SOPHOMORE CHEMISTRY Summer Homework Assignment Directions:
Welcome to Sophomore Chemistry! To get your prepared and excited for our class, this summer
homework has 3 components:
1) Watch some fun videos online! (45 minutes)
2) Read 3 articles on real life applications of chemistry and complete the attached worksheet.
(1 hour 30 minutes)
3) Become familiar with the PERIODIC TABLE OF ELEMENTS and practice rounding by
looking up the atomic mass of various element and rounding to the tenths place. (1 hour)
Why should I do this?
We study chemistry to help better understand the world around us by looking at it in terms of atoms
and molecules. The videos will introduce you to this idea and give you some background information
we can use to start our exploration in August. Also, a few of the videos are just fun! The articles will
give you some examples of how chemistry REALLY DOES affect our everyday life. Lastly, the
periodic table is THE most important tool a chemist uses and we will use it often in class. Practicing
with it over the summer (and refreshing your rounding skills) is going to help you enter class ready to
start the year and ready to learn some cool chemistry!
Videos to Watch:
1) My Robot is Better Than Your Robot: https://youtu.be/vYuOKb3gO7E
2) ASAP Science The Element Song: https://youtu.be/zUDDiWtFtEM
3) Chemistry in Life: https://youtu.be/L2Q2q20KaEk
4) Crash Course Chemistry, Episode 1: https://youtu.be/FSyAehMdpyI
5) Atoms, Elements, Molecules, and Compounds:
https://www.youtube.com/watch?v=AfXxZwNLvPA
T
he hottest chili pepper in the world is known as
the Moruga Scorpion. Only the very foolish or the
very brave would ever try it. To eat one is to experience
pain like you’ve never known. Your mouth, tongue
and throat would feel like they were on fire. Your eyes would
water, your ears would ring, and your lips would go numb. Your
face would turn red and you would sweat profusely. Once swallowed, the pain doesn’t diminish but intensifies. If you were to pop
an entire one in your mouth you would need to be rushed to the
hospital. The name is no accident: Eating this pepper is like eating a scorpion—a live one that stings your insides for hours.
Hot Peppers:
Muy Caliente!
By Brian Rohrig
The “hot” in hot peppers is due to capsaicin
(C18H27NO3), a colorless, odorless oil-like
compound found in the fruit of a plant that
is a close relative of the tomato. Capsaicin
is primarily found in the membrane that
holds the seeds. These plants are found in
the Americas and were brought to Europe by
explorer Christopher Columbus who mistakenly thought they were a relative of the black
pepper (the plant we get pepper from). To
distinguish them from the black pepper plant,
hot peppers are usually called chili peppers,
or just plain chilis in many parts of the world.
Capsaicin is also found, in smaller amounts,
in other spices, such as oregano, cinnamon,
and cilantro.
The hotness of a pepper is measured by the
Scoville heat scale (see sidebar 1), which is a
series of “heat units” that range from 0 to 16
million, depending on the capsaicin content
of a pepper. Pure capsaicin tops the scale at
16 million heat units, and bell peppers rank
at 0, since they contain no capsaicin. The
Moruga Scorpion comes in at around 2 million heat units, the same capsaicin concentra-
alamey
Hot, hot, hot!
tion as pepper spray! The jalapeno pepper
ranges from 5,000 to 50,000 heat units, while
the habanero ranks from 100,000 to 350,000
heat units.
Today, more sophisticated methods are
used to determine how much capsaicin is in
peppers, using instruments which measure
concentrations in parts per million (ppm). One
ppm of capsaicin means that 1 milligram of
capsaicin is present in 1 kilogram of pepper.
It is like having one red marble (one capsaicin
molecule) in a bucket along with 999,999
white marbles (other molecules present in
pepper). Capsaicin is so potent that even a
concentration of 10 ppm would produce a
long-lasting burning sensation on the tongue.
A large dose of capsaicin, in its concentrated
form, could be toxic if ingested, yet the amount
found in hot peppers is so small there is little
risk of harm from the toxic effects of capsaicin
itself. When dealing with it in its pure form,
you must wear gloves and a respirator.
O
CH3
N
H
CH3
HO
6 Chemmatters | DECEMBER 2013/JANUARY 2014
OCH3
www.acs.org/chemmatters
s
to
pho
.co
m
T
he Scoville heat scale was devised
in 1912 by the American pharmacist
Wilbur Scoville. To test the hotness of pepper,
Scoville would take an extract from a pepper and determine how much sugar water
was required to dilute it before its “heat”
could no longer be detected by a panel of
volunteer taste-testers. For example, if he
had 1 milliliter (ml) of pepper extract, and
it took 100 ml of sugar water to dilute it
until its hotness was no longer detectable,
then it would rank at 100 Scoville heat
units. If it took 1,000 ml of sugar water to
dilute 1 ml of extract, then it would rate
1,000 Scoville heat units.
–Brian Rohrig
EXTREME
}
}
}
A burning
sensation
100,000–250,000
Tabasco
50,000–100,000
Thai Hot, Chinese
Kwangsi
5,000–25,000
Jalapeño, Cayenne,
Serrano, Arbol
100–5,000
Guajillo,
Lousiana
hot sauce
shutterstock and photo.com
Scoville Heat Scale
Can You Tell
Which Pepper Is Hotter?
