Chapter 4: Exploring Materials

1. Chapter 4: Exploring Materials Section 1 “Polymers and Composites”

2. Objectives . . . • After completing the lesson, students will be able to . . . • Explain the composition of a polymer and give several examples of polymers; • Describe a composite material and state why composites are useful.

3. Carbon’s Strings, Rings, and Other Things • Carbon is present in more than two million known compounds, and more are being discovered or invented every day. • Carbon’s unique ability to form so many compounds comes from two properties. • They can form covalent bonds • They can also bond to each other in chains and ring-shaped groups. These structures form the “backbones” to which other atoms attach.

4. Carbon Compounds Form Polymers • Molecules of some organic compounds can hook together, forming larger molecules. • Polymers—a large, complex molecule built from smaller molecules joined together. • Monomers—the smaller molecules from which polymers are built. • Polymers form when chemical bonds link large numbers of monomers in a repeating pattern.

5. Carbon Compounds Form Polymers • Many polymers consist of a single kind of monomer that repeats over and over again. • In other cases, two or three monomers may join in an alternating pattern. • Sometimes links between monomer chains occur, forming large webs or netlike molecules. • The chemical properties of a polymer depend on the monomers from which it is made.

6. Natural Polymers • Plants, animals, and other living things produce the polymers they need from nutrients and other materials in the environment.

7. Plant Polymers • Cellulose—a flexible but strong natural polymer that gives shape to plant cells. • Cellulose is made in plants when sugar molecules (made earlier from carbon dioxide and water) are joined into long strands. • The cellulose then forms cell structures.

8. Animal Polymers • You can wear polymers made by animals. Silk is made from the fibers of silkworm cocoons. Wool is made from sheep’s fur. These polymers can be woven into thread and cloth. • Your own body makes polymers. Proteins are polymers. • Proteins are assembled from combinations of smaller molecules called amino acids. The properties of a protein depend on which amino acids are used and in what order.

9. Synthetic Polymers • Recall that a synthesis reaction occurs when elements or simple compounds combine to form complex compounds. • The starting materials for polymers come from coal or oil. • Plastics—synthetic polymers that can be molded or shaped.

10. Synthetic Polymers • Examples: Carpets, clothing, glue, and chewing gum. • Many products require (page 115) materials that are flexible, yet strong. Others must be hard or lightweight. • Synthetic polymers are often used in place of natural materials that are too expensive or wear out too quickly. • Other synthetic polymers have uses for which there is no suitable natural material.

11. Composites • Composites—combine two or more substances as a new material with different properties. • By combining the useful properties of two or more substances in a composite, chemists can make a new material that works better than either one alone.

12. Natural and Synthetic Composites • Read Pages 117-118

13. Too Many Polymers? • It is difficult to look around without seeing something made of synthetic polymers. • They have replaced many natural materials. • Polymers are inexpensive to make • They are strong • They last a long time

14. Too Many Polymers? • Synthetic polymers have caused some problems too . . . • Because they are inexpensive, it is easier to throw them away and make new ones than reusing them • Increase in volume of trash • They don’t break down into simpler materials in the environment • How do we solve this problem? • Recycle!!!!

15. Chapter 4: Exploring Materials Section 2 “Metals and Alloys”

16. Objectives . . . • After completing the lesson, students will be able to . . . • Identify properties of alloys that make them useful; • Cite examples of common alloys and list uses for those alloys

17. Properties of Metals • It’s hard and usually shiny • At room temperature all metallic elements (except mercury) are solids • They conduct electricity • They are ductile • They are malleable

18. Properties of Alloys • Alloys are used much more than pure metals because they are generally stronger and less likely to react with air or water. • Alloys (such as stainless steel) do not react as easily with air and water.

19. Making Alloys • Many alloys are made by melting metals and mixing them together in carefully measured amounts. • Ion implantation—involves firing a beam of ions at a metal. A thin layer of alloy then forms on the metal’s surface.

