What is the correct formula for barium chlorate?
The barium cation has the formula
An ionic compound is neutral, which means that its overall charge is
Now the formula represents a neutral compound. Notice that because there are two chlorate ions, which are polyatomic, we put the formula for the chlorate ion in parentheses with a subscript of
There is a method for writing formulas for ionic compounds which is called the crisscross rule. The following video explains how it works.
If you're not sure how to determine the charge of a monatomic ion from the periodic table, the following video should be helpful.