Chemistry Dictionary/Terms/Glossary/Word List A to Z

The chemistry dictionary offers definitions and examples of important chemistry and chemical-related terms, which are listed in alphabetical order. For each term, a brief definition is given. Each link leads to a more comprehensive discussion of the word. Additional definitions are also available.

Chemistry Terms Starting with A to Z

1absolute alcoholcommon name for high purity ethanol which contains only one percent water.Alcohols, Phenols, and Ethers (Organic)
2absolute configurationa way of representing the absolute structure of an optical isomer, dextrorotatory or laevorotatary.
3absolute temperaturea scale of temperature based on absolute zero.
4absolute zerozero of thermodynamic temperature (0 kelvin) and It is equivalent to –273.15°C or –459.67°F.
5absorptionthe take up of a gas by a solid in its bulk structure or liquid, or the take up of a liquid by a
6absorption coefficientThe molar absorption coefficient (symbol ε) is a quantity
that characterizes the absorption of light when it passes through a sample of the absorbing
7absorption towerA long vertical column which is used for absorbing gases in industry.
8ABS plasticA class of plastics based on acrylonitrile– butadiene–styrene copolymers.
9abstractionA chemical reaction that involves bimolecular removal of an atom or ion
from a molecule.
10acceleratorA substance which speed up the rate of a chemical reaction, i.e. a positive catalyst
11acceptorA compound, molecule, ion, etc., to which electrons are donated during the
formation of a coordinate bond.
12Acheson processprocess for the manufacture of graphite by heating coke mixed
with clay in the industrial.
13achirala molecule which is superimposible on its mirror image, not chiral
14acidchemical species that contains hydrogen and dissociates in water to
produce positive hydrogen ions.
15acidimetryVolumetric analysis to determine the
amount of base using standard solutions of acids
16acid rain form of precipitation having a pH value of less than about 5.0, which has adverse
effects on the fauna and flora on which it falls.
17acid saltA salt of a polybasic acid in which not all the hydrogen atoms have been replaced by
hydroxide ions
18acid valuethe amount of free acid present in a fat, equal to the number
of milligrams of potassium hydroxide needed to neutralize this acid.
19ACTActivated-Complex Theory.
20actinic radiationElectromagnetic radiation that is capable of initiating a chemical reaction.
21actinometera device used to measure the intensity of electromagnetic radiation.
22actinometryThe measurement of the intensity of electromagnetic radiation.
23action spectrumA graphical plot of the efficiency of electromagnetic radiation in
producing a photochemical reaction against the wavelength of the radiation
24activation analysisAn analytical technique that can be used to detect most elements when
present in a sample in milligram quantities (or less).
25activation energyThe minimum energy required for a chemical reaction to take place. it is
denoted by Ea .
26acyclica compound which does not have a ring in its molecules.
27acylationThe process of introducing an acyl group (RCO–) into a compound.
28acyl fissionThe breaking of the carbon–oxygen bond in an acyl group.
29Adams catalystA dark brown powder, a hydrated form of platinum(IV) oxide (PtO2), is
produced by heating chloroplatinic acid (H2PtCl6) with sodium nitrate
(NaNO3). It is used in hydrogenations of alkenes to alkanes, nitro
compounds to amines, and ketones to alcohol.
30adductcompounds formed by coordination between a Lewis acid (acceptor) and a
Lewis base (donor).
31adenineA purine derivative, major component bases of nucleotides
and the nucleic acids DNA and RNA.
32adhesiveA substance is used for joining surfaces together.
33adiabatic processAny process that occurs without exchange of heat or at constant heat
34adsorptionThe formation of a layer of gas, liquid, or solid on the surface of a solid.
35adsorption indicatorA type of indicator which is used in precipitation titration
36aerogelA low-density porous transparent material that consists of more than 90%
air which are used as drying agents.
37aerosolA colloidal dispersion of solid or liquid in a gas.
