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
|1||absolute alcohol||common name for high purity ethanol which contains only one percent water.||Alcohols, Phenols, and Ethers (Organic)|
|2||absolute configuration||a way of representing the absolute structure of an optical isomer, dextrorotatory or laevorotatary.|
|3||absolute temperature||a scale of temperature based on absolute zero.|
|4||absolute zero||zero of thermodynamic temperature (0 kelvin) and It is equivalent to –273.15°C or –459.67°F.|
|5||absorption||the take up of a gas by a solid in its bulk structure or liquid, or the take up of a liquid by a |
|6||absorption coefficient||The molar absorption coefficient (symbol ε) is a quantity|
that characterizes the absorption of light when it passes through a sample of the absorbing
|7||absorption tower||A long vertical column which is used for absorbing gases in industry.|
|8||ABS plastic||A class of plastics based on acrylonitrile– butadiene–styrene copolymers.|
|9||abstraction||A chemical reaction that involves bimolecular removal of an atom or ion |
from a molecule.
|10||accelerator||A substance which speed up the rate of a chemical reaction, i.e. a positive catalyst|
|11||acceptor||A compound, molecule, ion, etc., to which electrons are donated during the |
formation of a coordinate bond.
|12||Acheson process||process for the manufacture of graphite by heating coke mixed |
with clay in the industrial.
|13||achiral||a molecule which is superimposible on its mirror image, not chiral|
|14||acid||chemical species that contains hydrogen and dissociates in water to |
produce positive hydrogen ions.
|15||acidimetry||Volumetric analysis to determine the |
amount of base using standard solutions of acids
|16||acid 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.
|17||acid salt||A salt of a polybasic acid in which not all the hydrogen atoms have been replaced by |
|18||acid value||the amount of free acid present in a fat, equal to the number |
of milligrams of potassium hydroxide needed to neutralize this acid.
|20||actinic radiation||Electromagnetic radiation that is capable of initiating a chemical reaction.|
|21||actinometer||a device used to measure the intensity of electromagnetic radiation.|
|22||actinometry||The measurement of the intensity of electromagnetic radiation.|
|23||action spectrum||A graphical plot of the efficiency of electromagnetic radiation in |
producing a photochemical reaction against the wavelength of the radiation
|24||activation analysis||An analytical technique that can be used to detect most elements when |
present in a sample in milligram quantities (or less).
|25||activation energy||The minimum energy required for a chemical reaction to take place. it is |
denoted by Ea .
|26||acyclic||a compound which does not have a ring in its molecules.|
|27||acylation||The process of introducing an acyl group (RCO–) into a compound.|
|28||acyl fission||The breaking of the carbon–oxygen bond in an acyl group.|
|29||Adams catalyst||A 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.
|30||adduct||compounds formed by coordination between a Lewis acid (acceptor) and a |
Lewis base (donor).
|31||adenine||A purine derivative, major component bases of nucleotides |
and the nucleic acids DNA and RNA.
|32||adhesive||A substance is used for joining surfaces together.|
|33||adiabatic process||Any process that occurs without exchange of heat or at constant heat|
|34||adsorption||The formation of a layer of gas, liquid, or solid on the surface of a solid.|
|35||adsorption indicator||A type of indicator which is used in precipitation titration|
|36||aerogel||A low-density porous transparent material that consists of more than 90% |
air which are used as drying agents.
|37||aerosol||A colloidal dispersion of solid or liquid in a gas.|
|38||AES||Atomic Emission Spectroscopy|
|39||affinity chromatography||chromatographic technique for purifying natural polymers, especially proteins.|
|40||agar||An 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.
|41||albumin (albumen)||a group of globular proteins soluble in water but form |
insoluble coagulates when heated.
|42||aldol reaction||it is condensation reaction between aldehyde or ketone having alpha hydrogen and another aldehyde or ketone to give beta-hydroxy carbonyl compound.|
|43||aliphatic compounds||Organic compounds that are alkanes, alkenes, or alkynes or their |
|44||alkali||A base that dissolves in water to give hydroxide ions.|
|45||alkali metals||The elements of group 1 (formerly IA) of the periodic table: Li |
|46||alkalimetry||Volumetric analysis to determine the |
amount of acid using standard solutions of alkali.
