Standard atomic weight precise value is acceptable, CIAAW has published a single-number conventional atomic weight that can be used for example in trade. For hydrogen, . The twelve elements are: hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine and thallium. By using the abridged value, and the conventional value for the twelve interval values, a short IUPAC-defined value (5 digits plus uncertainty) can be given for all stable elements. In many situations, and in periodic tables, this may be sufficiently detailed. Standard atomic weight The standard atomic weight ("A", a relative atomic mass) is the atomic weight ("A") of a
Isotopes of curium in the periodic table. The shortest-lived isomer is Cm with a half-life of 34 milliseconds. Isotopes of curium Curium (Cm) is an artificial element with an atomic number of 96. Because it is an artificial element, a standard atomic weight cannot be given, and it has no stable isotopes. The first isotope synthesized was Cm in 1944, which has 146 neutrons. There are 21 known radioisotopes with atomic masses ranging from Cm to Cm. There are also four known nuclear isomers (Cm, Cm, Cm, and Cm). The longest-lived isotope is Cm, with a half-life of 15.6 million years – several