Ab Initio: A calculation or prediction that is based purely on theory rather than on experimental data. Accurat
Abrasive: A very hard, brittle, heat-resistant substance that is used to grind the edges or rough surfaces of
Absolute Error: Absolute uncertainty. Compare with relative error. The uncertainty in a measurement, expressed with
Absolute Temperature: Temperature measured on a scale that sets absolute zero as zero. In the SI system, the kelvin scale
Absolute Zero: (0 K) The temperature at which the volume of an ideal gas becomes zero; a theoretical coldest temper
Absorbance: (A, D, E) optical density; extinction; decadic absorbance. A measure of the amount of light absorbed
Absorption: Compare with adsorption and sorption. 1. Penetration of molecules into the bulk of a solid or liquid
Absorption Spectroscopy: A technique for determining the concentration and structure of a substance by measuring the amound o
Absorption Spectrum: A plot that shows how much radiation a substance absorbs at different wavelengths. Absorption spectr
Absorptivity: (a) extinction coefficient; absorption cross section; decadic absorptivity. Compare with molar absor
Accelerator: 1. A substance that makes vulcanization of rubber occur more quickly or at a lower temperature. 2. A
Accuracy: Compare with precision and trueness. Accuracy is the correctness of a single measurement. The accura
Acetate: (CH3COO-, C2H3O2-) acetate ion. 1. An ion formed by removing the acidic hydrogen of acetic acid, HC2
Acetic Acid: (CH3COOH, HC2H3O2) ethanoic acid; vinegar acid; methanecarboxylic acid. A simple organic acid that g
Acid: ([Lat. Acidus, sour]) Compare with base. 1. A compound which releases hydrogen ions (H+) in solution
Acid Anhydride: Nonmetallic oxides or organic compounds that react with water to form acids. For example, SO2, CO2,
Acid Dissociation Constant: (Ka) acid ionization constant. Compare with base hydrolysis constant. The equilibrium constant for t
Acid Error: A systematic error that occurs when glass pH electrodes are used in strongly acidic solutions. Glass
Acid Halide: Acid chloride; acyl halide; acyl chloride. Compounds containing a carbonyl group bound to a halogen
Acid-Base Indicator: A weak acid that has acid and base forms with sharply different colors. Changes in pH around the aci
Acidic Solution: A solution in which the hydrogen ion activity is higher than that of the hydroxide ion, when the sol
Acidulant: A substance added to food or beverages to lower pH and to impart a tart, acid taste. Phosphoric acid
Actinide: Elements 89-102 are called actinides. Electrons added during the Aufbau construction of actinide ato
Activated Charcoal: Activated carbon; active carbon. A porous form of carbon that acts as a powerful adsorbent, used to
Activated Complex: Transition state. An intermediate structure formed in the conversion of reactants to products. The a
Activation Energy: (Ea) The minimum energy required to convert reactants into products; the difference between the ener
Active Site: A pocket or crevice on an enzyme molecule that fits reactant molecules like a hand in a glove. The a
Activity: (a) An effective concentration used in thermodynamic calculations in place of the actual concentrati
Activity Coefficient: (gamma) The ratio of activity to concentration; a = gamma c where a, gamma, and c are the activity,
Addition Compound: An addition compound contains two or more simpler compounds that can be packed in a definite ratio i
Adhesion: (cohesion) Attraction between different substances on either side of a phase boundary.
Adiabat: A line on an indicator diagram that represents an adiabatic process.
Adiabatic: A process that neither absorbs nor releases energy into the surroundings. For example, a chemical re
Adiabatic Ionization Energy: The lowest energy required to remove an electron from an atom, ion, or molecule in the gas phase. Th
Adsorb: To collect molecules of a substance on a surface.
Adsorbent: A substance that collects molecules of another substance on its surface. For example, gases that mak
Adsorption: Adsorption is collection of a substance on the surface of a solid or a liquid. For example, gases th
Adsorption Chromatography: A technique for separating or analyzing mixtures that contain at least one component that is prefere
Adsorption Indicator: A substance that indicates an excess of a reactant in a precipitation reaction. For example, dichlor
Aeration: aerate Preparation of a saturated solution of air gases by either spraying the solution in air or by
Aerosol: A colloid in which solid particles or liquid droplets are suspended in a gas. Smoke is an example of
Agar: A gel made from seaweed used to make salt bridges.
Alanine: (A, CH3CH(NH2)COOH) Ala; alpha-aminopropionic acid. A naturally occurring aliphatic amino acid which
Alcohol: An alcohol is an organic compound with a carbon bound to a hydroxyl group. Examples are methanol, CH
Aldehyde: (RCHO) An aldehyde is an organic compound with a carbon bound to a -(C=O)-H group. Examples are form
Aliphatic: An organic compound that does not contain ring structures.
Aliquot: A sample of precisely determined amount taken from a material.
Alkali Metal: (alkaline earth metal) alkali metal element The Group 1 elements, lithium (Li), sodium (Na), potassi
Alkaline: Having a pH greater than 7.
Alkaline Earth: An oxide of an alkaline earth metal, which produces an alkaline solution in reaction with water.
Alkaline Earth Metal: (alkali metal) The Group 2 elements, beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), b
Alkaline Error: A systematic error that occurs when glass electrodes are used to read the pH of an extremely alkalin
Alkalinity: A measure of a material's ability to neutralize acids. Alkalinities are usually determined using tit
Alkaloid: A class of bitter-tasting, basic organic compounds with nitrogen-containing rings. Alkaloids often h
Alkane: A series of organic compounds with general formula CnH2n+2. Alkane names end with -ane. Examples are
Alkene: A compound that consists of only carbon and hydrogen, that contains at least one carbon-carbon doubl
Alkoxide: (RO- M+) alkoxide ion. An ionic compound formed by removal of hydrogen ions from the hydroxyl group
Alkyl: (-cnh2n+1) alkyl group. A molecular fragment derived from an alkane by dropping a hydrogen atom from
Alkyl Halide: An alkyl group attached to a halogen atom.
Alkyne: A compound that consists of only carbon and hydrogen, that contains at least one carbon-carbon tripl
Allo: A prefix that designates the more stable of a pair of geometric isomers. allo- is sometimes used les
Allobar: A form of an element that has isotopic abundances that are different from the naturally occuring for
Allomer: Allomerism. Substances with different chemical composition but the same crystalline form.
Allosteric Effect: allosteric interaction A change in the behavior of one part of a molecule caused by a change in anot
Allotrope: Some elements occur in several distinct forms called allotropes. Allotropes have different chemical
Alloy: A mixture containing mostly metals. For example, brass is an alloy of copper and zinc. Steel contain
Allyl: A molecular fragment derived by removing a methyl hydrogen from propene (-CH2-CH2=CH2). For example,
Alpha Particle: (42He) A particle that is commonly ejected from radioactive nuclei, consisting of two protons and tw
Alpha Ray: (alpha-ray) alpha radiation A stream of alpha particles. Alpha rays rapidly dissipate their energy a
Amalgam: An alloy that contains mercury.
American Chemical Society (Acs): A large and influential professional society for professionals and students in chemistry and related
Amide: An amide is an organic compound that contains a carbonyl group bound to nitrogen: . The simplest ami
Amine: An amine is an organic compound that contains a nitrogen atom bound only to carbon and possibly hydr
Amino Acid: Amino acids are molecules that contain at least one amine group (-NH2) and at least one carboxylic a
Ammine: `A metal ion complex containing ammonia as a ligand. The ammonia nitrogen is bound directly to a met
Ammonia: Pure NH3 is a colorless gas with a sharp, characteristic odor. It is easily liquified by pressure, a
Ammonium Ion: (NH4+) ammonium NH4+ is a cation formed by neutralization of ammonia, which acts as a weak base.
Amorphous: A solid that does not have a repeating, regular three-dimensional arrangement of atoms, molecules, o
Amperage: The amount of charge moved per second by an electric current, measured in amperes.
Ampere: (A) amp. The SI unit of electric current, equal to flow of 1 coulomb of charge per second. An ampere
Amperometry: Determining the concentration of a material in a sample by measuring electric current.
Amphi: A prefix used to name certain members of a series of geometric isomers or stereoisomers.
Amphiprotic Solvent: Solvents that exhibit both acidic and basic properties; amphiprotic solvents undergo autoprotolysis.
Amphoteric: A substance that can act as either an acid or a base in a reaction. For example, aluminum hydroxide
Amplitude: The displacement of a wave from zero. The maximum amplitude for a wave is the height of a peak or th
Amylopectin: A form of starch made of glucose molecules linked in a branching pattern.
Amylose: A form of starch made of long, unbranched chains of alpha-D-glucose molecules.
Analysis: Chemical analysis. Determination of the composition of a sample.
Analyte: An analyte is the sample constituent whose concentration is sought in a chemical analysis.
Angstrom: A non-SI unit of length used to express wavelengths of light, bond lengths, and molecular sizes. 1 Ã
Angular Momentum Quantum Number: (ell) azimuthal quantum number; orbital angular momentum quantum number. A quantum number that label
Anhydrous: A compound with all water removed, especially water of hydration. For example, strongly heating copp
Anion: An anion is a negatively charged ion. Nonmetals typically form anions.
Anode: The electrode at which oxidation occurs in a cell. Anions migrate to the anode.
Anodize: To coat a metal with a protective film by electrolysis.
Anthocyanin: A family of pigments that give flowers, fruits, and leaves of some plants their red or blue coloring
Antibonding Orbital: A molecular orbital that can be described as the result of destructive interference of atomic orbita
Antichlor: A chemical compound that reacts with chlorine-based bleaches to stop the bleaching. Thiosulfate comp
Antioxidant: Antioxidants are compounds that slow oxidation processes that degrade foods, fuels, rubber, plastic,
Antiozonant: Substances that reverse or prevent severe oxidation by ozone. Antiozonants are added to rubber to pr
Antipyretic: A substance that can lessen or prevent fever.
Antoine Equation: A simple 3-parameter fit to experimental vapor pressures measured over a restricted temperature rang
Aprotic Solvent: A solvent that does not act as an acid or as a base; aprotic solvents don't undergo autoprotolysis.
Aqua Regia: A mixture of nitric and hydrochloric acids, usually 1:3 or 1:4 parts HNO3 to HCl, used to dissolve g
Aqueous: (aq) A substance dissolved in water.
Arene: A hydrocarbon that contains at least one aromatic ring.
Arginine: (R, C6H14N4O2) Arg An essential amino acid and building block of proteins. Arginine acts as a base u
Aromatic Compound: A compound containing an aromatic ring. Aromatic compounds have strong, characteristic odors.
Aromatic Ring (Ar): An exceptionally stable planar ring of atoms with resonance structures that consist of alternating d
Arrhenius Equation: In 1889, Svante Arrhenius explained the variation of rate constants with temperature for several ele
Aryl (Ar): A molecular fragment or group attached to a molecule by an atom that is on an aromatic ring.
Asparagine: A natural amino acid that is the amide of aspartic acid.
Aspartic Acid: (D,HOOCCH2CH(NH2)COOH) A nonessential amino acid* that is abundant in molasses. The carboxylic acid*
Atmosphere (Atm): A unit of pressure, equal to a barometer reading of 760 mm Hg. 1 atmosphere is 101325 pascals and 1.
Atom: An atom is the smallest particle of an element that retains the chemical properties of the element.
Atomic Mass Unit: A unit of mass equal to 1/12 the mass of a carbon-12 nucleus, which is 1.660 538 73 Ã— 10-27 kg Â± 0
Atomic Nucleus: A tiny, incredibly dense positively charged mass at the heart of the atom. The nucleus is composed o
Atomic Number (Z): The number of protons in an atomic nucleus. The atomic number and the element symbol are two alterna
Atomic Orbital: A wavefunction that describes the behavior of an electron in an atom.
