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Unformatted text preview: 1 Chem 1AA3 Department of Department of 1 Chemistry Chemistry CHEM 1AA3: Intro. Chemistry II Ch.12: Liquids, Solids & Intermolecular Forces 2 Chem 1AA3 Chapter 12 Exclude: sections 12.7-12.9 Include: sections 12.1(only capillary action),12.2-12.6 (much of which was discussed in Chem 1A03 recall: properties of water) Intermolecular Forces = IMF 3 Chem 1AA3 In pure substances: van der Waals forces e.g., iodine Dipole-dipole forces e.g., acetone Hydrogen-bonding forces e.g., water In solutions we also see: Ion-dipole forces e.g., hydrated ions Ionic interactions e.g., hydrated ions 12.5 & 12.6: Intermolecular Forces 4 Chem 1AA3 12.5: van der Waals forces Also called induced dipole-induced dipole forces or London dispersion forces (a) nonpolar molecule, (b) experiences an instantaneous dipole, (c) which induces a dipole in its neighbour. Instantaneous dipoles propagate throughout the sample Force strength depends on polarizability (the tendency for charge separation to occur). Fig. 12-24, p. 490 5 Chem 1AA3 12.5: van der Waals forces van der Waals' forces increases with:- atomic number and size of the molecule (due to polarizability)- linear versus branched structures (due to increased intermolecular contact area) Fig. 12-25 Pentane, bp = 36.1 C Neopentane, bp = 9.5 C Table 9-5 (p. 359) Molecule Melting point Cl 2 172 K I 2 387 K 6 Chem 1AA3 12.5: Dipole-dipole forces Occur in polar molecules (molecules with permanent dipoles) polar molecules have bond dipoles and asymmetric shape Being polar increases b.p. over dispersion forces alone e.g., N 2 (77K), NO (121 K), O 2 (90 K) Fig. 12-26 e.g., acetone p. 491 7 Chem 1AA3 12.6: Hydrogen bonding Between an H atom in a polar bond (i.e., H-N, H-O, or H-F) and another electronegative atom (i.e., N, O, or F) One H-bond is small, but many are mighty....
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