Try this Bit of Review: For the molecules below can you do each of the following? 1. 2. 3. 4. Give the Lewis dot structure. Label any polar bonds. Identify the molecular geometry at central atoms. Determine if the molecule is polar or nonpolar overall. In other words, does it have a net dipole moment, or not? 5. What is the major intermolecular force involved? CH3CH2OH CH3CHO CO2 CHCl3 XeF4 Recall that some covalent bonds have as much as 1000 kJ/mol in bond energy! WELCOME to University Chemistry 2! Yes, it’s true that you are ultimately responsible for your own learning. However…… I take very seriously my responsibility to help you reach your goals, learn all you can, and to have your efforts evaluated fairly. I don’t feel successful unless you do! We are in this together! What I learned about how to succeed in chemistry: 1. Do ALL the homework; practice until you understand it. 2. Develop better study habits. 3. Wake up! Don’t sleep through class and pay attention in lecture. 4. Take excellent notes and review them daily. 5. Talk with the professor; ask for help. 6. Practice the goals A LOT! 7. Do NOT procrastinate. Study every night. What I learned about how to succeed in chemistry: 8. Do not get behind; learn good timemanagement. 9. Be organized; practice constantly. 10. Go to your SI group and be prepared. 11. Work with others; form a study group. 12. Use the study guides and practice exam questions; rework the LC ones, too. 13. Study for tests early. Do NOT cram! 14. Use the CLASS+; get tutoring if needed. 15. Remember the 3 hour rule; keep up and review constantly. Let’s try out our in-class platform! • Log in to “Learning Catalytics” by going to the Learning Catalytics website directly: https://learningcatalytics.com/sign_in • Enter today’s Session ID (on the board). • Choose your seat on the seating chart. • If you have problems raise your hand and help will come to you, thanks to our TAs and SI Leaders! More on homework! • See blackboard for full instructions and info! • Homework is due this semester by 11:59 pm on due dates shown in the program. • Dr. Moradi is your faculty person in charge of that portion of our course if you have questions. • There are computer labs and tech support available, but you will want to work ahead on these to avoid the frustration of last minute technical issues. • First assignment is due this coming Sunday. • LB’s suggestion: Take a look at the conceptual and terminology questions in your text as you read before class. The lecture will be more meaningful and LC questions easier if you prepare well for class. Then do the harder problemsolving ones in the textbook after we’ve worked on that learning objective in class. The MC work will be easier and quicker if you do the book work and review your lecture notes before getting into the problems in MC. CHEMISTRY 1123 DATE WEEK 1 (Week of January 14): University Chemistry II SPRING, 2019 LEARNING OBJECTIVES: ASSIGNMENT: 1. Introductions and expectations: What can I expect from this course and what is expected of me? Take the Learning Styles Inventory and bring your results to the SI group discussion next week. Go to the site: http://www.engr.ncsu.edu/learningstyles/ilsweb.html Be sure to register for your SI 2. Review your understanding of the solid, liquid and gas phases group through CLASS+ site. at the molecular level. Chapter 11.2 http://class.uark.edu 3. Review polar bonds and polar molecules. Chapter 5.2, 5.10 4. Review the interactions involving polar molecules and nonpolar Chapter 11.3; Learn Table 11.4 Start your Mastering Chemistry on-line homework! molecules as well. Practice identifying intermolecular forces. Complete your ALEKS pre-course work. 5. Review the importance of intermolecular forces in Chapter 11.3 properties such as solubility, boiling points, etc. 6. Review applications of the strengths of intermolecular forces to Chapter 11.4 properties like surface tension, viscosity, capillary action, etc. 7. Learn about the process and energetics of vaporization. Chapter 11.5 8. Learn about vapor pressure and the dynamic equilibrium Chapter 11.5 between liquid and gas phases WEEK 2 (Week of January 21) 9. Use the DHv ap and the Clausius-Clapeyron equation to LABS and SI Groups BEGIN! predict changes in vapor pressure with changes in temperature. Chapter 11.5 Martin Luther King, Jr. Celebration January 21 so no class on Monday! 