When is the term nuclide used instead of isotope?

The term nuclide is used instead of isotope when the focus is on the nuclear properties of an atom rather than its chemical properties.1

While the term isotope refers specifically to members of a set of atoms that share the same atomic number (position in the periodic table) but have different mass numbers, a nuclide is defined by its specific number of protons, number of neutrons, and the energy state of its nucleus. Consequently, the term nuclide is broader; it encompasses all distinct atomic species that have a measurable lifetime, including those that differ in their number of protons, neutrons, or nuclear energy levels.12

In scientific contexts, researchers use the term nuclide when discussing phenomena such as radioactive decay or when distinguishing between nuclear isomers—atoms that have the same number of protons and neutrons but differ in their energy content.12