Classes, Nomenclature, and Relationships of Inorganic Compounds
Classification links composition, name, typical reactions, and routes for converting one substance into another.
Learning goals
- Classify oxides, acids, bases, and salts from formula and behavior.
- Name compounds using composition and oxidation state.
- Predict neutralization, precipitation, and gas-evolution reactions.
- Build reaction networks that connect inorganic classes.
1. Four major classes
| Class | Structural clue | Examples | Typical behavior |
|---|---|---|---|
| Oxide | oxygen with one other element | CaO, CO2, Al2O3 | basic, acidic, amphoteric, or neutral |
| Acid | ionizable hydrogen and acid residue | HCl, H2SO4 | donates H+ in aqueous reactions |
| Base | metal or ammonium with OH groups | NaOH, Cu(OH)2 | provides or accepts through OH− behavior |
| Salt | cation plus acid-residue anion | NaCl, CuSO4 | ion exchange, hydrolysis, decomposition |
Classification is not just pattern matching. Al2O3 and Al(OH)3 are amphoteric: they react with both acids and strong bases. CO is a neutral oxide under ordinary acid-base classification.
2. Systematic naming
- Identify cation and anion or the two elements.
- Use charge neutrality to find an unknown oxidation state.
- For a variable-state metal, write the oxidation state in Roman numerals: FeCl2 is iron(II) chloride; FeCl3 is iron(III) chloride.
- Preserve polyatomic-ion names: sulfate SO4²−, nitrate NO3−, carbonate CO3²−, hydroxide OH−.
Subscripts belong to the formula; ionic charges belong to individual ions. The total positive and negative charge of a neutral compound must sum to zero.
3. Why exchange reactions proceed
In aqueous solutions, an ion-exchange reaction has a net chemical change when products remove ions from solution as a precipitate, a gas, or a weakly ionized substance such as water. Examples: