<Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Isotopes are variants of a particular chemical element which differ in neutron number . All isotopes of a given element have the same number of protons in each atom . The term isotope is formed from the Greek roots isos (ἴσος "equal") and topos (τόπος "place"), meaning "the same place"; thus, the meaning behind the name is that different isotopes of a single element occupy the same position on the periodic table . </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> <P> For example, carbon - 12, carbon - 13 and carbon - 14 are three isotopes of the element carbon with mass numbers 12, 13 and 14 respectively . The atomic number of carbon is 6, which means that every carbon atom has 6 protons, so that the neutron numbers of these isotopes are 6, 7 and 8 respectively . </P>

Elements with the same atomic number but with different atomic masses