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2.10 To determine the DU of a structure, add the number of rings plus the number of double bonds plus twice the number of triple bonds. a) 5 b) 4 c) 3 d) 7 e) 6 2.11 Intermolecular forces between molecules result from the attraction of opposite charges in the molecules. The different attractive forces are: the attractive force between two oppositely charged ions. This is the strongest attraction of all. the attractive force between an ion and a polar molecule. This attractive force is much weaker than an ion-ion interaction. Dipole-dipole: the attractive force between two polar molecules. This force is weaker than an ion-dipole interaction. Dipole-induced dipole: attraction between a polar molecule and a dipole that the polar molecule induces in a nonpolar molecule. This force is weaker than a dipole-dipole attraction. Instantaneous dipole-induced dipole (London force): attraction between two nonpolar molecules that results from the interaction of an instantaneous dipole in one with an induced dipole in the other. This is the weakest force of all, but there can be a large number of them. These last three are called van der Waals forces. Hydrogen bonding: a special type of dipole-dipole attraction between a hydrogen bonded to an electronegative atom in one molecule and an electronegative atom in another molecule. This force is stronger than a regular dipole-dipole attraction. a) London b) van der Waals c) ion-ion d) van der Waals and hydrogen bonding H H 2.12 H H hydrogen bond 2.13 Stronger intermolecular attractive forces result in a higher melting point. KBr is an ionic compound and has strong ion-ion interactions. CH₃Br is a covalent molecule and has only weak van der Waals forces of attraction. Therefore KBr has a higher melting point. 17