Allotropy (Gr. allos, other, and tropos, manner) is the phenomenon of an element existing in two or more physical forms in the same physical state. The difference between the forms involves either crystaline structure (white, red and black phosphorus), the number of atoms in the molecule of a gas (diatomic oxygen and triatomic ozone), or the molecular structure of a liquid (liquid helium an helium II).
In some cases, the allotropes are stable over a temperature range, with a definite transition point at which one changes into the other. For instance, tin has two allotropes: white (metallic) tin stable above 13.2 °C and grey (nonmetallic) tin stable below 13.2 °C. This form allotropy is called enantiotropy. Form of allotropy, in which there is no transition temperature at which the two are in equilibrium, is called monotropy.
Allotropy does not apply to the substance existing in different physical states as, for example, when ice melts and changes from solid ice to liquid water.
Allotropy is generally restricted to describing polymorphic behaviour in elements, while polymorphism may refer to any material having multiple crystal structures.
Amount concentration (also called molar concentration and in older literature molarity) is the amount of a given substance in a stated unit of a mixture, solution, or ore. The common unit is mole per cubic decimetre (moldm−3) or mole per litre (molL-1) sometimes denoted by M.
The concentration of an atom, ion, or molecule in a solution may be symbolised by the use of square brackets, as [Ca2+].
Antioxidants are compounds that slow down oxidation processes that degrade foods, fuels, rubber, plastic, and other materials. Antioxidants like butylated hydroxyanisole (BHA), are added to food to prevent fats from becoming rancid and to minimize decomposition of vitamins and essential fatty acids; they work by scavenging destructive free radicals from the food.
Aqueous solutions are those solutions where water is the solvent. An aqueous solution found in an equation describing a chemical reaction is denoted by the state symbol, (aq).
Auxochrome is a group or substructure in a molecule that influences the intensity of absorption of the molecule.
Azo compounds are organic compounds containing the group -N=N- linking two other groups. They can be formed by reaction of a diazonium ion with a benzene ring.
Biochemistry is the study of the chemistry of living organisms, especially the structure and function of their chemical components (principally proteins, carbohydrates, lipids and nucleic acids).
Bioelement is any chemical element that is found in the molecules and compounds that make up living organism.
Generalic, Eni. "Organska kemija." Croatian-English Chemistry Dictionary & Glossary. 29 June 2022. KTF-Split. {Date of access}. <https://glossary.periodni.com>.
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