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.
Hydrogen has 1 electron, one for every proton, so the atom carries no charge. Below is that one electron written two ways.
1s¹
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14.
Hydrogen sits in period 1 and has 1 shell. The period number counts the shells.
The outer shell holds 1 electron. Those are the ones hydrogen can lose, gain or share, so they are the ones that decide what it bonds with. For a main-group element the group number gives that count: group 1 means 1.
A nonmetal: it gains electrons to form negative ions with metals and shares them in covalent bonds with other nonmetals.
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.