C9.2a Group Properties Halogens.notebook
October 12, 2014
Group 7 The Halogens
Chlorine, bromine and iodine are examples and have 7 valency electrons. The halogens are diatomic ­ this means they exist as molecules, each with a pair of atoms. Chlorine molecules have the formula Cl2, bromine Br2 and iodine I2.
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C9.2a Group Properties Halogens.notebook
October 12, 2014
C9.2 Group Properties
The halogens show trends in physical properties down the group.
Boiling Point
Melting Point
Increases
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C9.2a Group Properties Halogens.notebook
October 12, 2014
C9.2 Group Properties
Physical Properties
pale yellow
Reactivity deceases
Colour gets deeper
black
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C9.2a Group Properties Halogens.notebook
October 12, 2014
C9.2 Group Properties
Reactions with metals
The halogens react with metals to make salts called metal halides.
metal + halogen metal halide
For example, sodium reacts with chlorine to make sodium chloride (common salt).
sodium + chlorine sodium chloride
2Na(s) + Cl2(g) 2NaCl(s)
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C9.2a Group Properties Halogens.notebook
October 12, 2014
C9.2 Group Properties
Displacement reactions
When chlorine (as a gas or dissolved in water) is added to sodium bromide solution (halide) the chlorine takes the place of the bromine. Because chlorine is more reactive than bromine, it displaces bromine from sodium bromide. The solution turns brown. This brown colour is the displaced bromine. The chlorine has gone to form sodium chloride.
In the following equation, Cl and Br have swapped places.
chlorine + sodium bromide sodium chloride + bromine
Cl2(aq) + 2NaBr(aq) 2NaCl(aq) + Br2(aq)
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C9.2a Group Properties Halogens.notebook
October 12, 2014
C9.2 Group Properties
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