THE SOLID STATE
Crystalline Solids
- Atoms in structure have a regular repeatable structure.
- Arrangement of atoms is called a lattice.
- Smallest repeatable unit is called a unit cell.
- Be able to recognize different cubic unit cells
- Simple (primitive) cubic
- Face centered cubic
- Body centered cubic
From Chemistry: The Central Science, 10th ed., Brown, LeMay and Bursten.
Counting atoms in unit cells
Atoms in a unit cell are shared with other unit cells. Thus an atom in a unit cell
does not wholly belong to one unit cell.
Atoms at corners are shared by seven other unit cells; thus, only 1/8 of an atom at
a corner belongs to a unit cell.
Atoms on edges are shared by three other unit cells; thus, only ¼ of an atom on an
edge belongs to a unit cell.
Atoms on faces are shared with another unit cell; thus, only ½ of an atom on a
face belongs to a unit cell.
Atoms within the body of a unit cell wholly belongs to that unit cell.
Thus in review
Corners = ⅛ atom
Edges = ¼ atom
Faces = ½ atom
Body = 1 atom
Number of atoms in simple cubic unit cell = 8 corners  1/8 = 1
Number of atoms in face-centered cubic unit cell = 8 corners  1/8 + 6 faces  1/2
=1+3=4
Number of atoms in body-centered cubic unit cell = 8 corners  1/8 + 1 body
=1+1=2
Atomic radii and unit cell length
Face-centered cubic
a 2  a 2   4r 
r2 
2
2a
16
2

 r
a
2 2
www.chemprofessor.com/solids_files/image_019.jpg
Body-centered cubic
Unit cell length and density
The density of solid can be calculated from knowing the number of atoms
in a unit cell and the unit cell length.
- calculate the mass from the number of atoms in the unit cell and the
atomic mass of the atoms
- calculate the volume from the unit cell length cubed
Example: Palladium is metal that has many industrial applications including as a
catalyst. Palladium has a face-centered cubic structure and a unit cell
length of 3.890 Å. Calculate the density of the metal.
mass  1unit cell 
106.42amu 4atoms
1g
 7.069 1022 g
23
atom
unit cell 6.022 10 amu
 1010 m 
volume   3.890 Å   

