30 Questions
Which of the following materials typically exhibit long-range periodic packing of atoms?
Most metals and many ceramics
Which of the following is an example of a single crystal material?
Diamond abrasives
What is the primary difference in atomic packing between crystalline and amorphous materials?
Amorphous materials have random packing, while crystalline materials have ordered packing.
Which of the following statements about neighbor bond lengths and energies in crystalline and amorphous materials is correct?
Crystalline materials have shorter bond lengths and higher bond energies.
Which statement is true about the energy and packing of crystalline materials compared to amorphous materials?
Crystalline materials have lower energy and higher density.
What is the primary advantage of single crystal materials like turbine blades?
Higher strength and durability
What is the primary characteristic of a polycrystalline material?
It contains many individual grains or small crystals
Which of the following statements about the unit cell in a crystal lattice is NOT true?
Opposite faces (or edges) are always parallel
In the hard-sphere model for crystal structures, what does it mean for atoms to "touch" their nearest neighbors?
The atoms are at their minimum possible distance apart
What is the coordination number of an atom in a crystal structure?
The number of nearest (or touching) neighboring atoms
Which of the following is NOT one of the seven crystal systems?
Hexagonal
In the context of crystal structures, what is the purpose of the hard-sphere model?
To provide a simplified representation of atom arrangements in crystals
What is the coordination number for a simple cubic (SC) structure?
6
What is the atomic packing factor (APF) for a simple cubic structure?
0.52
What is the number of atoms per unit cell in a simple cubic structure?
1
In which direction do the atoms touch each other in a body-centered cubic (BCC) structure?
Along the cube diagonals
Which crystal system has a 6-fold axis of rotation?
Hexagonal (Trigonal)
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?
$a = 2R$
What is the relationship between the densities of different material classes?
The density of metals is greater than the density of ceramics, which is greater than the density of polymers.
Why do metals typically have higher densities than ceramics and polymers?
Metals have close-packed structures and metallic bonding, leading to higher densities.
What is the main reason ceramics typically have lower densities than metals?
Ceramics have less dense packing and often contain lighter elements.
What is the relationship between the packing density and the density of different material classes?
Materials with higher packing density have higher densities, and vice versa.
Why do polymers typically have the lowest densities among the material classes?
Polymers have low packing density and often contain lighter elements like C, H, and O.
Which of the following statements about the densities of different material classes is NOT supported by the information provided in the text?
The density of a material is determined solely by its atomic composition and packing.
What is the coordination number (CN) for a body-centered cubic (BCC) structure?
8
What is the atomic packing factor (APF) for a face-centered cubic (FCC) structure?
0.74
How many atoms are present on average in a unit cell of a body-centered cubic (BCC) structure?
2
What is the relationship between the atomic radius (R) and the lattice parameter (a) for a body-centered cubic (BCC) structure?
$R = a/\sqrt{3}$
How many atoms are present on average in a unit cell of a face-centered cubic (FCC) structure?
4
What is the relationship between the atomic radius (R) and the lattice parameter (a) for a face-centered cubic (FCC) structure?
$R = a/\sqrt{2}$
Learn about how atoms assemble into solid structures and the dependence of material properties on crystal structures. Understand the differences between crystalline and noncrystalline (amorphous) materials, such as periodic 3D arrays with long-range translational symmetry in most metals, ceramics, and some polymers.
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