Ernest+Rutherford

Ernest Rutherford [] [] Describe the set-up for Rutherford’s Gold Foil Experiment. Include a visual. What was he doing in the experiment? Explain the outcome of the Gold Foil Experiment.

A beam of alpha particles, generated by the radioactive decay of radium, was directed onto a sheet of very thin gold foil. The gold foil was surrounded by a circular sheet of zinc sulfide (ZnS) which was used as a detector: The ZnS sheet would light up when hit with alpha particles. Summarize his model of the atom.

Rutherford’s model changed our view of the atom. Compare and contrast his model to Thomson’s model. What new knowledge did we gain? What was wrong with Thomson’s model? Did any of Thomson’s ideas continue to be valid?


 * **Partical** || **Symbol** || **Relative Charge** || **Relative Mass** ||
 * Electrons || E- || -1 || 1/1836 ||
 * Protons || P || 1 || 1 ||
 * Neutrons || N || 0 || 1 ||

Ernest Rutherford came up with the experiment to study how particles with a positive charge interact with a very thin piece of gold foil. Rutherford pelted a very thin piece of gold foil with a stream of positively charged particles known as alpha particles. Most of the particles pass straight through the foil. From this experiment Rutherford discovered that most of the atom is made up of empty space. However, some of the particles had bounced back and were defected, this means that the center of the atom, known as the nucleus us positively charged. “Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high velocity alpha particles at an atom then there would be very little to deflect the alpha particles. He decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil but to his amazement a few alpha particles rebounded almost directly backwards.” Key Points
 *  The electron cloud of the atom does not influence alpha particle scattering.
 *  Large number of the atom’s charges, up to a number equal to about half the atomic mass in hydrogen units, is concentrated in very small volume at the center of the atom. These are responsible for deflecting both alpha and beta particles.
 *  The mass of heavy atoms such as gold is mostly concentrated in the central charge region, since calculations show it is not deflected or moved by the high speed alpha particles, which have very high momentum in comparison to electrons, but not with regard to a heavy atom as a whole.