HOT
If you find yourself eating spicy chicken
wings that are hotter than you expected, what
do you do? You take a big gulp of water,
right? Actually, that would be a bad move.
Water only makes it worse, similar to throwing
water on a grease fire.
If you look at the structure of capsaicin
(p. 6), you will notice that one end of the
molecule is made of a long hydrocarbon tail.
Hydrocarbons are molecules made of hydrogen and carbon, and many common fuels,
such as gasoline and candle wax, are derived
from hydrocarbons.
Hydrocarbons tend to be nonpolar, meaning
that, in the molecule, the negatively charged
electrons and the positively charged protons
are evenly distributed throughout. A polar
molecule, on the other hand, has distinct
regions of positive and negative charge—the
shared electrons will tend to stay near the
atom with the higher electronegativity, or
greater ability to attract electrons. This side
of the molecule will develop a partial negative
charge while the other side develops a partial
positive charge. The reason these charges are
partial is because the bond is still covalent and
the electrons are still being shared; they are
just shared unequally. Any molecule that has
a partial positive charge and a partial negative
charge is called a polar molecule.
Water is a good example of a polar molecule
because its individual bond polarities do not
cancel, leaving the oxygen side of water with a
partial negative charge and the hydrogen side
with a partial positive charge.
In the case of the capsaicin
molecule, the individual bond
polarities are arranged in such a
way that they cancel each other
To determine how hot a pepper is, look at the stem.
out. The capsaicin molecule
In general, the thinner the stem, the hotter the pepends up being nonpolar, overall,
per. Some gardeners claim that if the stem is bent it
because of its molecular strucwill be hotter than if it is straight. If you look at
ture, especially the long nonpolar
peppers of the same species, small pephydrocarbon tail.
pers tend to be hotter than larger peppers.
Polar substances tend to disSince peppers get hotter as they ripen, a
solve in other polar substances,
red
one will be hotter than a green pepper.
while nonpolar substances tend
Also,
dried peppers will always be hotto dissolve in other nonpolar
ter
than fresh peppers, because as
substances. This tendency is
water
evaporates from the fruit, the
summed up by the principle
amount
of capsaicin remaining will
“like dissolves like.” When you
be
of
a
higher
concentration.
drink water after eating a hot
– Brian Rohrig
pepper, the water just spreads it
around your mouth, making the
shutterstock
pain worse.
molecules from your tongue. Casein forms the
Drinking milk or eating ice cream is the
curds in sour milk. So, cottage cheese, which
preferred solution because milk and ice cream
is primarily casein, would be great to ease
contain molecules that are nonpolar, called
the pain from eating chili peppers. A piece of
casein. Casein molecules attract capsaicin
bread or other starchy food, which is made of
molecules. They surround the capsaicin molnonpolar molecules, would also help ease the
ecules and wash them away, in the same way
discomfort.
that soap washes away grease. This explains
I had an experience once while traveling in
why milk and ice cream can remove capsaicin
Louisiana that I will never forget.
I bought a hot pickle at a gas station. I didn’t open it until I was
Ranking of Chili Peppers
driving on the highway. After one
Using the Scoville Heat Scale
bite, my mouth felt like it was on
fire. It seemed like an eternity
2 million–5 million
Standard Pepper Spray
until I found a convenience store,
2 million
where I purchased a snack cake
Moruga Scorpion
and shoved it into my mouth to
alleviate the pain. It helped some,
500,000–1 million
Scotch Bonnet,
but the pain persisted for quite
Red Savina Habanero
some time afterward. I have
avoided most hot foods since
250,000–500,000
then, especially hot pickles!
Long Slim Cayenne
MILD
Water or milk?
When you eat a hot pepper, it
definitely feels like your mouth
is on fire. But if you were to stick
a thermometer in your mouth, it
would not register an increase
in temperature. Believe it or not,
even the hottest peppers do not
really get hot. They trigger pain
receptors in your tongue, mouth,
and back of your throat that send
a signal to the brain, which is
chemmatters | DECEMBER 2013/JANUARY 2014 7
Pain
receptor
Capsaicin Ca2+
molecule
Tongue
Ca +
Capsaicin
molecule
2
Pain
receptor
Pain receptors
Nerves
Nerve
cell 1
Activation
of next
nerve cell
Nerve
cell 2
Figure 2. When a person eats a hot pepper, capsaicin molecules binds to pain receptors present on the
surface of the tongue. These receptors send a signal to the brain that tells the person that the pepper is
hot. This signal is relayed by successive neurons, each releasing brain chemicals that give that “hot’
sensation. (Inset) When capsaicin binds to a nerve cell in the tongue, calcium ions flood inside the
nerve cell, which causes it to release brain chemicals that lead to the activation of other nerve cells
and ultimately to the brain signal that tells the person “It’s hot!”
istock
interpreted as heat. Since capsaicin
is an irritant, this feeling of heat is
Eating Chili Peppers
the body’s way of compelling you to
to Cool Down?
take some food or drink in an effort to
Chili peppers are prevalent in hot climates, and
remove the irritant.
it is especially popular in Mexico and India. Why
Pain receptors are proteins that have
would you want to eat hot peppers if it is already
a certain shape that only fit specific
hot outside? Wouldn’t they make you hotter?
molecules. Some receptors have the
When you eat hot peppers, you tend to sweat.
