Mixtures and pure substances can be categorized and separated in different ways. Mixtures are combinations of substances that are not chemically combined and can be physically separated. Pure substances include elements, which consist of only one type of atom, and compounds, which are formed by chemical combination of two or more elements. Mixtures include heterogeneous mixtures where the parts can be easily distinguished, like mixtures, and homogeneous mixtures where the parts are evenly distributed and appear uniform, like solutions.