4.2 Naming Molecular Compounds (New Rules)
Remember that binary molecular compounds are substances that consist of just two different elements. These are the rules for molecular compounds, not ionic compounds! Use when both elements are nonmetals!
Nomenclature:
- Name the first element that appears in the formula.
- Name the second element that appears in the formula, changing its ending to –ide.
- Add Greek prefixes to elements (skip the mono- on the first element.)
Greek prefixes are used to denote the number of atoms of each element present.
| Prefix | Meaning |
|---|---|
Mono- |
1 |
Di- |
2 |
Tri- |
3 |
Tetra- |
4 |
Penta- |
5 |
Hexa- |
6 |
Hepta- |
7 |
Octa- |
8 |
Nona- |
9 |
Deca- |
10 |
4.2.1 Compounds Containing Hydrogen
The names of molecular compounds containing hydrogen usually do not conform to the systematic nomenclature guidelines. Many are common nonsystematic names that do not indicate explicitly the number of H atoms present.
| Compound | Name |
|---|---|
B2H6 |
Diborane |
NH3 |
Ammonia |
H2 |
Dihydrogen monoxide/water |
SiH4 |
Silane |
PH3 |
Phosphine |
H2S |
Hydrogen Sulfide |
An acid is a substance that produces hydrogen ions (H+) when dissolved in water (one definition). HCl is an example of a binary compound that is an acid when dissolved in water.
To name these types of acids:
- remove the –gen ending from hydrogen
- change the –ide ending on the second element to –ic.
Example: hydrogen chloride → hydrochloric acid
A compound must contain at least one ionizable hydrogen atom to be an acid upon dissolving. An ionizable hydrogen becomes a proton (H+).
Below is a table of some simple binary acids.
| Formula | Binary compound name | Acid Name |
|---|---|---|
HF |
Hydrogen fluoride |
Hydrofluoric acid |
HCl |
Hydrogen chloride |
Hydrochloric acid |
HBr |
Hydrogen bromide |
Hydrobromic acid |
HI |
Hydrogen iodide |
Hydroiodic acid |
Oxoacids, when dissolved in water, produce hydrogen ions and the corresponding oxoanions.
- An acid based on an –ate ion is called………ic acid
- HClO3 is chloric acid
- An acid based on an –ite ion is called………ous acid
- HClO2 is chlorous acid
- Prefixes in oxoanion names are retained in naming the oxoacids
- HClO4 is perchloric acid
- HClO is hypochlorous acid
4.2.2 Oxoacids
Oxoacids, can be monoprotic (one ionizable hydrogen/one H+) or polyprotic (more than one ionizable hydrogen/more than one proton)
The names of the anions indicate the number of the remaining hydrogens
- H3PO4 Phosphoric acid
- H2PO4– Dihydrogen phosphate ion
- HPO42– Hydrogen phosphate ion
- PO43– Phosphate ion