Most of the atomic mass of a substance is made up of protons and neutrons. When the existence of isotopes. What Is The Relative Atomic Mass And Relative Molecular Mass Of An Element A Plus Topper Https Www Aplusto Relative Atomic Mass Molecular Mass Molecular The unit of measure for mass is the atomic mass unit amu. . It is a bulk. Structures Trends Chemical Reactions Quantitative Chemistry and Analysis. The solution means the atomic mass of the specific element. M e is the mass of a stationary electron also known as the invariant mass of the electron. One atomic mass unit is equal to 166 x 10-24 grams. It has a unit of the unified mass unit u or the atomic mass unit amu. The atomic mass unit can be related with the other mass unit by using the conversion factor1u 166054 X 10-24 g. An atomic mass unit is a physical constant equal to one-twelfth of the mass of an unbound atom of carbon-12. The unified atomi