- The atomic mass of chromium is the weighted average of the atomic masses of the naturally occurring isotopes of chromium.
- Atomic mass calculations require the use of percentage abundance of each isotope.
Listing the known and unknown quantities and planning the problem:
Here is what we know:
- Chromium-50: atomic mass = 49.946 amu and the % abundance = 4.35%
- Chromium-52: atomic mass = 51.941 amu and the % abundance = 83.79%
- Chromium-53: atomic mass = 52.941 amu and the % abundance = 9.50%
- Chromium-54: atomic mass = 53.939 amu and the % abundance = 2.36%
Here is what we don't know:
- The average atomic mass of Chromium.
The percentage abundance of each isotope must be changed to its decimal form. This can be done by dividing the percentage by 100. After that multiply this value by the atomic mass of that isotope. Then add together for each isotope to get the average atomic mass.
Calculations:
Chromium-50: 0.0435 × 49.946 = 2.172651 amu
Chromium-52: 0.8379 × 51.941 = 43.5213639 amu
Chromium-53: 0.095 × 52.941 = 5.029395 amu
Chromium-54: 0.0236 × 53.939 = 1.2729604
Average atomic mass: 2.172651 + 43.5213639 + 5.029395 + 1.2729604 = 51.9963703 amu