In chemistry, matter is anything that has mass and takes up space. All matter is composed of atoms. Understanding how to classify matter is a foundational concept that allows chemists to predict and explain its behavior.

1. Pure Substances

A pure substance consists of only one type of particle and has distinct physical and chemical properties. These properties, such as melting point and boiling point, are constant. Pure substances are divided into two categories:

Elements: The simplest form of matter that cannot be broken down into simpler substances by chemical means. Each element is made of only one type of atom.
Examples: Iron (Fe), Oxygen (O₂), Helium (He).
Compounds: Formed when two or more different elements are chemically bonded together in a fixed ratio. Compounds can be broken down into simpler elements, but only through a chemical reaction.
Examples: Water (H₂O), Table salt (NaCl).

2. Mixtures

A mixture consists of two or more pure substances that are physically combined but not chemically bonded. The substances in a mixture retain their own chemical identities and properties. Mixtures have variable compositions and can be separated by physical means.

Homogeneous Mixtures: These mixtures have a uniform composition and appearance throughout. The individual components cannot be seen. They are also known as solutions.
Examples: Salt dissolved in water, air, metal alloys like brass.
Heterogeneous Mixtures: These mixtures do not have a uniform composition. You can often see the different components.
Examples: A salad, sand and water, a chocolate chip cookie.

Separation Techniques

The ability to separate mixtures is a key skill in chemistry. Since mixtures are physically combined, they can be separated using methods that rely on differences in physical properties:

Filtration: Separates a solid from a liquid in a heterogeneous mixture by passing it through a filter (e.g., separating sand from water).
Evaporation: Separates a dissolved solid from a liquid by heating the solution until the liquid turns into a gas, leaving the solid behind (e.g., obtaining salt from salt water).
Distillation: Separates two or more liquids with different boiling points. The mixture is heated until the liquid with the lower boiling point vaporizes, and then the vapor is cooled and condensed back into a liquid in a separate container.
Chromatography: A technique used to separate components of a mixture based on how they are distributed between a stationary phase (like paper) and a mobile phase (a solvent).

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Lesson 4: Building Blocks of Matter

Key TermsExpand to see a glossary of important terms from this lesson.

Atomic Structure

Chemical Bonds

Chemical Reactions

Stoichiometry

Classification of Matter

States of Matter

Energy in Chemical Reactions

Thermodynamics

Acids and Bases

Periodic Table