Contents
Key Stage 4
Meaning
Intermolecular forces are forces that act between molecules.
About Intermolecular Forces
- Intermolecular forces cause molecules to be attracted to one another or different parts of a molecule may have a negative or positive charge which can cause them to arrange into specific shapes in a solid.
- The strength of intermolecular forces determines the melting point and boiling point of a substance.
Intermolecular Forces and State Changes
- If a solid is heated enough the bonds, holding the particles in fixed positions, break allowing the particles to move past each other, turning the solid into a liquid.
- If a liquid is heated enough the particles can move so fast that they escape the bonds holding the particles to each other which allows them to leave the liquid to become part of a gas.
- The stronger the intermolecular forces the higher the melting point and boiling point of a substance.
Examples
- In Group 7 Fluorine is a gas at room temperature while Iodine is a solid at room temperature because the force of attraction between molecules of Iodine is greater than the force between molecules of Fluorine.
- In Group 6 Oxygen is a gas at room temperature while Sulphur is a solid at room temperature because the force of attraction between molecules of Sulphur is greater than the force between molecules of Oxygen.