliest laser designs used xenon flash lamps as pumps. Xenon is also being used to search for hypothetical weakly interacting massive particles and as the propellant for ion thrusters in spacecraft.
Occurrence and production
Xenon is a trace gas in Earth's atmosphere, occurring at 87±1 parts per billion (nL/L), or approximately 1 part per 11.5 million, and is also found in gases emitted from some mineral springs.
Xenon is obtained commercially as a byproduct of the separation of air into oxygen and nitrogen. After this separation, generally performed by fractional distillation in a double-column plant, the liquid oxygen produced will contain small quantities of krypton and xenon. By additional fractional distillation steps, the liquid oxygen may be enriched to contain 0.1–0.2% of a krypton/xenon mixture, which is extracted either via adsorption onto silica gel or by distillation. Finally, the krypton/xenon mixture may be separated into krypton and xenon via distillation. Extraction of a liter of xenon from the atmosphere requires 220 watt-hours of energy. Worldwide production of xenon in 1998 was estimated at 5,000–7,000 m3. Because of its low abundance, xenon is much more expensive than the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10 €/L for xenon, 1 €/L for krypton, and 0.20 €/L for neon; the much more plentiful argon costs less than a cent per liter.
Within the Solar System, the nucleon fraction of xenon is 1.56 × 10−8, for an abundance of approximately one part in 630 thousand of the total mass.Xenon is relatively rare in the Sun's atmosphere, on Earth, and in asteroids and comets. The planet Jupiter has an unusually high abundance of xenon in its atmosphere; about 2.6 times as much as the Sun. This high abundance remains unexplained and may have been caused by an early and rapid buildup of planetesimals—small, subplanetary bodies—before the presolar disk began to heat up. (Otherwise, xenon would not have been trapped in the planetesimal ices.) The problem of the low terrestrial xenon may potentially be explained by covalent bonding of xenon to oxygen within quartz, hence reducing the outgassing of xenon into the atmosphere.
Unlike the lower mass noble gases, the normal stellar nucleosynthesis process inside a star does not form xenon. Elements more massive than iron-56 have a net energy cost to produce through fusion, so there is no energy gain for a star when creating xenon. Instead, xenon is formed during supernova explosions,by the slow neutron capture process (s-process) of red giant stars that have exhausted the hydrogen at their cores and entered the asymptotic giant branch, in classical nova explosions and from the radioactive decay of elements such as iodine, uranium and plutonium.
| Symbol | Xe | |
| Atomic Number | 54 | |
| Atomic Weight | 131.29 | |
| Oxidation States | 0 | |
| Electronegativity, Pauling | 2.6 | |
| State at RT | Gas, Nonmetal | |
| Melting Point, K | 161.3 | |
| Boiling Point, K | 166.1 |
Appearance and Characteristics
Harmful effects:
Xenon is not considered to be toxic but many of its compounds are toxic as a result of their strong oxidizing properties.
Characteristics:
- Xenon is a rare, colorless, odorless heavy gas.
- Xenon is inert towards most chemicals.
- Many compounds of xenon have now been made, principally with fluorine or oxygen. Both oxides, xenon trioxide (XeO3) and xenon tetroxide (XeO4) are highly explosive.
Uses of Xenon
- Xenon is used in photographic flashes, in high pressure arc lamps for motion picture projection, and in high pressure arc lamps to produce ultraviolet light.
- It is used in instruments for radiation detection, e.g., neutron and X-ray counters and bubble chambers.
- Xenon is used in medicine as a general anesthetic and in medical imaging.
- Modern ion thrusters for space travel use inert gases – especially xenon – for propellant, so there is no risk of the explosions associated with chemical propulsion.
