B) Group 7 (halogens) – chlorine, bromine and iodine

Chlorine (Cl) colour + physical state at room temperature

pale green gas

Bromine (Br) colour + physical state at room temperature

reddish brown liquid

Iodine (I) colour + physical state at room temperature

grey-black solid

trends in physical properties of halogens

The melting and boiling point of the halogens increases down the group

Reactivity decreases down the group

how displacement reactions involving halogens and halides work

explain: chlorine dissolved in sodium bromide solution

When chlorine (as a gas or dissolved in water) is added to sodium bromide solution, 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.

• chlorine + sodium bromide → sodium chloride + bromine

• Cl₂(aq) + 2NaBr(aq) → 2NaCl(aq) + Br₂(aq)