Group seven halogens

Flourine

F2. Is a gas with a pale yellow colour

Chlorine

Cl2. Is a gas with a green colour

Bromine

Br2. Is a liquid with a red-brown colour

Iodine

I2. Is a solid with a grey colour

BP and MP down the group

Boiling and melting point increase down the group as the induced dipole-dipole forces between molecules increase in strength

Volatility down be group

Volatility the ability of the molecule to vaporise decreases down the group as the dipole-dipole bonds are harder to break

Reactivity down the group

Reactivity decreases down the group as atomic radius increases and so does electron shielding making it harder to gain an electron. This cancels out the increase in nuclear charge

Displacement reaction

When a more reactive halogen replaces a less reactive halogen in a compound

Ionic equation for displacement reactions

X2 + 2Y- ——> 2X- + Y2

Test for halide ions

Add dilute nitric acid to the unknown to acidify it and remove any hydroxide and carbonate ions that may be present and affect the results. The add a few drops of silver nitrate solution to the unknown as the Hal ice ions will react with it and form insoluble precipitates of different colours. Then add dilute ( and concentrated if needed) ammonia solution to the unknown as the precipitate becomes less soluble as you go down the group.

Results for test for halide ions

Chlorine forms a white precipitate of AgCl which dissolved in dilute ammonia solution. Bromide forms as cream precipitate of AgBr which dissolves in concentrated ammonia solution. Iodine forms a yellow precipitate of AgI which doesn’t dissolve in ammonia solution. Fluorine produces no precipitate

Hexane

An organic solvent used to identify the halogen present

How to identify using hexane

By shaking a reaction mixture with an organic solvent like hexane the halogen that’s present will readily dissolve in the hexane which will then settle out as a distinct layer above the aqueous solution

Results using hexane

A violet /pink colour for iodine. A orange/red colour for bromine. A very pale green/yellow colour for chlorine