Discovery of the Electron

JJ Thomson discovered the electron in 1897. Thomson used a tool called the cathode ray tube to discover these subatomic particles. The Cathode ray tube consists of a tube, not unlike a water bottle. Inside this tube were two metal plates. The first was connected to a power source and was positively charged, while the other was connected to the same power source, but was negatively charge and it had a hole in the middle of it. Once the power was fed to the plates, a ray shot out from the negatively charged plate, through the hole in the positively charged plate and to the end of the tube.

When Thomson saw this he was pretty sure that whatever this beam was made of was negatively charged because he saw them being attracted to the positive plate because opposites attract. To check his theory, Thomson put two charged plates on either side of the tube, once again one positively charged and one negatively charged. When he ran the experiment again sure enough, the ray bent toward the positively charged plate. Again, Thomson wanted to check this, he tried swapping the metal used for the plates inside the tube and he continued to get the same results over and over again. Thomson discovered that these Cathode rays must be made of "stuff" that was negatively charged, the particles that make up these cathode rays must be 1000* smaller than a Hydrogen atom, and all different metals give off Cathode Rays. When Thomson discovered the electron, he essentially had disproved the old model of the atom that it was one solid indivisible particle, but with Thomson's discovery of separating these new Electrons from atoms this was disproved. Thomson theorized that the atom is more like plum pudding. The atom being the whole pudding and the electron being mixed throughout the atom being the plums being mixed throughout the pudding. To back this up, Thomson used these three assumptions. First he said that electrons are negatively charged. Secondly he said that atoms on the whole are usually neutrally charged. And finally he said that there must be some positive charge in the atom to balance out the negative charge from the electron.