Glossary of chemistry terms

This glossary of chemistry terms is a list of terms and definitions relevant to chemistry, including chemical laws, diagrams and formulae, laboratory tools, glassware, and equipment. Chemistry is a physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions; it features an extensive vocabulary and a significant amount of jargon.

Note: All periodic table references refer to the IUPAC Style of the Periodic Table.

A
absolute zero:

absorbance:

absorption: The physical or chemical process by which a substance in one becomes incorporated into and retained by another substance of a different state. Absorption differs from in that the first substance permeates the entire bulk of the second substance, rather than just adhering to the surface. The process by which matter (typically bound in atoms) takes up the energy of and transforms it into any of various types of internal energy, such as thermal energy. This type of absorption is the principle on which is based.

abundance:

accuracy: How close a measured value is to the actual or true value. Compare.

acetyl:

achiral: (of a ) Having the geometric symmetry of being indistinguishable from its own mirror image; lacking.

acid: Any or that acts as a  donor when reacting with another species, because it loses at least one proton  which is then transferred or 'donated' to the other species, which by definition is a. When dissolved in an, a proton donor which increases the concentration of ion  by transferring protons to water molecules may also be called an. The term "acid", when not otherwise qualified, often refers implicitly to a Brønsted–Lowry acid. Any chemical species or molecular entity that acts as an acceptor when reacting with another species, forming a by accepting a  of electrons donated by the other species, which is known as a. This definition was intended as a generalization of the Brønsted–Lowry definition by proposing that acid-base reactions are best viewed as reorganizations of electrons rather than transfers of protons, with the acid being a species that accepts electron pairs from another species either directly or by releasing protons into the solution, which then accept electron pairs from the other species. The Lewis definition is inclusive of many Brønsted–Lowry acids, though not all: most Lewis acids are not Brønsted–Lowry acids, and most Brønsted–Lowry acids are not Lewis acids. Colloquially, any compound which, when dissolved in, yields a of less than 7.0. The term "acid" is commonly used to refer to the entire aqueous, whereas stricter definitions refer only to the acidic.

acid anhydride: Any chemical derived by the removal of molecules from an. Contrast.

acid dissociation constant:

A quantitative measure of the strength of an in expressed as an  for a chemical  reaction in the context of. It is often given as its base-10 cologarithm, pKa.

acid–base extraction: A in which are separated from other  and.

acid–base reaction:

acidic:

actinides:

The series of metallic elements with atomic numbers 89 to 103, from actinium through lawrencium.

activated complex: A structure that forms because of a collision between molecules while new bonds are formed.

activation energy: The minimum which must be available to a chemical system with potential in order to result in a particular.

activity series: See.

actual yield:

acyclic: Containing only linear structures of atoms (particularly in ).

addition reaction: In organic chemistry, a type of chemical reaction in which two or more molecules combine to make a larger one.

adduct: A distinct that is the sole of an  between two other distinct  species, in which all of the atoms comprising the reactants are retained in the single product. Changes in connectivity may occur, but there is no loss of any of the original atoms and no gain of atoms that are not present in the reactant molecules. other than 1:1 are also possible, e.g. a bis-adduct (2:1).

adhesion: The tendency of dissimilar particles or surfaces to cling to one another as a result of. Contrast.

adsorption: The chemical of atoms, ions, or molecules of one substance (either a,, or dissolved ) to the surface of another substance, resulting in a film of the first substance being weakly bonded to the interface between the two substances. Adsorption differs from in that it is exclusively a surface phenomenon, while absorption involves entire volumes of materials.

aeration: The mixing of air into a or a.

alcohol: Any consisting of at least one  attached to a  carbon atom. Alcohols have the general formula R–OH.

aldehyde:



aliphatic:

alkali metal: Any of the metallic belonging to of the : lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr).

alkaline:

alkaline earth metal: Any of the metallic belonging to of the : beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

alkane:

Any fully, i.e. one in which all carbon–carbon bonds are.

alkene:

Any unsaturated containing at least one carbon–carbon.

alkoxy:

alkyl: The form of an, i.e. any alkane missing a hydrogen atom. The term may be used to refer to many different functional groups, e.g. a or  group.

alkyne:

Any unsaturated containing at least one carbon–carbon.

allomer: A substance that differs in chemical composition but has the same structure as another substance.

allotrope: Any of a variety of different structural forms of the same element, as with, whose allotropes include diamonds, graphite, and fullerene.

alloy: A of or of a metal and another  which in combination exhibit a  character. Common examples include bronze, brass, and pewter.

amalgam: Any of mercury with another.

ambident: A or that has two alternative and interacting reaction sites, to either of which a  may be made during a.

amide:

ammoniacal: Describing a in which the is  ammonia.

amorphous solid:

amount of substance:

The number of discrete particles (such as,, , , or any other atomic-scale entity) in a given sample of , divided by the. The unit for amount of substance is the (mol).

amphipathic: (of a ) Composed of both and groups; e.g.  and membrane lipids.

amphoteric:

(of a ) Tending to behave both as an and as a, depending upon the medium in which the species is situated; e.g. sulfuric acid (H2SO4) is a in water but behaves more like a base in.

amyl: A common non-systematic name for a group.

analyte: The specific substance or chemical constituent that is of interest in a.

analytical chemistry: The branch of chemistry which studies and makes use of instruments and methods to separate, quantify, and identify chemical substances, both by classical techniques such as,, , and observational analysis, and by modern instrumental techniques such as , , and.

ångström (Å): A non-, metric unit of length equal to $$ metre, i.e. $1/undefined$ of a metre or 0.1 nanometre. The angstrom is commonly used in the natural sciences to express microscopic or atomic-scale distances, including the sizes of atomic nuclei, wavelengths of electromagnetic radiation, and lengths of chemical bonds (e.g. the of a chlorine atom averages about 1 angstrom).

anhydrous: Having or containing no molecules, referring especially to. Because many processes in chemistry are impeded in the presence of water, it is often of critical importance that water-free reagents and techniques are used. Anhydrous compounds tend to gradually from the atmosphere. Contrast.

anion: A negatively charged ; i.e. an atom or molecule with a net negative electric charge caused by an excess of compared to.

anode: An through which the conventional electric current (the flow of positive charges) enters into a electrical circuit. The wire or plate of an having an excess positive charge. Negatively charged always move toward the anode. Contrast.

anomer: Either of a pair of or   that are  of each other, differing at only one carbon, specifically the carbon that bears the  or  functional group in the compound's acyclic, open-chain configuration, known as the anomeric carbon.

aprotic:

aqua regia: A liquid of nitric acid (HNO3) and hydrochloric acid (HCl), optimally in a ratio of 1:3, so named by historical alchemists because it is capable of  the  gold and platinum.

aquation: The process by which molecules or form  with.

aqueous solution: A in which the is. It is denoted in chemical equations by appending (aq) to a.

aromatic:

aromaticity: A chemical property of conjugated rings of atoms, such as, which results in unusually high stability. Such rings are said to be.

Arrhenius acid: Any substance that, when dissolved in, increases the concentration of, or, more correctly, of ions , in the resulting. The definition is similar to that of a. Contrast.

Arrhenius base: Any substance that, when dissolved in, increases the concentration of, or, alternatively, decreases the concentration of ions , in the resulting. The definition is similar to that of a. Contrast.

arrow pushing:

aryl: Any or derived from an, such as phenyl or naphthyl. The symbol Ar is often used as a placeholder for a generic aryl group in structural diagrams.

atmolysis: The separation of a of by exploiting their different rates of, usually by allowing the gases to diffuse through the walls of a porous partition or membrane.

atom: A chemical element in its smallest form, made up of and within the nucleus and  circling the nucleus.

atomic mass: The of an, typically expressed in and nearly equivalent to the  multiplied by one dalton.

atomic mass unit: See.

atomic number (Z):

The number of found in the of an  of a given. It is identical to the of the nucleus and is used in the  to uniquely identify each chemical element.

atomic orbital: Any region in which one or more may be found in an individual (as opposed to that within ).

atomic radius:

atomic weight: See.

atomicity: The total number of present in a single of a given substance; e.g. ozone (O3) has an atomicity of 3, while benzene (C6H6) has an atomicity of 12.

autoignition temperature:

The lowest temperature at which a given substance will spontaneously ignite in a normal atmosphere without an external source of ignition such as a flame or spark, i.e. when the ambient temperature is sufficiently high to provide the needed for. Substances which spontaneously ignite at naturally occurring temperatures are termed pyrophoric. Compare.

Avogadro constant: The ratio of the number of discrete constituent particles (such as,, or ) to the , defined as exactly $6.022 mol-1$.

Avogadro number: The number of discrete constituent particles in one of a substance, defined as exactly 6.02214076. This dimensionless number differs from the in that it has no unit.

Avogadro's law:

azeotrope: A of whose  is unchanged by.

