Classification of inorganic compounds
Chemists group substances with similar composition and behavior into classes. At this introductory level, four major classes organize many familiar inorganic compounds: oxides, bases, acids, and salts.
Learning goals
- Recognize the four major inorganic classes from formulas.
- Describe the structural clue for each class.
- Distinguish a compound from a simple substance.
- Use a step-by-step classification routine without relying only on memorization.
The four-class map
1. Oxides
An oxide is a binary compound containing oxygen and one other element. Examples include MgO, CO2, and Fe2O3. “Binary” means that only two different elements are present.
2. Bases
At this level, a base is recognized as a metal cation joined to one or more hydroxide groups, OH−. Examples are NaOH and Ca(OH)2. The parentheses show that the whole OH group is repeated.
3. Acids
Many introductory acid formulas begin with hydrogen and contain an acid residue, such as HCl, HNO3, and H2SO4. Their acidic properties are discussed in the dedicated acids lesson.
4. Salts
A salt consists of a positive ion, usually a metal ion or NH4+, combined with a negative acid-residue ion. Examples include NaCl, K2SO4, and CaCO3.