When you name a binary compound, you have to add to the ending of the second element in the compound.

-ide

Explanation:

In order to ensure that you are accurate when naming an anion, or perhaps the second element in a binary compound, it is mandatory to add -ide to the ending of the second element or the end of the stem. For example when you want to name RbI, which is Rubidium and Iodine, this is called rubidium iodide.  Another example is CaO, which is calcium and oxygen, it is therefore called  calcium oxide.