Subatomic Particles

1
Subatomic Particles

• Beyond Daltons Atoms

2
William Crookes tube

• Crookes took a glass tube, and filled it with
  just a few gas molecules.
• He connected it to a battery, with negative at
  one end and positive at the other.

3
Power On!

• When the current was started, a glow was seen
  coming from the negative end (cathode) and
  flowing to the positive end (anode).

4
Cathode Ray Tube

• When two electrically charged metal plates are
  placed near the tube, the light (now called a
  cathode ray) moved toward the positive plate.
• Opposites attract, so the ray must be negatively
  charged.

5
Enter, J.J. Thomson

• J.J. Thomson worked with cathode ray tubes.
• What he found was that the mass was much less
  than the smallest known atoms.

6
Thomsons Conclusions

• This tiny negative particle was a newly
  discovered thing.
• It had to have come off of the gas atoms in the
  tube.
• This meant that atoms could be subdivided Dalton
  was wrong.

7
Thomsons model of the atom

• Thomson called his new particles negative
  corpuscles.
• Since there were no positive particles that he
  could find, JJ proposed that there was an overall
  positive region.
• He referred to this model as a plum pudding
  model
• Thomson is given credit for discovering the
  electron.

8
So now

• Thanks to Thomson, we now know that an atom has
  pieces.
• Daltons atomic theory had to be revised.
• Soon, other particles would be discovered.

9
Assignment

• Add to previous work
• Page 81 question 8
• Lab Thursday