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Argon,  18Ar
Template:Infobox element/symbol-to-top-image/alt
General properties
Pronunciation/ˈɑrɡɒn/ (AR-gon)
Appearancecolorless gas exhibiting a lilac/violet glow when placed in an electric field
Standard atomic weight (Ar, standard)[39.79239.963] conventional: 39.948
Argon in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ne

Ar

Kr
chlorineargonpotassium
Atomic number (Z)18
Groupgroup 18 (noble gases)
Periodperiod 3
Blockp-block
Element category  noble gas
Electron configuration[Ne] 3s2 3p6
Electrons per shell
2, 8, 8
Physical properties
Phase at STPAr: Gas
Melting point83.81 K ​(−189.34 °C, ​−308.81 °F)
Boiling point87.302 K ​(−185.848 °C, ​−302.526 °F)
Density (at STP)1.784 g/L
when liquid (at b.p.)1.3954 g/cm3
Triple point83.8058 K, ​68.89 kPa
Critical point150.687 K, 4.863 MPa
Heat of fusion1.18 kJ/mol
Heat of vaporization6.53 kJ/mol
Molar heat capacity20.85 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K)   47 53 61 71 87
Atomic properties
Oxidation states0
ElectronegativityPauling scale: no data
Ionization energies
  • 1st: 1520.6 kJ/mol
  • 2nd: 2665.8 kJ/mol
  • 3rd: 3931 kJ/mol
  • (more)
Covalent radius106±10 pm
Van der Waals radius188 pm
Color lines in a spectral range
Spectral lines of argon
Other properties
Natural occurrenceAr: Primordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for argon
Speed of sound323 m/s (gas, at 27 °C)
Thermal conductivity17.72×10−3  W/(m·K)
Magnetic orderingdiamagnetic
Magnetic susceptibility−19.6·10−6 cm3/mol
CAS Number7440-37-1
History
Discovery and first isolationLord Rayleigh and William Ramsay (1894)
Main isotopes of argon
Iso­tope Abun­dance Half-life (1/2) Decay mode Pro­duct
36Ar 0.334% stable
37Ar syn 35 d ε 37Cl
38Ar 0.063% stable
39Ar trace 269 y β 39K
40Ar 99.604% stable
41Ar syn 109.34 min β 41K
42Ar syn 32.9 y β 42K
36Ar and 38Ar content may be as high as 2.07% and 4.3% respectively in natural samples. 40Ar is the remainder in such cases, whose content may be as low as 93.6%.
| references

Argon is a chemical element. The symbol for argon is Ar, and its atomic number (or proton number) is 18. It is a noble gas and no electrons or protons can be lost or gained from this atom.

Argon atoms are found in air. About 1% of the Earth's atmosphere (the air around us) is argon.

Argon is often used when welding steel and similar work, to push away the air around the weld, so the oxygen in the air can't join with the metal being welded.  view more...