Chemistry

The science that deals with the properties, composition, and structure of substances (defined as elements and compounds), the transformations they undergo, and the energy that...

• Abel, John Jacob

  American pharmacologist and physiological chemist who made important contributions to a modern understanding of the ductless, or endocrine, glands. He isolated adrenaline in the form of a chemical derivative (1897) and crystallized insulin (1926). He...

• Abel, Sir Frederick Augustus

  English chemist and explosives specialist who, with the chemist Sir James Dewar, invented cordite (1889), later adopted as the standard explosive of the British army. Abel also made studies of dust explosions in coal mines, invented a device for testing...

• Abney, Sir William de Wiveleslie

  a specialist in the chemistry of photography, especially noted for his development of a photographic emulsion that he used to map the solar spectrum far into the infrared. Commissioned in the Royal Engineers (1861), he taught chemistry and photography...

• acid

  any substance that in water solution tastes sour, changes the colour of certain indicators (e.g., reddens blue litmus paper), reacts with some metals (e.g., iron) to liberate hydrogen, reacts with bases to form salts, and promotes certain chemical reactions...

• acid–base catalysis

  acceleration of a chemical reaction by the addition of an acid or a base, the acid or base itself not being consumed in the reaction. The catalytic reaction may be acid-specific (acid catalysis), as in the case of decomposition of the sugar sucrose into...

• acid–base reaction

  a type of chemical process typified by the exchange of one or more hydrogen ions, H +, between species that may be neutral (molecules, such as water, H 2 O; or acetic acid, CH 3 CO 2 H) or electrically charged (ions, such as ammonium, NH 4 +; hydroxide,...

• acrylic compound

  any of a class of synthetic plastics, resins, and oils used to manufacture many products. By varying the starting reagents and the process of forming, a material may be produced that is hard and transparent, soft and resilient, or a viscous liquid. Acrylic...

• actinium

  Ac radioactive chemical element, in Group 3 (IIIb) of the periodic table, atomic number 89. Actinium was discovered (1899) by French chemist André-Louis Debierne in pitchblende residues left after French physicists Pierre and Marie Curie had extracted...

• actinoid element

  any of a series of 15 consecutive chemical elements in the periodic table from actinium to lawrencium (atomic numbers 89–103). As a group, they are significant largely because of their radioactivity. Although several members of the group, including uranium...

• activation energy

  in chemistry, the minimum amount of energy that is required to activate atoms or molecules to a condition in which they can undergo chemical transformation or physical transport. In transition-state theory, the activation energy is the difference in...

• Adams, Roger

  chemist and teacher known for determining the chemical constitution of such natural substances as chaulmoogra oil (used in treating leprosy), the toxic cottonseed pigment gossypol, marijuana, and many alkaloids. He also worked in stereochemistry and...

• addition reaction

  any of a class of chemical reactions in which an atom or group of atoms is added to a molecule. Addition reactions are typical of unsaturated organic compounds— i.e., alkenes, which contain a carbon-to-carbon double bond, and alkynes, which have a carbon-to-carbon...

• Agre, Peter

  American doctor, corecipient of the Nobel Prize for Chemistry in 2003 for his discovery of water channels in cell membranes. He shared the award with Roderick MacKinnon, also of the United States. In 1974 Agre earned an M.D. degree from Johns Hopkins...

• alcohol

  any of a class of organic compounds characterized by one or more hydroxyl (−OH) groups attached to a carbon atom of an alkyl group (hydrocarbon chain). Alcohols may be considered as organic derivatives of water (H 2 O) in which one of the hydrogen atoms...

• aldehyde

  any of a class of organic compounds, in which a carbon atom shares a double bond with an oxygen atom, a single bond with a hydrogen atom, and a single bond with another atom or group of atoms (designated R in general chemical formulas and structure diagrams)....

• Alder, Kurt

  German chemist who was the corecipient, with the German organic chemist Otto Diels, of the 1950 Nobel Prize for Chemistry for their development of the Diels-Alder reaction, or diene synthesis, a widely used method of synthesizing cyclic organic compounds....

• aliphatic compound

  any chemical compound belonging to the organic class in which the atoms are not linked together to form a ring. One of the major structural groups of organic molecules, the aliphatic compounds include the alkanes, alkenes, and alkynes, and substances...

• alkali

  any of the soluble hydroxides of the alkali metals— i.e., lithium, sodium, potassium, rubidium, and cesium. Alkalies are strong bases that turn litmus paper from red to blue; they react with acids to yield neutral salts; and they are caustic and in concentrated...

• alkali metal

  any of the six chemical elements that make up Group 1 (Ia) of the periodic table —namely, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr). The alkali metals are so called because reaction with water forms alkalies...

• alkaline-earth metal

  any of the six chemical elements that comprise Group 2 (IIa) of the periodic table. The elements are beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Occurrence, properties, and uses Prior to the 19th century,...