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 hassium Isotopes of hassium Hassium (Hs) 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 Hs in 1984. There are 12 known isotopes from Hs to Hs and 1–4 isomers. The longest-lived isotope is Hs with a half-life of 10 seconds. Super-heavy elements such as hassium are produced by bombarding lighter elements in particle accelerators that induce fusion reactions. Whereas most of the isotopes of hassium can be synthesized directly this way, some heavier ones have only been observed as decay