On this day in 1897, Sir Joseph John (J. J.) Thomson along with John S. Townsend and Harold A. Wilson announced the discovery of the electron!
The Plum Pudding Model
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While several scientists before them has suggested that atoms were built up from more fundamental units, J.J. Thomson and colleagues were the first to suggest these units were actually 1000 times smaller than the smallest atom. In exploring the properties of cathode rays, or electron beams, Thomson noted that the beams could travel much further than could be expected from atom-sized particles. In addition, the cathode ray could be deflected in an electric field produced by two metal plates in very low pressure gas. The cathode ray moved away from the negatively charged plate and towards the positively charged plate indicating that the particles that compose cathode rays much be negatively charge. Thomson initially called these particles “corpuscles”, but today we know them as electrons. Thomson proposed what we now know as the “plum pudding” model where the electrons and protons were mixed together as shown above. Several years later, Ernest Rutherford came along and performed the Geiger-Marsden experiment disproving the plum pudding model, and instead finding that electrons actually exist in orbitals surrounding a positively charged nucleus. And if that’s not confusing enough, plum pudding isn’t even pudding nor does it contain plums.
This is not pudding.
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Runs with Atoms 