38AESAtomic Emission Spectroscopy
39affinity chromatographychromatographic technique for purifying natural polymers, especially proteins.
40agarAn extract of certain species of red seaweeds that is used as a gelling
agent in microbiological culture media, foodstuffs, medicines, and cosmetic
creams and jellies.
41albumin (albumen)a group of globular proteins soluble in water but form
insoluble coagulates when heated.
42aldol reactionit is condensation reaction between aldehyde or ketone having alpha hydrogen and another aldehyde or ketone to give beta-hydroxy carbonyl compound.
43aliphatic compoundsOrganic compounds that are alkanes, alkenes, or alkynes or their
44alkaliA base that dissolves in water to give hydroxide ions.
45alkali metalsThe elements of group 1 (formerly IA) of the periodic table: Li
Na,K, Rb,Cs,Fr.
46alkalimetryVolumetric analysis to determine the
amount of acid using standard solutions of alkali.
47alkalinea solution that has an excess of hydroxide ions (i.e. a pH
greater than 7).
48alkanes (paraffins)Saturated hydrocarbons with the general formula CnH2n+2.
49alkenes (olefenes, olefins)Unsaturated hydrocarbons contain one or more double carbon-carbon bonds in
their molecules.
50alkylationreaction that introduces an *alkyl group into an organic
51alkyl groupA group that contains carbon and Hydrogen atom only
52alkynes (acetylenes)Unsaturated hydrocarbons containing one or more triple carbon-carbon bonds in
their molecules.
53allenes>C=C=C linked by two adjacent double bonds. in a compound.
54allotropyThe existence of elements in two or more different
forms (allotropes).like diamond, graphite, fullerenes are the allotropes of carbon
55alloyA material consisting of two or more metals (e.g. brass is an alloy of
copper and zinc) or a metal and a nonmetal (e.g. steel is an alloy of iron
and carbon, sometimes with other metals included).
56alpha-naphthol testA biochemical test to detect the presence of carbohydrates in solution,
also known as *Molisch’s test* (after the Austrian chemist H. Molisch)
57alpha particleA helium nucleus that is emitted by a larger nucleus during the course of the
type of radioactive decay known as alpha decay
58alumsA group of double salts with the formula A2SO4.B2(SO4)3.24H2O, where A is a
monovalent metal and a trivalent metal. E.g. K2SO4⋅Al2(SO4)3⋅24H2O is potash alum
59amalgamAn alloy of mercury with another metals
60amatolAmmonium nitrate and trinitrotoluene combine to form a highly explosive chemical.
61amino acid racemization (AAR)The process of conversion of optically active amino acids into optically inactive active amino acids
62ammonia clockA form of the atomic clock in which the frequency of a quartz oscillator is
controlled by the vibrations of excited ammonia molecules.
63ammonium ionThe monovalent cation NH4+. It may be regarded as the product of the
reaction of ammonia (a Lewis base) with a hydrogen ion.
64amorphousDescribing a solid in which atoms are not well arranged, and do not posseses crystallinity; i.e. one that has no long-range
order in its lattice.
65amount of substanceA measure of the number of entities present in a substance.or number of particles that constitute the substance
Symbol ‘n’.
66ampereThe SI unit of electric current.
It's symbol is A.
67amperometric titrationA method of determining the chemical composition of a solution by measuring the current flowing through a solution-containing cell.
68amphiphilicDetermining a molecule that contains both hydrophilic and hydrophobic components, such as detergents.
69ampholyteIn the presence of a strong base, a substance that can act as either an acid or a base.
70amphotericA compound that can act both as an acid and a base . E.g. Water, amino acids, protein
71a.m.u.atomic mass unit. A unit of mass used to express relative atomic masses. It
is equal to 1/12 of the mass of an atom of the isotope carbon–12 and is
equal to 1.660 33 × 10–27 kg
72Analar reagentA high-purity chemical reagent with known impurities for use in chemical analyses.
