Fluorine is the most reactive element of all in Group 7.
You can see the trend in reactivity if you react the halogens with iron wool.
|Halogen||Reaction with iron wool|
|Fluorine||Reacts with almost anything instantly. Very few scientists handle fluorine because it is so dangerous. Produces iron(III) fluoride.|
|Chlorine||Reacts with heated iron wool very quickly, although not as quickly as fluorine does. Produces iron(III) chloride.|
|Bromine||Has to be warmed and the iron wool heated. The reaction is faster than that of iodine but slower than that of chlorine. Produces iron(III) bromide.|
|Iodine||Has to be heated strongly and so does the iron wool. The reaction is slow. Produces iron(III) iodide.|
Iron + chlorine → iron(III) chloride
2Fe + 3Cl2 → 2FeCl3
Iron + bromine → iron(III) bromide
2Fe + 3Br2 → 2FeBr3
Iron + iodine → iron(III) iodide
2Fe + 3I2 → 2FeI3