Calculating the average atomic mass of an element involves considering the masses of its isotopes and their relative abundances. Here's how to do it:
Steps to Calculate Average Atomic Mass
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Convert Percent Abundance to Decimal Form: The first step involves converting each isotope's percentage abundance into a decimal by dividing the percentage by 100. For example, if an isotope has an abundance of 75%, its decimal form would be 75/100 = 0.75.
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Multiply by Isotope Mass: Next, multiply each isotope's decimal abundance by its atomic mass. For instance, if an isotope's mass is 20 amu and its decimal abundance is 0.75, the result will be 0.75 * 20 = 15.
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Sum the Products: Finally, add up the results from step 2 for all the isotopes of the element. The total is the average atomic mass.
Formula:
Average Atomic Mass = (Decimal Abundance of Isotope 1 x Mass of Isotope 1) + (Decimal Abundance of Isotope 2 x Mass of Isotope 2) + ...
Example
Let's assume an element has two isotopes:
- Isotope 1: Atomic mass = 20 amu, Abundance = 75%
- Isotope 2: Atomic mass = 22 amu, Abundance = 25%
Here's how to find the average atomic mass:
| Isotope | Atomic Mass (amu) | Percent Abundance | Decimal Abundance | Calculation |
|---|---|---|---|---|
| Isotope 1 | 20 | 75% | 0.75 | 0.75 x 20 = 15 |
| Isotope 2 | 22 | 25% | 0.25 | 0.25 x 22 = 5.5 |
| Total | 15 + 5.5 = 20.5 amu |
Therefore, the average atomic mass of this element is 20.5 amu.
Key Points:
- Isotopes: These are atoms of the same element that have different numbers of neutrons. This means they have different atomic masses.
- Percent Abundance: This indicates how much of an isotope exists compared to the other isotopes of that same element on Earth.
- Average Atomic Mass: This is the weighted average of the atomic masses of all the isotopes of an element, considering their abundances. This is the atomic mass that appears on the periodic table.
- Importance: Calculating the average atomic mass is essential in various fields, such as chemistry and materials science.
By following these steps, as outlined in the reference, you can easily calculate the average atomic mass of any element given the atomic masses and percent abundances of its isotopes.
