Writing covalent compounds involves the use of Greek prefixes. They are
listed in the table to the right. The prefixes are used to indicate the
amount of each atom in the compound. The first element never uses the prefix
mono-, but does use all others. If no prefix is used before the first element's
name, there is only one of that element. The second element uses all prefixes.
Example #1: phosphorus pentachloride is written PCl5
Example #2: dihydrogen monoxide is written H2O
Step by step example: Write the formula for dinitrogen
pentasulfide.
Description
of Action |
Action |
| 1.
Look at the first word of the compound's name. Identify the element
name. Write the symbol for this element. |
N |
| 2.
If the first name of the compound has a prefix, write the number the
prefix refers to as the symbol’s subscript. |
N2
|
| 3.
Look at the second word in the compound's name and identify the element.
Only the root of the element's name is used so the ending will be
different. Write the symbol for the element referred to. |
N2S |
| 4.
Determine the number that the prefix of the second name refers to
and write this number after the second symbol as a subscript. |
N2S5 |
|
Covalent
Prefixes |
1 |
mono- |
2 |
di- |
3 |
tri- |
4 |
tetra- |
5 |
penta- |
6 |
hexa- |
7 |
hepta- |
8 |
octa- |
9 |
nona- |
10 |
deca- |
|
