A cation or a positive ion is an atom that has more protons (positive electric charge) than electrons (negative electric charge). This difference means the atom has a positive electric charge. Since electrons can move between atoms, a cation can become an anion, or vice-versa. Silver, ammonium, etc. are cations; meaning, they would carry a positive sign as a superscript when put down as a chemical formula. For example, the chemical symbol for ammonium would be NH4+.