Forces of attraction between molecules. The strength depends on the molecular polarity.
Van de Waals’ Forces
These include London dispersion forces, dipole-induced-dipole, dipole dipole attraction.
London dispersion forces
The random movements of electrons create temporary instantaneous dipoles. The strength depends on:
- Number of electrons: more easily polarized.
- Molecular size: greater electron cloud that is more easily polarized.
- Molecule shape: Longer molecules have more surface area to interact.
Dipole-induced dipole
A polar molecule induces the formation of a temporary dipole in a non-polar molecule.
Dipole-dipole
Intermolecular forces between two polar molecules.
Hydrogen bond
When high electronegative atom bonds with hydrogen, there is strong positive charge on Hydrogen. It allows the Hydrogen to form strong electromagnetic attraction with the negative poles on other atoms. Usually can only occur with: N, F, O. (no, fuck off!)
Properties
| Ionic Compounds | Polar Covalent | Non-polar covalent | |
|---|---|---|---|
| Melting Points | High | Medium | Low |
| Volatility | Low | Medium | High |
| Conductivity | Yes | In solution | No |
| Other than conductivity, these are due to intermolecular forces. Focus on the meaning of each property to explain why. Conductivity is whether or not there are mobile electrons. |