1. LECTURE 7.2

2. LECTURE OUTLINE Weekly Reading Weekly Reading Lesson 07 Prototype Quiz: Feedback Lesson 07 Prototype Quiz: Feedback

3. CHAPTER XXII: AMORPHOUS SOLIDS Chapter 22 reintroduces a class of materials called “amorphous,” or without form. Amorphous materials are non-crystalline—the atoms/monomers/molecules are not arranged in a periodic fashion. The concepts of short- range order and long-range order are introduced as an aid in distinguishing between a silicate crystal and a silicate glass. Chapter 22 reintroduces a class of materials called “amorphous,” or without form. Amorphous materials are non-crystalline—the atoms/monomers/molecules are not arranged in a periodic fashion. The concepts of short- range order and long-range order are introduced as an aid in distinguishing between a silicate crystal and a silicate glass.

4. CHAPTER XXIII: SYMMETRY IN ART, NATURE, AND SCIENCE Mankind has been fascinated by symmetry since the dawn of time. The relationship between left and right- handedness, the distribution of petals on a flower head, and many Paleolithic cave paintings deal with concepts of symmetry. In Chapter 23, the reader is introduced to the major classes of symmetry, yet the goal is to describe in uncomplicated terms the symmetries that are displayed by crystalline solids. The “form,” which has been described in numerous earlier chapters, is seen to be synonymous with the “lattice,” which is used to describe the translational symmetry of crystalline materials. Mankind has been fascinated by symmetry since the dawn of time. The relationship between left and right- handedness, the distribution of petals on a flower head, and many Paleolithic cave paintings deal with concepts of symmetry. In Chapter 23, the reader is introduced to the major classes of symmetry, yet the goal is to describe in uncomplicated terms the symmetries that are displayed by crystalline solids. The “form,” which has been described in numerous earlier chapters, is seen to be synonymous with the “lattice,” which is used to describe the translational symmetry of crystalline materials.

5. CHAPTER XXIV: THE MICROSTRUCTURE OF MATERIALS Chapter 24 is mostly a summary of previously presented “microstructures.” The term “microstructure” is used to describe level(s) of structure amenable to study using the light microscope (traditionally) and the electron microscope (more recently). Chapter 24 is mostly a summary of previously presented “microstructures.” The term “microstructure” is used to describe level(s) of structure amenable to study using the light microscope (traditionally) and the electron microscope (more recently). Two “case studies” of the microstructures of materials are presented: Two “case studies” of the microstructures of materials are presented: The microstructural studies of Rene-Antoine Ferchault de Reaumur. The microstructural studies of Rene-Antoine Ferchault de Reaumur. The microstructure of a naturally occurring composite: granite. The microstructure of a naturally occurring composite: granite.

6. PART D: EPILOGUE This book has it all: preambles, prologues, and even epilogues! This epilogue is important because it serves as an “executive summary” for the preceding thirteen chapters. It provides unifying themes by classifying solid materials by their bond types, relating the nature of the monomer to the material classification, and summarizing the various states of matter—a process that we first began in Chapter 13. The epilogue finishes with a discussion of the packing fraction” and “specific gravity” of materials, as they are affected by bond type. This latter discussion is somewhat convoluted but merits some thought and attention! This book has it all: preambles, prologues, and even epilogues! This epilogue is important because it serves as an “executive summary” for the preceding thirteen chapters. It provides unifying themes by classifying solid materials by their bond types, relating the nature of the monomer to the material classification, and summarizing the various states of matter—a process that we first began in Chapter 13. The epilogue finishes with a discussion of the packing fraction” and “specific gravity” of materials, as they are affected by bond type. This latter discussion is somewhat convoluted but merits some thought and attention!

7. PRACTICE QUIZ #7: FEEDBACK

9. Q2. The intermolecular bonding in solid bromine is_____. covalent ionic van der Waals hydrogen not applicable Reference to Figure 1 shows that bromine is in Group VII and is a non-metal. Bromine may only form one bonding pair, and Br forms a diatomic molecule. Within the molecule, the bonding (intramolecular) is covalent. Between the molecules, the bonding (intermolecular) is van der Waals.

11. Q5. The intermolecular bonding in iridium is ______. covalent ionic van der Waals hydrogen not applicable The answer is “not applicable.” The differentiation between intramolecular and intermolecular bonding only has meaning for covalently bonded molecular materials. Iridium is a metal!

13. Q7. Figure 2 (next slide) shows a cubic form that contains a silicon atom at the center of the cube and an oxygen atom at one of the corners. A silica tetrahedron could be completed by assigning ________. oxygen atoms to positions 1, 5, 7 silicon atoms to positions 1, 5, 7 oxygen atoms to positions 1, 7, 8 silicon atoms to positions 1, 7, 8 oxygen atoms to positions 1, 2, 4

14. Figure 2 Oxygen atoms to positions 1, 5, 7 (and see Figure 2). This creates the “two-up, two-down” bonding characteristic of a tetrahedron.

15. Q8. Figure 3 (next slide) plots the energy (as heat) in calories required to raise the temperature of a fixed mass of water from –50˚C to a temperature in excess of 100˚C. The energy required to raise the temperature of the solid water (ice) from – 50˚C to -5˚C is needed to ________. increase the vibrational energy associated with the intermolecular and intramolecular bonds within the ice-lattice break some of the hydrogen bonds between the water molecule break some of the covalent bonds between hydrogen and oxygen break all of the hydrogen bonds between the water molecules break all of the covalent bonds between hydrogen and oxygen

16. Increasing the temperature of crystalline ice from –50˚C to –5˚C results in no change in state, and the increase in thermal energy will be manifested in an increased vibrational energy of both the covalent and the hydrogen bonds. The breaking of hydrogen bonds will occur on melting and on vaporization, but will not occur during heating in the solid state. The breaking of the covalent bonds is much more difficult than the breaking of hydrogen bonds and will not occur during melting nor during vaporization. Very high temperatures will be required before the covalent bonds are disrupted.

17. Q12. Figure 5 (next slide) shows the “heat of fusion” for several “molecular liquids.” The heat of fusion is the heat required to convert a given mass of solid to a liquid. Water has a much higher heat of fusion than the other liquids because ___________. the molecules in water are hydrogen bonded to each other, whereas the other molecules are bonded only by van der Waals forces the organic molecules (carbon tetrachloride, acetone, benzene, and ethyl alcohol) are ionically bonded, whereas the intramolecular bonding in water is covalent The organic molecules form “glasses” on slow cooling the intermolecular bonding in water is covalent the intramolecular bonding in water is covalent

18. Figure 5 The intermolecular bonding in water is “hydrogen.” In the other liquids it is van der Waals only. Hence, it takes more energy to break the hydrogen bonds as opposed to the van der Waals bonds.

19. Q17. Bromine (Br) is in Group VII and forms two bonding pairs. True False False. Bromine is in Group VII and may only form a single bonding pair.

21. Q19. Arsenic is a __________. noble gas semiconductor metal non-metal polymer Arsenic is in Group V (Figure 14.17) and is a non-metal.

23. Q22. Vulcanized rubber is a ________. thermoset crystalline thermoplastic amorphous thermoplastic Vulcanized rubber is cross-linked. It is a thermoset (Figure 20.8).

24. Q24. Polytetrafluoroethylene (PTFE) is a _____. metallically bonded solid ionically bonded solid covalently bonded network solid covalently bonded molecular solid macromolecule/polymer It is a macromolecule/polymer.