Argon



This article pertains to the chemical element. For other uses, see argon (disambiguation).
18 potassium
Kr
General
number argon, Ar, 18
noble gases
block p
Appearancecolorless
(1) g·mol−1
Ne] 3s2 3p6
shell 2, 8, 8
Physical properties
PhasekJ·mol−1
Heat capacity(25 °C) 20.786 J·mol−1·K−1
Vapor pressure
P/Pa 1 10 100 1 k 10 k 100 k
at T/K   47 53 61 71 87
Atomic properties
Electronegativityno data (Pauling scale)
more) 1st: 1520.6 kJ·mol−1
2nd: 2665.8 kJ·mol−1
3rd: 3931 kJ·mol−1
Van der Waals radius188 pm
Miscellaneous
CAS registry number7440–37–1
Selected isotopes
Main article: Isotopes of argon
iso NA half-life DM DE (MeV) DP
36Ar 0.337% Ar is neutrons
37Ar syn 35 d ε 0.813 37Cl
38Ar 0.063% Ar is neutrons
39Ar syn 269 y β- 0.565 39K
40Ar 99.600% Ar is neutrons
41Ar syn 109.34 min β- 2.49 41K
42Ar syn 32.9 y β- 0.600 42K
References
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Argon (International Temperature Scale of 1990.



Characteristics

Argon has approximately the same nitrogen gas. This highly stable chemical element is colorless, odorless, tasteless and nontoxic in both its liquid and gaseous forms. Argon is inert under most conditions and forms no confirmed stable compounds at room temperature.

Although argon is a water when atoms of it are trapped in a lattice of the water molecules.[2] Also argon-containing ions e.g. ArH+ and excited state complexes e.g. ArF are well known. Theoretical calculations on computers have shown several argon compounds that should be stable but for which no synthesis routes are currently known.

History

Argon (Greek αργόν meaning "the lazy one," in reference to its chemical inactivity)[3][4][5] was suspected to be present in air by nitrogen from a sample of air.[6] 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. The symbol for argon is now Ar, but up until 1957 it was A.[7]

Applications

  There are several different reasons why argon is used in particular applications:

  • An nitrogen is not sufficiently inert.
  • Low thermal conductivity is required.
  • The electronic properties (ionization and/or the emission spectrum) are necessary.

Other liquid nitrogen, both of which are used on a large industrial scale. The other noble gases (except helium) are produced this way as well, but argon is the most plentiful since it has the highest concentration in the atmosphere. The bulk of argon applications arise simply because it is inert and relatively cheap. Argon is used:

  • As a fill gas in incandescent lighting, because argon will not react with the filament of light bulbs even at high temperatures.
  • As an inert gas shield in many forms of welding, including metal inert gas welding and tungsten inert gas welding.
  • For extinguishing fires where damage to equipment is to be avoided (see photo).
  • As the gas of choice for the plasma used in spectroscopy
  • As a non-reactive blanket in the processing of titanium and other reactive elements,
  • As a protective atmosphere for growing crystals, and in partial pressure heat treat furnaces.
  • By museum conservators to protect old materials or documents, which are prone to gradual oxidation in the presence of air. [8]
  • To keep open bottles of wine from oxidizing, and in a number of dispensing units and keeper cap systems.
  • In winemaking to top off barrels, displacing oxygen and thus preventing the wine from turning to vinegar during the aging process.
  • In the pharmaceutical industry to top off bottles of intravenous drug preparations (for example intravenous paracetamol), again displacing oxygen and therefore prolonging the drug's shelf-life.
  • Used to cool the seeker head of the US Air Force version of the AIM-9 Sidewinder missile. The gas is stored at high pressure, and the expansion of the gas cools the seeker[9].

The next most common reason for using argon is its low thermal conductivity. It is used for thermal insulation in energy efficient windows.[10] Argon is also used in technical scuba diving to inflate a dry suit, because it is inert and has low thermal conductivity.

Argon is also used for the specific way it ionizes and emits light. It is used in plasma globes and calorimetry in experimental particle physics. Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.[11] In microelectronics, argon ions are used for sputtering.

Finally, there are a number of miscellaneous uses. Argon-39, with a half life of 269 years, has been used for a number of applications, primarily igneous rocks.

