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

Chemistry focuses on the study of matter and the changes it undergoes.

The atom is the fundamental unit of matter.

Pure substances have a fixed composition and include elements (made of one kind of atom) and compounds (made of two or more different elements bonded together).

Mixtures can be separated physically and do not have a fixed composition (e.g., salt water).

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

Physical changes do not alter the composition of a substance (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.