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 americium Isotopes of americium Americium (Am) is an artificial element, and thus a standard atomic weight cannot be given. Like all artificial elements, it has no known stable isotopes. The first isotope to be synthesized was Am in 1944. The artificial element decays into alpha particles. Americium has an atomic number of 95 (the number of protons in the nucleus of the americium atom). Eighteen radioisotopes of americium from Am to Am (with the exception of Am) have been characterized, with the most stable being Am with a half-life of 7,370 years, and Am with a half-life of 432.2 years. All