Average Atomic Mass Calculator
Compute the weighted average atomic mass of an element based on the isotopic abundances.
Calculation Parameters
Specify your chemical inputs.
Calculated Result
Expert Tip
Double check molecular weights and balance equations to ensure stoichiometric ratios are correct.
How this Calculator Works
This calculator calculates the average atomic mass of an element from the masses and relative abundances of its stable isotopes. Adjust the parameters using the input sliders below:
- Isotope 1 Mass (u): Atomic mass of the first isotope (Range: 1 to 300, Default: 34.969)
- Isotope 1 Abundance (%): Percentage abundance of the first isotope (Range: 0 to 100, Default: 75.78)
- Isotope 2 Mass (u): Atomic mass of the second isotope (Range: 1 to 300, Default: 36.966)
- Isotope 2 Abundance (%): Percentage abundance of the second isotope (Range: 0 to 100, Default: 24.22)
The results are computed instantly and updated in the results panel on the right.
Formula & Methodology
Where:
- Mass_1, Mass_2: The unified atomic mass values of isotopes 1 and 2.
- Abundance_1, Abundance_2: The relative natural abundances in percent.
Step-by-Step Calculation Example
To calculate the average atomic mass of Chlorine manually from its stable isotopes, follow these steps:
- Identify the input parameters. For example:
- Isotope 1 Mass = 34.969 u, Abundance = 75.78%
- Isotope 2 Mass = 36.966 u, Abundance = 24.22%
- Apply the formula:
Average Mass = (34.969 * 0.7578) + (36.966 * 0.2422) = 26.499 + 8.953 = 35.45 u
- Verify the calculated value which is updated instantly in the results panel on the right.
Frequently Asked Questions
How is average atomic mass calculated? โผ
Average Atomic Mass = ฮฃ (Isotope Mass ร Fractional Abundance) for all naturally occurring isotopes.
Why are atomic masses on the periodic table decimals? โผ
Periodic table masses are weighted averages reflecting the natural relative abundances of all stable isotopes of that element.
Must the relative abundances sum to 100%? โผ
Yes, all fractional abundances must sum to 1.00 (or 100%) across all isotopes of an element.