Naming and Formulas for Molecular Compounds
- Molecular naming falls into two groups - organic and inorganic.
We will talk about inorganic for now. Molecular compounds consist of non-metal
atoms.
- Prefixes which indicate the number of atoms of each element are used in
the naming of inorganic molecular compounds. You should memorize the following:
| mono- = 1 |
di- = 2 |
tri- = 3 |
tetra- = 4 |
penta- = 5 |
| hexa- = 6 |
hepta- = 7 |
octa- = 8 |
nona- = 9 |
deca- = 10 |
- When given a formula the prefixes above are applied to the words that would
be used to name the compound as if it were ionic. For example, P2O3
would be named Phosphorous Oxide if it were ionic, but it consists of two
nonmetals, so it would be named Diphosphorous Trioxide.
- Whenever there is only one atom of the first element in a formula we drop
the term Mono-. For example CO is Carbon Monoxide, not Monocarbon Monoxide.
- To write formulas you just interpret the prefixes on the names and write
the appropriate symbolic representation. For example, Sulfur Dioxide is SO2.
- Try some of the following examples:
Carbon
Tetrachloride =  |
=N2O
|
| Trinitrogen
Pentoxide = |
= CO2 |
- There are special cases where we use common names for molecular compounds.
The only two that I want you to memorize are: Water = H2O
and Ammonia = NH3
(not to be confused with the ammonium ion = NH4+1