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argon

 
Dictionary: ar·gon   (är'gŏn') pronunciation
 
n. (Symbol Ar)

A colorless, odorless, inert gaseous element constituting approximately one percent of Earth's atmosphere, from which it is commercially obtained by fractionation for use in electric light bulbs, fluorescent tubes, and radio vacuum tubes and as an inert gas shield in arc welding. Atomic number 18; atomic weight 39.948; melting point −189.3°C; boiling point −185.9°C.

[From Greek ārgon, neuter of ārgos, idle, inert : a-, without; see a–1 + ergon, work.]


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A chemical element, Ar, atomic number 18, and atomic weight 39.948. Argon is the third member of group 18 in the periodic table. The gaseous elements in this group are called the noble, inert, or rare gases, although argon is not actually rare. The Earth's atmosphere is the only natural argon source; however, traces of this gas are found in minerals and meteorites. Argon constitutes 0.934% by volume of the Earth's atmosphere. Of this argon, 99.6% is the argon-40 isotope; the remainder is argon-36 and argon-38. There is good evidence that all the argon-40 in the air was produced by the radioactive decay of the radioisotope potassium-40. See also Inert gases; Periodic table.

Argon is colorless, odorless, and tasteless. The element is a gas under ordinary conditions, but it can be liquefied and solidified readily. Some salient properties of the gas are listed in the table. Argon does not form any chemical compounds in the ordinary sense of the word, although it does form some weakly bonded clathrate compounds with water, hydroquinone, and phenol. There is one atom in each molecule of gaseous argon.

Properties of argon

Property

Value

Atomic number

18

Atomic weight (atmospheric argon)

39.948

Melting point (triple point), °C

−189.4

Boiling point at 1 atm pressure, °C

−185.9

Gas density at 0°C and 1 atm (101.325 kPa) pressure, g/liter

1.7840

Liquid density at normal boiling point, g/ml

1.3998

Solubility in water at 20°C, ml argon (STP) per 1000 g water at 1 atm (101.325 kPa) partial pressure of argon

33.6

The oldest large-scale use for argon is in filling electric light bulbs. Welding and cutting metal consumes the largest amount of argon. Metallurgical processing constitutes the most rapidly growing application. Argon and argon-krypton mixtures are used, along with a little mercury vapor, to fill fluorescent lamps. Argon mixed with a little neon is used to fill luminous electric-discharge tubes employed in advertising signs (similar to neon signs) when a blue or green color is desired instead of the red color of neon. Argon is also used in gas-filled thyratrons, Geiger-Müller radiation counters, ionization chambers which measure cosmic radiation, and electron tubes of various kinds. Argon atmospheres are used in dry boxes during manipulation of very reactive chemicals in the laboratory and in sealed-package shipments of such materials.

Most argon is produced in air-separation plants. Air is liquefied and subjected to fractional distillation. Because the boiling point of argon is between that of nitrogen and oxygen, an argon-rich mixture can be taken from a tray near the center of the upper distillation column. The argon-rich mixture is further distilled and then warmed and catalytically burned with hydrogen to remove oxygen. A final distillation removes hydrogen and nitrogen, yielding a very high-purity argon containing only a few parts per million of impurities.


 

Chemical element, chemical symbol Ar, atomic number 18. Colourless, odourless, and tasteless, it is the most abundant of the noble gases on Earth and the one most used in industry. It constitutes about 1% of air and is obtained by distillation of liquid air. Argon provides an inert gas shield in welding and brazing, in lightbulbs and lasers, in Geiger counters, and in the production and fabrication of certain metals. Because a radioactive form of argon is produced by decay of a naturally occurring radioactive potassium isotope, it can be used to date rocks and samples more than 100,000 years old.

For more information on argon, visit Britannica.com.

