1. Chapter 9 Chemical Bonding Theories Valence Bond Theory: Uses Lewis Structures Bonds form using shared electrons between overlapping orbitals on adjacent atoms. Orbitals arrange around central atom to avoid each other. Two types of bonds: sigma and pi. Molecular Orbital Theory: Uses MO Diagrams Orbitals on atoms “mix” to make molecular orbtials, which go over 2 or more atoms. Two electrons can be in an orbital. Orbitals are either: bonding, antibonding, or nonbonding. Bonds are either: sigma or pi.

3. Orbitals on bonding atoms overlap directly between bonding atoms Sigma (  ) Bonding Between s orbitals Between p orbitals

4. Consider VSEPR Shapes and bonding: Sigma (s) Bonding

5. What’s wrong with this picture? Atoms bond by having their valence orbitals overlap

6. Orbitals don’t go in same directions as atomic orbitals. 2s 2p z 2p x 2p y Orbitals in CH 4 Orbitals on C

7. Orbitals don’t go in same directions as atomic orbitals. 2s 2p z 2p x 2p y Orbitals in CH 4 Conclusion: Atomic orbitals change shape when they make molecules.

8. Hybrid Orbitals Atomic valence orbitals “combine and mix” to form new “Hybrid Orbitals” Hybrid orbitals go in the VSEPR electron geometry directions.

9. Types of Hybrid Orbitals

10. Types of Hybrid Orbitals: 2 Pairs

11. Types of Hybrid Orbitals: 3 Pairs

12. Types of Hybrid Orbitals: 4 Pairs

13. Types of Hybrid Orbitals

14. Sigma Bonding Orbitals overlap directly between two nuclei:

17. Sigma Bonding involves hybrid orbitals and/or H 1s orbitals. Pi bonding involves unhybridized p orbitals. Sigma vs. Pi Bonding

18. Pi Bond Formation

19. Bonding in Ethene

20. Bonding in Acetylene

22. Bonding in Formaldehyde

24. Advanced: Allene Each end carbon is a flat trigonal. Are they co-planar or perpendicular?

25. Bonding in Allene

26. Bonding in Benzene

27. Conformations vs. Isomers Isomers: Molecules with same formula but different structure Conformers: Different temporary shapes of the same molecule

28. Bond Rotations CAN happen around single bonds Cannot happen around double bonds

30. Cis-Trans Isomerization When two groups are on a “side” of a molecule. cis trans

31. Can these molecules have cis-trans isomers?