 Å 
3
d
3
3
 1cm 
  2   5.886 1023 cm3
 10 m 
m
7.069 1022 g

 12.01g cm3
23
3
V 5.886 10 cm
Example: Tungsten is a dense metal that blends well with iron to form a “heavy
metal alloy” used in applications such jet turbine blades. Tungsten has
a body-centered cubic unit cell with a density of 19.25 g/cm3.
Calculate unit cell length of tungsten in Angstroms.
A body-centered unit cell has 2 atoms.
183.84amu
1g
1cm3
V  2atoms 
 3.172 1023 cm3
23
atom
6.022 10 amu 19.25g
V  l3
 l  3 V  3 3.172 1023 cm3  3.165 108 cm
l  3.165 108 cm
102 m 1Å
 3.165Å
1cm 1010 m
Three general types of crystalline solids
1. Ionic
- Ions are arranged in a lattice.
- Lattice is held together with ionic bonding.
- Characteristics
- Somewhat high melting points
- Brittle
- Soluble solids conduct electricity in solution
2. Molecular
- Molecules are arranged in a lattice.
- Intermolecular forces such as dipole – dipole or dispersion forces hold lattice
together.
- Characteristics
- Relatively low melting points
- Brittle
- Soluble solids are nonelectrolytes
3. Metallic
+
- Metal atoms are arranged in a lattice.
+
- Metallic bonding holds lattice together.
+
- Metallic bonds are much different from ionic,
+
covalent or other intermolecular bonds.
+
- Metal ions have a fixed position within a “sea of
+
electrons”.
+
- Metal ions have a fixed position within a “sea of electrons”.
- Characteristics
- Relatively high melting points
- Often very hard
- Conducts electricity (other solids are usually insulators)
- Often very hard
- Conducts electricity (other solids are usually insulators)
- Conducts heat
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Alloys
1. Substitutional alloys
- Atom of an alloy’s minor component replaces an atom of the major
component.
- Atoms in a substitutional alloy must have similar sizes
- Examples of substitutional alloys
- Brass (70% Cu, 30% Zn)
- Bronze (88% Cu, 12% Sn)
- White gold (90% Au, 10% Ni)
- Nichrome (80% Ni, 20% Cr)
- toasters, hair dryers
- Sterling silver (92% Ag, 8% Cu)
- 14k gold (58% Au, 14% Ag, 28% Cu)
www.sciencegeek.net/Chemistry/Powerpoint/
Unit3/Unit3_files/slide0109_image021.jpg
2. Interstitial alloys
knoll. google.com/k/-//a8npan5yj7ut/hp1erd/figure-3.png
- Atom of an alloy’s minor component fits into the empty space between
the major component atoms.
- Addition of interstitial atoms makes slippage of atoms more difficult;
thus, the material becomes harder (and sometimes more brittle).
- usually limited to C, B, Si, N or O.
- Examples
- Steel (98% Fe, 2% C)
- Titanium nitrides (and carbides) are used as coatings for saw blades
and drill bits.
Close-packing of metallic solids
Metal atoms can be considered spheres.
Within a metallic solid lattice, there are two ways in which the metal atom
spheres can pack together is an efficient manner.
Hexagonal close packing (hcp)
Stacking of spheres occurs as two distinct layers: ABABABABAB…
http://mrsec.wisc.edu/Edetc/SlideShow/slides/
contents/unit_cells_stoichiometry.html
Cubic close packing (ccp)
Same as face-centered cubic structure
Stacking of spheres occurs as three distinct layers: ABCABCABC…
http://mrsec.wisc.edu/Edetc/SlideShow/slide
s/contents/unit_cells_stoichiometry.html
www.uwgb.edu/dutchs/GraphicsGeol/ROCKMIN/ATOM-STRUCT/Cubcpack.gif
Amorphous Solids
- amorphous  without form
- Solids where atoms do not have regular structure
Two types
1.) Network solids
- Atoms are covalently bonded to each other in a network.
- Examples
a. Diamond
b. Graphite
c. Glass (SiO2)
From Chemistry: The Central Science, 10th ed., Brown, LeMay and Bursten.
- Characteristics (of network solids)
- very often hard and brittle
- high melting points (or decomposition temperatures)
- excellent electrical insulators
- some network solids are heat conductors (diamond, graphite, BN) and
others are not (glass)
Is a compound with nonmetals, a molecular compound or a network solid?
- Atoms other than C, N or O don’t form double bonds.
- If a “Lewis structure” of a binary nonmetal compound shows atoms other
than C, N or O with a double bond, the compound is probably a network
solid.
2.) Polymer solids
- Polymer molecules are long and “skinny”.
- The strength of a polymer depends on many factors including the
entanglement of the long skinny molecules like a pile of cooked spaghetti.
- Intermolecular forces such as hydrogen bonding and dispersion forces are
also very important.
Polymer types
a) Linear – continuous chain of carbon atoms
with no branching
Polytetrafluoroethylene – Teflon
1
F
F
F
F
F
F
C
C
C
C
C
C
F
F
F
F
F
F
Polyethyleneterephthalate – Soda bottles
H
O
H
C
C
C
C
O
C
C
C
H
b)
O
H
C
C
O
H
H
C
H
H
Branched – long continuous
chain of carbons with
occasional branching.
Polyethylene – Milk jugs
6
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
H
H
H
Polystyrene – Styrofoam
H
H
H
H
H
H
C
C
C
C
C
C
H
H
H
(Warning! Phenyl groups not to scale!)
c)
Crosslinked – polymer chains interconnected to
each other with covalent bonding
Poly(2-methyl-1,4-butadiene) [Polyisoprene]
– Tire rubber
H
H
H
H
H
H
H
C
C
C
C
C
H
C
H
C
H
C
C
C
H
H
H
H
H
H
Polymer Crystallinity
- Long hydrocarbon chains can fold back on each other and bind together via
dispersion forces to form regions of repeatable order called crystalline
regions
- When polymers have crystallinity, they are stronger than purely amorphous
polymers.
- High-density polyethylene (HDPE) (recycling code 2) is stronger than lowdensity polyethylene (LDPE) (recycling code 4) because it has more
crystallinity
http://www2.dupont.com/Plastics/en_US/Products/Zytel_HTN/Zytel_HTN_whitepaper_R8.html
Thermal Properties of Polymers
A. Thermoplastics
1. Softens and melts above specific temperatures
2. Molten polymer often used to shape objects
3. No or low crosslink density
4. Glass transition temperature (Tg)
- Above Tg, polymer does not flow, but elasticity is significantly
increased.
5. Can be recyclable
B. Thermosets
1. No softening or melting
2. High crosslink density
3. Decomposition occurs above a specific temperature rather than melting
4. Objects must be shaped as polymer is made
C. Elastomers
1. Moderately crosslinked thermoplastics
2. Rubber and Spandex are common elastomers.
3. Rubber can be strengthened with vulcanization
a. Heating rubber with sulfur, S8, yields crosslinked polymer.
b. Discovered by Charles Goodyear in 1839.
Polymer Synthesis
A Step polymers
- step polymers are made using two different
monomers that link together stepwise
- reaction is often a condensation reaction
(substitution reaction with water as a by-product)
- polymers grow by having chain grow at both ends
at the same time
Examples of step polymers
1. Polyamides [Nylon, Kevlar]
http://en.wikipedia.org/wiki/Step-growth_polymerization
2. Polyesters – clothing
3. Polycarbonates – lenses
4. Polyurethanes – foam insulation, bowling pins
Example: Synthesis of nylon
http://www.steinwall.com/ART-nylon.html
- In making nylon, a two-sided carboxylic acid reacts with a two-sided amine
to form an amide group and water as by-product
- Reaction is sometimes referred to as a condensation reaction
- The polymer forms as carboxylic acid groups continue to react with amine
groups
- Since amide groups are formed, nylons are also called polyamides
B. Chain polymers
- A free radical or an ion (cation or anion) causes alkene molecules to link
together.
- Chain polymers, like polyethylene, grow at one end of the chain (contrasts
with step polymers).
R
H
H
R
+ C
C
H
H
H
H
H
H
C
C
+ C
C
H
H
H
H
R
R
H
H
C
C
H
H
H
H
H
H
C
C
C
C
H
H
H
H
H2C
C
+
CH 3
CH 3
CH 3
CH 3
CH 3
F3B
H2
C
F3B
BF3
H2
C
C
CH 3
CH 3
H2
C
C
CH 3
Examples of chain polymers
A. Polyethylene - Plastic trash bags, milk jugs
B. Polypropylene – clear bags, food containers
C. Polytetrafluoroethylene (PTFE) [Teflon]
D. Polyvinyl chloride (PVC) – plumbing, gutters
C
CH 3
+
H2C
C
CH 3