Bromine occurs in nature mainly in the form of two isotopes `._(35)^(79)Br and ._(35)(81)Br`. If the abundance of `._(35)^(79)Br` isotope is 49.7 ^% and that of `._(35)^(81)Br` isotope is 50.3 %, calculate the average atomic mass of bromine.

Explanation

We know that upper digit in the symbol of an isotope represent its mass (which is the same as its mass number) Now :
(i) The mass of `._(35)^(79)Br` isotope is 79 u and its abundance is 19.7 %
(ii) The mass of `._(35)^(81)Br` isotope is 81 u and its abundance is 50.3 %
So, Average atomic mass of bromine `= 79xx(49.7)/(100)+81xx(50.3)/(100)`
`=(3926.3)/(100)+(4074.3)/(100)`
`= 39.263 + 40.743`
`= 80.006`
`= 80 u`
Thus, the average atomic mass of bromine is 80 u.