Atomic Radius: Metallic radius; covalent radius; atomic radii. Compare with ionic radius. One half the distance bet
Atomic Theory: An explanation of chemical properties and processes that assumes that tiny particles called atoms ar
Atomic Unit: Compare with Bohr radius and hartree. A system of non-SI units used in quantum chemistry to simplify
Atomic Weight: The average mass of an atom of an element, usually expressed in atomic mass units. The terms mass an
Atto (A): Prefix used in the SI system meaning 'multiply by 10-18'. For example, 3 am means 3Ã— 10-18 meters.
Aufbau Principle: An approximate procedure for writing the ground state electronic configuration of atoms. The configu
Auto-Ignition Temperature: Minimum temperature at which the vapor/air mixture over a liquid spontaneously catches fire.
Autoprotolysis: Transfer of a hydrogen ion between molecules of the same substance, e. g. the autoprotolysis of meth
Autoxidation: Oxidation caused by exposure to air. Rust is an example of autoxidation. Autoxidation makes ether ta
Auxochrome: A group or substructure in a molecule that influences the intensity of absorption of the molecule.
Average Bond Enthalpy: Average enthalpy change per mole when the same type of bond is broken in the gas phase for many simi
Avogadro: Italian chemist and physicist Amadeo Avogadro (1776-1856) proposed a correct molecular explanation f
Avogadro Number (Na, L): The number of particles in one mole, equal to 6.02214199 Ã— 1023 mol-1 (Â± 0.00000047 mol-1) [1998 C
Avogadros Law: Equal volumes of an ideal gas contain equal numbers of molecules, if both volumes are at the same te
Axial: 1. An atom, bond, or lone pair that is perpendicular to equatorial atoms, bonds, and lone pairs in a
Azeotrope: A solution that does not change composition when distilled. For example, if a 95% (w/w) ethanol solu
Azo: The azo group has the general structure Ar-N=N-Ar', where Ar and Ar' indicate substituted aromatic r
Back Titration: Determining the concentration of an analyte by reacting it with a known number of moles of excess re
Balanced Equation: A description of a chemical reaction that gives the chemical formulas of the reactants and the produ
Balmer Series: A series of lines in the emission spectrum of hydrogen that involve transitions to the n=2 state fro
Band: 1. A set of closely spaced energy levels in an atom, molecule, or metal. 2. A set of closely spaced
Band Spectrum: Compare with line spectrum and continuous spectrum. An emission spectrum that contains groups of sha
Bar: Unit of pressure. 1 bar = 105 pascals = 1.01325 atmospheres.
Barometer: An instrument that measures atmospheric pressure. A mercury barometer is a closed tube filled with m
Base: 1. A compound that reacts with an acid to form a salt. 2. A compound that produces hydroxide ions in
Base Hydrolysis Constant: The equilibrium constant for the hydrolysis reaction associated with a base. For example, Kb for amm
Base Unit: Base units are units that are fundamental building blocks in a system of measurement. There are seve
Basis Function: A mathematical function that can be used to build a description of wavefunctions for electrons in at
Basis Set: A set of mathematical functions that are combined to approximate the wavefunctions for electrons in
Battery Acid: A solution of approximately 6M sulfuric acid used in the lead storage battery.
Baumé: (, beÂ°BÃ©, Â°B) A, Be scale related to specific gravities, devised by the French chemist Antoine Ba
Beers Law: (A=abc or A=epsilonbc) Beer-Lambert law. In absorption spectroscopy, the absorbance of a dilute solu
Beryllium: (Be) Element 4, atomic weight 9.0122, an extremely toxic metal used as a neutron source and in phosp
Beta Particle: (ÃŸ-) An electron emitted by an unstable nucleus, when a neutron decays into a proton and an electro
Bidentate: A ligand that has two 'teeth' or atoms that coordinate directly to the central atom in a complex. Fo
Binary Compound: A compound that contains two different elements. Nacl is a binary compound; naclo is not.
Biochemistry: The chemistry of living things, including the structure and function of biological molecules and the
Bleach: A dilute solution of sodium hypochlorite or calcium hypochlorite which kills bacteria and destroys c
Block: A region of the periodic table that corresponds to the type of subshell (s, p, d, or f) being filled
Bohr Atom: A model of the atom that explains emission and absorption of radiation as transitions between statio
Bohr Radius: The atomic unit of length, equal to 0.529 177 2083 Ã— 10-10 m, with an uncertainty of 0.000 000 0019
Boiling: Conversion of liquid into gas as bubbles of gas that form within the liquid. Boiling begins at the t
Boiling Point: The temperature at which the vapor pressure of a liquid would be equal to the external pressure on t
Boiling Point Elevation: The boiling point of a solution is higher than the boiling point of the pure solvent. Boiling point
Boltzmann Constant: A fundamental constant equal to the ideal gas law constant divided by Avogadro's number, equal to 1.
Boltzmann Equation: A statistical definition of entropy, given by S = k ln W, where S and k are the entropy and Boltzman
Bond Energy: Energy change per mole when a bond is broken in the gas phase for a particular substance.
Bond Enthalpy: Enthalpy change per mole when a bond is broken in the gas phase for a particular substance.
Bond Length: The average distance between the nuclei of two bonded atoms in a stable molecule.
Bond Order: 1. In Lewis structures, the number of electron pairs shared by two atoms. 2. In molecular orbital th
Bond Strength: Some measure of how difficult it is to break a chemical bond, for example, a bond energy or a bond e
Boron: (B) Element 5, atomic weight 10.811. Hard yellow crystals or brown amorphous powder, used as a neutr
Boyles Law: The pressure of a ideal gas is inversely proportional to its volume, if the temperature and amount o
Brass: A shiny yellow to yellow-orange alloy that contains about two parts copper for every one part zinc.
Bronze: A yellow to yellow-brown alloy that contains mostly copper and tin, with small amounts of other meta
Brösted Acid: A material that gives up hydrogen ions in a chemical reaction.
Brösted Base: A material that accepts hydrogen ions in a chemical reaction.
Brownian Motion: Small particles suspended in liquid move spontaneously in a random fashion. The motion is caused by
Buckminsterfullerene: A form of carbon consisting of 60 carbon atoms bound together to make a roughly spherical 'buckyball
Buffer: A solution that can maintain its ph value with little change when acids or bases are added to it. Bu
Bunsen Burner: A gas burner with adjustable air intake, commonly used in laboratories.
Buret: A cylindrical glass tube closed by a stopcock on one end and open on the other, with volume gradatio
Butanol: An alcohol containing four carbon atoms. Example: 1-butanol.
Caffeine: A substance found in tea, coffee, and cola that acts as a stimulant. It is extremely soluble in supe
Calibration: Calibration is correcting a measuring instrument by measuring values whose true values are known. Ca
Calorie: The amount of heat required to raise the temperature of 1 g of water at 14.5Â°C to 15.5Â°C. One calo
Calorimeter: An insulated vessel for measuring the amount of heat absorbed or released by a chemical or physical
Calorimetry: Experimental determination of heat absorbed or released by a chemical or physical change.
Calutron: A device that separates isotopes (e. G. 235U from 238U) by ionizing the sample, accellerating the io
Capacitor: A device for storing electric charge, consisting of two metal plates separated by an insulating mate
Carbohydrate: A class of organic compounds including sugars and starches. The name comes from the fact that many (
Carbon: An element with atomic number 6. Carbon is a nonmetal found in all organic compounds. Carbon occurs
Carbon Dioxide: (CO_2) A colorless, odorless gas produced by respiration and combustion of carbon-containing fuels.
Carbon Monoxide: (CO) A colorless, odorless, poisonous gas produced by incomplete combustion.
Carbonate: (CO32-) 1. An inorganic ion with a charge of -2, containing carbon bound directly to three oxygens i
Carbonate Hardness: Water hardness due to the presence of calcium and magnesium carbonates and bicarbonates. The 'noncar
Carbonyl: A divalent group consisting of a carbon atom with a double-bond to oxygen. For example, acetone (CH3
Carboxylic Acid: A carboxylic acid is an organic molecule with a -(C=O)-OH group. The group is also written as -COOH
Carboy: A very large bottle. Glass carboys are usually encased in a wire mesh or wooden box for protection.
Carotene: Carotene is an unsaturated hydrocarbon pigment found in many plants. Carotene is the basic building
Catalyst: A substance that increases the rate of a chemical reaction, without being consumed or produced by th
Cathode: The electrode at which reduction occurs.
Cathode Ray: A negatively charged beam that emanates from the cathode of a discharge tube. Cathode rays are strea
Cation: A cation is a positively charged ion. Metals typically form cations.
Cellulose: A polysaccharide made of linked glucose molecules that strengthens the cell walls of most plants.
Celsius: A common but non-SI unit of temperature, defined by assigning temperatures of 0Â°C and 100Â°C to the
Centi: Prefix used in the SI system meaning 'one hundredth of'. For example 1 cm means 'one hundredth of a
Cgs: An older metric system of units that uses centimeters, grams, and seconds as base units.
Charles Law: The volume of a gas is directly proportional to its temperature in kelvins, if pressure and amount o
Chelate: A stable complex of a metal with one or more polydentate ligands. For example, calcium complexes wit
Chelating Agent: A ligand that binds to a metal using more than one atom; a polydentate ligand.
Chemical: 1. Of or pertaining to chemistry. 2. A substance.
Chemical Bond: A chemical bond is a strong attraction between two or more atoms. Bonds hold atoms in molecules and
Chemical Change: A chemical change is a dissociation, recombination, or rearrangement of atoms.
Chemical Equation: A compact notation for describing a chemical change. The formulas of the reactants are added togethe
Chemical Potential: The chemical potential is a partial molar Gibbs free energy, defined as Âµi = (partialg/partialni)T,
Chemical Property: Measurement of a chemical property involves a chemical change. For example, determining the flammabi
Chemiluminescence: A chemical reaction that releases energy as electromagnetic radiation.
Chemistry: The study of matter and its transformations. See What is chemistry? For other definitions.
Chiral: Having nonsuperimposable mirror images. For example, a shoe or a glove is chiral.
Chiral Center: An atom in a molecule that causes chirality, usually an atom that is bound to four different groups.
Chromatography: Chromatography is a method for separating mixtures based on differences in the speed at which they m
Chromophore: A group or substructure on a molecule that is responsible for the absorption of light.
Colligative Property: Properties of a solution that depend on the number of solute molecules present, but not on the natur
Collision Frequency: The average number of collisions that a molecule undergoes each second.
Collision Theory: A theory that explains reaction rates in terms of collisions between reactant molecules.
Colloid: A colloid is a heterogeneous mixture composed of tiny particles suspended in another material. The p
Colorimetry: A method for chemical analysis that relates color intensity to the concentration of analyte.
Column Chromatography: Column chromatography is a method for separating mixtures. A solution containing the mixture is pass
Combination Reaction: A reaction in which two or more substances are chemically bonded together to produce a product. For
Combustion: A chemical reaction between a fuel and an oxidizing agent that produces heat (and usually, light). F
Complete Combustion: A combustion reaction that converts all of the fuel's carbon, hydrogen, sulfur, and nitrogen into ca
Complete Ionic Equation: A balanced equation that describes a reaction occurring in solution, in which all strong electrolyte
Complex Ion: An ion formed by combination of simpler ions or molecules; for example, Co2+ combines with six molec
Complexing Agent: A ligand that binds to a metal ion to form a complex.
