An interhalogen is a binary compound of one halogen with another. Interhalogens have the general formula XX'n, where X' is the more electronegative halogen (electronegativity), and n = 1, 3, 5, or 7. They are volatile, covalent, reactive substances. Bromine (III) fluoride (BrF2) is a very powerful fluoridating agent, and a good solvent for fluorine compounds. Polyhalide salts, containing ions XX'n+1-, are formed by reacting halogens or interhalogens with halide.