Reactivity of Halogens
The halogens get less reactive going down the group. Or in other words the reactivity of the halogens decreases with increase in atomic number. This is the opposite trend to that seen in the alkali metals in Group 1 of the periodic table.
Fluorine is the most reactive element in Group 7. In fact it is the most reactive of all non-metals.
Reactions of Halogens with Iron Wool
The animation below demonstrates the trend in reactivity by the reaction of the halogens with iron wool.
Reaction with alkali metals
The halogens react with metals to make salts called metal halides.
metal + halogen ——→ metal halide
For example, sodium reacts with chlorine to make sodium chloride (common salt).
sodium + chlorine ——→ sodium chloride
2Na(s) + Cl2(g) ——→ 2NaCl(s)
The reaction between sodium and a halogen becomes less vigorous down the group. Fluorine reacts violently with sodium at room temperature. Chlorine reacts very vigorously when in contact with hot sodium. Iodine reacts slowly with hot sodium.