<Dl> <Dd> 2Fe + 3X → 2FeX </Dd> </Dl> <Dd> 2Fe + 3X → 2FeX </Dd> <P> However, when iron reacts with iodine, it forms only iron (II) iodide . </P> <P> Iron wool can react rapidly with fluorine to form the white compound iron (III) fluoride even in cold temperatures . When chlorine comes into contact with heated iron, they react to form the black iron (III) chloride . However, if the reaction conditions are moist, this reaction will instead result in a reddish - brown product . Iron can also react with bromine to form iron (III) bromide . This compound is reddish - brown in dry conditions . Iron's reaction with bromine is less reactive than its reaction with fluorine or chlorine . Hot iron can also react with iodine, but it forms iron (II) iodide . This compound may be gray, but the reaction is always contaminated with excess iodine, so it is not known for sure . Iron's reaction with iodine is less vigorous than its reaction with the lighter halogens . </P>

Compounds that contain only carbon fluorine and hydrogen (no chlorine) are called