Isotopes of chlorine Isotopes of chlorine Chlorine (Cl) has 25 isotopes with mass numbers ranging from Cl to Cl and 2 isomers (Cl and Cl). There are two principal stable isotopes, Cl (75.78%) and Cl (24.22%), giving chlorine a standard atomic weight of 35.45. The longest-lived radioactive isotope is Cl, which has a half-life of 301,000 years. All other isotopes have half-lives under 1 hour, many less than one second. The shortest-lived are Cl and Cl, with half-lives less than 20 and 30 nanoseconds, respectively—the half-life of Cl is unknown. Bromine is the only other halogen with more than one stable isotope. Trace
Origin and occurrence of fluorine fluorine in antozonite. It was suggested that radiation from small amounts of uranium within the crystals had caused the free fluorine defects. Origin and occurrence of fluorine Fluorine is relatively rare in the universe compared to other elements of nearby atomic weight. On earth, fluorine is essentially found only in mineral compounds because of its reactivity. The main commercial source, fluorite, is a common mineral. At 400 ppb, fluorine is estimated to be the 24th most common element in the universe. It is comparably rare for a light element (elements tend to be more common the lighter they are). All