2. Nitrogen has only two isotopes of appreciable natural abundance: 14N, with atomic mass of 14.00307 amu; and 15N with atomic mass of 15.00011 amu. From the atomic weight of nitrogen, determine the natural abundances of 14N and 15N. So, 14N is present at 99.63592% and 15N is present at 0.3640800% 3. Bromine exists naturally as a mixture of bromine-79 and bromine-81 isotopes. How many protons, neutrons, and electrons are in an atom of bromine-79?