Liquids and Solids:
Chapter 13
Chem 101
Fall 2004
Chapter Outline
The Solid State
• Melting Point
• Heat Transfer Involving Solids
• Sublimation and the Vapor Pressure of Solids
• Phase Diagrams (P versus T)
• Amorphous Solids and Crystalline Solids
• Structures of Crystals
• Bonding in Solids
• Band Theory of Metals
Chem 101
Fall 2004
The Solid State
Normal Melting Point
• The normal melting point is the temperature at
which the solid melts (liquid and solid in
equilibrium) at exactly 1.00 atm of pressure.
• The melting point increases as the strength of the
intermolecular attractions increase.
Chem 101
Fall 2004
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The Solid State
• Which requires more energy?
→ NaCl
NaCl (s ) ←
( )
or
→
H 2 O (s ) ← H 2 O ( )
Chem 101
Fall 2004
Heat Transfer Involving Solids
Heat of Fusion
• Heat of fusion is the amount of heat required to
melt one gram of a solid at its melting point at
constant temperature.
• Heat of crystallization is the reverse of the heat of
fusion.
Chem 101
Fall 2004
Heat Transfer Involving Solids
fusion
+ 334 J



→ 1.00 g H O at 0o C
1.00 g H 2 O (s) at 0o C ←

2 ( )
-334 J
crystallization
Chem 101
Fall 2004
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Heat Transfer Involving Solids
Molar heat of fusion or ∆Hfusion
• The molar heat of fusion is the amount of heat
required to melt a mole of a substance at its
melting point.
• The molar heat of crystallization is the reverse of
molar heat of fusion
+6012 J


→ 1.00 mole H O at 0o C
1.00 mole H 2O (s) at 0o C 
←
2 ( )
-6012 J
Chem 101
Fall 2004
Heats of Transformation for Water
+40.7 kJ


→1.00 mol H O at 100.0o C
1.00 mol H 2 O ( } ) at 100.0o C 
←
2 (g)
- 40.7 kJ
+6012 J


→ 1.00 mole H O at 0 o C
1.00 mole H 2 O (s) at 0 o C 
←
2 (} )
- 6012 J
Chem 101
Fall 2004
Sublimation and the Vapor Pressure
of Solids
Sublimation
• In the sublimation process the solid transforms
directly to the vapor phase without passing
through the liquid phase.
• Solid CO2 or “dry” ice does this well.
sublimation



