1. Bonds Forces that hold groups of atoms together and make them function as a unit. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1

2. Bond Energy 4 Is the energy required to break a bond. 4 It gives us information about the strength of a bonding interaction. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2

3. Bond Length The distance where the system energy is a minimum. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3

4. (a)The interaction of two hydrogen atoms. (b) Energy profile as a function of the distance between the nuclei of the atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4

5. Types of Chemical Bonds Ionic Covalent Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5

6. Ionic Bonds 4 Formed from electrostatic attractions of closely packed, oppositely charged ions. 4 Formed when an atom that easily loses electrons reacts with one that has a high electron affinity. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6

7. Ionic Bonds Follow Q 1 and Q 2 = numerical ion charges r = distance between ion centers (in nm) Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Coulomb’s Law

8. Calculate the Bond Energy for NaCl Where the distance between the ion centers is 0.276 nm (-8.37 x EE-19 J) Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8

9. Electronegativity The ability of an atom in a molecule to attract shared electrons to itself.  = (H  X) actual  (H  X) expected Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9

10. The Pauling electronegativity values. Electronegativity generally increases across a period and decreases down a group. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11

12. The three possible types of bonds (a) a covalent bond formed between identical atoms (b) a polar covalent bond, with both ionic and covalent components; and (c) an ionic bond with no electron sharing.

13. Polarity A molecule, such as HF, that has a center of positive charge and a center of negative charge is said to be polar, or to have a dipole moment. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13

14. The effect of an electric field on hydrogen fluoride molecules. When no electric field is present, the molecules are randomly oriented. When the field is turned on, the molecules tend to line up with their negative ends toward the positive pole and their positive ends toward the negative pole. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14

15. (a) The charge distribution in the water molecule. (b) The water molecule in an electric field. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15

16. The structure and charge distribution of the ammonia molecule. The polarity of the N—H bonds occurs because nitrogen has a greater electronegativity than hydrogen. (b) the ammonia molecule oriented in an electric field. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16

17. The carbon dioxide molecule. (b) The opposed bond polarities cancel out, and the carbon dioxide has no dipole moment. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17

18. Achieving Noble Gas Electron Configurations (NGEC) Two nonmetals react: They share electrons to achieve NGEC. A nonmetal and a representative group metal react (ionic compound): The valence orbitals of the metal are emptied to achieve NGEC. The valence electron configuration of the nonmetal achieves NGEC. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18

19. Isoelectronic Ions Ions containing the the same number of electrons (O 2 , F , Na +, Mg 2+, Al 3+ ) O 2  > F  > Na + > Mg 2+ > Al 3+ – largest smallest Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19

20. Sizes of ions related to positions of the elements on the periodic table. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20

21. Stop and do Problems 21-39 Blue on Page 403 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21

22. QUIZ Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22

23. Formation of an Ionic Solid 1.Sublimation of the solid metal – M(s)  M(g) [endothermic] 2.Ionization of the metal atoms – M(g)  M + (g) + e  [endothermic] 3.Dissociation of the nonmetal – 1 / 2 X 2 (g)  X(g) [endothermic] Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23

24. Formation of an Ionic Solid (continued) 4.Formation of X  ions in the gas phase: – X(g) + e   X  (g) [exothermic] 5.Formation of the solid MX – M + (g) + X  (g)  MX(s) [quite – exothermic] Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24

25. Figure 8.8: The energy changes involved in the formation of solid lithium fluoride from its elements.

26. Practice Work through Example on Page 362 Then work through Problem #41 Page 404 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26

27. Models Models are attempts to explain how nature operates on the microscopic level based on experiences in the macroscopic world. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27

28. Fundamental Properties of Models 4 A model does not equal reality. 4 Models are oversimplifications, and are therefore often wrong. 4 Models become more complicated as they age. 4 We must understand the underlying assumptions in a model so that we don’t misuse it. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28

29. Bond Energies Bond breaking requires energy (endothermic). Bond formation releases energy (exothermic).  H =  D( bonds broken )   D( bonds formed ) Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 energy requiredenergy released

30. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30

31. Calculate  H for the reaction of methane with chlorine to give Freon-12 Page 373 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31

32. Stop and do Problems 47-59 Blue on Page 404 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32

33. Localized Electron Model A molecule is composed of atoms that are bound together by sharing pairs of electrons using the atomic orbitals of the bound atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33

34. Localized Electron Model 1.Description of valence electron arrangement (Lewis structure). 2.Prediction of geometry (VSEPR model). 3.Description of atomic orbital types used to share electrons or hold long pairs. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34

35. Lewis Structure 4 Shows how valence electrons are arranged among atoms in a molecule. 4 Reflects central idea that stability of a compound relates to noble gas electron configuration. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35

36. Do Sample exercises on page 378 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36

37. Comments About the Octet Rule 4 2nd row elements C, N, O, F observe the octet rule. 4 2nd row elements B and Be often have fewer than 8 electrons around themselves - they are very reactive. 4 3rd row and heavier elements CAN exceed the octet rule using empty valence d orbitals. 4 When writing Lewis structures, satisfy octets first, then place electrons around elements having available d orbitals. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37

38. Now do Page 382 sample exercises Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38

39. Resonance Occurs when more than one valid Lewis structure can be written for a particular molecule. These are resonance structures. The actual structure is an average of the resonance structures. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39

40. Formal Charge The difference between the number of valence electrons (VE) on the free atom and the number assigned to the atom in the molecule. We need: 1.# VE on free neutral atom 2.# VE “belonging” to the atom in the – molecule Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40

41. Formal Charge Not as good Better Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41

42. VSEPR Model The structure around a given atom is determined principally by minimizing electron pair repulsions. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42

43. Predicting a VSEPR Structure 1.Draw Lewis structure. 2.Put pairs as far apart as possible. 3.Determine positions of atoms from the way electron pairs are shared. 4.Determine the name of molecular structure from positions of the atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43

44. Figure 8.14: The molecular structure of methane. The tetrahedral arrangement of electron pairs produces a tetrahedral arrangement of hydrogen atoms.

45. Figure 8.15:(a) The tetrahedral arrangement of electron pairs around the nitrogen atom in the ammonia molecule. (b) Three of the electron pairs around nitrogen are shared with hydrogen atoms as shown and one is a lone pair. Although the arrangement of electron pairs is tetrahedral, as in the methane molecule, the hydrogen atoms in the ammonia molecule occupy only three corners of the tetrahedron. A lone pair occupies the fourth corner. (c) Note that molecular geometry is trigonal pyramidal, not tetrahedral. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45

46. Figure 8.16: (a) The tetrahedral arrangement of the four electron pairs around oxygen in the water molecule. (b) Two of the electron pairs are shared between oxygen and the hydrogen atoms and two are lone pairs. (c) The V-shaped molecular structure of the water molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46

47. Figure 8.17: The bond angles in the CH 4, NH 3, and H 2 O molecules. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47

48. Figure 8.18: (a) In a bonding pair of electrons, the electrons are shared by two nuclei. (b) In a lone pair, both electrons must be close to a single nucleus and tend to take up more of the space around that atom.

49. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49

50. Figure 8.19: Possible electron-pair arrangements for XeF 4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50

51. Figure 8.20: Three possible arrangements of the electron pairs in the I 3 - ion. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51

52. Do problems #61-93 Blue on Page 405 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52