We can use the following equation:

$\overline{){\mathbf{Atomic}}{\mathbf{}}{\mathbf{Mass}}{\mathbf{=}}{\mathbf{[}\mathbf{mass}\mathbf{\times}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\mathbf{]}}_{\mathbf{isotope}\mathbf{}\mathbf{1}}{\mathbf{+}}{\mathbf{[}\mathbf{mass}\mathbf{\times}\mathbf{f}\mathbf{.}\mathbf{a}\mathbf{.}\mathbf{]}}_{\mathbf{isotope}\mathbf{}\mathbf{2}}}$

where atomic mass = average atomic mass of the element and f.a. = fractional abundance of the isotope. To get ** f.a.**, we simply need to divide the given percent abundance by 100.

Magnesium has three naturally occurring isotopes with the following masses and natural abundances:

Isotope | Mass (amu) | Abundance (%) |

Mg-24 | 23.9850 | 78.99 |

Mg-25 | 24.9858 | 10.00 |

Mg-26 | 25.9826 | 11.01 |

Calculate the atomic mass of magnesium.

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Atomic Mass concept. You can view video lessons to learn Atomic Mass. Or if you need more Atomic Mass practice, you can also practice Atomic Mass practice problems.