If you look at the classic Bohr model of the atom (from 1913), you have electrons orbiting around a nucleus of protons and neutrons. Normally there are as many electrons (negative charge) as protons (positive charge), so the net charge of the atom is zero. The various shells or orbit radii of the model have different characteristics as to how many electrons they are happy having orbiting in them. The first shell likes 2 max, the 2, and 6, etc. If there is one less electron that what the outermost used shell considers full, it will happily take on another electron, even if this unbalances the charge. If it has just one electron in a shell, it would happily give it up even if it unbalances the charge. Copper, one of the best conductors of electricity, has 29 electrons, which means in its 4th orbit, it has one electron. It is easily taken away by something pulling on it. In fact, if you put a bunch of copper atoms together, there is a cloud of electron sharing with that one electron moving from atom to atom, and others taking its place.