[wynn]

Here is my struggle:
I am told to write the formula for chlorate ion. How would you start approaching this question???
P.S. I have no previous knowledge of this ion.
Here is all I have in my mind:
1. The suffix -ate is telling me that this ion must have a higher number of oxygen if chlorine can form two different polyanions.
2. I know it is an ion, but I don't know the charge of it.
Btw,I don't want to simply memorize every common polyanions!

[Hunter2]

But I think you have to memorize.

The halogenes form Ions like XO_n^- X = Cl, Br, I, n = 1-4
Iodine also have higher oxygen numbers

The One what you mentioned has the number 3. Its not logical so you have to learn und remember it. The Charge of all Halogen ions is -1.