1. Chemistry 20

2. Review Predicting Polarity – Steps 1: Draw the Lewis Formula – Step 2: Bases on VSEPR Theory, draw the stereochemical formula – Step 3: Add the electronegativities, assign δ + or δ – Step 4: Draw in the bond dipoles – Step 5: Add the vectors – If cancel each other out or add to zero – non polar – If they do not cancel each other out – polar

3. Example OF 2 Therefore Polar

4. Dipole – Dipole – attractions between dipoles London Forces- due to the simultaneous attraction between a momentary dipole in a molecule and the momentary dipoles in the surrounding molecules

5. If other factors are equal then: – The more polar the molecule, the strong the dipole – dipole force therefore the higher boiling point it will have – The greater the number of electrons per molecule, the stronger the London force and therefore the higher boiling point Predicting with Dipole – Dipole and London Forces

6. You can explain and predict the relative boiling points of two substances if – The London force is the same but the dipole- dipole force is different – The dipole-dipole force is the same but the London force is different – Both the London force and the Dipole- Dipole force are greater for one substance

7. You cannot explain and predict the relative boiling points of two substances if One of the substances has a stronger dipole- dipole force, and the other substance has a stronger London force The molecules of the two substances differ significantly in shape The central atom of either molecule has an incomplete octet

8. Example Problem Using London Forces and dipole-dipole forces, state the kind of intermolecular forces (s) present between molecules of the following substance – Water (Solvent) - London forces – Carbon Dioxide (Dry Ice) – London Forces – Methane – London Forces

9. Questions Page 109 – Questions 2 & 3

10. Hydrogen Bonding Hydrogen nucleus could be shared between pairs of electrons on adjacent molecules