1. Roy Kennedy Massachusetts Bay Community College Wellesley Hills, MA Introductory Chemistry, 2 nd Edition Nivaldo Tro Chapter 10 Chemical Bonding 2006, Prentice Hall

2. Tro's Introductory Chemistry, Chapter 10 2 Bonding Theories bonding is the way atoms attach to make molecules an understanding of how and why atoms attach together in the manner they do is central to chemistry chemists have an understanding of bonding that allows them to: 1)predict the shapes of molecules and properties of substances based on the bonding within the molecules 2)design and build molecules with particular sets of chemical and physical properties

3. Tro's Introductory Chemistry, Chapter 10 3 Lewis Symbols of Atoms also known as electron dot symbols use symbol of element to represent nucleus and inner electrons use dots around the symbol to represent valence electrons put one electron on each side first, then pair remember that elements in the same group have the same number of valence electrons; therefore their Lewis dot symbols will look alike Li Be B C N O: :F: :Ne:

4. Tro's Introductory Chemistry, Chapter 10 4 Lewis Bonding Theory atoms bond because it results in a more stable electron configuration atoms bond together by either transferring or sharing electrons so that all atoms obtain an outer shell with 8 electrons Octet Rule there are some exceptions to this rule – the key to remember is to try to get an electron configuration like a noble gas

5. Tro's Introductory Chemistry, Chapter 10 5 Lewis Symbols of Ions Cations have Lewis symbols without valence electrons Lost in the cation formation Anions have Lewis symbols with 8 valence electrons Electrons gained in the formation of the anion Li Li +1 :F: [:F:] -1

6. Tro's Introductory Chemistry, Chapter 10 6 Ionic Bonds metal to nonmetal metal loses electrons to form cation nonmetal gains electrons to form anion ionic bond results from + to - attraction larger charge = stronger attraction smaller ion = stronger attraction Lewis Theory allow us to predict the correct formulas of ionic compounds

7. Tro's Introductory Chemistry, Chapter 10 7 Example 10.3 - Using Lewis Theory to Predict Chemical Formulas of Ionic Compounds Predict the formula of the compound that forms between calcium and chlorine. Draw the Lewis dot symbols of the elements Ca ∙ ∙ Cl ∙ ∙ ∙ ∙∙ ∙∙ Transfer all the valance electrons from the metal to the nonmetal, adding more of each atom as you go, until all electrons are lost from the metal atoms and all nonmetal atoms have 8 electrons Ca ∙ ∙ Cl ∙ ∙ ∙ ∙∙ ∙∙ ∙ ∙ ∙ ∙∙ ∙∙ Ca 2+ CaCl 2

8. Tro's Introductory Chemistry, Chapter 10 8 Covalent Bonds often found between two nonmetals typical of molecular species atoms bonded together to form molecules strong attraction sharing pairs of electrons to attain octets molecules generally weakly attracted to each other observed physical properties of molecular substance due to these attractions

9. Tro's Introductory Chemistry, Chapter 10 9 Single Covalent Bonds two atoms share one pair of electrons 2 electrons one atom may have more than one single bond F F H F F H O H H O FF

10. Tro's Introductory Chemistry, Chapter 10 10 Double Covalent Bond two atoms sharing two pairs of electrons 4 electrons shorter and stronger than single bond O O O O OO

11. Tro's Introductory Chemistry, Chapter 10 11 Triple Covalent Bond two atoms sharing 3 pairs of electrons 6 electrons shorter and stronger than single or double bond N N N N NN

12. Tro's Introductory Chemistry, Chapter 10 12 Bonding & Lone Pair Electrons Electrons that are shared by atoms are called bonding pairs Electrons that are not shared by atoms but belong to a particular atom are called lone pairs also known as nonbonding pairs O S O Lone PairsBonding Pairs

13. Tro's Introductory Chemistry, Chapter 10 13 Polyatomic Ions The polyatomic ions are attracted to opposite ions by ionic bonds Form crystal lattices Atoms in the polyatomic ion are held together by covalent bonds

14. Tro's Introductory Chemistry, Chapter 10 14 Lewis Formulas of Molecules shows pattern of valence electron distribution in the molecule useful for understanding the bonding in many compounds allows us to predict shapes of molecules allows us to predict properties of molecules and how they will interact together

