Chemistry is the natural science involved with elements and compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during a reaction with other substances.
In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both basic and applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant chemistry (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the properties of the soil on the moon (astrophysics), how medications work (pharmacology), and how to collect DNA evidence at a crime scene (forensics).
Chemistry addresses topics such as how atoms and molecules interact via chemical bonds to form new chemical compounds. There are four types of chemical bonds: covalent bonds, in which compounds share one or more electron(s); ionic bonds, in which a compound donates one or more electrons to another compound to produce ions (cations and anions); hydrogen bonds; and Van der Waals force bonds.
The cyclol hypothesis
was the first structural model
of a folded
, globular protein
. It was developed by Dorothy Wrinch
in the late 1930's, and was based on three assumptions. Firstly, the hypothesis assumes that two peptide groups
can be crosslinked
by a cyclol reaction
; these crosslinks are covalent
analogs of non-covalent hydrogen bonds
between peptide groups. These reactions have been observed in the ergopeptides
and other compounds. Secondly, it assumes that, under some conditions, amino acids will naturally make the maximum possible number of cyclol crosslinks, resulting in cyclol molecules
and cyclol fabrics
. Finally, the hypothesis assumes that globular proteins have a tertiary structure
corresponding to Platonic solids
and semiregular polyhedra
formed of cyclol fabrics with no free edges.
Although incorrect as a model for the structure of globular proteins, several elements of the cyclol model were later verified, such as the cyclol reaction itself and the hypothesis that hydrophobic interactions are chiefly responsible for protein folding. The cyclol hypothesis stimulated many scientists to research questions in protein structure and chemistry, and was a precursor of the more accurate models hypothesized for the DNA double helix and protein secondary structure. The proposal and testing of the cyclol model also provides an excellent illustration of empirical falsifiability acting as part of the scientific method.
History and Philosophy of Chemistry
Wikipedia:WikiProject Chemicals/Data is a collection of links and references that are useful for chemistry-related works. This includes free online chemical databases, publications, patents, computer programs, and various tools.
Science is Fun
University of Wisconsin–Madison Chemistry Professor Bassam Z. Shakhashiri, shares the fun of science.
A good place to figure out what equals what.
General Chemistry Online
Clear text and comprehensive coverage of general chemistry topics by Fred Senese, Dept. of Chemistry Frostburg State University
General Chemistry Demonstration at Purdue
Video clips (and descriptions) of lecture demonstrations.
Intota Chemistry Experts
A large online listing of real-world chemistry expert biographies provides examples of the many areas of expertise and careers in chemistry.
Chemistry Webercises Directory
A large listing of chemistry resources maintained by Steven Murov, Emeritus Chemistry Professor Modesto Junior College.
MathMol (Mathematics and Molecules) is a good starting point for those interested in the field of molecular modeling.
Educational Resources and Essential References from Wiley, the world's largest chemistry publisher
A directory of free full-text journals in chemistry, biochemistry and related subjects.
The Element Song
A goofy little song about all of the elements.
(1893-1981) was an American physical chemist
, who won the 1934 Nobel Prize in Chemistry
for his work on isotopes
, specifically the discovery of deuterium
, a hydrogen
isotope, and the production of heavy water
. He also performed pioneering research in cosmochemistry
, which studies the origin and development of elements
and their isotopes, primarily within the solar system. Urey, along with his student Stanley Miller
, may be best remembered for the renowned Miller-Urey experiment
, which shows that a mixture of ammonia
, when exposed to ultraviolet radiation
, can interact to form amino acids
, the "building blocks" of terrestrial life. This experiment followed on from Urey's work on the oxygen
, and is considered to be pioneering work in the field of paleoclimatology
, as it attempts to explain the composition of the early Earth's atmosphere.
Techniques used by chemists
Equipment used by chemists
Chemistry in society
Chemistry in industry
Background color shows subcategory in the metal–metalloid–nonmetal trend:
Note: Nihonium, moscovium, tennessine, and oganesson have only recently (June 2016) been named. 
Things you can do
Here are some things you can do: