How to Calculate Atomic Mass with Abundance?
Calculating the average atomic mass of an element involves considering the mass and abundance of each of its isotopes. Here's how:
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Convert Percentages to Decimals: Divide each isotope's percent abundance by 100 to obtain its decimal abundance.
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Multiply Mass and Abundance: For each isotope, multiply its decimal abundance by its atomic mass.
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Sum the Results: Add the results from step 2 for all isotopes. The sum is the average atomic mass of the element.
Example Calculation
Let's say an element has two isotopes:
- Isotope 1: Atomic mass = 10 amu, Abundance = 20%
- Isotope 2: Atomic mass = 12 amu, Abundance = 80%
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Convert to decimals:
- Isotope 1: 20% / 100 = 0.20
- Isotope 2: 80% / 100 = 0.80
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Multiply and sum:
- Isotope 1: 10 amu * 0.20 = 2 amu
- Isotope 2: 12 amu * 0.80 = 9.6 amu
- Average atomic mass: 2 amu + 9.6 amu = 11.6 amu
Understanding Isotopes and Atomic Mass
- Isotopes: Atoms of the same element with the same number of protons but a different number of neutrons. This results in different atomic masses for the isotopes of the same element.
- Atomic Mass: The weighted average mass of all the isotopes of an element. The weighting is based on the natural abundance of each isotope.
Multiple sources, including Chemistry LibreTexts and CK-12, confirm this calculation method. YouTube videos such as "How To Calculate The Average Atomic Mass" further illustrate the process visually.