B
balance:

barometer: A device used to measure atmospheric pressure.

base: A substance that accepts a and has a above 7.0. A common example is sodium hydroxide (NaOH).

base anhydride: An of a group I or II metal element.

basic:

basicity:

battery:

beaker: A cylindrical vessel or container with a flat bottom, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a occurs. Beakers are distinguished from by having straight rather than sloping sides; most beakers also have a small spout in the rim to aid pouring.

Beer–Lambert law:

biochemistry: The study of the chemistry of biological systems and organisms.

Bohr model:

A model of the general structure of the proposed by Niels Bohr and Ernest Rutherford in 1913, featuring a small, dense of  surrounded by, which are attracted to the nucleus by electrostatic forces. This interpretation replaced several earlier hypotheses and quickly became the prevailing standard model for depicting atomic structure.

boiling: See.

boiling flask:

boiling point:

The at which a substance changes from a  to a  (or ). It depends on and is usually specified for a given substance under.

boiling-point elevation: The process by which a substance's is elevated by adding another substance.

bond: Any persistent attraction between,, or that enables the formation of. Bonds are created as a result of a wide variety of electrochemical forces, whose strengths can vary considerably; they are broken when these forces are overcome by other forces. The types, strengths, and quantities of bonds holding together chemical substances dictate the structure and bulk properties of.

bond angle:

Boyle's law: For a given mass of gas at constant temperature, the volume varies inversely with the pressure.

Bragg's law:

Brønsted–Lowry acid: Any chemical species that readily donates a.

Brønsted–Lowry acid–base reaction:

Brønsted–Lowry base: Any chemical species that readily accepts a.

Brownian motion:

Büchner flask:

buffered solution:

An consisting of a weak and its  or a weak  and its  that resists changes in  when strong acids or bases are added.

bumping: A phenomenon in which a homogeneous liquid raised to its becomes and, upon, rapidly boils to the gas phase, resulting in a violent expulsion of the liquid from the container; in extreme cases, the container itself may shatter. Frequent stirring, the use of an appropriate container, and the use of boiling chips can help prevent bumping.

bung:

burette:

Glassware used to dispense specific amounts of when precision is necessary (e.g. during and ).

butyl:

C
calorific value: A measure of the per unit produced by complete  of a given substance, usually expressed in  per  (MJ/kg) or in kilojoules per gram (kJ/g).

calorimeter: Any of various devices used to measure thermal properties (i.e. ), such as or heats of chemical reactions.

calx: A metal oxide formed by heating an ore in air.

carbanion:

carbide: A class of composed of bonded to a particular  (usually a large-radius ) in a densely packed crystal lattice, where the carbon atoms occupy interstices between the metal atoms; e.g. tungsten carbide (WC).

carbocation:

carbon:

carbonic acid:

carbonyl:

An or  with carbon monoxide as a  (e.g. a metal carbonyl).

carboxyl:

carboxylic acid: A class of and a consisting of a  group attached to a  group. Carboxylic acids have the general formula (also written as ), where  can be an,, , or any other carbon-containing substituent.

CAS Registry Number (CAS RN):

A unique numerical identifier assigned by the Chemical Abstracts Service (CAS) to every described in the open scientific literature, including more than 182 million and  compounds,,, , , and , as well as so-called "UVCBs" (substances of unknown or variable composition, complex reaction products, or biological origin). CAS numbers are an internationally recognized standard used by scientists, industries, and regulatory bodies.

catalyst: Any element or compound that facilitates an increase in the speed of a but which is not consumed or destroyed during the reaction. It is considered both a and a  of the reaction.

cathode: An from which the conventional electric current (the flow of positive charges) exits a electrical circuit. Positively charged always move toward the cathode, though the cathode's polarity can be positive or negative depending on the type of electrical device and how it is being operated. Contrast.

cation: A positively charged.

cell potential: The force in a galvanic cell that pulls electrons through a reducing agent to an oxidizing agent.

centrifugation: A laboratory technique which involves the application of centrifugal force to separate particles from a according to their size, shape, and density. Larger and/or denser substances migrate away from the axis of a, while smaller and/or less dense substances migrate towards the axis.

centrifuge: A device used to separate substances based on size, shape, and density by, or the rotation of vessels containing the substances around a centred axis at extremely high velocities.

chain reaction:

charge number:

Charles's law: When the pressure on a sample of a dry gas is held constant, the Kelvin temperature is directly proportional to its volume.

chelating agent:

chelation: A type of involving the formation of two separate between a   and a single central. The ligand is usually an called a chelant or.

chemical: See ' and '.

chemical bond: See.

chemical composition: The identity and relative number of the that make up a, which can often be expressed with a.

chemical compound: See.

chemical decomposition: The breakdown of a single particle or entity (such as a or ) into two or more fragments, or a in which two or more  are formed from a single. Contrast.

chemical element: See.

chemical formula: Any of various means of concisely displaying information about the of a or  using letters, numbers, and/or typographical symbols. Chemical formulas, such as and, can only indicate the identities and numerical proportions of the atoms in a compound and are therefore more limited in descriptive power than  and.

chemical law: A law of nature relevant to, such as the.

chemical nomenclature:

chemical physics:

chemical process: Any method or means of changing one or more or in any way, either naturally or artificially, spontaneously or by the actions of external forces. In chemical engineering, any method used on an industrial scale (especially in manufacturing) to change the composition of one or more chemicals or materials.

chemical reaction: The change of one or more into one or more different substances.

chemical species:

A or ensemble of substances composed of chemically identical molecular entities which can explore the same set of molecular energy levels on a characteristic or delineated time scale.

chemical substance:

A form of that has constant and characteristic  and which cannot be separated into simpler components by purely physical methods (i.e. without breaking ). It is often called a pure substance to distinguish it from a.

chemical synthesis: The artificial execution of one or more in order to obtain one or more. In modern laboratory contexts, specific chemical syntheses are both reliable and reproducible.

chemistry: The scientific discipline that studies,, and composed of of various , as well as their , structures, properties, behaviors, and the changes they undergo during  with other substances.

chirality: A property of asymmetry in which a or is distinguishable from its mirror image such that it cannot be  upon it by any combination of geometric rotations, translations, or some  changes. Such a molecule or ion is said to be chiral, and exists in two forms, known as, which are of each other; these forms are distinguished as either "right-handed" or "left-handed" by their  or some other criterion. Several different types of asymmetry can give rise to chirality, most commonly when molecules possess stereogenic elements such as one or more, a stereogenic axis , or a stereogenic plane ; additionally, the inherent curvature of a molecule can cause it to possess.

chromatography:

chromometer: See.

cis–trans isomerism:

closed system:

cluster:

cohesion: The tendency of similar particles or surfaces to cling to one another as a result of. Contrast.

colligative property: Any property of a that depends upon the ratio of the number of particles to the number of  particles in the solution, and not on the nature of the  present. Examples include,, and.

colloid: A of evenly substances, such as many milks.

color standard: A liquid of known chemical composition and concentration, and hence of known and standardized color, used as a reference in the optical analysis of samples of unknown strength.

color test: The quantitative analysis of a substance by comparing the intensity of the color produced when the substance is exposed to a with a produced similarly in a solution of known strength.

colorimeter:

Any instrument used for based on optical comparison with, particularly a device used in that measures the  of specific wavelengths of light by a given solution in order to determine the  of a known  in the solution, by application of the principle that.

combustion: An reaction between an and a fuel that produces large amounts of heat and often light.

Commission on Isotopic Abundances and Atomic Weights (CIAAW):

complex: A molecular entity formed by loose between two or more component molecular entities ( or uncharged), or the corresponding. The between the components is normally weaker than in a. See also.

compound: A that is made up of two or more.

Compton rule: An empirical law of which states that the of a given  multiplied by its  and then divided by its  in  is always equal to approximately 2.

concatemer:

concentration: The quantity or abundance of a constituent of a per unit quantity of the mixture; e.g. the of a dissolved solute per unit  of the solution, a measure known as. Several different definitions of concentration are widely used in chemistry, including,, and.

condensation: The of a substance from a to a.

condosity: A comparative measurement of the electrical conductivity of a defined as the of a sodium chloride (NaCl) solution that has the same specific electrical conductance as the solution under test. It is typically expressed in units of per  (or per some other unit of volume).

conduction:

conductivity: See ' and '.

conductor: Any object or material that allows the flow of an in one or more directions. Contrast.

conformation: The spatial arrangement of atoms affording distinction between which can be interconverted by rotations about formally.

conjugate acid:

conjugate base:

conjugated system: A that contains or  bonds separated by one ; e.g. the compound buta-1,3-diene, with the chemical structure H2C=CH−CH=CH2, has conjugated double bonds. In such molecules, there is some of  in the  between the carbon atoms linked by the single bond.

constitutional isomer: See.

convection:

cooling curve:

coordinate chemistry:

coordinate covalent bond: See.

coordination complex: A chemical consisting of a central or, usually  and known as the coordination center,  to a surrounding array of other groups of atoms, e.g.  or ions, which are known as ' or complexing agents. Many metal-containing compounds, especially those of the, are coordination complexes. See also '.

