These 2 isotopes are all of bromine that is naturally found (their percentages add up to 100%). In order to calculate the mean atomic mass, we can use the following calculation: [tex] M_{79} *percent_{79}+M_{81}*percent_{81}[/tex] . This yields an average atomic mass of 79.903 amu. This procedure is general; whenever we have many types F of a specific genre G, the mean of the genre G can be calculated by:
[tex]\sum{T_i*p_i}[/tex]
where [tex]p_i[/tex] is the proportion of type i in the genre G. In this example, Br79 and Br81 are the 2 types and the genre is Bromine.
