What is the difference between an isotope and a radioisotope?
Isotope = An atom with a specific mass
Radioisotope = An atom with a specific mass that makes it radioactive.
There are isotopes of almost every known element on the periodic table. All an isotope means is that instead of talking about an element in general (every element with the same number of protons) we are talking about not only a specific element, but that elements mass.
Basically Isotopes are a way of separating atoms based on mass within the same element (all have the same number of protons).
Hydrogen has 1 proton - Here all we care about is the number of protons (basically that it is indeed Hydrogen and not something else), Mass never enters the picture.
Hydrogen has 1 proton and a mass of 1 AMU - Here we have both a mass and a number of protons, meaning that we now care about not only the identity of the element, but also the mass.
Hydrogen has 1 proton and a mass of 3 AMU - This is another isotope of hydrogen that has 2 Neutrons in its nucleus (along with that 1 proton mentioned earlier). This isotope is unstable and is radioactive because of those additional 2 neutrons. It is a Radioisotope. It is called this because not all Hydrogen atoms are radioactive, just this isotope; so it is a way of distinguishing within isotopes based on whether they are radioactive or not.