All practice pages/Interatomic theory/Diatomics
The molecule
Two oxygen atoms joined by a double bond: the gas that fire, rust and every breath depend on.
Oxygen does not burn, but almost everything burns in it. It reacts with nearly every element to form oxides: quickly and hot in a fire, slowly in the rusting of iron, and in a controlled way inside every cell of your body, where glucose is oxidized to carbon dioxide and water to release energy. Things that only smolder in air burn brightly in pure oxygen; a glowing splint bursts back into flame, which is the classic test for the gas.
Industry distills it from liquid air alongside nitrogen. Home oxygen concentrators pull it from air with adsorbent beds that trap the nitrogen. Splitting water with electricity gives it too. In a lab, hydrogen peroxide dripped onto manganese dioxide fizzes with oxygen. Nature makes it by photosynthesis.
Steelmaking uses the most: oxygen blown through molten iron burns out the carbon. Medical oxygen, oxy-acetylene cutting and welding torches, rocket engines that burn liquid oxygen with hydrogen or kerosene, water-treatment plants and fish farms all depend on it.
It makes fires burn far hotter and faster. Grease or oil in contact with high-pressure oxygen can ignite on its own, so oxygen fittings are kept oil-free. Liquid oxygen causes severe cold burns.