 
argon (är'gŏn) [Gr.,=inert], gaseous chemical element; symbol Ar; at. no. 18; at. wt. 39.948; m.p. −189.2°C; b.p. −185.7°C; density 1.784 grams per liter at STP; valence 0. Argon is a colorless, odorless, tasteless gas occurring in air (of which it constitutes 0.94% by volume) and in some volcanic gases. It is a member of Group 18 of the periodic table, a group called the noble or inert gases from the mistaken former belief that none of its members could form chemical compounds; in fact, other members of the group, e.g., krypton, xenon, and radon, do form compounds. Argon is prepared by fractional distillation of liquid air. Its extreme inertness has caused it to be substituted for nitrogen in electric light bulbs. It is mixed with neon in so-called neon signs (gas discharge tubes) to produce a green-to-blue glow. It is used as a protective atmosphere in arc welding, in the refining of reactive elements, and in the growing of crystals for use in semiconductor devices. Argon was first obtained by Lord Rayleigh and Sir William Ramsay in 1894. Previously Lord Rayleigh had noticed that a liter of supposedly pure nitrogen drawn from the air weighed more than a liter prepared from a nitrogen compound. This difference in weight led him to conclude that another gas was present in the supposedly pure nitrogen. Actually several unreactive gases were present; the first samples of “argon” also contained helium, neon, krypton, and xenon. Ramsay obtained pure argon later by evaporating it from liquid air.


 

A chemical element, atomic number 18, atomic weight 39.948, symbol Ar.

 
Wikipedia: Argon
Top
chlorineargonpotassium
Ne

Ar

Kr
Appearance
tasteless, odorless, colorless gas
General
Name, symbol, number argon, Ar, 18
Element category noble gases
Group, period, block 183, p
Standard atomic weight 39.948(1)g·mol−1
Electron configuration [Ne] 3s2 3p6
Electrons per shell 2, 8, 8 (Image)
Physical properties
Phase gas
Density (0 °C, 101.325 kPa)
1.784 g/L
Melting point 83.80 K
(−189.35 °C, −308.83 °F)
Boiling point 87.30 K
(−185.85 °C, −302.53 °F)
Triple point 83.8058 K (-189°C), 69 kPa
Critical point 150.87 K, 4.898 MPa
Heat of fusion 1.18 kJ·mol−1
Heat of vaporization 6.43 kJ·mol−1
Specific 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
Oxidation states 0
Electronegativity no data (Pauling scale)
Ionization energies
(more)
1st: 1520.6 kJ·mol−1
2nd: 2665.8 kJ·mol−1
3rd: 3931 kJ·mol−1
Covalent radius 106±10 pm
Van der Waals radius 188 pm
Miscellaneous
Crystal structure face-centered cubic
Magnetic ordering diamagnetic[1]
Thermal conductivity (300 K) 17.72x10-3  W·m−1·K−1
Speed of sound (gas, 27 °C) 323 m/s
CAS registry number 7440–37–1
Most stable isotopes
Main article: Isotopes of argon
iso NA half-life DM DE (MeV) DP
36Ar 0.337% 36Ar is stable with 18 neutrons
37Ar syn 35 d ε 0.813 37Cl
38Ar 0.063% 38Ar is stable with 20 neutrons
39Ar syn 269 y β 0.565 39K
40Ar 99.600% 40Ar is stable with 22 neutrons
41Ar syn 109.34 min β 2.49 41K
42Ar syn 32.9 y β 0.600 42K
References
Cavendish's method for the isolation of argon. The gases are contained in a test-tube (A) standing over a large quantity of weak alkali (B), and the current is conveyed in wires insulated by U-shaped glass tubes (CC) passing through the liquid and round the mouth of the test-tube. The inner platinum ends (DD) of the wire receive a current from a battery of five Grove cells and a Ruhmkorff coil of medium size.

Argon (pronounced /ˈɑrɡɒn/) is a chemical element designated by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table (noble gases). Argon is present in the Earth's atmosphere at 0.94%. Terrestrially, it is the most abundant and most frequently used of the noble gases. Argon's full outer shell makes it stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.

Contents

Characteristics

A small piece of rapidly melting argon ice.

Argon has approximately the same solubility in water as oxygen gas and is 2.5 times more soluble in water than nitrogen gas. Argon 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 noble gas, it has been found to have the capability of forming some compounds. For example, the creation of argon fluorohydride (HArF), a marginally stable compound of argon with fluorine and hydrogen, was reported by researchers at the University of Helsinki in 2000.[2] Although the neutral ground-state chemical compounds of argon are presently limited to HArF, argon can form clathrates with water when atoms of it are trapped in a lattice of the water molecules.[3] Also argon-containing ions and excited state complexes, such as ArH+ and ArF, respectively, are known to exist. Theoretical calculations have shown several argon compounds that should be stable but for which no synthesis routes are currently known.

