This was discussed in the formula writing lesson . Here is an example. N2O4 Use the prefix Di in front of the elemental name of Nitrogen and use the prefix tetra in front of the oxygen name with droping the ygen and adding the ide since it is a binary compound. Now let's see if you can do these. R. H. Logan, Instructor of Chemistry, Dallas County Community College District, North Lake College.
Magnesium has only one valence.
Mercury is one of the previously identified multi-valent elements. Halogens in any binary compound will be -1 each. Calcium has only one valence so use the element of the first element, use the element name of Oxygen drop the ygen and add ide. Copper is multi-valent so determine its valence in this compound. Use the element for Phosphorus, drop the orus and add ide.