Atomic mass in 12 grams of the carbon isotope C-12. The number of atoms in a mole is called Avogadro's number, the value of which is approximately 6.022 × 10. One mole of a substance always contains almost exactly the "standard atomic weight" or "molar mass" of that substance; however, this may or may not be true for the "atomic mass," depending on whether or not the element exists naturally in more than one isotope. For example, the standard atomic weight of iron is 55.847 g/mol, and therefore one mole of iron as commonly found on earth has a mass of 55.847
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