Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.;
and Bruce E. Bursten
Chapter 12
Modern Materials
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.
Modern
Materials
Types of Materials
Recall that atomic
orbitals mix to give
rise to molecular
orbitals.
Modern
Materials
Types of Materials
As the number of
atoms grows, so
does the number of
molecular orbitals.
Modern
Materials
Types of Materials
In such compounds,
the energy gap
between molecular
orbitals essentially
disappears, and
continuous bands of
energy states result.
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Materials
Types of Materials
Rather than molecular orbitals
separated by an energy gap,
these substances have energy
bands.
Modern
Materials
Types of Materials
The gap between bands
determines whether a
substance is a metal, a
semiconductor, or an insulator.
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Materials
Types of Materials
Modern
Materials
Metals
Valence electrons
are in a partially
filled band.
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Materials
Metals
• There is virtually no
energy needed for
an electron to go
from the lower,
occupied part of the
band to the higher,
unoccupied part.
• This is how a metal
conducts electricity.
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Materials
Semiconductors
Semiconductors have a
gap between the valence
band and conduction
band of ~50 to 300 J/mol
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Materials
Semiconductors
• Among elements, only silicon,
germanium, and graphite
(carbon), all of which have 4
valence electrons, are
semiconductors.
• Inorganic semiconductors (like
GaAs) tend to have an
average of 4 valence electrons
(3 for Ga, 5 for As).
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Materials
Doping
By introducing very
small amounts of
impurities that have
more (n-type) or fewer
(p-type) valence
electrons, one can
increase the
conductivity of a
semiconductor.
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Materials
Insulators
• The energy band
gap in insulating
materials is
generally greater
than ~350 kJ/mol.
• They are not
conductive.
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Materials
Ceramics
• They are inorganic solids, usually hard and brittle.
• Highly resistant to heat, corrosion, and wear.
 Ceramics do not deform under stress.
 They are much less dense than metals, and so are
used in their place in many high-temperature
applications.
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Materials
Superconductors
At very low
temperatures, some
substances lose
virtually all
resistance to the
flow of electrons.
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Materials
Superconductors
Much research has
been done recently
into the development
of high-temperature
superconductors.
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Materials
Superconductors
The development of
higher and higher
temperature
superconductors will have
a tremendous impact on
modern culture.
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Materials
Polymers
Molecules of high molecular mass made by
sequentially bonding repeating units called
monomers.
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Materials
Some Common Polymers
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Materials
Addition Polymers
Made by coupling the monomers by
converting -bonds within each monomer to
-bonds between monomers.
Ethylene
Polyethylene
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Materials
Condensation Polymers:
• Made by joining two subunits through a
reaction in which a smaller molecule (often
water) is also formed as a by-product.
• These are also called copolymers.
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Materials
Synthesis of Nylon
Nylon is one
example of a
condensation
polymer.
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Materials
Properties of Polymers
Interactions
between chains of a
polymer lend
elements of order to
the structure of
polymers.
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Materials
Properties of Polymers
Stretching the polymer chains as they form
can increase the amount of order, leading to
a degree of crystallinity of the polymer.
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Materials
Properties of Polymers
Such differences in
crystallinity can lead
to polymers of the
same substance
that have very
different physical
properties.
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Materials
Cross-Linking
Chemically bonding
chains of polymers
to each other can
stiffen and
strengthen the
substance.
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Materials
Cross-Linking
Naturally occurring rubber is too soft and
pliable for many applications.
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Materials
Cross-Linking
In vulcanization, chains are cross-linked by
short chains of sulfur atoms, making the
rubber stronger and less susceptible to
degradation.
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Materials
Ceramics
Made from a
suspension of metal
hydroxides (called a
sol)
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Materials
Ceramics
These can undergo
condensation to
form a gelatinous
solid (gel), that is
heated to form a
metal oxide, like the
SiO2 shown here.
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Materials
Biomaterials
• Materials must
 Be biocompatible.
 Have certain physical
requirements.
 Have certain chemical
requirements.
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Materials
Biomaterials
• Biocompatibility
 Materials cannot cause
inflammatory
responses.
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Materials
Biomaterials
• Physical
Requirements
 Properties must mimic
the properties of the
“real” body part (e.g.,
flexibility, hardness,
etc.).
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Materials
Biomaterials
• Chemical
Requirements
 Cannot contain even
small amounts of
hazardous impurities.
 Cannot degrade into
harmful substances
over a long period of
time in the body.
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Materials
Biomaterials
• These substances
are used to make:
 Heart valves
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Materials
Biomaterials
• These substances
are used to make:
 Heart valves
 Vascular grafts
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Materials
Biomaterials
• These substances
are used to make:
 Heart valves
 Vascular grafts
 Artificial skin grafts
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Materials
Biomaterials
• These substances
are used to make:
 Heart valves
 Vascular grafts
 Artificial skin grafts
 “Smart” sutures
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Materials
Electronics
• Silicon is very
abundant, and is a
natural
semiconductor.
• This makes it a
perfect substrate for
transistors,
integrated circuits,
and chips.
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Materials
Electronics
In 2000, Alan J. Heeger, Alan G. MacDiarmid, and
Hideki Shirakawa won a Nobel Prize for the
discovery of “organic semiconductors” like the
polyacetylene below.
H
H
C
H
C
H
C
H
C
H
C
H
C
H
C
H
C
C
C
C
C
C
C
C
C
C
C
H
H
H
H
H
H
H
H
H
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Materials
Electronics
Noncrystalline
silicon panels can
convert visible light
into electrical
energy.
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Materials
Liquid Crystals
• Some substances do
not go directly from
the solid state to the
liquid state.
• In this intermediate
state, liquid crystals
have some traits of
solids and some of
liquids.
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Materials
Liquid Crystals
Unlike liquids, molecules in liquid crystals
have some degree of order.
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Materials
Liquid Crystals
In nematic liquid crystals, molecules are only
ordered in one dimension, along the long
axis.
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Materials
Liquid Crystals
In smectic liquid crystals, molecules are
ordered in two dimensions, along the long
axis and in layers.
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Materials
Liquid Crystals
In cholesteric liquid
crystals, nematiclike crystals are
layered at angles to
each other.
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Materials
Liquid Crystals
These crystals can
exhibit color
changes with
changes in
temperature.
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Materials
Light-Emitting Diodes
In another type of
semiconductor, light
can be caused to be
emitted (LEDs).
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Materials
Light-Emitting Diodes (LEDs)
• Organic light-emitting
diodes (OLEDs) are
lighter and more
flexible, and can be
brighter and more
energy efficient.
• Soon OLEDs may
replace incandescent
lights in some
applications.
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Materials
Nanoparticles
Different-sized
particles of a
semiconductor (like
Cd3P2) can emit
different wavelengths
of light depending on
the size of the energy
gap between bands.
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Materials
Nanoparticles
Finely divided metals
can have quite different
properties than larger
samples of metals.
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Materials
Carbon Nanotubes
Carbon nanotubes
can be made with
metallic or
semiconducting
properties without
doping.
Modern
Materials