Now, every Element has a different amount of protons, neutrons, and electrons, but regular microscopes cannot see them because normal light is too “big”. High-tech microscopes use electron light, which has shorter wavelengths, an thus they are able to see the individual atom, but how can you see and count the individual electrons, which are a few hundred times smaller than the actual atom?
Well, around 1920, a man named Niels Bohr was trying, like everyone else, to come up with a model of the Atom. From Thomson, he knew that there are Electrons, so came up with the idea of a Nucleus at the cener and electrons floating around it, but the electrons don’t stick to the Nucleus because they repel each other. When the Electrons get close to each other, they repel each other with the like charged energy, and some “shoot” away, gradually they come back, and go away again. That charged energy must go somewhere, so it “flashes” as light. More or less energy bursts causes light of different colors, and from that the Spectrometer, a machine that can see those colors, was developed. Actually, the spectrometer was featured around the beginning of a Tintin book by Herge: the shooting star, published around 1940. In it, professor Phostle holds up to the light a black band with colors or lines on it, showing the Electrons energy level and thus the number of Electrons.