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CHAPTER SEVEN Predicting Polarity 7.35 Define dipole moment. What are the units and symbol for dipole moment? 7.36 What is the relationship between the dipole moment and bond moment? How is it possible for a molecule to have bond moments and yet be nonpolar? 7.37 Explain why an atom cannot have a permanent dipole moment. 7.38 The bonds in beryllium hydride (BeH2) molecules are polar, and yet the dipole moment of the molecule is zero. Explain. 7.39 Referring to Table 10.3, arrange the following molecules in order of increasing dipole moment: H2O, H2S, H2Te, H2Se. 7.40 The dipole moments of the hydrogen halides decrease from HF to HI (see Table 10.3). Explain this trend. 7.41 List the following molecules in order of increasing dipole moment: H2O, CBr4, H2S, HF, NH3, CO2. 7.42 Does the molecule OCS have a higher or lower dipole moment than CS2? 7.43 Which of the following molecules has a higher dipole moment? Br \ C=C / \ H (a) H / H Br \ C=C / H (b) \ H Br / 7.46 Draw Lewis structures and give the other information requested for the following molecules: (c) H2O. Show the direction of the resultant dipole moment. (d) OF2. Polar or nonpolar molecule? 7.47 Draw Lewis structures and give the other information requested for the following: (a) SO3. Polar or nonpolar molecule? (b) PF3. Polar or nonpolar molecule? (c) F3SiH. Show the direction of the resultant dipole moment (e) Br2CH2. Polar or nonpolar molecule? 7.48 The compound 1,2-dichloroethane (C2H4Cl2) is nonpolar, while cisdichloroethylene (C2H2Cl2) has a dipole moment: Cl Cl HCCH H H 1, 2-dichloroethane Cl / C=C / \ H H cis-dichloroethylene Cl \

The reason for the difference is that groups connected by a single bond can rotate with respect to each other, but no rotation occurs when a double bond connects the groups. On the basis of bonding considerations, explain why rotation occurs in 1,2-dichloroethane but not in cis-dichloroethylene. 7.49 Does the following molecule have a dipole moment? Cl H \ / C=C=C / \ H Cl (Hint: See the answer to Problem 10.39.) 7.50 So-called greenhouse gases, which contribute to global warming, have a dipole moment or can be bent or distorted into shapes that have a dipole moment. Which of the following gases are greenhouse gases? N2, O2, O3, CO, CO2, NO2, N2O, CH4, CFCl3

7.44 Arrange the following compounds in order of increasing dipole moment:

7.45 Sketch the bond moments and resultant dipole moments for the following molecules: H2O, PCl3, XeF4, PCl5, SF6.

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