Chemical properties of the halogens

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 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. The reaction of sodium with fluorine will be more vigorous than the reaction between sodium and chlorine.


Write a balanced equation for the reaction of potassium with bromine to produce solid potassium bromide, KBr. Include state symbols.

2K(s) + Br2(l) → 2KBr(s)

The halogens also react with other metals, such as iron. The table describes what is seen when halogens react with iron wool.

FluorineCold iron wool burns to produce white iron(III) fluoride
ChlorineHot iron wool burns vigorously to produce orange-brown iron(III) chloride
BromineHot iron wool burns quickly to produce red-brown iron(III) bromide
IodineHot iron wool reacts slowly in iodine vapour to produce grey iron(II) iodide

Write a balanced equation for the reaction of iron with chlorine to produce solid iron(III) chloride, FeCl3. Include state symbols.

2Fe(s) + 3Cl2(g) → 2FeCl3(s)

Chemical 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.