Friday, November 12, 2010

Exam Review Question # 14

Rutherford's Gold Foil Experiment
-Focused a beam of positively charged particles (alpha particles) on a thin sheet of gold foil and set up a ring of detectors around the foil
*It was thought that the positively charged alpha particles would pass through atoms with very little deflection because the positive charges were thought to be spread out evenly.
Rutherford and his colleagues were shocked to see:
-A few alpha particles had very large deflections or bounced straight back towards the source
-They concluded that the alpha particles going straight through were passing through nearly empty space and that the particles bouncing back were hitting dense, positively charged centers.


  1. Observations:
    Rutherford observed that most of the alpha particles passed straight through the gold atoms. According to a well-known theory, there would be a slight deflection caused by the supposed “evenly spread positive charge” throughout the gold atoms. Surprisingly, the majority of the alpha particles passed straight through the gold atoms without any deflection. However, some of the particles did bounce off the gold foil at strangely large angles. Some of the particles were even deflected straight back to the source of the alpha particles. Rutherford stated: “This is almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you.”
    Rutherford was able to use these observations in creating a new theory of the atom. He offered the idea that the majority of an atom is composed of empty space. This is why most of the alpha particles were not deflected and were easily able to pass through the foil. Rutherford also concluded that all the positive charge and almost all of the mass occupy one small region. This region has enough positive charge to cause the observed deflections of some of the alpha particles. Rutherford described this region as a tiny central core of an atom that is composed of protons and neutrons. He called it the nucleus. The Rutherford atomic model is today known as the nuclear atom. In the nuclear atom, the protons and neutrons are all located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.

  2. Good answer but more detail could be used when describing the outcome of the experiment. Over all though I thought you did a good job explaining the experiment