Question

An element has four naturally occurring isotopes with the masses and natural abundances given here. find the atomic mass of the element. isotope mass (amu) abundance (%) 1 135.90714 0.1900 2 137.90599 0.2500 3 139.90543 88.43 4 141.90924 11.13

Answer 1

Abundance of each isotope = 0.1900 x100 = 0.001900
0.2500 = 0.002500
88.43 =  0.8843
11.13 = 0.1113
Atomic mass of the element = (135.90714  x 0.001900) + (137.90599 x 0.002500) + (139.90543 x 0.8843) + (141.90924 x 0.1113)
= 0.258223566 + 0.344764975 + 123.718371749 + 15.794498412
= 140.1 amu is the atomic mass of the element