Average Atomic Mass Calculator
Calculate weighted average atomic mass from isotopic abundances
Isotopes are atoms of the same element with different numbers of neutrons. Key points about isotopes:
- Same atomic number: All isotopes of an element have the same number of protons
- Different mass numbers: Each isotope has a different number of neutrons
- Natural abundance: Most elements exist as a mixture of isotopes in nature
The average atomic mass is calculated using this formula:
Average Mass = Σ(Isotope Mass × Abundance Percentage / 100)
This weighted average takes into account both the mass of each isotope and how commonly it occurs in nature.
- Enter the mass and abundance for each isotope
- Add more isotopes if needed using the "Add Another Isotope" button
- Ensure the total abundance equals 100%
- Click Calculate to find the average atomic mass
The calculator will determine the weighted average based on the mass and abundance of each isotope.
Why don't atomic masses on the periodic table match any isotope exactly?
The atomic masses shown on the periodic table are weighted averages of all naturally occurring isotopes of that element, taking into account their relative abundances.
Why must abundances add up to 100%?
The abundance percentages represent the relative proportion of each isotope in nature. Since these are all the possible forms of the element, they must sum to 100%.
How accurate are abundance measurements?
Natural abundances can vary slightly depending on the source of the sample. The values used in calculations are typically averaged from multiple measurements and standardized by international chemistry organizations.