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
Bromine participate in chemical reactions (the noble gases, with the exception of xenon in the very unstable XeBr); extreme nuclear instability hampering chemical investigation before decay and transmutation (many of the heaviest elements beyond bismuth); and having an electronegativity higher than bromine's (oxygen, nitrogen, fluorine, and chlorine), so that the resultant binary compounds are formally not bromides but rather oxides, nitrides, fluorides, or chlorides of bromine. (Nonetheless, nitrogen tribromide is named as a bromide as it is analogous to the other nitrogen trihalides.) Bromination of metals with Br tends to yield lower oxidation states than chlorination with Cl when a variety