15. Tro's Introductory Chemistry, Chapter 10 15 Lewis Structures some common bonding patterns C = 4 bonds & 0 lone pairs  4 bonds = 4 single, or 2 double, or single + triple, or 2 single + double N = 3 bonds & 1 lone pair, O = 2 bonds & 2 lone pairs, H and halogen = 1 bond, Be = 2 bonds & 0 lone pairs, B = 3 bonds & 0 lone pairs B C NOF

16. Tro's Introductory Chemistry, Chapter 10 16 Writing Lewis Structures for Covalent Molecules 1)Attach the atoms together in a skeletal structure most metallic element generally central halogens and hydrogen are generally terminal many molecules tend to be symmetrical in oxyacids, the acid hydrogens are attached to an oxygen 2)Calculate the total number of valence electrons available for bonding use group number of periodic table

17. Tro's Introductory Chemistry, Chapter 10 17 Writing Lewis Structures for Covalent Molecules 3)Attach atoms with pairs of electrons and subtract electrons used from total bonding electrons 4)Add remaining electrons in pairs to complete the octets of all the atoms remember H only wants 2 electrons don’t forget to keep subtracting from the total complete octets on the terminal atoms first, then work toward central atoms

18. Tro's Introductory Chemistry, Chapter 10 18 Writing Lewis Structures for Covalent Molecules 5)If there are not enough electrons to complete the octet of the central atom, bring pairs of electrons from an attached atom in to share with the central atom until it has an octet try to follow common bonding patterns

19. Tro's Introductory Chemistry, Chapter 10 19 Example HNO 3 1)Write skeletal structure since this is an oxyacid, H on outside attached to one of the O’s; N is central 2)Count Valence Electrons and Subtract Bonding Electrons from Total N = 5 H = 1 O 3 = 3∙6 = 18 Total = 24 e - Electrons Start24 Used8 Left16

20. Tro's Introductory Chemistry, Chapter 10 20 Example HNO 3 3)Complete Octets, outside-in H is already complete with 2  1 bond 4)Re-Count Electrons N = 5 H = 1 O 3 = 3∙6 = 18 Total = 24 e - Electrons Start24 Used8 Left16 Electrons Start16 Used16 Left0

21. Tro's Introductory Chemistry, Chapter 10 21 Example HNO 3 5)If central atom does not have octet, bring in electron pairs from outside atoms to share follow common bonding patterns if possible

22. Example 10.4: Writing Lewis Structures for Covalent Compounds

23. Tro's Introductory Chemistry, Chapter 10 23 Example: Write the Lewis structure of CO 2.

24. Tro's Introductory Chemistry, Chapter 10 24 Example: Write the Lewis structure of CO 2. Write down the given quantity and its units. Given: CO 2

25. Tro's Introductory Chemistry, Chapter 10 25 Write down the quantity to find and/or its units. Find: Lewis structure Information Given: CO 2 Example: Write the Lewis structure of CO 2.

26. Tro's Introductory Chemistry, Chapter 10 26 Design a Solution Map. Information Given: CO 2 Find:Lewis structure formula of compound Example: Write the Lewis structure of CO 2. skeletal structure count and distribute electrons Lewis structure

27. Tro's Introductory Chemistry, Chapter 10 27 Apply the Solution Map. write skeletal structure  least metallic atom central  H terminal  symmetry Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2.

28. Tro's Introductory Chemistry, Chapter 10 28 Apply the Solution Map. Count and Distribute the Valence Electrons  count valence electrons C = 4 O = 2 ∙ 6 totalCO 2 = 16 Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2. CO 1A 2A 3A4A5A6A7A 8A

29. Tro's Introductory Chemistry, Chapter 10 29 Apply the Solution Map. Count and Distribute the Valence Electrons  attach atoms C = 4 O = 2 ∙ 6 totalCO 2 = 16 Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2. start = 16 e - use = 4 e - left = 12 e -

30. Tro's Introductory Chemistry, Chapter 10 30 Apply the Solution Map. Count and Distribute the Valence Electrons  complete octets –outside atoms first C = 4 O = 2 ∙ 6 totalCO 2 = 16 Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2. start = 16 e - use = 4 e - left = 12 e - start = 12 e - use = 12 e - left = 0 e -