Complexometric Titration: A titration based on a reaction between a ligand and a metal ion to form a complex. For example, fre
Component: 1. A substance whose concentration must be specified to describe the state of a mixture in which rea
Compound: A compound is a material formed from elements chemically combined in definite proportions by mass. F
Computational Chemistry: A branch of chemistry concerned with the prediction or simulation of chemical properties, structures
Computer-Assisted Drug Design: Using computational chemistry to discover, enhance, or study drugs and related biologically active m
Concentrate: To increase the amount of substance present in a unit amount of mixture. For example, allowing solve
Concentrated: Having a relatively large amount of substance present in a unit amount of mixture. For example, a 12
Concentration: 1. A measure of the amount of substance present in a unit amount of mixture. The amounts can be expr
Condensation: 1. The conversion of a gas into a liquid is called condensation. Condensation usually occurs when a
Conformers: Molecular arrangements that differ only by rotations around single bonds. For example, the 'boat' an
Congener: 1. Elements belonging to the same group on the periodic table. For example, sodium and potassium are
Constructive Interference: When the peaks and troughs of two interfering waves match, the amplitudes add to give the resultant
Continuous Spectrum: A plot of the relative absorbance or intensity of emitted light vs. Wavelength or frequency that sho
Conversion Factor: A conversion factor is a fraction that relates one unit to another. Multiplying a measurement by a c
Coordination Number: The number of bonds formed by the central atom in a metal-ligand complex.
Copolymer: A polymer composed of two or more different monomers. The different monomers can be linked randomly,
Core Electron: Electrons occupying completely filled shells under the valence shell.
Corrosion: Corrosion is a reaction that involves action of an oxidizing agent on a metal. The oxidizing agent i
Coulomb (C): The SI unit of electric charge, equal to the amount of charge delivered by a current of 1 ampere run
Coulombic Interactions: Attractions between opposite charges or repulsions between like charges that grow stronger as the ch
Covalent Bond: A covalent bond is a very strong attraction between two or more atoms that are sharing their electro
Covalent Compound: A compound made of molecules- not ions. The atoms in the compound are bound together by shared elect
Critical Molar Volume (Vc): The molar volume at the critical point.
Critical Point: State at which two phases of a substance first become indistinguishable. For example, at pressures h
Critical Temperature (Tc): The temperature at the critical point. A gas above the critical temperature will never condense into
Cryogen: A gas that has been liquified by lowering temperature, usually to a temperature under about -100Â°C.
Crystal: A sample of a crystalline solid that has a regular shape bound by plane surfaces (facets) that inter
Crystal Field Splitting Energy: (Delta) Ligands complexed to a metal ion will raise the energy of some of its d orbitals and lower t
Crystal Field Theory: The color, spectra, and magnetic properties of metal-ligand complexes can be explained by modeling t
Crystalline Solid: A solid that has a repeating, regular three-dimensional arrangement of atoms, molecules, or ions.
Crystallite: A perfect crystalline part of a larger imperfect crystal. Real crystals are usually built of a large
Crystallization: Production of a purer sample of a substance by slow precipitation of crystals from a solution of the
Crystallization: The process of forming pure crystals by freezing a liquid, evaporating a solution, or precipitating
Cupric: 1. The copper(II) ion, Cu2+. 2. A compound that contains copper in the +2 oxidation state.
Cuprous: 1. The copper(I) ion, Cu+. 2. A compound that contains copper in the +1 oxidation state.
Curie Point: Temperature above which a ferromagnetic material loses its ferromagnetism.
Cyanide: (CN-) 1. An ion with a -1 charge containing one atom of carbon bound to one atom of nitrogen. 2. A c
Cyanide Process: A method for separating a metal from an ore. Crushed ore is treated with cyanide ion to produce a so
Cysteine: A naturally occuring amino acid with an SH group on its side chain.
Cystine: A naturally occuring amino acid with a disulfide bridge group on its side chain, formed by condensat
D: Prefix used to designate a dextrorotatory enantiomer.
Daltons Law: Dalton's law of partial pressure. The total pressure exerted by a mixture of gases is the sum of the
Debye: A common non-SI unit of dipole moment, named for Dutch physical chemist Peter Debye. A charge separa
Decomposition: A reaction in which a compound is broken down into simpler compounds or elements. Compounds sometime
Degenerate: A set of orbitals are said to be degenerate if they all have the same energy. This degeneracy can so
Deliquescent: Deliquescent compounds absorb so much moisture from the air that they dissolve. Examples are calcium
Denature: 1. A loss of chemical function, usually due to some heat or chemically-induced structural change. Fo
Density: Mass of a substance per unit volume. Saying 'the density of mercury is 13.55 g/cm3 ' is the same as
Density Functional: A model that describes the electronic structure of an atom or molecule by approximating the total en
Deoxyribonucleic Acid (Dna): A nucleic acid with 2-deoxy-D-ribose as the sugar in its nucleotides. DNA contains encoded genetic i
Dependent Variable: A dependent variable changes in response to changes in independent variables. For example, in an exp
Derived Unit: Derived units are units constructed from the SI system's base units. For example, the SI unit for de
Desalination: Removal of dissolved salts from seawater.
Destructive Interference: When the peaks of one wave match the troughs of another, the waves interfere destructively. The ampl
Deuterium: (D, 2H) An isotope of hydrogen that contains one neutron and one proton in its nucleus.
Dextrorotatory: Having the property of rotating plane-polarized light clockwise.
Dialysis: Dialysis is the separation of components in a mixture by passing them across a semipermeable membran
Diamagnetism: Diamagnetic materials are very weakly repelled by magnetic fields. The atoms or molecules of diamagn
Diamond: A crystalline form of carbon, made of a network of covalent, tetrahedrally bound carbon atoms.
Diastereomer: Stereoisomers which are not mirror images of each other. Diastereomers are chemically similar but di
Diatomic Molecule: A molecule that contains only two atoms. All of the noninert gases occur as diatomic molecules; e. G
Diazonium Salt: A diazonium salt is a compound with general form Ar-nidentn+X-, where Ar represents a substituted be
Diazotization: Diazotization is a reaction that converts an -NH2 group connected to a phenyl ring to a diazonium sa
Dichloromethane: (CH2Cl2) Dichloromethane (CH2Cl2) is an organic solvent often use to extract organic substances from
Differential Thermal Analysis (Dta): A technique that is often used to analyze materials that react or decompose at higher temperatures.
Diffraction: The ability of a wave to bend around the edges of obstacles or holes. The effect is most noticeable
Diffusion: The mixing of two substances caused by random molecular motions. Gases diffuse very quickly; liquids
Diffusion Rate: The number of randomly moving molecules that pass through a unit area per second. Diffusion rates ar
Dilatometer: A device for measuring volume changes.
Dilute: Having a relatively low concentration.
Dilution: Adding solvent to a solution to lower its concentration.
Dipole-Dipole Interaction: Electrostatic attraction between oppositely charged poles of two or more dipoles.
Displacement: A reaction in which a fragment of one reactant is replaced by another reactant (or by a fragent of a
Disproportionation: A reaction involving a substance that produces two different forms of the substance, one more oxidiz
Dissolved Oxygen (Do): The amount of oxygen dissolved in a solvent (usually water). Dissolved oxygen levels are used as a g
Distillate: The vapor collected and condensed from a distillation.
Distillation: Distillation is a technique for separating components of a mixture on the basis of differing boiling
Divalent: Binds to two other things (which may be other atoms, molecules, ions, or electrons). See also divale
Divalent Anion: An ion with a charge of -2.
Divalent Cation: An ion with a charge of +2.
Domoic Acid: Domoic acid is a toxic amino acid produced by certain species of algae. Domoic acid binds to a recep
Double Displacement: A double displacement or metathesis is a reaction in which two reactants trade fragments: AB + CD =
Drug: A biologically active compound or mixture used to cure, prevent, or detect disease, to control biolo
Dry Cell: A electrolytic cell that uses a moist paste rather than a liquid as an electrolyte. Flashlight batte
Ductile: Capable of being drawn into wire. Metals are typically ductile materials.
Dynamic Equilibrium: Dynamic equilibrium is established when two opposing processes are occuring at precisely the same ra
Dyne: The unit of force in the obsolete cgs system of units. A dyne is the force required to accelerate a
Ebulliometry: Determination of average molecular weight of a dissolved substance from the boiling point elevation
Edta: A polydentate ligand that tightly complexes certain metal ions. EDTA is used as a blood preservative
Effective Nuclear Charge: The nuclear charge experienced by an electron when other electrons are shielding the nucleus.
Efflorescent: Efflorescent substances lose water of crystallization to the air. The loss of water changes the crys
Effusion: Gas molecules in a container escape from tiny pinholes into a vacuum with the same average velocity
Electric Charge: A property used to explain attractions and repulsions between certain objects. Two types of charge a
Electric Current: A flow of electric charges. The SI unit of electric current is the ampere.
Electric Dipole: An object whose centers of positive and negative charge do not coincide. For example, a hydrogen chl
Electric Dipole Moment: A measure of the degree of polarity of a polar molecule. Dipole moment is a vector with magnitude eq
Electric Field: A field of forces that act on any electric charge placed within it. The stronger the field, the stro
Electrical Conductivity: A measure of how easily an electric current can pass through a material. The conductivity is the rec
Electrical Resistance: The ability of a material to oppose the flow of an electric current, converting electrical energy in
Electrochemical Cell: A device that uses a redox reaction to produce electricity, or a device that uses electricity to dri
Electrode: An electrically conducting surface that allows electrons to be transferred between reactants in an e
Electrolysis: The process of driving a redox reaction in the reverse direction by passage of an electric current t
Electrolyte: A substance that dissociates fully or partially into ions when dissolved in a solvent, producing a s
Electrolytic Cell: A device that uses electricity from an external source to drive a redox reaction.
Electromagnetic Radiation: A wave that involves perpendicular oscillations in the electric and magnetic fields, moving at a spe
Electron: A fundamental consituent of matter, having a negative charge of 1.602 176 462 Ã— 10-19 coulombs Â± 0
Electron Affinity: The enthalpy change for the addition of one electron to an atom or ion in the gaseous state. For exa
Electron Configuration: A list showing how many electrons are in each orbital or subshell. There are several notations. The
Electron Volt: Energy required to move an electron through a potential difference of 1 volt. An electron volt is eq
Electronegativity: Electronegativity is a measure of the attraction an atom has for bonding electrons. Bonds between at
Electrorefining: Electrorefining is a method for purifying a metal using electrolysis. An electric current is passed
Element: An element is a substance composed of atoms with identical atomic number. The older definition of el
Element Symbol: An international abbreviation for element names, usually consisting of the first one or two distinct
Elementary Reaction: A reaction that occurs in a single step. Equations for elementary reactions show the actual molecule
Emission Spectrum: A plot of relative intensity of emitted radiation as a function of wavelength or frequency.
Emollient: A substance added to a formulation that gives it softening ability. For example, oils that can softe
Empirical Formula: Empirical formulas show which elements are present in a compound, with their mole ratios indicated a
Empirical Temperature: A property that is the same for any two systems that are in thermodynamic equilibrium with each othe
Emulsion: A colloid formed from tiny liquid droplets suspended in another, immiscible liquid. Milk is an examp
Enantiomer: Two molecules that are nonsuperimposable mirror images of each other. One enantiomer rotates plane-p
Endothermic: A process that absorbs heat. The enthalpy change for an endothermic process has a positive sign.
Endpoint: The experimental estimate of the equivalence point in a titration.
