How we came to know what we think we know

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How we came to know what we think we know

• ABOUT THE ATOM
• Part 1

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5 people worth noting

• Aristotle
• Democritis
• Dalton
• Thomson
• Rutherford

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Aristotle
Greek Philosopher 384-322 B.C. No underlying
structure to matter. Things could be subdivided
indefinitely.
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Democritus

• 460-370 BC
• There is an underlying structure to matter
• Smallest unit atom,
• from greek a tomos , not cuttable

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• For about 2,000 years, most people accepted
  Aristotles view, because the acceptance of a
  hypothesis back then was based upon the authority
  of a philosopher.
• Aristotle was considered superior, so his
  views win out.
• - However, by the 1500s and 1600s, a revolution
  occurred experimentation became the test of
  credibility, not philosophy!!

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Dalton 1803 , British

• - Atoms are small, indestructible, indivisible
  particles
• Like billiard balls
• Thats why
  7 lbs. of oxygen,
  and 1 lb. of hydrogen 8 lbs. of water

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Thomson 1898 - Cambridge

• Its actually more like Plum Pudding.
• Atoms have subdivisions, namely electrons

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• He came to this conclusion by experimenting with
  a cathode ray tube, positively and negatively
  charged plates.
• --The ray was attracted to the positive plate and
  rebelled by the negative plate

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Rutherford

• Alpha particle vs. Gold Foil experiment 1911
• He put radioactive material (that releases
  positively charged alpha particles) in a box with
  a small slit on one side
• Aimed the slit at super-thin gold foil.
• Most ripped through as expected
• A small amount deflected greatly, and a few even
  bounced back!

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• Because most of an atom is flimsy electrons, most
  of the alpha particles would rip right through
  missing the small, tiny nucleus.
• Since all of the mass is in the small, tiny
  nucleus, when an alpha particle would by chance
  hit it, the particle would be deflected.

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