All practice pages/Interatomic theory/Elements
Element 1, a nonmetal
The lightest and most abundant element in the universe, and the first box on the periodic table.
Period 1, group 1: alone in the top left corner, the one nonmetal on the metal side of the table. The other nonmetals are tinted, and every cell opens its own article.
A hydrogen atom has one electron in a shell with room for two. Two hydrogen atoms share a pair and both shells are full, so the stable form is H-H.
About three quarters of the ordinary matter in the universe by mass is hydrogen; it is what stars burn. On Earth almost none of it is free. The air holds about one part per million of H₂, because the gas is light enough to escape to space. Nearly all of Earth's hydrogen is bound up in water, in living things and in fossil fuels.
Henry Cavendish collected it in 1766 by dropping metals into acid and called it inflammable air. Antoine Lavoisier showed in 1783 that burning it made water, and named it hydrogen: water-former.
Most hydrogen goes into making ammonia for fertilizer and into refining crude oil. It also hardens vegetable oils, powers fuel cells and, as a liquid, fuels rockets. Its heavy isotope deuterium is used in nuclear research, and radioactive tritium makes self-lit exit signs and watch dials glow.