Element 9, fluorine, is the first of the halogens, from the Greek halos, “salt”, and gonos, “to bring forth”. All of the members of this family tend to form salts with metals, but fluorine is unique amongst the halogens in that it forms compounds with EVERY element ever tried except for helium and neon.
Fluorine is by far the most reactive element, having everything just right for extreme chemical behavior. It is a small atom that forms a small ion. Its electrons are tightly bound in its ionic form, but oddly molecular fluorine has a remarkably weak bond for a halogen, only iodine having a weaker one.
The element has been known in the form of naturally occurring salts since the Middle Ages, when these minerals were used as fluxes in metal smelting. The purpose of a flux is to make the ore and reducing agent mixture easier to melt, thus speeding the reaction since liquid state reactions occur much faster than solid state ones. A secondary use of a flux is to protect the newly won metal from atmospheric oxygen by forming a protective layer that floats on the metal.