Chapter 4: Exploring Materials

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Chapter 4 Exploring Materials

• Section 1
• Polymers and Composites

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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.

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Carbons Strings, Rings, and Other Things

• Carbon is present in more than two million known
  compounds, and more are being discovered or
  invented every day.
• Carbons 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.

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Carbon Compounds Form Polymers

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

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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.

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Natural Polymers

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

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Plant Polymers

• Cellulosea 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.

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Animal Polymers

• You can wear polymers made by animals. Silk is
  made from the fibers of silkworm cocoons. Wool
  is made from sheeps 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.

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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.
• Plasticssynthetic polymers that can be molded or
  shaped.

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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.

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Composites

• Compositescombine 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.

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Natural and Synthetic Composites

• Read Pages 117-118

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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

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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 dont break down into simpler materials in
  the environment
• How do we solve this problem?
• Recycle!!!!

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Chapter 4 Exploring Materials

• Section 2
• Metals and Alloys

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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

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Properties of Metals

• Its hard and usually shiny
• At room temperature all metallic elements (except
  mercury) are solids
• They conduct electricity
• They are ductile
• They are malleable

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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.

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Making Alloys

• Many alloys are made by melting metals and mixing
  them together in carefully measured amounts.
• Ion implantationinvolves firing a beam of ions
  at a metal. A thin layer of alloy then forms on
  the metals surface.

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Using Alloys

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

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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.

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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

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Chapter 4 Exploring Materials

• Section 3
• Ceramics and Glass

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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

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Making Ceramics

• Ceramicshard, 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.

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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.

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Making Glass

• Glassa 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.

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Communication Through Glass

• Optical fibera 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.

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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.

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Chapter 4 Exploring Materials

• Section 4
• Radioactive Elements

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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

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Radioactive Elements

• Nuclear Reactionsreactions involving the
  particles in the nucleus of an atom.

• IsotopesAtoms with the same number of protons
  and different numbers of neutrons.
• Mass numberthe sum of the protons and neutrons
  in the nucleus of an atom.

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Radioactive Decay

• Radioactive decaythe atomic nuclei of unstable
  isotopes release fast-moving particles and
  energy.
• Nuclear RadiationParticles and energy produced
  during radioactive decay.
• There are three types of radioactive decay
• Radioactive decay can produce alpha particles,
  beta particles, and gamma rays.

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Radioactive Decay

• Alpha particleconsists of two protons and two
  neutrons.
• Beta particlean electron given off by a nucleus
  during radioactive decay.
• Gamma radiationhigh energy waves, similar to
  X-rays.

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Half-life

• Half-lifethe 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 datingThe process of determining the
  age of an object using the half-life of one or
  more radioactive isotopes

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Using Radioactive Isotopes

• Radioactive isotopes are useful both as sources
  of radiation and as tracers.
• Tracersradioactive isotopes that can be followed
  through the steps of a chemical reaction or
  industrial process.
• Radiation TherapyRadioactive elements are used
  to destroy unhealthy cells.

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Read on your own (page 137-139)

• Tracers in Chemical Reactions
• Uses in Industry
• Uses in Medicine
• Nuclear Power
• Safe Use of Radioactive Materials