Group 7Oxford AQA IGCSE Chemistry: Revision notes
Section 1
What are Group 7 elements called?
Group 7 of the periodic table contains the halogens: fluorine, chlorine, bromine, iodine, and astatine. They are non-metals and exist as diatomic molecules (pairs of atoms), such as Cl2, Br2 and I2.
Section 2
How do halogens react with metals?
Halogens react with metals to form ionic compounds. Because halogens have seven electrons in their outer shell, they gain one electron to form a halide ion with a single negative charge (-1).
Sodium reacts with chlorine to form sodium chloride (NaCl), where the chloride ion (Cl-) carries a -1 charge.
Section 3
How does state and colour change down the group?
At room temperature, the halogens change state as you go down the group, reflecting their increasing melting and boiling points:
| Halogen | State at room temperature | Colour |
|---|---|---|
| Fluorine | Gas | Pale yellow |
| Chlorine | Gas | Pale green |
| Bromine | Liquid | Red-brown |
| Iodine | Solid | Grey/purple-black |
Going down Group 7, the elements have higher melting and boiling points.
Section 4
How does reactivity change down Group 7?
Reactivity decreases going down Group 7. This means fluorine is the most reactive halogen and iodine is the least reactive. This is the opposite trend to Group 1, where reactivity increases down the group.
A common error is assuming all groups get more reactive going down — Group 1 does, but Group 7 gets less reactive going down.
Must Know
- Group 7 = the halogens: fluorine, chlorine, bromine, iodine (all diatomic, non-metal)
- Halogens react with metals to form ionic compounds; the halide ion carries a -1 charge
- Going down the group: melting and boiling points increase (gas → liquid → solid)
- Going down the group: reactivity decreases
- Fluorine is the most reactive halogen; iodine is the least reactive
- This trend is the opposite of Group 1, where reactivity increases down the group
That's the notes covered.
Carry on to the next subtopic.