Sweating is a cooling mechanism for the body.
correct shape for capsaicin to fit into,
As sweat evaporates, energy is removed from
like a lock and a key. When a capsaicin
the body. Evaporation is an endothermic phase
molecule binds to one of these recepchange, because energy must be absorbed to
tors, calcium ions (Ca2+) flood in. This
overcome the forces of attraction between the
flood of calcium ions triggers the release
molecules in the liquid phase that are
present in sweat, allowing them to
of neurotransmitters that send a mesenter the vapor phase, so sweat
sage to the brain. Neurotransmitters are
can turn into a gas. So, it makes
chemicals that are transmitted from one
sense that eating hot peppers
neuron to the next. The brain interprets
would be a more common practice
this message as pain. Capsaicin also
in warmer regions of the
world. –Brian Rohrig
stimulates those receptors that perceive
heat, known as thermoreceptors
You can build up a tolerance to eating
hot foods. The general consensus is that the
and it can damage your intestinal tract, as well.
pain receptors in the tongue and the mouth
Also, if you eat too many hot peppers at once,
become desensitized over time if you have
you will likely throw up, as your body will try to
eaten a lot of hot food, allowing you to eat
eliminate the perceived toxin.
increasingly hotter foods.
But if you have not worked a tolerance for hot
Capsaicin’s many uses
peppers, not only will your pain receptors trick
Capsaicin is used as a pain reliever, and
your brain into thinking you are being burned,
it can be applied to the skin as a patch or a
but your body may mount an inflammatory
cream. It has been used to treat the pain of
response, as well. This response can cause your
arthritis, shingles, and sore muscles. When
throat to swell, making it difficult to breathe,
8 Chemmatters | DECEMBER 2013/JANUARY 2014
www.acs.org/chemmatters
photos.com
George Retsick/Monell Chemical Senses Center. inset diagram by anthony fernandez.
Release of
brain chemicals
capsaicin is applied to your skin, a steady
stream of neurotransmitters is sent to the
brain, stimulating pain signals in the body.
Once these neurotransmitters are depleted,
you no longer experience pain. You are
exchanging short-lived intense pain for constant, low-level pain that your body gets used
to. Once the nerve cells become depleted of
neurotransmitters, they lose their ability to
sense pain. But after you remove the capsaicin
from your skin, the pain may return, because
the neurotransmitters build up again.
It is generally accepted that peppers contain
capsaicin as a defense against predators. It
seems to play a role against certain types of
fungus that are partial to hot peppers.
Chili peppers are actually good for you.
They contain
three times as
much vitamin
C as oranges,
and they are
also loaded with
vitamins A and
E, as well as folic
acid and potassium. There
is some evidence that chili
peppers can help people
lose weight by raising their
metabolism. In particular, capsaicin
increases the rate of thermogenesis, the process
by which cells produce body heat.
So the next time you decide to go wild
and try the 5-alarm chili, make sure you can
handle the 1-alarm chili first. Just make sure
you have a large glass of milk on hand. No
matter how intense the pain of consuming
chili peppers, just remember that your mouth
is not really on fire.
Selected references:
Williams, C. Pepper Power. ChemMatters, April
1995, pp 10–13.
Helmenstine, A. M. How to Make Hot Peppers
Stop Burning. About.com Chemistry: http://
chemistry.about.com/b/2013/03/08/how-tomake-hot-peppers-stop-burning.htm [accessed
Oct 2013].
Raloff, J. Understanding Why Hot Peppers Are
Slimming. Science News, June 3, 2010: http://
www.sciencenews.org/view/generic/id/59930/
description/Understanding_why_hot_peppers_are_slimming [accessed Oct 2013].
Brian Rohrig teaches chemistry at Metro Early
College High School in Columbus, Ohio. His
most recent ChemMatters article, “Keeping Cool,
Staying Warm: How Animals Survive Temperature
Extremes,” appeared in the October 2013 issue.
So Tired in the Morning...
The Science
of
SLEEP
By Kristin Harper
Jilly set up a Facebook page and a Twitter account to encourage her
fellow students to show up at the school board meeting where the vote
was taking place. With their help, she made hundreds of posters and
flyers. Then, armed with a mountain of scientific research that she and
her friends had collected, she stood before the board and made the
case against an earlier start time.
It worked.
The school board abandoned the idea of beginning the day at 7:20
a.m. Jilly was not through, though. The next day, she started campaigning for an even later start time, and her persistence paid off. Eventually, the board voted 6 to 1 to ring the first bell more than an
hour later, at 9 a.m.
Why do teenagers find it so hard to wake up
early, and why are more and more school
districts opting for later high school start
times? It turns out the answer can be
found in the chemistry of sleep.
