Chemical properties of the group 7 elements

Atoms of group 7 elements all have seven electrons in their outer shell. This means that the halogens all have similar chemical properties.

Reactions with group 1 metals

The halogens react with metals to produce salts (the word 'halogen' means 'salt former'). For example, chlorine reacts with sodium:

sodium + chlorine → sodium chloride

2Na(s) + Cl2(g) → 2NaCl(s)

Sodium and chlorine react vigorously when heated, giving an orange flame and clouds of white sodium chloride.

The halogens become less reactive going down group 7.


Write the balanced chemical equation for the reaction of lithium with bromine to produce lithium bromide, LiBr. Include state symbols.

2Li(s) + Br2(g) → 2LiBr(s)

Chemical test for chlorine

A glass jar contains chlorine gas and a piece of damp-blue litmus paper.Test for chlorine

Damp litmus paper is bleached white when it is placed in chlorine. If damp-blue litmus paper is used, the paper turns red then white.

Halogen displacement reactions

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 and iodine solution forms.

Determining a reactivity series

A reactivity series can be worked out by carrying out several displacement reactions. Different combinations of halogen solution and salt solution should be tested so that a reactivity series for Group 7 can be worked out:

  • 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 sodium salts or potassium salts are used - it works the same for both types of salt.

The periodic table, containing all the known elements, arranged in groups and periods