# What is the correct formula for barium chlorate?

Nov 9, 2016

$\text{Ba(ClO"_3)_2}$

#### Explanation:

The barium cation has the formula $\text{Ba"^(2+)}$. The chlorate polyatomic anion has the formula ${\text{ClO"_3}}^{-}$.

An ionic compound is neutral, which means that its overall charge is $0$. Since the barium ion has a charge of ${2}^{+}$, the negative charge will have to be ${2}^{-}$. We can't change the formula or charge of the chlorate ion, but we can change the number of chlorate ions. Two chlorate ions will have a charge of ${2}^{-}$. So the formula for barium chlorate is:

$\text{Ba(ClO"_3)_2}$

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 $2$.

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.