73Andrews titrationA titration that is used to estimate amounts of reducing agents.
74angle-resolved photoelectron
spectroscopy (ARPES)
A technique for studying the composition and structure of surfaces by
measuring both the kinetic energy and angular distribution of
photo-electron ejected from a surface by electromagnetic radiation.
75anhydrideA compound that is formed by the elimination of water in a molecule.
For instance, sulphur trioxide is the (acid) anhydride of sulphuric acid.
SO3 + H2O → H2SO4.
76anhydrouschemical compound that exists in salt form, lacking water: or the water of crystallizations.
77anionA negatively charged ion, or an ion attracted to the anode during electrolysis.
78anisotropicThe medium/substance in which certain physical properties are different in
different directions.
79annealingA type of heat treatment used to soften a metal, relieve internal stresses and instabilities, and make it easier to work with or machine.
80annulationA chemical reaction in which two new bonds are formed to fuse a ring to a molecule.
81anodeA positive electrode.
82antifoaming agentA chemical that prevents foam from forming in processes like electroplating and papermaking, as well as in boiler water.
83aqua regiaA mixture consist of concentrated nitric acid and concentrated hydrochloric acid in
the ratio 1:3 respectively.
84aquo ionA hydrated positive ion present in solution.
85arene complexA complex in which an aromatic ring is linked to a metal atom through its
86arenesAromatic hydrocarbons, such as benzene, toluene, and naphthalene.
87Arndt–Eisert synthesisA process of converting a carboxylic acid into the next higher homologue
acid (or one of its derivatives).
88aromatic compoundAn organic compound that contains a benzene ring in its molecules or that
has chemical properties similar to benzene.
89aromaticityThe peculiar characteristic of aromatic compounds.
90ARPESangle-resolved photoelectron spectroscopy.
91aryneA chemical that is created by removing two neighboring hydrogen atoms from an arene to change a double bond into a triple bond.
92asbestosAmosite, crocidolite (blue asbestos), tremolite, anthophyllite, and actinolite are fibrous amphibole minerals, while chrysotile is a fibrous serpentine mineral
93astrochemistryThe study of chemical species in interstellar space. Interstellar molecules are
usually detected by their spectra in the radio, microwave, or infrared
regions of the electromagnetic spectrum.
94asymmetric inductionThe phenomenon of preferential formation of one particular enantiomer or diastereoisomer
in a reaction due to chiral element in one of the reactants or in
the catalyst used.
95atmolysisThe process of separating a mixture of gases based on their different diffusion rates.
96atomThe smallest entity of an element that can exist chemically
97atomic absorption spectroscopy
The nonexcited atoms in a vaporized sample absorb electromagnetic radiation at specific wavelengths, which is used to analyze the sample.
98atomic clockA device that uses periodic events within atoms or molecules to standardize time.
99atomic emission spectroscopy
A method of analysis in which a sample is vaporized and the atoms present are detected through the emission of electromagnetic radiation at specific wavelengths.
100atomic force microscope (AFM)A type of microscope in which a small probe, consisting of a tiny diamond chip, is maintained in contact with the sample surface by a springloaded cantilever.
101atomicity number of atoms in a given molecule. For example, oxygen (O2) has an atomicity of 2,
102atomic numbernumber of protons in the nucleus of an atom. It is denoted by symbol Z.
103atom-probe field-ion microscopyA technique for identifying individual atoms on surfaces. In the atom-probe
field-ionization microscope (FIM) there is a hole in the fluorescent
screen, with which the FIM image of an adsorbed atom is brought into
104atropisomersConformers that have highly restricted rotation about a single bond therefore can be separated as distinct species.
105attenuated total reflectance
spectroscopy (ATRS)
A variation of infrared spectroscopy in which the IR source is reflected
from the sample and absorption occurs only in the surface layer.
106Aufbau principleA principle that gives the order in which orbitals are filled in successive
elements in the periodic table.
