Title: Atomic Structure—The Rutherford Experiment
Purpose:

to use indirect measurement to determine the size and shape of an object

to duplicate Rutherford’s Gold Foil Experiment.
Background: Read about the Rutherford Gold Foil experiment in your textbook
Materials: Virtual ChemLab Environment
Procedure:
1. Start Virtual ChemLab.
2. Enter the General Chemistry Laboratory (Click Guest)
3. Open the Quantum Lab by clicking on the lab table to the far right of the lab. There is a
starburst ---- symbol on the lab table.
4. READ THE ENTIRE EXPERIMENT BEFORE YOU START
5. You will need to set up the optics table for the Rutherford experiment:
a. Go to SOURCES on the top shelf in the Stockroom area to enter the Stockroom.
b. Click on the clipboard that is on the right wall, just above the help bell.
c. Now Click on Preset Experiment 2: Rutherford Backscattering.
This will set up the lab for you!
d. Click the green Return to Lab arrow.
You should see a large green screen with a large, light green dot in the center
and several small moving green dots. This is the Phosphor Screen.
e. (If you hit the off button, the screen will disappear and you will see the entire
setup: Alpha Source, Metal Foil Sample Holderv(Au), and the Phosphor Screen.
f. Move the cursor over the different items so you can identify them!
6. Now that the setup is complete, turn on the Phosphor Screen.
7. The large dot in the center represents alpha particles moving straight through the metal
foil or slightly deflected. The smaller dots represent alpha particles being deflected at
small angles. The particles are being emitted from the alpha particle at a rate of 10 6 alpha
particles/second.
8. Click the persist button (The button with the dotted arrow). This will allow you to see the
alpha particle traces without them disappearing!
9. Estimate the number of particles hitting the screen in 60 seconds. Record your estimate
in Data Table 1. Repeat.
10. Click on the gray lab table to move it to the front. Grab the phosphor screen by its base
and move it to the spotlight in the top right corner. The persist button should still be on.
Estimate the number of hits in 60 seconds. Repeat.
11. Move the phosphor screen to the other spotlights and estimate the number of hits/minute
in each of the spots. Make sure you record your observations in Data Table 1. Determine
the average number of hits/minute for each location.
12. Graph average # hits/minute vs detection angle (Use Graph Pad or Create-a-Graph).
13. Now, turn off the phosphor screen and double-click the base of the metal foil sample
holder to move it to the Stockroom window. Click on Stockroom to enter and, once in the
Stockroom, click on the Metal Foil sample box on the top shelf and select sodium (Na).
Click the green Return to Lab arrow.
14. Move the Na—metal sample holder to the spotlight in the center of the lab table and turn
on the Phosphor Screen. Record your observations.
15. Repeat steps 12 and 13 with several other metals, including those listed in Data Table 2.
Record the mass number of each of these metals in the data table as well.
Judith Nuño
Chemistry
2006/2006
Results:
Data Table 1: Alpha Particle Detection with Gold Foil
Location of Detector
Number of Hits/Minute
(estimate)
Screen Image
Trial 1
Trial 2
Average*
Baseline
(Center of Table)
0o
Top Right
45o
Top Middle
135o
Top Left
150o
Bottom Left
150o
Bottom Middle
135o
Bottom Right
45o
*Determine the Average # hits/minute for the same angles BEFORE graphing.
Data Table 2: Alpha Particle Detection with Various Metal Foils
Metal
Mass #
Screen Image
Na
Al
Ca
Co
Cu
Ag
_______
________
Judith Nuño
Chemistry
2006/2006
Discussion:
1. Summarize the similarities and differences between Thomson and Rutherford’s atomic
models.
2. Describe the different patterns seen on the phosphor screen when it was placed at
different locations relative to the alpha source and gold foil.
3. Discuss how the results of this Rutherford simulation disproved Thomson’s plum pudding
atomic model.
4. Use the results of the experiments with metals other than Au to explain why Rutherford
used gold foil in his experiments.
Conclusion: None required for this lab.
Reflection: Personal statement about what you learned from the simulation.
Save a copy of this lab writeup in your folder and in your Virtual Lab NB Folder on the Shared
Folder. (You may email this lab writeup to jdenuno@mhs-la.org and I will save it in your Virtual
Lab NB)
Print out a copy of this lab and tape it into your Lab NB!
Judith Nuño
Chemistry
2006/2006