CHAPTER 2
Q1
How many grams are there in a one amu of a material?
A1
In order to determine the number of grams in one amu of material, appropriate manipulation of the
amu/atom, g/mol, and atom/mol relationships is all that is necessary, as
# g/amu =
1 mol
6.023 x 10
23
atoms
1 g/mol
1 amu/atom
= 1.66 x 10
24
g/amu
Q2
Show the electron configuration for Fe
3+
, Cu
+
, and S
2
A2
Fe
3+
 1s
2
2s
2
2p
6
3s
2
3p
6
3d
5
Cu
+
 1s
2
2s
2
2p
6
3s
2
3p
6
3d
10
S
2
 1s
2
2s
2
2p
6
3s
2
3p
6
Q3.
Why water expands on freezing?
A3.
The geometry of the H
2
O molecules, which are hydrogen bonded to one another, is more
restricted in the solid phase than for the liquid. This results in a more open molecular structure in
the solid, and a less dense solid phase.
CHAPTER 3
Q1
What is the difference between a crystal structure and a crystal system?
A1
A crystal structure is described by both the geometry of, and atomic arrangements within, the unit
cell, whereas a crystal system is described only in terms of the unit cell geometry.
For example,
facecentered cubic and bodycentered cubic are crystal structures that belong to the cubic
crystal system.
Q2
Show that the ideal
c
/
a
ratio for HCP is 1.633.
A2
A sketch of onethird of an HCP unit cell is shown below.
Consider the tetrahedron labeled as
JKLM
, which is reconstructed as
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The atom at point
M
is midway between the top and bottom faces of the unit cellthat is
MH
=
c
/
2.
And, since atoms at points
J
,
K
, and
M
, all touch one another,
JM
= JK
= 2R = a
where
R
is the atomic radius.
Furthermore, from triangle
JHM
,
(JM
)
2
= (
JH
)
2
+
(
MH
)
2
, or
a
2
= (JH
)
2
+
c
2
2
Now, we can determine the
JH
length by consideration of triangle
JKL
, which is an equilateral
triangle,
cos 30
°
=
a/ 2
JH
=
3
2
, and
JH
=
a
3
Substituting this value for
JH
in the above expression yields
a
2
=
a
3
2
+
c
2
2
=
a
2
3
+
c
2
4
and, solving for
c
/
a
c
a
=
8
3
= 1.633
Q3
Calculate the unit cell volume for Co which has an HCP crystal structure.
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 Spring '09
 FredLange
 Crystallography, Cubic crystal system, Crystal system, Atomic packing factor

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