corrosion: An irreversible interfacial of a material, especially a, with its environment, which results in consumption of the material or into the material of an external component of the environment.

coulomb (C): The unit of, defined as the charge transported by a constant of one ampere in one second.

counterion: The that is the counterpart to an oppositely charged ion in a dissociated ; the that pairs with a given, or vice versa. For example, is the counterion to, and vice versa, in solutions of sodium chloride (NaCl).

covalent bond:

A that involves the sharing of between. The stable balance of attractive and repulsive forces that occurs between atoms when they share electrons is known as covalent bonding.

critical point: The end point of a equilibrium curve or - curve at which conditions are such that vanish and a substance's different phases, such as  and, can coexist. The critical point is defined by the intersection of a critical temperature, Tc, and a critical pressure, pc; above this temperature and pressure, all distinction between phases disappears and the substance becomes a.

crucible: A ceramic or metal dish or other vessel in which substances can be melted or otherwise subjected to very high temperatures.

crystal: A whose constituent particles (such as atoms, ions, or molecules) are arranged in an orderly periodic microscopic structure, forming a that extends in all directions. Such materials are often described as crystalline.

crystallization:

crystallization point: See.

crystallography: The branch of chemistry concerned with determining the arrangement of within solids.

cuvette: A type of glassware used in experiments. It is usually made of plastic, glass, or quartz and should be as clean and clear as possible.

cyclic:

D
dalton (Da):

A unit of defined as $1/undefined$ of the mass of a free unexcited atom of carbon-12 at rest. It is approximately equal to the mass of one.

Dalton's law of partial pressures: An empirical law which states that in a mixture of non-reacting, the total exerted by all of the gases combined is equal to the sum of the partial pressures exerted by each gas individually.

d-block:

dative bond: See.

debye (D): A non-SI unit of measurement of, defined as statcoulomb-centimetres. See also.

deionization: The removal of from a solution by any method. In the case of water, this typically refers to mineral ions such as sodium, iron, and calcium.

deliquescence: A substance's affinity for water, often characterized as its tendency to absorb moisture from the atmosphere to form. Most strongly deliquescent substances are, such as calcium chloride and potassium carbonate.

delocalized electron: Any in a molecule, ion, or solid that is not associated with an individual atom or. The term may refer to electrons involved in in  or  compounds; to free electrons which facilitate electrical conductivity; or to electrons within delocalized  encompassing several adjacent atoms.

density:

denticity: The number of donor groups in a single that bind to a central atom in a.

dependent variable:

deposition: The settling of particles within a solution or mixture.

depression of freezing point: See.

desiccant:

A substance used to induce or sustain a state of dryness or desiccation (i.e. the absence of moisture) in its vicinity by abstracting water molecules from other substances. Desiccants come in many different forms and work by many different principles, ranging from simple to the chemical bonding of water molecules.

desiccation:

deuterium:

deuteron:

Dewar flask: See.

diastereomer:

diatomic: Composed of two atoms, of the same or different elements. Contrast ' and '.

diatomic molecule: Any composed of only two, of the same or different.

diffusion: The net movement of or from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in chemical potential of the diffusing species and depends on the random walk of particles; hence it results in mixing or mass transport without required directed bulk motion.

dilatant: A substance with the ability to increase in when its shape is changed.

dilution:

dimer: An consisting of two joined by chemical bonds that may variably be strong or weak,  or. A homodimer consists of two identical molecules; a heterodimer consists of two different molecules.

dipolar bond:

A type of formed by the of two or more electrically neutral, the combination of which results in a  or, in which two  deriving from the same atom are shared between the donor atom and an acceptor atom, creating an internal two-center.

dipole: The electric or magnetic separation of into a pair of charges of equal magnitude but opposite sign, one positively charged and one negatively charged, separated by some typically small distance.

dipole moment: See ', ', ', ', ', ', and.

dispersion: A system in which particles of one material are distributed within a continuous of another material; the two phases may be in the same or different. Dispersions of particles sufficiently large for sedimentation are called, while those of smaller particles are called or.

dissociation: Any process by which a or molecular entity (e.g. an  or ), or an aggregate of molecular entities, separates or splits into two or more molecules, atoms, ions, radicals, or other constituents, usually in a  manner. Examples include unimolecular and, the  of, and. Contrast.

dissolution:

The interaction of a with the molecules or ions of a, involving bond formation,, and.

distillation: The process of separating the component substances of a by exploiting differences in the relative  of the mixture's components through selective  and subsequent. The apparatus used to distill a substance is called a still, and the re-condensed substance yielded by the process is called the distillate.

double bond: A involving the sharing of two.

double decomposition:

double displacement:

double salt: A composed of more than one different or, or which upon  forms two different cations and anions. A salt that is a molecular combination of two other salts.

double-replacement reaction:

dropping point: The at which a changes from a semi- to a  state under standardized conditions, i.e. the upper limit at which the grease retains its structure, though not necessarily the maximum temperature at which it can be used.

dry box: A chamber or container in which the interior is maintained at very low humidity, often by filling it with argon or with air lacking carbon dioxide, in order to provide an atmosphere in which manipulation of very reactive chemicals or moisture-sensitive procedures can be carried out in the laboratory.

drying agent: See.

ductility:

A measure of a material's ability to undergo significant plastic deformation before rupturing, typically expressed as percent elongation or percent area reduction from a tensile test and popularly characterized by the material's ability to be stretched into a wire.

dystectic mixture: A of two or more substances which has the highest of all possible mixtures of these substances. Contrast.

E
earth metal: See.

effective molecular diameter: The physical extent of the surrounding a of a particular gas, as calculated in any of several ways and usually expressed in  or.

effervescence: The escape of from an  without the application of heat, and the bubbling, foaming, or fizzing that results; e.g. the release of carbon dioxide from carbonated water.

electric charge: A measured property that determines electromagnetic interaction.

electric dipole moment: A measure of the of positive and negative within an electrical system, i.e. a measure of the system's overall electrical. The SI unit for measuring electric dipole moment is the (C⋅m), but the  (D), a non-SI unit, is also widely used in chemistry and atomic physics.

electrical conductivity:

electrical resistivity:

electricity:

electride: An for which the is an.

electrochemical cell: A device capable of either generating electrical energy from chemical reactions, in which case it is known as a galvanic or voltaic cell, or using electrical energy to cause chemical reactions, in which case it is known as an electrolytic cell. For example, a battery contains one or more galvanic cells, each of which consists of two arranged such that an reaction produces an.

electrochemistry: A branch of concerned with the relationship between electrical potential difference and identifiable chemical change, as understood through either the accompanying the passage of an electric current or the potential difference that results from a particular chemical reaction.

electrolyte: A that conducts a certain amount of electric current and can be split categorically into weak and strong electrolytes.

electromagnetic radiation: A type of wave that can go through vacuums as well as material and is classified as a self-propagating wave.

electromagnetic spectrum:

electromagnetism: Fields with an electric charge and electrical properties that change the way that particles move and interact.

electromotive force (emf):

electron: A type of with a net charge that is negative. Contrast.

electron acceptor:

electron capture: A type of nuclear transformation by which the -rich of an electrically neutral atom absorbs or 'captures' an from one of its own inner shells, often those closest to the nucleus, which provokes a reaction that results in a nuclear proton changing into a  accompanied by the simultaneous emission of an.

electron configuration: The distribution of the of an or  within  or. An extensive system of notation is used to concisely and uniquely display information about the electron configuration of each atomic species. Knowledge of the specific arrangements of electrons in different atoms is useful for understanding and the organization of the.

electron deficiency:

electron donor:

electron electric dipole moment: An intrinsic property of an such that its potential energy is linearly related to the strength of its electric field; a measure of the distribution of an electron's negative charge within the electric field it creates. See also.

electron magnetic dipole moment:

The of an, caused by the intrinsic properties of its spin and, equal to approximately &minus;9.284764 per tesla.

electron neutrino:

electron pair: Two which occupy the same but have opposite spins. Electron pairs form or occur as  of ; it is also possible for electrons to occur individually as.

electron shell: An around the of an  which contains a fixed number of  (usually two or eight).

electronegativity (χ): A chemical property that describes the tendency of an to attract a shared of  (or ) towards itself. An atom's electronegativity is affected both by its (which is proportional to the  in its ) and the number and location of the electrons present in its  (which influences the distance of the nucleus from the ). The higher an atom or 's electronegativity, the more it attracts electrons towards itself. As it is usually calculated, electronegativity is not a property of an atom alone but rather of an atom within a ; it therefore varies with an element's chemical environment, though it is generally considered a.

electron-volt (eV):

electrophile: Any atom or molecule which can accept an. Most electrophiles carry a net, include an atom carrying a partial positive charge, or include a neutral atom that does not have a complete of electrons, and therefore they attract electron-rich regions of other species; an electrophile with vacant orbitals can accept an electron pair donated by a, creating a chemical bond between the two species. Because they accept electrons, electrophiles are by definition.

