1. Bonding and Structure 1 Chemical Bonding and Molecular Structure Ionic vs. covalent bonding Molecular orbitals and the covalent bond Valence electron Lewis dot structures octet vs. non-octet resonance structures formal charges VSEPR - predicting shapes of molecules Bond properties polarity, bond order, bond strength TOPICS:

2. Bonding and Structure2 Forms of Chemical Bonds There are 2 extreme forms of connecting or bonding atoms: Ionic —complete transfer of electrons from one atom to another Covalent —electrons shared between atoms

3. Bonding and Structure3 Covalent Bonding The bond arises from the mutual attraction of 2 nuclei for the same electrons. A covalent bond is a balance of attractive and repulsive forces.

4. Bonding and Structure4 Bond Formation A covalent bond can result from a “head-to-head” overlap of atomic orbitals on neighboring atoms. HH Cl Cl + Overlap of H (1s) and Cl (2p) This type of overlap places bonding electrons in a MOLECULAR ORBITAL along the line between the two atoms and forms a SIGMA BOND (s).

5. Bonding and Structure5 Sigma Bond Formation by Orbital Overlap Two s Atomic Orbitals (A.O.s) overlap to form an s  (sigma) Molecular Orbital (M.O.)

6. Bonding and Structure6 Sigma Bond Formation by Orbital Overlap Similarly, two p A.O.s can overlap end-on to from a p  M.O. e.g. F 2

7. Bonding and Structure7 Valence Electrons 1A 2A3A4A5A6A7A 8A Number of valence electrons is equal to the Group number.

8. Do Worksheet Lewis Dot Diagrams/Types of Bonds Bonding and Structure 8

9. 9 Electron Distribution in Molecules Electron distribution is depicted with Lewis electron dot structures Electrons are distributed as: shared or BOND PAIRS and unshared or LONE PAIRS. G. N. Lewis 1875 - 1946

10. Bonding and Structure10 Bond and Lone Pairs Electrons are distributed as shared (BOND PAIRS) and unshared (LONE PAIRS). H Cl This is a LEWIS ELECTRON DOT structure. shared or bond pair Unshared or lone pair (LP)

11. Bonding and Structure11 Rules of Lewis Structures #Bond Pairs + #Lone Pairs = 4 For Groups 5A-7A (N - F), no. of BOND PAIRS = 8 - group No. For Groups 1A-4A (Li - C), no. of BOND PAIRS = group number Except for H (and atoms of 3rd and higher periods )

12. Chapter 1212 Add the valence electrons. Identify the central atom (usually the one with the lowest electron affinity and closest to the center of the periodic table). Place the central atom in the center of the molecule and add all other atoms around it. Place one bond (two electrons) between each pair of atoms. Complete the octet for the central atom. Complete the octets for all other atoms. Use double bonds if necessary. Drawing Lewis Structures

13. Bonding and Structure13 2. Count valence electrons H = 1 and N = 5 Total = (3 x 1) + 5 = 8 electrons or 1. Decide on the central atom; never H. Central atom is atom of lowest affinity for electrons. In ammonia, N is central Building a Dot Structure Ammonia, NH 3 4 pairs

14. Bonding and Structure14 4. Remaining electrons form LONE PAIRS to complete octet as needed. 3. Form a sigma bond between the central atom and surrounding atoms. Building a Dot Structure H H H N 3 BOND PAIRS and 1 LONE PAIR. Note that N has a share in 4 pairs (8 electrons), while each H shares 1 pair.

15. Electron-dot formula for Ammonia (NH 3 ) N H H H Here is a Nitrogen atom (5 val e - ’s) and three Hydrogen atoms (1 val e - each)

16. Electron-dot formula for Ammonia (NH 3 ) N H H H Here is a Nitrogen atom (5 val e - ’s) and three Hydrogen atoms (1 val e - each)

17. Electron-dot formula for Ammonia (NH 3 ) NH H H Here is a Nitrogen atom (5 val e - ’s) and three Hydrogen atoms (1 val e - each)

18. Electron-dot formula for Ammonia (NH 3 ) NH H H Here is a Nitrogen atom (5 val e - ’s) and three Hydrogen atoms (1 val e - each)

19. Electron-dot formula for Ammonia (NH 3 ) N H H H

20. N H H H

21. N H H H “N” now feels like it has a stable octet

22. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet

23. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet

24. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet

25. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet

26. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet

27. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

28. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

29. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

30. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

31. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

32. Electron-dot formula for Ammonia (NH 3 ) N H H H “N” now feels like it has a stable octet Each “H” feels like it has 2 e - like Helium.

33. Electron-dot formula for Ammonia (NH 3 ) N H H H Each “H” feels like it has 2 e - like Helium.

34. Electron-dot formula for Ammonia (NH 3 ) N H H H

35. N H H H

36. N H H H

37. N H H H

38. N H H H

39. N H H H

40. N H H H

41. N H H H

42. N H H H

43. N H H H

44. N H H H I’m so HAPPY!

45. Electron-dot formula for Methane (CH 4 ) C H H H H Here is a Carbon atom (4 val e - ’s) and four Hydrogen atoms (1 val e - each)

46. Electron-dot formula for Methane (CH 4 ) CH H H H Here is a Carbon atom (4 val e - ’s) and four Hydrogen atoms (1 val e - each)

47. Electron-dot formula for Methane (CH 4 ) C H H H H Here is a Carbon atom (4 val e - ’s) and four Hydrogen atoms (1 val e - each)

48. Electron-dot formula for Methane (CH 4 ) C H H H H Here is a Carbon atom (4 val e - ’s) and four Hydrogen atoms (1 val e - each)

49. Electron-dot formula for Methane (CH 4 ) C H H H H

50. C H H H H

51. C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

52. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

53. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

54. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

55. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet.

56. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet. Each H atom “feels” like a stable “He” atom with 2e - s

57. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet. Each H atom “feels” like a stable “He” atom with 2e - s

58. Electron-dot formula for Methane (CH 4 ) C H H H H Now they have formed a stable molecule. Each C atom “feels” like it has a stable octet. Each H atom “feels” like a stable “He” atom with 2e - s

59. Bonding and Structure59 Carbon Dioxide, CO 2 1. Central atom = __C__ 2. Valence electrons = 16 or 8 pairs 3. Form sigma bonds. This leaves 6 pairs. 4. Place lone pairs on outer atoms.

60. Bonding and Structure60 Carbon Dioxide, CO 2 (2) 4. Place lone pairs on outer atoms. The second bonding pair forms a pi (  ) bond. 5. To give C an octet, form DOUBLE BONDS between C and O.

61. Bonding and Structure61 SO 3 H 2 CO Double and even triple bonds are commonly observed for C, N, P, O, and S C2F4C2F4

62. Bonding and Structure62 Urea (NH 2 ) 2 CO 1. Number of valence electrons = 24 e- 2. Draw sigma bonds. 4. Place remaining electron pairs on oxygen 3. Complete C atom octet with double bond. Leaves 24 - 14 = 10 (5 e- pairs). and nitrogen atoms.

63. Chapter 1263 Electron Dot Structures - Ions To draw the electron dot structure of an ion, you must add the charges to the number of electrons (for a negative ion) See p.342 in Heath

64. Do Worksheet Electron Dot Structures for Molecules and Polyatomic Ions Bonding and Structure64