The average atomic weight of an element is the weighted average of the atomic masses of all the naturally occurring isotopes of that element. It takes into account the relative abundance of each isotope.
To calculate the average atomic weight, you need the following information:
- The atomic masses of the isotopes of the element.
- The natural abundance (percentage composition) of each isotope.
The average atomic weight can be calculated using the formula:
Average Atomic Weight = (Mass1 × Abundance1 + Mass2 × Abundance2 + ... + Massn × Abundancen)
where Mass1, Mass2, ..., Massn are the atomic masses of the isotopes, and Abundance1, Abundance2, ..., Abundancen are the natural abundances of those isotopes.
For example, let's calculate the average atomic weight of chlorine (Cl) using the atomic masses and abundances of its isotopes:
Isotope Atomic Mass Abundance Cl-35 34.9689 75.77% Cl-37 36.9659 24.23%
Average Atomic Weight = (34.9689 × 0.7577 + 36.9659 × 0.2423) = 35.453 amu
Therefore, the average atomic weight of chlorine is approximately 35.453 atomic mass units (amu).
Note that the values used for atomic masses and abundances may vary depending on the specific data available, as isotopic compositions can vary for different sources of an element.