http://www.ck12.org Chapter 24. Atomic Physics
FIGURE 24.4
J. J. Thomson’s model of atomic structure.straight back, while leaving most undeflected.
Rutherford’s Model of the Atom
Rutherford explained the Geiger-Marsden result by suggesting that the atom was mostly empty space, and that the
mass of the atom was all compacted into a dense core at the center. A tiny, dense core would mean that most
particles would pass through without being deflected. A few would be deflected to the side, and some would hit
dead-on and head backward. The differences between Thomson’s model prediction (top diagram) and Rutherford’s
explanation of the Geiger-Marsden result (bottom diagram) are shown inFigure24.5.
FIGURE 24.5
The top diagram shows Thomson’s model and the bottom diagram Ruther-
ford’s interpretation of the atom having a densely packed positive nucleus.Rutherford decided that the results could only mean that the positive charge was confined to a very small part of
each atom that he named the nucleus. The nucleus would, therefore, be a very small region of very dense positive
charge containing almost 99.99 % of the entire mass of the atom. This could account for the scattering of the alpha
particles that came close enough to the nucleus.
For more information on Rutherford’s experiment follow the link below.
http://www.youtube.com/watch?v=Zd6_zVdMgJk
Rutherford’s experiment suggested that the nucleus of an atom had a size between 10−^15 m and 10−^14 m. It was
already known, however, that the size of an atom was about 10−^10 m. Rutherford conjectured that the size of the
electron orbits must be many thousands of times larger than the nucleus of the atom. Thus, the atom must have