Students beginning their study of chemistry are faced with understanding many terms that are puzzling and unrelated to contexts that make them understandable. Others may seem familiar, but in chemistry they have meanings that are not quite the same as when used in popular discourse. In science, terms need to have definite and specific meanings. One of the purposes of the Encyclopedia of Chemistry is to provide definitions for many of these terms in a manner and at a level that will make their meanings clear to those with limited backgrounds in chemistry, and to those in other fields who need to deal with chemistry. The International Union of Pure and Applied Chemistry (IUPAC), an international organization of chemists and national chemistry societies, makes the final determination of terminology and nomenclature in chemistry. Among other things, this organization decides the names for new elements and sets up systematic rules for naming compounds so that a given structure can be defined uniquely. Compounds are frequently called by common or trade names, often because their IUPAC names may be long and complex, but the IUPAC name permits a chemist to know the structure of any compound based on the rules of the terminology, while the common name requires remembering what structure goes with what name.
Chemistry has been called “the central science” because it relates to and bridges all of the physical and biological sciences. For example, biology, as it focuses more and more on processes at the cellular and molecular level, depends heavily on chemistry. There is great overlap within the fields in biochemistry, the study of the chemical processes that take place in biological systems, and in chemical biology, the latter term being used to describe the broader area of the application of chemical techniques and principles to biology-related problems. Because of this overlap, this encyclopedia has many entries that relate to biological sciences as well as to chemistry. Similarly, there is overlap with geology, some areas of physics, and any field related to the environment, among others.