Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is chiefly concerned with atoms and molecules and their interactions and transformations, for example, the properties of the chemical bonds formed between atoms to create chemical compounds. As such, chemistry studies the involvement of electrons and various forms of energy in photochemical reactions, oxidation-reduction reactions, changes in phases of matter, and separation of mixtures. Preparation and properties of complex substances, such as alloys, polymers, biological molecules, and pharmaceutical agents are considered in specialized fields of chemistry.
Chemistry is sometimes called the central science because it bridges other natural sciences like physics, geology and biology. Chemistry is a branch of physical science but distinct from physics.
The etymology of the word chemistry has been much disputed. The history of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world.