All practice pages/Interatomic theory/Elements
Element 9, a halogen
The most electronegative element and the most reactive one, found in nature only as fluoride and never on its own.
Period 2, group 17: the corner of the 7, where the top stroke turns down the halogen column. The other halogens are tinted, and every cell opens its own article.
Fluorine has 9 electrons, one for every proton, so the atom carries no charge. Below are the same 9 electrons written two ways.
1s² 2s² 2p⁵
Short form: [He] 2s² 2p⁵, 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 2p⁵, and 2 + 5 is 7.
Fluorine sits in period 2 and has 2 shells. The period number counts the shells.
The outer shell holds 7 electrons. Those are the ones fluorine 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 17 means 7.
Seven valence electrons, one short of a full shell, so it gains one to form the F⁻ ion or shares one in a covalent bond.
Seven valence electrons, one short of eight. Two fluorine atoms share one pair, a single bond, and each has its octet.
About the thirteenth most common element in the crust, always as fluoride: in fluorite (CaF₂), in the fluorapatite of phosphate rock and of tooth enamel, and in cryolite (Na₃AlF₆). It is never free in nature, because F₂ reacts with almost everything it touches.
The hardest element to isolate. Several chemists in the 1800s were poisoned trying, and some died. Henri Moissan finally made F₂ in 1886 by electrolysis of potassium fluoride dissolved in liquid hydrogen fluoride, and won the 1906 Nobel Prize for it. The name comes from fluorspar, from the Latin fluere, to flow: the mineral was added to ores to make them melt.
Fluoride in toothpaste and drinking water hardens tooth enamel. Fluorine compounds make non-stick Teflon coatings, refrigerants, the uranium hexafluoride used to enrich nuclear fuel, and about a fifth of modern medicines.