Chemical Names for Compounds
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Chemical Names for Compounds

We will spend some time later in this course working with the intricacies of chemical names. But there are a couple important things you should learn now. One is the reason for having a systematic method for naming chemical compounds. The other is identifying the elements contained in compounds, which is the first step in determining the formula and composition of compounds.

As chemists learned more and more about the composition of simple compounds, it became important to develop a system for naming these compounds in a way that showed their elemental composition. Common and descriptive names like salt, cinnabar, laughing gas, and blue vitriol tell us nothing about what is in a compound. Chemical names like sodium chloride, magnesium oxide, mercuric sulfide, nitrous oxide and cupric sulfate do a better job of conveying information about what elements are contained in a compound.
Common name Chemical name Elements contained
salt sodium chloride Na Cl  
magnesia magnesium oxide Mg O  
cinnabar mercuric sulfide Hg S  
laughing gas nitrous oxide N O  
blue vitriol cupric sulfate Cu S O

Here are some simple guidelines of what to look for in chemical names. (These compounds are also listed in Example 2 in your workbook.)

Generally when two elements combine, the name of the compound contains the names of both elements with the ending on the second element changed to "-ide."
Simple names of compounds with two elements
Name of compound Elements contained
sodium chloride sodium and chlorine
When the elements can form two compounds, the ending on the first element is changed to indicate how much of the second element it has combined with. The "-ic" ending indicates that the first element has combined with a large amount of the second element. The "-ous" ending indicates that the first element has combined with a small amount of the second element. The terms "large" and "small" are, of course, relative and they are related to the ratios in the Law of Simple Multiple Proportions.
Latin endings in names of compounds
Name of compound Elements contained
mercuric sulfide mercury with more sulfur
mercurous sufide mercury with less sulfur
nitric oxide nitrogen with more oxygen
nitrous oxide nitrogen with less oxygen

Sometimes you will see a Roman numeral in parentheses attached to the end of the first element. These are Stock names and the Roman numeral tells us about the condition (charge or oxidation state) of the element it follows. We will have to deal with that when we talk about how atoms bond to one another later in this course.
Roman numerals in names of compounds
iron(III) oxide iron (in a +3 state) with oxygen
iron(II) oxide iron (in a +2 state) with oxygen
When an "-ate" ending is found in a name, it indicates that oxygen has combined with the other two elements.
Compound names with -ate endings
cupric sulfate copper with sulfur and oxygen

Sometimes names will contain prefixes.  The prefix is used to indicate the relative amounts of each element expressed in a way that I will soon discuss. For the moment, let's just leave it at the understanding that carbon dioxide contains both carbon and oxygen. In time you will learn which types of compounds have prefixes in their names and which do not.

Names containing prefixes

carbon dioxide 1 carbon with 2 oxygens


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E-mail instructor: Sue Eggling

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1998, 2002 Clackamas Community College, Hal Bender