Togetherness

Togetherness - Then larger dipole Then more attraction...

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Togetherness Why would molecules/ions/atoms “stick together” to form a solid of liquid? Text: section 7.3 *Don’t confuse In H 2 O: H covalently bonds to O Inside molecule Here we look at: One molecule attracted to the next “Intermolecular Forces” *Intermol. Forces affect Physical properties Ex. If stronger attractive forces, then higher boiling point A.        Dipole-Dipole Forces     Boling points: F 2 85K HCl 188K Br 2 332K ICl 370K 1. F – F H +  Cl ∆ EN = 0 ∆ EN /= 0 non-polar polar 2. Dipole-dipole forces occur in polar molecules 3. For molecules with 1 central atom Symmetrical e- groups and terminal atoms are the same =>non-polar Asymmetrical e- groups or terminal atoms are different =>polar ex. CO2 vs SO2 ex. Tetrahedral C B.        Dispersion Forces     1. Why should non-polar molecules condense at all? 2. Random e- motion  Temporary dipole 3. This can  induce  a dipole in a neighboring molecule 4. If more e-
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Unformatted text preview: Then larger dipole Then more attraction Heavier molecules greater dispersion forces C. Hydrogen Bonding 1. B.p. of H cpds (fig 7.17) Cpds with N-H O-H F-H Extra attractive force 2. Hydrogen bond Interaction between S+ H and lone pair on next molecule 3. Not a covalent bond but partway D. Summary of Forces Molecule Forces Non-polar dispersion Polar dispersion + dipole-dipole if N-H, dispersion O-H, F-H + dipole-dipole + hydrogen bonding usually : more forces = stronger interaction careful : dispersion can get large Goals Determine how the three intermolecular forces arise Determine if a molecule is polar Determine what intermolecular forces are present in a compound...
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This note was uploaded on 03/30/2008 for the course CH 101 taught by Professor Bigham during the Fall '08 term at N.C. State.

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Togetherness - Then larger dipole Then more attraction...

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