10. Learn about the transitions that occur at the critical point, and during sublimation, fusion, melting, and freezing. Chapter 11.5, 11.6 Learning Objective #2: Comparing the solid, liquid, and gas phases (states) at the molecular level • The state of a sample of matter depends on the strength of the ______________ forces between the particles relative to the amount of thermal energy in the sample. • Molecules and atoms are in constant random motion that __creases with increasing temperature. As temperature increases, a change of state may occur. What observations can you make about water in its 3 states? Fig. 11.1 Fig.11.2 Are there other states of matter? The three we experience daily and study in this course: • Solid • Liquid • Gas But there are others: • Plasma • Bose-Einstein Condensate (Nobel Prize in Physics 2001) http://www.nasa.gov/mission_pages/solar-b/solar_017.html http://patapsco.nist.gov/imagegallery/details.cfm?imageid=193 Figure 11.3 Changes Between States We can transition between states by changing temperature, pressure, or both. endothermic e exothermic LO 2 What is going on here? The propane in an LP gas tank is in the liquid state. When you open the tank, some propane vaporizes and escapes as gas. Propane is a gas at room temp and atmospheric pressure. Under high pressure (>2.7 atm) it liquefies. In general if you increase pressure, the __________ state is favored. If the diagram to the left represents liquid water, which one below represents what happens to the water when a pot of water boils? Liquid to gaseous water Figure 11.20 Figure 11.26 Figure 11.33 LEARNING OBJECTIVE #3: Another Review Goal! 1. Can you draw Lewis dot structures? 2. Can you find polar bonds? 3. Can you determine molecular geometry? 4. Can you determine if the molecule has a net dipole? REVIEW Chapter 5 material as needed! Now let’s learn to predict polarity in bonds. We will use the electronegativity values given in Figure 5.3. Look for the trends in EN here, too! So, what is electronegativity? • It’s the ability of an atom in a molecule to attract shared electrons to itself….it’s the “greediness” factor! • If the difference in EN is > 0.4 we’ll consider the bond polarized. • The polarity of the bond increases as the difference in EN values increases. Do NOT memorize, but know trends and the most EN top four! Figure 5.3 • On the periodic table, electronegativity generally ___creases across a period (row) and ___creases up a group (column). • The range of electronegativity values is from 4.0 for fluorine (the most electronegative) to 0.7 for cesium and francium (the least electronegative). _______________developed a scale for us to use. B.S. in chemical engineering Ph.D. in chemistry Copyright © Cengage Learning. All rights reserved Nobel Prizes: 1954 (__________) 27 1963 (_________) Electrostatic Diagram Showing Three Possible Types of Bonds __Pure__ covalent __Polar___covalent DEN = 1.9 ___Ionic______ DEN > 1.9 So, why are some molecules with polar bonds behaving as if they are not polar? For Example: CCl4, CO2, XeF4? 1. Label all “dipoles” or polar bonds. 2. Now consider the geometry (shape) of the molecule. Why? 3. In a symmetrical arrangement, identical dipoles can actually cancel each other out giving the molecule a net dipole moment of ___zero_____. 4. When the dipoles cancel, the molecule behaves as if it is ___nonpolar______! How does this new knowledge of molecular geometry apply to polarity issues? Ask: 1. Does my molecule have any polar bonds? 2. If it does, how are they arranged? 3. If the polar bonds are equal in magnitude, AND symmetrically arranged in the opposite directions, the dipoles can cancel each other and result in a molecule that is “nonpolar”overall (with no net dipole). 4. Geometries with no lone pairs on the central atom are symmetrical. Most with lone pairs are not. 5. Geometries with 2 bonds and 3 lone pairs (________) or 4 bonds with 2 lone pairs (_____________) are also symmetrical. Molecular Shape and Polarity If a molecule has one polar bond, the molecule will be ____________. For example: HF, HCl, CH3F If a molecule has two or more identical polar bonds, it may or may not be polar, depending on the _____________. Why is water so different? The lone pairs give a _____ geometry and dipoles do not cancel, but are additive here instead. Three identical bonds in trigonal planar geometry will cancel, so _________dipole. Four identical bonds in a tetrahedral geometry as with CCl4 will cancel, so ____________dipole. What about CH3Cl? Notice the lone pair, the trigonal pyramidal geometry and the net dipole that results. In both of these, there is a symmetrical geometry with identical dipoles, so _________dipole. Which of these has no net dipole? Can you name their molecular geometries, too? What is going on here? Will the dipoles cancel? In which of these will the dipoles cancel giving no net dipole? Practice: Label each of the following by molecular geometry and as polar covalent or nonpolar covalent (with no net dipole). A. B. C. D. E. F. G. H. PCl3 SiCl4 BCl3 ICl3 AsF5 ClF5 XeF4 Cl2CO Practice: Label each of the following by molecular geometry and as polar covalent or nonpolar covalent (with no net dipole). A. B. C. D. E. F. G. H. PCl3 trigonal pyramidal SiCl4 tetrahedral BCl3 trigonal planar ICl3 T-shaped AsF5 trigonal bipyramidal ClF5 square pyramidal XeF4 square planar Cl2CO trigonal planar polar nonpolar nonpolar polar nonpolar polar nonpolar polar TABLE 5.5 First a comparison: Intramolecular Bonding • Bonds that form “_________” the