The nuclides 16O8 and 15O8 differs in their atomic weight. 16O8 has an atomic weight of 16 amu while 15O8 has an atomic weight of 15 amu. They also differ in the amount of neutrons, 16O8 has 8 protons and 8 neutrons (16 - 8) while 15O8 only has 7 neutrons (15 - 8 protons).