All practice pages/Interatomic theory/Diatomics
The molecule
Two hydrogen atoms sharing one pair of electrons: the lightest gas there is, and one that burns to nothing but water.
Hydrogen burns in air with an almost invisible pale-blue flame and gives water and nothing else. Mixed with air anywhere between 4% and 75% hydrogen, it explodes when lit, which is what destroyed the airship Hindenburg in 1937. It combines directly with the halogens (with fluorine on contact, with chlorine when the mixture is lit or hit by bright light) and, with a catalyst and pressure, with nitrogen to make ammonia. It pulls oxygen away from many metal oxides, leaving the metal behind.
Industry makes most of it by reacting methane with steam over a nickel catalyst, and some by splitting water with electricity. In a lab, an active metal such as zinc dropped into acid releases it, which is how Cavendish first collected it.
Most hydrogen goes into ammonia for fertilizer and into oil refineries, where it strips sulfur out of fuels. It hardens vegetable oils into margarine, makes methanol, powers fuel cells and, as a liquid at −253 °C, fuels rockets.
Flammable over a very wide range of mixtures, and its flame is nearly invisible. It is so light that a leak rises and disperses quickly outdoors, but collects under ceilings indoors.