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

The atomic mass is the weighted average of the masses of all the naturally occurring isotopes of an element. Using the percent abundance of each isotope and their respective atomic masses, we can calculate the atomic mass of silicon.
- S1U1P28S1S1P0Si (92.23% abundance) has an atomic mass of 27.9769 amu
- S1U1P29S1S1P0Si (4.67% abundance) has an atomic mass of 28.9765 amu
- S1U1P30S1S1P0Si (3.1% abundance) has an atomic mass of 29.9738 amu
Using the formula:
(0.9223)(27.9769 amu) + (0.0467)(28.9765 amu) + (0.0310)(29.9738 amu) = 28.0855 amu
Therefore, the best choice is D) 28.0855 amu as it is the calculated atomic mass of silicon.

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