Answer:
[tex]A=\sum_i A_i r_i[/tex]
Explanation:
Before answering the question, we introduce two definitions:
- Isotope: isotopes of the same element are atoms of the same element having same number of protons but different number of neutrons --> this means that they have same atomic number, but different atomic mass
- Relative abundance: each isotope is present with a certain relative abundance, which gives the % of that isotope compared to the total.
When we know the mass spectrum of a certan element, it means we know the relative abundance of each isotope, together with the atomic mass of the isotope.
For instance, we can have:
- Isotope 1 with atomic mass [tex]A_1[/tex] and relative abundance [tex]r_1[/tex], where [tex]r_1[/tex] is a fraction in the form [tex]\frac{r}{100}[/tex] (it gives the percentage of that isotope relative to the total)
- Isotope 2 with atomic mass [tex]A_2[/tex] and relative abundance [tex]r_2[/tex]
... and so on
So, the average atomic mass of the element is calculated with the formula:
[tex]A=\sum_i A_i r_i[/tex]
So, basically by calculating the sum of the product of each atomic mass by its relative abundance.
