The halogens are all non-metals with coloured vapours
Fluorine is a very reactive, poisonous yellow gas
Chlorine is a fairly reactive, poisonous dense green gas
Bromine is a dense, poisonous red-brown volatile liquid
Iodine is a dark grey crystalline solid or a purple vapour
They all exist as molecules which are pairs of atoms
Learn these trends
As you go down Group 7 the halogens
* Become less reactive
* It’s harder to gain an extra electron, because the outer shell’s further from the nucleus
* Have higher melting and boiling points
* Have higher relative atomic mass
All the Group 7 elements react in similar ways.
This is because they all have seven electrons in their outer shell
Halogens can form molecular compounds
Halogen atoms can share electrons via covalent bonding with other non-metals so as to achieve a full outer shell
* For example, HCI, PCI5, HF and CCI4 contain covalent bonds
* The compounds that form when halogens react with non-metals all have simple molecular structures
Halogens form ionic bonds with metals
The halogens from 1-ions called halides
* F-, CI-, Br- and I-
When they bond with metals
* Na+Ci or Fe3+Br-3
The compounds that form have ionic structures
The diagram shows the bonding in sodium chloride, NaCI
More reactive halogens will displace less reactive ones
A displacement reaction can occur between a more reactive halogen and the salt of a less reactive one
* E.g. Chlorine can displace bromine and iodine form an aqueous solution of its salt(a bromine or iodine)
* Bromine will also displace iodine because of the trend in reactivity
* Cl2 + 2KI - I2 + 2KCI
* Pale green - Brown
* CL2 + 2KBr - Br2 + 2KCI
* Pale green - Orange