AP Chemistry Chapter 12 Outline


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AP Chemistry Chapter 12 Outline

  1. 1. Chapter 12 Modern Materials John D. Bookstaver St. Charles Community College Cottleville, MO Chemistry, The Central Science , 11th edition Theodore L. Brown, H. Eugene LeMay, Jr., and Bruce E. Bursten
  2. 2. Types of Materials <ul><li>Recall that atomic orbitals mix to give rise to molecular orbitals. </li></ul>
  3. 3. Types of Materials <ul><li>In such compounds, the energy gap between molecular orbitals essentially disappears, and continuous bands of energy states result. </li></ul>
  4. 4. Types of Materials <ul><li>Rather than having molecular orbitals separated by an energy gap, these substances have energy bands. </li></ul>
  5. 5. Types of Materials <ul><li>The gap between bands determines whether a substance is a metal , a semiconductor , or an insulator . </li></ul>
  6. 6. Types of Materials
  7. 7. Metals <ul><li>Valence electrons are in a partially-filled band. </li></ul>
  8. 8. Metals <ul><li>There is virtually no energy needed for an electron to go from the lower, occupied part of the band to the higher, unoccupied part. </li></ul><ul><li>This is how a metal conducts electricity. </li></ul>
  9. 9. Semiconductors <ul><li>Semiconductors have a gap between the valence band and conduction band of ~50-300 kJ/mol. </li></ul>
  10. 10. Semiconductors <ul><li>Among elements, only silicon, germanium and graphite (carbon), all of which have 4 valence electrons, are semiconductors. </li></ul><ul><li>Inorganic semiconductors (like GaAs) tend to have an average of 4 valence electrons (3 for Ga, 5 for As). </li></ul>
  11. 11. Doping <ul><li>By introducing very small amounts of impurities that have more (n-Type) or fewer (p-Type) valence electrons, one can increase the conductivity of a semiconductor. </li></ul>
  12. 12. Insulators <ul><li>The energy band gap in insulating materials is generally greater than ~350 kJ/mol. </li></ul><ul><li>They are not conductive. </li></ul>
  13. 13. Ceramics <ul><li>These are inorganic solids, usually hard and brittle. </li></ul><ul><li>They are highly resistant to heat, corrosion and wear. </li></ul><ul><ul><li>Ceramics do not deform under stress. </li></ul></ul><ul><ul><li>They are much less dense than metals, and so are used in place of metals in many high-temperature applications. </li></ul></ul>
  14. 14. Superconductors <ul><li>At very low temperatures, some substances lose virtually all resistance to the flow of electrons. </li></ul>
  15. 15. Superconductors <ul><li>Much research has been done recently into the development of high-temperature superconductors. </li></ul>
  16. 16. Superconductors <ul><li>The development of higher and higher temperature superconductors will have a tremendous impact on modern culture. </li></ul>
  17. 17. Polymers <ul><li>Polymers are molecules of high molecular mass made by sequentially bonding repeating units called monomers . </li></ul>
  18. 18. Some Common Polymers
  19. 19. Addition Polymers <ul><li>Addition polymers are made by coupling the monomers by converting  -bonds within each monomer to  -bonds between monomers. </li></ul>Ethylene Polyethylene
  20. 20. Condensation Polymers <ul><li>Condensation polymers are made by joining two subunits through a reaction in which a smaller molecule (often water) is also formed as a by-product. </li></ul><ul><li>These are also called copolymers . </li></ul>
  21. 21. Synthesis of Nylon <ul><li>Nylon is one example of a condensation polymer. </li></ul>
  22. 22. Properties of Polymers <ul><li>Interactions between chains of a polymer lend elements of order to the structure of polymers. </li></ul>
  23. 23. Properties of Polymers <ul><li>Stretching the polymer chains as they form can increase the amount of order, leading to a degree of crystallinity of the polymer. </li></ul>
  24. 24. Properties of Polymers <ul><li>Such differences in crystallinity can lead to polymers of the same substance that have very different physical properties. </li></ul>