107Auger effectejection of an electron from an atom due to the de-excitation
of an excited electron within the atom.
108autocatalysisCatalysis in which one of the products of the reaction acts as catalyst for that reaction.
109autoprotolysisA transfer of a hydrogen ion (H+) between molecules of an amphiprotic
solvent, one molecule acting as a Brønsted acid and the other as a Brønsted
110Avogadro constantThe number of atoms or molecules in one mole of substance. It has the value
6.022 1367(36) × 1023. it was called as Avogadro’s number NA.
111Avogadro’s lawEqual volumes of all gases contain equal numbers of molecules at the same
pressure and temperature. The law, often called Avogadro’s hypothesis, is
true only for ideal gases.
112AX spectrumA general pattern of the nuclear magnetic resonance spectrum of a molecule
AX, where A and X are both spin-½ nuclei.
113azeotropeA mixture of two liquids that boils at constant composition.
114azeotropic distillationA technique for separating components of an azeotrope by adding a third
liquid to form a new azeotrope with one of the original components
115azo compoundsOrganic compounds containing the group –N=N– group.
116back titrationA technique in volumetric analysis in which a known excess amount of a reagent is added to the solution to be estimated
117Baeyer strainangle strain
118Baeyer testtest for unsaturated compounds in which potassium permanganate is used.
119Baeyer–Villiger reactionA rearrangement reaction used in organic synthesis in which a ketone reacts with a peroxy acid to form an ester.
120banana bondelectron-deficient three centre bond holding the B–H–B
bridges in boranes and similar compounds.
121Barbier–Wieland degradationstepwise degradation of a carboxylic acid to the next lower homologue
122baseA compound that reacts with a protonic acid to give water (and a salt).
123base metalA common inexpensive metal, such as iron or lead, that corrodes, oxidizes, or tarnishes on exposure to air, moisture, or heat.
124bathochromic shiftA shift of a spectral band to longer wavelengths as a result of substitution in a molecule or a change in the conditions.
125Beattie–Bridgman equationAn equation of state that relates the pressure, volume, and temperature of a gas and the gas constant.
126Beckmann rearrangementThe chemical reaction in which a ketone oxime is converted to an amide,using sulphuric acid as a catalyst.
127Beilstein’s testa chemical test which is used to detect halogens such as chlorine,bromine, iodine present in organic compound.
128B–Z reactionBelousov–Zhabotinskii reaction
129Benedict’s testA biochemical test to detect reducing sugars in solution
130benzilic acid rearrangementAn organic rearrangement reaction in which benzil (1,2-diphenylethan-1,2-
dione) is treated with hydroxide and then acid to give benzilic acid (2-hydroxy-2,2-diphenylethanoic acid)
131benzoylationA chemical reaction in which a benzoyl group ( C6H5CO) is introduced into a molecule.
132Berry mechanismA mechanism by which ligands in trigonal bipyramidal complexes can interchange between axial and equatorial positions.
133Berthollide compoundA solid compound with slight variations in chemical composition
134Bessemer processA process used to convert pig iron from a blast furnace into steel.
135beta decayradioactive decay in which an unstable atomic nucleus changes into a nucleus of the same mass number but different proton number
136BET isothermAn isotherm that takes account of the possibility of multilayer adsorption on the solid surface.
137bifurcationA phenomenon in dynamical systems in which the number of solutions for a type of behaviour suddenly changes when one of the parameters deÜning the system reaches a critical value.
138Birge–Sponer extrapolationA method used to calculate the heat of bioreactor dissociation of a molecule by extrapolation from observed band spectra.
139Birkeland–Eyde processA process for the fixation of nitrogen by passing air through an electric arc to produce nitrogen oxide.
140biuret test A test to detect proteins in solution,
141bleaching powderA white solid which is a mixture of calcium chlorate(I), calcium chloride, and calcium hydroxide.
142boiling point (b.p.)The temperature at which the saturated vapour pressure of a liquid equals the external atmospheric pressure.
