Section 7: Atomic Theory
[RUTHERFORD SCATTERING VIRTUAL LAB]
Purpose
The purpose of this lab is to gain an understanding of how scientists gather information using indirect evidence.
Background
Often we can look at or touch an object to learn about it. Sometimes, objects are too small or too large for us to learn
about them this way. When this happens, we need to use indirect measurement techniques. Ernest Rutherford
realized that atoms and the building blocks that make up an atom are much too small to be measured directly (say,
by using a ruler or other measurement device). Rutherford and his colleagues designed an experiment to measure
the characteristics of atoms indirectly. The scientists used a thin piece of gold foil at which they directed alpha
particles, which were like very small bullets. Though they could not see the atoms in the gold foil, they knew that if
they watched where the alpha particles went after hitting the gold foil, they could draw conclusions about what was
inside of the gold atoms. When the alpha particles exited the foil after colliding with the gold atoms in the foil, they
were detected with a specially designed screen that Rutherford placed around the experiment. The screen would
light up at the point of the collision where the alpha particles struck it.
Lab Procedure (Using RED font, answer the following questions on this document and upload to the website.)
1. Click on the top tab that says “plum pudding atom”. Who was the person that hypothesized the atom looked like
this?
2. Describe the location and size of the protons, neutrons, and electrons in this model of the atom.
3. What is an alpha particle? (What does it consist of?)
4. PREDICT: What do you think will happen if you fire an alpha particle at this blob of atom?
5. Make sure the energy level is set in the middle and press the large red button on the “alpha particle emitter”.
Record your observations.
6. This is what Rutherford believed would happen when he built his alpha emitting device and set up the “gold
foil experiment”. This never actually happened. Click on the “Rutherford atom” tab at the top of the screen and
hit the big red button on the alpha particle emitter. How do the alpha particles behave compared with in the
plum pudding atom?
7. Why do they behave differently than in the plum pudding atom?
8. Use the features in the simulation to explore the behavior of atoms. Adjust the different variables and explain
provide possible explanations for the observations you made.
Variable changed
Energy
Observation
Possible explanation of the result
Number of Protons
Number of Neutrons
9. This experiment showed Rutherford that most of the mass of an atom is in the _____________ of an atom and it is
______________ charged.
10. Can we SEE individual atoms? How do we know they exist?