History of Elementary
Particles
• Greeks invented concept
of Atom approximately
Let’s call
2500 years ago
it … an
atom.
• Later thought matter was
made up of
fire,water,air,earth
Definition of Atom:
Smallest particle of an
element that retains the
chemical identity of the
element
400 B.C
1492 A.D.
1700 A.D.
0
Greeks invent
concept of atom
Columbus Discovers About late 1700s some
the West
new ideas through
experiments came to be
discussed.
What Were Some of the Results
of These Experiments?
• Law of Conservation
of Mass
• Law of Constant
Composition (also
called Law of Definite
Proportions)
• Law of Multiple
Proportions
Law of Conservation of Mass
+
=
• Matter is not created or destroyed in a chemical
reaction
Law of Constant Composition
or Law of Definite Proportions


OR
A chemical has exactly the
same proportions no matter the
size
Example:
Doesn’t matter if 3 crystals
or a jar of salt
 66 % of mass is always
Chloride
 33 % of the mass is always
Sodium

Same “Proportions”, Same
“Composition”
Example of the Law or Constant
Composition (Law of Definite
Proportions)




What would happen if I take a
small bite of cake or a GIANT bite
of cake?
Would it taste the same?
The “Composition” of the cake is
the same all the way through.
A COMPOUND (like sugar or salt)
is the SAME no matter where you
find it, or how much you have.
The Law of Multiple Proportions


Chemicals always
combine in ratios of small
whole numbers
Example:
H2O - Water
 There will always be a 2
to 1 ratio between
Hydrogen and Oxygen
 Whether you have one
water molecule or an
ocean full water

Law of Multiple Proportions
Example



Molecules are not made
up of “1/2” or an atom or
pieces of an atom
This proportion might be
1: 3/4
Remember WHOLE
numbers.
1492
400 B.C
0
Greeks
invent
concept of
atom
.
A.D
Late
1700s
1803
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Columbus
Discovers
the West
New
Experiment
s and Laws
John Dalton and the
Atomic Theory of Matter
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• At age 12 Dalton was
teaching the local
school
• Was reading Newton’s
Book in Latin
• Color Blindness was
called “Daltonism” for
a lengthy time
John Dalton - 1803
Atomic Theory of Matter
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• UNIQUE - Atoms are unique
from other elements
• GROUPS - Compounds are
combined in small whole
numbers.
• LAW OF CONSERVATION
OF MATTER - atoms are
rearranged or combined but
not destroyed
• INDIVIDUALS - Elements are
composed of atoms (smallest
building block)
1492
400 B.C
0
.
A.D
Late
1700s
1803
Almost
1900
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Greeks
invent
concept of
atom
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Columbus
Discovers
the West
New
Experiments
and
Laws
John
Dalton
and the
Atomic
Theory
of
Matter
Thompson
Discovers the
Electron
John Thompson, circa 1900
Discovers Electron
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• Prior to this a man
named Faraday
hypothesized that
atoms had a charge
• Thompson
hypothesized that the
electrical charge was
negative and that the
particle had mass
Thompson’s Experiment using a
Cathode Ray Tube (CRT)
• Elements are neutral (no
charge)
• Thompson could alter path
of particles by using
magnets (that showed they
had a charge)
• The type of magnet
showed that it had a
negative charge
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battery
magnets
Thompson (continued)
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• Now Thompson knew
that there was a
negative particle in the
atom but where???
I’m tired…
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1492
400 B.C
0
.
Late
1700s
A.D
Almost 1900
1803
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Greeks
invent
concept of
atom
Columbus
Discovers
the West
John
Dalton
New
and the
Exper-Atomic
imentsTheory
of
and
Matter
Laws
1910
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Thompson Discovers
the
Electron
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Rutherford
discovers
the nucleus
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• Rutherford was not a
brilliant man, often
getting lost in Math,
not terribly clever in
experimentation, just
tenacious and openminded
• His assistant was Hans
Geiger, inventer of the
“Geiger Counter”
Rutherford’s Model of the Atom
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Rutherford hypothesized that the
inside of an atom was a mass
with bits of matter mixed in.
Yum
Yum!
He called the
model the
“Plum
Pudding”
Model
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Rutherford’s Gold Foil
Experiment
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• Rutherford set up very
thin gold foil as a
target
• “shot” positive
charges to foil
• Watched patterns that
positive particles made
Results of the Rutherford’s
Experiment
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• Alpha particles (positive
particles) went through
• Only sometimes
‘bounced” back
• Proved that nucleus was
mostly empty space
• Called center “nucleus”
Rutherford’s NEW Model of the
Atom
Rutherford hypothesized that the
inside of an atom was a small
mass called a nucleus.
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Yuck!
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Rutherford’s Gold Foil
Experiment Animation
http://micro.magnet.fsu.edu/electromag/java/rutherfor
d/index.html
What Do I Need to Remember ?
•
•
•
•
•
Greeks came up with Atom
3 Laws that started it all…
Dalton - Atomic Theory of Matter
Thompson CRT Experiment
Rutherford’s Gold Foil Experiment
Memory Helps
• Rutherford
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–
–
–
–
A Ford Truck carrying
Plum Pudding
Covered in Gold Foil
Discovered the
Nucleus
I’d “Rather” have a Ford (Rutherford)
3 Laws
Always
One You
Already
Know…
Law of
Conservation of
Matter
Whole #s
Law of Definite
Proportions
Law of Multiple
Proportions
Thompson Cathode Ray Tube
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Daltons Theory of Matter
• UGLI
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– U Unique (Elements are..)
– G Groups (They are grouped
in small whole number groups
Law of Multiple Proportions)
– L Law of Conservation of
Matter
– I Individual (Matter is made
up of individual atoms)