Isotopes of chlorine

Chlorine (₁₇Cl) has 25 isotopes, ranging from ²⁸Cl to ⁵²Cl, and two isomers, ^34mCl and ^38mCl. There are two stable isotopes, ³⁵Cl (75.8%) and ³⁷Cl (24.2%), giving chlorine a standard atomic weight of 35.45. The longest-lived radioactive isotope is ³⁶Cl, 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 proton-unbound ²⁹Cl and ³⁰Cl, with half-lives less than 10 picoseconds and 30 nanoseconds, respectively; the half-life of ²⁸Cl is unknown.