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The United Nations has proclaimed 2019 the International Year of the Periodic Table of Chemical Elements (IYPT2019). The same year also marks the 150th anniversary of the publication of Russian chemist Dmitri Mendeleev’s periodic table, containing…

Either the taking up of energy from radiation by the medium through which radiation is passing, or the taking up of matter in bulk by other matter. A simple example of the absorption of energy is how sunlight warms a tree's leaves (see…

A geminal diether (R1 = H). Ketals, considered a subclass of acetals, are also geminal diethers (R1 = C, aliphatic or aromatic). Acetals are (1) independent structural units or a part of certain biological and commercial polymers, (2) blocking or…

An organic compound with the formula C2H2 or HCCH. The first member of the alkynes, acetylene is a gas with a narrow liquid range; the triple point is −81°C (−114°F). The heat of formation (ΔH°f ) is +227 kilojoules/mole, and acetylene is the most…

One of an important class of reactive organic compounds derived from acids via formal intermolecular dehydration; thus, acetic acid (1), on loss of water, forms acetic anhydride (2). Anhydrides of straight-chain acids containing from 2 to 12…

An explosive, poisonous, flammable liquid, boiling at 77.3°C (171°F), partly soluble in water. The formula CH2 CH C N indicates it may be regarded as vinyl cyanide, and its systematic name is 2-propenonitrile. Acrylonitrile is prepared by…

The series of elements beginning with actinium (atomic number 89) and including thorium, protactinium, uranium, and the transuranium elements through the element lawrencium (atomic number 103). These elements, chemically similar, have a strong…

A chemical element, Ac, atomic number 89, and atomic weight 227.0. Actinium was discovered by A. Debierne in 1899. Milligram quantities of the element are available by irradiation of radium in a nuclear reactor. Actinium-227 is a beta-emitting…

A powdered, granular, or pelleted form of amorphous carbon characterized by very large surface area per unit volume because of an enormous number of fine pores. Activated carbon is capable of collecting gases, liquids, or dissolved substances on the…

A technique in which a neutron, charged particle, or gamma photon is captured by a stable nuclide to produce a different, radioactive nuclide which is then measured. The technique is specific, highly sensitive, and applicable to almost every element…

The activity of a substance is a thermodynamic property that is related to the chemical potential of that substance. Activities are closely related to measures of concentration, such as partial pressures and mole fractions, and are more convenient…

A process in which a hydrogen atom in an organic compound is replaced by an acyl group (RCO where R = an organic group). The reaction involves substitution by a nucleophile (electron donor) at the electrophilic carbonyl group (CO) of a carboxylic…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

A material capable of fastening together two other materials by means of surface attachment. The terms glue, mucilage, mastic, and cement are synonymous with adhesive. In a generic sense, an adhesive is any material capable of fastening by means of…

A process in which atoms or molecules move from a bulk phase (that is, solid, liquid, or gas) onto a solid or liquid surface. An example is purification by adsorption where impurities are filtered from liquids or gases by their adsorption onto the…

A suspension of small particles in a gas. The particles may be solid or liquid or a mixture of both. Aerosols are formed by the conversion of gases to particles, the disintegration of liquids or solids, or the resuspension of powdered material.…

Behavior that is intended to threaten or inflict physical injury or emotional harm on another person or organism. Aggression is a type of behavior (physical or verbal, or both) displayed by an individual who aims or is motivated to harm another…

Any disorder of recognition. Agnosias were named originally by Sigmund Freud in 1891 to denote disturbances in the ability to recognize and name objects. Usually the misrecognition involves one sensory modality, with primary sensation in that…

The repeated and/or excessive use of alcohol (ethanol) that continues despite negative physical, psychiatric, or social consequences. Alcoholism is characterized by consuming alcohol more often, in larger amounts, or over longer periods than…

One of a class of organic chemical compounds represented by the general formula RCHO. Aldehydes are closely related to ketones, since both types of compounds contain the carbonyl group In the case of ketones, the carbonyl group is attached to…

An organic compound that contains one or more closed rings of carbon atoms. The term alicyclic specifically excludes carbocyclic compounds with an array of π-electrons characteristic of aromatic rings. Compounds with one to five alicyclic rings of…

Any compound having highly basic properties, strong acrid taste, and ability to neutralize acids. Aqueous solutions of alkalies are high in hydroxyl ions, have a pH above 7, and turn litmus paper from red to blue. Caustic alkalies include sodium…

Usually calcium, strontium, and barium, the heaviest members of group 2 of the periodic table (excepting radium). Other members of the group are beryllium, magnesium, and radium, sometimes included among the alkaline-earth metals. Beryllium…

An organic compound with the general formula CnH2n+2. Alkanes are open-chain (aliphatic or noncyclic) hydrocarbons with no multiple bonds or functional groups. They consist of tetrahedral carbon atoms, up to 105 carbons or more in length. The C-C σ…

A hydrocarbon that contains a carbon-carbon double bond (C C); dienes or polyenes contain two or more double bonds. The synonym olefin is often used, especially in connection with industrial-scale production and applications. The term unsaturated…

A hydrocarbon that contains a triple carbon bond, C C. The first compound in the series is acetylene. Names of alkynes are formed by changing the -ane ending of the corresponding alkane to -yne and numbering as needed, for example, 2-pentyne…

A colorless to white crystalline substance which occurs naturally as the mineral kalunite and is a constituent of the mineral alunite. Alum is produced as aluminum sulfate by treating bauxite with sulfuric acid to yield alum cake or by treating the…

A chemical element, Al, with an atomic number of 13, and an atomic weight of 26.982. Pure aluminum is soft and lacks strength, but it can be alloyed with other elements to increase strength and impart a number of useful properties. Alloys of…

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

A chemical element, symbol Am, atomic number 95. The isotope 241Am is an alpha emitter with a half-life of 433 years. Other isotopes of americium range in mass from 232 to 247, but only the isotopes of mass 241 and 243 are important. The isotope…

A derivative of a carboxylic acid with general formula (1),where R is hydrogen or an alkyl or aryl radical. Amides are divided into subclasses, depending on the number of substituents on nitrogen. The simple, or primary, amides are considered to be…

A member of a group of organic compounds which can be considered as derived from ammonia by replacement of one or more hydrogens by organic radicals. Generally amines are bases of widely varying strengths, but a few which are acidic are known.Amines…

One of a group of complex compounds formed by the coordination of ammonia molecules with metal ions and, in a few instances, such as calcium, strontium, and barium, with metal atoms. Some typical examples of ammines include [Co(NH3)6]Cl2 (rose),…

A product of a reaction between ammonia, NH3, and various acids. The general reaction for formation is (1).1 Examples of ammonium salts are ammonium chloride, NH4Cl, ammonium nitrate, NH4NO3, and ammonium carbonate, (NH4)2CO3. These compounds are…

A significant but relatively selective inability to remember. Amnesia can be characterized along two dimensions with respect to its onset: an inability to remember events that occurred after the onset of amnesia is referred to as anterograde…