Energy: Energy is an abstract property associated with the capacity to do work.
Enkephalin: Enkephalins are molecules produced naturally by the central nervous system to numb pain. Enkephalins
Enthalpy: Enthalpy (H) is defined so that changes in enthalpy (deltah) are equal to the heat absorbed or relea
Enthalpy Of Atomization: The change in enthalpy that occurs when one mole of a compound is converted into gaseous atoms. All
Enthalpy Of Combustion: The change in enthalpy when one mole of compound is completely combusted. All carbon in the compound
Enthalpy Of Fusion: The change in enthalpy when one mole of solid melts to form one mole of liquid. Enthalpies of fusion
Enthalpy Of Neutralization: The heat released by an acid-base neutralization reaction running at constant pressure.
Enthalpy Of Reaction: The heat absorbed or released by a chemical reaction running at constant pressure.
Enthalpy Of Solution: The heat absorbed or released when a solute is dissolved in a solvent. The heat of solution depends
Enthalpy Of Sublimation: The change in enthalpy when one mole of solid vaporizes to form one mole of gas. Enthalpies of subli
Enthalpy Of Vaporization: The change in enthalpy when one mole of liquid evaporates to form one mole of gas. Enthalpies of vap
Entropy: Entropy is a measure of energy dispersal. Any spontaneous change disperses energy and increases entr
Environmental Chemistry: The study of natural and man-made substances in the environment, including the detection, monitoring
Enzyme: Protein or protein-based molecules that speed up chemical reactions occurring in living things. Enzy
Equilibrium Constant: The product of the concentrations of the products, divided by the product of the concentrations of t
Equivalence Point: The equivalence point is the point in a titration when enough titrant has been added to react comple
Equivalent: 1. The amount of substance that gains or loses one mole of electrons in a redox reaction. 2. The amo
Ester: An ester is a compound formed from an acid and an alcohol. In esters of carboxylic acids, the -COOH
Ethanol: A colorless, flammable liquid produced by fermentation of sugars. Ethanol is the alcohol found in al
Ethyl: A molecular fragment produced by removing a hydrogen atom from ethane (CH3-CH3). For example, ethyl
Ethyl Acetate: A flammable liquid with a fruity odor, used in flavorings and as a solvent.
Eutectic Mixture: A mixture of two or more substances with melting point lower than that for any other mixture of the
Eutectic Point: The composition and the melting point of a eutectic mixture. For example, the eutectic point of a mi
Evaporate: To convert a liquid into a gas.
Evaporation: Conversion of a liquid into a gas.
Excited State: An atom or molecule which has absorbed energy is said to be in an excited state. Excited states tend
Excitotoxin: An excitotoxin is a toxic molecule that stimulates nerve cells so much that they are damaged or kill
Exothermic: A process that releases heat. The enthalpy change for an exothermic process is negative. Examples of
Experiment: An experiment is direct observation under controlled conditions. Most experiments involve carefully
Experimental Yield: The measured amount of product produced in a chemical reaction.
Extensive Property: A property that changes when the amount of matter in a sample changes. Examples are mass, volume, le
Extraction: A technique for separating components in a mixture that have different solubilities. For example, ca
F Orbital: An orbital with angular momentum quantum number ell = 2. The f orbitals generally have 3 nuclear nod
Fahrenheit: A temperature scale proposed by Daniel Gabriel Fahrenheit (1686-1736) which uses the melting point o
Fatty Acid: Fatty acids are carboxylic acids with long hydrocarbon side chains. Most natural fatty acids have hy
Femto: Prefix used in the SI system meaning 'multiply by 10-15'. For example 22 fg means 22Ã— 10-15 g.
Fermentation: A class of biochemical reactions that break down complex organic molecules (such as carbohydrates) i
Ferric: Deprecated. 1. The iron(III) ion, Fe3+. 2. A compound that contains iron in the +3 oxidation state.
Ferroin: A blood-red complex of Fe2+ ion with 1,10-phenanthroline, used as a redox indicator. Ferroin changes
Ferromagnetism: Ferromagnetic materials exhibit magnetism even in the absence of an external magnetic field. Ferroma
Ferrous: Deprecated. 1. The iron(II) ion, Fe2+. 2. A compound that contains iron in the +2 oxidation state.
First Ionization Energy: The energy needed to remove an electron from an isolated, neutral atom.
First Law: The first law states that energy cannot be created or destroyed. Many equivalent statements are poss
First Order Reaction: The sum of concentration exponents in the rate law for a first order reaction is one. Many radioacti
Fission: A nuclear reaction in which an atomic nucleus breaks into smaller nuclei of comparable mass, releasi
Flash Point: The temperature when vapor pressure of a substance becomes high enough to allow the air/vapor layer
Fluorescence: A fluorescent substance absorbs short wavelength radiation and re-emits it as radiation with a longe
Foam: A colloid in which bubbles of gas are suspended in a solid or liquid. Aerogel (solid smoke) and Styr
Formation: A reaction that forms one mole of a compound from its elements in their most stable forms. For examp
Formula Unit: One formula weight of a compound.
Formula Weight: The formula weight is the sum of the atomic weights of the atoms in an empirical formula. Formula we
Fractional Distillation: A technique for separation of liquid mixtures by distillation that uses a tower attached to a flask
Free Energy: Energy that is actually available to do useful work. A decrease in free energy accompanies any spont
Free Radical: A free radical is a molecule with an odd number of electrons. Free radicals do not have a completed
Freezing Point: The temperature at which the vapor pressure of a liquid is equal to the vapor pressure of the corres
Freezing Point Depression: The freezing point of a solution is always lower than the freezing point of the pure solvent. The fr
Frequency: The number of cycles of a wave that move past a fixed observation point per second. The SI unit of f
Fuel Cell: A device that converts the chemical energy obtained from a redox reaction directly into electrical e
Functional Group: A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carboxyl
Gamma Rays: A very high energy form of electromagnetic radiation, typically with wavelengths of less than 3 pm.
Gas: Matter in a form that has low density, is easily compressible and expandable, and expands spontaneou
Gel: A gell is a sol in which the solid particles fuse or entangle to produce a rigid or semirigid mixtur
Geochemistry: The study of materials and chemical reactions in rocks, minerals, magma, seawater, and soil.
Geometric Isomer: Geometric isomers are molecules that have the same molecular formula and bond connections, but disti
Gibbs Free Energy: A thermodynamic property devised by Josiah Willard Gibbs in 1876 to predict whether a process will o
Gibbs Free Energy Of Formation: The change in Gibbs free energy that accompanies the formation of one mole of a compound from its el
Glutamate: Ionic salts of glutamic acid used as flavor enhancers in many foods. Glutamate is usually manufactur
Glutamate Receptors: Glutamate receptors are protein molecules that helps gate the flow of ions across a nerve cell's mem
Glutamine: The amide of the amino acid glutamic acid. Glutamic acid often occurs as glutamine when built into p
Glyceride: Glycerides are fats and oils that are esters of glycerol with one or more fatty acids. Monoglyceride
Glycerol: Glycerol is a small molecule with three alcohol groups. It is a basic building block of fats and oil
Glycine: A naturally occurring aliphatic amino acid, found in large quantities in gelatin.
Gram: A metric unit of mass, equal to 1/1000 of a kilogram. Kilograms are the base SI units for mass, not
Graphite: An amorphous form of carbon, made of carbon atoms bound hexagonally in sheets (like chickenwire).
Gross Error: Gross errors are undetected mistakes that cause a measurement to be very much farther from the mean
Ground State: The lowest energy state for an atom or molecule. When an atom is in its ground state, its electrons
Group: 1. A substructure that imparts characteristic chemical behaviors to a molecule, for example, a carbo
Half Life: The half life of a reaction is the time required for the amount of reactant to drop to one half its
Halide: A compound or ion containing fluorine, chlorine, bromine, iodine, or astatine.
Halogen: An element of group VIIA (a. K. A. Group 18). The name means 'salt former'; halogens react with meta
Hartree: The atomic unit of energy, equal to 4.359 743 81 Ã— 10-18 J Â± 0.000 000 34 Ã— 10-18 J [1998 CODATA
Heat: Heat is a transfer of energy that occurs when objects with different temperatures are placed into co
Heat Capacity: The heat required to raise the temperature of an object by 1Â°C is called the heat capacity of the o
Heavy Water: Water that contains 2H, rather than 1H. Heavy water is about 11% denser than ordinary water.
Helium: Element 2, atomic weight 4.0026. A colorless, odorless, inert gas, first discovered in the emission
Helmholtz Free Energy: A thermodynamic property that can be used to predict whether a process will occur spontaneously at c
Henrys Law: Henry's law predicts that the solubility (C) of a gas or volatile substance in a liquid is proportio
Hertz: The SI unit of frequency, equal to one cycle of the wave per second (s-1).
Hesss Law: The heat released or absorbed by a process is the same no matter how many steps the process takes. F
Heterocyclic: An organic group or molecule containing rings with at least one noncarbon atom on the ring.
Heterogeneous Mixture: A sample of matter consisting of more than one pure substance and more than one phase. Blood, protop
Heterogenous Mixture: A common misspelling of heterogeneous.
High Performance Liquid Chromatography: An efficient form of column chromatography that pumps a liquid solution of the sample at very high p
High Spin Complex: A metal-ligand complex with the same number of unpaired electrons as the uncomplexed metal ion. When
Homogeneous: Having uniform properties or composition.
Homogeneous Mixture: A sample of matter consisting of more than one pure substance with properties that do not vary withi
Homogenous: A common misspelling of homogeneous.
Homolog: A compound belonging to a series of compounds that differ by a repeating group. For example, propano
Hormone: A molecule produced by endocrine glands that controls specific biological processes like growth and
Humectant: A substance that absorbs or retains moisture, added to a product to keep it from drying out.
Hunds Rule: A rule of thumb stating that subshells fill so that the number of unpaired spins is maximized, or 's
Hybridization: The combination of a set of atomic orbitals to produce a new set of 'hybrid' orbitals. Hybridized or
Hydrate: A hydrate is an addition compound that contains water in weak chemical combination with another comp
Hydration: Combination with water.
Hydrazine: A colorless, fuming, corrosive liquid that is a powerful reducing agent. NH2NH2 is used in jet and r
Hydride Ion: A -1 ion formed from hydrogen. Hydride ions and hydride ionic compounds react instantly and sometime
Hydrocarbon: Hydrocarbons are organic compounds that contain only hydrogen and carbon. The simplest hydrocarbons
Hydrogen: Element 1, atomic weight 1.00797. The most abundant element in the universe. Hydrogen occurs as H2 a
Hydrogen Bond: An especially strong dipole-dipole force between molecules X-H...Y, where X and Y are small electron
Hydrolysis: A catch-all term for any reaction in which the water molecule is split.
Hydrometer: An instrument for measuring the specific gravity of liquids. A hydrometer is a weight with a vertica
Hydronium Ion: The H3O+ ion, formed by capture of a hydrogen ion by a water molecule. A strong covalent bond is for
Hydrophilic: A polar molecule or group that can form strong hydrogen bonds with water.
Hydrophobic: A nonpolar molecule or group that has little affinity for water. Hydrophobic groups on molecules in
Hydroxide: 1. The OH- ion. 2. Compounds containing the OH- ion. See also: hydroxide compounds.
Hydroxyl: 1. An -OH group within a molecule. 2. A free radical formed by abstraction of a hydrogen atom from w
Hygroscopic: Able to absorb moisture from air. For example, sodium hydroxide pellets are so hygroscopic that they
Hygroscopically: By absorbing moisture from air.
