Group 7 - Halogens

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Group 7 elements are known as 'Halogens'

Group 7 is made up of fluorine, chlorine, bromine, iodine and astatine

All Group 7 elements have 7 electrons in their outer shell so they all react by gaining one electron to form a negative ion.

This means they all have similar properties.

As you go down group 7 the melting points and boiling points of the halogens increase.

This means at room temperature:

As you go down group 7, the halogens become less reactive - there's less inclination to gain the extra electron to fill the outer shell when it's further out from the nucleus (there's a larger atomic radius).

Chlorine (Cl2) is a fairly reactive, poisonous, dense green gas (low boiling point)

Bromine (Br2) is a dense, poisonous, orange liquid

Iodine (I2) is a dark grey crystalline solid (high boiling point)

Reduction is the gain of electrons:-

Halogens are keen to gain an electron to form 1- ion with a stable electronice structure.

The more reactive the halogen the happier it is to gain an electron.

Gain of electrons is called reduction

The Halogens react vigorously with alkali metals (group 1 elements) to form salts called 'metal halides'.

sodium + chlorine → sodium chloride

2Na(s) + Cl2(g) → 2NaCl(s)

More reactive halogens will displace less reactive ones:-

Chlorine can displace bromine and iodine from a solution of bromide or iodide. Bromine will also displace iodine. You could be asked to predict the results of displacement reactions using other halogens - just remember, more reactive halogens displace less reactive ones.

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