electrosynthesis:

element: A species of having the same number of in their  and hence the same. Chemical elements constitute all of the ordinary in the universe; 118 elements have been identified and are organized by their various chemical properties in the.

elementary reaction: Any in which one or more react directly to form  in a single  and with a single, i.e. without any. Contrast.

elution: The process of extracting one material from another by washing with a. Elution works by running a solution containing an past an matrix designed to selectively bind the analyte molecules, and subsequently washing the adsorbent/analyte complex with a solvent, known as an eluent. The solvent molecules displace the analyte by binding to the adsorbent in its place, allowing the analyte, now part of the eluate, to be carried out of the complex and into a collector for analysis.

empirical formula: The simplest whole-number ratio of the of each present in a.

emulsion: A type of in which small particles of one are  in another liquid; e.g. a dispersion of water in an oil, or of an oil in water. Emulsions are often stabilized by the addition of a substance, known as an emulsifier, that has both lyophilic and lyophobic parts in its molecules.

enantiomer:

enantiomorph:

endothermic process:

energy: A system's ability to do.

enplethy: See.

enthalpy: A measure of the total internal energy of a thermodynamic system, usually symbolized by H.

enthalpy of fusion:

entropy: The amount of energy that is not available for in a closed thermodynamic system, usually symbolized by S.

environmental chemistry:

enzyme: A biological protein that speeds up a chemical reaction.

epimer:

Eppendorf tube: A generalized and trademarked name used to refer to a.

equation of state:

equilibrium: The condition of a system in which all competing influences are balanced. Chemical equilibrium is the state in which the concentrations of the and in a  system have stopped changing in time.

equimolar: Having an equal number of s, or s of equal.

Erlenmeyer flask:

ester: A class of and compounds derived from the reaction of an  with an, in which at least one  group (–OH) is replaced by an  group (–O–). Esters have the general formula RCO2R′, where R and R' represent any or  group.

ether: A class of and a containing an oxygen atom connected to two  or  groups, which may be the same or different. Ethers have the general formula R–O–R′, where R and R′ represent the alkyl or aryl groups.

ethyl:

eutectic mixture: A consisting of two or more substances which collectively have the lowest  of any possible mixture of these components.

evaporation:

exothermic process:

extensive property: A physical quantity whose value is proportional to the size of the system it describes or to the quantity of in the system. Examples include,, , and. Contrast.

extraction: A separation process in which a component is separated from its by selective. See also. The separation of a component from a.

extrinsic property:

F
family: See.

Faraday constant (F):

Faraday's laws of electrolysis: A set of two laws pertaining to electrolysis which hold that: a) the mass of a substance altered at an electrode during electrolysis is directly proportional to the quantity of electricity transferred at that electrode; and b) the mass of an elemental material altered at an electrode is directly proportional to the element's equivalent weight.

f-block:

Fick's laws of diffusion:

filtration: Any physical, biological, or chemical operation that separates large particles (often matter) from smaller particles (often a fluid) by passing the through a complex lattice structure through which only particles of a sufficiently small size can pass, called a filter. The fluid and small particles which successfully pass through the filter are called the filtrate.

fire point: The lowest at which the above a  material will continue to  for at least five seconds after ignition by an open flame of standard dimension. The fire point should not be confused with the, a slightly lower temperature at which a substance will ignite briefly but at which vapor is not produced at a rate sufficient for sustained combustion.

first-order reaction:

flash point: The lowest at which the above a  material will  if given an ignition source. At the flash point, the application of an open flame causes only a momentary "flash" rather than sustained combustion, for which the ambient temperature is still too low. The flash point should not be confused with the, which occurs at a slightly higher temperature, nor with the, which is higher still.

flask: A vessel or container, most commonly a type of glassware, widely used in laboratories for a variety of purposes, such as preparing, holding, containing, collecting, or volumetrically measuring chemicals, samples, or solutions, or as a chamber in which a occurs. Flasks come in a number of shapes and sizes but are typically characterized by a wider vessel "body" and one or more narrower tubular sections with an opening at the top.

flocculation: The process by which the dispersed particles in a come out of to aggregate into larger clumps known as floc or flake, either spontaneously or due to the addition of a clarifying agent. The term is often used to refer to a reversible aggregation in which the forces holding the particles together are weak and the colloid can be re-dispersed by agitation.

formal charge (FC): The assigned to an in a, assuming that all  in all  are shared equally between atoms, regardless of each atom's relative. The formal charge of any atom that is part of a molecule can be calculated by the equation $FC = V - N - \frac{B}{2}\ $, where $V$ is the number of of the neutral atom in its ; $N$ is the number of valence electrons of the atom which are not participating in bonds in the molecule; and $B$ is the number of electrons shared in bonds with other atoms in the molecule.

formula weight (FW): A synonym for and, frequently used for non-molecular compounds such as.

fraction:

fractional distillation: The of a of  into its component parts, or, by the process of, typically by using a long vertical column attached to the distillation vessel and filled with glass beads. The mixture is heated to a temperature at which one or more of the component compounds will ; the rises up the column until it  and runs back into the vessel, creating a temperature and  gradient and permitting various fractions to be drawn off at different points along the length of the column. Common in industrial chemistry, the technique is sensitive enough to separate compounds which have that differ by less than 25 C-change from each other at standard pressure.

fractionation: A separation process in which a particular quantity of a is divided during a into a number of smaller quantities, known as, for which the chemical composition varies according to a gradient. Fractionation exploits subtle differences in some specific property (e.g., , , etc.) between the mixture's component , making it possible to isolate more than two components of a mixture at the same time. There are many varieties of fractionation employed in many branches of science and technology.

free radical: See.

freeze-drying: See.

freezing: The of a substance from a to a.

freezing point:

The at which a substance changes from a  to a. Because is the reverse of, the freezing point of a substance is identical to its, but by convention only the melting point is referred to as a characteristic property of a substance.

freezing-point depression:

frequency: A measurement of the number of cycles of a given process per unit of time. The unit for measuring frequency is the hertz (Hz), with 1 Hz = 1 cycle per second.

functional group:

G
galvanic cell: A type of made up of electrochemicals with two different metals connected by a.

gas: One of the four fundamental, characterized by high-energy particles which fill their container but have no definite shape or volume.

gas chromatography: A type of commonly used in to isolate and analyze chemical compounds that can be  without. Gas chromatography is often used to test the purity of substances, to identify unknown substances, and to measure the relative amounts of the different components of.

gauche: In, a structural involving a  of 60°, or a  alignment of functional groups attached to adjacent atoms.

Gay-Lussac's law: A chemical law used for each of the two relationships derived by French chemist Joseph Louis Gay-Lussac and which concern the properties of gases, though the name is more usually applied to his law of combining volumes.

geochemistry: The study of the chemistry and chemical composition of the Earth and geological processes.

Gibbs energy: A value that indicates the spontaneity of a reaction. Usually symbolized as G.

glass:

glycol: Any of a class of in which the two  groups are bonded to two different carbon atoms, which are usually but not necessarily adjacent to each other; e.g. ethylene glycol.

gram (g):

gram-atom: A former term for a.

Grignard reaction:

ground glass joint: An apparatus designed to quickly and easily fit two pieces of leak-tight glassware together, featuring ground glass surfaces and typically a custom-made conical taper.

ground state:

The lowest possible energy state for a given quantum mechanical system, at which the is actually or theoretically minimized. Whatever energy remains in the system in its ground state is called the. Contrast.

group:

A vertical column of the and the elements that share it. Contrast.

H
hadron: A subatomic particle of a type including the baryons and mesons that can take part in the strong interaction.

halogen: Any of the five of  of the : fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At).

hard acid: A with an electron-accepting centre that is only weakly. Hard acid species also tend to have high charge states and relatively small atomic nuclei, in contrast to.

hard water: that has very high content, generally formed when water through deposits rich in calcium, magnesium, and certain other metal.

heat: Energy transferred from one system to another by thermal interaction.

heat of fusion: See.

heat of vaporization: See.

heavy water:

Henry's law:

Hess' law of constant heat summation:

A law of which states that the total change during the course of a chemical reaction is the same whether the reaction is completed in one step or in multiple steps.