  25. 25. Cross-Linking <ul><li>Chemically bonding chains of polymers to each other can stiffen and strengthen the substance. </li></ul>
  26. 26. Cross-Linking <ul><li>Naturally-occurring rubber is too soft and pliable for many applications. </li></ul>
  27. 27. Cross-Linking <ul><li>In vulcanization , chains are cross-linked by short chains of sulfur atoms, making the rubber stronger and less susceptible to degradation. </li></ul>
  28. 28. Ceramics <ul><li>Ceramics are made from a suspension of metal hydroxides (called a sol ). </li></ul>
  29. 29. Ceramics <ul><li>These can undergo condensation to form a gelatinous solid ( gel ), that is heated to form a metal oxide, like the SiO 2 shown here. </li></ul>
  30. 30. Biomaterials <ul><li>Materials used in the body must </li></ul><ul><ul><li>be biocompatible, </li></ul></ul><ul><ul><li>have certain physical requirements, and </li></ul></ul><ul><ul><li>have certain chemical requirements. </li></ul></ul>
  31. 31. Biomaterials <ul><li>Biocompatibility </li></ul><ul><ul><li>The materials used cannot cause inflammatory responses. </li></ul></ul>
  32. 32. Biomaterials <ul><li>Physical Requirements </li></ul><ul><ul><li>The properties of the material must mimic the properties of the “real” body part (i.e., flexibility, hardness, etc.). </li></ul></ul>
  33. 33. Biomaterials <ul><li>Chemical Requirements </li></ul><ul><ul><li>It cannot contain even small amounts of hazardous impurities. </li></ul></ul><ul><ul><li>Also it must not degrade into harmful substances over a long period of time in the body. </li></ul></ul>
  34. 34. Biomaterials <ul><li>These substances are used to make: </li></ul><ul><ul><li>Heart valves </li></ul></ul>
  35. 35. Biomaterials <ul><li>These substances are used to make: </li></ul><ul><ul><li>Heart valves </li></ul></ul><ul><ul><li>Vascular grafts </li></ul></ul>
  36. 36. Biomaterials <ul><li>These substances are used to make: </li></ul><ul><ul><li>Heart valves </li></ul></ul><ul><ul><li>Vascular grafts </li></ul></ul><ul><ul><li>Artificial skin grafts </li></ul></ul>
  37. 37. Electronics <ul><li>Silicon is very abundant, and is a natural semiconductor. </li></ul><ul><li>This makes it a perfect substrate for transistors, integrated circuits, and chips. </li></ul>
  38. 38. Electronics <ul><li>In 2000, Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa won a Nobel Prize for the discovery of “organic semiconductors” like the polyacetylene below. </li></ul>
  39. 39. Electronics <ul><li>Noncrystalline silicon panels can convert visible light into electrical energy. </li></ul>
  40. 40. Liquid Crystals <ul><li>Some substances do not go directly from the solid state to the liquid state. </li></ul><ul><li>In this intermediate state, liquid crystals have some traits of solids and some of liquids. </li></ul>
  41. 41. Liquid Crystals <ul><li>Unlike liquids, molecules in liquid crystals have some degree of order. </li></ul>
  42. 42. Liquid Crystals <ul><li>In nematic liquid crystals , molecules are only ordered in one dimension, along the long axis. </li></ul>
  43. 43. Liquid Crystals <ul><li>In smectic liquid crystals , molecules are ordered in two dimensions, along the long axis and in layers. </li></ul>
  44. 44. Liquid Crystals <ul><li>In cholesteryl liquid crystals , nematic-like crystals are layered at angles to each other. </li></ul>
  45. 45. Liquid Crystals <ul><li>These crystals can exhibit color changes with changes in temperature. </li></ul>
  46. 46. Light-Emitting Diodes <ul><li>In another type of semiconductor, light can be caused to be emitted (LEDs). </li></ul>
  47. 47. Nanoparticles <ul><li>Different sized particles of a semiconductor (like Cd 3 P 2 ) can emit different wavelengths of light depending on the size of the energy gap between bands. </li></ul>
  48. 48. Nanoparticles <ul><li>Finely divided metals can have quite different properties than larger samples of metals. </li></ul>
  49. 49. Carbon Nanotubes <ul><li>Carbon nanotubes can be made with metallic or semiconducting properties without doping. </li></ul>