| Argon - Ar
CAS:CAS: 7440-37-1 Description: Colorless, odorless, tasteless gas Classification: Noble Gas Date of Discovery: 1894 Discoverer: Sir William Ramsey Name Origin: Greek word argon, "inactive" |
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Atomic Number: 18
Number of Neutrons: 22 Atomic Mass: 39.948(1) amu Triple Point: -189.3442 °C Boiling Point: -185.89 °C Density (293 K): 1.7837 g/cm3 Atomic volume: 28.5 cm3/mol Electrical resistivity: 0.630 10-6/cm 
Thermal conductivity: 0.0001772 W/cmK Enthalpy of atomization: Enthalpy of vaporization: 6.447 kJ/mol Enthalpy of fusion: 1.188 kJ/mol Specific heat capacity: 0.520 J/gK |
Energy levels: 2-8-8
Electron configuration: [Ne]3s23p6 Crystal Structure: Cubic face centered Atomic radius: 0.88 Å Covalent radius: 0.98 Å Oxidation States: 0 Electronegativity, Pauling: 1.93 Electron affinity: not stable First ionization energy: 15.759 eV 2nd ionization energy: 27.629 eV 3rd ionization energy: 40.74 eV Polarizability: 1.6411 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 31Ar | 31.0121 | 15 ms |  +; +, 2p; +, 3p |
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| 32Ar | 31.99766 | 98 ms | +, p |
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| 33Ar | 32.98993 | 174 ms | + |
1/2+ | |
| 34Ar | 33.980270 | 0.844 s | + |
0+ | |
| 35Ar | 34.975257 | 1.77 s | + |
3/2+ | |
| 36Ar | 0.3365(30) | 35.9675463 | Stable | 0+ | |
| 37Ar | 36.9667759 | 35.0 d | EC | 3/2+ | |
| 38Ar | 0.0632(5) | 37.9627322 | Stable | 0+ | |
| 39Ar | 38.964313 | 268 y | - |
7/2- | |
| 40Ar | 99.6003(30) | 39.962383124 | Stable | 0+ | |
| 41Ar | 40.964501 | 1.82 h | - |
7/2- | |
| 42Ar | 41.96305 | 33 y | - |
0+ | |
| 43Ar | 42.9657 | 5.4 m | - |
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| 44Ar | 43.96537 | 11.87 m | - |
0+ | |
| 45Ar | 44.96809 | 21.5 s | - |
7/2- | |
| 46Ar | 45.96809 | 8.4 s | - |
0+ | |
| 47Ar | 46.9722 | ||||
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Its presence in air was suspected 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 soluble in 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's used in 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 inert gas shield for arc welding and cutting, as a blanket for the production of titanium
and other reactive elements, and as a protective atmosphere for growing silicon and germanium crystals. Argon is colorless and odorless, both as a gas and liquid. It is available in high-purity form. Commercial argon is available 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)+, and
(NeAr)+ have been observed spectroscopically. Argon also forms a clathrate with P-hydroquinone. This clathrate is stable and can be stored for a considerable time, 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.
LINKS: The Argon Gas Laser System Argon Thermochronometry - UCLA Argon Laboratory Fun with Argon Potassium-Argon Dating Return
Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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