Hund's rules:

hydrate: Any substance that contains water or its constituent elements, or any formed by the addition of water or its elements to another molecule.

hydration reaction:

hydride:

hydrocarbon:

hydrogen:

hydrogen bond: A form of electrostatic interaction between an and a  atom bound to a second electronegative atom. Hydrogen bonding is unique because the small size of the hydrogen atoms permits proximity of the interacting, and may occur as an or  force.

hydrogenation: Any chemical reaction between molecular and another chemical species, typically resulting in the  or  of the other species by the addition of one or more pairs of hydrogen atoms to a compound or element. The presence of a is usually required for hydrogenation reactions to occur; non-catalytic hydrogenation takes place only at extreme temperatures.

hydrolysis: The cleavage of a by the addition of.

hydron:

The form of atomic ; i.e. a positively charged hydrogen of any  composition. Thus the term can refer to a, , or.

hydrous: Having or containing molecules, referring especially to. Contrast.

hydroxide: A consisting of a hydrogen atom covalently bonded to an oxygen atom, having an overall negative charge, with the chemical formula ; or any member of a class of organic and inorganic compounds containing a, e.g. sodium hydroxide.

hydroxy:

hygroscopy:

I
ideal gas: A hypothetical composed of many randomly moving point particles that do not participate in any interparticle interactions, thereby making it mathematically convenient to describe and predict their behavior as state variables change. The ideal gas concept is useful because it obeys the and can be analyzed within the framework of statistical mechanics.

ideal gas constant:

The proportionality constant in the, defined as 0.08206 ·/(·).

ideal gas law:

The of a hypothetical, which states that the of such a  is proportional to the  of gas and its , and inversely proportional to its. The ideal gas law combines, , , and into a single equation, conventionally formulated as $PV = nRT$, where $R$ is the. The relationships between the state variables described in this equation are a good approximation of the behavior of many gases under a wide range of conditions, though there are some limitations.

ideal solution: A for which the phase exhibits thermodynamic properties analogous to those of a mixture of.

independent variable:

indicator: A special compound added to a that changes color depending on the of the solution. Different indicators have different colors and are effective within different ranges.

induced radioactivity: caused by bombarding a with elementary particles, forming an unstable, radioactive isotope.

inert:

inorganic compound:

Any chemical compound that does not contain, though there are exceptions. Contrast.

inorganic chemistry: The branch of chemistry concerning the chemical properties and reactions of. Contrast.

insolubility: The inability of a substance (the ) to form a by being dissolved in another substance (the ); the opposite of.

inspissation: The process of thickening a by any method of, especially.

insulator: Any material that resists the flow of an. Contrast.

intensive property: A physical quantity whose value does not depend on the size of the system or the quantity of for which it is measured. Examples include,, and. Contrast.

interface: The boundary between two spatial regions occupied by different, especially by matter in different or physical. See also ' and '.

intermetallic: A type of that forms an ordered solid-state compound between two or more elements. Intermetallics are generally hard and brittle, and have useful mechanical properties at high temperatures.

intermolecular force: Any force that mediates interaction between, e.g. forces of attraction or repulsion,, and the , all of which act between the atoms of one molecule and the atoms or ions of nearby molecules. Intermolecular forces are weak compared to such as, which hold individual molecules together.

International System of Units (SI):

International Union of Pure and Applied Chemistry (IUPAC): An international federation of chemists that is recognized as the world authority in developing standards for and other methodologies in chemistry.

interstitial compound: A composed of a bonded to either hydrogen, boron, carbon, or nitrogen, whose  structure consists of closely packed metal ions with the  atoms located in the interstices.

intramolecular force:

intrinsic property:

ion: A that has gained or lost one or more from its neutral state and therefore possesses a negative or positive.

ionic bond: An electrostatic attraction between oppositely charged.

ionic strength: A measure of the of in a, usually expressed in terms of  (mol/L solution) or  (mol/kg solvent).

ionization: The breaking up of a chemical into separate.

isoelectronicity: The phenomenon of two or more (,,, etc.) being composed of different but having the same number of   and the same structural arrangement (i.e. the same number of atoms with the same connectivity). Isoelectronic species typically show useful consistency and predictability in their chemical properties.

isomerization:

isomers: or with identical but distinct structures or spatial arrangements. Isomers do not necessarily share similar properties. The two main types of isomers are and.

isotope: A variant of a particular which differs in the number of present in the. All isotopes of a given element have the same number of in each.

J
joule (J): The unit of (symbol: J). One joule is defined as one newton-metre.

K
kelvin (K): The unit of (symbol: K). The Kelvin scale is an absolute thermodynamic temperature scale that uses as its null point.

keto acid:

Any organic compound that can be classified as both a and a, by virtue of containing a group and a  group.

ketone:



kindling point: See.

kinetics: A subfield of chemistry specializing in.

kinetic energy: The of an object due to its motion.

L
lability:

lanthanides:

The series of elements with atomic numbers 57 through 71, from lanthanum through lutetium.

lattice: The unique arrangement of atoms or molecules in a liquid or solid.

lattice energy: The energy released upon the formation of one of a crystalline from its constituent ions, which are assumed to exist initially in the gaseous state. Lattice energy can be viewed as a measure of the cohesive forces that bind ionic solids; it is therefore directly related to many other physical properties of the solid, including,, and.

law of conservation of energy:

law of conservation of mass:

law of multiple proportions:

laws of thermodynamics:

leveling effect: The effect of a on the chemical properties of or  which are dissolved in the solvent. The strength of a strong acid is limited or "leveled" by the basicity of the solvent, and likewise the strength of a strong base is limited by the acidity of the solvent, such that the effective of the solution is higher or lower than might be suggested by the acid's or base's.

Lewis acid:

Lewis base:

Lewis structure:

ligand: An,, or other that binds to a central atom to form a. Such bonding can range from to, but generally involves formal donation of one or more of the ligand's  to the metal.

light:

The portion of the which is visible to the unaided human eye.

liquefaction: Any process that generates a from a or a, or that generates a non-liquid phase that behaves as a.

liquefaction point: See.

liquid: One of the four fundamental, characterized by nearly incompressible fluid particles that retain a definite volume but no fixed shape.

 liquid–liquid extraction (LLE):

locant:

London dispersion forces: A type of weak.

M
macromolecule: A very large comprising many and, or any  with a high, especially one whose structure is formed by the multiple repetition of discrete subunits derived, actually or conceptually, from molecules with low relative molecular mass (e.g. , , and ). The term is often used interchangeably with.

magnetic quantum number:

malleability: See.

manometer: An instrument used to measure invented by Evangelista Torricelli in 1643.

masking agent: A used in a which reacts with one or more other  that may interfere in the analysis.

mass: A of physical that is a measure of its resistance to acceleration when a net force is applied. The unit for mass is the kilogram (kg).

mass concentration:

mass fraction:

mass number (A):

The total number of and (together known as ) within the  of an. It determines the of the atom. Mass number varies between different of the same chemical element, and is often included either after the element's name (as in carbon-12) or as a superscript to the left of the element's symbol (as in 12C) to identify a specific isotope.

mass spectrometry (MS): An analytical technique that measures the mass-to-charge ratio of in a chemical sample by bombarding the sample with electrons to the point of and then separating the charged fragments by subjecting them to an electric or magnetic field, typically in order to determine the elemental or  of an unknown substance, the  of its constituent particles, and/or the identities or structures of the molecules within it. The results are presented as a mass spectrum, a plot of the intensity of ion signals as a function of the mass-to-charge ratio.

matter: Any substance that has and takes up space by having.

metal: Any chemical element which is a good of both and  and which readily forms  and  with.

melting: The of a substance from a to a.

melting point:

The at which a substance changes from a  to a. It depends on and is usually specified for a given substance under. The melting point of a substance is identical to its.

mercaptan: See.

mercapto: See.

metalloid: A or possessing properties of both  and.

metamer: See.

metathesis: A chemical reaction involving the exchange of elements or functional groups between two or more compounds, as described by the general equation $\mathrm{{AX} + {BY}} \rightarrow \mathrm{{AY} + {BX}}$. See: See also.
 * Alkane metathesis
 * Alkyne metathesis
 * Olefin metathesis
 * Salt metathesis reaction

methyl:

The group derived from methane, consisting of one carbon atom bonded to three hydrogen atoms, with the chemical formula. It is the simplest  and occurs as a  in numerous organic compounds, though it may also exist independently as an ion or radical. The presence of a methyl substituent may be indicated with the prefix methyl in the name of the compound, or with the abbreviation Me in chemical formulae; e.g. methyl alcohol (methanol), which is often written with the formula or.

methylene blue: A heterocyclic with the  16183SCl.

microcentrifuge tube: A small plastic, sealable container that is used to store small volumes of liquid, generally less than 2 milliliters.

mineral: A with a fairly well-defined  and a specific  that occurs naturally in pure form.

miscibility: The tendency or capability of two or more substances (most commonly liquids, but also applicable to solids and gases) to blend uniformly when combined, i.e. to in each other, forming a homogeneous that exists in a single, without separation of phases, regardless of the proportions of each substance. Substances that do not mix uniformly in all proportions are said to be immiscible.

mixture: A material made up of two or more different substances which are mixed physically but are not combined chemically (i.e. a chemical reaction has not taken place which has changed the molecules of the substances into new substances).

moiety: Any named characteristic group, branch, or other part of a large that may be identified within other kinds of molecules as well. are typically smaller and more generic than moieties, whereas and  may often be classified as moieties and vice versa.

molality:

A measure of the of a in a  in terms of the  of the solute per unit  of the. Molality is typically expressed in units of per  (mol/kg); a solution with a concentration of exactly 1 mol/kg is sometimes said to be 1 molal. Contrast.

