lecture 2 - Exam Conflicts Our course is #53546 If our exam...

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Unformatted text preview: Exam Conflicts Our course is #53546 If our exam conflicts with another exam exam, you take a makeup exam in the course with the higher final diget diget. When Wh would you prefer to ld f have SI sessions held? A. Sunday 7-8:30 pm y p B. Monday 7-8:30 pm C. C Tuesday 7 8:30 pm 7-8:30 D. Wednesday 7-8:30 pm E. Thursday 7-8:30 pm Why no fingerprints? In 1993 in Knoxville, TN a young girl was y abducted from her home and driven away in a green car. The girl managed to escape from her attacker and was able to describe the car to the police. After four days the police found the car g and arrested the owner. Even using the latest technique, fuming with superglue, no finger p prints were ever found. Why not? y Questions to consider: What controls how long fingerprints last? Why are some compounds liquid at room temperature while others are solids or gases? Why does water boil at 100C but ethanol boil at 78C? Ideal gas law Ideal solid & liquid law Which is solid, liquid or gas? Why? Why no fingerprints? In 1993 in Knoxville, TN a young girl was abducted from her home and driven away in a green car. The girl managed to escape from her attacker and was able to describe the car to the police. After four days the police found the car and arrested the owner. Even using the latest technique, fuming with superglue, no finger prints were ever found. Why not? Chemically, what are the forces that control whether fingerprints evaporate or not? What causes polarity in a p y chemical bond? 1. 1 When two bonded atoms have the same molecular weight 2. 2 When two bonded atoms share electrons 3. 3 When two bonded atoms have different electronegativities 4. 4 When two bonded atoms have the same electronegativities Polarity & Electronegativity Electronegativity: The ability of an atom in a molecule to attract electrons to itself. Polarity: A molecule is polar if it has a dipole moment. It is polar if two atoms have substantially different electronegativities. Picture of a Dipole Calculating Dipoles Like Dissolves Like Which is more soluble in water? Ethane or Ethanol? Intermolecular Forces I Di l Ion-Dipole Dipole-Dipole H d Hydrogen b di bonding Dipole-Induced dipole I d Induced di l I d d dipole-Induced di l d dipole Wh a higher IMF is present the lower ones are too (with When hi h i t th l t ( ith the exception of Hydrogen bonding. Na+ in water Which types of intermolecular forces are at work when we dissolve salt (NaCl) in water (H2O)? 1. Ion-Dipole 2. Dipole-Dipole 3. Dipole-Induced Dipole 4. 4 Induced Dipole Induced Dipole Dipole-Induced Dipole-Dipole Forces DipoleDipole-dipole forces occur between molecules h i permanent di l l l having t dipoles. Dipole-Dipole Forces Influence of dipole-dipole forces is seen in the boiling dipolep points of simple molecules. p Compound N2 CO Br2 ICl Mol. Wt. 28 28 160 162 Boiling Point -196C 196 -192C 192 59 59C 97C 97 Forces Involving Induced Dipoles How can non-polar molecules such as O2 and I2 nondissolve in water? The water dipole INDUCES a dipole in the O2 electric cloud cloud. DipoleDipole-induced dipole Which types of intermolecular forces are at work when NH3 interacts with BF3? 1. Ion-Dipole 2. Dipole-Dipole 3. Dipole-Induced Dipole 4. 4 Induced Dipole Induced Dipole Dipole-Induced Forces Involving Induced Dipoles Solubility increases with mass of the gas because the electron cloud is more polarizable. polarizable. Forces Involving Induced Dipoles Formation of a dipole in two nonpolar I2 molecules. Induced dipole-induced dipole dipole- Induced Dipole-Induced Dipole Works with all molecule types Works better with larger atoms and molecule (those are more polarizable) weak, These forces are weak but they add up Intermolecular Forces: Induced Dipoles Consider I2 dissolving in ethanol, CH3CH2OH. I-I - O R H + The alcohol temporarily creates or INDUCES a dipole in I2. I-I + - O R H + - Forces Involving Induced Dipoles The induced forces between I2 molecules are very weak, so solid I2 sublimes (goes from a solid to gaseous molecules) molecules). ). I2 sublimes Which types of intermolecular forces are at work when CH3CH2CH3 interacts with itself? 1. Ion-Dipole 2. Dipole-Dipole 3. Hydrogen Bonding 4. Dipole-Induced 4 Dipole Induced Dipole 5. Induced Dipole-Induced Dipole Which intermolecular forces are at work when propane CH3CH2CH3 interacts with ethanol CH3CH2OH? 1. Ion-Dipole 2. Dipole-Dipole 3. Hydrogen Bonding 4. Dipole-Induced 4 Dipole Induced Dipole 5. Induced Dipole-Induced Dipole Forces Involving Induced Dipoles The magnitude of the induced dipole depends on the tendency to be distorted. distorted Higher molecular weight means more electrons and larger induced dipoles. . Molecule CH4 (methane) C2H6 (ethane) ( th ) C3H8 (propane) C4H10 (butane) Boiling Point (oC) -161.5 -88 6 88.6 -42.1 -0.5 05 Why no fingerprints? In 1993 in Knoxville, TN a young girl was abducted from her home and driven away in a green car. The girl managed to escape from her attacker and was able to describe the car to the police. After four days the police found the car and arrested the owner Even using the owner. latest technique, fuming with superglue, no finger prints were ever found. Why not? What intermolecular forces govern these two compounds? p Friday: Chapt 13.3-4 Why hydrogen bonding is the basis of life! ...
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This note was uploaded on 04/15/2008 for the course CHEM 112 taught by Professor Hardy during the Spring '08 term at UMass (Amherst).

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