|47||alkaline||a solution that has an excess of hydroxide ions (i.e. a pH |
greater than 7).
|48||alkanes (paraffins)||Saturated hydrocarbons with the general formula CnH2n+2.|
|49||alkenes (olefenes, olefins)||Unsaturated hydrocarbons contain one or more double carbon-carbon bonds in |
|50||alkylation||reaction that introduces an *alkyl group into an organic |
|51||alkyl group||A group that contains carbon and Hydrogen atom only|
|52||alkynes (acetylenes)||Unsaturated hydrocarbons containing one or more triple carbon-carbon bonds in |
|53||allenes||>C=C=C< containing group in which three carbon atoms are |
linked by two adjacent double bonds. in a compound.
|54||allotropy||The existence of elements in two or more different|
forms (allotropes).like diamond, graphite, fullerenes are the allotropes of carbon
|55||alloy||A 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).
|56||alpha-naphthol test||A biochemical test to detect the presence of carbohydrates in solution, |
also known as *Molisch’s test* (after the Austrian chemist H. Molisch)
|57||alpha particle||A helium nucleus that is emitted by a larger nucleus during the course of the |
type of radioactive decay known as alpha decay
|58||alums||A 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
|59||amalgam||An alloy of mercury with another metals|
|60||amatol||Ammonium nitrate and trinitrotoluene combine to form a highly explosive chemical.|
|61||amino acid racemization (AAR)||The process of conversion of optically active amino acids into optically inactive active amino acids|
|62||ammonia clock||A form of the atomic clock in which the frequency of a quartz oscillator is |
controlled by the vibrations of excited ammonia molecules.
|63||ammonium ion||The monovalent cation NH4+. It may be regarded as the product of the |
reaction of ammonia (a Lewis base) with a hydrogen ion.
|64||amorphous||Describing 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.
|65||amount of substance||A measure of the number of entities present in a substance.or number of particles that constitute the substance|
|66||ampere||The SI unit of electric current.|
It's symbol is A.
|67||amperometric titration||A method of determining the chemical composition of a solution by measuring the current flowing through a solution-containing cell.|
|68||amphiphilic||Determining a molecule that contains both hydrophilic and hydrophobic components, such as detergents.|
|69||ampholyte||In the presence of a strong base, a substance that can act as either an acid or a base.|
|70||amphoteric||A compound that can act both as an acid and a base . E.g. Water, amino acids, protein|
|71||a.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
|72||Analar reagent||A high-purity chemical reagent with known impurities for use in chemical analyses.|
|73||Andrews titration||A titration that is used to estimate amounts of reducing agents.|
|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.
|75||anhydride||A 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.
|76||anhydrous||chemical compound that exists in salt form, lacking water: or the water of crystallizations.|
|77||anion||A negatively charged ion, or an ion attracted to the anode during electrolysis.|
|78||anisotropic||The medium/substance in which certain physical properties are different in |
|79||annealing||A type of heat treatment used to soften a metal, relieve internal stresses and instabilities, and make it easier to work with or machine.|
|80||annulation||A chemical reaction in which two new bonds are formed to fuse a ring to a molecule.|
|81||anode||A positive electrode.|
|82||antifoaming agent||A chemical that prevents foam from forming in processes like electroplating and papermaking, as well as in boiler water.|
|83||aqua regia||A mixture consist of concentrated nitric acid and concentrated hydrochloric acid in |
the ratio 1:3 respectively.
|84||aquo ion||A hydrated positive ion present in solution.|
|85||arene complex||A complex in which an aromatic ring is linked to a metal atom through its |
|86||arenes||Aromatic hydrocarbons, such as benzene, toluene, and naphthalene.|
|87||Arndt–Eisert synthesis||A process of converting a carboxylic acid into the next higher homologue |
acid (or one of its derivatives).
|88||aromatic compound||An organic compound that contains a benzene ring in its molecules or that |
has chemical properties similar to benzene.
