1. Agenda: Hand in your Assignment (last chance!) Check your note on 4.7
Explain key ideas from 4.7 – physical properties of water
Mini-Lab on boiling points of alcohols (page 258)
Homework: from 4.7, p. 247 #1-8
From Lab: p. 258 Analyze and Evaluate a) – d)

2. Intermolecular Forces
Chapter 4.7

3. Intramolecular vs. Intermolecular
An intramolecular bond is the chemical bond within a molecule
An intermolecular force is a force that occurs between molecules

4. States of Matter

5. 3 Types of Intermolecular (Van der Waals) Forces
London Dispersion Force
Dipole-Dipole Force
Hydrogen Bonds

6. London Dispersion Force

7. London Dispersion Force
All molecules experience London Dispersion Forces, but they have the greatest impact in non-polar molecules
London Dispersion Force is the weakest intermolecular force
The strength of the London force increases with:
Increasing size
Increasing surface area of contact or proximity

8. Dipole-Dipole Force
The dipole-dipole force is the electrostatic attraction that is caused when the dipoles of polar molecules position their positive and negative ends near each other

9. Dipole-Dipole Force
Only polar molecules experience Dipole-Dipole forces
Dipole-Dipole forces are stronger than London Dispersion forces (but are still only 1% as strong as covalent or ionic bonds)
The strength of the Dipole-Dipole force increases with:
Increasing polarity
Decreased distance between molecules

10. Hydrogen Bonds
A hydrogen bond is the strong dipole-dipole interaction that occurs when a hydrogen atom bonded to a small highly electronegative atom (oxygen, nitrogen, or fluorine) is attracted to a partially negative atom on a nearby molecule

11. Hydrogen Bonds
Only molecules that have O, N, or F attached to H experience hydrogen bonding
Hydrogen bonds are the strongest type of intermolecular force (but they are still times weaker than covalent bonds)

12. Intermolecular Forces and Physical Properties
The stronger the intermolecular forces are, the more energy it will require to pull the molecules apart
Molecules that have strong intermolecular forces also have high melting points and boiling points
Intermolecular forces can also affect solubility

13. Intermolecular Forces and Physical Properties

14. Intermolecular Forces and Physical Properties

15. Intermolecular Forces and Physical Properties

16. Intermolecular Forces and Physical Properties

17. Physical Properties of Liquids
Surface Tension is the resistance of a liquid to increase its surface area
The stronger the intermolecular forces, the greater the surface tension

19. Physical Properties of Liquids
Capillary action is the spontaneous rising of a liquid in a narrow tube due to adhesive and cohesive forces
Cohesive forces: IMF between like molecules
Adhesive forces: IMF between unlike molecules

20. Physical Properties of Liquids
Viscosity is the measure of a liquid’s resistance to flow
Liquids with strong intermolecular forces tend to be more viscous
Ex: Vegetable oil is more viscous than water

21. Homework
Read p. 239 – 246
Questions:
p. 244 #1,2
P. 247 #1-8