Naturally occurring silicon consists of three isotopes with the following isotopic masses and abundances.

Question

IsotopeIsotopic mass (u)Abundance (%)
28Si	27.9769265327	92.2297
29Si	28.97649472	4.6832
30Si	29.97377022	3.0872

Calculate the average atomic mass of naturally occurring silicon to at least four significant figures.

average atomic mass =

Answer 1

You table isn't formatted correctly, but we can assume that the 2nd column is the atomic mass and the 3rd column is the % abundance for each isotope listed in the first column.

(0.922297 x 27.9769) + (0.046832 x 28.9765) + (0.030872 x 29.9738) = 25.803 + 1.3570 + 0.92535

= 28.09 = average atomic mass for Si to 4 significant figures