<P> The number of protons within the atom 's nucleus is called atomic number and is equal to the number of electrons in the neutral ( non-ionized ) atom . Each atomic number identifies a specific element , but not the isotope ; an atom of a given element may have a wide range in its number of neutrons . The number of nucleons ( both protons and neutrons ) in the nucleus is the atom 's mass number , and each isotope of a given element has a different mass number . </P>
<P> The number of protons within the atom 's nucleus is called atomic number and is equal to the number of electrons in the neutral ( non-ionized ) atom . Each atomic number identifies a specific element , but not the isotope ; an atom of a given element may have a wide range in its number of neutrons . The number of nucleons ( both protons and neutrons ) in the nucleus is the atom 's mass number , and each isotope of a given element has a different mass number . </P>
elements with the same atomic number but with different atomic masses
elements with the same atomic number but with different atomic masses
isotope
isotope