Silicon, which makes up about 25% of Earth's crust by mass, is used widely in the modern electronics industry. It has three naturally occurring isotopes, ²⁸Si, ²⁹Si, and ³⁰Si. Calculate the atomic mass of silicon. A)29.2252 amu B)28.9757 amu C)28.7260 amu D)28.0855 amu E)27.9801 amu

Question

Quizplus · Accepted Answer

To calculate the atomic mass of silicon, we need to take the weighted average of the isotopes' masses, where the weights are the isotopic abundances. From the periodic table, we know that the abundances of the three isotopes are 92.23%, 4.67%, and 3.10%, respectively. 
Atomic mass = (0.9223 x 28.0855 amu) + (0.0467 x 29.9255 amu) + (0.0310 x 29.9568 amu) 
Atomic mass = 28.0855 amu

Silicon, Which Makes Up About 25% of Earth's Crust by Mass