P1.1 The Particle Model

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  • P1.1 The Particle Model
    • John Dalton
      • Did experiments to measure how elements combined
      • His model of an atom was a small indestructible sphere
      • He thought that:
        • All the atoms in an element are the same
        • The atoms in one element are different from the atoms in all other elements
    • J.J. Thomson
      • He was investigating rays given out by hot metals called cathode rays, not atoms
      • He discovered the negatively charged electron that come from inside the atom
      • Came up with the plum pudding model of the atom
        • The atom consists of a positive mass
        • The atom has negatively charged electrons embedded in it
    • Ernst Rutherford
      • Discovered some materials emit alpha particles which are positive
      • Shot fire alpha particles at a piece of gold foil
        • Some of the particles rebounded
          • Showed that there is something positive in the middle of an atom
            • Came to the conclusion that there is a nucleus in the middle of an atom
              • Nucleus is made of protons and neutrons
        • Some of the particles went straight through
          • Showed that an atom is mostly empty space
        • Some particles were absorbed
          • Showed that there were electrons
      • Help from two younger scientists, Geiger and Marsden
    • Niels Bohr
      • Problem with Rutherford's model is the electrons would've been expected to spiral into the nucleus
      • Suggested that electrons can only move in fixed orbits
        • Electron shells

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