An ion is an atom with a net electric charge due to the loss or gain of one or more electrons.
An isotope is each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Isotopes are often radioactive.
The standard scientific notation for ions is as follows:
And for isotopes:
So the isotope of Helium that has two protons and a neutron – atomic mass 3 – is written:
If 3He loses 2 electrons, it becomes an ion with a positive charge of 2:
So 3He is an isotope, He2+ is an ion, and 3He2+ is both an ion and an isotope.