The ElectronWhat is it and whats it doing in my pudding?

Excuse me how can you discover a particle so small that nobody has ever seen one?J.J. Thomson 1897

Glowing tubes full of gas proliferated and gained scientific importance in 1855, when glassblower Heinrich Geissler developed an improved vacuum pump. It was one of Geissler's tubes that Julius Plcker used when he first observed cathode rays in 1859.

Plucker's student, Johann Wilhelm Hittorf, put solid objects inside the tube between the cathode and the glow. The objects cast shadows. Hittorf concluded that the cathode was emitting something that traveled in straight lines, like light rays.

Crookes TubeInvented by William Crookes 1875Maltese Cross Tube (on left)

A later manifestation of Crookes TubeGerman physicist Eugen Goldstein called them cathode raysSince they well were emitted from the cathodeGoldstein discovered positive rays which were emitted by the anode (Canal rays)

J.J. ThomsonUsing devices similar to Crookes tube, studied cathode raysIdentified cathode rays as electronsTerm coined by G. Johnstone Stoney (1891)Determined with basic physicse/m = 1.8 x 10-8 C/gEither theyre really small or highly chargedProblem solved w/ Millikans oil-drop exp. in 1908

J. J. Thomson in his office at the Cavendish Laboratory. A colleague of Thomson's, Lord Rayleigh, said that "J.J. had something to say on nearly any subject that might turn up. He as a good raconteur, but also a good listener, and knew how to draw out even shy members of the company.... J.J., while talking, paced the room vigorously in a manner rather suggestive of a caged lion."

Plum-Pudding Model

Ernest Rutherford (1871-1937)came to the Cavendish Laboratory as a young man from New Zealand, and was a research student under Thomson. Using a-rays emitted by radioactive elements to probe into atoms, around 1913 he showed that Thomson's plum pudding model of the atom was untenable.

Gold-Foil ExperimentOther names to remember: Hans Geiger, Ernest Marsden

Modern View of the Atom

So what do you do with a newly characterized electron beam?Shoot it at things, of course

Introducing Wilhelm Rntgen (1895)Using a Crookes tube, accidentally discovered x-raysDiscovery ranks among shortest scientific gestation periods1st Nobel Prize

Crookes-Hittorf X-ray Tube