molar attenuation coefficient:

molar concentration:

A measure of the of a, especially of a in a, in terms of the  of the species per unit  of solution. Molarity is typically expressed in units of per  (mol/L); a solution with a concentration of exactly 1 mol/L is commonly said to be 1 molar, abbreviated 1 M. Contrast.

molar fraction:

molar mass:

For a given, the of a sample of that compound divided by the of compound in the sample, usually expressed in  per  (g/mol). As a bulk property, molar mass is an average of the masses of many instances of the compound, each of which may vary slightly due to the presence of of the compound's constituent atoms; it is commonly derived from the compound's, which itself is a sum of the  of the constituent atoms, and is therefore a function of the relative abundance of the isotopes as they occur naturally on Earth. Molar mass allows easy conversion between mass and number of moles when considering bulk quantities of a substance.

mole (mol): A unit (symbol: mol) used to measure the of a in terms of the absolute number of particles or entities composing the substance. By definition, one mole of any substance contains exactly the (i.e. 6.022) of particles or entities.

molecular formula:

molecular orbital (MO): Any region in which one or more may be found in a (as opposed to that within ).

molecular orbital diagram:

molecular weight:

molecule: A number of that are chemically together and collectively electrically neutral.

monatomic: Having only one, as opposed to a composed of more than one. Virtually all elements are monatomic in the phase at sufficiently high temperatures. Contrast ' and '.

N
natural abundance:

neat: Conditions with a liquid or gas performed with no added solvent or cosolvent.

neutron: A type of that is electrically neutral, having no net charge.

nitrogen:

noble gas:

Any of the six of  of the : helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). All of the noble gases have outer that are completely filled in their naturally occurring states, giving them very low chemical reactivity.

non-metal: Any chemical element which is not a.

nonpolar compound: A consisting of  with no permanent.

normality:

nuclear: Of or pertaining to the.

nuclear chemistry: The branch of chemistry that studies the various processes and properties relevant to, including.

nuclear magnetic resonance spectroscopy: A technique that exploits the magnetic properties of certain atomic nuclei, useful for identifying unknown compounds. Nuclear magnetic resonance is often abbreviated NMR.

nuclear transmutation:

nucleon: Either a or a, considered in its role as a component of an.

nucleophile: Any atom or molecule which can donate an to another atom or molecule. All molecules or ions with a free pair of electrons or at least one can act as nucleophiles, by which they are attracted to  regions of other species; a chemical reaction involving a nucleophile donating an electron pair to an  may be referred to as nucleophilic attack. Because they donate electrons, nucleophiles are by definition.

nucleus: The centre of an, made up of and and possessing a net positive electric charge.

nuclide: A species of characterized by its,, and nuclear energy state, provided that the mean life in that state is long enough to be observable.

number density: A measure of the of countable objects (atoms, molecules, etc.) in space, expressed as the number per unit.

O
octet rule:

A classical rule for describing the of atoms in certain molecules: the maximum number of that can be accommodated in the   of an element in the first row of the  is four (or eight total electrons). For elements in the second and subsequent rows, there are many exceptions to this rule.

olefin: A trivial (non-) name for any.

optical activity:

orbital: Any region of an atom or molecule in which one or more can be found. The term may refer to either an or a.

orbital hybridisation:

order of reaction:

organic acid: Any with properties. Contrast.

organic base: Any with properties. Contrast.

organic chemistry: The branch of chemistry concerned with the chemical properties and reactions of. Contrast.

organic compound: Any that contains one or more atoms. Contrast.

organic redox reaction:

organosulfur compound: Any which contains both and sulfur atoms.

osmole:

osmosis: The spontaneous net movement or of molecules of a (e.g. ) through a  separating two  with different  of dissolved, in the direction that tends to equalize the solute concentrations on the two sides, i.e. from the more dilute solution to the more concentrated solution, or, equivalently, from a region of high  to a region of low water potential. Because the solute is unable to cross the membrane, the tendency towards equilibration compels the solvent to cross the membrane instead. This continues until an equilibrium is reached, where neither side of the membrane is more or less concentrated than the other.

osmotic concentration:

osmotic pressure:

other metal: Any of the elements in the, which are characterized by having a combination of relatively low (all less than 950 K) and relatively high  values (all more than 1.6, revised Pauling).

oxidation: The increase in the of a chemical species in a reaction, generally by losing. Contrast.

oxidation state:

The degree of of an individual atom in a chemical compound, measured as the decrease in the number of relative to the atom's naturally occurring  state. The hypothetical (positive, negative, or zero) that an atom would have if all bonds to atoms of different elements were 100%, with no component.

oxidizing agent:

A chemical species that gains or accepts one or more from another species, called the, in a reaction, thereby causing the  of the other species and in turn being itself. The oxidizing agent's decreases, while the reducing agent's increases. A chemical species that transfers strongly, usually oxygen, to a substrate.

oxoacid:

Any having in the acidic group. Any compound which contains oxygen, at least one other element, and at least one atom bound to oxygen, and which produces a by the loss of positive hydrogen.

oxygen:

P
p-block:

paired electron: One of two that together form a between two. Contrast.

paraffin: A trivial (non-) name for any. Another name for kerosene.

partial pressure:

partition coefficient:

pascal (Pa):

passivation: The process of coating a substance with a thin layer of a protective material, often a, to create a shield against or other chemical reactions with the environment, thereby rendering the coated substance "passive" or less susceptible to undesirable reactions.

passivity: A state of chemical inactivity, especially of a that is relatively resistant to due to natural or induced loss of chemical reactivity (as with ).

pentabasic: (of a chemical compound) Having five atoms which may be replaced by or.

pentoxide: Any containing five atoms of oxygen, e.g. iodine pentoxide.

pentyl:

An containing five carbon atoms, with the chemical formula –. It is the form of the  pentane.

per-: A prefix in chemical nomenclature meaning complete, exhaustive, or extreme, as in a completely ; or indicating the presence of a  group.

peracid: An containing an acidic group ; e.g. periodic acid.

period: A horizontal row of the and the elements that share it. Contrast.

periodic table of the elements:

A tabular arrangement of the organized by their,, and other chemical properties, whose adopted structure shows periodic trends and is used by chemists to derive relationships between various elements as well as predict the properties and behaviors of undiscovered or newly synthesized elements. The first periodic table of the elements was published by Russian chemist Dmitri Mendeleev in 1869.

peroxide: A class of compounds which contain a group, having the generic, where R is any element or ; e.g. hydrogen peroxide (empirically , structurally ). Another name for the peroxy group itself. A of the.

peroxy:

A consisting of two atoms directly connected to each other by a  and each also connected to one other atom. Peroxides have the general structural formula.

pH:

phase: A region of space throughout which all physical properties of a substance are essentially uniform, or a region of material that is chemically uniform, physically distinct, and often mechanically separable. The term phase may have several different uses in chemistry contexts; colloquially, it is often used interchangeably with, but many distinct phases may exist within a single state of matter.

phase diagram: A graphical representation of the equilibrium relationships between distinct of a chemical compound, mixture, or solution, indicating the physical conditions (e.g. temperature and pressure) under which various phases (e.g.,, and ) occur or coexist.

phase transition: A transformation of a between,, and  and, in rare cases,. The measurable values of the external conditions at which such a transformation occurs.

phenyl: A consisting of a cyclic ring of six carbon atoms with the chemical formula. It is the form of the  benzene.

phi bond:

photon: A carrier of of all wavelengths (such as gamma rays and radio waves).

physical chemistry: The branch of chemistry that studies chemical systems in terms of the principles, practices, and concepts of physics, such as motion, energy, force, time, thermodynamics,, and statistical mechanics, among others. In contrast to chemical physics, physical chemistry is predominantly (though not entirely) a macroscopic science that studies the physical and chemical interactions of bulk quantities of matter.

pi bond:

pipette:

A laboratory tool commonly used in chemistry, biology, and medicine to transfer and dispense a precisely measured volume of liquid.

plasma: One of the four fundamental, in which very high-energy particles are partially or fully to the point that they display unique properties and behaviors unlike those of the other three states. Plasma does not exist freely on the Earth's surface under natural conditions.

pnictogen: Any of the chemical belonging to of the : nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi), and moscovium (Ms). These elements are united by their common pentavalency; i.e. in their non-ionized states, atoms of these elements all have exactly five in their outermost, three short of a complete.

polarity:

polyatomic: Composed of two or more atoms, of the same or different elements. Contrast ' and '.

polyatomic ion: A composed of two or more  which collectively bear a net  and therefore act as an.

polymerization: The chemical bonding of two or more individual molecules to form a chain or network; or any reaction that produces such a bonding.

potential energy: The stored energy in a body or in a system due to its position in a force field or due to its configuration.

precipitant: A chemical compound or that causes a chemical reaction resulting in the formation of a solid when added to a.

precipitate: (n.) A solid substance that separates from a liquid solution or out of a solid during the process of. (v.) To separate from another substance by forming a distinct, condensed solid.

precipitation: The process of producing a separable within a  medium, e.g. by transforming the dissolved  of a supersaturated  into an insoluble solid; or the  of a distinct solid phase out of a solid. A reagent that causes such a reaction is called the, and the separable solid itself is the. More generally, the term may refer to the formation of any new condensed phase by changing the physical properties of a system (e.g. condensing into liquid water droplets).

precision: How close the results of multiple experimental trials or observations are to each other. Compare.

pressure: The force applied perpendicular to the surface of an object per unit area. The unit for pressure is the (Pa), though many other units of pressure are also commonly used in chemistry.

primary: The simplest, most commonly known, or canonical form of a chemical compound with multiple similar or forms. For example, in a primary alcohol, the carbon is bonded to a single group, whereas a secondary alcohol is doubly substituted  and a tertiary alcohol is triply substituted.

protective group:

proton: A with a positive electric charge that is found in the of an. Often denoted with the symbol H+.

protonation: The addition of a (H+) to an atom, molecule, or ion.

pure substance: See.

pyrolysis: The thermal decomposition of materials at elevated temperatures in an inert atmosphere such as a vacuum gas.

