The invariant mass of an electron is approximately 9.109 × 10 −31 kilograms, or 5.489 × 10 −4 atomic mass units. Due to mass–energy equivalence, this corresponds to a rest energy of 0.511 MeV (8.19 × 10 −14 J). The ratio between the mass of a proton and that of an electron is about 1836.
The molecular mass of a substance is the number of times the molecule of the substance is heavier than one-twelth the mass of an atom of carbon -12. Or, the molecular mass is equal to the sum of its atomic masses of all the atoms present in one molecule of a substance. For eg: Water (H 2 O) Atomic mass of H= 1 unit. Atomic mass of O =16 units. A weighted average is found by multiplying each mass by its fractional occurrence (in decimal form) and then adding all the products. The sum is the weighted average and serves as the formal atomic mass of the element. In this example, we have the following: 0.50 × 10 u. = 5.0 u. 0.50 × 11 u. = 5.5 u. Sum. The atomic mass is usually measured in the units unified atomic mass unit (u), or dalton (Da). Both units are derived from the carbon-12 isotope, as 12 u is the exact atomic mass of that isotope. So 1 u is 1/12 of the mass of a carbon-12 isotope: 1 u = 1 Da = m(12 C)/12 BExiSIK.is atomic mass atomic weight
