Fluorine belongs to group 17/7A (the halogens), has an atomic number 9, mass of 19.00 amu, and electron configuration of [He] 2s2 2p5. Fluorine is generally found in minerals such as Fluorite, but it can also exist in it's elemental form as a yellow gas F2. It is the most electronegative element, and is also the most reactive of all the elements. It was discovered in 1810 by André-Marie Ampère and was first isolated in 1886 by Henri Moissan.
Fluorine has many uses in industrial chemistry including the enrichment of uranium, hydrofluoric acid, steel and aluminium production, and refrigerants. CFC's (Cholofluorcarbons) were widely used as refrigerants, propellants, and solvents. Products containing CFC's were banned due to Ozone (O3) depletion in the upper atmosphere.
Fluoride ions (F-) reduces decay when applied to teeth, so toothpastes and water are fluroidated. However Fluoride can be toxic and lethal in higher doses (5-10 g for adults). Ingested fluoride forms hydrofluoric acid in the stomach and can then cross cell membranes and binds with calcium, which can interrupt activity of various enzymes. So please don't eat your toothpaste!