Hygroscopicity: The ability of a substance to absorb moisture from air. For example, sodium hydroxide pellets are so
Hypergolic Mixture: An oxidizing agent and a fuel that react or ignite instantly and spontaneously on contact. Methylhyd
Hypertonic: Describes a solution which has higher osmotic pressure than some other solution (usually, higher osm
Hypothesis: A hypothesis is a conjecture designed to guide experimentation. Hypotheses are extremely useful in p
Hypotonic: Describes a solution which has lower osmotic pressure than some other solution (usually, lower osmot
Ideal Gas: A gas whose pressure P, volume V, and temperature T are related by PV = nrt, where n is the number o
Ideal Gas Law Constant: A constant R equal to PV/(nt) for ideal gases, where the pressure, volume, moles, and temperature of
Ideal Solution: All molecules in an 'ideal solution' interact in exactly the same way; the solvent-solvent, solvent-
Immiscible: Two liquids are considered 'immiscible' or unmixable if shaking equal volumes of the liquids togethe
Incomplete Combustion: A combustion reaction or process that does not convert all of the fuel's carbon and hydrogen into ca
Incomplete Octet: 1. An atom with less than eight electrons in its valence shell. 2. An atom with less than eight tota
Independent Variable: An independent variable that can be set to a known value in an experiment. Several independent varia
Indicator: A substance that undergoes an sharp, easily observable change when conditions in its solutions chang
Indicator Diagram: A plot of pressure vs. Volume. Lines or curves on the indicator diagram represent processes. The are
Inductive Effect: An inductive effect is the polarization of a chemical bond caused by the polarization of an adjacent
Inert Gas: Any of the elements of Group 18, which includes helium, neon, argon, krypton, xenon, radon, and elem
Inert Pair: Valence electrons in an s orbital penetrate to the nucleus better than electrons in p orbitals, and
Inertia: The tendency of a body to stay at rest or to continue to move at the same velocity, unless acted on
Infrared Radiation: Electromagnetic radiation with wavelength longer than visible light but shorter than that of microwa
Infrared Spectroscopy: A technique for determining the structure (and sometimes concentration) of molecules by observing ho
Inorganic Chemistry: The study of inorganic compounds, specifically their structure, reactions, catalysis, and mechanism
Inorganic Compound: A compound that does not contain carbon chemically bound to hydrogen. Carbonates, bicarbonates, carb
Insoluble: Refers to a substance that does not dissolve in a solvent to any significant degree. Compounds with
Integral Enthalpy Of Solution: The heat absorbed or released when a solute is dissolved in a definite amount of solvent. The heat o
Integrated Rate Law: Rate laws like d[A]/dt = -k[A] give instantaneous concentration changes. To find the change in conce
Intensive Property: A property that does not change when the amount of sample changes. Examples are density, pressure, t
Interference: The amplitudes of waves moving into the same region of space add to produce a single resultant wave.
Intermediate: A highly reactive substance that forms and then reacts further during the conversion of reactants to
Intermolecular Force: An attraction or repulsion between molecules. Intermolecular forces are much weaker than chemical bo
Internal Energy: Internal energy (U) is defined so that changes in internal energy (deltau) are equal to the heat abs
Ion: An atom or molecule that has acquired a charge by either gaining or losing electrons. An atom or mol
Ion Exchange: Ion exchange is a method of separating ions from a solution by reversibly binding them onto a resin
Ionic Bond: An attraction between ions of opposite charge. Potassium bromide consists of potassium ions (K+) ion
Ionic Compound: A compound made of distinguishable cations and anions, held together by electrostatic forces.
Ionic Dissociation: When ionic substances dissolve, their ions are surrounded by solvent molecules and separated from ea
Ionic Equation: An ionic equation is a balanced chemical equation in which strong electrolytes are written as dissoc
Ionic Radius: The radii of anions and cations in crystalline ionic compounds, as determined by consistently partit
Ionization Energy: The energy needed to remove an electron from a gaseous atom or ion.
Isobar: 1. A contour line that corresponds to values measured at identical pressures. For example, curves on
Isobaric: Having constant pressure.
Isochore: A contour line that corresponds to values measured at identical volumes. For example, a curve on a p
Isochoric: Having constant volume.
Isoelectronic: Refers to a group of atoms or ions having the same number of electrons. For example, F-, Ne, and Na+
Isoleucine: A naturally occuring amino acid with a nonpolar side chain.
Isomer: Molecules with identical molecular formulas but different structural formulas.
Isomerization: A chemical change that involves a rearrangement of atoms and bonds within a molecule, without changi
Isosteric: Having identical valence electron configurations.
Isotherm: A contour line that corresponds to values measured at identical temperatures. For example, curves on
Isothermal: Having constant temperature.
Isotone: One of a group of atoms or ions with nuclei that contain the same number of neutrons but different n
Isotonic: Refers to solutions that have equal osmotic pressure.
Isotope: Atoms or ions of an element with different numbers of neutronsin their atomic nucleus. Isotopes have
Isotopic Abundance: The fraction of atoms of a given isotope in a sample of an element.
Isotopic Mass: The mass of a single atom of a given isotope, usually given in daltons.
Iupac: International Union of Pure and Applied Chemistry, an organization which sets international standard
Joule: The SI unit of energy, equal to the work required to move a 1 kg mass against an opposing force of 1
Kelvin: The SI base unit of temperature, defined by assigning 273.16 K to the temperature at which steam, ic
Ketone: An organic compound that contains a carbonyl group. For example, methyl ethyl ketone is CH3COCH2CH3_
Kilo: Prefix used in the SI system meaning 'one thousand of'. For example 1 km means 'one thousand meters'
Kilogram: The kilogram (kg) is the base unit of mass in the SI system of units. The standard kilogram is a 1 k
Kinetic Energy: The energy an object possesses by virtue of its motion. An object of mass m moving at velocity v has
Kw: Symbol for the autoprotolysis constant for water, equal to 1.01 Ã— 10-14 at 25Â°C.
Lamberts Law: The intensity of radiation passing through a material decays exponentially with path length b.
Lanthanide: Elements 57-70 are called lanthanides. Electrons added during the Aufbau construction of lanthanide
Lanthanide Contraction: An effect that causes sixth period elements with filled 4f subshells to be smaller than otherwise ex
Latent Heat: Heat that is absorbed without causing a rise in temperature. For example, 'latent heat of vaporizati
Lattice: A regular array of ions or atoms.
Law: Natural laws summarize patterns that recur in a large amount of data. Unlike human laws, natural law
Law Of Combining Volumes: When gases react, they do so in a definite proportion by volume, if the volumes are measured at the
Law Of Conservation Of Mass: There is no change in total mass during a chemical change. The demonstration of conservation of mass
Law Of Definite Proportions: When two pure substances react to form a compound, they do so in a definite proportion by mass. For
Law Of Multiple Proportions: When one element can combine with another to form more than one compound, the mass ratios of the ele
Le Chateliers Principle: Le Chatelier's principle predicts that when a stress is applied to an equilibrium mixture, the equil
Leucine: A naturally occuring aliphatic amino acid with a nonpolar side chain.
Levorotatory: Having the property of rotating plane-polarized light counterclockwise.
Lewis Structure: A model pioneered by Gilbert N. Lewis and Irving Langmuir that represents the electronic structure o
Ligand: 1. In inorganic chemistry, a molecule or ion that binds to a metal cation to form a complex. 2. In b
Limit Of Quantitation: The smallest detectable concentration an analytical instrument can determine at a given confidence l
Limiting Reactant: The reactant that limits the amount of product produced in a chemical reaction. For example, mixing
Line Spectrum: A emission spectrum that contains very sharp peaks, corresponding to transitions between states in f
Lipid: A diverse group of organic molecules that contain long hydrocarbon chains or rings and are hydrophob
Lipophilic: Refers to a substance's solubility in fat. Lipophilicity can be measured by shaking the substance wi
Liquid: A state of matter that has a high density and is incompressible compared to a gas. Liquids take the
Lithium: Element 3, atomic weight 6.939. The lightest alkali metal, used in special-purpose metal alloys and
Litmus: A mixture of pigments extracted from certain lichens that turns blue in basic solution and red in ac
Litmus Paper: Paper impregnated with litmus, usually cut in narrow strips. Dipping red litmus paper into a basic s
Lock And Key Model: A model that explains the role of enzymes in chemical reactions by assuming that the reactants fit i
London Force: An intermolecular attractive force that arises from a cooperative oscillation of electron clouds on
Lone Pair: Electrons that are not involved in bonding.
Low Spin Complex: A metal-ligand complex with fewer unpaired electrons than the uncomplexed metal ion. When a strong l
Lysine: A naturally occurring amino acid with an amine group on its side chain.
Magnetic Quantum Number: Quantum number that labels different orbitals within a subshell. Mell can take on values from -ell t
Main Group Elements: Elements of the s and p blocks.
Malleable: Capable of being hammered into sheets. Metals are typically malleable materials.
Manometer: An instrument for measuring gas pressures. A mercury or oil manometer measures gas pressure as the h
Mass: Mass is a measure of the tendency of an object to resist acceleration. It's harder to roll a tractor
Mass Number: The total number of protons and neutrons in an atom or ion. In nuclide symbols the mass number is gi
Mass Percentage: Mass percentages express the concentration of a component in a mixture or an element in a compound.
Mass Spectrometer: An instrument that measures the masses and relative abundances of a sample that has been vaporized a
Mass Spectrometry: A method for experimentally determining isotopic masses and isotopic abundances. A sample of an elem
Mass Spectrum: A plot showing the results of a mass spectrometry experiment, which shows the presence of particles
Matter: Matter is anything that has mass. Air, water, coffee, fire, human beings, and stars are matter. Ligh
Measurement: Measurement is the collection of quantitative data. Measurement involves comparison of the quantity
Medicinal Chemistry: A branch of chemistry concerned with the discovery, design, synthesis, and investigation of biologic
Mega: SI prefix meaning 'multiply by 106'. For example, 3.2 MJ is 3200000 J.
Meniscus: A phase boundary that is curved because of surface tension.
Metabolism: A sequence of biochemical reactions that converts fuel molecules into energy used to drive other bio
Metabolite: A compound produced by metabolic reactions.
Metal: A metal is a substance that conducts heat and electricity, is shiny and reflects many colors of ligh
Metallic Compounds: Compounds that contain at least one metallic element.
Metalloid: An element with both metallic and nonmetallic properties. Examples are silicon, arsenic, and germani
Meter: The meter is the basic unit of length in the SI system of units, defined as the distance light trave
Methyl: A group -CH3, derived from methane. For example, CH3Cl is 'methyl chloride' (systematic name: chloro
Micro: Prefix used in the SI system meaning 'one millionth of'. For example 1 Âµm means 'one millionth of a
Micron: A unit of length, equivalent to 10-6 meters.
Microwave: Electromagnetic radiation with wavelength between 3 mm and 30 cm.