Cryosurgery procedures such as cryoablation use liquified argon to destroy cancer cells. In surgery it is used in a procedure called "argon enhanced coagulation" which is a form of argon plasma beam electrosurgery. The procedure carries a risk of producing gas embolism in the patient and has resulted in the death of one person via this type of accident. [12]

Occurrence

  Argon constitutes 0.934% by volume and 1.29% by mass of the xenon.[13]

The Martian atmosphere in contrast contains 1.6% of argon-40 and 5 ppm of argon-36. The Mariner spaceprobe fly-by of the planet Mercury in 1973 found that Mercury has a very thin atmosphere with 70% argon, believed to result from releases of the gas as a decay product from radioactive materials on the planet. In 2005, the Huygens probe also discovered the presence of argon-40 on Titan, the largest moon of Saturn.[14]

Compounds

  Argon’s complete octet of C).

The discovery of argon difluoride (ArF2) was announced in 2003. But this is unconfirmed and most probably incorrect.

Isotopes

The main rocks.[16]

In the Earth's atmosphere, 39Ar is made 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.[16]

Potential hazards

Although argon is non-toxic, it does not satisfy the body's need for oxygen and is a simple asphyxiant. People have suffocated by breathing argon by mistake.[17]

References

  1. ^ "Periodic Table of the Elements: Argon." Lenntech. 1998. Retrieved on September 3, 2007.
  2. ^ Belosludov, V. R.; O. S. Subbotin, D. S. Krupskii, O. V. Prokuda, and Y. Kawazoe (2006). Microscopic model of clathrate compounds (English) 1. Institute of Physics (has blown up once in a while) Publishing. Retrieved on 2007-03-08.
  3. ^ Hiebert, E. N. Historical Remarks on the Discovery of Argon: The First Noble Gas. In Noble-Gas Compounds; Hyman, H. H., Ed.; University of Chicago Press: Chicago, IL, 1963; pp 3–20.
  4. ^ Travers, M. W. The Discovery of the Rare Gases; Edward Arnold & Co.: London, 1928; pp 1–7.
  5. ^ Rayleigh, Lord; Ramsay, W. Argon: A New Constituent of the Atmosphere. Chem. News 1895 (February 1), 71, 51–58.
  6. ^ William Ramsay (1894 - 1895). "Argon, a New Constituent of the Atmosphere.". Proceedings of the Royal Society of London 57 (1): 265-287.
  7. ^ Holden, Norman E. (12). History of the Origin of the Chemical Elements and Their Discoverers (English). National Nuclear Data Center (NNDC).
  8. ^ USA National Archives description of how the Declaration of Independence is stored and displayed. More detail can be found in this more technical explanation, specially Page 4, which talks about the argon keeping the oxygen out.
  9. ^ Description of Aim-9 Operation
  10. ^ Energy-Efficient Windows. Bc Hydro. Retrieved on 2007-03-08.
  11. ^ Fujimoto, James; Rox Anderson, R. (2006). Tissue Optics, Laser-Tissue Interaction, and Tissue Engineering (English) 77-88. Biomedical Optics. Retrieved on 2007-03-08.
  12. ^ Fatal Gas Embolism Caused by Overpressurization during Laparoscopic Use of Argon Enhanced Coagulation (English). MDSR (24).
  13. ^ Argon, Ar. Retrieved on 2007-03-08.
  14. ^ Seeing, touching and smelling the extraordinarily Earth-like world of Titan (English). European Space Agency (21).
  15. ^ Bartlett, Neil. The Noble Gases (English). Chemical & Engineering News.
  16. ^ a b 40Ar/39Ar dating and errors. Retrieved on 2007-03-07.
  17. ^ Middaugh, John; Bledsoe, Gary. "Welder's Helper Asphyxiated in Argon-Inerted Pipe (FACE AK-94-012)." State of Alaska Department of Public Health. June 23, 1994. Retrieved on September 3, 2007.

Further reading

  • Los Alamos National Laboratory – Argon
  • USGS Periodic Table - 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.
  • Triple point temperature: 83.8058 K - Preston-Thomas, H. (1990). "The International Temperature Scale of 1990 (ITS-90)". Metrologia 27: 3-10.
  • Triple point pressure: 69 kPa - (2005) "Section 4, Properties of the Elements and Inorganic Compounds; Melting, boiling, triple, and critical temperatures of the elements", CRC Handbook of Chemistry and Physics, 85th edition, Boca Raton, Florida: CRC Press. 
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E numbers

pH regulators & anti-caking agents (E500–599) • Flavour enhancers (E600–699) • Miscellaneous (E900–999) • Additional chemicals (E1100–1599)

Foaming agents (E990–999)

Calcium peroxide (E930) • Argon (E938) • Hydrogen (E949)

 
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