Argon

  • argon, 18ar
    vial containing a violet glowing gas
    argon
    pronunciationn/ (ar-gon)
    appearancecolorless gas exhibiting a lilac/violet glow when placed in an electric field
    standard atomic weight ar, std(ar)[39.79239.963] conventional: 39.95[1]
    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 shell2, 8, 8
    physical properties
    phase at stpgas
    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[2]
    critical point150.687 k, 4.863 mpa[2]
    heat of fusion1.18 kj/mol
    heat of vaporization6.53 kj/mol
    molar heat capacity20.85[3] 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 occurrenceprimordial
    crystal structureface-centered cubic (fcc)
    face-centered cubic crystal structure for argon
    speed of sound323 m/s (gas, at 27 °c)
    thermal conductivity17.72×103  w/(m·k)
    magnetic orderingdiamagnetic[4]
    magnetic susceptibility−19.6·10−6 cm3/mol[5]
    cas number7440-37-1
    history
    discovery and first isolationlord rayleigh and william ramsay (1894)
    main isotopes of argon
    iso­tope abun­dance half-life (t1/2) 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
    36
    ar
    and 38
    ar
    content may be as high as 2.07% and 4.3% respectively in natural samples. 40
    ar
    is the remainder in such cases, whose content may be as low as 93.6%.
    category category: argon
    | references

    argon is a chemical element with the symbol ar and atomic number 18. it is in group 18 of the periodic table and is a noble gas.[6] argon is the third-most abundant gas in the earth's atmosphere, at 0.934 % (9340 ppmv). it is more than twice as abundant as water vapor (which averages about 4 000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). argon is the most abundant noble gas in earth's crust, comprising 0.00015 % of the crust.

    nearly all of the argon in the earth's atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the earth's crust. in the universe, argon-36 is by far the most common argon isotope, as it is the most easily produced by stellar nucleosynthesis in supernovas.

    the name "argon" is derived from the greek word ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive", as a reference to the fact that the element undergoes almost no chemical reactions. the complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. its triple point temperature of 83.8058 k is a defining fixed point in the international temperature scale of 1990.

    argon is produced industrially by the fractional distillation of liquid air. argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. argon is also used in incandescent, fluorescent lighting, and other gas-discharge tubes. argon makes a distinctive blue-green gas laser. argon is also used in fluorescent glow starters.

  • characteristics
  • history
  • occurrence
  • isotopes
  • compounds
  • production
  • applications
  • safety
  • see also
  • references
  • further reading
  • external links

Argon, 18Ar
Vial containing a violet glowing gas
Argon
Pronunciationn/ (AR-gon)
Appearancecolorless gas exhibiting a lilac/violet glow when placed in an electric field
Standard atomic weight Ar, std(Ar)[39.79239.963] conventional: 39.95[1]
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 shell2, 8, 8
Physical properties
Phase at STPgas
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[2]
Critical point150.687 K, 4.863 MPa[2]
Heat of fusion1.18 kJ/mol
Heat of vaporization6.53 kJ/mol
Molar heat capacity20.85[3] 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 occurrenceprimordial
Crystal structureface-centered cubic (fcc)
Face-centered cubic crystal structure for argon
Speed of sound323 m/s (gas, at 27 °C)
Thermal conductivity17.72×103  W/(m·K)
Magnetic orderingdiamagnetic[4]
Magnetic susceptibility−19.6·10−6 cm3/mol[5]
CAS Number7440-37-1
History
Discovery and first isolationLord Rayleigh and William Ramsay (1894)
Main isotopes of argon
Iso­tope Abun­dance Half-life (t1/2) 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
36
Ar
and 38
Ar
content may be as high as 2.07% and 4.3% respectively in natural samples. 40
Ar
is the remainder in such cases, whose content may be as low as 93.6%.
Category Category: Argon
| references

Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas.[6] Argon is the third-most abundant gas in the Earth's atmosphere, at 0.934 % (9340 ppmv). It is more than twice as abundant as water vapor (which averages about 4 000 ppmv, but varies greatly), 23 times as abundant as carbon dioxide (400 ppmv), and more than 500 times as abundant as neon (18 ppmv). Argon is the most abundant noble gas in Earth's crust, comprising 0.00015 % of the crust.

Nearly all of the argon in the Earth's atmosphere is radiogenic argon-40, derived from the decay of potassium-40 in the Earth's crust. In the universe, argon-36 is by far the most common argon isotope, as it is the most easily produced by stellar nucleosynthesis in supernovas.

The name "argon" is derived from the Greek word ἀργόν, neuter singular form of ἀργός meaning "lazy" or "inactive", as a reference to the fact that the element undergoes almost no chemical reactions. The complete octet (eight electrons) in the outer atomic shell makes argon stable and resistant to bonding with other elements. Its triple point temperature of 83.8058 K is a defining fixed point in the International Temperature Scale of 1990.

Argon is produced industrially by the fractional distillation of liquid air. Argon is mostly used as an inert shielding gas in welding and other high-temperature industrial processes where ordinarily unreactive substances become reactive; for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon is also used in incandescent, fluorescent lighting, and other gas-discharge tubes. Argon makes a distinctive blue-green gas laser. Argon is also used in fluorescent glow starters.