Argon: Difference between revisions

Argon is the chemical element in the periodic table that has the symbol Ar and atomic number 18. The third noble gas, in group 18, argon is present in the Earth's atmosphere at slightly less than 1 %. This makes it the most common noble gas on Earth.

Notable characteristics

Argon is 2.5 times as soluble in water as nitrogen which is approximately the same solubility as oxygen. This highly stable chemical element is colorless and odorless in both its liquid and gaseous forms. There are few known true chemical compounds that contain argon, which is one of the reasons it was formerly called an inert gas. The creation of argon hydrofluoride (HArF), a highly unstable compound of argon with fluorine, was reported by researchers at the University of Helsinki in 2000, but has not been confirmed as of yet.

Although no chemical compounds of argon are presently confirmed, argon can form clathrates with water when atoms of it are trapped in a lattice of the water molecules. Theoretical calculations on computers have shown several argon compounds that should be stable but for which no synthesis routes are currently known.

Applications

It is used in incandescent lighting since it will not react with the filament in a lightbulb even under high temperatures and other cases where diatomic nitrogen is an unsuitable (semi-)inert gas. Other uses:

Argon is used as an inert gas shield in many forms of welding, including metal inert gas welding and tungsten inert gas welding.
as the gas of choice for the plasma used in ICP Spectroscopy.
as a non-reactive blanket in the manufacture of titanium and other reactive elements.
as a protective atmosphere for growing silicon and germanium crystals.
as a gas for use in plasma globes.
as a gas for thermal insulation in energy efficient windows.
Argon-39 has been used for a number of applications, primarily ice coring. It has also been used for ground water dating.
Cryosurgery procedures such as cryoablation use liquified argon to destroy cancer cells.
Liquid argon is used in calorimetry in experimental particle physics.
Argon is used in technical SCUBA diving to inflate the dry suit, because it is inert and has low thermal conductivity.
Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.
Due to its inert qualities, it is commonly used by museum conservators to protect old materials or documents, which are prone to gradual oxidisation in the presence of air.
Argon is used in the tires of luxury cars to protect the rubber from oxygen and to ensure quiet tires when the car moves at fast speeds.

History

Argon (Greek αργός meaning "inactive") was suspected to be present in air by Henry Cavendish in 1785 but was not discovered until 1894 by Lord Rayleigh and Sir William Ramsay in an experiment in which they removed all of the oxygen and nitrogen from the air. Argon was also encountered in 1882 through independent research of H.F. Newall and W.N. Hartley. Each observed new lines in the color spectrum of air but were unable to identify the element responsible for the lines. Argon became the first member of the noble gases to be discovered.

Occurrence

This gas is isolated through liquid air fractionation since the atmosphere contains only 0.934% volume of argon (1.29% mass). The Martian atmosphere in contrast contains 1.6% of argon-40 and 5 ppm of argon-36. In 2005, the Huygens probe also discovered the presence of argon-40 on Titan, the largest moon of Saturn [1].

Compounds

Argon’s complete octet of electrons indicates full s and p subshells. This full outer energy level makes argon very stable and extremely resistant to bond with other elements.Before 1962, argon and the other noble gases were generally considered to be chemically inert and not able to form compounds. However, since then, scientists have been able to force the heavier noble gases to form compounds. In 2000, the first argon compounds were formed by researchers at the University of Helsinki. By shining ultraviolet light onto frozen argon containing a small amount of hydrogen fluoride, they were able to form argon hydrofluoride (HArF): see http://pubs.acs.org/cen/80th/noblegases.html in its paragraph starting "Many recent findings". It is stable up to 40 kelvin.

Isotopes

The main isotopes of argon found on Earth are ⁴⁰Ar, ³⁶Ar, and ³⁸Ar. Naturally occurring ⁴⁰K with a half-life of 1.250 x 10⁹ years, decays to stable ⁴⁰Ar (11.2%) by electron capture and by positron emission, and also transforms to stable ⁴⁰Ca (88.8%) via beta decay. These properties and ratios are used to determine the age of rocks.

In the Earth's atmosphere, ³⁹Ar is made by cosmic ray activity, primarily with ⁴⁰Ar. In the subsurface environment, it is also produced through neutron capture by ³⁹K or alpha emission by calcium. ³⁷Ar is created from the decay of ⁴⁰Ca as a result of subsurface nuclear explosions. It has a half-life of 35 days.

References

Los Alamos National Laboratory – Argon

Emsley, J. Nature’s Building Blocks; Oxford University Press: Oxford, NY, 2001; pp 35-39.

Brown, T.L.; Bursten, B.E.; LeMay, H.E. In Chemistry: The Central Science, 10th ed.; Challice, J.; Draper, P.; Folchetti, N. et al.; Eds.; Pearson Education, Inc.: Upper Saddle River, NJ, 2006; pp 276 and 289.

@@ Line 63: / Line 63: @@
 *Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.
 *Due to its inert qualities, it is commonly used by museum conservators to protect old materials or documents, which are prone to gradual oxidisation in the presence of air.
+*Argon is used in the tires of luxury cars to protect the rubber from oxygen and to ensure quiet tires when the car moves at fast speeds.
-*Argon sucks!!!!!!!!!!!!
 == History ==

Fahrer / Team für die Suche eingeben: