Question

If the formula for a compound is represented by X2Y3 and the charge on the Y ion is -2, what is the charge in the X ion?

Answer 1

To figure out and write ionic compounds, you take the charge of each ion, switch it around and put it as the subscript on the bottom of the element.

If Y has a charge of -2, then that means the charge would be given to X and would be put on the bottom. Therefore you would write X as: X2 (As seen in the question)

Because ionic compounds are made from positive and negative ions, we can tell that the charge of X will be positive (as Y has a charge of negative 2).

All we have to do is take the subscript of X and switch it over so it will go to Y, and then turn it into a charge.

So that means the charge of X is +3, because there are 3 Y elements in the compound, and we already know X will be positive.

As long as you know how to make and write ionic compounds, these sorts of questions will be easier to write in the future. I hope this could help :)

Answer 2

Here's what I was talking about, as a diagram. You do this to write any ionic compound and to work out the charge of any element in an ionic compound, you just have to work backwards.