Isotopic Abundance Calculator: Average Atomic Mass
Calculate the average atomic mass of an element from the masses and natural abundances of its isotopes. Understand why atomic masses are not whole numbers on the ...
What is Isotopic Abundance?
Most elements exist as a mixture of isotopes — atoms with the same number of protons but different numbers of neutrons. The atomic mass on the periodic table is a weighted average of all stable isotopes based on their natural abundances. Isotopic analysis has applications in forensics, food authentication, archaeology, and nuclear science.
⚛️ Isotopic Abundance Calculator
Free calculator for instant results.
📐 Formula
Avg Atomic Mass = Σ (abundance × mass)
Abundance expressed as decimal (not percentage). Sum over all stable isotopes. Result in atomic mass units (u or Da).
📝 Worked Example
Chlorine isotopes: ³⁵Cl (34.969 u, 75.77%) and ³⁷Cl (36.966 u, 24.23%):
Avg = 0.7577×34.969 + 0.2423×36.966
= 26.496 + 8.957 = 35.45 u ✓ (matches periodic table)
📝 How to Use
❓ FAQ
Why are atomic masses not whole numbers?
Because they are weighted averages over multiple isotopes, each with slightly different masses due to nuclear binding energy differences (mass defect).
What is a mass spectrometer?
An instrument that separates ions by mass-to-charge ratio. It measures isotopic abundances precisely and is the source of the values used in these calculations.
Veer Kumavat
Founder & AuthorVeer is a 14-year-old student from Nashik, Maharashtra, who built SciFi Calculators to help students worldwide master STEM subjects. He is passionate about making complex science and math problems accessible through intuitive digital tools.