Summary

• Atoms proposed at least since classical Greece - Democrites - 5th Century BC

• Appealing way to understand properties of matter

  • Solid, Liquid, Gas

• Strong evidence in chemistry

  • Compounds formed from “elements” - definite ratios

• Atoms explain heat, behavior of gasses

  • Absolute zero of temperature

• But what are atoms made of?

  • Radiation shows that atoms change, Bequerel & Curie

• Electron discovered by Thomson (1897)

• Planetary Model with Nucleus : Rutherford (1911)

  • Electrons around a heavy positive nucleus

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