J. J. Thomson Discoverer of the Electron 1897

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J. J. Thomson Discoverer of the Electron
(1897)
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In J.J. Thomsons experiments he was able to bend
the cathode ray (which travels in a straight
line) by applying either an electric field or a
magnetic field. By finding the displacement of
the ray he was able to calculate electric charge
mass ratio the electron. And later that they
were associated with the proton H
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Using the Cathode Ray Tube, he presented 3
hypotheses

• Cathode rays are charged particles
• These charged particles are part of the atom.
• These particles are the only constituents of the
  atom

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Thomsons Model of the Atom (1904)

• He described his atom as tiny negatively charged
  electrons that are embedded in a cloud of
  positive charge. He imagined the electrons are
  bits of plum in plum pudding.
• Today it is also explained to resemble a
  blueberry muffin or raisin pudding.

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Prior Knowledge Remember it was J.J. Thomson who
identified that the atom was composed of positive
and negative charges and had proposed that the
atom was a solid mass of these particles.
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Significant Contributions to Atomic Theory 1900
-gt 1930

• 1909 11 E. Rutherford, H. Geiger
• 1913 R. A. Millikan
• 1913 H. Moseley
• 1919 N. Bohr
• 1931 J. Chadwick

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1909 1911 Ernest Rutherford and Hans Geiger
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The Gold Foil Experiment
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It was quite the most incredible event that
has ever happened in my life. It was almost as
incredible as if you fired a 15 inch shell at a
piece of tissue paper and it came back and hit
you.
Ernest
Rutherford
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Robert Milliken (1868 1953)
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• Milliken's Chamber

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Henry Moseley (1887 1915)
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Mosleys X-ray Experiment
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Moseley's Graph of Atomic Number
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Neils Bohr (1885-1962)
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No ..no . You are not thinking you are only
being logical !! - Bohr 
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Neils Bohr Atomic Model Niels Bohr applies
quantum theory to Rutherford's atomic structure.
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James Chadwick (1891 - 1974)
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Old Explanation of Atomic Mass
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New Explanation of Atomic Mass
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The End of Group 3s Presentation

• Next
• 1930s -gt
• Closing the book on Atomic Theory?