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Unformatted text preview: solis (nrs545) – H10: Solids and Liquids – McCord – (53130) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF 3 )? 1. ionic 2. dipole-dipole correct 3. covalent 4. hydrogen bonding 5. dispersion Explanation: London forces, dispersion forces, van der Waals or induced dipoles all describe the same intermolecular force. London forces are in- duced, short-lived, and very weak. Molecules and atoms can experience London forces be- cause they have electron clouds. London forces result from the distortion of the elec- tron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur be- tween polar covalent molecules due to charge separation. 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. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. CHF 3 is a polar molecule that does not con- tain H bonds; therefore, dipole-dipole forces will be the most significant type of intermolec- ular forces present. 002 10.0 points Forces between particles (atoms, molecules, or ions) of a substance are called 1. armed forces. 2. None of these 3. intramolecular forces. 4. intermolecular forces. correct Explanation: Bonds within molecules or formula units are called intramolecular forces. Bonds between particles are called intermolecular forces. 003 10.0 points What is the predominant intermolecular force between IBr molecules in liquid IBr? 1. hydrogen bonds 2. ionic forces 3. dipole forces 4. dispersion forces correct 5. covalent bonds Explanation: You might have thought that dipole forces was right. The fact is that the dipole be- tween iodine and bromine is incredibly weak- too weak to account for the fact that this compound is a liquid. Another FACT is that dispersion forces are the dominant forces here due to the SIZE of these atoms and hence molecule. Just know that not ALL dipole forces are bigger than any set of dispersion forces. Size matters, and dispersion forces win out here. 004 10.0 points Which of the following structures represents a possible hydrogen bond? 1. F H · · · F correct 2. Br H · · · Br 3. Cl H · · · Cl solis (nrs545) – H10: Solids and Liquids – McCord – (53130) 2 4. C H · · · O Explanation: H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electroneg-...
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This note was uploaded on 09/24/2010 for the course CH 301 taught by Professor Fakhreddine/lyon during the Spring '07 term at University of Texas.
- Spring '07