Group: 18 or VIII A
Atomic Weight: 39.948
CAS Number: 7440-37-1
No Stable Isotopes
Description • Uses/Function
Its presence in air wassuspected by Cavendish in 1785, discovered by Lord Rayleigh and Sir William Ramsay in 1894. The gas is prepared by fractionation of liquid air,the atmosphere containing 0.94% argon. The atmosphere of Mars contains 1.6% of 40Ar and 5 p.p.m. of 36Ar. Argon is two and one half times as solublein water as nitrogen, having about the same solubility as oxygen. It is recognized by the characteristic lines in the red end of the spectrum. It is usedin electric light bulbs and in fluorescent tubes at a pressure of about 400 Pa, and in filling photo tubes, glow tubes, etc. Argon is also used as an inertgas shield for arc welding and cutting, as a blanket for the production of titanium and other reactive elements, and as a protective atmosphere for growingsilicon and germanium crystals. Argon is colorless and odorless, both as a gas and liquid. It is available in high-purity form. Commercial argon isavailable at a cost of about 3¢ per cubic foot. Argon is considered to be a very inert gas and is not known to form true chemical compounds, as do krypton,xenon, and radon. However, it does form a hydrate having a dissociation pressure of 105 atm at 0°C. Ion molecules such as (ArKr)+, (ArXe)+, (NeAr)+have been observed spectroscopically. Argon also forms a clathrate with b-hydroquinone. This clathrate is stable and can be stored for a considerabletime, but a true chemical bond does not exist. Van der Waals’ forces act to hold the argon. Naturally occurring argon is a mixture of three isotopes.Seventeen other radioactive isotopes are now known to exist. Commercial argon is priced at about $70/300 cu. ft. or 8.5 cu. meters. 1
• "Both helium and argon are used in large amounts in noble-gas-shielded arc-welding processes. The noble gas protects the hot welded metal from oxidation by air...In addition to its use in arc-welding, argon is used in filling incandescent and fluorescent lamps. The presence of the noble gas in incandescent lamps retards the sublimation of the filament and thus both prolongs the life of the lamp and retards its blackening. In fluorescent lamps, argon serves as an ionizable gas for starting the lamp and for carrying the current during its operation." 2
• "Argon is often used in chemical laboratories to provide an inert atmosphere for the handling of substances that are reactive toward water, oxygen, or nitrogen." 3
• "inert atmosphere for welding...filling incandescent light bulbs" 4
• "In 1914, Langmuir...substituted argon, [in place of nitrogen] which was a little more expensive but which increased the lifetime of the bulbs more than enough to compensate for the additional cost. Electric light bulbs are routinely argon-filled now, so that the first important industrial use of the noble gases still retains its value.
The inertness of argon is its most important characteristic as far as uses are concerned. This is true in light bulbs, and it is true so far as argon's connection with welding is concerned.
In 1929...A jet of argon gas was pushed through the arc so that it constantly enveloped the area to be welded. Such shielded arc-welding produced excellent joints of full strength, not only in steel, but in other metals such as copper, nickel, magnesium, and so on. The most important single use of argon is in connection with shielded arc-welding nowadays.
Argon is also used on other occasions where it is important to keep oxygen and nitrogen away. For instance, aluminum can be cut by an "atomic hydrogen torch"...However, in the presence of air, the melting aluminum combines readily with oxygen, and the brittle oxide flakes away, so that the cut is ragged and irregular. For that reason, argon is added to the hydrogen. It doesn't affect the reunion of hydrogen atoms, but does serve to surround the melting aluminum with an inert atmosphere.
Argon is also used in the preparation of metallic titanium...Today titanium is prepared under an atmosphere of argon, and the resultant pure titanium is particularly tough and strong.
Melting Point:6* -189.35 °C = 83.8 K = -308.83 °F
Boiling Point:6* -185.85 °C = 87.3 K = -302.53 °F
Critical Point:6 -122.28 °C = 150.87 K = -188.104 °F 6
Density:7 1.633 g/L
* - at 1 atm
Electron Configuration: [Ne] 3s2 3p6
Highest Occupied Energy Level: 3
Valence Electrons: 8
n = 3
ℓ = 1
mℓ = 1
ms = -½
Electron Affinity:8 not stable eV
Oxidation States: 0
|Ionization Potential||eV 9||kJ/mol|
|Ionization Potential||eV 9||kJ/mol|
|Ionization Potential||eV 9||kJ/mol|
Specific Heat: 0.520 J/g°C 10 = 20.773 J/mol°C = 0.124 cal/g°C = 4.965 cal/mol°C
Heat of Fusion: 1.188 kJ/mol 12 = 29.7 J/g
Heat of Vaporization: 6.447 kJ/mol 13 = 161.4 J/g
|State of Matter||Enthalpy of Formation (ΔHf°)14||Entropy (S°)14||Gibbs Free Energy (ΔGf°)14|
|Nuclide||Mass 15||Half-Life 15||Nuclear Spin 15||Binding Energy|
|30Ar||30.02156(32)#||<20 ns||0+||208.50 MeV|
|31Ar||31.01212(22)#||14.4(6) ms||5/2(+#)||224.95 MeV|
|32Ar||31.9976380(19)||98(2) ms||0+||246.99 MeV|
|33Ar||32.9899257(5)||173.0(20) ms||1/2+||262.52 MeV|
|34Ar||33.9802712(4)||844.5(34) ms||0+||278.97 MeV|
|35Ar||34.9752576(8)||1.775(4) s||3/2+||291.70 MeV|
|37Ar||36.96677632(22)||35.04(4) d||3/2+||316.23 MeV|
|39Ar||38.964313(5)||269(3) a||7/2-||334.23 MeV|
|41Ar||40.9645006(4)||109.61(4) min||7/2-||350.38 MeV|
|42Ar||41.963046(6)||32.9(11) a||0+||359.38 MeV|
|43Ar||42.965636(6)||5.37(6) min||(5/2-)||365.59 MeV|
|44Ar||43.9649240(17)||11.87(5) min||0+||374.59 MeV|
|45Ar||44.9680400(6)||21.48(15) s||(1/2,3/2,5/2)-||378.93 MeV|
|46Ar||45.96809(4)||8.4(6) s||0+||387.01 MeV|
|47Ar||46.97219(11)||1.23(3) s||3/2-#||391.35 MeV|
|48Ar||47.97454(32)#||0.48(40) s||0+||397.56 MeV|
|49Ar||48.98052(54)#||170(50) ms||3/2-#||400.04 MeV|
|50Ar||49.98443(75)#||85(30) ms||0+||404.39 MeV|
|51Ar||50.99163(75)#||60# ms [>200 ns]||3/2-#||405.94 MeV|
|52Ar||51.99678(97)#||10# ms||0+||409.35 MeV|
|53Ar||53.00494(107)#||3# ms||(5/2-)#||409.97 MeV|
|Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 15|
Earth - Source Compounds: uncombined 16
Earth - Seawater: 0.45 mg/L 17
Earth - Crust: 3.5 mg/kg = 0.00035% 17
Earth - Total: 2.20E-8 cm^3/g 18
Mercury - Total: 18
Venus - Total: 210E-8 cm^3/g 18
Chondrites - Total: 0.4 (relative to 106 atoms of Si) 19
Material Safety Data Sheet - ACI Alloys, Inc.
For More Information
Chemical & Engineering News
HyperPhysics from Georgia State University's Department of Physics and Astronomy
Los Alamos National Laboratory
Physics Department of the University of Coimbra
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