Milli: Prefix used in the SI system meaning 'one thousandth of'. For example 1 ml means 'one thousandth of
Miscible: Two liquids are considered 'miscible' or mixable if shaking them together results in a single liquid
Mistake: A mistake is a measurement which is known to be incorrect due to carelessness, accidents, or the ine
Mixed Glyceride: A diglyceride or triglyceride that contains more than one type of fatty acid connected to glycerol v
Molality: Concentration measured as moles of solute per kilogram of solvent. For example, a 1 m nacl solution
Molar: 1. Of or pertaining to moles. 2. An synonym for molarity; for example, a 'six molar solution of hydr
Molar Absorptivity: The absorbance per centimeter of path length when the concentration of absorbing material is 1 M; ep
Molar Heat Capacity: The heat required to raise the temperature of one mole of a substance by 1Â°C is called the molar he
Molar Mass: The mass of one mole of a material. For example, the molar mass of H2O is 18.015 g (obtained by addi
Molar Volume: The volume occupied by one mole of a material. For example, the molar volume of an ideal gas at STP
Molarity: Concentration of a solution measured as the number of moles of solute per liter of solution. For exa
Mole: SI unit for amount of substance, defined as the number of atoms in exactly 12 g of carbon-12. One mo
Mole: The mole is the SI unit for amount of substance. 1 mole of particles is equal to the number of atoms
Mole Fraction: Concentration of a substance in a mixture measured as moles of the substance per mole of mixture. Fo
Molecular Equation: A molecular equation is a balanced chemical equation in which ionic compounds are written as neutral
Molecular Formula: A notation that indicates the type and number of atoms in a molecule. The molecular formula of gluco
Molecular Geometry: 1. The three-dimensional shape of a molecule. For example, methane (CH4) has a tetrahedral molecular
Molecular Model: A representation of a molecule. The model can be purely computational or it can be an actual physica
Molecular Orbital: A wavefunction that describes the behavior of an electron in a molecule. Molecular orbitals are usua
Molecular Sieve: A material that contains many small cavities interconnected with pores of precisely uniform size. Ze
Molecular Weight: The average mass of a molecule, calculated by summing the atomic weights of atoms in the molecular f
Molecule: The smallest particle of an element or compound that retains the chemical properties of the element
Momentum: Momentum is a property that measures the tendency of a moving object to keep moving in the same dire
Monochromatic: Radiation that has a single wavelength.
Monodentate: A ligand that has only one atom that coordinates directly to the central atom in a complex. For exam
Monomer: A small molecule that is linked with large numbers of other small molecules to form a chain or a net
Monosaccharide: A carbohydrate that cannot be decomposed into simpler carbohydrates by hydrolysis.
Mother Liquor: The solution in recrystallization.
Msds: Safety information sheet for a particular substance that lists physical properties, hazards, cleanup
Msg: MSG is monosodium glutamate, used as a flavor enhancer in many foods.
Multiple Bond: Sharing of more than one electron pair between bonded atoms. A double bond consists of two shared pa
Nano: Prefix used in the SI system meaning 'multiply by 10-9'. For example 1 nm means '0.000000001 m'; 2.8
Nanometer: A unit of length, equal to 10-9 meters, and equal to 10 Ã… (Angstroms).
Native: Naturally occuring forms of precious metals, for example, native copper, native gold, and native sil
Natural Abundance: The average fraction of atoms of a given isotope of an element on Earth.
Natural Gas: A mixture of methane and other gases, found trapped over petroleum deposits under the earth.
Needle Valve: A valve which allows fine control over the rate of gas or liquid flowing through it. The valve conta
Net Chemical Reaction: A reaction that actually occurs as several elementary steps. Equations for net reactions often omit
Net Ionic Equation: A net ionic equation is an ionic equation with all DEFINE[spectator ions'>spectator ions eliminated.
Network Covalent Solid: A substance which consists of an array of atoms held together by an array of covalent bonds. A cryst
Neurotransmitter: Neurotransmitters are molecules that are used to carry signals from one neuron to another. One neuro
Neutral: 1. Having no net electrical charge. Atoms are electrically neutral; ions are not. 2. A solution cont
Neutralization Reaction: A chemical change in which one compound aquires H+ from another. The compound that receives the hydr
Neutrino: An elementary particle produced by certain nuclear decay processes. Neutrinos have no charge and ext
Neutron: An elementary particle found the atomic nucleus of all stable atoms except the hydrogen-1 atom. Neut
Neutron Activation Analysis: An extremely sensitive technique for analyzing trace amounts of elements in a sample. The sample is
Newtonian Fluid: A fluid whose viscosity doesn't depend on gradients in flow speed. Gases and low-molecular weight li
Nitrate: 1. The NO3- ion, formed by reaction of nitric acid with a base. 2. A compound containing the NO3- io
Nitric Acid: A corrosive liquid with a sharp odor that acts as a strong acid when dissolved in water. Nitric acid
Nitrite: 1. The NO2- ion, formed by reaction of nitrous acid with a base. 2. A compound containing the NO2- i
Nitrogen: Element number 7, a colorless, odorless, tasteless gas that makes up about 80% of the earth's atmosp
Noble Gas Core: All completely filled shells underneath the valence shell.
Node: A point, region, or surface where the amplitude of a standing wave is zero. The probability of findi
Nomenclature: A system for naming things. For example, 'organic nomenclature' is the system used to name organic c
Non-Newtonian Fluid: A fluid whose viscosity changes when the gradient in flow speed changes. Colloidal suspensions and p
Nonelectrolyte: A nonelectrolyte is a substance which does not ionize in solution.
Nonmetal: A nonmetal is a substance that conducts heat and electricity poorly, is brittle or waxy or gaseous,
Nonparticulate: Not composed of distinct particles.
Nonpolar: Having a relatively even or symmetrical distribution of charge.
Nonpolar Molecule: A molecule in which the center of positive charge and the center of negative charge coincide. Exampl
Normality: A measure of solution concentration, defined as the number of equivalents of solute per liter of sol
Nuclear Binding Energy: Energy needed to break an atomic nucleus into separate protons and neutrons.
Nuclear Fission: Splitting of a nucleus into two smaller nuclei and neutrons. The smaller nuclei have higher binding
Nuclear Fusion: Combination of two smaller nuclei to form a larger nucleus. The larger nucleus has higher binding en
Nucleation: The process of providing sites for 1) new bubbles to form in a liquid that is boiling or supersatura
Nucleic Acid: A polymer made of repeating nucleotides. Examples are DNA and RNA.
Nucleon: A proton or a neutron in the atomic nucleus.
Nucleoside: A nucleotide base bound to a five-carbon sugar.
Nucleotide: A molecule which is a basic building block of nucleic acids and which plays a key role in energy tra
Nucleotide Base: A heterocyclic nitrogen-containing base that is a constituent of nucleotides. Examples are adenine,
Nuclide: An atom or ion with a specified mass number and atomic number. For example, uranium-235 and carbon-1
Nuclide Symbol: A symbol for an nuclide that contains the mass number as a leading superscript and the atomic number
Octane: Flammable liquid compounds found in petroleum and natural gas. There are 18 different octanes- they
Octet: A set of eight valence electrons.
Octet Rule: A guideline for building Lewis structures that states that atoms tend to gain, lose, or share valenc
Ohm: The SI unit of electrical resistance, equal the resistance between two points when a constant voltag
Ohmmeter: An instrument for measuring electrical resistance.
Oligosaccharide: A carbohydrate that consists of only a few linked monosaccharide units.
Optical Activity: A substance that is capable of rotating plane-polarized light. Molecules of an optically active subs
Orbital: A wavefunction that describes what an electron with a given energy is doing inside an atom or molecu
Order: The order of a reaction is the sum of concentration exponents in the rate law for the reaction. For
Organic: Compounds that contain carbon chemically bound to hydrogen. They often contain other elements (parti
Organic Chemistry: The study of compounds that contain carbon chemically bound to hydrogen, including synthesis, identi
Organochromic Indicators: Colored organic compounds that change color when they chelate different metals. Organochromic indica
Osmometry: Determination of the average molecular weight of a dissolved substance from measurements of osmotic
Osmosis: Passage of solvent molecules from a dilute solution through a semipermeable membrane to a more conce
Osmotic Pressure: Pressure which must be applied to a solution to prevent water from flowing in via a semipermeable me
Oxidation: Oxidation is the loss of one or more electrons by an atom, molecule, or ion. Oxidation is accompanie
Oxidation Half Reaction: That part of a redox reaction that involves loss of electrons. In the oxidation half reaction, the o
Oxidation Number: A convention for representing a charge of an atom embedded within a compound, if the compound were p
Oxide: A binary compound that contains oxygen in the -2 oxidation state.
Oxidizing Agent: A reactant that removing electrons from other reactants in a chemical reaction. Oxidizing agents cau
Oxygen: Element 8, atomic weight 15.9994, a colorless, odorless gas that makes up about 1/5 of the earth's a
Paraffin: 1. A waxy substance that is a mixture of alkanes with chains containing 18 to 36 carbon atoms. 2. An
Paramagnetism: Paramagnetic materials are attracted to a magnetic field due to the presence of least one unpaired s
Partial Miscibility: Two liquids are considered partially miscible if shaking equal volumes of the liquids together resul
Partial Vaccuum: A volume that contains traces of gas at very low pressure.
Particulate: Composed of distinct particles. Smoke is particulate; pure gases are not.
Parts Per Million: Concentration expressed as parts of solute per million parts of solution. Usually refers to parts pe
Pascal: The SI unit of pressure, equal to a force of one newton per square meter. 101325 pascals = 1 atmosph
Path Length: In absorption spectroscopy, the length of a path taken by radiation through a sample.
Patina: A thin layer of corrosion products with a distinctive coloration that forms on a metal surface expos
Pattern Recognition: A computational technique used to find patterns and develop classification schemes for data in very
Pauli Principle: No two electrons in an atom can have the same set of 4 quantum numbers. Because the n, ell, and mell
Penetration: Electrons in penetrating orbitals can reach the nucleus. The n and ell quantum numbers determine how
Peptide: A short polymer made by linking together amino acid molecules.
Percent Error: The relative error times 100%.
Percent Yield: Percent yield equals experimental yield divided by theoretical yield times 100%.
Perfect Crystal: A crystal with no defects or impurities, made of completely identical repeating subunits. Further, a
Period: Rows in the periodic table are called periods. For example, all of the elements in the second row ar
Periodic Law: The periodic law states that physical and chemical properties of the elements recur in a regular way
Periodic Table: An arrangement of the elements according to increasing atomic number that shows relationships betwee
Periodic Trend: A regular variation in element properties with increasing atomic number that is ultimately due to re
Permanent Hardness: Water hardness that remains after boiling the water, mainly due to dissolved calcium sulfate. Chlori
Permanganate: Permanganate ion (mno4-) is a powerful oxidizing agent used in chemical analysis and water treatment
pH: Ph is a measure of effective concentration of hydrogen ions in a solution. It is approximately relat
Pharmacognosy: Identification, isolation, and characterization of biologically active substances in living things.
Pharmacology: The study of drugs, which includes determination of biological activity, biological effects, breakdo
Phase: 1.A phase is a part of a sample of matter that is in contact with other parts but is separate from t
Phase Boundary: A phase boundary is a surface where two samples of matter with different properties are in contact.
Phase Change: A change in the state of a sample of matter; for example, solid to liquid or liquid to gas. Phase ch
Phase Diagram: A map that shows which phases of a sample are most stable for a given set of conditions. Phases are
Phenol: A group or molecule containing a benzene ring that has a hydroxyl group substituted for a ring hydro
Phenolphthalein: An organic compound used as an acid-base indicator. The compound is colorless in acidic solution and
Phenolpthalein: A common misspelling of phenolphthalein.
Phenyl: A molecular group or fragment formed by abstracting or substituting one of the hydrogen atoms attach
Phosphate: 1. The PO4-3 ion. 2. A compound containing the PO4-3 ion.
Phospholipid: An ester of glycerol with two fatty acids and phosphoric acid (H3PO4) or a derivative of phosphoric
Phospholipid Bilayer: In an aqueous environment phospholipids can form a two-layered 'sandwich' with the hydrophobic lipid
Photochemistry: The study of chemical changes caused by light. For example, many of the key reactions that generate
Photoelectric Effect: Ejection of electrons from an atom or molecule that has absorbed a photon of sufficient energy. The
Photoelectron: An electron ejected from an atom or molecule that has absorbed a photon.