Jilly Dos Santos, a teenager from Columbia,
Mo., convinced her high school to shift to a
later start time.
8 Chemmatters | DECEMBER 2014 /JANUARY 2015
Our internal clocks
Our bodies release chemicals in a 24-hour
cycle, nudging us to do certain activities at
certain times. Each of these cycles is called a
circadian rhythm (see “Circadian Rhythms and
Life,” p. 10). One of the most important chemicals involved in this process is melatonin, a hormone that makes us
feel drowsy. The amount of melatonin in our bodies starts increasing
in the evening and peaks in the middle of the night, letting us know it
is time to sleep. It then decreases by morning, allowing us to wake up
refreshed.
To maintain our 24-hour sleep schedule, our bodies translate information about the time of day into melatonin production. This process
starts in the eye’s retina. When the retina is exposed to light, a signal is
relayed from the retina to an area of the brain, called the suprachiasmatic
nucleus, which plays a role in making us feel sleepy or wide awake.
The suprachiasmatic nucleus sends signals to other parts of
the brain that control hormones and body temperature.
Then, signals travel from the brain down the
spinal cord and back up to the pineal gland, a
small pinecone-shaped organ in the brain
where melatonin production takes place.
During the day, such signals prevent the
pineal gland from producing melatonin.
But when it is dark outside, these signals
are not activated, and the pineal gland is
able to produce melatonin (Fig. 1). In other
words, exposure to light prevents melatonin
release, which keeps us awake, and lack of
www.acs.org/chemmatters
Dan Gill; shelley russell
When the Columbia, Mo., school board announced they were
considering moving Rock Bridge High School’s start time from
7:50 a.m. to 7:20 a.m., it was the last straw for sophomore
Jilly Dos Santos. “I thought if that happens, I will die.
I will drop out of school!” she said.
Polish Physiological Society © Konturek, S. J., Konturek, P. C., Brzozowski, T. & Bubenik, G. A. J. Physiol. Pharmacol. 58 (Suppl. 6), 23–52 (2007); anthony fernandez; http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/otherendo/pineal.html
exposure to light causes melatonin release,
which tells us to “go to sleep!”
These brain signals explain how our bodies
know when to produce melatonin, but how is
melatonin synthesized? Melatonin is actually
derived from an amino acid called tryptophan,
which is absorbed from the bloodstream to
the pineal gland. An amino acid is an organic
acid used to make proteins.
The synthesis of melatonin from tryptophan
occurs through a multistep process (Fig. 2).
First, tryptophan is converted to another
amino acid, 5-hydroxytryptophan, through the
action of the enzyme tryptophan hydroxylase,
of SNAT. However, at night, SNAT is phosphorylated. Phosphorylation, which is simply
the addition of a phosphate group (PO43−) to a
protein or another organic molecule, prevents
SNAT from being degraded and thus increases
melatonin production.
When it is morning time, SNAT is degraded
again, the amount of melatonin decreases,
and you feel ready to start the day.
they haven’t slept long enough, they feel perpetually drowsy, which affects their ability to
pay attention in classes and to learn.
What happens when a high school, such
as Jilly’s, starts later? So far, schools have
reported big gains. For example, the Minneapolis Public School District shifted its start
time from 7:15 a.m. to 8:40 a.m. It found that
students averaged more than five additional
hours of sleep each week, and attendance and
enrollment rates improved, as well. Also, day-
CH2–CH–NH2
I
COOH
Tryptophan
N
I
H
Tryptophan hydroxylase
CH2–CH–NH2
I
COOH
HO
5-hydroxytryptophan
Aromatic amino acid
decarboxylase
N
I
H
CH2–CH2–NH2
HO
Serotonin
Figure 1. When a part of the brain called the suprachiasmatic nucleus does not detect light,
the pineal gland is free to produce melatonin, which makes us feel drowsy.
and then to a brain chemical called serotonin
by an enzyme called aromatic amino acid
decarboxylase. An enzyme is a biological
catalyst that speeds up the rate of a chemical
reaction.
Serotonin’s conversion to melatonin
involves two enzymes: serotonin-N-acetyltransferase (SNAT), which converts the serotonin to N-acetylserotonin with the addition of
an acetyl group (COCH3), and hydroxyindoleO-methyltransferase (HIOMT), which transfers
a methyl group (CH3) to the N-acetylserotonin.
The activities of both enzymes rise soon after
the onset of darkness.
