Isotopes are atoms of the same element. Remember that an atom is made up of three important components: neutrons, protons, and electrons. Isotopes of an element will contain the same number of protons and electrons but will differ in the number of neutrons they contain. In other words, isotopes have the same atomic number because they are the same element but have a different atomic mass because they contain a different number of neutrons. This is reflected in the name of the isotope. For example, Carbon-12 tells us that there is 6 neutrons because atomic mass= number of nutrons + number of protons. Carbon-14 tells us that there are two extra neutrons (because the number of protons does not change between isotopes), which means this isotope has 8 neutrons.
isotopes of an element have same atomic number(number of electrons/protons) but different atomic masses(number of electrons + neutrons).so,they are different from each other on the basis of number of neutrons.