Question

What is the correct formula for barium chlorate?

Answer 1

`"Ba(ClO"_3)_2"`

Explanation:

The barium cation has the formula `"Ba"^(2+)"`. The chlorate polyatomic anion has the formula `"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:

`"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.