The scientific study of the elements and their compounds, and the reactions they undergo. Inorganic chemistry is concerned with the elements and all their compounds except those of carbon, which are the subject of organic chemistry . Physical chemistry studies their physical properties and structures and the relations between energy and physical and chemical change.
Analytical chemistry is concerned with determining the composition of substances.
What began with the belief that earth, air, fire, and water combine to form all things, and proceeded through alchemy to the scientific approach of Robert Boyle in the 17th century, has now reached the point where elements can be made that are not found in nature. The discovery of radioactivity and the electron, and theories such as those of valency and the chemical bond , have resulted in many chemical phenomena being explained in terms of atomic physics. The applications are wide. Industry, agriculture, medicine, are all supported by chemical research in specialist fields. Some 4 million chemicals have been identified, of which not more than 35,000 are in common use.