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Chem 161-2011 Lecture 24 truncated

Chem 161-2011 Lecture 24 truncated - CHEMISTRY 161-2011...

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Chem 161-2011 Lecture 24 1 CHEMISTRY 161-2011 LECTURE 24 – DEC. 6TH CHAPTER 12 -- INTERMOLECULAR FORCES ANNOUNCEMENTS PHILOSOPHY Come to class early for philosophy. - Career: Job money vs. Job love - Career: Grades as guide? ATTENDANCE MISCELLANEOUS Tue, 12/6 Lecture 24 – Ch. 12 Fri, 12/9 Lecture 25 (last lecture) – Ch. 12 Tue, 12/13 Review for final exam (only Tavss’ review) Fri, 12/16 Final exam; noon – 3 PM Sections 50-52 Van Dyke 211 Sections 53-54 Voorhees Hall 105 Section 55 ? FINAL EXAM 240 (out of 725 points) Trend counts 35% = automatic F Do you have a part-time job or are on sport teams? EXAM III : How did we do? :>)
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Chem 161-2011 Lecture 24 2 Chaper 12 - Intermolecular Forces and the Physical Properties of Liquids and Solids Intermolecular Forces Dipole-dipole interactions Hydrogen bonding Dispersion forces Ion-dipole interactions Properties of liquids Surface tension Viscosity Vapor pressure
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Chem 161-2011 Lecture 24 3 CHAPTER 12 – INTERMOLECULAR FORCES Intermolecular forces: Forces between molecules; the forces that attract one molecule to another. “Inter”, Latin = between, e.g., intercollegiate athletics “Intra”, Latin = within, e.g., intramural athletics Up until now we studied intramolecular forces, e.g., C-C, N N; now we’ll discuss intermolecular forces, e.g., H 2 O. . . H 2 O e.g., intranet vs. internet; a net within a company vs. a net between all people of the world
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Chem 161-2011 Lecture 24 4 INTERMOLECULAR FORCES THE DIFFERENCE IS THE STRENGTH OF THE INTERMOLECULAR FORCES strong weak none
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Chem 161-2011 Lecture 24 5 ET: Intramolecular bonds are much stronger than intermolecular bonds; e.g., H 2 (g) 2H(g) BE=436 kJ/mol; H 2 (l) H2( g ) Hvapn = 0.90 kJ/mol ET: Only ideal gases don’t have intermolecular forces. ET: Discuss each force. Relative Strength * Electrostatic interaction (ion-ion interaction) 1000 = charge-charge interaction = ionic interaction Coulomb’s Law: F = k(Q 1 x Q 2 )/r 2 Ion dipole 500 Hydrogen bonding 100 Y,Y’ = N, O or F Y H Y’ ET: Strong bond because very strong dipole-dipole interaction due to electron-naked small H getting close to small strongly electronegative atoms. F = k(Q 1 x Q 2 )/r 2 ; r is small, so force is large. Dipole-dipole interaction** 10*** polar molec. & polar molec. London forces** 1*** non-polar molecules & non-polar molecules, or non-polar molecules & polar molecules. Magnitude of London forces very sensitive to size/MW/surface area because the greater the size the easier the formation of dipoles (i.e., the greater the polarizability). Compare Xe to Ne. More electrons and electrons further from the nucleus make xenon more polarizable. Also, the greater the surface area, the more the contact. *Relative numbers made up. They are used simply to provide the concept. ** Dipole-dipole interaction dominates over London dispersion forces when comparing molecules of approximately the same size (i.e., central atom in same period). London dispersion forces dominate over dipole-dipole interaction when comparing molecules of different size (i.e., from vertical groups).
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