Photon: A discrete packet of energy associated with electromagnetic radiation. Each photon carries energy E
Photosynthesis: A complex process used by many plants and bacteria to build carbohydrates from carbon dioxide and wa
Physical Change: A change which does not transform one substance into another. For example, freezing water is a physi
Physical Chemistry: A branch of chemistry that studies chemical phenomena from a physical and mathematical perspective.
Physical Property: Measurement of a physical property may change the arrangement but not the structure of the molecules
Phytochemistry: The study of substances found in plants. 'Phytochemicals' are materials extracted from plant tissue.
Pi Bond: In the valence bond theory, a pi bond is a valence bond formed by side-by-side overlap of p orbitals
Pico: Prefix used in the SI system meaning 'multiply by 10-12'. For example, 3 pm means 3Ã— 10-12 meters.
Picogram: One picogram is 10-12 grams.
Picoliter: One picoliter is 10-12 liters.
Picometer: One picometer is 10-12 meters.
Pka: The pka of an acid is minus the base-10 log of its acid dissociation constant, pka = - log Ka. For e
Pkb: The pkb of an base is minus the base-10 log of its base hydrolysis constant, pkb = - log Kb. For exa
Plancks Constant: A proportionality constant that relates the energy carried by a photon to its frequency. Planck's co
Plasma: 1. In biology, the fluid in which blood cells or lymph cells are suspended. 2. A gaslike state of ma
Poise: A cgs unit of resistance to fluid flow (viscosity). If a force of 1 dyne is needed to force two flui
Polar Bond: A bond involving electrons that are unequally shared. Polar bonds can be thought of as intermediate
Polar Molecule: An asymmetric molecule containing polar bonds. H2O, NH3, and hcl are examples of polar molecules. No
Polarity: A property associated with molecules when the center of positive charge and the center of negative c
Polyatomic Ion: A polyatomic ion is a charged particle that contains more than two covalently bound atoms. See Polya
Polyatomic Molecule: A polyatomic molecule is an uncharged particle that contains more than two atoms.
Polydentate: A ligand that has more than one atom that coordinates directly to the central atom in a complex. Pol
Polymer: A large molecule made by linking smaller molecules ('monomers') together.
Polymerization: A process that links smaller molecules together to form a larger molecule.
Polymerize: To link smaller molecules together to form a larger molecule.
Polymorph: Solid substances that occur in several distinct forms. Polymorphs have different chemical and physic
Polysaccharide: A carbohydrate consisting of a large number of linked monosaccharide units. Examples of polysacchari
Position Of Equilibrium: When a reaction's equilibrium 'lies to the right', the concentrations of products will be greater th
Potential Difference: Work that must be done to move an electric charge between specified points. Electric potential diffe
Potential Energy: Energy an object possesses by virtue of its position. For example, lifting a mass mby h meters incre
Power: The rate at which energy is supplied. Power has define[SI] units of J/s, sometimes called 'Watts' (W
Precipitate: An insoluble substance that has been formed from substances dissolved in a solution. For example, mi
Precipitation: Precipitation is the conversion of a dissolved substance into insoluble form by chemical or physical
Precision: Precision is reproducibility. Saying 'These measurements are precise' is the same as saying, 'The sa
Pressure: Force per unit area. The SI unit of pressure is the pascal, defined as one newton per square meter.
Primary Standard: A stable, high-purity material used in titrations and other chemical analyses to prepare solutions o
Principal Quantum Number: The quantum number that determines the size and (in hydrogen atoms) the energy of an orbital. N is u
Product: A substance that is produced during a chemical change.
Proline: A naturally occurring amino acid with a heterocyclic ring that is classified as nonessential in the
Propane: A colorless, odorless, flammable gas, found in petroleum and natural gas. It is used as a fuel and a
Propellant: 1. A mixture of fuel and oxidizing agent that reacts to produce a high-energy stream of product gase
Protein: A complex polymer made by linking together amino acid molecules. Proteins sometimes contain non-amin
Proton: An elementary particle found the atomic nucleus with a positive charge equal and opposite that of th
Proton Donor: Because a free H+ ion is technically a bare proton, acids are sometimes referred to as 'proton donor
Pseudocore: Electrons in d or f subshells which are outside the noble gas core.
Pure Substance: A sample of matter that cannot be separated into simpler components without chemical change. Physica
Pyrophoric: Catches fire spontaneously when exposed to air at normal room temperature. For example, powdered pot
Qualitative Analysis: A chemical analysis that detects the presence of a substance in a sample.
Quantitative Analysis: A chemical analysis that determines the concentration of a substance in a sample.
Quantitative Structure-Activity Relationship: A mathematical connection between chemical structure and biological activity, established by statist
Quantum: A discrete packet of energy.
Quantum Mechanics: A branch of physics that describes the behavior of objects of atomic and subatomic size.
Quantum Number: Indices that label quantized energy states. Quantum numbers are used to describe the state of a conf
Racemic: A mixture of equal parts of the levorotatory and dextrorotatory isomers of the the same substance. R
Radian: An angle with vertex at the center of a circle of radius r that encompasses an arc of length r.
Radiant Intensity: Energy of radiation striking a unit area per unit time. The SI unit of radiant power is J m-2 s-1.
Radioactivity: Spontaneous emission of particles or high-energy electromagnetic radiation from the nuclei of unstab
Radioisotope: A radioactive isotope. For example, tritium is a radioisotope of hydrogen.
Random Error: Random errors are errors that affect the precision of a set of measurements. Random error scatters m
Raoults Law: The vapor pressure of a solvent in an ideal solution equals the mole fraction of the solvent times t
Rare Earth: An oxide of a rare earth element.
Rare Earth Element: A metallic element that belongs to Group 3B or to the lanthanide series.
Rate Constant: A rate constant is a proportionality constant that appears in a rate law. For example, k is the rate
Rate Law: A rate law or rate equation relates reaction rate with the concentrations of reactants, catalysts, a
Reactant: A substance that is consumed during a chemical change.
Reaction Mechanism: A list of all elementary reactions that occur in the course of an overall chemical reaction.
Reaction Quotient: The product of the concentrations of the products, divided by the product of the concentrations of t
Reaction Rate: A reaction rate is the speed at which reactants are converted into products in a chemical reaction.
Reagent: A substance or mixture that is useful in chemical analysis or synthesis.
Rearrangement Reaction: A reaction in which a reactant and product are isomers of each other. Chemical bonds within the reac
Receptor: A molecule or surface in a cell that recognizes and binds to a specific messenger molecule, leading
Redox Indicator: An organic molecule that has reduced and oxidized forms with different colors; interconversion of th
Redox Reaction: A reaction that involves transfer of electrons from one substance to another. Redox reactions always
Redox Titration: A titration based on a redox reaction. For example, iron in water can be determined by converting di
Reducing Agent: A reducing agent is a substance that reduce another substance by supplying electrons to it. Reducing
Reduction: Reduction is gain of one or more electrons by an atom, molecule, or ion. Reduction is accompanied by
Reduction Half Reaction: That part of a redox reaction that involves gain of electrons. In the oxidation half reaction, the o
Relative Error: The uncertainty in a measurement compared to the size of the measurement. For example, if three repl
Relative Standard Deviation: The relative standard deviation is a measure of precision, calculated by dividing the standard devia
Residue: 1. The substances left after an evaporation or distillation. 2. A recognizable molecular fragment em
Resonance: Description of the ground state of a molecule with delocalized electrons as an average of several Le
Resonance Effect: If electron density at a particular point in a molecule is higher or lower than what you'd expect fr
Reverse Osmosis: Solvent molecules flow spontaneously from a dilute solution through a semipermeable membrane to a mo
Reversible: A process or reaction that can be reversed by an infinitesimally small change in conditions. For exa
Rna: A nucleic acid with D-ribose as the sugar component in its nucleotides.
Salifiable: Capable of reacting with an acid to form a salt. Lavoisier classified lime, baryta, alumina, and sil
Salt Bridge: A tube (often filled with ion-laced agar) that allows two solutions to be in electrical contact with
Saponification: The hydrolysis of esters using hot sodium hydroxide solution to produce the salt of a carboxylic aci
Satp: Used to describe a substance at standard pressure and a temperature of 25Â°C (298.15 K).
Saturated Fat: A lipid that contains no carbon-carbon double bonds. Animal fats like butter and lard are composed o
Saturated Solution: A solution which does not dissolve any more solute. When a saturated solution is placed in contact w
Scientific Method: An inefficient but highly successful method of knowledge construction based on experimental testing
Scientific Notation: A system for reporting very small or very large numbers by writing the number as a decimal number be
Second: The second (s) is the base unit of time in the SI system of units, defined as the duration of 9,192,
Second Ionization Energy: The energy needed to remove an electron from an isolated +1 ion. The third ionization energy would b
Second Law: The second law states that every spontaneous process causes a net increase in the entropy of the uni
Second Order Reaction: A reaction with a rate law that is proportional to either the concentration of a reactant squared, o
Sedimentation: Separation of a dense material (usually a solid) from a less dense material (usually a liquid) by al
Semipermeable Membrane: A membrane that allows some but not all of the components in a mixture to pass through it. Semiperme
Serine: A naturally occuring amino acid with an hydroxyl group on its side chain.
Shell: A set of electrons with the same principal quantum number. The number of electrons permitted in a sh
Shielding: Electrons in orbitals with high penetration can shield the nucleus from less penetrating electrons.
Short Term Memory: Short term memory is a mechanism for storing temporary information, such as where you parked your ca
Siemens: The SI unit of electrical conductance. A material has a conductance of one siemens if one ampere of
Sigma Bond: In the valence bond theory, a sigma bond is a valence bond that is symmetrical around the imaginary
Significant Figure: A convention for recording measurements. Measurements are rounded so that they contain only the digi
Silicate: 1. A negatively charged ion containing silicon and oxygen, usually sio3-2, Si2O7-6, and Si3O7-2. 2.
Single Displacement: A reaction of the form A + BC = B + AC. For example, zinc displaces hydrogen from hydrochloric acid
Soap: A salt of a fatty acid. For example, sodium stearate is a soap made by neutralizing stearic acid. C
Sol: A colloid with solid particles suspended in a liquid. Examples are protoplasm, starch in water, and
Solid: A solid is a relatively dense, rigid state of matter, with a definite volume and shape. Molecules in
Solubility: The solubility of a substance is its concentration in a saturated solution. Substances with solubili
Solubility Product: The equilibrium constant for a reaction in which a solid ionic compound dissolves to give its consti
Solubilizing Group: A group or substructure on a molecule that increases the molecule's solubility. Solubilizing groups
Soluble: Capable of being dissolved in a solvent (usually water).
Soluble Salt: An ionic compound that dissolves in a solvent (usually water).
Solute: A substance dissolved in a solvent to make a solution.
Solution: A sample of matter consisting of more than one pure substance with properties that do not vary withi
Solvent: The most abundant component in a solution.
Solvent Extraction: Solvent extraction is a method for separating mixtures by exploiting differences in the solubilities
Sorption: Assimilation of molecules of one substance by a material in a different phase. Adsorption (sorption
Specific Gravity: The mass of a unit volume of a substance relative to the mass of a unit volume of water. Temperature
Specific Heat: The heat required to raise the temperature of 1 g of a substance by 1Â°C is called the specific heat
Specific Volume: The volume of a unit mass of substance. For example, the specific volume of water at 4Â°C is 1.00000
Spectator Ion: A spectator ion is an ion that appears as both a reactant and a product in an ionic equation. For ex
Spectrophotometer: An instrument for measuring the amount of light absorbed by a sample.
