Orbital Hybridization

1. Orbital Hybridization Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

2. Atomic Orbitals & Covalent Bonding Atomic orbitals are mathematical descriptions of the probable locations of electrons around an atom. s, px, py, pz, dxy, dxz, dyz, dx2-y2, dz2, ... Atomic orbitals can be “blended” together to form new orbitals called hybrid orbitals.

3. Be Be Be Be Be sp Orbital Hybridization The shape is determined by the linear combinations of atomic orbitals y2s + y2pz y2s - y2pz and

4. C + + C C sp2 Orbital Hybridization The 2s, 2px and 2pz atomic orbitals of each carbon are used. = 2pz 2px 2s sp2 The angle between the orbitals is 120°.

5. x y + + + z 2py 2pz 2px 2s sp3 Orbital Hybridization

6. sp3 Orbital Hybridization The angle between the orbitals is 109.5°. Why isn’t the angle 90°? four sp3orbitals tetrahedral shape

7. Groups Ideal of Hybridization Bond Electrons Angle 2 sp 180º 3 sp2 120º 4 sp3 109.5º

8. • • • H • O • • • • • • • • N • • • • • H Be H • • • • • • • • • • • H • • C O • • • • • • • • • • • • H N O H • • O H C N H C H Predict the bond angles and the hybridization of the central atoms in each of the following structures.

9. • • • H • O • • • • • • • • N • • • • • H Be H • • • • • • • • • • • H • • C O • • • • • • • • • • • • H N O H • • O H C N H C H Predict the bond angles and the hybridization of the central atoms in each of the following structures. spBe sp3N sp3O sp2C sp2N sp3C spC

10. Be and Be Be Be Beryllium sp Hybridization Two orbitals each can hold two electrons

11. 2p sp energy Be 2s ao sp Hybridization px, py Maximum angle that two orbitals can be apart is 180°. hao atomic orbtials hybrid atomic orbtials

12. x y Be z sp Hybridized BerylliumValence Orbitals The other p-orbitals of beryllium (px, py) remain unchanged Open orbital contains no electrons Lined orbital contains one electron Filled in orbital contains two electrons

13. H two sigma bonds H H Be H H Be H sp Hybridized BerylliumValence Orbitals The other p-orbitals of beryllium (px, py) remain unchanged Why is it a linear molecule? Open orbital contains no electrons Lined orbital contains one electron Filled in orbital contains two electrons

14. • • • H • O • • • • • • • • N • • • • • • • • • • • • H • • C O • • • • • • • • • • • • H N O H • • O H C N H C H Sketch the hybrid atomic orbitals and fill or shade-in the lobes for each indicated atom sp3N sp3O sp2O sp2C sp2N spN sp3C spC

15. Sketch the hybrid atomic orbitals and fill or shade-in the lobes for each indicated atom sp3O sp2C sp3N sp2O sp2N sp3C spC spN

16. H H • • • • • • C C • • • • • • H H Ethene • Also called ethylene • Polymerizes to form polyethylene • Each carbon forms three sp2 hybrid orbitals.

17. 2p sp2 energy 2s ao sp2 Hybridization 2py hao This hybrid set can hold six electrons. The unhybridized py orbital is perpendicular to the sp2 orbitals.

18. y Edge on view Top down view (xz plane) Ethene To allow for overlap of the unhybridized py orbitals, the bonding in this molecule requires that ethene is planar. All six atoms lie in the same plane.

19. H H C C H H Ethene carbon-carbon sigma bond due to sp2-sp2 overlap carbon-hydrogen sigma bonds due to sp2-s overlap carbon-carbon pi bond due to 2py- 2py overlap

20. H • • • • H C H • • • • H Methane The 2s, 2px, 2py and 2pz atomic orbitals of carbon are used. What would be the name of a hybrid orbital made from these orbitals?

21. 2p energy 2s hao carbon ao sp3 Hybridization sp3 All four hybrid atomic orbitals have the same energy. These four orbitals are energetically degenerate.

22. H C H H H carbon-hydrogen sigma bonds due to sp3-s overlap Methane

23. • • • • • • • • Ammonia H N H H The 2s, 2px, 2py and 2pz atomic orbitals of nitrogen are used

24. 2p energy 2s sp3 Hybridization sp3 By hybridizing its atomic orbitals nitrogen gains more stable (lower energy) orbitals for bonding. hao nitrogen ao Which of the electrons in these hybrid atomic orbitals are available for bonding?

