Define average atomic mass

Explanation

Average atomic mass is defined when an element exists in isotopic form. For defining the average atomic mass of an element, we take atomic mass of each isotope and also the proportion of their occurrence. For example, chlorine occurs in nature in two isotopic forms having atomic mass 35 and 37. These isotopes occurs in nature in the ratio of `3:1`. Then average atomic mass of chlorine is, `=(35 xx 3 + 37 xx 1)/(3+1)= 35.5` a.m.u