Clarke Earley, Ph.D.
Department of Chemistry
Kent State University Stark Campus
North Canton, OH 44720
The rules for naming compounds differ depending on what type of compound is being named. (An introduction to different types of compounds is available here).
Ionic compounds are named with the name of the metallic element first, followed by the name of the non-metallic element. The name of the non-metallic element is altered by changing the suffix of this element to -ide.
|NaCl||sodium chloride||common table salt|
|MgO||magnesium oxide||oxygen ® oxide (not oxygenide)|
|For ionic compounds, name
ignores number of each element.
For ionic compounds containing transition metals, a problem arises: The charge of the metal usually is not fixed. For example, both Fe+2 and Fe+3 exist as stable ions. For ionic compounds containing these metals, the charge of the metal must first be determined based on the known charge of the anion. The name for these compounds will show this charge using roman numerals, which are placed in parentheses immediately following the name of the metal.
The most common mistake with this is to forget what the number in Roman numerals means. It does NOT indicate the number of atoms. It gives the (positive) charge of the transition metal. Iron(III) bromide contains a single iron atom with a +3 charge. It does not contain three iron atoms.
Covalent compounds are named in a manner very similar to that used with ionic compounds, but with two differences. First, the element that is in the leftmost column is named first (no metal actually present). If both elements in the compound are in the same column, then whichever element is lower is named first. The second difference is that Greek prefixes are used to indicate the number of each element. (Note that the "mono-" prefix is optional and typically not used). Several examples are given below.