Physics 10
The Atomic Nature
of Matter
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⇒ The idea that matter is made up of tiny
particles called atoms was first proposed by
the Greeks about 2500 years ago.
⇒ Aristotle didn’t believe in the idea of
atoms; he believed that all matter on Earth
was made up of 4 elements: earth, water, air,
and fire.
⇒ Aristotle’s ideas about matter lasted for
more than 2000 years!
⇒ All matter, even solid matter, is made
up of tiny particles called atoms.
⇒ Atoms themselves, are mostly empty
space. About 99.999% of an atom is
empty space.
⇒ This means that our bodies, even
though they appear solid, are actually
about 99.999% empty space!
⇒ The idea of the atom was revived in the
early 1800’s by a schoolteacher named John
Dalton.
⇒ Dalton, however, didn’t have any
convincing evidence for the existence of
atoms.
⇒ The next breakthrough came in 1827, when
a botanist named Robert Brown noticed that
grains of pollen in water continually moved as
if they were alive.
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Brownian Motion
Brownian Motion
⇒ Brownian motion arises because atoms
(way, way too small to see) hit the grains of
pollen and cause them to move.
Robert Brown
Brownian Motion
⇒ In 1905, Albert Einstein explained Brownian
motion using atoms.
⇒ Einstein used statistical analysis to predict
the masses of atoms and to predict the motion
of the grains of pollen.
⇒ Finally, in the early 1900’s, most scientists
came to believe in the idea that all matter was
made up of tiny particles called atoms.
The Elements
⇒ As of 2002, scientists have discovered 118
different kinds of atoms. Each type of atom is
called a chemical element.
⇒ Only 88 of the 118 known elements occur
naturally. The other elements were made in
nuclear accelerators.
⇒ Living things are made up of mostly 4
elements: hydrogen (H), carbon (C), oxygen
(O), and nitrogen (N).
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The Elements
⇒ The early universe (soon after the Big
Bang approximately 15 billion years ago),
was composed entirely of hydrogen with a
very, very small amount of helium (and
possibly some lithium).
⇒ All other elements up to iron were formed
in the deep interiors of stars by nuclear fusion.
⇒ All elements heavier than iron were
formed in supernovae (when giants stars
explode).
The Elements
⇒ After the stars exploded, the elements that were
fused in the stars interiors were released to the
universe where they could then form planets and
other matter.
⇒ Except for some of the hydrogen and small
amounts of helium (and possibly lithium), all of the
elements in the universe are the remnants of stars
that exploded billions of years ago.
⇒ We are stardust!
Properties of atoms
Properties of atoms
Atoms are incredibly small.
Atoms are numerous.
⇒ The size of an atom is to the size of an
apple as the size of an apple is to the size of
the Earth.
⇒ If you want to imagine an apple full of
atoms, think of the Earth packed solid with
apples!
⇒ In order to see an atom in a tiny drop of
water, you would have to blow up the drop of
water until is is more than 15 miles wide.
⇒ In a single thimble full of of water, there
are about 1023 atoms.
(100,000,000,000,000,000,000,000 atoms)
(One hundred thousand, billion, billion atoms)
⇒ If you counted by a thousand every second
(1000, 2000, …), it would take you about 3
trillion years to count the number of atoms in
one thimble full of water!
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Properties of atoms
Properties of atoms
Atoms are ageless.
Atoms get around.
⇒ Many of the atoms in your body are almost
as old as the universe and were created when
giant stars exploded billions of years ago.
⇒ Atoms are constantly being shared and
recycled among all living and nonliving things
on the Earth.
⇒ Some of the atoms in your body were
probably once a part of me.
⇒ All atoms are constantly in a state of motion,
even atoms that make up solid objects. Atoms
in a gas are moving the fastest, and then atoms
in a liquid, and finally atoms in a solid.
⇒ Atoms of gas in the atmosphere diffuse
rapidly, so the air that you breath today could
have been on the other side of the country
only a couple of days ago.
Properties of atoms
Properties of atoms
Atoms get around.
Atoms get around.
⇒ There are about as many atoms in a breath
full of air as there are breath fulls of air in the
atmosphere.
⇒ There have been approximately 100 billion
people who have ever lived on the Earth since
day one.
⇒ This means that given enough time (a few
years), all the atoms from one of your exhaled
breaths will have evenly distributed themselves
throughout the entire atmosphere.
⇒ Each breath you take contains about ten
thousand, billion, billion atoms.
⇒ This happens with every breath you take.
⇒ This means that with every breath that you
take, you breathe in atoms that were once a part
of everyone who has ever lived.
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Exercise 15
How many atoms are in a molecule
of ethanol, C2H6O?
⇒ Nine. There are 2 atoms of carbon, 6
atoms of hydrogen, and 1 atom of
oxygen.
Antimatter
⇒ every particle has a partner particle
called an antiparticle
⇒ antiparticles have the same mass as a
normal particle but the opposite charge
Examples: electron and positron
proton and antiproton
Antimatter
Dark Matter
antimatter ⇒ matter composed of atoms
with negative nuclei and positive electrons
(positrons)
⇒ scientists can calculate how much mass
should be in distant galaxies from the
gravitational force they exert on other
objects
⇒ if matter and antimatter came into contact,
they completely annihilate each other and
transform into energy (E = mc2)
⇒ an equal amount of matter and antimatter
is consumed in the process
⇒ when we add up all the visible mass, it is
only 10% of what it should be
⇒ the 90% of the mass that can’t be seen is
called dark matter
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