1. What’s Going on in There?
Subatomic Particles
Vocabulary:
nuclear model
proton
vacuum
neutron
electrode
J.J. Thomson
electron
cathode ray tube (CRT)
Thomson’s experiment
Plum Pudding Model
Robert Millikan
Oil Drop Experiment
Ernest Rutherford
Gold Foil Experiment
nucleus
“The Kiss”, Gustov Klimt, 1908

2. - + Take a look Facts: The tube contains a vacuum.
There is a positive electrode on one side of the tube and a negative electrode on the other side of the tube.
The electrodes are hooked up to a 10,000V electrical source.
A magnet is the object in the person’s hand. - +

3. So what’s going on in there?
Take a look
So what’s going on in there?

4. Take a look

5. J.J. Thomson (1897 / England)
Thomson concluded that the beam contained “corpuscles” that were small particles inside atoms and were negatively charged. We now call them electrons
Thomson knew atoms were neutrally charged, but couldn’t find the positive particle.

6. Cathode Ray Tube, CRT, demonstrated properties of electrons
Thomson’s Experiment
Cathode Ray Tube, CRT, demonstrated properties of electrons

7. Thomson’s Atomic Model
Determined that the negatively charged particles have same mass and amount of charge regardless of the type of atom.
Developed the “Plum Pudding” model of the atom with negative electrons in positive sphere.

8. Robert Millikan (1909 / America)
Used “Oil Drop” experiment to find the charge of the electron (q = 1.60x10-19 C)
He did this by carefully balancing the gravitational and electric forces on tiny charged droplets of oil suspended between two metal electrodes.

9. Ernest Rutherford (1911 / England)
That’s good stuff!
Used Gold Foil Experiment
He knew that atoms had positive and negative particles, but could not decide how they were arranged.
Conducted an experiment to isolate the positive particles in an atom. Decided that the atoms were mostly empty space, but had a dense central core.

10. Gold Foil Experiment

11. Gold Foil Experiment

12. Ernest Rutherford’s “Nuclear” Atomic Model
Dense, positive nucleus surrounded by negative electrons

13. James Chadwick (1932/ England)
Mass of atom was too high to contain only protons and electrons

14. James Chadwick (1932/ England)
The unknown radiation emitted from the beryllium had no charge but the same mass as the protons. Must be an undiscovered neutral particle in the atom. This was the neutron.

15. James Chadwick’s Atomic Model
Revision of Rutherford’s Nuclear Model

16. electron e- elec. cloud -1 1/1840 9.11 X 10-28 proton p nucleus +1 1
Particle
Symb
Location
Relative
charge
Relative mass (amu)
Actual mass (g)
electron e-
elec. cloud -1
1/1840
9.11 X 10-28
proton p
nucleus +1 1
1.67 X 10-24
neutron n

17. Quiz What particles have opposite charges?
What particles have the same mass?
What particles are located in the nucleus?
What particles would be the easiest to leave the atom?
What particles attract each other?