What would you need to tell the number of protons and electrons present in an ion?

Answer 1

The atomic number of the element in the ion, when there is only one such element, and the atomic charge on the ion. For example, in Na+1, the atomic number is 11; this gives the number of protons. The number of electrons is equal to the atomic number minus the charge on the ion, in this instance, 10 electrons. If the sign on the ion is negative, as in O-2, remember that subtracting a negative number is equivalent to adding the positive number of the same magnitude. Thus, oxygen has an atomic number of 8, and 8 - (-2) equals 10 electrons.

Answer 2

To determine the number of protons in an ion, you can refer to the element's atomic number on the Periodic Table. The atomic number represents the number of protons in the nucleus of the atom. Since ions are atoms that have gained or lost electrons, the number of electrons in an ion may differ from the number of protons, depending on the charge of the ion.