|89||aromaticity||The peculiar characteristic of aromatic compounds.|
|90||ARPES||angle-resolved photoelectron spectroscopy.|
|91||aryne||A chemical that is created by removing two neighboring hydrogen atoms from an arene to change a double bond into a triple bond.|
|92||asbestos||Amosite, crocidolite (blue asbestos), tremolite, anthophyllite, and actinolite are fibrous amphibole minerals, while chrysotile is a fibrous serpentine mineral|
|93||astrochemistry||The 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.
|94||asymmetric induction||The 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.
|95||atmolysis||The process of separating a mixture of gases based on their different diffusion rates.|
|96||atom||The smallest entity of an element that can exist chemically|
|97||atomic absorption spectroscopy|
|The nonexcited atoms in a vaporized sample absorb electromagnetic radiation at specific wavelengths, which is used to analyze the sample.|
|98||atomic clock||A device that uses periodic events within atoms or molecules to standardize time.|
|99||atomic 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.|
|100||atomic 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.|
|101||atomicity||number of atoms in a given molecule. For example, oxygen (O2) has an atomicity of 2,|
|102||atomic number||number of protons in the nucleus of an atom. It is denoted by symbol Z.|
|103||atom-probe field-ion microscopy||A 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
|104||atropisomers||Conformers that have highly restricted rotation about a single bond therefore can be separated as distinct species.|
|105||attenuated total reflectance|
|A variation of infrared spectroscopy in which the IR source is reflected |
from the sample and absorption occurs only in the surface layer.
|106||Aufbau principle||A principle that gives the order in which orbitals are filled in successive |
elements in the periodic table.
|107||Auger effect||ejection of an electron from an atom due to the de-excitation |
of an excited electron within the atom.
|108||autocatalysis||Catalysis in which one of the products of the reaction acts as catalyst for that reaction.|
|109||autoprotolysis||A 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
|110||Avogadro constant||The 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.
|111||Avogadro’s law||Equal 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.
|112||AX spectrum||A general pattern of the nuclear magnetic resonance spectrum of a molecule |
AX, where A and X are both spin-½ nuclei.
|113||azeotrope||A mixture of two liquids that boils at constant composition.|
|114||azeotropic distillation||A technique for separating components of an azeotrope by adding a third |
liquid to form a new azeotrope with one of the original components
|115||azo compounds||Organic compounds containing the group –N=N– group.|
|116||back titration||A technique in volumetric analysis in which a known excess amount of a reagent is added to the solution to be estimated|
|117||Baeyer strain||angle strain|
|118||Baeyer test||test for unsaturated compounds in which potassium permanganate is used.|
|119||Baeyer–Villiger reaction||A rearrangement reaction used in organic synthesis in which a ketone reacts with a peroxy acid to form an ester.|
|120||banana bond||electron-deficient three centre bond holding the B–H–B|
bridges in boranes and similar compounds.
|121||Barbier–Wieland degradation||stepwise degradation of a carboxylic acid to the next lower homologue|
|122||base||A compound that reacts with a protonic acid to give water (and a salt).|
|123||base metal||A common inexpensive metal, such as iron or lead, that corrodes, oxidizes, or tarnishes on exposure to air, moisture, or heat.|
|124||bathochromic shift||A shift of a spectral band to longer wavelengths as a result of substitution in a molecule or a change in the conditions.|
|125||Beattie–Bridgman equation||An equation of state that relates the pressure, volume, and temperature of a gas and the gas constant.|
|126||Beckmann rearrangement||The chemical reaction in which a ketone oxime is converted to an amide,using sulphuric acid as a catalyst.|
|127||Beilstein’s test||a chemical test which is used to detect halogens such as chlorine,bromine, iodine present in organic compound.|
|128||B–Z reaction||Belousov–Zhabotinskii reaction|
|129||Benedict’s test||A biochemical test to detect reducing sugars in solution|
|130||benzilic acid rearrangement||An 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)
|131||benzoylation||A chemical reaction in which a benzoyl group ( C6H5CO) is introduced into a molecule.|
|132||Berry mechanism||A mechanism by which ligands in trigonal bipyramidal complexes can interchange between axial and equatorial positions.|
|133||Berthollide compound||A solid compound with slight variations in chemical composition|
