A hexagonal close-packed layer in two dimensions is shown in figure 2. By identifying a suitable unit cell, calculate the packing fraction of this structure.

Chemistry: Principles and Practice
3rd Edition
ISBN:9780534420123
Author:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Publisher:Daniel L. Reger, Scott R. Goode, David W. Ball, Edward Mercer
Chapter11: Liquids And Solids
Section: Chapter Questions
Problem 11.87QE
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Figure 2: A hexagonal close-packed layer of atoms in two dimensions.
(b)
Figure 3: Conventional unit cells for: (a) the fcc structure; (b) the bcc structure.
(a)
a)
A hexagonal close-packed layer in two dimensions is shown in figure 2.
By identifying a suitable unit cell, calculate the packing fraction of this structure.
b) Two possible cubic crystal structures are shown in figure 3. Part (a) shows the fcc struc-
ture, in which atoms are touching along a face-diagonal. Part (b) shows the bcc structure,
in which atoms are touching along a body diagonal of the cube.
Calculate the packing fractions of each of these structures. Which one of them is close-
packed?
c) Copper (Cu) has an fcc structure, where the mass of a Cu atom is 63 in atomic mass units.
The density of Cu is 8.9x10³ kgm-³.
Tungsten (W) typically has a bcc structure, where the mass of a W atom is 184 in atomic
mass units. The density of W is 19.3x10³ kgm-³.
(i) Use the above data to find the radius of a Cu atom, and of a W atom.
(ii) Which atom has the larger radius, and why?
You may use the fact that 1 atomic mass unit is equivalent to 1.66 × 10-27 kg.
Transcribed Image Text:Figure 2: A hexagonal close-packed layer of atoms in two dimensions. (b) Figure 3: Conventional unit cells for: (a) the fcc structure; (b) the bcc structure. (a) a) A hexagonal close-packed layer in two dimensions is shown in figure 2. By identifying a suitable unit cell, calculate the packing fraction of this structure. b) Two possible cubic crystal structures are shown in figure 3. Part (a) shows the fcc struc- ture, in which atoms are touching along a face-diagonal. Part (b) shows the bcc structure, in which atoms are touching along a body diagonal of the cube. Calculate the packing fractions of each of these structures. Which one of them is close- packed? c) Copper (Cu) has an fcc structure, where the mass of a Cu atom is 63 in atomic mass units. The density of Cu is 8.9x10³ kgm-³. Tungsten (W) typically has a bcc structure, where the mass of a W atom is 184 in atomic mass units. The density of W is 19.3x10³ kgm-³. (i) Use the above data to find the radius of a Cu atom, and of a W atom. (ii) Which atom has the larger radius, and why? You may use the fact that 1 atomic mass unit is equivalent to 1.66 × 10-27 kg.
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