Atoms and their structure

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Atomic Mass

Magnesium has three isotopes. 78.99% magnesium 24 with a mass of 23.9850 amu, 10.00% magnesium 25 with a mass of 24.9858 amu, and the rest magnesium 25 with a mass of 25.9826 amu. What is the atomic mass of magnesium?

If not told otherwise, the mass of the isotope is the mass number in amu

Slide 59

Atomic Mass

Is not a whole number because it is an average.

are the decimal numbers on the periodic table.