An atom is electrically neutral because it has the same number of electrons as it does protons. The atoms neutrality can only be changed by altering the number of electrons present in the atom.
Changing the electrons not only changes the neutrality of the atom, but it can also change the physical and and chemical properties of the atom. Adding an electron to a chlorine atom changes its reactiveness dramatically. Regular, neutral chlorine atoms will automatically combine to make chlorine gas, which is highly toxic. By adding an electron to the gas, it becomes so unresponsive it can safely be moved and handled as needed. The same changes can be made by removing electrons from other types of atoms also.