1. Orbitalsand Covalent Bonds

2. Atomic Orbitals Don’t Work n to explain molecular geometry. n In methane, CH 4, the shape s tetrahedral. n The valence electrons of carbon should be two in s, and two in p. n the p orbitals would have to be at right angles. n The atomic orbitals change when making a molecule

3. Hybridization n We blend the s and p orbitals of the valence electrons and end up with the tetrahedral geometry. n We combine one s orbital and 3 p orbitals. n sp 3 hybridization has tetrahedral geometry.

4. In terms of energy Energy 2p 2s Hybridizationsp 3

5. How we get to hybridization n We know the geometry from experiment. n We know the orbitals of the atom n hybridizing atomic orbitals can explain the geometry. n So if the geometry requires a tetrahedral shape, it is sp 3 hybridized n This includes bent and trigonal pyramidal molecules because one of the sp 3 lobes holds the lone pair.

6. sp 2 hybridization nC2H4nC2H4nC2H4nC2H4 n Double bond acts as one pair. n trigonal planar n Have to end up with three blended orbitals. n Use one s and two p orbitals to make sp 2 orbitals. n Leaves one p orbital perpendicular.

7. In terms of energy Energy 2p 2s sp 2 Hybridization 2p

8. Where is the P orbital? n Perpendicular The overlap of orbitals makes a sigma bond (  bond) The overlap of orbitals makes a sigma bond (  bond)

9. Two types of Bonds n Sigma bonds from overlap of orbitals. n Between the atoms. Pi bond (  bond) above and below atoms Pi bond (  bond) above and below atoms n Between adjacent p orbitals. n The two bonds of a double bond.

10. CC H H H H

11. sp 2 hybridization n When three things come off atom. n trigonal planar n 120º on  one  bond on  one  bond

12. What about two n When two things come off. n One s and one p hybridize. n linear

13. sp hybridization n End up with two lobes 180º apart. n p orbitals are at right angles Makes room for two  bonds and two sigma bonds. Makes room for two  bonds and two sigma bonds. n A triple bond or two double bonds.

14. In terms of energy Energy 2p 2s Hybridization sp 2p

15. CO 2 C can make two  and two  C can make two  and two  O can make one  and one  O can make one  and one  COO

16. Breaking the octet n PCl 5 n The model predicts that we must use the d orbitals. n dsp 3 hybridization n There is some controversy about how involved the d orbitals are.

17. dsp 3 n Trigonal bipyrimidal can only  bond. can only  bond. can’t  bond. can’t  bond. n basic shape for five things.

18. PCl 5 Can’t tell the hybridization of Cl Assume sp 3 to minimize repulsion of electron pairs.

19. d 2 sp 3 n gets us to six things around n octahedral

20. Molecular Orbital Model n Localized Model we have learned explains much about bonding. n It doesn’t deal well with the ideal of resonance, unpaired electrons, and bond energy. n The MO model is a parallel of the atomic orbital, using quantum mechanics. n Each MO can hold two electrons with opposite spins n Square of wave function tells probability

21. What do you get? n Solve the equations for H 2 n H A H B n get two orbitals n MO 1 = 1s A - 1s B n MO 2 = 1s A + 1s B

22. The Molecular Orbital Model The molecular orbitals are centered on a line through the nuclei –MO 1 the greatest probability is between the nuclei –MO 2 it is on either side of the nuclei –this shape is called a sigma molecular orbital

23. The Molecular Orbital Model In the molecule only the molecular orbitals exist, the atomic orbitals are gone MO 1 is lower in energy than the 1s orbitals they came from. –This favors molecule formation –Called an bonding orbital MO 2 is higher in energy MO 2 is higher in energy –This goes against bonding –antibonding orbital

24. The Molecular Orbital Model Energy MO 2 MO 1 ssss ssss

25. The Molecular Orbital Model We use labels to indicate shapes, and whether the MO’s are bonding or antibonding. –MO 1 =  1s –MO 2 =  1s * (* indicates antibonding) Can write them the same way as atomic orbitals –H 2 =  1s 2

26. The Molecular Orbital Model Each MO can hold two electrons, but they must have opposite spins Orbitals are conserved. The number of molecular orbitals must equal the number atomic orbitals that are used to make them.

27. H2-H2-H2-H2- Energy  1s  1s * ssss ssss

28. Bond Order n The difference between the number of bonding electrons and the number of antibonding electrons divided by two