Ernest Rutherford (1871-1937)
               • Learned physics in J.J.
                 Thomson’ lab.
               • Not...
Rutherford ‘Scattering’

• In 1909 Rutherford undertook a series of experiments
• He fired (alpha) particles at a very thi...
Rutherford’s Apparatus


                                                             beam of alpha particles



         ...
What he expected…




California WEB
Because he thought the mass was
evenly distributed in the atom.

                        -
                               ...
Because, he thought
the mass was evenly                                               -               -
distributed in the...
What he got…
Density and the Atom

            • Since most of the particles went through, the
              atom was mostly empty.
   ...
The Rutherford Atom




                                                              n+




Zumdahl, Zumdahl, DeCoste, Wo...
Niels Bohr
     • In the Bohr Model (1913)
       the neutrons and protons
       occupy a dense central
       region cal...
Bohr Model


    Planetary
      model




   After Rutherford’s discovery, Bohr proposed
that electrons travel in definit...
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Atomic history day #2 1

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Atomic history day #2 1

  1. 1. Ernest Rutherford (1871-1937) • Learned physics in J.J. Thomson’ lab. • Noticed that ‘alpha’ particles were sometime deflected by something in the air. • Gold-foil experiment
  2. 2. Rutherford ‘Scattering’ • In 1909 Rutherford undertook a series of experiments • He fired (alpha) particles at a very thin sample of gold foil • According to the Thomson model the particles would only be slightly deflected • Rutherford discovered that they were deflected through large angles and could even be reflected straight back to the source Lead collimator Gold foil particle source
  3. 3. Rutherford’s Apparatus beam of alpha particles radioactive substance fluorescent screen circular - ZnS coated gold foil Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 120
  4. 4. What he expected… California WEB
  5. 5. Because he thought the mass was evenly distributed in the atom. - - - - -
  6. 6. Because, he thought the mass was evenly - - distributed in the atom - - - - - - - - - - - - - - - - - - - - - - -
  7. 7. What he got…
  8. 8. Density and the Atom • Since most of the particles went through, the atom was mostly empty. • Because the alpha rays were deflected so much, the positive pieces it was striking were heavy. • Small volume and big mass = big density • This small dense positive area is the nucleus California WEB
  9. 9. The Rutherford Atom n+ Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 57
  10. 10. Niels Bohr • In the Bohr Model (1913) the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. • They are not confined to a planar orbit like the planets are.
  11. 11. Bohr Model Planetary model After Rutherford’s discovery, Bohr proposed that electrons travel in definite orbits around the nucleus.
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