What is Argon atom?

     

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.  Argon is the third-most abundant gas in the Earth's atmosphere, at 0.934%.  It is more than twice as abundant as water vapor (which averages about 4000 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 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. 

     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 form burning.  Argon is also used in incandescent, fluorsecent lighting and other gas-discharge tubes.  Argon makes a distinctive blue-green gas laser.  Argon is also used in fluorescent glow starters.