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| General | |||||||||||||||||||||||||||||||||||||
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| Name, Symbol, Number | Argon, Ar, 18 | ||||||||||||||||||||||||||||||||||||
| Chemical series | Noble gases | ||||||||||||||||||||||||||||||||||||
| Group, Period, Block | 18 (VIIIA), 3 , p | ||||||||||||||||||||||||||||||||||||
| Density, Hardness | 1.784 kg/m (273 K), NA | ||||||||||||||||||||||||||||||||||||
| Appearance | Colorless File:Ar,18-thumb.jpg | ||||||||||||||||||||||||||||||||||||
| Atomic properties | |||||||||||||||||||||||||||||||||||||
| Atomic weight | 39.948 amu | ||||||||||||||||||||||||||||||||||||
| Atomic radius (calc.) | no data (71) pm | ||||||||||||||||||||||||||||||||||||
| Covalent radius | 97 pm | ||||||||||||||||||||||||||||||||||||
| van der Waals radius | 188 pm | ||||||||||||||||||||||||||||||||||||
| Electron configuration | 3s 3p | ||||||||||||||||||||||||||||||||||||
| e 's per energy level | 2, 8, 8 | ||||||||||||||||||||||||||||||||||||
| Oxidation states (Oxide) | 0 (unknown) | ||||||||||||||||||||||||||||||||||||
| Crystal structure | Cubic face centered | ||||||||||||||||||||||||||||||||||||
| Physical properties | |||||||||||||||||||||||||||||||||||||
| State of matter | gas (nonmagnetic) | ||||||||||||||||||||||||||||||||||||
| Melting point | 83.8 K (-308.7 °F) | ||||||||||||||||||||||||||||||||||||
| Boiling point | 87.3 K (-302.4 °F) | ||||||||||||||||||||||||||||||||||||
| Molar volume | 22.56 ×10 m/mol | ||||||||||||||||||||||||||||||||||||
| Heat of vaporization | 6.447 kJ/mol | ||||||||||||||||||||||||||||||||||||
| Heat of fusion | 1.188 kJ/mol | ||||||||||||||||||||||||||||||||||||
| Vapor pressure | NA | ||||||||||||||||||||||||||||||||||||
| Speed of sound | 319 m/s at 293.15 K | ||||||||||||||||||||||||||||||||||||
| Miscellaneous | |||||||||||||||||||||||||||||||||||||
| Electronegativity | no data (Pauling scale) | ||||||||||||||||||||||||||||||||||||
| Specific heat capacity | 520 J/(kg*K) | ||||||||||||||||||||||||||||||||||||
| Electrical conductivity | no data | ||||||||||||||||||||||||||||||||||||
| Thermal conductivity | 0.01772 W/(m*K) | ||||||||||||||||||||||||||||||||||||
| 1 ionization potential | 1520.6 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 2 ionization potential | 2665.8 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 3 ionization potential | 3931 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 4 ionization potential | 5771 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 5 ionization potential | 7238 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 6 ionization potential | 8781 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 7 ionization potential | 11995 kJ/mol | ||||||||||||||||||||||||||||||||||||
| 8 ionization potential | 13842 kJ/mol | ||||||||||||||||||||||||||||||||||||
| Most stable isotopes | |||||||||||||||||||||||||||||||||||||
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| SI units & STP are used except where noted. | |||||||||||||||||||||||||||||||||||||
Argon is a chemical element in the periodic table that has the symbol Ar and atomic number 18. The third noble gas, in period 8, argon makes up about 1% of the Earth's atmosphere.
Notable characteristics
Argon is 2.5 times as soluble in water as nitrogen which is approximately the same solubility as oxygen. This chemically inert element is colorless and odorless in both its liquid and gaseous forms. There are no known true chemical compounds that contain argon.
Applications
It is used in lighting since it will not react with the filament in a lightbulb even under high temperatures and other cases where diatomic nitrogen is an unsuitable (semi-)inert gas. Other uses;
- Used as an inert gas shield in arc welding and cutting,
- as a non-reactive blanket in the manufacture of titanium and other reactive elements,
- as a protective atmosphere for growing silicon and germanium crystals.
- Argon-39 has been used for a number of applications, primarily ice coring. It has also been used for ground water dating
Argon is also used in technical SCUBA diving to inflate the drysuit, due to its nonreactive, heat isolating effect.
History
Argon (Greek argos meaning "lazy") was suspected to be present in air by Henry Cavendish in 1785 but wasn't discovered until 1894 by Lord Rayleigh and Sir William Ramsay.
Occurrence
This gas is isolated through liquid air fractionation since the atmosphere contains only 0.94% argon. The Martian atmosphere in contrast contains 1.6% of Ar-40 and 5 ppm Ar-36.
Isotopes
The main isotopes of argon found on earth are Ar-40, Ar-36, and Ar-38. Naturally occurring K-40 with a half-life of 1.250 x 10 years, decays to stable Ar-40 (11.2%) by electron capture and by positron emission, and also decays to stable Ca-40 (88.8%) by negatron emission. These properties and ratios are used to determine the age of rocks.
In earth's atmosphere, Ar-39 is made by cosmic ray activity, primarily with Ar-40. In the subsurface environment, it is also produced through neutron-capture by K-39 or alpha emission by calcium. Argon-37 is produced from the decay of calcium-40, the result of subsurface nuclear explosions. It has a half-life of 35 days.