Elements and compounds together are known as pure substances . They consist of only one chemical entity, and can be interchanged only through chemical processes. Mixtures are two or more substances mixed together, with each component retaining its chemical identity. Likewise when salt dissolves in water, there is a similar retention of individual characters. Mixtures are formed and unformed by physical processes, not chemical.
Mixtures can be homogenous or heterogeneous .
In a homogenous mixture, the intermingling is on such a fine level that the mixture looks and behaves uniform throughout the sample. Homogenous mixtures are also known as solutions . In a heterogeneous mixture, there are regions that are distinctly one component or the other. In these materials you can see pockets of one material or another. At some level it becomes very difficult to make the distinction between homogenous and heterogeneous.