The halogens are all extremely reactive elements. The first halogen, fluorine, is the most reactive element in the periodic table. There are six halogens, and they are fluorine, chlorine, bromine, iodine, astatine, and the recently discovered ununseptium. Astatine and ununseptium are radioactive, and as of right now no one knows what they look like due to their short half-lives. The halogens are the only group that contains elements in all three states of matter at room temperature. Fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids. Ununseptium's properties are unknown, but it is thought to be a solid. The halogens make up Group 17 of the periodic table, and all of them are nonmetals.
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