Science, Tech, Math › Science How to Calculate Atomic Abundance from Atomic Mass Share Flipboard Email Print REB Images / Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 25, 2018 In chemistry, one often needs to calculate different forms of measurement. In this example, we calculate atomic abundance from atomic mass. The element boron consists of two isotopes, 105B and 115B. Their masses, based on the carbon scale, are 10.01 and 11.01, respectively. The abundance of 105B is 20.0%.What is the atomic abundance of and the abundance of 115B? Solution The percentages of multiple isotopes must add up to 100%.Since boron only has two isotopes, the abundance of one must be 100.0 - the abundance of the other. abundance of 115B = 100.0 - abundance of 105B abundance of 115B = 100.0 - 20.0abundance of 115B = 80.0 Answer The atomic abundance of 115B is 80%.