1. Lewis Structures & Stability Multiple Bonds Bond Energies Resonance Exceptions to Octet Rule

2. Stability and Bond Energies Bond energy is a measure of stability. Bond energy is a measure of stability. Bond energy – amount of energy required to break a bond holding two atoms together. Bond energy – amount of energy required to break a bond holding two atoms together. The values of bond energies decrease in order: triple > double > single. The values of bond energies decrease in order: triple > double > single. Example: N 2 > O 2 > H 2 Example: N 2 > O 2 > H 2

3. Bond Length Bond length – distance of separation of the bonded nuclei Bond length – distance of separation of the bonded nuclei Bond length is related to the presence or absence of multiple bonding. Bond length is related to the presence or absence of multiple bonding. Bond length decreases as the number of bonds increase: single > double > triple Bond length decreases as the number of bonds increase: single > double > triple

4. Resonance In some cases, it is possible to write more than one Lewis structure that satisfies the octet rule. In some cases, it is possible to write more than one Lewis structure that satisfies the octet rule. Experimental evidence shows no double bond exists. The actual structure is a hybrid of these two. Experimental evidence shows no double bond exists. The actual structure is a hybrid of these two.

5. Practice - Resonance Draw the resonance structures for: Draw the resonance structures for: Ozone (O 3 ) Ozone (O 3 ) Benzene (C 6 H 6 ) Benzene (C 6 H 6 )

6. Ozone

7. Benzene

8. Exceptions to the Octet Incomplete octet Incomplete octet Example: BeH 2 Example: BeH 2 Odd electron molecules Odd electron molecules Example: NO Example: NO Expanded octet Expanded octet Example: PF 5 Example: PF 5

9. Homework End of Ch problems: pg. 115- 116: 30, 34, 48, 56, 58, 60 – due before test (will be graded) MORE TO COME! End of Ch problems: pg. 115- 116: 30, 34, 48, 56, 58, 60 – due before test (will be graded) MORE TO COME!