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

Do you know the proper name for this insect?

Proper naming (or nomenclature) is important for identification purposes. Medicine names must be precise so that the correct drug is given—one that will help the patient and not harm them. Biological classification of species requires accurate naming for proper categorization. Insects are categorized by genus and species, so they are uniquely identified. Names must be correct for the tracing of family trees in genealogical studies. Compounds used in chemical reactions must be correctly specified in order for the reaction to occur.

Binary Ionic Compounds

A binary ionic compound is a compound composed of a monatomic metal cation and a monatomic nonmetal anion.

Naming Binary Ionic Compounds

When examining the formula of a compound in order to name it, you must first decide what kind of compound it is. For a binary ionic compound, a metal will always be the first element in the formula, while a nonmetal will always be the second. The metal cation is named first, followed by the nonmetal anion. Subscripts in the formula do not affect the name. The table below shows three examples.

Notice that in each of the formulas above, the overall charge of the compound is zero. Potassium ion is \(\ce{K^+}\), while fluoride ion is \(\ce{F^-}\). Since the magnitude of the charges is equal, the formula contains one of each ion. This would also be the case for a compound such as \(\ce{MgS}\), in which the ions are \(\ce{Mg^{2+}}\) and \(\ce{S^{2-}}\). For sodium nitride, the sodium ion is \(\ce{Na^+}\), while the nitride ion is \(\ce{N^{3-}}\). In order to make a neutral compound, three of the \(1+\) sodium ions are required in order to balance out the single \(3-\) nitride ion. So the \(\ce{Na}\) is given a subscript of 3. For calcium phosphide, the calcium ion is \(\ce{Ca^{2+}}\), while the phosphide ion is \(\ce{P^{3-}}\). The least common multiple of 2 and 3 is 6. To make the compound neutral, three calcium ions have a total charge of \(6+\), while two phosphide ions have a total charge of \(6-\). The \(\ce{Ca}\) is given a subscript of 3, while the \(\ce{P}\) is given a subscript of 2.

Summary

• A binary ionic compound is a compound composed of a monatomic metal cation and a monatomic nonmetal anion.
• The metal part of the compound is named as the element.
• The nonmetallic part of the compound is named by dropping the end of the element and adding -ide.
• For binary compounds, it is not necessary to indicate the number of ions in the compound.

Review

1. What is a binary compound?
2. Which of the following is not a binary compound?
   1. NaCl
   2. KH2PO4
   3. KBr
3. Name the following compounds:
   1. NaBr
   2. MgCl2
   3. LiI
   4. CaO
   5. CuBr2
   6. FeO