The amount of melatonin produced depends
on the activity of SNAT, which peaks when it is
dark outside. Exposure to light induces signals
that, as explained earlier, travel from the retina
to the suprachiasmatic nucleus and then to
the pineal gland, resulting in the degradation
Teens and
melatonin
Serotonin-N-acetyltransferase (SNAT)
N
I
H
O
II
CH2–CH2–NH–C–CH3
HO
N-acetylserotonin
N
I
H
As we have learned more about
Hydroxyindole-Othe chemistry of sleep in the
O
methytransferase (HIOMT)
II
past few decades, we have come
CH2–CH2–NH–C–CH3
to realize that it really is harder
H3CO
for teens, such as Jilly, to wake
up early. In teens, melatonin is
Melatonin
produced about three hours later
N
in the 24-hour sleep cycle than
I
H
in children or adults. This keeps
them up late, and when they
wake up early, SNAT is still active
Figure 2. The synthesis of melatonin occurs
and they are still producing melatonin, which
in four steps. First, tryptophan is converted
leaves them feeling sleepy in the morning.
into 5-hydroxytryptophan, which is converted
Teens typically require nine hours of sleep
to serotonin. Then, serotonin is converted into
N-acetylserotonin, which is converted into
per night. But because of their late bedtimes
melatonin. Activity of SNAT, an enzyme that
and schools’ early start times, they average
adds an acetyl group to serotonin to produce
only seven hours of sleep per night. Because
N-acetylserotonin, peaks when it is dark outside.
chemmatters | DECEMBER 2014/JANUARY 2015 9
time alertness increased, and rates of depression decreased.
Even more surprising is the number of car
crashes involving teenagers in Fayette County,
Kentucky, decreased by almost 17% in the
two years following its adoption of a later start
time for school. So, it appears that taking into
consideration a shift in the timing of melatonin production in teens can have all sorts of
benefits.
Many teens are not lucky enough to attend
a school with a later start time, however. In
the 2011–2012 academic year, about 40% of
U.S. high schools were still starting before
8 a.m. So what can you do if you are in this
group? First, minimize exposure to artificial
light at night. This includes light from TV,
computers, and phones. By signaling to your
body that it is daytime, these light sources
facilitate the degradation of SNAT and interfere with the production of melatonin. This
means you won’t feel drowsy, making it difficult to go to sleep at a reasonable time.
Another way to get more sleep is to avoid
sleeping in too late on weekends. It may seem
counterintuitive because if you are not getting
enough sleep during the week, your body will
urge you to stay in bed on weekend mornings
to make up for your lost sleep. But the reality
is that sleeping in on weekends can confuse
your body’s biological clock, making it even
tougher to wake up on weekdays.
Circadian
Rhythms
and Life
Circadian rhythms
are not unique to
humans—they are also
found in plants, animals, fungi, and
even bacteria. External signals, such
as light, trigger the cyclical release of
chemicals that signal when to start
and stop different actions. Circadian
rhythms govern all types of activities:
feeding times in bees, leaf movement
in plants, and DNA replication in
fungus, among others. In humans,
circadian rhythms are best
known for governing our sleep
schedules.
A balancing act
Jilly was able to use her knowledge of
chemistry to convince her school district to
move to a later start time. The logistics of this
kind of shift can be tough, though, which prevents many school districts from adopting this
solution. Because most districts have a limited
number of school buses to transport students, if high schools start later, elementary
and middle schools may need to start earlier.
Often, parents of younger kids do not like this
idea. After all, most people don’t like to wake
up earlier than they have to!
Also, some high school students involved
in after-school activities dislike having to stay
at school until dark. Clearly, balancing the
biological sleep schedule of teenagers with the
demands of society is difficult, but more and
more districts are interested in trying to make
later start times work.
This is a perfect example of how our
understanding of chemistry—in this case,
a three-hour shift in melatonin production
in teens—can translate into a change that
improves teens’ lives.
Why Does
Melatonin is not the only chemical that
determines our sleep schedule. Adenosine
also plays an important role: it slows down
the activity of neurons. It gradually builds up
in our bodies when we are awake and makes us
feel sleepy by the end of the day. Then, when we
sleep, adenosine molecules break down, so the
cycle can start all over again. Our neurons, or nerve cells, are embedded with adenosine
receptors. When adenosine binds to these receptors, a variety of proteins that inhibit neurons
are released. This suppression of nerve-cell activity is what causes the feeling of drowsiness.
Caffeine has a chemical structure similar to that of adenosine (Fig. 1). Both molecules have
a double-ring structure, which allows caffeine to bind to adenosine receptors. Unlike adenosine, however, caffeine does not activate these receptors or suppress neuron activity. By reducing the concentration of available adenosine receptors, caffeine slows the rate of reaction:
Less-bound adenosine means we feel less sleepy.
Caffeine Wake
You Up?
N
H3C
O
N
N
N
NH2
O
N
HO
O
CH3
OH
Caffeine
N
N
N
OH
Adenosine
A little caffeine can be a good thing. Figure 1. Caffeine and adenosine have a very similar
double-ring structure. This allows caffeine to bind to
It can temporarily improve memory,
cell receptors for adenosine, blocking adenosine’s
decrease fatigue, and improve mental
ability to make us feel drowsy.
functioning. But too much caffeine can
cause negative side effects, such as insomnia, tremors, nausea, chest pain, and heart
palpitations. In fact, over a three-year period, the Illinois Poison Center in Chicago counted
more than 250 cases of medical complications that involved caffeine, 12% of which ended in
hospitalization. The average age of the patients was 21, suggesting that young people are
particularly prone to overindulging in caffeine. So be careful not to overdo it!
