History of the Atom

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History of the Atom

• Unit 6 Chapter 18
• Courtney Lewis
• Stapley Junior High School

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3. Democritus (c. 460370 BC)
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4. John Dalton (17661844)
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5. JJ Thomson (18561940)

• Gases in tubes generate streams of particles
  conducted currentcathode ray tube
• Identified the electron, negative charge
• Atom neutral, so atom a positive sphere with
  negative electrons embedded
• plum pudding
• Charges equal and opposite

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6. Ernest Rutherford (18711937)

• Gold Foil Experimentbombarded gold foil with
  radioactive particles, most passed through, some
  bounced back!
• Some parts of atom must be more dense, no longer
  uniform throughout
• New picture of the atom dense at the center,
  electrons on the outside
• Atom mostly empty space, most of mass found in
  the centernucleus with positively charged protons

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7. Niels Bohr (18851962)

• Used light to modify Rutherfords model
• Electrons moving around nucleus in fixed orbits
  w/fixed energy
• Commonly used today

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8. Other Scientists

• Louis de Broglie (18921987) mathematical
  description of electrons in atoms
• James Chadwick (18911974) discovered the
  neutron, another massive particle in the nucleus