what is a pure substance

A pure substance is a type of matter that has a definite and constant composition, meaning it is made up of only one type of particle, either an element or a compound. It has uniform physical and chemical properties throughout and usually participates in predictable chemical reactions. Examples of pure substances include elements such as gold, copper, oxygen, and chlorine, and compounds such as water, salt, and baking soda. In contrast, a mixture is a physical combination of two or more pure substances, and each substance retains its individual properties.