Bonding, Vapour Pressure and Boiling Point
There is a relationship between :
- intermolecular bond strength
- vapour pressure, and
- boiling point
These diagrams summarises these concepts.
If a liquid has strong intermolecular forces holding its molecules together :
If the molecules of a liquid are strongly bonded to each other, irrespective of the reason,
- then obviously this liquid will not easily evaporate.
- There will be less vapour above the surface of the liquid, which means that there will be a low vapour pressure (the pressure caused by this vapour).
- Also, since the bonds are strong, this liquid will be difficult to boil, and will thus have a high boiling point.
You must ensure that you follow the relationships between the three concepts above.
If a liquid has weak intermolecular forces holding its molecules together :
If the molecules of a liquid are weakly bonded to each other, irrespective of the reason,
- then obviously this liquid will easily evaporate.
- There will be more vapour above the surface of the liquid, which means that there will be a high vapour pressure (the pressure caused by this vapour).
- Also, since the bonds are weak, this liquid will be easy to boil, and will thus have a low boiling point.
You must ensure that you follow the relationships between the three concepts above.