Fluoride is the anion F−, the reduced form of fluorine when as an ion and when bonded to another element. Both organofluorine compounds and inorganic fluorine containing compounds are called fluorides.[2] Fluoride, like other halides, is a monovalent ion (−1 charge). Its compounds often have properties that are distinct relative to other halides. Structurally, and to some extent chemically, the fluoride ion resembles the hydroxide ion. Fluorine-containing compounds range from potent toxins such as sarin to life-saving pharmaceuticals such as efavirenz, and from inert materials such as carbon tetrafluoride to the highly reactive sulfur tetrafluoride. The range of fluorine-containing compounds is vast because fluorine is capable of forming compounds with all the elements except helium and neon.