Boron has two naturally occurring isotopes: boron-10 (abundance = 19.8 %, mass = 10.013 amu) and boron-11 (abundance = 80.2%, mass = 11.009 amu). Calculate the (average) atomic mass of boron.Click to see full answer. Consequently, how do you calculate percent abundance? Finding the Average Atomic Mass of an Element with Isotopes Multiply each isotope’s mass by its percent abundance. Add each product of mass times percent abundance of each isotope. This sum represents the weighted average atomic mass of the element.Similarly, which isotope of boron is most abundant? boron-11 Thereof, what is the percentage of each isotope in boron? Example 1 The natural abundance for boron isotopes is: 19.9% 10B (10.013 amu) and 80.1% 11B (11.009amu). Calculate the atomic weight of boron. If you look in the periodic table you will be able to check that our answer is correct! Determining the percent abundance of each isotope from atomic mass.What is the percent abundance of an isotope?The relative abundance of an isotope is the percentage of atoms with a specific atomic mass found in a naturally occurring sample of an element.