Chemistry is the study of matter and how it changes, focusing on the composition, structure, and properties of substances.

The atom is the basic unit of matter, forming the foundation for elements and compounds.

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

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

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

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

Mass and volume are properties used to describe matter; mass measures the amount of matter, and volume measures the space it occupies.

Intensive properties, such as density, do not depend on the amount of substance present, while extensive properties, like mass and volume, do.

Density=MassVolume