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Nomenclature , a collection of rules for naming things, is important in science and in many other situations. This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO 3 , and N 2 O 4 . The simplest of these are binary compounds , those containing only two elements, but we will also consider how to name ionic compounds containing polyatomic ions, and one specific, very important class of compounds known as acids (subsequent chapters in this text will focus on these compounds in great detail). We will limit our attention here to inorganic compounds, compounds that are composed principally of elements other than carbon, and will follow the nomenclature guidelines proposed by IUPAC. The rules for organic compounds, in which carbon is the principle element, will be treated in a later chapter on organic chemistry.
To name an inorganic compound, we need to consider the answers to several questions. First, is the compound ionic or molecular? If the compound is ionic, does the metal form ions of only one type (fixed charge) or more than one type (variable charge)? Are the ions monatomic or polyatomic? If the compound is molecular, does it contain hydrogen? If so, does it also contain oxygen? From the answers we derive, we place the compound in an appropriate category and then name it accordingly.
The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix – ide ). Some examples are given in [link] .
| Names of Some Ionic Compounds | |
|---|---|
| NaCl, sodium chloride | Na 2 O, sodium oxide |
| KBr, potassium bromide | CdS, cadmium sulfide |
| CaI 2 , calcium iodide | Mg 3 N 2 , magnesium nitride |
| CsF, cesium fluoride | Ca 3 P 2 , calcium phosphide |
| LiCl, lithium chloride | Al 4 C 3 , aluminum carbide |
Compounds containing polyatomic ions are named similarly to those containing only monatomic ions, except there is no need to change to an – ide ending, since the suffix is already present in the name of the anion. Examples are shown in [link] .
| Names of Some Polyatomic Ionic Compounds | |
|---|---|
| KC 2 H 3 O 2 , potassium acetate | (NH 4 )Cl, ammonium chloride |
| NaHCO 3 , sodium bicarbonate | CaSO 4 , calcium sulfate |
| Al 2 (CO 3 ) 3 , aluminum carbonate | Mg 3 (PO 4 ) 2 , magnesium phosphate |
Every day you encounter and use a large number of ionic compounds. Some of these compounds, where they are found, and what they are used for are listed in [link] . Look at the label or ingredients list on the various products that you use during the next few days, and see if you run into any of those in this table, or find other ionic compounds that you could now name or write as a formula.
| Everyday Ionic Compounds | |
|---|---|
| Ionic Compound | Use |
| NaCl, sodium chloride | ordinary table salt |
| KI, potassium iodide | added to “iodized” salt for thyroid health |
| NaF, sodium fluoride | ingredient in toothpaste |
| NaHCO 3 , sodium bicarbonate | baking soda; used in cooking (and as antacid) |
| Na 2 CO 3 , sodium carbonate | washing soda; used in cleaning agents |
| NaOCl, sodium hypochlorite | active ingredient in household bleach |
| CaCO 3 calcium carbonate | ingredient in antacids |
| Mg(OH) 2 , magnesium hydroxide | ingredient in antacids |
| Al(OH) 3 , aluminum hydroxide | ingredient in antacids |
| NaOH, sodium hydroxide | lye; used as drain cleaner |
| K 3 PO 4 , potassium phosphate | food additive (many purposes) |
| MgSO 4 , magnesium sulfate | added to purified water |
| Na 2 HPO 4 , sodium hydrogen phosphate | anti-caking agent; used in powdered products |
| Na 2 SO 3 , sodium sulfite | preservative |
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