History

Argon (Greek meaning "inactive", in reference to its chemical inactivity)[4][5][6] was suspected to be present in air by Henry Cavendish in 1785 but was not isolated until 1894 by Lord Rayleigh and Sir William Ramsay in Scotland in an experiment in which they removed all of the oxygen, carbon dioxide, water and nitrogen from a sample of clean air.[7][8] They had determined that nitrogen produced from chemical compounds was one-half percent lighter than nitrogen from the atmosphere. The difference seemed insignificant, but it was important enough to attract their attention for many months. They concluded that there was another gas in the air mixed in with the nitrogen.[9] Argon was also encountered in 1882 through independent research of Hugh Frank 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.[10]

Occurrence

Argon constitutes 0.934% by volume and 1.29% by mass of the Earth's atmosphere, and air is the primary raw material used by industry to produce purified argon products. Argon is isolated from air by fractionation, most commonly by cryogenic fractional distillation, a process that also produces purified nitrogen, oxygen, neon, krypton and xenon.[11]

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.[12]

Isotopes

The main isotopes of argon found on Earth are 40Ar (99.6%), 36Ar (0.34%), and 38Ar (0.06%). Naturally occurring 40K with a half-life of 1.25 × 109 years, decays to stable 40Ar (11.2%) by electron capture and positron emission, and also to stable 40Ca (88.8%) via beta decay. These properties and ratios are used to determine the age of rocks.[13]

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.[13]

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 bonding with other elements. Before 1962, argon and the other noble gases were considered to be chemically inert and unable to form compounds; however, compounds of the heavier noble gases have since been synthesized. In August 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, argon fluorohydride (HArF) was formed.[2][14] It is stable up to 40 kelvins (−233 °C).

Production

Industrial

Argon is produced industrially by the fractional distillation of liquid air, a process that separates liquid nitrogen, which boils at 77.3 K, from argon, which boils at 87.3 K and oxygen, which boils at 90.2 K. About 700,000 tons of argon are produced worldwide every year. [15]

In radioactive decays

Argon-40, the most abundant isotope of argon, is produced by the decay of potassium-40 with a half-life of 1.26 × 109 years by electron capture or positron emission. Because of this, it is used in potassium-argon dating to determine the age of rocks.

Applications

Cylinders containing argon gas for use in extinguishing fire without damaging server equipment

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

  • An inert gas is needed. In particular, argon is the cheapest alternative when diatomic nitrogen is not sufficiently inert.
  • Low thermal conductivity is required.
  • The electronic properties (ionization and/or the emission spectrum) are necessary.

Other noble gases would probably work as well in most of these applications, but argon is by far the cheapest. Argon is inexpensive since it is a byproduct of the production of liquid oxygen and 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.

Industrial processes

Argon is used in some high-temperature industrial processes, where ordinarily unreactive substances become reactive. For example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning.

For some of these processes, the presence of nitrogen or oxygen gases might cause defects within the material. Argon is used in various types of metal inert gas welding such as tungsten inert gas welding, as well as in the processing of titanium and other reactive elements. An argon atmosphere is also used for growing crystals of silicon and germanium.

Argon is an asphyxiant in the poultry industry, either for mass culling following disease outbreaks, or as a means of slaughter more humane than the electric bath. Argon's relatively high density causes it to remain close to the ground during gassing. Its non-reactive nature makes it suitable in a food product, and since it replaces oxygen within the dead bird, argon also enhances shelf life.[16]

Argon is sometimes used for extinguishing fires where damage to equipment is to be avoided (see photo).

Preservative

A sample of caesium is packed under argon to avoid reactions with air

Argon is used to displace oxygen- and moisture-containing air in packaging material to extend the shelf-lives of the contents. Aerial oxidation, hydrolysis, and other chemical reactions which degrade the products are retarded or prevented entirely. Bottles of high-purity chemicals and certain pharmaceutical products are available in sealed bottles or ampules packed in argon. In winemaking, argon is used to top-off barrels to avoid the aerial oxidation of ethanol to acetic acid during the aging process.

Argon is also available in aerosol-type cans, which may be used to preserve compounds such as varnish, polyurethane, paint, etc. for storage after opening.[17]

Since 2001 the American National Archives stores important national documents such as the Declaration of Independence and the Constitution within argon-filled cases to retard their degradation. Using argon reduces gas leakage, compared with the helium used in the preceding five decades. [18]

Laboratory equipment

Gloveboxes are typically filled with argon, which recirculate over scrubbers to maintain an oxygen- and moisture-free atmosphere

Argon may be used as the inert gas within Schlenk lines and gloveboxes. The use of argon over comparatively less expensive dinitrogen is preferred where nitrogen may react.

