Chem1201PReviewCh11 - Chemistry 1201 Review/Preview Chapter...

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Chemistry 1201 Review/Preview Chapter Eleven Review Guide Dr. Saundra McGuire Spring 2007 Director, Center for Academic Success Adj. Prof., Dept. of Chemistry Intermolecular Forces, Liquids, and Solids I. A Molecular Comparison of Gases, Liquids, and Solids Gases, liquids, and solids are very different in the way the molecules move in the substance. As we saw in Chapter 10, the molecules of gases move freely to occupy the entire volume of the container. The molecules of liquids, however, are held close together, but move freely enough to assume the shape of the container the liquid is in. The molecules of a solid are held close together, and are essentially locked into place so that the shape of a solid does not change. The three states (or phases) -- gas, liquid, and solid -- can be changed into one another by heating, cooling, or changing the pressure, as described in detail in Section 11.1 of the textbook. II. Intermolecular Forces A. Description of Intermolecular Forces The attraction between the molecules in a substance is referred to as intermolecular forces. Note that intermolecular forces are different from chemical bonds within a molecule. (Bonds are intramolecular forces.) Intermolecular forces cause molecules to stick to one another to form a liquid or a solid under normal conditions. Substances with very weak intermolecular forces are likely to be gases at room temperature, those with very strong intermolecular forces are likely to be solids, and those that have intermolecular forces between very weak and very strong are likely to be liquids at room temperature. (See Section 11.2 on page 445 for more discussion of this.) B. Types of Intermolecular Forces When an ionic compound is dissolved in a polar solvent, the intermolecular forces are referred to as ion-dipole forces There are three types of intermolecular forces that operate between neutral molecules. These are listed below: 1. Dipole - dipole forces These forces are present in neutral, polar molecules. The partially positive end of one molecule is attracted to the partially negative end of another molecule. (See Figure 11.4 in the textbook.) 2. London Dispersion Forces (also called London forces or dispersion
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Chem1201PReviewCh11 - Chemistry 1201 Review/Preview Chapter...

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