SUPPLEMENT 6 S45
Now the equation is balanced, and the law of
conservation of matter has been observed. For
every two molecules of water through which we
pass electricity, two hydrogen molecules and one
oxygen molecule are produced.
THINKING ABOUT
Chemical Equations
Try to balance the chemical equation for the
reaction of nitrogen gas (N 2 ) with hydrogen gas
(H 2 ) to form ammonia gas (NH 3 ).Scientists Are Learning How
to Build Materials from the
Bottom Up: Nanotechnology
Nanotechnology (Science Focus, p. 362) uses
atoms and molecules to build materials from the
bottom up using atoms of the elements in the
periodic table as its raw materials. A nanometer
(nm) is one-billionth of a meter—equal to the
length of about 10 hydrogen atoms lined up side
by side. A DNA molecule (Figure 10) is about
2.5 nanometers wide. A human hair has a width
of 50,000 to 100,000 nanometers.
For objects smaller than about 100 nano-
meters, the properties of materials change dra-
matically. At this nanoscale level, materials can
exhibit new properties, such as extraordinary
strength or increased chemical activity, that they
do not exhibit at the much larger macroscale level
that we are all familiar with.
For example, scientists have learned how
to make tiny tubes of carbon atoms linked
together in hexagons. Experiments have shown
that these carbon nanotubes are the strongest
material ever made—60 times stronger than
high-grade steel. Such nanotubes have been
linked together to form a rope so thin that it is
invisible, but strong enough to suspend a pickup
truck.
At the macroscale, zinc oxide (ZnO) can be
rubbed on the skin as a white paste to protect
against the sun’s harmful UV rays; at the nano-
scale it becomes transparent and is being used as
invisible coatings to protect the skin and fabrics
from UV damage. Because silver (Ag) can kill
harmful bacteria, silver nanocrystals are being
incorporated into bandages for wounds.
Researchers hope to incorporate nanopar-
ticles of hydroxyapatite, with the same chemical
structure as tooth enamel, into toothpaste to
put coatings on teeth that prevent bacteria from
penetrating. Nanotech coatings now being used
on cotton fabrics form an impenetrable barrier
that causes liquids to bead and roll off. Such
stain-resistant fabrics used to make clothing,
rugs, and furniture upholstery could eliminate
the need to use harmful chemicals for removing
stains.
Self-cleaning window glass coated with a
layer of nanoscale titanium dioxide (TiO 2 ) par-
ticles is now available. As the particles interact
with UV rays from the sun, dirt on the surface of
the glass loosens and washes off when it rains.
Similar products can be used for self-cleaning
sinks and toilet bowls.
Scientists are working on ways to replace
the silicon in computer chips with carbon-based
nanomaterials that greatly increase the process-
ing power of computers. Biological engineers are
working on nanoscale devices that could deliver
drugs. Such devices could penetrate cancer cells
and deliver nanomolecules that could kill the
cancer cells from the inside. Researchers also
hope to develop nanoscale crystals that could
change color when they detect tiny amounts
(measured in parts per trillion) of harmful
substances such chemical and biological warfare
agents and food pathogens. For example, a color
change in food packaging could alert a consumer
when a food is contaminated or has begun to
spoil. The list of possibilities could go on.
By 2008, more than 1,000 products contain-
ing nanoscale particles were commercially avail-
able and thousands more were in the pipeline.
Examples are found in cosmetics, sunscreens,
fabrics, pesticides, and food additives.
So far, these products are unregulated and
unlabeled. This concerns many health and
environmental scientists because the tiny size of
nanoparticles can allow them to penetrate the
natural defenses of the body against invasions
by foreign and potentially harmful chemicals
and pathogens. Nanoparticles of a chemical
tend to be much more chemically reactive than
macroparticles of the chemical, largely because
the tiny nanoparticles have relatively large sur-
face areas for their small mass. This means that a
chemical that is harmless at the macroscale maybe hazardous at the nanoscale when they are
inhaled, ingested, or absorbed through the skin.
We know little about such effects and risks at
a time when the use of untested and unregu-
lated nanoparticles is increasing exponentially.
A few toxicological studies are sending up red
fl ags:- In 2004, Eva Olberdorster, an environmental
toxicologist at Southern Methodist Uni-
versity, found that fish swimming in water
loaded with a certain type of carbon nano-
molecule called buckyballs experienced brain
damage within 48 hours. - In 2005, NASA researchers found that inject-
ing commercially available carbon nanotubes
into rats caused significant lung damage. - A 2005 study by researchers at the U.S. Na-
tional Institute of Occupational Safety and
Health found substantial damage to the heart
and aortic arteries of mice exposed to carbon
nanotubes. - In 2005, researchers at New York’s University
of Rochester found increased blood clotting
in rabbits inhaling carbon buckyballs.
In 2004, the British Royal Society and Royal
Academy of Engineering recommended that we
avoid the environmental release of nanoparticles
and nanotubes as much as possible until more
is known about their potential harmful impacts.
They recommended as a precautionary measure
that factories and research laboratories treat
manufactured nanoparticles and nanotubes as if
they were hazardous to their workers and to the
general public. GREEN CAREER: Nanotechnology
THINKING ABOUT
Nanotechnology
Do you think that the benefits of nanotechnol-
ogy outweigh its potentially harmful effects?
Explain. What are three things you would do to
reduce its potentially harmful effects?RESEARCH FRONTIER
Learning more about nanotechnology and how
to reduce its potentially harmful effects. See
academic.cengage.com/biology/miller.