T his idea was only partly correct. W e have discovered that all the different kinds of atoms can be built out of only three even simpler particles - protons, neutrons, and electrons. Two of these three particles, the proton and the electron, carry an electric charge, and we must now see what this means. E lectric charge is a property of some basic particles that makes them behave in characteristic ways. A proton carries one unit of positive charge, and an electron has one unit of negative charge.
Neutrons are never charged, they are neutral.
I ncidentally, an electric current, which serves so many useful purposes in our homes, is nothing but a stream of electrons moving along a metal wire. A toms and lesser particles are very small indeed. However, single atoms are far too small to be seen clearly by even the most powerful microscope. W e can learn about atoms mainly by studying bigger pieces of matter containing millions of them. By watching how these bullets bounce off any nuclei they strike, and by detecting the fragments from any atoms that are shattered in this process, we can obtain information about the properties of our target atoms.