Draw these shapes Cl 2, HCl, H 2 O, NH 3, CH 4, BF 3 and NH 4 +, SF 6 trigonal planar tetrahedral octahedral pyramidal non-linear linear.

Dipoles and Van der Waals forces LOs Describe intermolecular forces based on permanent dipoles, induced dipoles (van der Waals forces), and noble gases.

Key words you need to understand by the end of the lesson Electronegativity Dipole Polar molecules Hydrogen bonding Non-polar molecules Intermolecular forces Van der Waals forces

What are intermolecular forces? What is electronegativity?

Permanent Dipole

Describing with key words Molecules with permanent dipoles have intermolecular forces between them. These intermolecular forces are weak electrostatic forces.

What molecules have permanent dipoles? Molecules that have asymmetric bonds usually have dipoles.

Van der Waals forces These are intermolecular forces caused by temporary induced dipoles. Electrons move around randomly, so occasionally there are more one side of a molecule than the other.

Two examples Molecules cause the other molecules to have a temporary dipole. This is called an induced dipole More electrons = stronger Van der Waals Noble gases Noble gases are electrically stable, but they can still experience Van der Waals forces.

Boiling Points What do you think these intermolecular attractions mean for boiling points?

Plenary 1) What is the different between permanent dipole interactions and Van der Waals forces? 2) Why does xenon have a higher boiling point than helium? 3) Explain why symmetric molecules don’t have dipoles. 4) What type of bonding are dipole-dipole interactions similar to?