If the proton number changes, then it is a new element.
Example: Carbon has the proton number of 6. If the proton number becomes 7... the atom is no longer carbon; it would be Nitrogen.
If the number of electrons changes, this means that the atom or element turns into an ion. Because the electron in the valence shell is gained by another element.
The number of protons and electrons must be equal, so the atom could be balanced, with a charge of +0 (not -1 or +1)
Mass is affected when protons and neutrons change.
Mass number = protons + neutrons.
But remember! if proton number changes, then it's a new element
