Chemistry is conventionally divided into three sub-disciplines: organic, inorganic,
and physical. Organic chemistry studies the reactions of molecules that have a
carbon and hydrogen skeleton, with additional atoms of oxygen, nitrogen,
phosphorous, and sulfur. Organic chemistry is so named, as these are the
elements that make up life; most of its applications are the pharmaceutical and
petrochemical industries. Inorganic chemistry deals with the reactions of
molecules without a carbon and hydrogen-based skeleton, and has a wide
range of applications, from catalysts to nuclear reactors. Physical chemistry is
the study of the underlying structure of matter and the mechanisms and speed
of chemical changes that underpin the other subdisciplines. Physical chemistry
is also concerned with the interaction of radiation and matter. Other important
subdivisions include biochemistry (study of organic molecules in cells), analytical
chemistry (study of techniques to separate and quantify chemicals), atmospheric
chemistry, ocean chemistry, and biogeochemistry