And Quiz Isotopes Atoms Ions [RINJ1L] Worksheet: Atoms, Isotopes, and Ions Atoms The number of protons in an atom determines the identity of the atom. A)Element Y and Z are isotopes of X. Examples of Ions: Na +, Mg 2+, Cl-, O 2-. Ions are atoms (or molecules) that have lost or gained electrons and have an electrical charge. 0 percent 37Xatoms, and 2.