A-level Chemistry/OCR/Group 7
Group 7 consists of highly reactive non-metals called halogens.
Some main properties of the first 4 elements in group 7 are listed below.
| halogen | formula | colour | physical state | electronic structure |
|---|---|---|---|---|
| fluorine | F2 | pale yellow | gas | 1s22s22p5 |
| chlorine | Cl2 | greenish-yellow | gas | 1s22s22p63s23p5 |
| bromine | Br2 | red-brown | liquid | 1s22s22p63s23p64s23d104p5 |
| iodine | I2 | grey black, purple if in vapour form | solid | 1s22s22p63s23p64s23d104p65s24d105p5 |
Trends
[edit | edit source]The boiling and melting points increase as you go down the group. This is because the strength of the Van Der Waals forces (or induced dipole-dipole interactions) increases since the atoms have more electrons as you descend the group. This trend is highlighted by the fact that the physical state of the halogens changes from gaseous (fluorine) to solid (iodine) down the group. Volatility decreases down the group as the boiling points increase.
As you go down group 7, the halogens become less reactive.
This is because:
Decreasing reactivity,
- Atomic radius increases.
- Nuclear charge increases, so the nuclear attraction on the outer electrons are stronger.
- Electron Shielding increases and outweighs the nuclear attraction.
Redox
[edit | edit source]-Halogens are oxidising agents
-Halogen + electron -> Halide Ion or Reduction agent