|134||Bessemer process||A process used to convert pig iron from a blast furnace into steel.|
|135||beta decay||radioactive decay in which an unstable atomic nucleus changes into a nucleus of the same mass number but different proton number|
|136||BET isotherm||An isotherm that takes account of the possibility of multilayer adsorption on the solid surface.|
|137||bifurcation||A 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.|
|138||Birge–Sponer extrapolation||A method used to calculate the heat of bioreactor dissociation of a molecule by extrapolation from observed band spectra.|
|139||Birkeland–Eyde process||A process for the fixation of nitrogen by passing air through an electric arc to produce nitrogen oxide.|
|140||biuret test||A test to detect proteins in solution,|
|141||bleaching powder||A white solid which is a mixture of calcium chlorate(I), calcium chloride, and calcium hydroxide.|
|142||boiling point (b.p.)||The temperature at which the saturated vapour pressure of a liquid equals the external atmospheric pressure.|
|143||bond dissociation energy||An amount of energy associated with a bond in a chemical compound.|
|144||bond order||A value indicating the degree of bonding between two atoms in a molecule relative to a single bond.|
|145||borax-bead test||A simple laboratory test for certain metal ions in salts.|
|146||Born–Haber cycle||A cycle of reactions used for calculating the lattice energies of ionic crystalline solids.|
|147||Boyle’s law||The volume (V) of a given mass of gas at a constant temperature is inversely proportional to its pressure (p), i.e. pV = constant.|
|148||brown-ring test||A test for nitrates ions.|
|149||buckminsterfullerene||allotrope of carbon composed of clusters of 60 carbon atoms bonded together in a polyhedral structure composed of pentagons and hexagons|
|150||buffer||A solution that resists change in pH when small amounts of an acid or alkali are added over a certain range.|
|151||burette||A 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).
|152||by-product||A side product formed during a chemical reaction at the same time as the main product.|
|153||B–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.|
|154||cage effect||An effect occurring in certain condensed-phase reactions in which fragments are formed and their diffusion is hindered by a surrounding ‘cage’ of molecules.|
|155||Cannizzaro reaction||A reaction of aldehydes without alpha hydrogens give carboxylic acids and alcohols in presence of strong base.|
|156||carboranes||Compounds similar to the *boranes, in which one or more borons are replaced by carbon atoms.|
|157||carbylamine reaction||isocyanide test.|
|158||carbyne||A reaction intermediate of the type R–C≡, with three nonbonding electrons on the carbon atom|
|159||carcinogen||Any agent that produces cancer, e.g. tobacco smoke,certain industrial chemicals, and ionizing radiation.|
|160||Carius method||A method of determining the amount of sulphur and halogens in an organic compound|
|161||Carnot cycle||The most efficient cycle of operations for a reversible heat engine.|
|162||carrier gas||The gas that carries the sample in gas chromatography.|
|163||carrier molecule||A molecule that plays a role in transporting electrons through the electron transport chain|
|164||cascade liquefier||An apparatus for liquefying a gas of low critical temperature.|
|165||cascade process||Any process that takes place in a number of steps.|
|166||cast iron||A group of iron alloys containing 1.8 to 4.5% of carbon.|
|167||catalysis||The process of changing the rate of a chemical reaction by use of a catalyst.|
|168||catalyst||A substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change|
|169||catenane||A type of compound consisting of two or more large rings that are interlocked like the links of a chain|
|170||catenation||The formation of chains of atoms in chemical compounds.|
|171||cathode||A negative electrode.|
|172||cation||A positively charged ion|
|173||CD 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.|
|174||chain reaction||A reaction in which the products of one step initiating a subsequent step.|
|175||change of phase (change of state)||A change of matter in one physical *phase (solid, liquid, or gas) into another.|
|176||Charles’ law||The 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.|
|177||chelate||An 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.|
|178||cheletropic reaction||A 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.|
|179||chemical bond||A strong force of attraction holding atoms together in a molecule or crystals.|
|180||chemical dating||An absolute *dating technique that depends on measuring the chemical composition of a|
|181||chemical fossil||Any 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.|