Group 7 halogens

What you need to know

• Group 7 elements are halogens with seven electrons in their outer shell and similar reactions.
• Halogens are non-metals that exist as diatomic molecules made of pairs of atoms.
• Relative molecular mass, melting point and boiling point increase down Group 7, while reactivity decreases.
• A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

The big picture

The elements in Group 7 are called the halogens. They are non-metals, have seven electrons in their outer shell and exist as diatomic molecules made from pairs of atoms. Going down Group 7, relative molecular mass, melting point and boiling point increase, while reactivity decreases. A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt, and these trends can be used to make predictions.

Build the Group 7 picture

Move from shared structure to trends and displacement.

1. 1

   Start with seven

   Every Group 7 halogen has seven electrons in its outer shell, which links the group to similar reactions.

2. 2

   Picture pairs

   Halogens are non-metals whose molecules consist of pairs of atoms, so they are diatomic molecules.

3. 3

   Follow the physical trends

   Going down Group 7, relative molecular mass, melting point and boiling point all increase.

4. 4

   Reverse for reactivity

   Unlike those three increasing trends, reactivity decreases going down Group 7.

5. 5

   Use the reactivity order

   A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

6. 6

   Turn trends into predictions

   A position further down Group 7 lets you predict higher relative molecular mass, melting point and boiling point, but lower reactivity.

Tap any cell to reveal it. Tap a column header to read one property down every item.

Predict the displacement

Commit to the reactivity rule before revealing the answer.

Halogen A is more reactive than halogen B. What happens when A is added to an aqueous solution of a salt containing B?

Chlorine, bromine and iodine reactions

The required comparison includes reactions with both metals and non-metals.

Group 7 essentials

Keep the core vocabulary tied to the trends.

Memory hook

Down Group 7: mass, melting and boiling go UP; reactivity goes DOWN.

Check yourself

If one halogen is below another in Group 7, what can you predict about their relative reactivity and boiling points?