history of elementary particles. greeks invented concept of atom approximately 2500 years ago later...
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History of Elementary Particles
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• Greeks invented concept of Atom approximately 2500 years ago
• 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
Let’s call it … an atom.
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400 B.C
0
1700 A.D.1492 A.D.
Columbus Discovers the
West
Greeks invent concept of atom
About late 1700s some new ideas through experiments came to be discussed.
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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
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Law of Conservation of Mass
• Matter is not created or destroyed in a chemical reaction
+ =
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Law of Constant Composition or Law of Definite Proportions
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
OR
Same “Proportions”, Same “Composition”
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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.
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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
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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.
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400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton and the Atomic Theory of
Matter
New Experiments and Laws
1803
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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
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John Dalton - 1803Atomic Theory of Matter
• 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)
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400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton
and the
Atomic Theory
of Matter
New Exper-iments and Laws
1803
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Almost 1900
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Thompson Discovers the Electron
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John Thompson, circa 1900 Discovers Electron
• 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
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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
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Thompson (continued)
• Now Thompson knew that there was a negative particle in the atom but where???QuickTime™ and a
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I’m tired…
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400 B.C0
Late 1700s
1492
A.D.
Columbus
Discovers the West
Greeks invent concept of atom
John Dalton
and the
Atomic Theory
of Matter
New Exper-iments and Laws
1803
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Almost 1900
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Thomp-son Dis-covers the Electron
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Rutherford discovers the nucleus
1910
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• Rutherford was not a brilliant man, often getting lost in Math, not terribly clever in experimentation, just tenacious and open-minded
• His assistant was Hans Geiger, inventer of the “Geiger Counter”
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Rutherford’s Model of the Atom
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Yum Yum!
Rutherford hypothesized that the inside of an atom was a mass with bits of matter mixed in.
He called the model the
“Plum Pudding”
Model
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Rutherford’s Gold Foil Experiment
• Rutherford set up very thin gold foil as a target
• “shot” positive charges to foil
• Watched patterns that positive particles made
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Results of the Rutherford’s Experiment
• Alpha particles (positive particles) went through
• Only sometimes ‘bounced” back
• Proved that nucleus was mostly empty space
• Called center “nucleus”
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Rutherford’s NEW Model of the Atom
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Yuck!
Rutherford hypothesized that the inside of an atom was a small mass called a nucleus.
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Rutherford’s Gold Foil Experiment Animation
http://micro.magnet.fsu.edu/electromag/java/rutherford/index.html
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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
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Memory Helps
• Rutherford– A Ford Truck carrying
– Plum Pudding
– Covered in Gold Foil
– Discovered the Nucleus
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I’d “Rather” have a Ford (Rutherford)
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3 Laws
One You Already Know…
Always
Whole #s
Law of Conservation of Matter Law of Definite
Proportions Law of Multiple Proportions
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Thompson Cathode Ray Tube
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Daltons Theory of Matter
• UGLI– 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)
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