What Are the Four Classifications of Substances?

Substances can be classified into four main categories based on their properties and behavior. These classifications are:

1. Elements: These are pure substances that consist of only one type of atom. Elements cannot be broken down into simpler substances by chemical means. Examples include gold (Au), oxygen (O₂), and carbon (C).
2. Compounds: Compounds are substances formed when two or more elements are chemically bonded together in fixed proportions. They can be broken down into simpler substances by chemical reactions. Examples include water (H₂O) and sodium chloride (NaCl).
3. Homogeneous Mixtures: Also known as solutions, these are mixtures where the components are uniformly distributed throughout the mixture. The individual substances in a homogeneous mixture cannot be visually distinguished. Examples include air and saltwater.
4. Heterogeneous Mixtures: These are mixtures where the components are not uniformly distributed and can be visually distinguished. The different parts of a heterogeneous mixture can often be separated by physical means. Examples include a salad and a mixture of sand and iron filings.

Understanding these classifications helps in studying the properties and interactions of different substances in chemistry.