Appendix E: Chemical Names, Symbols and Relative Atomic Masses of the Elements

• An integer within brackets thus [227] is strictly not an atomic mass but is the mass number of one particular isotope of the element. The mass number is however quite close to the atomic mass of that isotope. It is given in this list when all isotopes of that element are radioactive, and indicates the isotope with the longest known half-life. This is not necessarily the most common isotope. Other isotopic half-lives are listed in the IUPAC report referred to above.