example of average atomic mass
Average atomic mass of copper = (62.93 amu Ã 0.6909) + (64.94 amu Ã 0.3091)= 63.55. From the calculation, we know that an AVERAGE atom of copper has a mass of 63.55 amu. Notice that in this problem, we would predict that the average is closer to the weight of the lighter isotope.