| Chemical Formula of a Compound |
| There are certain procedures for writing down chemical formula of a compound. For example, we do not write ClNa for salt, but NaCl, or OH2 for water. The sequence of writing the elements in a chemical formula for inorganic compounds is from the left to right representation of elements in the periodic table of elements . To write a chemical formula it is better to know the atomic structure (electron configuration and valence) of the interacting elements and the reactions preceding the formation of the compound. |
| Guideline 1 |
| The name of the element farther to the left in the chemical formula of the compound, is followed by the name of the element farther to the right, with the suffix -ide added to the name of the latter: |
NaCl -------- Sodium chloride HCl -------- Hydrogen chloride
Li2O -------- Lithium oxide MgO ---------- Magnesium oxide
CaF2 -------- Calcium fluoride Sr3P2 ------ Strontium phosphide |
| Guideline 2 |
| When two or more non-metal compounds have different numbers of the same elements, prefixes are added to remove the ambiguity. The first four prefixes are mono- ("one"), di- ("two"), tri- ("three"), and tetra- ("four"). The prefix mono-, however, is commonly omitted from the beginning of the first word of the name: |
| Carbon
and oxygen |
|
| CO |
Carbon monoxide |
| CO2 |
Carbon dioxide |
|
| Nitrogen and oxygen |
|
| NO2 |
Nitrogen
dioxide |
| N2O4 |
Dinitrogen tetroxide |
|
| Sulfur and oxygen |
|
| SO2 |
Sulphur dioxide |
| SO3 |
Sulphur trioxide |
|
| Guideline 3 |
| Many compounds are not usually referred to by their systematic names. Instead, they are assigned common names that are more convenient or have been used traditionally for many years. Some common names we use are water for H2O, ammonia for NH3 , and methane for CH4 . |
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