→
solid ←
 gas
condensation
Chem 101
Fall 2004
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Phase Diagrams (P versus T)
• Phase diagrams are a convenient way to display all
of the different phase transitions of a substance.
• This is the phase diagram for water.
Chem 101
Fall 2004
Phase Diagrams (P versus T)
• Compare water’s phase diagram to carbon
dioxide’s phase diagram.
Chem 101
Fall 2004
Amorphous Solids and Crystalline Solids
• Amorphous solids do not have a well ordered
molecular structure.
• Examples of amorphous solids include waxes, glasses,
asphalt.
• Crystalline solids have well defined structures that
consist of extended array of repeating units called
unit cells.
• Crystalline solids display X-ray diffraction patterns
which reflect the molecular structure.
• The Bragg equation, detailed in the textbook, describes
how an X-ray diffraction pattern can be used to
determine the interatomic distances in crystals.
Chem 101
Fall 2004
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The Structure of Crystals
• Unit cells are the smallest repeating unit of a
crystal.
• As an analogy, bricks are repeating units for buildings.
• There are seven basic crystal systems.
Chem 101
Fall 2004
The Structure of Crystals
• We shall look at the three variations of
the cubic crystal system.
• Simple cubic unit cells.
• The balls represent the positions of atoms,
ions, or molecules in a simple cubic unit
cell.
Chem 101
Fall 2004
The Structure of Crystals
• In a simple cubic unit cell each atom,
ion, or molecule at a corner is shared
by 8 unit cells
• Thus 1 unit cell contains 8(1/8) = 1 atom,
ion, or molecule.
Chem 101
Fall 2004
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The Structure of Crystals
• Body centered cubic (bcc) has an
additional atom, ion, or molecule in
the center of the unit cell.
• On a body centered cubic unit cell
there are 8 corners + 1 particle in
center of cell.
• 1 bcc unit cell contains 8(1/8) + 1 = 2
particles.
Chem 101
Fall 2004
The Structure of Crystals
• A face centered cubic (fcc) unit cell
has a cubic unit cell structure with an
extra atom, ion, or molecule in each
face.
• 1 fcc unit cell contains 8(1/8) + 6(1/2) =
4 particles.
Chem 101
Fall 2004
Bonding in Solids
• Molecular Solids have molecules in each of the
positions of the unit cell.
• Molecular solids have low melting points, are volatile,
and are electrical insulators.
• Examples of molecular solids include:
• water, sugar, carbon dioxide, benzene
Chem 101
Fall 2004
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Bonding in Solids
• Covalent Solids have atoms that are covalently
bonded to one another
• Some examples of covalent solids are:
• Diamond, graphite, SiO2 (sand), SiC
Chem 101
Fall 2004
Bonding in Solids
• Ionic Solids have ions that occupy the positions in
the unit cell.
• Examples of ionic solids include:
• CsCl, NaCl, ZnS
Chem 101
Fall 2004
Bonding in Solids
• Metallic Solids may be thought of as positively
charged nuclei surrounded by a sea of electrons.
• The positive ions occupy the crystal lattice
positions.
• Examples of metallic solids include:
• Na, Li, Au, Ag, ……..
Chem 101
Fall 2004
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Bonding in Solids
Variations in Melting Points for Molecular Solids
What are the intermolecular forces in each solid?
Compound
ice
ammonia
benzene, C6H6
napthalene, C10H8
benzoic acid, C6H5CO2H
Melting Point (oC)
0.0
-77.7
5.5
80.6
122.4
Chem 101
Fall 2004
Bonding in Solids
Variations in Melting Points for Covalent Solids
Substance
sand, SiO2
carborundum, SiC
diamond
graphite
Melting Point (oC)
1713
~2700
>3550
3652-3697
Chem 101
Fall 2004
Bonding in Solids
Variations in Melting Points for Metallic Solids
Metal
Na
Pb
Al
Cu
Fe
W
Melting Point (oC)
98
328
660
1083
1535
3410
Chem 101
Fall 2004
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Band Theory in Metals: Na
Na3
Non-bonding
Energy
Energy
Na2
Chem 101
Fall 2004
Energy
Band Theory in Metals: Na
Na4
• As we add atoms, energy levels get closer together.
• With one electron per atom, bonding orbitals always
filled, antibonding always empty.
Chem 101
Fall 2004
Band Theory in Metals: Na
Band diagram
empty
3s
filled
Na2
Na3
Na4
Nan
Nabulk
Chem 101
Fall 2004
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Band Theory in Metals: Na
• Bonding half (“bottom”) of band is filled up to the
nonbonding point.
• Antibonding half (“top”) is empty.
• Availability of empty delocalized orbitals at low
energies allows electrons to move through the crystal,
conducting electricity.
Chem 101
Fall 2004
Insulators: Diamond
• Pick one carbon atom and look at its
bonds to four neighbor atoms.
• Mix 4 sp3 orbitals from central atom
with one sp3 orbital from each of
the other 4.
• Get 8 new orbitals, 4 bonding and 4
antibonding.
• Bonding orbitals filled, antibonding
empty.
Chem 101
Fall 2004
Insulators: Diamond
• A “band gap” exists between the filled and unfilled
orbitals.
• The gap is big; the bonding (and antibonding) interactions
are strong.
Empty
“conduction
band”
sp3-sp3 antibonding
Band gap energy
Chem 101
Fall 2004
Filled
“valence
band”
sp3-sp3 bonding
10
Band Diagrams
Metal
Semiconductor
Insulator
Chem 101
Fall 2004
Next Class: Solutions: Chapter 14
• Start Reading Chapter 14
• Only material up to and
including 14-15 will be
covered
• Finish OWL
Chem 101
Fall 2004
11