Chlorine-37 has an atomic mass of 36.966 amu and a percent abundance of 24.23%. To calculate the average atomic mass of chlorine, use the information in a periodic table of the element (see Resources) to find the (weighted) average but changing the percents to decimals: ...
Other carbon isotopes do exist, but they exist in quantities so small that, for this example problem, they can be ignored. 3 Multiply the atomic mass of each isotope by its proportion in the sample. Multiply the atomic mass of each isotope by its percent abundance (written as a decimal)....