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Rutherford atom model

  1. Apr 25, 2009 #1
    Did Rutherford knew the structure of alpha particles?

    If so, why was so important the scattering of alpha particles in the gold foil experiment?

    He knew the structure of helium atom!!!

    What is wrong with me?

    Thanks for your friendly collaboration and excuse me if the post makes no sense.
  2. jcsd
  3. Apr 27, 2009 #2
    The Wilson cloud chamber was developed in the 1890s. The famous Rutherford scattering of alpha particles was done 1n 1909. At this time, alpha particles were known to make ZnS (zinc sulphide) foils scintillate. He used a purified radium source for the alphas, and scattered them off a gold foil. What he did not expect was to observe essentially Coulomb scattering from a point (actually two, counting the alpha), rather than a plum pudding. Rutherford developed the theory of Coulomb scattering from point charges. Read below from Wiki

    In physics, Rutherford scattering is a phenomenon that was explained by Ernest Rutherford in 1909, and led to the development of the Rutherford model (planetary model) of the atom, and eventually to the Bohr model.

    The discovery was made by Hans Geiger and Ernest Marsden in 1909 when they performed the gold foil experiment under the direction of Rutherford, in which they fired a beam of alpha particles (helium nuclei) at layers of gold leaf only a few atoms thick. At the time of the experiment, the atom was thought to be analogous to a plum pudding (as proposed by J.J. Thomson), with the negative charges (the plums) found throughout a positive sphere (the pudding). If the plum-pudding model were correct, the positive “pudding”, being more spread out than in the current model of a concentrated nucleus, would not be able to exert such large coulombic forces, and the alpha particles should only be deflected by small angles as they pass through.

    However, the intriguing results showed that around 1 in 8000 alpha particles were deflected by very large angles (over 90°), while the rest passed straight through with no deflection. From this, Rutherford concluded that the majority of the mass was concentrated in a minute, positively charged region (the nucleus) surrounded by electrons. When a (positive) alpha particle approached sufficiently close to the nucleus, it was repelled strongly enough to rebound at high angles. The small size of the nucleus explained the small number of alpha particles that were repelled in this way. Rutherford showed that the size of the nucleus was less than about 10−14 m.
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