1. Unit 2 Atoms and Bonding 2.87 Resonance Textbook ch 8.6

2. Big Idea 2: Chemical and physical properties of materials can be explained by the structure and the arrangement of atoms, ions, or molecules and the forces between them. Students will be able to demonstrate understanding by laboratory investigation, analysis of data and creation of models. SWBAT: Recognize molecules where resonance structures are needed to describe the bonding and draw the dominant resonance structures. Learning Objectives :

3. Resonance This is the Lewis structure we would draw for ozone, O 3. But could you flip it?... Yes Would the formal charges be same?... Yes How do you know which one is “right”? Neither, actually

4. Resonance In fact… the Lewis structure does not agree with observed structure of ozone, in which… –…both O—O bonds are the same length according. –…both outer oxygens have a formal charge of  1/2 if you measure it in lab.

5. One Lewis structure cannot accurately depict a molecule such as ozone. We use multiple structures, resonance structures, to describe the molecule. Need brackets Need double sided arrows in between resonance structures How we represent resonance structures symbolically

6. Resonance Just as green is a blend of blue and yellow… …ozone is a blend of these two resonance structures. blended

7. Resonance Resonance is invoked when more than one valid Lewis structure can be written for a particular molecule. The actual structure is an blend of the resonance structures. Benzene, C 6 H 6 The bond lengths in the ring are identical, and in between lengths of single and double bonds.

8. References I modified the information to fit our needs in AP Chemistry needs. Our textbook: Brown, Lemay et all. AP edition chemistry, 13 th edition, 2015

9. Resonance Bond Length and Bond Energy Resonance bonds are shorter and stronger than single bonds. Resonance bonds are longer and weaker than double bonds.

10. References I modified the information to fit our needs in AP Chemistry needs. Our textbook: Brown, Lemay et all. AP edition chemistry, 13 th edition, 2015