AntoineLaurent Lavoisier 17431794

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Antoine-Laurent Lavoisier 1743-1794
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Monsieur Lavoisier et sa femme, 1788 By
Jacques-Louis David She was 13 when he married
her!
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Activity Pool your knowledge and make a list of
substances and decide if each is an element,
mixture or compound, and what elements are
involved. Water Oxygen Air Carbon
dioxide Propane Iron Rust Carbon Diamond Gasoline

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There had always been a natural interest in
substances, what stuff is made of. Obviously
substances can change, iron turns into rust, wood
burns into smoke. Not surprisingly, the idea of
turning something into gold got high priority for
a long time. According to Bryson, what did early
chemists try to make into gold? What did the
Swedes end up being especially good at
producing? What happened to Carl Scheele
personally? professionally?
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Lavoisiers (tax collector, like the Sheriff of
Nottingham) did lots of experiments and they
must have done a lot of careful thinking
too. Discovered that iron did not just turn into
rust, it gained mass. Basically their work, and
the experiments and thinking of many others led
to a realization that when substances convert
into different things by chemical changes, it is
basically a recombining of some fundamental
substances Elements. There are about 120
elements. Each is made up of tiny little things
called atoms (in a later chapter, youll read how
tiny they are). Each element has its own
special type of atom.
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But there are a lot more than 100 substances.
All the other substances are combinations of
elements. One way to combine elements is to just
mix them up. For example, the air in this room
is a mixture of different kinds of gases mostly
nitrogen (80) and oxygen (20), and a small
amount of other gases like carbon dioxide . So
air is a mixture. Ignoring the details of the
minor parts, it has a lot of nitrogen and oxygen
atoms buzzing around and bumping into one another
and into the wall sand into us, but the atoms of
oxygen are not connected to the atoms of
nitrogen. Mixture.
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A lot of substances are made of elements
combined in a different way The atoms themselves
get stuck together. So, e.g., carbon dioxide
is made by combining atoms of oxygen with atoms
of carbon into little clumps, each one made of
two oxygen atoms combined with one carbon atom
(hence name carbon di-oxide, and symbol CO2).
These little clumps are called molecules, and
substances made of molecules of different
elements are called compounds. Most of the
substances around you are compounds or mixtures
of compounds.
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So what the Lavoisiers figured out was that the
element iron did not just change when it rusted.
It actually combined with oxygen into a new
compound (rust) made of molecules. Each rust
molecule is a clump of oxygen atoms plus iron
atoms. And rust is just a big bunch of these
molecules. When something combines into a
compound with oxygen, it has a special name
oxidation. What does it means if you see INOX
on a knife or kitchenware?
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I want to give special consideration to
oxidation, because it is so important in how life
works on our planet, and how life has even
changed our planet, in other words, the big
themes of this course. Anyone know other
examples of oxidation besides rusting?
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Burning! Usually oxidation needs a little
push to get the atoms to start combining
(otherwise it would have happened already!).
Iron needs a little wetness, burning requires
bit of heat to start. But once it gets going,
it generates heat. You would have to use a lot
of energy to reverse the process, in other words
to pull the oxygen apart from the other
elements. This is important Oxidation gives
off heat energy when it happens, but you need to
add energy to reverse it.
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The main way we get energy to use is by oxidizing
dead plant and animals Burning wood in a
fireplace, burning coal in an electricity plant,
burning gasoline in a car. Its all the same
thing Oxidizing compounds from plants made of
carbon and hydrogen, and getting energy.
Inside, our bodies need energy to live. We get
the fuel from eating plants or other animals,
lots of compounds with lots of H and C. The way
we convert that stuff into energy that our bodies
can use is by oxidizing it. Activity How do we
get the oxygen into our bodies to oxidize the C
and H compounds that we ate? What are the main
compounds produced in our bodies when we oxidize
the stuff? How do we get rid of it?
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Antoine-Laurent Lavoisier conducts an experiment
on human respiration in this drawing made by his
wife, who depicted herself at the table on the
far right. Courtesy Edgar Fahs Smith Memorial
Collection, Department of Special Collections,
University of Pennsylvania Library.
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How do we get the oxygen into our cars to oxidize
the C and H compounds that we pump into our gas
tank? What are the main compounds produced when
we burn gasoline in a car to get energy? How do
we get rid of it?
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Burning dead tree parts Wood
(a mixture of substances, mostly
C and H compounds)
Air, (with 20 active O2 )
CO2 and H2O PLUS
ENERGY
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Making energy in our bodies Food
(dead plant and animal bits,
mostly C and H compounds)
Air, (with 20 active O2 , gets in via breath and
blood stream )
CO2 and H2O PLUS
ENERGY
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Making energy in an auto engine gasoline
(left over from
ancient organisms, mostly C and H compounds)
Air, (with 20 active O2 )
CO2 and H2O PLUS
ENERGY
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There is a down-side to all this useful
oxidation Damage to our bodies by oxygen.
