1. Rutherfords Gold Foil Experiment The History of Atomic Theory

2. Intro Questions In the ‘Plum pudding’ model, what part of the atom holds the positive charge that balances the negative charge of the electrons? In the ‘Plum pudding’ model, what part of the atom holds the positive charge that balances the negative charge of the electrons? If the idea was that the ‘plums’ were electrons, what was the rest of the ‘pudding’ made of? If the idea was that the ‘plums’ were electrons, what was the rest of the ‘pudding’ made of? Is the ‘Plum pudding’ model the best way of representing the atom? Is the ‘Plum pudding’ model the best way of representing the atom?

3. Rutherford’s Gold Foil Experiment In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure. In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.

4. Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick) Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick)

5. Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all. Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges. Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.

7. http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html http://chemmovies.unl.edu/ChemAnime/R UTHERFD/RUTHERFD.html

8. This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material. This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material. Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.” Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.” He called the center of the atom the “nucleus” He called the center of the atom the “nucleus” The nucleus is tiny compared to the atom as a whole. The nucleus is tiny compared to the atom as a whole.

9. Rutherford Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge. Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.

10. Focus Questions: What development in technology allowed Rutherford to direct a stream of alpha particles? What development in technology allowed Rutherford to direct a stream of alpha particles? Why was gold foil used? Why was gold foil used? Why did the foil need to be very thin? Why did the foil need to be very thin? How did the alpha particle emitter allow for nuclei to be identified as subatomic particles? How did the alpha particle emitter allow for nuclei to be identified as subatomic particles? What is a nucleus? What is a nucleus?

11. Focus Questions How did Rutherford’s scattering experiment results change the accepted model of how the atom is structured? How did Rutherford’s scattering experiment results change the accepted model of how the atom is structured? How might Rutherford have determined that the nucleus was much larger than the electrons? How might Rutherford have determined that the nucleus was much larger than the electrons? Once the nucleus had been discovered, what questions might scientists have asked about this nucleus? Once the nucleus had been discovered, what questions might scientists have asked about this nucleus? How does the nucleus compare with electrons? How does the nucleus compare with electrons? Where in the atom is the nucleus located? Where in the atom is the nucleus located? Why is the term ‘planetary model’ used for the atom? Why is the term ‘planetary model’ used for the atom?