Editing Period 3 element (section)

=== Argon ===
{{Main|Argon}}
''Argon'' (symbol '''Ar''') is the third element in group 18, the [[noble gas]]es. Argon is the third most common gas in the [[Earth's atmosphere]], at 0.93%, making it more common than [[carbon dioxide]]. Nearly all of this argon 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, being the preferred argon isotope produced by [[stellar nucleosynthesis]].

The name "argon" is derived from the [[Greek language|Greek]] neuter adjective ''ἀργόν'', meaning "lazy" or "the inactive one", as the element undergoes almost no chemical reactions. The complete [[octet rule|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&nbsp;[[Kelvin|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 non-reactive substances become reactive: for example, an argon atmosphere is used in graphite electric furnaces to prevent the graphite from burning. Argon gas also has uses in incandescent and fluorescent lighting, and other types of gas discharge tubes. Argon makes a distinctive [[Ion laser#Argon laser|blue–green gas laser]].