31. Tro's Introductory Chemistry, Chapter 10 31 Apply the Solution Map. Count and Distribute the Valence Electrons  complete octets –if not enough electrons to complete octet of central atom, bring in pairs of electrons from attached atom to make multiple bonds Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2. start = 12 e - use = 12 e - left = 0 e -

32. Tro's Introductory Chemistry, Chapter 10 32 Check Information Given: CO 2 Find:Lewis structure SM: formula → skeletal → electron distribution → Lewis Example: Write the Lewis structure of CO 2. Start C = 4 e - O = 2 ∙ 6 e - totalCO 2 = 16 e - End bonding = 4 ∙ 2 e - lone pairs = 4 ∙ 2 e - total CO 2 = 16 e - The skeletal structure is symmetrical. All the electrons are accounted for.

33. Tro's Introductory Chemistry, Chapter 10 33 Writing Lewis Structures for Polyatomic Ions the procedure is the same, the only difference is in counting the valence electrons for polyatomic cations, take away one electron from the total for each positive charge for polyatomic anions, add one electron to the total for each negative charge

34. Tro's Introductory Chemistry, Chapter 10 34 Example NO 3 - 1)Write skeletal structure N is central because it is the most metallic 2)Count Valence Electrons and Subtract Bonding Electrons from Total N = 5 O 3 = 3∙6 = 18 (-) = 1 Total = 24 e - Electrons Start24 Used6 Left18

35. Tro's Introductory Chemistry, Chapter 10 35 Example NO 3 - 3)Complete Octets, outside-in 4)Re-Count Electrons N = 5 O 3 = 3∙6 = 18 (-) = 1 Total = 24 e - Electrons Start24 Used6 Left18 Electrons Start18 Used18 Left0

36. Tro's Introductory Chemistry, Chapter 10 36 Example NO 3 - 5)If central atom does not have octet, bring in electron pairs from outside atoms to share follow common bonding patterns if possible

37. Tro's Introductory Chemistry, Chapter 10 37 Exceptions to the Octet Rule H & Li, lose one electron to form cation Li now has electron configuration like He H can also share or gain one electron to have configuration like He Be shares 2 electrons to form two single bonds B shares 3 electrons to form three single bonds expanded octets for elements in Period 3 or below using empty valence d orbitals some molecules have odd numbers of electrons NO

38. Tro's Introductory Chemistry, Chapter 10 38 Resonance we can often draw more than one valid Lewis structure for a molecule or ion in other words, no one Lewis structure can adequately describe the actual structure of the molecule the actual molecule will have some characteristics of all the valid Lewis structures we can draw

39. Tro's Introductory Chemistry, Chapter 10 39 Resonance Lewis structures often do not accurately represent the electron distribution in a molecule Lewis structures imply that O 3 has a single (147 pm) and double (121 pm) bond, but actual bond length is between, (128 pm) Real molecule is a hybrid of all possible Lewis structures Resonance stabilizes the molecule maximum stabilization comes when resonance forms contribute equally to the hybrid

40. Tro's Introductory Chemistry, Chapter 10 40 Drawing Resonance Structures 1.draw first Lewis structure that maximizes octets 2.move electron pairs from outside atoms to share with central atoms 3.if central atom 2 nd row, only move in electrons if you can move out electron pairs from multiple bond

41. Tro's Introductory Chemistry, Chapter 10 41 Molecular Geometry Molecules are 3-dimensional objects We often describe the shape of a molecule with terms that relate to geometric figures These geometric figures have characteristic “corners” that indicate the positions of the surrounding atoms with the central atom in the center of the figure The geometric figures also have characteristic angles that we call bond angles

42. Tro's Introductory Chemistry, Chapter 10 42 Some Geometric Figures Linear 2 atoms on opposite sides of central atom 180° bond angles Trigonal Planar 3 atoms form a triangle around the central atom Planar 120° bond angles Tetrahedral 4 surrounding atoms form a tetrahedron around the central atom 109.5° bond angles 180° 120° 109.5°

