protons determine what element it is, but there are still electrons and neutrons. if, for example, there are three protons in an atom, it's a lithium atom no matter what. however, if it has any more or any less than three electrons, it's an ion (an atom with a charge). if it has any more or any less than three neutrons, it's an isotope (which has a different mass than a normal atom of an element, and is also radioactive).