—Kristin Harper
10 Chemmatters | DECEMBER 2014/JANUARY 2015
www.acs.org/chemmatters
Hoffman, J. To Keep Teenagers Alert, Schools
Let Them Sleep In. The New York Times,
March 13, 2014: http://well.blogs.nytimes.
com/2014/03/13/to-keep-teenagers-alertschools-let-them-sleep-in/?_php=true&_
type=blogs&_php=true&_type=blogs&_r=1&
[accessed Sept 2014].
School Start Time and Sleep, National Sleep
Foundation: http://sleepfoundation.org/sleepnews/school-start-time-and-sleep/ [accessed
Sept 2014].
Pannoni, A. Later High School Start Times
a Challenge for Districts. US News and
World Report, March 24, 2014: http://www.
usnews.com/education/blogs/high-schoolnotes/2014/03/24/later-high-school-start-timesa-challenge-for-districts [accessed Sept 2014].
Kristin Harper is a science writer who lives in
Seattle, Wash. Her latest ChemMatters article, “Skin
Color: A Question of Chemistry,” appeared in the
April/May 2014 issue.
thinkstock; anthony fernandez
Selected references
CH3
Smartphones
Smart
Chemistry
As many as 84% of U.S.
residents could not, according to a recent poll conducted
by Time magazine. It is hard
to believe that 20 years ago,
hardly anyone even owned a
cell phone. And now the cell
phone has morphed into something bigger and better—the smartphone. Worldwide,
more than one billion smartphones were purchased last
year. If you own a smartphone you are probably aware
that in a year or two, it will be practically obsolete,
because the smartphone just keeps getting smarter.
In the 1950s, you would have needed a whole bank
of computers on an entire floor of an office building to
do what you are able to do with a single smartphone
today. Even a low-end smartphone has more computing power than the computer system the National Aeronautics and Space Administration (NASA) used to put a
man on the moon. Amazingly, you can surf the Internet,
listen to music, and text your friends with something
that fits in the palm of your hand. None of this would
be possible without chemistry, and every time you use
your smartphone, you are putting chemistry into action.
Smartphone chemistry
If you are wondering what chemistry has to do with
smartphones, just look at the periodic table. Of the 83
stable (nonradioactive) elements, at least 70 of them
can be found in smartphones! That’s 84% of all of the
stable elements.
10 ChemMatters | APRIL/MAY 2015
www.acs.org/chemmatters
Metals are what make smartphones so “smart.”
An average smartphone may contain up to 62 different types of metals. One rather obscure group
of metals—the rare-earth metals—plays a vital
role. The rare-earth metals include scandium and
yttrium, as well as elements 57–71. Elements 57–71
are known as the lanthanides, because they begin
with the element lanthanum. The lanthanides often
appear as the first of two free-floating rows located
at the bottom of the periodic table. Scandium and
yttrium are included in the rare-earth metals because
their chemical properties are similar to those of the
lanthanides.
A single iPhone contains eight different rare-earth
metals. If you examine several varieties of smartphones, you can find 16 of the 17 rare-earth metals.
The only one you will not find is promethium, which
is radioactive.
Many of the vivid red, blue, and green colors you
see on your screen are due to rare-earth metals,
which are also used in the smartphone’s circuitry
and in the speakers. Also, your phone would not be
able to vibrate without neodymium and dysprosium.
Rare-earth metals are not only used in smartphones but in many other high-tech devices, too.
They are found in televisions, computers, lasers,
missiles, camera lenses, fluorescent light bulbs,
and catalytic convertors. Rare-earth elements are
so important in the electronics, communications,
and defense industries that the U.S. Department of
Energy dubbed them the “technology metals.”
Rare-earth metals are not necessarily rare, but
they tend to be scattered within the Earth. You typically do not find high concentrations of them in any
SHUTTERSTOCK; THINKSTOCK; MASTERFILE
Could you last a day
without your cell phone?
By Brian Rohrig
one place. Extracting them from the earth can
be costly and difficult. Rare-earth metals are
a finite resource, and there is no known substitute for many of these elements. One of the
biggest current challenges for the cell-phone
industry is finding suitable replacements for
many of these elements.
SHELLEY RUSSELL, ADAPTED FROM A FIGURE AT: HTTP://CGG-DEV.ANGELVISION.TV/GORILLA-CHANNEL/ION-EXCHANGE-PROCESS
Smartphone’s display
it difficult for one plane to slip past another.
Ceramics are therefore brittle. They resist
compression, but they can break when they
are bent.
The combination of glass and ceramic
forms a material that is tougher and stronger
than each of the materials by themselves.
A glass-ceramic is formed by overheating
the glass, so a portion of its structure is
transformed into a fine-grained crystalline
would eventually make its way to nearly every
smartphone screen. It is so strong it goes by
the name, Gorilla Glass. Laboratory tests
have shown that Gorilla Glass can withstand
100,000 pounds of pressure per square inch!
Gorilla Glass is composed of an oxide of
silicon and aluminum—also called aluminosilicate glass—along with sodium ions (Fig. 2).
But Gorilla Glass gains its tremendous
strength through one final step, in which the
glass is chemically strengthened. The glass
is put into a molten bath of potassium salt,
usually potassium nitrate (KNO3), at 300 °C.
