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

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

-Halogens are oxidising agents

-Halogen + electron -> Halide Ion or Reduction agent