What are some examples of isotopes?
Some examples include H-1, H-2, H-3, C-12 and C-14.
For the isotopes of carbon. C-12 has 6 protons and 6 neutrons, C-14 has 6 protons and 8 neutrons. Notice that the mass of the isotope comes from the added masses of the protons and neutrons. Each proton and neutron has a mass of approximately 1 atomic mass unit (amu).
Here is a video which provides further explanation of isotopes.