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Reconstructing Atomic Theory | ACTIVITY SHEET
RUTHERFORD STATION ACTIVITY SHEET
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Imagine firing a cannon at a piece of tissue paper. What if the cannonball bounced off the tissue and
shot back toward you? Not the result you would expect, right? Ernest Rutherford had the same
reaction after he performed his famous gold foil experiment and got some similarly incredible results.
Rutherford was testing the “plum pudding model” proposed a few years earlier by J.J. Thomson. In
Thomson’s model, electrons (negatively charged particles) were embedded in a positively charged
sphere, like chocolate chips in cookie dough, with the mass evenly distributed throughout the atom.
To test the plum pudding model, Rutherford performed an alpha scattering experiment; he aimed a
beam of minute radioactive alpha particles through a thin piece of gold foil, and detected the
deflections using a zinc sulfide coated screen. If the plum pudding model accurately depicted the
atom as having its positive mass evenly distributed throughout the atom, Rutherford expected that
most of the alpha particles would be deflected at small angles. Instead, Rutherford made a surprising
discovery. He observed that the vast majority of the particles passed through the foil without any
deflection, as if the foil were not there, while a few particles were deflected at large angles or even
deflected back.
Rutherford reasoned that most of the particles passed through empty space, while a few collided and
were deflected by the relatively dense, positively charged nucleus. Rutherford’s experiment verified
that an atom is mostly empty space, and that the bulk of the mass is concentrated in a very small
volume of the atom called the nucleus.
Answer the following questions.
1. Draw an atom as Rutherford might have envisioned it after his gold foil experiment.
2. What let Rutherford to suggest that there were positively charged particles in the nucleus?
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Reconstructing Atomic Theory | ACTIVITY SHEET
3. Based on the reading above and the results of your simulation experiments, explain how the
behavior of positively charged alpha particles supports Rutherford’s model of the atom with the
protons in the middle and refutes J.J. Thomson’s “plum pudding” model.
4. How would the stability of the nucleus be affected if it were composed of only protons?
5. Use the information below to answer the questions that follow.
Carbon has a mass of 12.0 atomic mass units (amu) and contains 6 protons and 6 electrons.
The mass of a proton is 1,835 times heavier than an electron.
Mass of an electron: 9.10939 x 10-31 kg = 1/1,835 amu = 0.00055 amu
Mass of a proton = 1.672 x 10-27 kg = 1 amu
What let scientists to believe there were other particles besides protons in the nucleus, based on…
a. …the mass of the atom?
b. …the structure of the atom?
6. Based on your current knowledge of the atom, what problems, if any, do you see in Rutherford’s
model?