The isotopes are a group of atoms that have the same atomic numbers but different mass numbers.
That means all isotopes of an element have the same number of protons in their atomic nuclei and the same number of electrons in the electron cloud surrounding the nucleus.
Difference between isotopes
Isotopes differ in the total number of neutrons present in their respective atomic nuclei.
Thus they have different mass numbers.
Different isotopes of the same element are having different masses.
Protium(1 proton,1 electron, and no neutrons), Deuterium(1 proton, 1 electron, and 1 neutron), and Tritium(1 proton, 1 electron, and 2 neutrons) are examples of isotopes of Hydrogen.