Chelates are compounds which contain atoms that can bond with metals. The bonding atoms typically contain donor electrons that form coordinate bonds with metals. When multiple chelates bond with a single metal, a cyclic structure called a chelation complex is formed. This bonding ability of chelating agents is reflected by its name which comes from the Greek word chela meaning "claw of the lobster."

The basic theory related to the structure of chelating agents was developed by Alfred Werner during the late 1800's. Before he began his work, scientists were trying to determine the molecular structure of colored compounds that contained metal atoms. The most widely accepted theory was the chain theory. This theory suggested that metals were bonded chains of ligands. In 1890, Werner challenged this thinking. As the story goes, he was dreaming about molecular structures, and after awaking from one of these dreams, he wrote down...