1. Intermolecular Forces

2. Intermolecular forces allow liquids and solids to exist and are responsible for the differences in boiling points and melting points, etc.
You must overcome IMF forces to change from solid to liquid, liquid to gas
Stronger IMF=higher boiling points

3. Describe the movement of the particles

4. How to change between phases?

5. To change between phases we must break intermolecular forces, forces between the molecules
We add energy to break them
But what causes them?

6. Remember Electronegativity?
Non sharers =Ionic Bonds (EN difference = 4.0 – 1.7): e- gained by strong atom and lost by weak atom
Poor sharers =Polar Covalent Bonds (EN difference = 1.7 – 0.4): e- shared unequally by 2 atoms
Good sharers=Nonpolar Covalent Bonds (EN difference = 0.4 – 0.0): e- shared equally by 2 atoms

7. Types of intermolecular forces
Intermolecular force: attraction between molecules in a substance
In covalent substances
Hydrogen bonding
Dipole dipole
London dispersion forces

8. Dipole-dipole Unequal sharing causes polarity A dipole is a polar bond
Non symmetrical geometry can cause polarity
Shown like this
Dipole dipole attractions between polar covalent molecules

11. Hydrogen Bonding
Attractions due to polar covalent bonding due to Hydrogen-Oxygen, Hydrogen-Nitrogen and Hydrogen-Fluorine bonds
If Hydrogen is bonded to an O, N or F, it will have a large enough electronegativity difference to attract to dipoles or other hydrogen bonds

12. Examples of hydrogen bonding
DNA

13. Example of hydrogen bonding
Water and ice and density

14. London dispersion forces
Occur in non polar covalent bonds, because electrons are not equally distributed