Because the potassium ions are more reactive
than sodium ions, they displace them. Potassium atoms are bigger than sodium atoms,
and the same holds true for ions—potassium
ions are larger than sodium ions. Therefore,
When shopping for a smartphone, the single
most important feature that people look for is
the display. The screen allows you to see the
As many as 84%
phone’s display. If you have ever dropped your
of
U.S. residents
phone without damaging the screen, you were
would
not last
probably relieved. Smartphone screens are
a
day
without
designed to be extremely tough.
their cell
This toughness is actually the result of a
phone.
serendipitous accident. In 1952, a chemist
at Corning Glass Works was trying to heat a
sample of glass to 600 °C in a furnace when,
Molten bath
of potassium
unbeknownst to him, a faulty thermostat
nitrate (KNO3)
caused it to be heated to 900 °C. Upon opening the door, he was glad—and surprised—to
find that his glass sample was not a melted
material. Glass-ceramics are at
Glass surface
pile of goo and that it had not ruined the
least 50% crystalline, and, in some
furnace. When he took it out with tongs, he
cases, they are more than 95%
dropped it on the floor (another accident). But
crystalline.
instead of breaking, it bounced!
This amazing glass-ceramic
Thus was born the world’s first synthetic
material is so resistant to heat that
glass-ceramic, a material that shares many
it has been used in the nose cones
O
properties with both glass and ceramic.
of supersonic-guided missiles used
Si
Al
Glass is an amorphous solid, because it
by the military. As a result of the
Na
lacks a crystalline structure (Fig. 1(a)). The
success of glass-ceramic materials,
K
molecules are not in any kind of order but are
the Corning Glass Works Company
Figure 2. Gorilla Glass, which is used in smartphone displays,
arranged like a liquid, yet they are frozen in
undertook a large research projis a type of glass that is strengthened by the addition of
place. Because glass does not contain planes
ect to find ways to make ordinary
potassium ions, which replace smaller sodium ions.
(Note: This drawing is for illustration purposes only.)
of atoms that can slip past each other, there
transparent glass as strong as
is no way to relieve stress. Excessive stress
glass-ceramic products. By 1962,
forms a crack, and molecules on the surface
Corning had developed a very strong type of
these potassium ions take up more space in
of the crack become separated. As the crack
chemically strengthened glass, unlike anything
the glass than do sodium ions.
grows, the intensity of the stress increases,
ever seen before. This super-strong glass
Cramming larger ions into the spaces formore bonds break, and the
merly occupied by smaller ions results in a
crack widens until the glass
compression of the glass. Consider this analbreaks.
(b)
(a)
ogy to visualize the process: The world record
Ceramics, on the other
for the most people crammed into a Volkswahand, tend to be crystalline
gen Beetle, which is a little car, is 25. These
(Fig. 1(b)), and they are
were most likely small people. Now imagine
often characterized by ionic
replacing these 25 people with 25 National
bonds between positive and
Football League linebackers, each weighing
negative ions—even though
in at 350 pounds. To squeeze such large men
they can also contain covainto such a small space would require a fair
lent bonds. When they form
amount of compression. Compression will
crystals, the strong force
always try to make things smaller.
of attraction between ions
In the same way, as the larger potassium
of opposite charges in
ions
push against each other, the glass is
Figure 1. Comparison of the chemical structures of (a) an amorphous solid
made of silicon dioxide (glass), and (b) a crystal of silicon dioxide (ceramic)
the planes of ions makes
compressed. Compressed glass is very
ChemMatters | APRIL/MAY 2015 11
What’s behind a
touchscreen?
As every smartphone user knows, the
screen on a smartphone is far more than
just a tough piece of glass. It is a screen
that responds to your touch—aptly named a
touchscreen—giving you a personal connection to your phone.
There are two basic categories of touchscreens. The first category of touchscreens,
called resistive touchscreens, can be touched
with any type of material and they will still
work. A pencil works just as well as a finger.
You can activate the screen even if wearing
gloves. Resistive touchscreens are found in
an automated teller machine (ATM) and at
Spacer dot or insulating pad
Transparent metal coating
Bottom resistive circuit layer
a resistive touchscreen, it physically indents,
causing the two layers to touch, completing
the circuit and changing the electrical current at
the point of contact. The software recognizes a
change in the current at these coordinates and
carries out the action that corresponds with that
spot. Resistive touchscreens are also known as
pressure-sensitive screens. Only one button at a
time can be pressed. If two or more buttons are
pressed at once, the screen does not respond.
Smartphones
Small amount of voltage is
use the second
applied to the four corners
basic category
of the touchscreen
of touchscreens,
called capacitive
A finger touches
touchscreens
the touchscreen and
(Fig. 4), which
draws a minute
amount of current
are electrical in
to the point of
contact
nature. A capacitor is any device
that stores electricity.
Polyester film
Top resistive circuit layer
The location of the point
of contact is calculated
by the controller
Figure 4. When a finger presses down on a capacitive touchscreen, a very
small electrical charge is transferred to the finger, creating a voltage drop on
that point of the touchscreen. A controller within the smartphone processes the
location of this voltage drop and orders the appropriate action.
