Molecular mass Molecular mass Relative molecular mass or molecular weight is the mass of a molecule. It is calculated as the sum of the relative atomic masses of each constituent element multiplied by the number of atoms of that element in the molecular formula. The molecular mass of small to medium size molecules, measured by mass spectrometry, determines stoichiometry. For large molecules such as proteins, methods based on viscosity and light-scattering can be used to determine molecular mass when crystallographic data are not available. Both atomic and molecular masses are usually obtained relative to the mass of the isotope C (carbon 12),
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