Magnesium has three naturally occurring isotopes with masses of 23.99, 24.99, and 25.98 amu and natural abundances of 78.99%, 10.00%, and 11.01%. Calculate the atomic mass of magnesium.

24.309

Explanation:

Let A, B, and C represent the three isotopes.

For isotope A:

Mass number = 23.99

Abundance = 78.99%

For isotope B:

Mass number = 24.99

Abundance = 10.00%

For isotope C:

Mass number = 25.98

Abundance = 11.01%

Atomic mass of Mg =?

Atomic mass = [(Mass of AxA%)/100] + [(Mass of BxB%)/100] + [(Mass of CxC%)/100]

Atomic Mass = [(23.99x78.99)/100] + [(24.99x 10)/100] + [(25.98x11.01)/100]

Atomic number = 18.950 + 2.499 + 2.860

Atomic mass of Mg = 24.309

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