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 rutherfordium Isotopes of rutherfordium Rutherfordium (Rf) is a synthetic element, and thus a standard atomic weight cannot be given. Like all synthetic elements, it has no stable isotopes. The first isotope to be synthesized was either Rf in 1966 or Rf in 1969. There are 16 known radioisotopes from Rf to Rf (3 of which, Rf, Rf, and Rf are unconfirmed) and 4 isomers. The longest-lived isotope is Rf with an estimated half-life of 5 hours. The longest directly measured half-life is Rf at 11 minutes, and the longest-lived isomer is Rf with a half-life of 81 seconds. Super-heavy elements such