1. 1 Molecular Orbitals in Chemical Bonding

2. 2 Molecular Orbital Theory zTypes of molecular orbitals that can be produced by the overlap of atomic orbitals.  Head-on overlap of atomic orbitals produces  (sigma) orbitals.  Side-on overlap of atomic orbitals produces  (pi) orbitals.  Two s atomic orbitals can overlap and produce two molecular orbitals designated as a  s and a  s * molecular orbital.

3. 3 Molecular Orbital Theory zGraphically we can represent this as

4. 4 Molecular Orbital Theory

5. 5

6. 6  The head-on overlap of two corresponding p atomic orbitals on different atoms, say p x with p x produces  p and  p * molecular orbitals.

7. 7 Molecular Orbital Theory

8. 8  Side-on overlap of two corresponding p atomic orbitals on different atoms (say p y with p y or p z with p z ) produces  and    (pi) molecular orbitals.

9. 9 Molecular Orbital Theory

10. 10 Molecular Orbital Energy- Level Diagram zOrder of filling of MO’s obeys same rules as for atomic orbitals. zIncluding yAufbau principle yHund’s Rule

11. 11 Molecular Orbital Energy- Level Diagram

12. 12 Bond Order and Bond Stability zBond order (bo) of a molecule is defined as half the number of electrons in bonding orbitals minus half the number of electrons in antibonding orbitals

13. 13 Homonuclear Diatomic Molecules zConsider the overlap of the atomic orbitals of two nitrogen atoms to form an N 2 molecule. zEach N atom has 7 electrons thus the N 2 molecule has 14 electrons.

14. 14 Homonuclear Diatomic Molecules

15. 15 Homonuclear Diatomic Molecules zIn shorthand notation we represent this configuration as

16. 16 Homonuclear Diatomic Molecules zThe greater the bond order of a bond the more stable we predict it to be. zFor N 2 the bond order is

17. 17 Homonuclear Diatomic Molecules zMO treatment can also be applied to ions. yIons are charged and that charge affects the stability as well as the bond order.  Write out the electron configuration of the N 2 + ion in abbreviated notation (   s 2   s *2 ……). What is the bond order?

18. 18 Homonuclear Diatomic Molecules  Write out the electron configuration of the N 2 + ion in abbreviated notation (   s 2   s *2 ……). What is the bond order?

19. 19 Homonuclear Diatomic Molecules zWrite out the electron configuration of the O 2 molecule in abbreviated notation. What is the bond order? Is the molecule paramagnetic or diamagnetic?

20. 20 Homonuclear Diatomic Molecules zWrite out the electron configuration of the O 2 molecule in abbreviated notation. What is the bond order? Is the molecule paramagnetic or diamagnetic?

21. 21 Homonuclear Diatomic Molecules zWrite out the electron configuration of the Be 2 molecule in abbreviated notation. What is the bond order? Would you predict that the molecule exists? You do it!

22. 22 Homonuclear Diatomic Molecules zWrite out the electron configuration of the Be 2 molecule in abbreviated notation. What is the bond order? Would you predict that the molecule exists?

23. 23 Homonuclear Diatomic Molecules  Write out the electron configuration for F 2. In this molecule the  p molecular orbital is lower than the  p molecular orbitals. What is the bond order? Is F 2 paramagnetic?

24. 24 Homonuclear Diatomic Molecules  Write out the electron configuration for F 2. In this molecule the  p molecular orbital is lower than the  p molecular orbitals. What is the bond order? Is F 2 paramagnetic?

25. 25 Delocalization and Shapes of Molecular Orbitals zValence bond theory discusses resonance formulas. yCarbonate ion (CO 3 2- ) is an example.

26. 26 Delocalization and Shapes of Molecular Orbitals zMolecular orbital theory describes shapes in terms of delocalization of electrons. yAgain carbonate ion (CO 3 2- ) is a good example.

27. 27 Delocalization and Shapes of Molecular Orbitals zThe structure of benzene is described well by molecular orbital theory.

28. 28 Delocalization and Shapes of Molecular Orbitals zResonance structure - VB theory.

29. 29 Delocalization and Shapes of Molecular Orbitals zMolecular orbital theory

30. 30 Delocalization and Shapes of Molecular Orbitals zMolecular orbital theory