Chapter12 - 11/13/2011 CHEMISTRY CHEMISTRY 1307 Chapter XII...

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11/13/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307 Chapter XII Intermolecular Forces and Liquids 2 Why? Why is water usually a liquid and not a gas? Why does liquid water boil at such a high temperature for such a small molecule? Why does ice float on water? Why do snowflakes have 6 sides? Why is I 2 a solid whereas Cl 2 is a gas? Why are NaCl crystals little cubes? All of these questions may be answered by __________________ 3 Intermolecular Forces The forces holding solids and liquids together are called _____________________ . Intermolecular Forces are the attractions and repulsions between molecules. They are _______ chemical bonds. The intermolecular forces a substance may exhibit are a function of: 1. charge (ions vs. neutrals) 2. polarity (molecular shape, dipoles) 3. molar mass
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11/13/2011 2 4 Intermolecular Forces Intermolecular forces influence chemistry in many ways: They are directly related to properties such as _______ point , ________ point , and the energy needed to convert a solid to a liquid or a liquid to a vapor. They are important in determining the solubility of gases, liquids, and solids in various solvents. They are crucial in determining the structures of biologically important molecules such as DNA and proteins. 5 Magnitude of Intermolecular Forces Intermolecular forces are much ________ than the bonds that make up compounds. 20 to 30 kJ/mol D (H-Cl) = 432 kJ/mol 6 Ion-Ion Forces: Formal Charges The forces that govern charged particles are defined by Coulomb s law. These are the strong forces that lead to salts with high melting temperatures. 2 Q Q F k r   NaCl, mp = 800 ° C Q = the charges on the cation and anion r = the distance between k = a constant MgO, mp = 2800 ° C H 2 O, mp = 0 ° C Greater charge = __________ attraction Greater distance = ___________ attraction
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11/13/2011 3 7 Attractions Between Ions & Permanent Dipoles The polar nature of water is the source of attractive forces between ions and water. 8 Solvation of Ions When a cation exists in solution, it is surrounded by the __________ dipole ends of water molecules. When as anion exists in solution, it is surrounded by the _________ dipole ends of water molecules. + 9 Enthalpies of Hydration As the size of the ion _________, the exothermicity of the process decreases. This is due to the weaker ion-dipole forces.
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11/13/2011 4 10 Enthalpies of Hydration As the size of the ion increases, the exothermicity of the process decreases. This is due to the weaker ion-dipole forces. 11 Attraction Between Ions & Permanent Dipoles Water is highly polar and can interact with positive ions to give __________ ions in water. 12 Polar and Nonpolar Solvents A liquid composed of polar molecules is a ______ solvent . Water and ethanol are polar solvents. A liquid composed of nonpolar molecules is a ________ solvent . Hexane is a nonpolar solvent.
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11/13/2011 5 13 Molecular Polarity Molecular Geometry Non-Polar Molecule Linear Both atoms the same (outer the same for linear tri-atomic) Trigonal Planar All bonding groups the same Tetrahedral All bonding groups the same Trigonal bipyramidal All bonding groups the same or both axial
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Chapter12 - 11/13/2011 CHEMISTRY CHEMISTRY 1307 Chapter XII...

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