Argon may be used as the carrier gas in gas chromatography and in electrospray ionization mass spectrometry; it is the gas of choice for the plasma used in ICP spectroscopy. Argon is preferred for the sputter coating of specimens for scanning electron microscopy. Argon ions are also used for sputtering in microelectronics.

Medical use

Cryosurgery procedures such as cryoablation use liquefied 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.[19] Blue argon lasers are used in surgery to weld arteries, destroy tumors, and to correct eye defects.[20] It has also used experimentally to replace nitrogen in the breathing or decompression mix, to speed the elimination of dissolved nitrogen from the blood.[21] See Argox (scuba).

Lighting

An argon & mercury vapour discharge tube.

Incandescent lights are filled with argon, to preserve the filaments at high temperature. It is used for the specific way it ionizes and emits light, such as in in plasma globes and calorimetry in experimental particle physics. Gas-discharge lamps filled with argon provide blue light. Argon is also used for the creation of blue laser light.

Miscellaneous uses

It is used for thermal insulation in energy efficient windows.[22] Argon is also used in technical scuba diving to inflate a dry suit, because it is inert and has low thermal conductivity.[23]

Compressed argon is allowed to expand, to cool the seeker heads of the AIM-9 Sidewinder missile, and other missiles that use cooled thermal seeker heads. The gas is stored at high pressure.[24]

Argon-39, with a half life of 269 years, has been used for a number of applications, primarily ice core and ground water dating. Also, potassium-argon dating is used in dating igneous rocks.

Safety

Although argon is non-toxic, it does not satisfy the body's need for oxygen and is thus an asphyxiant. Argon is 25% more dense than air and is considered highly dangerous in closed areas. It is also difficult to detect because it is colorless, odorless, and tasteless. In confined spaces, it is known to result in death due to asphyxiation. A 1994 incident in Alaska that resulted in one fatality highlights the dangers of argon tank leakage in confined spaces, and emphasizes the need for proper use, storage and handling.[25]

