solut16 - CHAPTER SIXTEEN LIQUIDS AND SOLIDS Intermolecular...

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473 CHAPTER SIXTEEN LIQUIDS AND SOLIDS Intermolecular Forces and Physical Properties 11. There is an electrostatic attraction between the permanent dipoles of the polar molecules. The greater the polarity, the greater the attraction among molecules. 12. London dispersion (LD) < dipole-dipole < hydrogen bonding < metallic bonding, covalent network, ionic. Yes, there is considerable overlap. Consider some of the examples in Exercise 16.22. Benzene (only LD forces) has a higher boiling point than acetone (dipole-dipole). Also, there is even more overlap of the stronger forces (metallic, covalent, and ionic). 13. As the size of the molecule increases, the strength of the London dispersion forces also increases. As the electron cloud gets larger, it is easier for the electrons to be drawn away from the nucleus (more polarizable). 14. Fusion refers to a solid converting to a liquid and vaporization refers to a liquid converting to a gas. Only a fraction of the hydrogen bonds are broken in going from the solid phase to the liquid phase. Most of the hydrogen bonds are still present in the liquid phase and must be broken during the liquid to gas phase transition. Thus, the enthalpy of vaporization is much larger than the enthalpy of fusion since more intermolecular forces are broken during the vaporization process. 15. Dipole forces are generally weaker than hydrogen bonding. They are similar in that they arise from an unequal sharing of electrons. We can look at hydrogen bonding as a particularly strong dipole force. 16. a. Polarizability of an atom refers to the ease of distorting the electron cloud. It can also refer to distorting the electron clouds in molecules or ions. Polarity refers to the presence of a permanent dipole moment in a molecule. b. London dispersion (LD) forces are present in all substances. LD forces can be referred to as accidental dipole - induced dipole forces. Dipole - dipole forces involve the attraction of molecules with permanent dipoles for each other.
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CHAPTER 16 LIQUIDS AND SOLIDS 474 c. inter: between; intra: within; For example, in Br 2 the covalent bond is an intramolecular force, holding the two Br-atoms together in the molecule. The much weaker London dispersion forces are the intermolecular forces of attraction which hold different molecules of Br 2 together in the liquid phase. 17. Ionic compounds have ionic forces. Covalent compounds all have London Dispersion (LD) forces, while polar covalent compounds have dipole forces and/or hydrogen bonding forces. For hydrogen bonding (H-bonding) forces, the covalent compound must have either a N-H, O-H or F- H bond in the molecule. a. LD only b. dipole, LD c. H-bonding, LD d. ionic e. LD only (CH 4 in a nonpolar covalent compound.) f. dipole, LD g. ionic h. ionic i. LD mostly; C - F bonds are polar, but polymers like teflon are so large that LD forces are the predominant intermolecular forces.
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This homework help was uploaded on 04/06/2008 for the course CHEM 142 taught by Professor Zoller,williamh during the Fall '07 term at University of Washington.

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solut16 - CHAPTER SIXTEEN LIQUIDS AND SOLIDS Intermolecular...

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