43. Tro's Introductory Chemistry, Chapter 10 43 Predicting Molecular Geometry VSEPR Theory Valence Shell Electron Pair Repulsion The shape around the central atom(s) can be predicted by assuming that the areas of electrons on the central atom will try to get as far from each other as possible areas of negative charge will repel each other

44. Tro's Introductory Chemistry, Chapter 10 44 Areas of Electrons Each Bond counts as 1 area of electrons single, double or triple all count as 1 area Each Lone Pair counts as 1 area of electrons Even though lone pairs are not attached to other atoms, they do “occupy space” around the central atom Lone pairs take up slightly more space than bonding pairs Effects bond angles

45. Tro's Introductory Chemistry, Chapter 10 45 Linear Shapes Linear 2 areas of electrons around the central atom, both bonding  Or two atom molecule as trivial case 180° Bond Angles

46. Tro's Introductory Chemistry, Chapter 10 46 Trigonal Shapes Trigonal 3 areas of electrons around the central atom 120° bond angles All Bonding = trigonal planar 2 Bonding + 1 Lone Pair = bent

47. Tro's Introductory Chemistry, Chapter 10 47 Tetrahedral Shapes Tetrahedral 4 areas of electrons around the central atom 109.5° bond angles All Bonding = tetrahedral 3 Bonding + 1 Lone Pair = trigonal pyramid 2 Bonding + 2 Lone Pair = bent

48. Tro's Introductory Chemistry, Chapter 10 48 Tetrahedral Derivatives

49. Tro's Introductory Chemistry, Chapter 10 49 Molecular Geometry: Linear Electron Groups Around Central Atom = 2 Bonding Groups = 2 Lone Pairs = 0 Electron Geometry = Linear Angle between Electron Groups = 180°

50. 50 Molecular Geometry: Trigonal Planar Electron Groups Around Central Atom = 3 Bonding Groups = 3 Lone Pairs = 0 Electron Geometry = Trigonal Planar Angle between Electron Groups = 120°

51. Tro's Introductory Chemistry, Chapter 10 51 Molecular Geometry: Bent Electron Groups Around Central Atom = 3 Bonding Groups = 2 Lone Pairs = 1 Electron Geometry = Trigonal Planar Angle between Electron Groups = 120°

52. 52 Molecular Geometry: Tetrahedral Electron Groups Around Central Atom = 4 Bonding Groups = 4 Lone Pairs = 0 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5°

53. 53 Molecular Geometry: Trigonal Pyramid Electron Groups Around Central Atom = 4 Bonding Groups = 3 Lone Pairs = 1 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5°

54. Tro's Introductory Chemistry, Chapter 10 54 Molecular Geometry: Bent Electron Groups Around Central Atom = 4 Bonding Groups = 2 Lone Pairs = 2 Electron Geometry = Tetrahedral Angle between Electron Groups = 109.5°

55. Tro's Introductory Chemistry, Chapter 10 55 Bond Polarity bonding between unlike atoms results in unequal sharing of the electrons one atom pulls the electrons in the bond closer to its side one end of the bond has larger electron density than the other the result is bond polarity the end with the larger electron density gets a partial negative charge and the end that is electron deficient gets a partial positive charge H Cl 

56. Tro's Introductory Chemistry, Chapter 10 56 Electronegativity measure of the pull an atom has on bonding electrons increases across period (left to right) decreases down group (top to bottom) larger difference in electronegativity, more polar the bond negative end toward more electronegative atom  + H — F  -

57. Tro's Introductory Chemistry, Chapter 10 57 Electronegativity

58. Tro's Introductory Chemistry, Chapter 10 58 Electronegativity

59. 59 Electronegativity & Bond Polarity If difference in electronegativity between bonded atoms is 0, the bond is pure covalent equal sharing If difference in electronegativity between bonded atoms is 0.1 to 0.3, the bond is nonpolar covalent If difference in electronegativity between bonded atoms 0.4 to 1.9, the bond is polar covalent If difference in electronegativity between bonded atoms larger than or equal to 2.0, the bond is ionic

60. Tro's Introductory Chemistry, Chapter 10 60 Bond Polarity 00.42.0 4.0 Electronegativity Difference covalentionic polar non polar 3.0-3.0 = 0.0 4.0-2.1 = 1.9 3.0-0.9 = 2.1

