Argon is a chemical element whose symbol is Ar and whose atomic number is 16. It is an inert gas located in group 16 of the periodic table. With a presence of 0.943% (9340 ppmv) , argon is the third largest gas in the Earth's atmosphere. This amounts to more than twice that of water vapor (average 4,000 ppmv), 23 times that of carbon dioxide (400 ppmv) , and 500 times that of neon (16 ppmv) . Argon is the cheapest of the inert gases present in the Earth's crust , where its presence is 0.00015%.