All matter is composed of either elements or compounds. Elements are made of only one type of atom, while compounds contain two or more elements chemically bonded together. Matter can also exist as substances, which are either elements or compounds, or as mixtures of multiple substances. Mixtures are not uniform and their components can be separated, while substances cannot be decomposed further. There are two main types of mixtures: homogeneous mixtures which are uniform, and heterogeneous mixtures where the components are not evenly distributed and can be seen separately.