61. Tro's Introductory Chemistry, Chapter 10 61 Dipole Moments a dipole is a material with positively and negatively charged ends polar bonds or molecules have one end slightly positive,  + ; and the other slightly negative,  - not “full” charges, come from nonsymmetrical electron distribution Dipole Moment, , is a measure of the size of the polarity measured in Debyes, D

62. Tro's Introductory Chemistry, Chapter 10 62 Polarity of Molecules in order for a molecule to be polar it must 1)have polar bonds  electronegativity difference - theory  bond dipole moments - measured 2)have an unsymmetrical shape  vector addition polarity effects the intermolecular forces of attraction

63. Tro's Introductory Chemistry, Chapter 10 63 polar bonds, but nonpolar molecule because pulls cancel polar bonds, and unsymmetrical shape causes molecule to be polar

64. Tro's Introductory Chemistry, Chapter 10 64 CH 2 Cl 2  = 2.0 D CCl 4  = 0.0 D

65. 65 Adding Dipole Moments

66. Example 10.11: Determining if a Molecule is Polar

67. Tro's Introductory Chemistry, Chapter 10 67 Example: Determine if NH 3 is polar.

68. Tro's Introductory Chemistry, Chapter 10 68 Example: Determine if NH 3 is polar. Write down the given quantity and its units. Given: NH 3

69. Tro's Introductory Chemistry, Chapter 10 69 Example: Determine if NH 3 is Polar. Write down the quantity to find and/or its units. Find: if Polar Information Given: NH 3

70. Tro's Introductory Chemistry, Chapter 10 70 Example: Determine if NH 3 is Polar. Design a Solution Map. Information Given: NH 3 Find:if Polar formula of compound Lewis Structure molecular polarity molecular shape bond polarity&

71. Tro's Introductory Chemistry, Chapter 10 71 Example: Determine if NH 3 is Polar. Apply the Solution Map. Draw the Lewis Structure  write skeletal structure Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity

72. Tro's Introductory Chemistry, Chapter 10 72 Example: Determine if NH 3 is Polar. Apply the Solution Map. Draw the Lewis Structure  count valence electrons Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity N = 5 H = 3 ∙ 1 totalNH 3 = 8

73. Tro's Introductory Chemistry, Chapter 10 73 Example: Determine if NH 3 is Polar. Apply the Solution Map. Draw the Lewis Structure  attach atoms Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity N = 5 H = 3 ∙ 1 totalNH 3 = 8 start8 e - use6 e - left2 e -

74. Tro's Introductory Chemistry, Chapter 10 74 Example: Determine if NH 3 is Polar. Apply the Solution Map. Draw the Lewis Structure  complete octets Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity N = 5 H = 3 ∙ 1 totalNH 3 = 8 start2 e - use2 e - left0 e - ∙∙

75. Tro's Introductory Chemistry, Chapter 10 75 Example: Determine if NH 3 is Polar. Apply the Solution Map. Determine if Bonds are Polar Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity ∙∙ Electronegativity N = 3.0 H = 2.1 3.0 – 2.1 = 0.9  polar covalent

76. Tro's Introductory Chemistry, Chapter 10 76 Example: Determine if NH 3 is Polar. Apply the Solution Map. Determine Shape of Molecule Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity ∙∙ 4 areas of electrons around N; 3 bonding areas 1 lone pair shape = trigonal pyramid

77. Tro's Introductory Chemistry, Chapter 10 77 Example: Determine if NH 3 is Polar. Apply the Solution Map. Determine Molecular Polarity Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity bonds = polar shape = trigonal pyramid molecule = polar

78. Tro's Introductory Chemistry, Chapter 10 78 Example: Determine if NH 3 is Polar. Check. Information Given: NH 3 Find:if Polar SM: formula → Lewis → Polarity & Shape → Molecule Polarity bonds = polar shape = trigonal pyramid molecule = polar N = 5 H = 3 ∙ 1 totalNH 3 = 8 ∙∙ bonding = 3 ∙ 2 e - lone pairs = 1 ∙ 2 e - totalNH 3 = 8 e - The Lewis structure is correct. The bonds are polar and the shape is unsymmetrical, so it should be polar.