References

  1. ^ Magnetic susceptibility of the elements and inorganic compounds, in Handbook of Chemistry and Physics 81th edition, CRC press.
  2. ^ a b "HArF! Argon's not so noble after all - researchers make argon fluorohydride". http://findarticles.com/p/articles/mi_m1200/is_9_158/ai_65368548. 
  3. ^ Belosludov, V. R.; O. S. Subbotin, D. S. Krupskii, O. V. Prokuda, and Y. Kawazoe (2006). "Microscopic model of clathrate compounds". J. Phys.: Conf. Ser. 29: 1. doi:10.1088/1742-6596/29/1/001. 
  4. ^ Hiebert, E. N. (1963). "In Noble-Gas Compounds". in Hyman, H. H.. Historical Remarks on the Discovery of Argon: The First Noble Gas. Chicago, IL: University of Chicago Press. pp. 3–20. 
  5. ^ Travers, M. W. (1928). The Discovery of the Rare Gases. London: Edward Arnold & Co.. pp. 1–7. 
  6. ^ Rayleigh, Lord; Ramsay, W. (1895). "Argon: A New Constituent of the Atmosphere". Chemical News 71,: 51–58. 
  7. ^ Lord Rayleigh;William Ramsay (1894 - 1895). "Argon, a New Constituent of the Atmosphere". Proceedings of the Royal Society of London 57 (1): 265–287. doi:10.1098/rspl.1894.0149. http://links.jstor.org/sici?sici=0370-1662%281894%2F1895%2957%3C265%3AAANCOT%3E2.0.CO%3B2-X. 
  8. ^ William Ramsay. "Nobel Lecture in Chemistry, 1904". http://nobelprize.org/nobel_prizes/chemistry/laureates/1904/ramsay-lecture.html. 
  9. ^ "About Argon, the Inert; The New Element Supposedly Found in the Atmosphere". The New York Times. http://query.nytimes.com/gst/abstract.html?res=9B04E3D61139E033A25750C0A9659C94649ED7CF. Retrieved on 2009-02-01. 
  10. ^ Holden, Norman E. (12). "History of the Origin of the Chemical Elements and Their Discoverers". National Nuclear Data Center (NNDC). http://www.nndc.bnl.gov/content/elements.html. 
  11. ^ "Argon, Ar". http://elements.etacude.com/Ar.php. Retrieved on 2007-03-08. 
  12. ^ "Seeing, touching and smelling the extraordinarily Earth-like world of Titan". European Space Agency. 21. http://www.esa.int/esaCP/SEMHB881Y3E_index_0.html. 
  13. ^ a b "40Ar/39Ar dating and errors". http://www.geoberg.de/text/geology/07011601.php. Retrieved on 2007-03-07. 
  14. ^ Bartlett, Neil. "The Noble Gases". Chemical & Engineering News. http://pubs.acs.org/cen/80th/noblegases.html. 
  15. ^ "Periodic Table of Elements: Argon – Ar". Environmentalchemistry.com. http://environmentalchemistry.com/yogi/periodic/Ar.html. Retrieved on 2008-09-12. 
  16. ^ ""Humane" Poultry Slaughter: Humane Slaughter: Animal Rights vs. Animal Welfare - Downbound.com". Downbound.com. http://www.downbound.com/Humane_Poultry_Slaughter_s/231.htm. Retrieved on 2008-09-12. 
  17. ^ US Patent 6629402
  18. ^ http://www.archives.gov/press/press-kits/charters.html#pressrelaese1 Accessed Feb 9, 2009
  19. ^ "Fatal Gas Embolism Caused by Overpressurization during Laparoscopic Use of Argon Enhanced Coagulation". MDSR. 24. http://www.mdsr.ecri.org/summary/detail.aspx?doc_id=8248. 
  20. ^ Fujimoto, James; Rox Anderson, R. (2006). "Tissue Optics, Laser-Tissue Interaction, and Tissue Engineering". Biomedical Optics. 77-88. http://www.spie.org/Conferences/Programs/06/pw/BiOSAbstracts.pdf. Retrieved on 2007-03-08. 
  21. ^ Pilmanis Andrew A, Balldin UI, Webb James T, Krause KM (December 2003). "Staged decompression to 3.5 psi using argon-oxygen and 100% oxygen breathing mixtures". Aviation, Space, Environmental Medicine 74 (12): 1243–50. PMID 14692466. http://www.ingentaconnect.com/content/asma/asem/2003/00000074/00000012/art00004. 
  22. ^ "Energy-Efficient Windows". Bc Hydro. http://www.bchydro.com/powersmart/elibrary/elibrary644.html. Retrieved on 2007-03-08. 
  23. ^ Nuckols ML, Giblo J, Wood-Putnam JL. (September 15-18, 2008). "Thermal Characteristics of Diving Garments When Using Argon as a Suit Inflation Gas.". Proceedings of the Oceans 08 MTS/IEEE Quebec, Canada Meeting (MTS/IEEE). http://archive.rubicon-foundation.org/7962. Retrieved on 2009-03-02. 
  24. ^ "Description of Aim-9 Operation". planken.org. http://home.wanadoo.nl/tcc/rnlaf/aim9.html. Retrieved on 2009-02-01. 
  25. ^ Middaugh, John (1994-06-23). "Welder's Helper Asphyxiated in Argon-Inerted Pipe (FACE AK-94-012)". State of Alaska Department of Public Health. http://www.hss.state.ak.us/dph/ipems/occupation_injury/reports/docs/94ak012.htm. Retrieved on 2009-02-01. 

Further reading

  • Triple point pressure: 69 kPa - "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 ed.). Boca Raton, Florida: CRC Press. 2005. 

External links


 
Translations: Argon
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Dansk (Danish)
n. - argon

Nederlands (Dutch)
argon (soort edelgas)

Français (French)
n. - argon

Deutsch (German)
n. - Argon

Ελληνική (Greek)
n. - (χημ.) αργόν

Italiano (Italian)
argo

Português (Portuguese)
n. - argônio (m) (Quím.)

Русский (Russian)
аргон

Español (Spanish)
n. - argón

Svenska (Swedish)
n. - argon (kem.)

中文(简体)(Chinese (Simplified))

中文(繁體)(Chinese (Traditional))
n. - 氬

한국어 (Korean)
n. - 아르곤(회 가스 원소)

日本語 (Japanese)
n. - アルゴン

العربيه (Arabic)
‏(الاسم) أرغون : عنصر عاز عديم اللون والرائحه يوجد في الهوا والغازات البركانيه‏

עברית (Hebrew)
n. - ‮ארגון (יסוד גזי אציל, RA, מס' אטומי 81)‬


 
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