Matter: Anything that has mass and occupies space.

Pure Substance: A form of matter with a constant composition and distinct properties; includes elements and compounds.

Element: A substance that cannot be broken down into simpler substances by chemical means; composed of one type of atom.

Compound: A substance formed from two or more elements chemically combined in fixed proportions.

Mixture: A combination of two or more substances in which each retains its own properties; can be separated by physical means.

Homogeneous Mixture (Solution): A mixture with uniform composition throughout; components are not visibly distinguishable.

heterogeneous Mixture: A mixture with non-uniform composition; components are visibly distinguishable.