J. J. Thomson Discoverer of the Electron (1897)

1
J. J. Thomson Discoverer of the Electron
(1897)
2
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
3
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

4
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.

5
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.
6
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

7
1909 1911 Ernest Rutherford and Hans Geiger
8
The Gold Foil Experiment
9
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
10
Robert Milliken (1868 1953)
11

• Milliken's Chamber

12
Henry Moseley (1887 1915)
13
Mosleys X-ray Experiment
14
Moseley's Graph of Atomic Number
15
Neils Bohr (1885-1962)
16
No ..no . You are not thinking you are only
being logical !! - Bohr 
17
Neils Bohr Atomic Model Niels Bohr applies
quantum theory to Rutherford's atomic structure.
18
James Chadwick (1891 - 1974)
19
Old Explanation of Atomic Mass
20
New Explanation of Atomic Mass
21
The End of Group 3s Presentation

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