Groupe: 18 or VIII A
Poids atomique: 39.948
Numero CAS: 7440-37-1
Pas d'isotopes stables
La description • Usages / Fonction
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.
Point de fusion:6* -189.35 °C = 83.8 K = -308.83 °F
Point d'ébullition:6* -185.85 °C = 87.3 K = -302.53 °F
Point critique:6 -122.28 °C = 150.87 K = -188.104 °F 6
Densité:7 1.633 g/L
* - at 1 atm
Configuration de l'électron
Configuration de l'électron: [Ne] 3s2 3p6
Plus haut niveau d'énergie occupés: 3
Électrons de valence: 8
n = 3
ℓ = 1
mℓ = 1
ms = -½
Electron Affinity:8 not stable eV
oxydation États: 0
|ionisation potentiel||eV 9||kJ/mol|
|ionisation potentiel||eV 9||kJ/mol|
|ionisation potentiel||eV 9||kJ/mol|
Chaleur spécifique: 0.520 J/g°C 10 = 20.773 J/mol°C = 0.124 cal/g°C = 4.965 cal/mol°C
Température de fusion: 1.188 kJ/mol 12 = 29.7 J/g
Chaleur de vaporisation: 6.447 kJ/mol 13 = 161.4 J/g
|État de la matière||Enthalpie de formation (ΔHf°)14||Entropy (S°)14||Gibbs Free Energy (ΔGf°)14|
|Nuclide||Masse 15||Demi vie 15||Spin nucléaire 15||Énergie de liaison|
|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|
|Les valeurs marquées # ne sont pas purement dérivées des données expérimentales, mais au moins en partie des tendances systématiques. Spins avec de faibles arguments d'affectation sont entre parenthèses. 15|
Terre - composés Source: uncombined 16
Terre - Seawater: 0.45 mg/L 17
Terre - Croûte: 3.5 mg/kg = 0.00035% 17
Terre - Total: 2.20E-8 cm^3/g 18
Planète Mercure) - Total: 18
Vénus - Total: 210E-8 cm^3/g 18
chondrites - Total: 0.4 (relative to 106 atoms of Si) 19
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