ion is an atom that has different number of protons and electrons. An isotope is an atom of an element with a specific number of neutrons. Two different isotopes of the same element will have two different neutron counts.
When writing the symbol for an ion, the one- or two-letter element symbol is written first, followed by a superscript. The superscript has the number of charges on the ion followed by a + (for positive ions or cations) or - (for negative ions or anions). Neutral atoms have a charge of zero, so no superscript is given.
