All practice pages/Interatomic theory/Elements
Element 7, a nonmetal
Four fifths of every breath you take, and nearly inert in that form; in compounds, the element that every protein and every gene is built on.
Period 2, group 15: the first of the three that draw the top of the 7. The other nonmetals are tinted, and every cell opens its own article.
Nitrogen has 7 electrons, one for every proton, so the atom carries no charge. Below are the same 7 electrons written two ways.
1s² 2s² 2p³
Short form: [He] 2s² 2p³, where [He] stands for the 2 electrons helium already has.
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. Shell 2 here is 2s² 2p³, and 2 + 3 is 5.
Nitrogen sits in period 2 and has 2 shells. The period number counts the shells.
The outer shell holds 5 electrons. Those are the ones nitrogen 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 15 means 5.
A nonmetal: it gains electrons to form negative ions with metals and shares them in covalent bonds with other nonmetals.
Five valence electrons, three short of eight. Two nitrogen atoms share three pairs, a triple bond, and each ends up with a full octet.
Nitrogen gas is 78% of the air by volume. In the ground it is scarce, because most nitrates dissolve and wash away; the one great natural deposit was the caliche of the Atacama desert in Chile. Every protein and every strand of DNA contains it, which is why nitrogen fertilizer matters so much.
Daniel Rutherford separated it from air in 1772 and called it noxious air, because a mouse could not live in it. Lavoisier called it azote, without life. The name nitrogen, nitre-former, came from Jean-Antoine Chaptal in 1790.
As N₂ gas it keeps food and chemicals from reacting with air, and as a liquid it freezes and preserves. Its compounds do even more: ammonia and nitrates feed the world's crops, nitrates and nitro compounds make explosives, and nitrogen is part of every protein, of nylon and of many medicines.