Pet & Animal: How to Name Ionic Compounds

Saturday, 4 April 2015

How to Name Ionic Compounds

Ionic compounds are made up of cations (positive ions) and anions (negative ions). To name an ionic compound, you should first write out the name of the metal, followed by the name of the nonmetal with its respective new ending. If you want to know how to name ionic compounds in a variety of situations, just follow these steps.

Steps

Basic Ionic Compounds

Write down the formula of the ionic compound. Let's say the ionic compound you're working with is NaCl.^[1]

Write the name of the metal. Na is sodium. So, write Sodium.

Write the name of the nonmetal with the "-ide" ending. Cl is chlorine. To add the "ide" ending, just drop the last syllable, "-ine," and add "-ide" instead. Chlorine becomes chloride.

Combine the names. NaCl can be written as sodium chloride.

Practice naming more simple ionic compounds. Once you've gotten this formula down, try naming a few more simple ionic compounds. Even memorizing a few can help you have a better understanding of how to name ionic compounds. Here are a few more:
- Li₂S = Lithium sulfide
- Ag₂S = Silver sulfide
- MgCl₂ = Magnesium chloride

Transition Metals

Write down the formula of the ionic compound. Transition metals can be found in the middle of the periodic tables. They get their name because their oxidation numbers, or their charges, are constantly changing. Let's say you're working with this compound: Fe₂O₃.^[2]

Write down the charge of the metal. You know that the metal will have a positive charge, so cross over the 3 from the O₃ and write that Fe has a charge of +3. (For fun, do the reverse and write that O has a charge of -2.) Sometimes, the charge will be provided for you.

Write down the name of the metal. Since you know that Fe is iron and that it has a charge of +3, you can call it Iron (III). Remember to only use the Roman numeral when you're writing out the name, not writing the formula.

Write down the name of the nonmetal. Since you know that O is oxygen, you can call add the "-ide" ending and call it "oxide."

Put the first name and second name together. Now you have it. Fe₂O₃ = Iron (III) oxide.

Use the older naming method. Under the older naming method, which is also used, you use "-ous" and "-ic" endings for the metals instead of the Roman numerals. If the metal ion has a lower oxidation state (a lower numerical charge, disregarding the "+" or "-"), then you add the "-ous" ending. If it has a higher charge, then it has an "-ic" ending. Fe²⁺ has the lower state (Fe³⁺ has the higher state), so it becomes ferrous. The name of Fe²⁺O can also be written as ferrous oxide.

Remember the exceptions. There are two transition metals that do have a definite charge. Those are zinc (Zn) and silver (Ag). This means that you don't have to use Roman numerals or the older naming method in describing those elements.

Compounds with Polyatomic Ions

Write the formula for the polyatomic ion. This compound will have more than two ions in it. Let's say you're working with the following compound: FeNH₄(SO₄)₂.^[3]

Find the charge of the metal. You'll have to do some math to find it. First, you know that the sulfate, or the SO₄ ion has a charge of -2, and that there are two of them because of the 2 below the parenthesis. So, 2 x -2 = -4. Then, you know that the NH₄, or the ammonia ion, has a charge of +1. Add up -4 and 1 and you get -3. This means that the iron ion, Fe, must have a charge of +3 to make up for it and to make the compound neutral.

Write the name of the metal. In this case you can either write Iron (III) or ferric.

Write the name of the nonmetal ions. In this case, you're working with ammonium and sulfate, or ammonium sulfate.

Combine the name of the metal with the names of the non-metals. You can name the compound FeNH₄(SO₄)₂ by either writing iron (III) ammonium sulfate or ferric ammonium sulfate.