Chapter 11 Study Guide

Chapter 11 introduces the various forces that attract molecules to each other (we saw the first of these, the Coulombic interaction, way back in Chapter 2, while discussing ionic compounds.) Dispersion forces, dipolar interactions, and hydrogen bonds are all rooted in Coulombic interactions, but have very different interaction strengths and ranges, leading to large differences in the phase behavior of different substances.

The "solid", "liquid" and "gas" terms that we have used beforehand are now more concretely defined, as well as the different processes, such as melting and boiling, by which one phase transforms into another under changing conditions. This is largely an issue of terminology. The precise why of phase changes requires a deeper exploration of thermodynamics, which comes in Chapter 17. Phase Diagrams are the graphical tool by which we keep track of phase behavior, and are of great practical interest.

Finally, Chapter 11 ends with a presentation of network covalent solids and the detailed structure of ionic crystals, which will not be covered in this course.

Suggested Problems

You should be able to:

1. Qualitatively explain the different kinds of intermolecular forces.
2. Identify the intermolecular forces present in a given compound.
3. Correlate the strength of intermolecular forces with boiling and melting temperatures.
4. Read a phase diagram
5. Explain the differences between solids, liquids and gases.

Important topics and Concepts

1. Intermolecular forces
   1. Coulombic forces
   2. Dipole-dipole interactions
   3. Charge-induced-dipole forces
   4. Induced-dipole-induced dipole (dispersion) forces
   5. polarizeability - what is it?
   6. hydrogen bonds
      • cause
      • geometry
      • strength
2. Phases
   1. Solids - high density and positional order
   2. Liquids - high density, no positional order
   3. Gases - low density, no positional order
3. Phase changes
   1. Names of phase changes
   2. Phase diagrams
      • Lines
      • Triple points
      • Critical points
   3. Relationship between coexistence line slope and the relative densities of the two phases.