2:07 understand how displacement reactions involving halogens and halides provide evidence for the trend in reactivity in Group 7
Group 7 elements are called the Halogens. As you go up group 7 (decreasing atomic number), the elements become more reactive. For example, fluorine is the most reactive and astatine is the least reactive.
A more reactive halogen will displace a less reactive halogen, e.g. chlorine will displace bromine:
By reacting a halogen solution with a potassium halide solution and making observations, the order of their reactivity can be deduced:
Potassium chloride, KCl(aq)
Potassium bromide, KBr(aq)
Potassium iodide, KI(aq)
Chlorine, Cl2(aq)
No change
Colourless to orange
Colourless to brown
Bromine, Br2(aq)
No change
No change
Colourless to brown
Iodine, I2(aq)
No change
No change
No change
From the above results, chlorine displaces both bromine and iodine, and bromine displaces iodine. Therefore the order of reactivity is: chlorine is more reactive than bromine, which in turn is more reactive than iodine.
