Fluorine has only one stable isotope, which is 19-Fluorine. This isotope contains 9 protons and 10 neutrons as shown in the bohr-style atom diagram to the right. Other isotopes with neutron numbers ranging from 5 to 22 have been discovered, but all except 19-Fluorine are unstable and radioactive. The most stable is 18-Fluorine with a half life of just under two hours.