1. The Nuclear Model of the Atom

2. Radioactivity
JJ Thomson undermined Dalton’s idea that atoms were hard spheres – they were more complex than that.
Around the same time in France, Marie and Pierre Curie were making discoveries that put into doubt another aspect of Dalton’s theory – that all atoms were indestructible.

3. Marie Curie and Radioactivity
After a 10-year struggle, the Curies isolated two sources of radiation, discovering polonium and radium.
These elements are unstable, and give off radiation and bits of their mass when they decay.

4. Alpha Radiation
Some radioactive elements give off “alpha particles,” which are equivalent to helium atoms without electrons.

5. Ernest Rutherford
Ernest Rutherford initially studied the radiation given off by the purified radioactive materials produced in the Curie lab.
He immediately seized on the idea of using alpha particles as probes to test the current model of the atom, proposed by his mentor JJ Thomson.

6. The Gold Foil Experiment (1909)
Thomson’s model thought of an atom as a positively charged matrix with mobile electrons imbedded in it.
Rutherford anticipated that the atoms would slightly deflect the incoming alpha particles.

7. Rutherford’s Results
The small number of widely scattered particles indicated that the plum pudding model was incorrect.
It took Rutherford two years to come to grips with his results.

8. Rutherford’s Atomic Theory (1911)
atoms were made of a positively charged nucleus
the smaller electrons are found at a relatively large distance from the nucleus.
Atoms are electrically neutral because the nucleus and the electrons charges balance each other.

9. Problems with Rutherford’s Theory
Based on the laws of physics known at the time, (-) charged electrons should immediately crash into the (+) nucleus
Although electron general location is known, the behavior of electrons is not a part of Rutherford’s model.

10. Lab 2 Gold Foil Simulation
Objective: to recreate Rutherford’s ground-breaking research on the floor or your lab bench.
Materials: lab bench (or floor), 3 large magnets, small magnet, tape

11. Procedure
Place the three large magnets 30 cm apart on the lab bench. Tape them to the bench using masking tape.
Stand 1.5 m away and slide the small magnet across the tabletop towards the weighted magnets.
On a separate sheet of paper, sketch the path of the free-sliding magnet.
Repeat step two 50 times.

12. Questions What do the stationary magnets represent in this simulation?
What does the free sliding magnet represent?
How many trials did the magnet pass straight through without deflection?
Calculate the percentage of shots that were deflected.
Calculate the percentage of shots that were not deflected.
Calculate the percentage of shots that were deflected straight back toward you.
What can you conclude about the number of head-on collisions from your answer to question 6?

13. Summary Questions
What did scientists believe an atom looked like before Rutherford’s experiment?
Describe Rutherford’s experiment. What were his results?
Summarize Rutherford’s conclusions about the structure of the atom after he analyzed his results.
Write a paragraph on whether or not you think this simulation is an accurate depiction of Rutherford’s experiment.
Draw a diagram of what Rutherford’s atom would look like.