Name the ionic compound ##"CrO"##?

Chromium(II) oxide.

The first thing to recognize here is that you're dealing with an , since you hae a transition metal, chromium, ##"Cr"##, bonded to a nonmetal, oxygen, ##"O"##.

The second important thing to recognize here is that chromium, being a transition metal, can have multiple , which is another way of saying that it can form multiple cations.

This means that you're going to have to use a Roman numeral to describe its oxidation state in the name of the compound.

So, start with what you know. Oxygen, being located in group 16 of , forms ##2-## anions aclled oxide anions, ##"O"^(2-)##.

Now, are always neutral. This means that the positive charge on the chromium cation must balance out the negative charge on the oxide anion.

Since the formula unit for this compound, ##"CrO"##, contains one chromium anion and one oxygen anion, you can say that the charge on the chromium cation must be equal to ##2+##.

When , the cation is always named first, followed by the Roman numeral, when needed, and the anion.

In this case, the Roman numeral that must be used is ##"(II)"##, which means that the name of the compound will be

chromium(II) oxide ##->## ##"CrO"##