Physical Properties of the Halogens
Trend in boiling points
- Boiling point increases down the group
- We can explain this trend by looking at the forces between the molecules
- Halogens are non-metals and are diatomic molecules at room temperature
- This means that they exist as molecules that are made up of two similar atoms, such as F2
- The halogens are simple molecular structures with weak London forces between the diatomic molecules caused by instantaneous dipole-induced dipole forces
The diagram shows that a sudden imbalance of electrons in a nonpolar molecule can cause an instantaneous dipole. When this molecule gets close to another non-polar molecule it can induce a dipole as the cloud of electrons repel the electrons in the neighbouring molecule to the other side
- The more electrons there are in a molecule, the greater the instantaneous dipole-induced dipole forces
- Therefore, the larger the molecule the stronger the London forces between molecules
- This is why as you go down the group, it gets more difficult to separate the molecules and the boiling point increases