Q
quantum:

quantum mechanics: The study of how atoms, molecules,, etc. behave and are structured.

quark: An elementary particle and a fundamental constituent of matter.

R
racemate: An of a pair of  which does not exhibit. The chemical name or formula of a racemate is distinguished from those of the enantiomers by the prefix (±)- or by the symbols RS and SR.

radiation: Energy released in the form of waves or when there is a change from high-energy to low-energy states.

radical:

Any atom, molecule, or ion that has at least one. With few exceptions, such unpaired electrons make radicals highly chemically reactive, and therefore organic radicals are usually short-lived.

radioactive decay: The process by which an unstable atomic loses excess nuclear energy by emitting in any of several forms, including as, as  or, or by ejecting  from its atomic.

radiochemistry: The branch of chemistry involving the study of radioactive substances and, including the use of radioactive to study non-radioactive isotopes and ordinary chemical reactions.

radionuclide:

A of a specified, especially a particular  of that element which characteristically undergoes spontaneous  into one or more  by emitting excess energy from the nucleus.

Raoult's law: A law of thermodynamics which states that the of each component of an  of  is equal to the  of the pure component multiplied by its  in the mixture.

rare-earth element:

Any of the 17 nearly indistinguishable, silvery-white, soft,  belonging to a set including the  series (atomic numbers 57 through 71) as well as scandium and yttrium.

rate equation:

rate-determining step:

The slowest step in a that involves more than one step. The rate of this step determines the overall.

reactant:

Any substance that is consumed in the course of a.

reaction barrier: The energy deficit that must be overcome in order for a particular to proceed. In, the reaction barrier is interpreted as the difference between the of the  formed in the reaction and that of the initial. See also.

reaction mechanism: The step-by-step sequence of by which a larger or overall change occurs. A complete mechanism must describe and explain which are broken and which are formed (and in what order), as well as all,, and  involved; the amounts of each; all , , and ; and the  of each chemical species. Because the detailed processes of a complex reaction are not observable in most cases, a reaction mechanism is often a theoretical conjecture based on thermodynamic feasibility and what little support can be gained from experiment.

reaction rate: The speed at which are converted into in a.

reaction rate constant:

reactive bond: A between atoms which, in a particular context, is relatively unstable and therefore easily broken or invaded by other or ; e.g. the  in ethylene  is highly reactive in the presence of other ethylene molecules, leading to a  reaction that forms polyethylene.

reactive intermediate:

reactivity: The tendency of a particular to undergo a, either by itself or with other substances, generally referring to either or both of two distinct observations: whether or not a substance reacts under a specific set of circumstances, and how quickly it reacts (i.e. the ). , a chemical reaction occurs because the (taken as a group) exist at a lower  than the, and hence are more energetically "stable", but the concept of reactivity may also embody  factors, depending on the usage. and are related but distinct concepts.

reactivity series:

An empirical, calculated, and structurally analytical progression of a series of, arranged by their general from highest to lowest and used to summarize information about their reactions with and water and the methods used to extract them from ores.

reagent: Another name for a. A test substance that is added to a system in order to bring about a, or to see whether a reaction occurs.

redox:

reducing agent:

A chemical species that loses or donates one or more to another species, called the, in a reaction, thereby causing the  of the other species and in turn being itself. The reducing agent's increases, while the oxidizing agent's decreases.

reduction: The decrease in the of a chemical species in a reaction, generally by gaining. Contrast.

reduction potential:

refractory: Having a high. A material that is resistant to by heat, pressure, or chemical attack, and retains its strength and form at high temperatures, making it suitable for applications in environments exposed to such conditions. Refractories are usually polycrystalline, polyphase,, non-metallic, porous, and heterogeneous compounds.

resonance:

retort: A laboratory apparatus used for the or of chemical substances, traditionally consisting of a spherical vessel with a long, downward-pointing neck that conducts the condensed vapors produced by distillation into a separate collection vessel.

reversible reaction: A that can proceed in either direction depending on the reaction conditions, i.e. from reactants to products or from products to reactants, especially implying one in which both conversions occur simultaneously. Contrast.

rotamer:

round-bottom flask:

rust:

S
s-block: The collective name for the elements in Groups 1 and 2 of the (the and ), as well as hydrogen and helium.

saline solution: A common term for a of sodium chloride (NaCl) dissolved in water (H2O).

salt: Any composed of one or more and one or more.

salt bridge: A device used to connect reduction with oxidation half-cells in an.

saturation:

Schrödinger equation: A quantum state equation which represents the behaviour of an electron around an atom.

second-order reaction:

semiconductor: An electrically conductive solid whose degree of conductivity lies somewhere between that of a and that of an.

serial dilution:

side chain: A chemical that is attached to the core part or "backbone" of a larger, especially an oligomeric or polymeric chain that branches off of the longer primary chain of a macromolecule. The term is most commonly encountered in and.

single bond: A that involves the sharing of one.

skeletal formula:

sol: A of solid particles in a liquid. Artificial examples include sol-gels.

solid: One of the four fundamental, characterized by relatively low-energy particles packed closely together in rigid structures with definite shape and volume. See.

solid-phase extraction (SPE):

solubility: The property of a,, or to  in a solid, liquid, or gaseous. It is typically expressed as the proportion of solute dissolved in the solvent in a fully.

undefined: A measure of the of an ionic, expressed as the arithmetic product of the of its  in a fully saturated solution, with respect to the solute's particular   and the particular ions present. For a dissociation equilibrium $\mathrm{{A_x}{B_y}_{(s)}} \leftrightharpoons \mathrm{xA^+_{(aq)}} + \mathrm{yB^-_{(aq)}}$, the solubility product of the ionic solute $\mathrm{A_x}\mathrm{B_y}$ is given by , where [\ce{A+}] and [\ce{B-}] are the concentrations of the solute's ionic constituents in a saturated solution. The solubility product is derived from and functions like the equilibrium constant of dissociation, though unlike an equilibrium constant it is not dimensionless. If the product of ionic concentrations in a solution exceeds the solubility product, then occurs. |undefined

solute: The part of a that is dissolved into the. For example, sodium chloride (NaCl) is the solute in a solution of saline water.

solution: A homogeneous made up of multiple substances generally referred to as and.

solvated electron:

solvation: Any stabilizing interaction of a with a, or a similar interaction between a solvent and groups of an insoluble material (e.g. the ionic groups of an ion-exchange resin). Such interactions generally involve electrostatic forces and, as well as compound-specific effects such as. See also.

solvation shell:

solvent: The part of a that dissolves the. For example, water (H2O) is the solvent in a solution of saline water.

sonication:

The process of irradiating a substance with sound energy, usually at ultrasound (>20 kHz) frequencies, in order to agitate the particles in a sample for various purposes, such as increasing the of a chemical reaction or preparing vesicles in mixtures of surfactants and water.

spatial isomer: See.

undefined:

The of a sample of a substance divided by the of the sample. Informally, it is the amount of that must be added to one unit of mass of the substance in order to cause an increase of one unit in. The unit of specific heat capacity is  per  per  (J/K/kg). Specific heat capacity often varies with temperature and with each.

spectrochemistry:

spectrometry: See.

spectroscopy: The study of and, such as absorption and emission spectroscopy.

standard solution:

standard conditions of temperature and pressure (STP): A standardisation of ambient and used in order to easily compare experimental results. Standard temperature is 25 degrees Celsius (°C) and standard pressure is 100.000 kilopascals (kPa). Standard conditions are often denoted with the abbreviation STP or SATP.

state of matter: The condition of existing in a distinct, homogeneous, macroscopic form.,, , and are the four traditional states of matter and the most well-known. See also.

stepwise reaction:

stereochemistry:

stereogenic center:

stereoisomer:

An which possesses an identical but which differs in the spatial arrangement of its atoms.

