3.10: Nomenclature of Ionic Compounds
The simplest ionic compounds consist of a single type of cation associated with a single type of anion. Nomenclature for these compounds is trivial; the cation is named first, followed by the anion. If the anion is a single element, the suffix ide is added to the root name of the element.
When you are constructing names for ionic compounds, you do not use “multipliers” to indicate how many cations or anions are present in the compound. For example NaI is named sodium iodide; Na 2 S is named sodium sulfide; CaCl 2 is named calcium chloride. The chemist reading the name is assumed to have sufficient knowledge to pair the elements properly based on their common valence states. There are exceptions to this simple nomenclature, however. Many transition metals exist as more than one type of cation. Thus, iron exists as Fe 2+ and Fe 3+ cations (they are referred to as “oxidation states”, and will be covered in detail in Chapter 5 ). When you are naming an ionic compound containing iron, it is necessary to indicate which oxidation state the metal has. For metals, the oxidation state is the same as the charge. Thus Fe 2+ in a compound with chloride would have a formula FeCl 2 and would be named iron (II) chloride, with the oxidation state (the charge on the iron) appearing as a Roman numeral in parenthesis after the cation. The cation Fe 3+ paired with oxygen would have the formula Fe 2 O 3 and would have the name iron (III) oxide.
The procedure for naming ionic compounds contain polyatomic ions is identical to that described above for simple ions. Thus, CaCO 3 is named calcium carbonate; Na 2 SO 4 is named sodium sulfate; (NH 4 ) 2 HPO 4 (a compound with two polyatomic ions) is named ammonium hydrogen phosphate; and Pb 2+ paired with SO 4 2- , PbSO 4 is named lead (II) sulfate.
Write a correct chemical formula for each of the following ionic compounds:
- Calcium bromide
- Aluminum oxide
- Copper (II) chloride
- Iron (III) oxide
Solution
- Calcium is 2+, bromide is 1-; CaBr 2 .
- Aluminum is 3+, oxide is 2-; Al 2 O 3 .
- From the oxidation state that is given, copper is 2+, chloride is 1-; CuCl 2 .
- From the oxidation state, iron is 3+, oxide is 2-; Fe 2 O 3 .
Write a proper chemical name for each of the following ionic compounds:
- Li 2 S
- CaO
- NiCl 2
- FeO
Solution
- We don’t use multipliers, so this is simply lithium sulfide.
- This is simply calcium oxide.
- We don’t have to specify an oxidation state for nickel, so this is nickel chloride.
- We must specify that iron is 2+ in this compound; iron (II) oxide.
Write a correct chemical formula for each of the following ionic compounds:
- Sodium phosphide
- Iron (II) nitrite
- Calcium hydrogen phosphate
- Chromium (III) oxide
Write a proper chemical name for each of the following ionic compounds:
- NaBr
- CuCl 2
- Fe(NO 3 ) 3
- (NH 4 ) 3 PO 4