The compound you're likely thinking of is copper(II) nitrate, with the chemical formula Cu(NO₃)₂.

Here's why:

* Copper (Cu) is a transition metal that can form multiple oxidation states. In this case, it's in the +2 oxidation state, hence the Roman numeral II in the name.

* Nitrate (NO₃⁻) is a polyatomic ion composed of nitrogen and oxygen.

To balance the charges, two nitrate ions (each with a -1 charge) are needed for each copper(II) ion (+2 charge).