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Lecture 25
The Solid State
Tutorial
1) Sodium exists in a body centered cubic structure.
a. How many sodium atoms are contained within one unit cell?
1
8
atom × 8corners + 1atom = 2atoms
b. Sodium has a density of 0.97g/cm3. What is the volume of a single unit
cell of sodium?
2 atom Na×
V=
m
ρ
=
1 mol
22.99g
×
=7.635×10-23g
23
6.022×10 atoms 1 mol
7.635×10-23g
=7.9×10-23cm3
0.97 g/cm3
2) What factor makes metals good conductors of heat and electricity?
The electron sea model accounts for these properties of metals. The free movement of
electrons allows metals to conduct electricity. Electron movement also enables metals to
conduct heat rapidly. If you heat one end of metal bar, you will transfer heat to the
electrons in that area. These energized electrons will move to the other end of the bar
carrying the heat with them.
3) Which substance, KCl or SiO2, has the highest melting point? Justify your
answer using chemical principals.
KCl has ionic bonds. SiO2 is a network solid held together with covalent bonds.
Network solids are stronger than ionic compounds, thus, SiO2 will have a higher melting
temperature.
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