143bond dissociation energyAn amount of energy associated with a bond in a chemical compound.
144bond orderA value indicating the degree of bonding between two atoms in a molecule relative to a single bond.
145borax-bead testA simple laboratory test for certain metal ions in salts.
146Born–Haber cycleA cycle of reactions used for calculating the lattice energies of ionic crystalline solids.
147Boyle’s lawThe volume (V) of a given mass of gas at a constant temperature is inversely proportional to its pressure (p), i.e. pV = constant.
148brown-ring testA test for nitrates ions.
149buckminsterfullereneallotrope of carbon composed of clusters of 60 carbon atoms bonded together in a polyhedral structure composed of pentagons and hexagons
150bufferA solution that resists change in pH when small amounts of an acid or alkali are added over a certain range.
151buretteA graduated glass tube with a tap at one end leading to a fine outlet tube, used for delivering
known volumes of a liquid (e.g. in titration).
152by-productA side product formed during a chemical reaction at the same time as the main product.
153B–Z reaction (Belousov–Zhabotinskii reaction)A chemical reaction that shows a periodic colour change between magenta and blue with a period of about one minute.
154cage effectAn effect occurring in certain condensed-phase reactions in which fragments are formed and their diffusion is hindered by a surrounding ‘cage’ of molecules.
155Cannizzaro reactionA reaction of aldehydes without alpha hydrogens give carboxylic acids and alcohols in presence of strong base.
156carboranesCompounds similar to the *boranes, in which one or more borons are replaced by carbon atoms.
157carbylamine reactionisocyanide test.
158carbyneA reaction intermediate of the type R–C≡, with three nonbonding electrons on the carbon atom
159carcinogenAny agent that produces cancer, e.g. tobacco smoke,certain industrial chemicals, and ionizing radiation.
160Carius methodA method of determining the amount of sulphur and halogens in an organic compound
161Carnot cycleThe most efficient cycle of operations for a reversible heat engine.
162carrier gasThe gas that carries the sample in gas chromatography.
163carrier moleculeA molecule that plays a role in transporting electrons through the electron transport chain
164cascade liquefierAn apparatus for liquefying a gas of low critical temperature.
165cascade processAny process that takes place in a number of steps.
166cast ironA group of iron alloys containing 1.8 to 4.5% of carbon.
167catalysisThe process of changing the rate of a chemical reaction by use of a catalyst.
168catalystA substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change
169catenaneA type of compound consisting of two or more large rings that are interlocked like the links of a chain
170catenationThe formation of chains of atoms in chemical compounds.
171cathodeA negative electrode.
172cationA positively charged ion
173CD spectrum (circular dichroism spectrum)The spectrum obtained by plotting the variable IR – IL against frequency of the incident electromagnetic radiation, where IR and IL are the absorption intensities for right- and left-circularly polarized light, respectively.
174chain reactionA reaction in which the products of one step initiating a subsequent step.
175change of phase (change of state)A change of matter in one physical *phase (solid, liquid, or gas) into another.
176Charles’ lawThe volume of a fixed mass of gas at constant pressure expands by a constant fraction of its volume at 0°C for each Celsius degree or kelvin its temperature is raised.
177chelateAn inorganic complex in which a *ligand is coordinated to a metal ion at two (or more) points, so that there is a ring of atoms including the metal. The process is known as chelation.
178cheletropic reactionA type of addition reaction in which a conjugated molecule forms two single bonds from terminal atoms of the conjugated system to a single atom on another molecule to give a cyclic adduct. Cheletropic reactions are types of *pericyclic reaction.
179chemical bondA strong force of attraction holding atoms together in a molecule or crystals.
180chemical datingAn absolute *dating technique that depends on measuring the chemical composition of a
181chemical fossilAny of various organic compounds found in ancient geological strata that appear to be biological in origin and are assumed to indicate that life existed when the rocks were formed.

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