Matter is defined as anything that has mass and occupies space.

Chemistry focuses on the study of matter and its transformations.

The atom is the fundamental unit of matter.

Pure substances have a fixed composition and include elements (composed of one type of atom) and compounds (composed of two or more different elements chemically bonded).

Mixtures consist of two or more substances physically combined and can be separated by physical means (e.g., salt water).

Chemical changes result in the formation of new substances (e.g., burning wood).

Physical changes alter the form or appearance of matter without changing its composition (e.g., melting ice).

Mass and volume are basic properties used to describe matter.

Intensive properties, such as density, do not depend on the amount of substance present.