forces acting between molecules

3 types of intermolecular forces (weakest to strongest)

1. Van der Waals- act between all atoms and molecules

2. Dipole-dipole- certain molecules

3. Hydrogen bonding- certain molecules

When does dipole-dipole happen

When molecules are polar

Van der waals

Temporary dipole-dipole, it increase when more number of e-

How does van der Waals forces work

Electrons move rapidly and randomly in a molecule

This causes a temporary dipole in a molecule (A)

This repels electrons in a neighbors (B)

This causes B to have a temporary dipole

Molecule A and B now attract FOR an instant

The strength of van der waals depend on

No of e-

Shape

For hydrogen bonding to be present it must bond directly to

N,O or F

Explain what happens in hydrogen bonding

The polar bond between the H and the N/O/F leaves the H nucleus exposed as H only has one electron. Therefore there is a strong attraction from the lone pair on the N/O/F of one molecule to the exposed H nucleus of another molecules. This is simply a strong intermolecular force- it is NOT a bond.