Chapter 3: Structure of Crystalline Solids
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Questions and Answers

Which of the following materials typically exhibit long-range periodic packing of atoms?

  • Liquids and gases
  • All glasses and some polymers
  • Most metals and many ceramics (correct)
  • Noncrystalline solids and amorphous materials

    • Which of the following is an example of a single crystal material?

  • Window glass
  • Polyethylene plastic
  • Diamond abrasives (correct)
  • Concrete

    • What is the primary difference in atomic packing between crystalline and amorphous materials?

  • Crystalline materials have shorter bond lengths between neighbors.
  • Amorphous materials have stronger neighbor bond energies.
  • Crystalline materials have higher energy and lower density.
  • Amorphous materials have random packing, while crystalline materials have ordered packing. (correct)

    • Which of the following statements about neighbor bond lengths and energies in crystalline and amorphous materials is correct?

    <p>Crystalline materials have shorter bond lengths and higher bond energies.</p> Signup and view all the answers

    Which statement is true about the energy and packing of crystalline materials compared to amorphous materials?

    <p>Crystalline materials have lower energy and higher density.</p> Signup and view all the answers

    What is the primary advantage of single crystal materials like turbine blades?

    <p>Higher strength and durability</p> Signup and view all the answers

    What is the primary characteristic of a polycrystalline material?

    <p>It contains many individual grains or small crystals</p> Signup and view all the answers

    Which of the following statements about the unit cell in a crystal lattice is NOT true?

    <p>Opposite faces (or edges) are always parallel</p> Signup and view all the answers

    In the hard-sphere model for crystal structures, what does it mean for atoms to "touch" their nearest neighbors?

    <p>The atoms are at their minimum possible distance apart</p> Signup and view all the answers

    What is the coordination number of an atom in a crystal structure?

    <p>The number of nearest (or touching) neighboring atoms</p> Signup and view all the answers

    Which of the following is NOT one of the seven crystal systems?

    <p>Hexagonal</p> Signup and view all the answers

    In the context of crystal structures, what is the purpose of the hard-sphere model?

    <p>To provide a simplified representation of atom arrangements in crystals</p> Signup and view all the answers

    What is the coordination number for a simple cubic (SC) structure?

    <p>6</p> Signup and view all the answers

    What is the atomic packing factor (APF) for a simple cubic structure?

    <p>0.52</p> Signup and view all the answers

    What is the number of atoms per unit cell in a simple cubic structure?

    <p>1</p> Signup and view all the answers

    In which direction do the atoms touch each other in a body-centered cubic (BCC) structure?

    <p>Along the cube diagonals</p> Signup and view all the answers

    Which crystal system has a 6-fold axis of rotation?

    <p>Hexagonal (Trigonal)</p> Signup and view all the answers

    If the radius of an atom in a simple cubic structure is R, what is the edge length a of the unit cell in terms of R?

    <p>$a = 2R$</p> Signup and view all the answers

    What is the relationship between the densities of different material classes?

    <p>The density of metals is greater than the density of ceramics, which is greater than the density of polymers.</p> Signup and view all the answers

    Why do metals typically have higher densities than ceramics and polymers?

    <p>Metals have close-packed structures and metallic bonding, leading to higher densities.</p> Signup and view all the answers

    What is the main reason ceramics typically have lower densities than metals?

    <p>Ceramics have less dense packing and often contain lighter elements.</p> Signup and view all the answers

    What is the relationship between the packing density and the density of different material classes?

    <p>Materials with higher packing density have higher densities, and vice versa.</p> Signup and view all the answers

    Why do polymers typically have the lowest densities among the material classes?

    <p>Polymers have low packing density and often contain lighter elements like C, H, and O.</p> Signup and view all the answers

    Which of the following statements about the densities of different material classes is NOT supported by the information provided in the text?

    <p>The density of a material is determined solely by its atomic composition and packing.</p> Signup and view all the answers

    What is the coordination number (CN) for a body-centered cubic (BCC) structure?

    <p>8</p> Signup and view all the answers

    What is the atomic packing factor (APF) for a face-centered cubic (FCC) structure?

    <p>0.74</p> Signup and view all the answers

    How many atoms are present on average in a unit cell of a body-centered cubic (BCC) structure?

    <p>2</p> Signup and view all the answers

    What is the relationship between the atomic radius (R) and the lattice parameter (a) for a body-centered cubic (BCC) structure?

    <p>$R = a/\sqrt{3}$</p> Signup and view all the answers

    How many atoms are present on average in a unit cell of a face-centered cubic (FCC) structure?

    <p>4</p> Signup and view all the answers

    What is the relationship between the atomic radius (R) and the lattice parameter (a) for a face-centered cubic (FCC) structure?

    <p>$R = a/\sqrt{2}$</p> Signup and view all the answers

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