## Chemistry 9th Edition

$$^{28}Si \quad 27.98 \quad 92.21 \%$$ $$^{29}Si \quad 28.9 \quad 4.70\%$$ $$^{30}Si \quad 29.97 \quad 3.09\%$$
Abundance of $^{28}Si$ = 100%-3.09%-4.70%= 92.21 % We refer to the periodic table to determine the average atomic mass of Si. Let m be the atomic mass of $^{29}Si$: $28.085=0.9221*27.98+0.0470*m+0.0309*29.97$ $m=\frac{28.085-0.9221*27.98-0.0309*29.97}{0.0470}=28.9$