Argon (Greek word argos = inactive) is a gaseous, mono- atomic, zerovalent, chemical element belonging to the group of rare gases. No genuine rare gas compounds containing argon are known. Argon is heavier than air and has a suffocating effect. The gas is colourless, odourless and non toxic. In enclosed spaces the breathing air is displaced. There are no discernible warning symptoms. Because of its low heat conductivity and chemical inertness, argon is used in a mixture with 10-20% nitrogen for filling light bulbs and, in a mixture with other rare gases, for filling discharge tubes in order to achieve certain colour effects. Argon is also used as a protective gas when steel is electrically welded. 12H2 + O2 -> 2H2O
