A more reactive halogen can displace a less reactive halogen from solutions of its salts. For example, chlorine is more reactive than iodine. A solution of chlorine can displace iodine from potassium iodide solution:
chlorine + potassium iodide → potassium chloride + iodine
Cl2(aq) + 2KI(aq) → 2KCl(aq) + I2(aq)
The reaction mixture turns darker as iodine solution forms.
The slideshow shows what happens when solutions of chlorine, bromine and iodine are added to various potassium halide salts.
Adding chlorine, bromine and iodine to halogen salts
Write a balanced equation for the displacement reaction of bromine solution with sodium iodide solution.
Br2(aq) + 2NaI(aq) → 2NaBr(aq) + I2(aq)
Can iodine displace chlorine from sodium chloride solution? Explain your answer.
No, because iodine is less reactive than chlorine.
When a group 7 element takes part in a reaction, its atoms each gain one electron. These atoms form negatively charged ions. The ions have a stable arrangement of electrons, with a complete outer shell.
Going down group 7: