Naming Covalent Compounds

We also need to take up the matter of naming covalent compounds. Covalent compounds are named in different ways than are ionic compounds (although there is some overlap). Many of these compounds have common names such as "methane", "ammonia" and "water". However, simple covalent compounds are generally named by using prefixes to indicate how many atoms of each element are shown in the formula. Also, the ending of the last (most negative) element is changed to -ide.

The prefixes used are mono-, di-, tri-, tetra-, penta-, hexa-, and so forth. The mono- prefix is usually not used for the first element in the formula. The "o" and "a" endings of these prefixes are dropped when they are attached to "oxide."

1	mono-
2	di-
3	tri-
4	tetra-
5	penta-
6	hexa-

You also need to know which element to put first in the formulas and names of these compounds. Generally, they are in the same left-to-right order that they have on the periodic table, except that you would have to squeeze hydrogen in between nitrogen and oxygen.

At this time, try the following practice problems (also found in exercise 12 in the workbook).

Name the following compounds.

PH₃

N₂O₃

Answers:

phosphorus trihydride

carbon monoxide

hydrogen monoiodide (This compound also is often called by its simple name, hydrogen iodide.)

dinitrogen trioxide

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E-mail instructor: Eden Francis

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