HW 10 IMF-solutions - nanni (arn437) HW 10 IMF vanden bout...

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nanni (arn437) – HW 10 IMF – vanden bout – (50985) 1 This print-out should have 20 questions. Multiple-choice questions may continue on the next column or page – fnd all choices be±ore answering. NOTICE THIS IS DUE WED MORNING INSTEAD OF TUESDAY MORNING!! 001 10.0 points What would be the most signifcant type o± intermolecular ±orces in a liquid sample o± ²uoro±orm (CHF 3 )? 1. hydrogen bonding 2. covalent 3. dispersion 4. dipole-dipole correct 5. ionic Explanation: London ±orces, dispersion ±orces, van der Waals or induced dipoles all describe the same intermolecular ±orce. London ±orces are in- duced, short-lived, and very weak. Molecules and atoms can experience London ±orces be- cause they have electron clouds. London ±orces result ±rom the distortion o± the elec- tron cloud o± an atom or molecule by the presence o± nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London ±orces and occur be- tween polar covalent molecules due to charge separation. H-bonds are a special case o± very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg- ative atoms – F, O or N only. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought o± as both inter- and intramolecular bonding. CHF 3 is a polar molecule that does not con- tain H bonds; there±ore, dipole-dipole ±orces will be the most signifcant type o± intermolec- ular ±orces present. 002 10.0 points Forces between particles (atoms, molecules, or ions) o± a substance are called 1. intermolecular ±orces. correct 2. armed ±orces. 3. intramolecular ±orces. 4. None o± these Explanation: Bonds within molecules or ±ormula units are called intramolecular ±orces. Bonds between particles are called intermolecular ±orces. 003 10.0 points What is the predominant intermolecular ±orce between IBr molecules in liquid IBr? 1. covalent bonds 2. dispersion ±orces correct 3. dipole ±orces 4. hydrogen bonds 5. ionic ±orces Explanation: You might have thought that dipole ±orces was right. The ±act is that the dipole be- tween iodine and bromine is incredibly weak - too weak to account ±or the ±act that this compound is a liquid. Another FACT is that dispersion ±orces are the dominant ±orces here due to the SIZE o± these atoms and hence molecule. Just know that not ALL dipole ±orces are bigger than any set o± dispersion ±orces. Size matters, and dispersion ±orces win out here. 004 10.0 points Which o± the ±ollowing structures represents a possible hydrogen bond? 1. Cl H ··· Cl 2. C H ··· O
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nanni (arn437) – HW 10 IMF – vanden bout – (50985) 2 3. Br H ··· Br 4. F H ··· F correct Explanation: H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg- ative atoms – F, O or N only. 005
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This note was uploaded on 11/02/2011 for the course CHEMISTRY 301 taught by Professor Mccord during the Fall '10 term at University of Texas.

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HW 10 IMF-solutions - nanni (arn437) HW 10 IMF vanden bout...

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