Unit3Day5 Crawford Wednesday October 23 2013 2 58 PM Vanden Bout LaBrake Crawford CH301 WHY IS EVERYTHING SO DIFFERENT Gas Liquid or Solid UNIT 3 Day 5 CH302 Vanden Bout LaBrake Fall 2013 Important Information HW08 DUE Tue 9AM Laude LM Lecture 16 17 CH302 Vanden Bout LaBrake Spring 2013 Unit3Day5 Crawford Page 1 What are we going to learn today Use VSEPR VB MO to get a better picture of POLAR and NONPOLAR MOLECULES Recognize different molecules have different physical properties Classify Intermolecular Forces IMF CH302 Vanden Bout LaBrake Fall 2013 QUIZ iClicker Question 1 Chemists use a localized electron theory and a delocalized electron theory to help predict and explain bonding in molecules these models are referred to respectively as a VSEPR VB b VB VSEPR c VB MO d MO VB e VSEPR MO CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 2 COMBINE VB and MO THEORIES VB for sigma bonds CH302 Vanden Bout LaBrake Fall 2013 COMBINE VB and MO THEORIES MO for the pi bond Where are the electrons Delocalized around the molecule CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 3 Visualize Ethanol We use VSEPR and VB to get visual image We predict polarity just from the ball and stick model CH302 Vanden Bout LaBrake Fall 2013 Chemical Composition Shape What are the Physical Properties Is the molecule a gas or a liquid CH302 Vanden Bout LaBrake Fall 2013 Chemical Composition Shape What are the Physical Properties What is the density of a liquid Unit3Day5 Crawford Page 4 Chemical Composition Shape What are the Physical Properties What is the density of a liquid CH302 Vanden Bout LaBrake Fall 2013 Physical Properties What dominates the interaction in condensed phases What are these forces How are they classified Define Intermolecular Forces IMF NOTE Remember Tape Charged Rods and Liquids CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 5 Activity Open Course Pack to Page 79 IMF Unit Electrostatic Forces Liquids 1 Draw the Lewis Structures 2 Identify any trends CH302 Vanden Bout LaBrake Fall 2013 Identify a Few Trends Relationship between Chemical Formula and Boiling Point 1 2 3 4 5 CH302 Vanden Bout LaBrake Fall 2013 Intermolecular Forces The dominate force in chemistry is Coulombic Unit3Day5 Crawford Page 6 The dominate force in chemistry is Coulombic CH302 Vanden Bout LaBrake Fall 2013 Intermolecular Forces The dominate force in chemistry is Coulombic The boiling point of NaCl is 1413 C Why is it so high Qualify the word intermolecular CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 7 Intermolecular Forces The molecule is in a condensed phase but not ionic A molecular condensed phase is a molecular liquid or a molecular solid PARTICLE IS A MOLECULE CH302 Vanden Bout LaBrake Fall 2013 Intermolecular Forces Dipole Dipole Attractive force between partial negative end of one molecule and partial positive end of another molecule Strength depends on distance and dipole moment CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 8 Poll iClicker Question 2 ALL NONPOLAR COMPOUNDS ARE GASES A TRUE B FALSE CH302 Vanden Bout LaBrake Fall 2013 Look at the Data ALL NONPOLAR COMPOUNDS ARE NOT GASES Methane BP 161 C Nonpolar Gas Ethane BP 88 7 C Nonpolar Gas Hexane BP 68 7 C Nonpolar Liquid CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 9 Intermolecular Forces Fact Check How is it possible for Hexane and Carbon Tetrachloride to exist as liquids How is it possible for Octane to have a higher boiling point than Water How is it possible for Water and Ethanol to be attracted to a charged rod whereas Hexane and Carbon Tetrachloride are not attracted to it There must be an ELECTROSTATIC ATTRACTION CH302 Vanden Bout LaBrake Fall 2013 Intermolecular Forces Induced DipoleInduced Dipole Induced Dipole Induced Dipole interactions exist in ALL condensed substances Caused by induced dipoles which come and go in nonpolar molecules and atoms CH302 Vanden Bout LaBrake Fall 2013 Intermolecular Forces Induced DipoleInduced Dipole This type of IMF goes by several different names Induced dipole Induced dipole Dispersion Forces Unit3Day5 Crawford Page 10 This type of IMF goes by several different names Induced dipole Induced dipole Dispersion Forces London Forces Van der Waal s Forces CH302 Vanden Bout LaBrake Fall 2013 Poll iClicker Question 3 Consider the following alkane data Alkane MW g mol 1 BP C Methane 16 161 Ethane 30 88 7 Propane 44 42 1 Butane 58 0 5 Pentane 72 36 1 Hexane 86 68 7 A molecule with a MW of 80 g mol 1 will be a at room temperature A Solid B Liquid C Gas CH302 Vanden Bout LaBrake Fall 2013 Poll iClicker Question 4 Now consider an array of atoms and molecules Alkane MW g mol 1 BP C Helium 4 268 9 Krypton 83 153 2 Propane 44 42 1 CCl4 154 77 Octane 114 126 The IMF strength is dependent on A MW B Shape C PolarizabilityPage 11D B C Unit3Day5 Crawford CCl4 154 77 Octane 114 126 The IMF strength is dependent on A MW B Shape C Polarizability D B C CH302 Vanden Bout LaBrake Fall 2013 Polarizability Induced Dipole Induced Dipole forces exist in ALL condensed substances Strength depends on polarizability CH302 Vanden Bout LaBrake Fall 2013 Shape Why can t the charged glass rod induce a dipole Distance Dependence is HUGE This is why shape is so important how close can the individual atoms get to each other in space Common examples are oils vs fats and plastic wrap vs milk jugs FAVORITE ANALOGY VELCRO CH302 Vanden Bout LaBrake Fall 2013 Unit3Day5 Crawford Page 12 We can evaluate SIMILAR molecules Ionic MW g mol 1 BP C LiCl 42 1382 Alkane MW g mol 1 BP C NaCl 58 1413 Methane 16 161 KCl 74 1420 Ethane 30 88 7 Propane 44 42 1 Alcohol MW g mol 1 BP C Butane 58 0 5 Methanol 32 65 Pentane 72 36 1 Hexane 86 68 7 Ethanol 46 78 Propanol 60 97 CH302 Vanden Bout LaBrake Fall 2013 Explore Real Data Activity IMF Unit Electrostatic Forces Liquids Course Pack Page 80 CH302 Vanden Bout LaBrake Fall 2013 Poll iClicker Question 5 The BP of Sn hydride less than the BP of the Te hydride because a The Sn compound has a larger dipole Unit3Day5 Crawford Page 13 Poll iClicker Question 5 The BP of Sn hydride less than the BP of the Te hydride because a The Sn compound has a larger dipole b The Sn compound has a smaller dipole c The Sn compound is more polarizable d The Sn compound is less polarizable e Sn was abducted by aliens obviously CH302 Vanden Bout LaBrake Fall 2013 Poll iClicker Question 6 The BP of S hydride less than the BP of the Te hydride because a The S compound
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