stoichiometry: The calculation of quantities of and in. Stoichiometry is based on the and the observation that quantities of reactants and products typically exist in ratios of positive integers, implying that if the amounts of the separate reactants are known, then the amounts of the products can be calculated, and vice versa.

strong acid: An that completely in solution according to the reaction, or to such an extent that the  of the undissociated species  is too low to be measured. Any acid with a of less than approximately -2 is generally considered a strong acid; an example is hydrochloric acid (HCl). Contrast.

strong base:

structural formula: A graphical representation of the molecular structure and geometry of a particular, showing how the are arranged in real, three-dimensional space. within the molecule is also shown, either implicitly or explicitly. When known with certainty, structural formulas are very useful because they allow chemists to visualize the molecules and the structural changes that occur in them during.

structural isomer:

subatomic particle: Any particle that is smaller than an. Examples include,, and.

sublimation: The of a substance from a to a limewater fuel or  without an apparent intervening transition to a  in the process.

substance: See.

substituent: An or a group of atoms which replaces another atom or group of atoms within a larger as the  of a, thereby becoming a  of the newly formed compound, generally without causing any significant change to other parts of the same molecule. For example, a may be substituted for any of the hydrogen atoms in  to form. See also ' and '.

substitution reaction: A type of in which one within a larger compound replaces or is substituted for another functional group.

superheavy elements: See.

surface science:

surface tension:

surfactant: A substance which lowers the of the medium in which it is dissolved, and/or the interfacial tension with other phases, and, accordingly, is positively at the liquid–vapor and/or other interfaces.

suspension: A heterogeneous that contains particles which are sufficiently large for sedimentation to occur, by which such particles separate from and settle out of the fluid over time if left undisturbed. In a suspension, the does not  but remains  or suspended throughout the fluid  only transiently and with mechanical agitation. Contrast ' and '.

T
tarnish: A thin layer of that forms on the surface of copper, brass, aluminum, magnesium, and other soft or  as their outermost layer undergoes a chemical reaction with the surrounding air, often but not necessarily involving atmospheric oxygen. Tarnish usually appears as a dull grey, black, or sometimes iridescent film or coating on the metal. It is a self-limiting surface phenomenon, as the tarnished top layers of the metal protect underlying layers from reacting.

temperature: A proportional measure of the average of the random motions of the constituent microscopic particles of a system. The unit for temperature is the.

ternary compound: A chemical containing three different.

terpene: A class of naturally occurring with carbon skeletons derived from one or more units of isoprene. Terpenes are often subclassified according to the total number of carbon atoms they contain, e.g. the hemiterpenes,  monoterpenes,  diterpenes, etc.

theoretical yield: See.

thermal conductivity: The property of a material that allows it to conduct thermal energy or (a quantity often denoted by $k$).

thermochemistry: The study of the absorption or release of during a.

thermodynamic stability: The condition of a system being in its lowest energy state with its environment (equilibrium).

thermodynamics: The study of the effects of changing temperature, volume or pressure (or work, heat, and energy) on a macroscopic scale.

thermometer: An instrument used to measure.

thiol: Any of a class of consisting of a sulfur atom attached to a hydrogen atom and any other organic, with the general formula R–SH. Thiols are the sulfur analogues of. Also thiol derivative and mercaptan. The –SH itself. Also sulfhydryl, sulfanyl, and mercapto.

titration:

A laboratory method of quantitative chemical analysis that is used to determine the of an identified. The procedure involves preparing a particular as a  of known concentration and volume (called the titrant or titrator) and allowing it to  with a solution of the analyte (called the titrand) to determine the latter's concentration.

torr: A unit for measuring, equivalent to 133.322 Pa or 1.3158 × 10−3 atm.

trace element: An in a sample which has an average of less than 100 parts per million atoms or less than 100 micrograms per gram.

transactinides:

In the, the set of with an greater than 103, i.e. those heavier than the. The transactinides are a subset of the.

transition metal: An whose atoms naturally occur with incompletely filled "d" sub-shells. These elements are grouped as the so-called in the.

transuranic elements:

The set of with an greater than 92, i.e. occurring after uranium in the. None of the transuranic elements are stable in natural conditions.

triple bond: A that involves the sharing of three  (for example, the diatomic nitrogen molecule, N2, is composed of two nitrogen atoms linked by a triple bond).

triple point: The place where and of three  are the same. Water has a special phase diagram.

Tyndall effect: The effect of light scattering by or particles.

U
UN number: A four-digit code used to note hazardous and flammable substances.

uncertainty: The notion that any measurement that involves estimation of any amount cannot be exactly reproducible.

uncertainty principle: Knowing the location of a particle makes the momentum uncertain, while knowing the momentum of a particle makes the location uncertain.

unit cell: The smallest repeating unit of a crystalline.

unit factor: Statements used in converting between units.

unpaired electron:

V
vacuum flask:

A storage vessel consisting of two or other containers, placed one within the other and joined at the neck, and a space in between that is partially evacuated of air, creating a near-vacuum that significantly reduces the transfer of between the vessel's interior and its ambient environment. Vacuum flasks can greatly lengthen the time over which their contents remain warmer or cooler than the ambient environment.

valence electron: Any of the outermost of an atom, which are located in.

valence bond theory: A theory explaining the chemical bonding within molecules by discussing valencies, the number of chemical bonds formed by an atom.

valency: The combining capacity of an element.

van der Waals force: One of the forces (attraction/repulsion) between molecules.

van 't Hoff factor: The ratio of of particles in to moles of  dissolved.

vapor: When a substance is below the critical temperature while in the phase.

vapor pressure:

The exerted by a which is in thermodynamic equilibrium with its condensed phases ( or ) at a given temperature in a. It is commonly described as the tendency of particles to spontaneously escape from the liquid or solid state into the gaseous state and is used as an indication of a liquid's rate.

vaporization:

The of a substance from a to a.

vaporization point: See.

viscosity: A measure of the resistance of a to flow.

volatility: A material quality which describes how readily a substance. At a given temperature and pressure, a substance with high volatility is more likely to exist as a, while a substance with low volatility is more likely to exist as a or ; equivalently, less volatile substances will more readily from a gaseous state than highly volatile ones.

volt (V): A derived unit of electric potential, electric potential difference, and, defined as one of per.

voltmeter: An instrument that measures electrical cell potential.

volume: The quantity of three-dimensional space enclosed by a closed surface, or the space that a (solid, liquid, gas, or plasma) or shape occupies or contains. The unit for volume is the cubic metre (m3).

volumetric analysis: See.

volumetric flask:

W
watch glass: A circular, concave piece of glass commonly used in chemistry laboratories as a working surface for various purposes, such as evaporating liquids, holding solids while they are being weighed, heating small amounts of a substance, or as a cover for a.

water: A with the chemical formula H2O that is a tasteless, odorless, and generally colorless  at, though it also occurs naturally as a  and a  at the Earth's surface. It is the most abundant substance on Earth and therefore an integral component of virtually all chemical and biological systems. Water is often described as the "universal " for its inherent ability to many substances.

water of crystallization:

molecules that are present inside. Upon from water or, many compounds incorporate water in their crystalline frameworks; the water molecules are typically present in a ratio and may interact to varying degrees with the atoms of the crystal.

wave function: A mathematical function describing the position of an in a three-dimensional space.

weak acid: An that only partially when dissolved in a  because, according to the reaction,  is reached while the  of the undissociated species  is still significant; an example is acetic acid (CH3COOH). Contrast.

weak base:

wet chemistry:

A form of which uses classical laboratory methods such as simple observation and elementary chemical tests to study chemicals and chemical reactions, i.e. without the use of sophisticated instruments or automated or computerized analysis. It is often used in schools to teach the principles of chemistry to students.

wetting agent:

work:

work-up: The series of manipulations required to isolate and purify the desired or products of a.

X
X-ray: A form of ionizing, electromagnetic radiation between gamma and UV rays in the electromagnetic spectrum.

X-ray diffraction: a method for establishing structures of crystalline solids using single wavelength X-rays and looking at diffraction pattern.

X-ray photoelectron spectroscopy: A technique used to measure the of a material.

Y
yield: The quantifiable amount of produced during a.

Z
zero-point energy (ZPE):

zone melting: Any of several methods of crystalline solids which involve applying heat to a small region of a larger solid (particularly a metal ingot) until localized occurs, creating a molten zone which is then slowly moved along the surface to other parts of the solid by moving the target of the heating element. As it moves, the forward edge of the molten zone continuously melts new areas of impure solid, while leaving a path of purer solid behind it as previously melted areas are cooled and resolidified; because the molten phase can hold a higher  of impurities than the  phase, the impurities of melted areas tend to concentrate in the molten zone and be carried along as it moves, leaving behind regions with fewer impurities. The process is commonly used in the refinement of high-purity for use in.

zinc: A metallic with 30 and  Zn.

zwitterion:

Any molecule that contains an internal by virtue of having an equal number of positively charged and negatively charged.