Tuesday, October 5, 2010

Rutherfords Gold Foil Experiment

In 1909 Rutherford's gold foil experiment changed the way people viewed the atom forever. The experiment was conducted at the University of Manchester by Hans Geiger and Ernest Marsden under the direction of Ernest Rutherford. Rightfully so, this experiment is also known as The Geiger- Marsden experiment. This was revolutionary in that it proved for the first time, the existence of the atomic nucleus, thus killing the idea of the plum pudding model. Geiger, Marsden, and Rutherford's work will be studied forever.


The Plum Pudding Model composed by J.J. Thomson said that negative electrons were placed throughout and everything else (the pink) was positively charged "pudding" to balance the negative electrons.

The experiment was set by placing a particle emitter that would shoot particles made by radioactive decay of radium directly to a thin sheet of gold foil. Gold Foil was used because it is inert and malleable. In order for the particles to go through the material, it had to be really thin and gold was the perfect metal. Around the particles that would shoot toward the gold foil there was a circle of zinc sulfide which would detect when and where the alpha particles would deflect.

Rutherford hypothesized that the particles would pass straight through the foil or at most only deflect a couple of degrees. If this had occurred, it would have measured the distribution of charge through the "plum pudding" atom. This assumption was based on the theory that positive and negative charges were spread evenly through the atom, thus making their forces weak allowing for very little, if any deflection.

What ended up happening was the slit in which the particles were passed through, when made larger (greater than two nanometers), more particles were able to get through and the majority of these particles passed straight through the foil. Only one out of 8,000 were deflected at very dramatic angles. These angles were even greater than 90 degrees and in some cases the particles completely back fired.

In conclusion, this allowed Rutherford the prove J.J. Thomson's plum pudding model false.  Rutherford found that an atom is mostly made up of empty space with a concentrated charge in the middle.  He was able to conclude this because the majority of the particles passed through the empty space of the atoms and were not noticeably deflected, but the positive charge of the particles would repel against the one focused area of positive electrons in the atoms.  The focused and concentrated area that was discovered was named the nucleus.  Rutherford along with Geiger and Marsden came up with the following model of an atom.  It is because of these scientist curiosity that the model of an atom kept evolving and became more accurate.


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