Intermolecular Forces

Means the forces that take place between separate molecules. Much weaker than ionic or covalent bonds (almost 100x weaker) so they aren’t held together as strongly.

Dipole-dipole forces

Present between polar molecules, both molecules must be polar. The more polar the molecules, the strogner the force. Attraction happens between the partial positive charge of one molecule, and the partial negative charge of the other, as opposites attract.

Hydrogen bonding

A very strong dipole-dipole force found only when hydrogen (H) is bonded to: Fluorine (F), Oxygen (F) or Nitrogen (N), three largest EN values on chart. F-H, O-H, N-H bonds only.

London Dispersion forces

Happens between non-polar molecules, normally these molecules are not attracted to each other, but since their electrons are in motion they can temporarily gain dipole-dipole attraction with temporary partial positive and negative changes. All molecules experience this force, but it depends on two factors:

• size; bigger molecules have more London dispersion forces and a better chance of gaining more

• surface area;

Ion-dipole forces

Not really an intermolecular force, happens between a polar molecule with partial charges and an ion (not a molecule).