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NCSUGenChem102LabV1 6.POST.03.
Many metals pack in cubic unit cells. The density of a metal and length of the unit cell can be used to determine the
type for packing. For example,
iron
has a density of
7.87
g/cm
3
and a unit cell side length
a
of
2.87
Å
. (1
1.
10
-8
cm.)
(a) How many
iron
atoms are in exactly 1 cm
3
Å
=
?
(b) How many unit cells are in exactly 1 cm
3
?
(c) How many
iron
atoms are there per unit cell?
(d) The atoms/unit cell suggests that
iron
packs as a
body-centered
body-centered
unit cell.
Knowledge of the type of packing and side length
a
of the unit cell will allow calculation of the atomic radius, using
one of the equations below. You may need to draw the unit cell to determine which formula to use to calculate the
atomic radius.
(e) What is the atomic radius of
iron
?
1.24
1.24
Å
Additional Materials
Solid State Modeling
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NCSUGenChem102LabV1 6.POST.04.
Green checks
and
red X's
are not displayed for this question.
Use what you learned in lab about atoms in cubic structures to answer the following questions about a solid whose
crystal structure was found to have atoms "A" in
corner and center sites
and "B" in the
face sites
of a cubic unit cell.
How many "A"s are there in a unit cell?
2
2
"A"(s)
How many "B"s are there in a unit cell?
3
3
"B"(s)
