Calculating the average atomic mass of an element with multiple isotopes involves a straightforward three-step process. Here's how you do it, using information from the reference:
Understanding Isotopes
Isotopes are versions of the same element that have the same number of protons but different numbers of neutrons, leading to variations in atomic mass. The average atomic mass considers these variations and their relative abundance to provide an average mass for an element's atoms.
Steps to Calculate Average Atomic Mass
-
Identify Isotope Data:
- Mass: Determine the atomic mass of each isotope in atomic mass units (amu).
- Percent Abundance: Find the percentage of each isotope in the element's composition.
Example: Consider an element with two isotopes:
- Isotope 1: Mass = 10 amu, Abundance = 20%
- Isotope 2: Mass = 12 amu, Abundance = 80%
-
Multiply Mass by Percent Abundance:
- For each isotope, multiply its mass by its percentage abundance (expressed as a decimal).
- Calculations for Example:
- Isotope 1: (10 amu) * (20/100) = 2 amu
- Isotope 2: (12 amu) * (80/100) = 9.6 amu
-
Sum the Results:
- Add up the results from step 2 for all the isotopes.
- Calculation for Example: 2 amu + 9.6 amu = 11.6 amu
Result: The average atomic mass of the element is 11.6 amu.
Summary in Table Format:
| Isotope | Mass (amu) | Percent Abundance (%) | Mass * Abundance |
|---|---|---|---|
| Isotope 1 | 10 | 20 | 2 |
| Isotope 2 | 12 | 80 | 9.6 |
| Total | 11.6 amu |
Key Points:
- The percentages of all the isotopes of an element must equal 100%.
- Average atomic mass is usually not a whole number because it's an average of all the isotope masses.
- This value is used in chemical calculations to get an idea of the mass of an element's atoms.
- The reference materials outline these exact steps ( "Step 1: Identify the percentage of each isotope in the composition of the element and its mass. Step 2: For each isotope, multiply its mass by the percent. Step 3: Add the results for all the isotopes from Step 2. This is the average atomic mass of the given element.")