20. Using Alloys • Alloys are used for its strength, hardness, and resistance to corrosion

21. Steels • Carbon steel • Tools, knives, machinery, and appliances • Steels with less than 0.8% carbon are more ductile and malleable. Examples include nails, cables, and chains.

22. Other Alloys • Examples: Bronze, brass, and solder. • These materials are used to make items ranging from plumbing materials and sprinkler systems to tableware and doorknobs. • Dentistry: Alloys used in fillings • Mercury • Silver • Gold

23. Chapter 4: Exploring Materials Section 3 “Ceramics and Glass”

24. Objectives . . . • After completing the lesson, students will be able to . . . • Identify properties of ceramics and tell how ceramics are used; • Describe the composition of glass and tell how glass can be changed to serve many different purposes

25. Making Ceramics • Ceramics—hard, crystalline solids made by heating clay and other mineral materials to high temperatures. • When a clay object is heated, much of the water present on its surface evaporates, and the particles of clay sticks together.

26. Properties and Uses of Ceramics • Ceramics are brittle and can shatter when struck. • Ceramics resist moisture, do not conduct electricity, and can withstand temperatures higher than molten metals. • Roofing tiles, bricks, and sewer pipes all are long-standing uses of ceramics.

27. Making Glass • Glass—a clear, solid material with no crystal structure • Forms when sand is mixed with limestone is melted into a thick, hot liquid, followed a quick cooling process. • Different materials may be added to glass to make it useful for particular purposes.

28. Communication Through Glass • Optical fiber—a threadlike piece of glass (or plastic) that can be used for transmitting light. • Light shining into one end of the fiber travels through the glass to the other end. • When you speak into a telephone, the signal created by your voice is converted to light signals that travel through the glass fiber. At the other end, the light may be converted into electronic signals that can then be converted to sound.

29. Communication Through Glass • A pair of optical fibers, each the thickness of a human hair, can carry 625,000 phone calls at one time. • Because optical fibers are so efficient, they are being used to replace most copper telephone and cable television lines. • Another benefit of glass fiber is its stability. Since the glass does not corrode as metals do, the lines are easier to maintain.

30. Chapter 4: Exploring Materials Section 4 “Radioactive Elements”

31. Objectives . . . • After completing the lesson, students will be able to . . . • Describe radioactive decay and the emissions produced during decay; • Explain why half-life is a useful property of radioactive isotopes; • Identify uses and dangers of radioactive isotopes; • Explain isotopes in terms of mass numbers

32. Nuclear Reactions—reactions involving the particles in the nucleus of an atom. Isotopes—Atoms with the same number of protons and different numbers of neutrons. Mass number—the sum of the protons and neutrons in the nucleus of an atom. Radioactive Elements

33. Radioactive Decay • Radioactive decay—the atomic nuclei of unstable isotopes release fast-moving particles and energy. • Nuclear Radiation—Particles and energy produced during radioactive decay. • There are three types of radioactive decay • Radioactive decay can produce alpha particles, beta particles, and gamma rays.

34. Radioactive Decay • Alpha particle—consists of two protons and two neutrons. • Beta particle—an electron given off by a nucleus during radioactive decay. • Gamma radiation—high energy waves, similar to X-rays.

35. Half-life • Half-life—the length of time needed for half of the atoms of a sample to decay. • Fossils are the traces or remains of living things that have been preserved • The half-lives of certain radioactive isotopes are useful in determining the ages of rocks and fossils. • Radioactive dating—The process of determining the age of an object using the half-life of one or more radioactive isotopes

36. Using Radioactive Isotopes • Radioactive isotopes are useful both as sources of radiation and as tracers. • Tracers—radioactive isotopes that can be followed through the steps of a chemical reaction or industrial process. • Radiation Therapy—Radioactive elements are used to destroy unhealthy cells.

37. Read on your own (page 137-139) • “Tracers in Chemical Reactions” • “Uses in Industry” • “Uses in Medicine” • “Nuclear Power” • “Safe Use of Radioactive Materials”