All practice pages/Interatomic theory/Elements
Element 8, a nonmetal
The most abundant element in the Earth's crust, in the oceans and in your body, and the one that makes fire and breathing possible.
Period 2, group 16: the middle of the top stroke of the 7. The other nonmetals are tinted, and every cell opens its own article.
Oxygen has 8 electrons, one for every proton, so the atom carries no charge. Below are the same 8 electrons written two ways.
1s² 2s² 2p⁴
Short form: [He] 2s² 2p⁴, 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 2p⁴, and 2 + 4 is 6.
Oxygen sits in period 2 and has 2 shells. The period number counts the shells.
The outer shell holds 6 electrons. Those are the ones oxygen 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 16 means 6.
A nonmetal: it gains electrons to form negative ions with metals and shares them in covalent bonds with other nonmetals.
Six valence electrons, two short of eight. Two oxygen atoms share two pairs, a double bond, and both reach eight.
Nearly half of the Earth's crust by mass is oxygen, locked into silicate rock and sand. It is 21% of the air by volume, 89% of water by mass and about 65% of your body by mass. Almost all of the free O₂ in the air was put there by photosynthesis. Oxygen has a second elemental form, ozone, O₃: three atoms instead of two, made by lightning and by ultraviolet light high in the atmosphere.
Carl Wilhelm Scheele made it in 1771 or 1772 by heating mercury oxide and other compounds, and called it fire air. Joseph Priestley made it independently in 1774 and published first. Lavoisier named it oxygen, acid-former, in 1777 because he believed every acid contained it. He was wrong about that, but the name stuck.
Steelmaking, hospitals, welding torches and rocket engines use oxygen gas. In compounds it is everywhere: water, rock, glass, cement, and every carbohydrate, fat and protein in food.