Chemistry is the study of matter, energy, and the interactions between them. It tends to focus on the properties of substances and the interactions between different types of matter, particularly reactions that involve electrons. It is a physical science which studies various substances, and which incorporates the concepts of energy and entropy in relation to chemical processes. Chemistry is often called "the central science" because it connects the other natural sciences such as astronomy, physics, material science, biology, and geology.
Chemistry is related to physics, materials engineering, and biology. It contains many subfields such as organic, inorganic, biochemistry, physical chemistry, and analytical chemistry.