History of Atomic Theory

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History of Atomic Theory

• Democritus (430 B.C.)
• Greek
• Matter is made of particles called atomos
  indivisible

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History of Atomic Theory

• Aristotle (384 300 B.C.)
• Greek
• Matter is made of four elements
• Earth
• Wind
• Fire
• Water
• People believed this for the next 2000 years

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History of Atomic Theory

• Alchemists (2nd 14th Century)
• First Chemists
• Combine magic and chemistry
• Two Goals
• Make Gold cheaply
• Cure diseases

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History of Atomic Theory

• John Dalton (1808)
• English schoolteacher
• Atomic Theory
• Matter is made up of particles that
• Have spaces between them
• Are compressible
• Combine in whole numbers

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History of Atomic Theory

• Dimitri Mendeleev (1869)
• Russian
• Arranged the known elements into the Periodic
  Table by
• atomic mass
• similar properties

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History of Atomic Theory

• J.J. Thomson (1897)
• English
• Cathode ray experiments
• http//www.chem.uiuc.edu/clcwebsite/video/Cath.mov

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History of Atomic Theory

• J.J. Thomson (1897)
• Discovered electrons
• Moving at 160,000 miles per second
• Negative charge
• Chocolate Chip Cookie Dough Model of Atom (or
  Plum Pudding Model)
• Hypothesized that some part of an atom must be
  positive

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History of Atomic Theory

• Ernest Rutherford (1911)
• English
• Gold Foil Experiment
• showed that
• Most of an atom
• is empty space
• There is a small
• positively charged
• nucleus surrounded
• by negative electrons

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Rutherford Demos

• physical demo
• http//www.shsu.edu/7Echm_tgc/sounds/ruther.mov

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History of Atomic Theory

• Niels Bohr (1914)
• Danish
• Solar System Model of Atom
• Electrons are arranged in energy levels or shells
  like the layers of an onion

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History of Atomic Theory

• Erwin Schrödinger (1926)
• Quantum Mechanical Model
• Electrons are not moving around the nucleus in a
  defined path
• Led to concept of orbitals

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History of Atomic Theory

• James Chadwick (1932)
• Discovered the neutron
• Has a neutral charge
• Same mass as proton (1 amu)
• Atomic mass unit
• Found with protons in the nucleus

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Science as a Process

• Example
• Observations Cathode Ray Tube
• Gold Foil
• etc.
• Hypothesis Charge/Electrons
• Small Nucleus
• Quarks, Leptons etc.
• Theory Particle Theory of Matter
• Helps explain the world we live in.

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• Particle Adventure

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Particle Physics Timeline
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