Transparent metal coating
Glass, being an
insulator,
does not
Glass or acrylic
conduct electricity.
Even though glass
contains ions, they
are locked into place,
stopping electricity
from flowing through.
So, the glass screen
must be coated with
Finger touch creates contact
between resistive circuit layers
a thin transparent
layer of a conductive
Figure 3. When a finger presses
substance, usually
down on a resistive touchscreen,
Controller
the top and bottom resistive circuit indium tin oxide,
which is usually laid
layers are pressed against each
other, causing the two transparent
out in crisscrossing
metal coatings (left and right)
Controller determines voltage
thin strips to form a
to touch. This leads to a change
between layers to get coordinates
grid pattern.
in the electrical current at the
of touch position
point of contact, which allows a
This conductive
controller within the smartphone
grid
acts as a capacito determine the position of the
tor,
storing
small
point of contact.
electrical charges.
checkout counters in stores, where you sign
When you touch the screen, a tiny bit of this
your name for a credit purchase on the display
stored electrical charge enters your finger—
screen.
not enough for you to feel but enough for
Resistive touchscreens are composed of
the screen to detect. As this electrical charge
two thin layers of conductive material under
enters your finger, the screen registers a voltthe surface (Fig. 3). When you press down on
age drop, the location of which is processed
12 ChemMatters | APRIL/MAY 2015
by the software, which orders the resulting
action.
This tiny bit of electrical current enters your
finger because your skin is an electrical conductor—primarily due to the combination of
salt and moisture on your fingertips, creating
an ionic solution. Your body actually becomes
part of the circuit, as a tiny bit of electricity
flows through you every time you use the
touchscreen on your phone.
www.acs.org/chemmatters
Smartphone technology is evolving at a dizzying pace. You can now use your smartphone
to check your blood sugar, adjust your home’s
thermostat, and start your car. Twenty years
ago, no one envisioned that people would
someday take more pictures with their cell
phones than with their stand-alone cameras. It
is anyone’s guess what will come next. Thanks
to the intersection of chemistry and innovation, the possibilities are limitless.
SELECTED REFERENCES
Gardiner, B. Glass Works: How Corning Created
the Ultrathin, Ultrastrong Material of the
Future. Wired, Sept 24, 2012: http://www.
wired.com/2012/09/ff-corning-gorilla-glass/all/
[accessed Dec 2014].
Collins, K. Study: No Adequate Substitutes Found
for Rare Metals Used in Smartphones. Wired,
Dec 6, 2013: http://www.wired.co.uk/news/
archive/2013-12/06/rare-metals-smartphones
[accessed Dec 2014].
Ask an Engineer. How Do Touch-Sensitive Screens
Work? Massachusetts Institute of Technology,
June 7, 2011: http://engineering.mit.edu/
ask/how-do-touch-sensitive-screens-work
[accessed Dec 2014].
Brian Rohrig is a science writer who lives in
Columbus, Ohio. His most recent ChemMatters
article, “Air Travel: Separating Fact from Fiction,”
appeared in the February/March 2015 issue.
RHONDA SAUNDERS
strong. As a result of this compression, a
lot of elastic potential energy is stored in the
glass, much like the elastic potential energy
that you might find in a compressed spring.
Chemistry Summer Homework
Reading Questions
Directions: After reading the articles, please answer the questions below IN COMPLETE
SENTENCES.
Hot Peppers: Muy Caliente!
1. Describe some of the effects of eating a Moruga Scorpion, one of the hottest chili peppers in the world.
2. What compound causes the “hot” taste we experience when eating chili peppers?
3. How is the hotness of a chili pepper measured?
4. Discuss why capsaicin’s structure makes water a poor choice to cool the heat of a chili pepper in your
mouth.
5. What are some preferred foods/drinks to cool the heat of a chili pepper in your mouth? Why?
6. How do chili peppers generate the feeling of heat without actually increasing the temperature of your
tongue, mouth, and throat?
7. Describe what happens when a capsaicin molecule bonds to a pain receptor.
8. What happens in the body when capsaicin is applied to skin as a pain reliever?
So Tired in the Morning: The Science of Sleep
1. Why was Jilly Dos Santos concerned about the school board’s pending decision?
2. In what ways did Jilly use technology in her quest for more sleep time?
3. Was Jilly successful in her quest to delay the time for opening school? Explain.
4. How does the chemical melatonin help regulate our sleep cycle?
5. Give three examples of positive results reported from school districts that adopted later start times.
6.
If your school has an early start time, what is one way that you can help signal your body that it is time to
go to sleep?
7.
How did understanding the chemistry in this article help Jilly and her friends improve their lives?
8.
Circadian rhythms regulate our sleep schedule. Are other life forms controlled by these cycles?
Smartphones, Smart Chemistry
1. Why will your smartphone be obsolete in a year or two?
2. How many nonradioactive elements can be found in smartphones?
3. What other electronic devices use rare-earth metals?
4. What major challenge faces the cell-phone industry, according to the author?
5. What are the characteristic properties of a glass-ceramic?
6. List the materials of which Gorilla Glass is composed.
7. How does a resistive touchscreen work?
8. How does a capacitive touchscreen work?