How does the periodic table help in predicting the formula of a stable ionic compund

You use the atomic number to find out how many protons and neutrons there are in the atom. you use the atomic mass to find out how many protons and electrons there are in the atom. 

Is a logical series of steps

Use a magnet to separate iron, evaporate water, i'm not sure how to separate the other two i'm sorry but good luck

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