Reactivity series
If you test different combinations of the halogens and their salts, you can work out a A list of elements in order of their reactivity, usually from most reactive to least reactive. for Group 7:
- the most reactive halogen displaces all of the other halogens from solutions of their salts, and is itself displaced by none of the others
- the least reactive halogen displaces none of the others, and is itself displaced by all of the others
It doesn’t matter whether you use sodium salts or potassium salts – it works the same for both types.
The slideshow shows what happens when chlorine, bromine and iodine are added to various halogen salts:
Image caption, Adding chlorine, bromine and iodine to halogen salts
Chlorine water is added to three solutions
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Halogen displacement reactions are redox reactions because the halogens gain electrons and the halide Electrically charged particle, formed when an atom or molecule gains or loses an electron/electrons. lose electrons.
When we consider one of the displacement reactions, we can see which element is being oxidised and which is being reduced.
bromine + potassium iodide → iodine + potassium bromide
Br2 + 2KI → I2 + 2KBr
As an A chemical equation that shows how positively charged ions join with negatively charged ions to make a compound. (ignoring the ‘spectator’ potassium ions):
Br2 + 2I– → I2 + 2Br–
We can see that the bromine has gained electrons, so it has been reduced. The iodide ions have lost electrons, so they have been oxidised.
Explaining reactivity [Higher tier only]
As we descend Group 7, the reactivity decreases. For stability, the atom needs to have a full outer shell. Group 7 elements need to gain 1 electron to have a full shell.
As a result, a negative ion is formed:
Cl + e– → Cl–
As we descend the group:
- there are more shells between the nucleus and the outer electron
- the force of attraction between the nucleus and outer electron decreases
- it becomes harder to gain the outer electron
