Plum pudding model: Difference between revisions

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In a lecture delivered to the [[Royal Institution of Great Britain]] in 1905,<ref>{{citation |url=http://www.ub.edu/hcub/hfq/sites/default/files/Thomson_model%286%29.pdf |first=J. J. |last=Thomson |date=10 March 1905 |title=The Structure of the Atom}}. Reprinted in {{harvnb|Davis|Falconer|1997}}</ref> Thomson explained that it was too computationally difficult for him to calculate the movements of large numbers of electrons in the positive sphere, so he proposed a practical experiment. This involved magnetised pins pushed into cork discs and set afloat in a basin of water. The pins were oriented such that they repelled each other. Above the centre of the basin was suspended an electromagnet that attracted the pins. The equilibrium arrangement the pins took informed Thomson on what arrangements the electrons in an atom might take, although the insight was limited as the experiment functioned in two dimensions instead of three.

For instance, he observed that while five pins would arrange themselves in a stable pentagon around the centre, six pins could not form a stable hexagon. Instead, one pin would move to the centre and the other five would form a pentagon around the centre pin, and this arrangement was stable. As he added more pins, they would arrange themselves in concentric rings around the centre.

FromThe thisexperiment functioned in two dimensions instead of three, but Thomson believedinferred the electrons in the atom arranged themselves in concentric shells and the could move within these shells but did not move from one shell to another them except when electrons were added or subtracted from the atom.

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