molecule. • Molecules are formed by sharing electrons between the atoms. Intermolecular Forces • Forces that occur ________________ molecules. Dipole–dipole forces Hydrogen bonding London dispersion forces NOTE: Intramolecular bonds are stronger than intermolecular forces. Types of Intermolecular (Attractive) Forces • Temporary polarity in the molecules due to unequal electron distribution leads to attractions called dispersion forces (sometimes called London dispersion forces). • Permanent polarity in the molecules due to their structure leads to attractive forces called dipole– dipole attractions. You can predict net dipole now, right? • An especially strong dipole–dipole attraction results when H is attached to an extremely electronegative atom like a ___________. These are called hydrogen bonds (H-bonding). Recall that some covalent bonds have as much as 1000 kJ/mol in bond energy! A summary of IMFs and their strength. 1. Typically London dispersion forces are the weakest of the IMFs and are most significant in nonpolar molecules. a) _________ molecules or atoms have greater strength b) more surface area ___creases strength 2. Polar molecules have net dipoles, and the stronger the dipole, the stronger the dipole-dipole IMFs. 3. Hydrogen bonding is an extra strong dipole-dipole force. Some more practice on today’s work: 1. Which of the following would have only London dispersion forces as the IMFs? 1. ICl3 2. AsF5 4. XeF4 5. Cl2CO 3. ClF5 2. Give the major intermolecular force at work in each of the following: a) CH3OCH3 c) CH3CH2CH3 e) H2CO b) CH3CH2NH2 d) CF4 London Dispersion Forces • Instantaneous dipoles that occur spontaneously and fleetingly in a given atom and then induce similar dipoles in neighboring atoms • Significant in large atoms/molecules • Larger surface area facilitates the formation of these induced dipoles. • Occurs in all molecules, including ____________ ones Figure 11.4 Why the increase in boiling point with increase in molar mass? Another example of how size impacts dispersion forces (Fig. 11.6): Why the difference in boiling points? The molar mass is the same for these “isomers”. Figure 11.5 Dipole-Dipole Forces • Dipole moment – molecules with polar bonds often behave in an electric field as if they had a center of positive charge and a center of negative charge (a _____ _________, right?). • Molecules with dipole moments can attract each other electrostatically. They line up so that the positive and negative ends are close to each other. • Only about 1% as strong as covalent or ionic bonds. Polar molecules have a _____________dipole. • Bond polarity and molecular geometry (shape) determine the substances polarity • If the molecule has a dipole moment, then it will interact with another polar molecule. NOTE: A permanent dipole adds to the attractive forces between the molecules, _____________ the boiling and melting points relative to nonpolar molecules of similar size and shape. Shows how a nonpolar and a polar molecule of comparable size compare! Fig. 11.7 Hydrogen Bonding in Water The blue dotted lines are the intermolecular forces between the water molecules called “hydrogen bonds”. Hydrogen bonds are very strong dipole-dipole forces Hydrogen is bound to a highly __________________ atom. Look for hydrogen bound to ________________________. Fig. 11.11 Shows the difference hydrogen bonding makes. Which of the following would have the highest boiling point? Explain your choice to your neighbor. Figure 11.13 The Boiling Points of the Covalent Hydrides of the Elements in Groups 4A, 5A, 6A, and 7A In general, the boiling and the melting points ____crease with the strength of intermolecular forces in the substance. Copyright © Cengage Learning. All rights reserved 61 Which of the following compounds is likely to have an unexpectedly high boiling point? And, there is one more to consider! Figure 11.14 Recall that some covalent bonds have as much as 1000 kJ/mol in bond energy! Attractive Forces and Solubility • Solubility depends, in part, on the attractive forces of the solute and solvent molecules. – Like dissolves ______. – Miscible liquids will always dissolve in each other. • Polar substances dissolve in ________ solvents. • Nonpolar molecules dissolve in ________ solvents. • Many molecules have both hydrophilic (________) and hydrophobic (_______________) parts. – Solubility in water becomes a competition between the attraction of the polar groups for the water and the attraction of the nonpolar groups for another nonpolar group. Pentane is a ________ liquid and water is a _______ one, so they are immiscible. Gasoline Floating on Water E.R. Degginger/Color-Pic, Inc. Would you think hexane or methanol would be a better solvent for grease? Vitamin A and Vitamin C Which is a “fat soluble” and which is a “water soluble” vitamin? (hydrophobic vs. hydrophilic) And what do polar bears have to do with it??? Frank Cox Nonpolar region polar Fat-soluble or water soluble vitamin?