# Module 1 Lab 3: Quantum Mechanics and Rutherford Scattering

Learning Objective:

You will contrast two different models of the atom. You will obbserve and record results of a famous experiment using a simulation. Additionally, you will analyze the scattering effect using different atoms and relate the results of the scattering experiment to later quantum theories.

Prerequisites: Complete reading Chapters 4, 5, and S4. Engagement in Module 1 Content: Quantum Physics.

### Materials Required:

• Computer and internet access
• Colored pencils
• Two pieces of blank paper
• Protractor
• Graphing software like Excel or Tables in Word

Total Time Required: Approximately 2-3.5 Hours

**If you use any outside sources beyond the sites found below, make sure to use proper citations.

Procedure

A. Either open the Rutherford applet from the link in your Quantum Mechanics Lab manual or from this link Rutherford Scattering Simulation, you can chose to download or run.

B. Choose the Plum Pudding Atom by double clicking on it.

C. Before Rutherford’s famous experiment, the popular model for the atom envision it like “Plum Pudding “. It had positive charges spread throughout the atom (red), with negative electrons (blue) like raisins in the cake. Alpha particles were very small and positively charged so Rutherford used them to investigate the inside of other larger atoms. The alpha particles were fired at a very thin foil.

In the simulation, turn on alpha particle gun for at least 1 minute. (click blue button on Alpha Particles gun)

1. What are the alpha particles doing? Are there any interactions taking place? (1 or more complete sentences)

D. Click the Traces box to show traces, and then change the energy level to max, observe for ~30 seconds, then change energy level to min and observe ~30 seconds.

2. Has anything changed with the alpha particle pattern? What is happening to the trace lines from start to finish? (speak to both energy levels observed)

3. Do you believe the atom is exerting a force on the alpha particles? (Explain your answer)

4. On a separate piece of paper near the top left, sketch the plum pudding model using color pencils in an area of about 3×3 inches. Make sure to include the alpha particles as well, and make a key for labeling the different elements involved. IMPORTANT: include your signature and date next to your drawing, written by hand.

E. Prior to Rutherford’s Experiment this is actually what was expected to happen when alpha particles were aimed at atoms. NOTE – Rutherford could NOT see inside the atom but DID observe many alpha particle tracks like this.

Now in the simulation, switch over to the Rutherford Atom by double-clicking on the icon at the bottom. In the main window, make sure you are looking at the setting with multiple circles (each an atom) rather than the single atom. Click the yellow reset button at the bottom right. Note that some piece of foil is being used and the energy is set to nearly the middle of min and max. Near the bottom right there is a window with a number of protons and neutrons.

7. Look on a periodic table, Periodic Table, what atom is being used as the target? (Note the number of protons are the key and can be found as the top number of any element. The approximate number of neutrons can be found by taking the atomic mass, the bottom number of the entry, and subtracting the number of protons.) _____

8. What is the atomic scale shown for the main window? ____

F. Turn on the alpha particle gun, watch is for about 30 seconds. Note that there is a play/pause button under the main window, and a step button right next to it.

9. Explain the alpha particle motion with reference to the center of the atoms being observed (you should be able to see ~3 full atoms), what happens when the particle approaches the center dot of the atom?

G. Click on the show traces.

H. Observe the traces for about 20 seconds, then click pause.

10. On the same piece of paper as your #4 below your plum pudding model, with your colored pencils sketch the 3 atoms and the approximate traces you see. IMPORTANT: include your signature and date next to your drawing, written by hand.

11. How many traces stayed directly on their original path: ___

12. How many are deflected slightly (less than 10 degrees use a protractor for this):

13. How many are deflected between 10 to 45 degrees: How many are deflected between 45 and 90:

14. How many are deflected more than 90 degrees: ____

I. Click the play button, observe the traces for about another 20 seconds, then click pause.

15. Repeat your measurements as you made in #11. through #14., noting your numbers in the same order separated by commas.

16. Does the location of the starting position of the alpha particle (where it comes onto the screen from the bottom) have anything to do with the amount the trace changes direction? (Explain your answer using 1 or more sentences)

J. Reset the simulation (yellow button bottom right) and click on show traces and change the amount of energy, to max and min observing for ~10 seconds each.

17. Does the amount of energy given initially to the alpha particles have any effect on the way the trace changes?

K. Using a periodic table try using 3 other atoms/targets by changing the number of protons and neutrons. Keep the energy near the middle. Keep traces on.

18. Create a table and place it in your report (must be typed):

Atom

# of Protons

# of Neutrons

# of traces deflected (no matter the angle)

19. Is additional or less electrical force acting on the alpha particles in these models? (Explain your answer using 1 or more sentences)

20. What should the traces of the alpha particles look like if no electrical force was present?

21. If the alpha particles have a positive charge, what can you say about the charge of the center of the other atoms. (Explain your answer using 1 or more sentences)

L. Reset your simulation and now select the single nucleus found right above the foil, turn traces on and your alpha particle beam.

22. Describe what you see, speak to if the alpha particle is coming directly at the nucleus or if it is further out. (Using more than 1 sentences.)

23. Conclusion: Do you think Rutherford’s theory was easily accepted by other physicists? How did his findings lead us to more theories in quantum mechanics? Find a timeline on the internet, after Bohr’s atom model in 1913, list out about 5 of the big names (and dates) that led us to the quantum model we know today (think about some of the observations that were noted in the billiards ball example given). Include at least one sentence of what their main discovery was. Include any references (using APA citation) you used in this lab.

**The attached file has the above instructions and table (it wouldn’t allow me to post the table)

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