what is the difference between lithium 6 and lithium 7?
Nuclei of lithium can have 3, 4 or 5 neutrons. We call these different isotopes of lithium. Since different isotopes of an element have different numbers of neutrons (but always the same number of protons) they have different mass numbers. ... Lithium-6 and lithium-7 are both stable isotopes of lithium.