Group VII properties
| English | Chinese | Pinyin |
|---|---|---|
| Group VII | 第七族 | dì qī zú |
| halogens | 卤素 | lǔ sù |
| diatomic molecules | 双原子分子 | shuāng yuán zi fèn zǐ |
| displace | 置换 | zhì huàn |
The reactive Group VII 第七族 non-metals
- Chlorine bleaches, iodine stains — the Group VII elements (the halogens 卤素) are reactive non-metals.
- They show clear trends down the group.
Group VII trend lab
Follow halogens down the group and watch reactivity decrease.
How many electrons are in the outer shell of a Group VII element?
Halogens have seven outer electrons.
Halogens gain one electron to form ions with a charge of:
Gaining one electron gives a −1 ion.
Halogens exist as molecules made of two atoms, described as ______.
Cl₂, Br₂ and I₂ are diatomic.
Properties of the halogens
- They exist as diatomic molecules 双原子分子 (Cl₂, Br₂, I₂).
- They have seven outer electrons and gain one to form −1 ions.
Group I gets more reactive down the group; Group VII gets less reactive down
Going down Group VII, reactivity:
Halogens get less reactive down the group.
Trends down the group
- Going down: colour gets darker and they become less reactive.
- The melting and boiling points increase (fluorine gas → bromine liquid → iodine solid).
A more reactive halogen will:
More reactive halogens displace less reactive ones.
Displacement reactions
- A more reactive halogen will displace 置换 a less reactive one from its salt.
- For example, chlorine displaces bromine from a bromide solution.
Worked example. Add chlorine to potassium bromide solution. Chlorine is more reactive, so it displaces the bromine: the solution turns orange as bromine is released. Reactivity decreases down the group.
Chlorine is more reactive, so it displaces bromine; the released bromine turns the colourless solution orange
You've got it
- Group VII (halogens) are diatomic, with seven outer electrons (form −1 ions)
- down the group: darker colour, less reactive, higher melting/boiling points
- a more reactive halogen displaces a less reactive one from its salt