How to Name ionic Compounds

Write the chemical formula of the ionic compound. You can find transition metals in the middle of the periodic table. They are called transition metals because their oxidation number or charge varies continuously. Suppose we have the following compound: Fe ₂ O ₃ . ^[2]

Determine the electrical charge of the metal. Since metal has a positive charge, you take the number 3 from O ₃ cross it and then Fe has a charge of +3 (if you want you can do the opposite and write O with a charge of -2). Sometimes people will give you an electric charge.

Write the metal name. You know Fe is iron and has a charge of +3 so it can be called Iron(III) . Remember to use Roman numerals when writing names, when writing chemical formulas do not use Roman numerals.

Write the name of the nonmetal. You know O is oxygen, add “t” to the end and you have “oxide”.

Put the first name and the second name next to each other. Now we have the name of the compound. Fe ₂ O ₃ = Iron (III) oxide .

Use the old naming convention. When you refer to English books, you may encounter the old naming. According to the old naming convention, you use the endings “-ous” and “-ic” when naming metals instead of using Roman numerals. If ferrous metal has a lower oxidation number (less than one charge unit, regardless of “+” or “-“), we add the “-ous” suffix. If it has a higher oxidation number, add the “-ic” suffix. Fe ²⁺ has a lower oxidation number (Fe ³⁺ has a higher oxidation number), so it is called ferrous . Thus, the name of the compound Fe ²⁺ O is ferrous oxide .

Remember the exceptions. There are two transition metals with constant charge, zinc (Zn) and silver (Ag). That means you don’t need to use Roman numerals to name these elements.

Write the formula of the polyatomic ion. This compound is composed of more than two ions. Suppose we have the following compound: FeNH ₄ (SO ₄ ) ₂ . ^[3]

Find the metal charge. You have to do some math to figure it out. First, you know the sulfate ion or SO ₄ has a charge of -2, and there are these two because there is a 2 under the parentheses. We have 2 x -2 = -4. Next you know NH ₄ , or ammonium ion, has a charge of +1. Add -4 to 1 to get -3. That is, the iron ion Fe must have a charge of +3 for the compound to be electrically neutral.

Write the metal name. In this case you can write Iron(III) .

Write the name of the non-metal ion. In the above example, the names of the two ions are ammonium and sulfate respectively, or collectively, ammonium sulfate.