Protons can never change for any particular element because they're in the nucleus and the force keeping them there is extremely strong and hard to overcome. Electrons, however, orbit the nucleus and they change all the time. When electrons either leave or join an atom they form ions.
Positive ions (cations) are when electrons leave, so the positive charge is greater than the negative charges, and negative ions (anions) are when electrons join so the negative charge is greater than the positive charge.
hope this helps!
