History of the Atomic Model

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History of the Atomic Model

• Seeing the Invisible

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A Big Debate

• Can matter be divided into smaller and smaller
  pieces forever?

What do you think?
YES!
NO!
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Atomic Models Greek

• Democritus (460-370 B.C.) ? Matter can not be
  divided forever
• Smallest piece atom
• (Gk atomos not to be cut)
• He had no way of knowing what atoms looked like!

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The word atom comes from a Greek word that
means unable to be cut
and you kept on cutting the leftover piece in
half
Imagine you had a piece of gold that you then cut
in half
and then you cut one of these smaller pieces in
half
Gold
Go
ld
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The word atom comes from a Greek word that
means unable to be cut
and kept going
Eventually you would have 1 piece of gold left.
If you cut it in half, you wouldnt have gold any
more youd have something else. This tiny,
tiny single piece of gold is called an atom of
gold. An atom is the smallest particle of an
element that acts like the element.
and kept going
and kept going
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Democritus

• He hypothesized that atoms were
• Small Hard
• Diff in shape size
• Infinite
• Always moving
• Capable of joining

But no one believed him!
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Clicker Content Check
Questions 1 2
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Time Goes By

• 1600s-1700s Key experiments occur which support
  Democrituss ideas.
• Robert Boyle (1627-1691)
• Antoine Lavoisier (1743-1794)

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Dalton (1766-1844)

• English chemist and school teacher
• Did many experiments, studying gasses and
  proposed atomic theory

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Atomic Models Dalton

• 1. Elements composed of atoms atoms are
  indestructible
• 2. Atoms of the same element are exactly alike
• 3. Atoms of different elements are different
• 4. Compounds formed by joining 2 atoms

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Clicker Content Check
Questions 3, 4 5
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Atomic Models J.J. Thompson

• Passed electricity through an uncharged gas
• The gas gave off rays to show it was NEGATIVELY
  charged
• How?
• Negative charges must come from inside the atom!
• gt Electrons!

Click here for more on the Discovery of the
electron
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But wait

• How can an atom be NEUTRAL if it is full of
  negatively charged particles (electrons?)

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Atomic Models J.J. Thompson

• The atoms are neutral How?
• charges must be present to balance - charges
• - lumped in a cluster he said looked like
  plum pudding

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Thompsons Model
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Clicker Content Check
Questions 6, 7, 8 9
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Atomic Models Rutherford

• Passed Charged Particles through gold foil
• Most passed right through
• Atom is mostly empty space
• Some bounced off at odd angles
• Nucleus must be
• Calculate size of nucleus

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Rutherfords Gold Foil Experiment

start experiment
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Rutherfords Work

What's Different This Time???
start experiment
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Rutherfords Model
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Clicker Content Check
Questions 10 11
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Okay

• So the atom is made up of positive and negative
  particles.
• Where are the electrons found in the atom?

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Atomic Models Bohr

• Electrons are found in specific energy levels
• Like planets around the sun

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Bohrs Model
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Atomic Models Wave

• Electrons move so fast that it is impossible to
  determine their location
• Move in all directions around the nucleus

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Clicker Content Check
Questions 12 13