Noncovalent Molecular Forces

Noncovalent Molecular Forces - CFQ PP Noncovalent Molecular...

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80 Reading Brown and Foote: Sections 1.5, 2.8, 5.3, 7.3, 9.2, 10.3, 11.3, 16.3 and 17.3 Oxtoby, Gillis and Nachtrieb: Sections 5.1 - 5.3 Optional Web Site Reading Predicting Physical Properties: chemdept/general/molecule/ Suggested Text Exercises Brown and Foote: Chapter 1; 14, 48, 49 Chapter 2: 16, 46 – 48 Chapter 7: 8 – 10 Chapter 9: 4, 5, 18 – 24 Chapter 11: 2, 12, 13 Chapter 17: 15, 16 Chapter 18: 15 Oxtoby, Gillis and Nachtrieb Chapter 5: 13, 15, 17, 21, 25 and 27 Concept Focus Questions 1. What holds molecules, ions, and atoms in a liquid or solid state? 2. Describe what happens at a molecular level when a liquid evaporates. 3. What is the relationship between the magnitude of intermolecular attractions and a compound's boiling point? 4. List three important noncovalent intermolecular interactions. Briefly explain the operation of each, and mention the factors that control the magnitude of these interactions. 5. Define "hydrogen bonding." What are the specific molecular structure requirements for hydrogen bonding to occur? Use a pair of compounds to illustrate and briefly explain these requirements. 6. Why does argon not have a boiling point of absolute zero? 7. What is the relationship between molecular surface area and van der Waals forces? Give an example that clearly illustrates this relationship. 8. What are the approximate energy ranges in kcal mol -1 for each of the forces described in questions 4 and 5? 9. Using both words and a diagram, explain why NaCl is expected to be soluble in acetic acid, but not in benzene.
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CFQ & PP: Noncovalent Molecular Forces 81 Concept Focus Questions Solutions 1. Intermolecular attractive forces hold molecules, ions, or atoms in a liquid or solid state. 2. When a liquid evaporates, the molecules move from liquid phase (more order) to gaseous phase (less order). To do this, the molecules must overcome the attractive forces that hold them in the liquid phase. This requires a certain amount of energy, dependent upon the nature and strength of the attractive forces. 3. Boiling point is defined as the temperature at which the vapor pressure of a compound is equal to ambient pressure (usually about 760 mm Hg). It is a rough measure of how much energy is required for a molecule to overcome attractive forces in the liquid phase and to escape to the gas phase. Compounds with stronger intermolecular attractions will require more energy to overcome these attractions, and thus have a higher boiling point. 4. Ionic bonding: Two ions of opposite charge are attracted electrostatically. The greater the charge difference, the stronger the attraction. Dipole-dipole interactions: The oppositely charged ends of two bond dipoles are
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Noncovalent Molecular Forces - CFQ PP Noncovalent Molecular...

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