1. Ch. 11: Liquids, Solids, and Intermolecular Forces
Dr. Namphol Sinkaset
Chem 200: General Chemistry I

2. I. Chapter Outline
Introduction
Intermolecular Forces

3. I. Condensed States
Liquids and solids are the condensed states because of the close proximity of atoms/molecules to one another.
This proximity leads to much more frequent interactions than in gases.
Structure determines properties via the nature of the interactions that occur.

4. I. Ethanol vs. Dimethyl Ether
How can the same 9 atoms form two compounds with such different boiling points?
It’s because of the structure of the molecules!

5. I. Electrostatic Forces
Every molecule in a sample of matter experiences two types of electrostatic forces.
Intramolecular forces: the forces that exist within the molecule (bonding). These forces determine chemical reactivity.
Intermolecular forces: the forces that exist between molecules. These forces determine physical properties.

6. II. Intermolecular Forces
IM forces originate from interactions between charges, partial charges, and temporary charges on molecules.
IM forces are relatively weak because of smaller charges and the distance between molecules.

7. II. Types of IM Forces
There are different kinds of IM forces, each with a different level of strength.
Dispersion force
Dipole-dipole force
*Hydrogen “bonding”
Ion-dipole force

8. II. Dispersion Force
Dispersion force (London force) is present in all molecules and atoms and results from changes in e- locations.

9. II. Instantaneous Dipoles
Charge separation in one creates charge separation in the neighbors.

10. II. Dispersion Force Strength
The ease with which e-’s can move in response to an external charge is known as polarizability.
Large atoms with large electron clouds tend to have stronger dispersion forces.
Larger molecules tend to have stronger dispersion forces.

11. II. Noble Gas Boiling Points

12. II. Dispersion Force and Shape
Molecular size is not the only factor…

13. II. Dispersion Force and Shape
Shape influences how the molecules interact with one another…structure determines properties.

14. II. Dispersion Force in a Family

15. II. Dipole-Dipole Force
Occurs in polar molecules which have permanent dipoles, so attraction is always present.

16. II. Effect of Dipole-Dipole Force
Polar molecules have dispersion forces and dipole-dipole forces.
Effects can be seen in boiling and melting points.

17. II. Increasing Polarity
If we increase the polarity, but keep molar mass approximately the same…

18. II. “Like Dissolves Like”
Polar liquids are miscible (mix without separating) with other polar liquids, but not with nonpolar liquids.
Can be explained with intermolecular forces.

19. II. Hydrogen “Bonding”
This IM force is a misnomer since it’s not an actual bond.
Occurs between molecules in which H is bonded to a highly electronegative element (N, O, F), leading to high partial positive and partial negative charges.
It’s a “super” dipole-dipole force.

20. II. H “Bonding” Ethanol

21. II. Ethanol vs. Dimethyl Ether
We compared these earlier.
Hydrogen “bonding” is so much stronger than dipole-dipole that one is a liquid at room temp. while the other is a gas.

22. II. Effect of H “Bonding”
Hydrogen “bonding” is a very strong intermolecular force.
Without hydrogen “bonding” life as we know it could not exist!

23. II. Ion-Dipole Force
Present in mixtures of ionic compounds & polar compounds.
Example: NaCl(s) dissolved in water.

24. II. Summary of IM Forces

25. II. Sample Problem 11.1
Which substance has the highest boiling point and why?
CH3OH CO N2