This is a video tutorial in the Education category where you are going to learn how to understand polyatomic chemical formulas. When writing the formula using polyatomics, the same cross-over rule applies. 1st identify the metal and non-metal. Then you write the symbols, write the charges, cross-over the charges from top to bottom, remove the charge and simplify the numbers and remove the 1s. for example, iron (II) phospahate. The "ate" ending implies that phosphate is polyatomic. The symbol and charge for iron are Fe and +2. The symbol and charge for phosphate are PO4 and negative 3. You have to watch the video for further steps as it will not make sense without the demonstration.