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.
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.