Branches
The traditional division is by the kind of substance studied and the kind of question asked. The borders are porous: most research now sits on two or three of them at once.
| Branch | What it studies | Typical question |
|---|---|---|
| Organic chemistry | Compounds of carbon: their structure, reactions and synthesis | How can this molecule be built in six steps instead of twenty? |
| Inorganic chemistry | Everything else — metals, minerals, salts, coordination compounds | Why is this complex blue, and that one magnetic? |
| Physical chemistry | The physics underneath: thermodynamics, kinetics, quantum mechanics, spectroscopy | How fast, how far, and why? |
| Analytical chemistry | Identifying and measuring what is in a sample | What is in this, how much, and how sure are we? |
| Biochemistry | The chemistry of living systems: proteins, nucleic acids, metabolism | How does this enzyme speed a reaction a million-fold? |
| Theoretical and computational chemistry | Predicting structure and reactivity from the equations of quantum mechanics | Can the experiment be skipped? |
| Materials and polymer chemistry | Solids, surfaces and long-chain molecules with designed properties | What makes this plastic tough and that one brittle? |
| Environmental and atmospheric chemistry | Chemical processes in air, water and soil | Where does this pollutant go, and what does it become? |
Where the rules are kept
Names, symbols and atomic weights are agreed by the International Union of Pure and Applied Chemistry (IUPAC), founded in 1919. Substances reported in the scientific literature are given a number in the CAS Registry, kept by CAS, a division of the American Chemical Society. Measured properties are collected in open references such as the NIST Chemistry WebBook and PubChem, which the US National Institutes of Health opened in 2004.