25. • • N H H H nitrogen-hydrogen sigma bonds due to sp3-s overlap Ammonia a completely filled in orbital contains two electrons Because of this bonding, the Ð H-N-H bond angle is close to 109.5° (actually 107°).

26. The Structure of Ammonia What bond angle would be expected if the lone pair of electrons didn't affect the structure? What bond angle would be expected if the atomic orbitals of nitrogen did not hybridize? Why is the actual bond angle not exactly 109.5°? Draw the orbital overlap diagram for the reaction of ammonia and a hydrogen ion.

27. H N C • • • • • H C N • • • • • sp hybridization Ð H-C-N = 180° Hydrogen Cyanide 2 groups of electrons around carbon What does the orbital overlap diagram look like?

28. • • • • • H C N • • • • • Hydrogen Cyanide hydrogen 1s orbital carbon sp hybridized nitrogen sp hybridized How many electrons are in each orbital? How many electrons are in each orbital?

29. • • • • • H C N • • • • • sigma bonds px orbital overlap py orbital overlap Hydrogen Cyanide

30. • • • • • H C N • • • • • 2 pi bonds sigma bonds Hydrogen Cyanide (between carbon and nitrogen) (between hydrogen and carbon and carbon and nitrogen)

31. O O N • • N • • • • • • • • • • O O • • • • • • sp2 hybridization Nitrite Ion Why is the bond angle approximately 120°? 3 groups of electrons around nitrogen ÐO-N-O @ 120° Draw the hybridized atomic orbitals for each atom O1 sp2 hybridized O2 sp3 hybridized

32. • • N O O • • • • • • • • • • • • • • • • _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1s 1s sp2 sp2 p p 1s sp3 Nitrite Ion -1 charge 1s2 2s2 2p4 1s2 2s2 2p3 1s2 2s2 2p4

33. • • N O O • • • • • • • • • • • • • • • • Nitrite Ion What other kind of bond is formed?

34. • • N • • • • • • • • • • O O • • • • • • Nitrite Ion N O O Where is the pi bond located?

35. O O N 3 groups of electrons around nitrogen • • N • • • • • • • • • • O O • • • • • sp2 hybridization • ÐO-N-O @ 120° Nitrite Ion How would the bonding change if O2 was unhybridized?

36. • • N O O • • • • • • • • • • • • • • • • 1s2 2s2 2p4 1s2 2s2 2p3 _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1s 1s sp2 sp2 p p 1s 2s 2p Nitrite Ion -1 charge 1s2 2s2 2p4

37. • • N O O • • • • • • • • • • • • • • • • Nitrite Ion What other kind of bond is formed?

38. • • N • • • • • • • • • • O O • • • • • • Nitrite Ion pi bond formation How could resonance in this molecule be explained?

39. H H C C H H H H • • • • • • C C • • • • sp2 hybridization • • H H Ethene 3 groups of electrons around carbon ÐC-C-H @ 120° ÐH-C-H @ 120°

40. H H • • • • • • C C • • • • • • H H Ethene How many sigma bonds and how many pi bonds are formed?

41. H H H H C C H H H H • • • • sp3 hybridization • • • • H C C H • • • • • • • • H H Ethane 4 groups of electrons around carbon ÐC-C-H @ 109.5° ÐH-C-H @ 109.5°

42. H H • • • • • • • • H C C H • • • • • • • • H H Ethane What kind of bonds are formed?

43. Dipole Moments • Charge is not always equally distributed in a molecule. • There can be a region of positive charge and of negative charge. • The vector connecting these regions is called the dipole moment.

44. Predictions • For molecular compounds • solubility and miscibility are related to the polarity (i.e., dipole moment) of the molecule. • "Like dissolves like" is a rule of thumb for solubility • polar molecules dissolve in polar solvents • nonpolar molecules dissolve in nonpolar solvents

45. 2- O C O O Carbonate Ion The concept of dipole moments can also be applied to ions, although they generally dissolve in polar solvents (e.g., water) because of their charge. Although carbonate ion has no net dipole moment, it dissolves in polar solvents because of its ionic charge.

46. Like Dissolves Like • The rule "like dissolves like" is not perfect; • However, it does serve as a starting point in determining what type of solvent to use when attempting to dissolve a solid.

47. H • • • • O C Cl Cl H H Cl Polarity Predictions • Rank the following molecules in terms of polarity: • water, benzene, chloroform

49. Electronegativity