Fluorie is the reduced form of fluorine. Both organic and inorganic compounds containing the element fluorine are considered fluorides. As a halogen, fluorine forms a monovalent ion (−1 charge). The range of fluorides is considerable as fluorine forms compounds with all elements except He and Ne. Fluorides range from severe toxins such as sarin to life-saving pharmaceuticals such as efavirenz and from refractory materials such as calcium fluoride to highly reactive sulfur tetrafluoride.