# What is the average atomic mass of silicon?

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Given the following data, calculate the average atomic mass of silicon.

isotope = Si-28

amu =27.9769

abundance(%) =92.18

isotope = Si-29

amu =28.9765

abundance(%) =4.71

isotope =Si-30

amu =29.9738

abundance(%) =3.12

Given the following data, calculate the average atomic mass of silicon.

isotope = Si-28

amu =27.9769

abundance(%) =92.18

isotope = Si-29

amu =28.9765

abundance(%) =4.71

isotope =Si-30

amu =29.9738

abundance(%) =3.12

##### 1 Answer

Multiply the amu by the percentage of occurrence to arrive at an average atomic mass of

#### Explanation:

We take the amu of each isotope, multiply it by the percentage of occurrence, and end up with a weighted average:

This simplifies to:

Checking "the internet" to verify our answer, I found 28.0855 u ± 0.0003 u, so the answer calculated for our question is pretty close.