Save guides, add subjects and pick up where you left off with your BBC account. The relative atomic masses of elements are proportional measures. For example, the Ar for helium is 4.0, and the A r ...

In other words, in every 100 chlorine atoms, 75 atoms have a mass number of 35, and 25 atoms have a mass number of 37. To calculate the relative atomic mass, A r , of chlorine: ...