Fluorine

Fluorine is the lightest member of the halogen family. At room temperature, it is a pale yellow, highly toxic gas that reacts readily with many substances. In nature, fluorine is found mainly bound to other elements in minerals such as fluorite, also called fluorspar. Industry mines fluorite and converts it into hydrogen fluoride; an electric current passed through a mixture containing hydrogen fluoride and a fluoride salt releases fluorine gas. Its compounds have very different properties from the element itself: fluoride compounds in toothpaste help prevent tooth decay, while the fluorine-containing plastic PTFE, known as Teflon, is used for nonstick coatings.