Chlorine has 25 isotopes, ranging from ²⁸Cl to ⁵²Cl, and two isomers, ³⁴ᵐCl and ³⁸ᵐCl. There are two stable isotopes, ³⁵Cl and ³⁷Cl, giving chlorine a standard atomic weight of 35.45. The longest-lived radioactive isotope is ³⁶Cl, which has a... Wikipedia