Environmental effects of too much CO2.
Eventually, the oxygen would get used up.
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Aging your body Bits of your cells
(mostly C and H compounds)
Oxygen from air, (with 20 active O2 , gets in
via breath and blood stream )
CO2 and H2O PLUS
ENERGY (But I will
pass on this)
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NASA 2005 could be warmest year recorded
Friday, February 11, 2005 Posted 1126 AM EST
(1626 GMT)
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Most living things are made up mostly of
compounds of the elements carbon hydrogen (C
H). But C and H tend to get oxidized by all the
oxygen around. To make living things the food
for living things, something must strip the H
and C off of the H2O and the CO2. (plus put O2
back in the air) Un-burning! Burning gives off
energy -- Un-burning uses energy. Plants get
energy from sunlight and then they use it to
reverse the oxidation. They take water (H2O)
through their roots and carbon dioxide CO2 from
the air and make compounds mostly made of C and
H, the stuff that all living things are made
of. PLUS they put the oxygen into the atmosphere
for us to breathe! SAY THANKS TO A
GREEN PLANT TODAY!
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Un-Burning in a plant Wood other parts
(a mixture of substances, mostly C and H
compounds)
O2 into the Air
CO2 and H2O Plus energy
from the Sun
Same as burning, but it goes from left to
right! Also, it uses energy instead of giving it
off!
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Remember what a big deal geology was amoung rich
folks during the 1700s and 1800s? Chemistry
(except for the Lavoisiers and a few others) was
not popular among the leisure classes (rich
people). Why was chemistry different from
geology?
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It was viewed as an industrial thing for the
working classes to deal with. Also, it was
viewed as cheap entertainment -- substance
abuse! (laughing gas)
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Benjamin Thompson of Woburn, Mass. Pronounced
how? Curious that a Tory has statue in front of
Woburn public library. Whom did he
marry? He died, universally esteemed by all but
his former wives, in 1814. As Count
Rumford! Why does Bryson mention Count Rumford?
What was his contribution to Chemistry?
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Not your typical Woburn kid.
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By 1900, Chemistry was in pretty good
shape. Successful industrial science. Main point
of chemistry seemed to be that substances do not
get created and disappear, but rather recombine.
Conservation of atoms. That is why Lavoisiers
saw rust be more massive than the iron O got
added. More generally Conservation of
Mass But something was not fitting that
picture Radioactive elements were discovered
(esp. Marie Curie), and then Rutherford realized
that as radioactive elements gave off energy they
were gradually changing into other elements.
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Marie Sklodowska Curie 1867-1934 In 1995 her
ashes were transferred to the Pantheon, the first
women entombed with the greats of
France. Radioactivity is so 20th century! So
much for 19th century conservation of mass.
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Radioactivity Unlike regular chemistry, elements
can get transformed into other elements.
WOW! For example, Uranium turns into Lead, and
gives off heat and dangerous radiation.
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So much for Conservation of Atoms. The main
principle of Chemistry turned out to be false, at
least in these special cases. Usually, for
practical purposes, it is okay though, but only
where radioactive effects are not too
important. Conservation of mass turned out to be
wrong too during these atomic transformations,
Mass can turn into energy!
Emc2 Energy source Drives stars
remember that is how the heavier elements were
formed. Explains how Earth can be very old
and still be warm inside (remember Kelvin?)
Source of useful energy (nuclear reactors), but
careful This stuff is dangerous Both Pierre
and Marie Curie died of it.
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Summary of oxidation Metals rust Other examples
breathing, cars, electric plants (except
nuclear), all producing CO2 H2O. Photosynthesis
is just the opposite uses CO2 H2O to make
compounds of C and H, in other words wood, coal,
gasoline, other fossil fuels, and most of the
other things we burn. It also makes the oxygen
needed for the burning. That is why Earth has an
atmosphere with plenty of oxygen for us. If all
the CH stuff were burned again (undoing the
photosynthesis), we would have no more oxygen to
breathe! Also, the burning puts CO2 into the
atmosphere which affects capture of solar heat
(Greenhouse effect)! Photosynthesis (by
plants) gets rid of the excess CO2 . Animals
have helped get rid of it too shells make
carbonates (Fossils!)
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But oxygen is so active, it wants to oxidize
everything Forest fires! Houses burn down!
Germs get killed! Living things need oxygen, but
it is also dangerous. Our living tissue gets
damaged! (Anti-oxidant skin cream and vitamins
can help prevent this kind of aging somewhat, but
dont believe advertising.)