Spectrophotometry: Determination of the concentration of a material in a sample by measurement of the amount of light t
Spectroscope: An instrument for measuring the spectrum of light or radiation.
Spectroscopy: Spectroscopy is analysis of the interaction between electromagnetic radiation and matter. Different
Spectrum: 1. A sequence of colors produced by passing light through a prism or diffraction grating. 2. A range
Spin: Electrons have an intrinsic angular momentum that is similar to what would be observed if they were
Spin Pair: Two electrons with opposite spins, usually occupying the same orbital.
Spontaneous: A spontaneous process occurs because of internal forces; no external forces are required to keep the
Stabilizer: A substance that makes a mixture more stable. Antioxidants and antiozonants are examples of stabiliz
Standard Deviation: The standard deviation is a statistical measure of precision. The best estimate of the standard devi
Standard Enthalpy Change: A change in enthalpy associated with a reaction or transformation involving substances in their stan
Standard Enthalpy Of Formation: The change in enthalpy when one mole of compound is formed from its elements in their most stable fo
Standard Enthalpy Of Reaction: A change in enthalpy associated with a reaction involving substances in their standard states.
Standard Entropy Of Reaction: A change in entropy associated with a reaction involving substances in their standard states. A supe
Standard Hydrogen Electrode: A platinum electrode that runs the half reaction 2 H+(aq, 1M) + 2 e- rightarrow H2(g, 1 atm), chosen
Standard Molar Entropy: The entropy of one mole of a substance in its standard state.
Standard Molar Volume: The volume of 1 mole of an ideal gas at STP, equal to 22.414 liters.
Standard Pressure: Standard pressure is a pressure of 1 bar. Before 1982, the standard pressure was 1 atm (1 atm = 1.01
Standard Reduction Potential: The voltage associated with a reduction process at standard state. The reduction potential of 2H+(aq
Standard Solution: A solution of precisely known concentration.
Standard State: A set of conditions defined to allow convenient comparison of thermodynamic properties. The standard
Standard Temperature And Pressure: Used to describe a substance at standard pressure and a temperature of 0Â°C (273.15 K).
Starch: A polysaccharide used by plants to stockpile glucose molecules. The most common forms are amylose an
State Function: A property that depends only on the condition or 'state' of the system, and not on the path used to
State Of Matter: There are three common states of matter: gases, liquids, and solids. States of matter differ in the
Stationary Phase: A stationary phase is a substance that shows different affinities for different components in a samp
Steel: An alloy of iron and carbon. Steel contains anywhere between 0.2% carbon (for soft wire and sheet st
Steradian: A solid angle with vertex at the center of a sphere of radius r that encompasses an area of r2 on th
Stereochemistry: Stereochemistry is the study of how the properties of a compound are affected by the spatial positio
Stereoisomer: Molecules with the same atoms and bond structure, but different three dimensional arrangements of at
Stoichiometric Coefficient: The coefficients given before substances in a balanced chemical equation. For example, the stoichiom
Stoichiometry: 1. Ratios of atoms in a compound. 2. Ratios of moles of compounds in a reaction. 3. A branch of chem
Stripping: Stripping is a technique for removing volatile components in a mixture by bubbling a stream of an ch
Strong Acid: A strong acid is an acid that completely dissociates into hydrogen ions and anions in solution. Stro
Strong Base: A strong base is an base that completely dissociates into ions in solution. Strong bases are strong
Strong Electrolyte: A strong electrolyte is a solute that completely dissociates into ions in solution. Solutions of str
Strong Ligand: A ligand that causes a large crystal field splitting which results in a low-spin complex.
Structural Formula: A structural formula is a diagram that shows how the atoms in a molecule are bonded together. Atoms
Sublimation: Conversion of a solid directly into a gas, without first melting into a liquid.
Subshell: A set of electrons with the same azimuthal quantum number. The number of electrons permitted in a su
Substitution: A reaction in which an atom or fragment within a molecule is replaced with another.
Substrate: A substance that is acted upon by an enzyme during a biochemical reaction.
Sugar: A carbohydrate with a characteristically sweet taste. Sugars are classified as monosaccharides, disa
Sulfate: 1. The SO42- ion, formed by reaction of sulfuric acid with a base. 2. A compound containing the SO42
Sulfite: 1. The SO32- ion, formed by reaction of sulfurous acid with a base. 2. A compound containing the SO3
Sulfuric Acid: An oily, corrosive liquid that acts as a strong acid when dissolved in water. Sulfuric acid has so m
Sulfurous Acid: A colorless liquid that acts as a weak acid when dissolved in water, sometimes used as a bleach. Sal
Superconductivity: The ability of certain materials to carry an electric current with zero electrical resistance.
Supercooling: Liquids at temperatures below their normal freezing points are said to be 'supercooled'.
Supercritical Fluid: A fluid state that occurs when the pressure and temperature exceed the substance's critical pressure
Superoxide.: A binary compound containing oxygen in the -Â½ oxidation state. For example, KO2 is potassium supero
Supersaturated Solution: A supersaturated solution has concentration of solute that is higher than its solubility. A crystal
Surface Tension: The work required to expand the surface of a liquid by unit area.
Surfactant: A material that spreads along a surface, changing the properties of the surface. For example, soap s
Surroundings: In thermodynamics, the surroundings refer to the universe outside the system.
Suspension: A heterogenous mixture in which droplets or particles are suspended in a liquid.
Synthesis: Formation of a complex product from simpler reactants. For example, water can be synthesized from ox
Synthetic: A substance manufactured by chemical synthesis.
System: In thermodynamics, the system is the part of the universe that is of interest.
Systematic Error: Systematic errors have an identifiable cause and affect the accuracy of results.
Systeme Internationale: Le SystÃ©me Internationale (SI) is a system of units introduced to remove barriers to international
T-Shape: A molecular shape that results when there are 3 bonds and 2 lone pairs around the central atom in th
T-Shape: A molecular shape that results when there are 3 bonds and 2 lone pairs around the central atom in th
Tautomer: A structure formed by facile motion of a hydrogen from one site to another within the same molecule.
Temperature: Temperature is an intensive property associated with the hotness or coldness of an object. It determ
Temporary Hardness: The component of total water hardness that can be removed by boiling the water. Ca(HCO3)2 and Mg(HCO
Teratogen: A substance that can cause deformities in embryos. Dioxin is a teratogen.
Terminal: 1. The end of a polymer molecule. 2. A point at which electrical connections can easily be made or b
Terminal Reaction: A reaction that ends a cycle or chain of other chemical reactions.
Terminus: The end of a polymer molecule.
Tetrahedral: A molecular shape that results when there are four bonds and no lone pairs around the central atom i
Theoretical Yield: The amount of product obtained when all of the limiting reagent reacts.
Theory: Theories are well-established explanations for experimental data. To become established, the theory
Thermal: Pertaining to heat.
Thermal Energy: Energy an object possesses by virtue of its temperature. For example, 1 g of water at 15Â°C has 4.18
Thermionic Emission: The emission of electrons or ions by a hot object. For example, the filament in a mass spectrometer
Thermistor: A device that senses temperature changes by using a resistor with an electrical resistance that fall
Thermochemical Equation: An compact equation representing a chemical reaction that describes both the stoichiometry and the e
Thermochemistry: The study of heat absorbed or released during chemical changes.
Thermocouple: A device that senses temperature changes by using a pair of joined wires made of dissimilar metals t
Thermodynamic Equilibrium: A system is at thermodynamic equilibrium if the energy it gains from its surroundings is exactly bal
Thermodynamics: The study of energy transfers and transformations.
Thermoelectron: An electron emitted by a very hot object.
Thermometer: An instrument for measuring temperature.
Thermometry: The science of temperature measurement.
Thermoplastic: A polymer that softens or melts on heating, and becomes rigid again on cooling. Thermoplastic polyme
Thermosetting: A polymer that solidifies on heating and cannot be remelted. The setting action results from crossli
Thin Layer Chromatography: A technique for separating components in a mixture on the basis of their differing polarities. A spo
Thio: A prefix that means, 'replace an oxygen with sulfur'. For example, sulfate ion is SO42-; thiosulfate
Third Law: The entropy of a perfect crystal is zero at absolute zero.
Thixotropic Fluid: A liquid that becomes less viscous when stirred. Paint and printing inks are thixotropic fluids; the
Titrant: The substance that quantitatively reacts with the analyte in a titration. The titrant is usually a s
Titration: A procedure for determining the amount of some unknown substance (the analyte) by quantitative react
Titration Curve: A plot that summarizes data collected in a titration. A linear titration curve plots moles of analyt
Torr: A unit of pressure, defined so that 760 Torr is exactly 1 atmosphere. A Torr is equivalent to 1 mm H
Toxicology: The study of poisons, including identification, isolation, biological effects, mechanism of action,
Transition Metal: An element with an incomplete d subshell. Elements which have common cations with incomplete d subsh
Transmittance: The transmittance is the fraction of radiant intensity transmitted by a sample, T = I/I0 where T is
Transuranium Element: An element with an atomic number higher than 92 (uranium's atomic number). Transuranium elements are
Triglyceride: A triglyceride is an ester of glycerol and three fatty acids. Most animal fats are composed primaril
Trigonal Bipyramidal: A molecular shape that results when there are five bonds and no lone pairs on the central atom in th
Trigonal Planar: A molecular shape that results when there are three bonds and no lone pairs around the central atom
Trigonal Pyramidal: A molecular shape that results when there are three bonds and one lone pair on the central atom in t
Triple Bond: A covalent bond that involves 3 bonding pairs. In the valence bond theory, one of the bonds in a tri
Triple Point: The temperature and pressure at which the solid, liquid, and gaseous forms of a substance are at equ
Tritium: A radioisotope of hydrogen with two neutrons and one proton in its nucleus.
Trueness: Trueness is the closeness of an average measurement to a 'true' value, while accuracy is the the clo
Tyndall Effect: Light passing through a colloid is scattered by suspended particles. The light beam becomes clearly
Ultraviolet Light: Electromagnetic radiation with wavelength longer than that of x-rays but shorter than that of visibl
Uncertainty Principle: The exact momentum and exact location of a particle cannot be specified. Werner Heisenberg stated th
Unimolecular Reaction: A reaction that involves isomerization or decomposition of a single molecule.
Unit: A standard for comparison in measurements. For example, the meter is a standard length which may be
Unit Cell: The simplest arrangement of atoms or molecules that regularly repeats in a crystal structure.
Universal Indicator: A universal indicator is an indicator which undergoes several color changes over a wide range of ph.
Unpaired Spin: A single electron occupying an orbital.
Unsaturated Compound: An organic compound with molecules containing one or more double bonds.
Unsaturated Fat: A lipid containing one or more carbon-carbon double bonds. Unsaturated fats tend to be oily liquids
Unsaturated Solution: A solution with a concentration lower than its equilibrium solubility.
Vacuum: A volume which contains no matter.
Valence: The number of hydrogen atoms that typically bond to an atom of an element. For example, in H2O, oxyg
Valence Bond: In the valence bond theory, a valence bond is a chemical bond formed by overlap of half-filled atomi
Valence Bond Theory: A theory that explains the shapes of molecules in terms of overlaps between half-filled atomic orbit
Valence Electron: Electrons that can be actively involved in chemical change; usually electrons in the shell with the
Valence Shell: The shell corresponding to the highest value of principal quantum number in the atom. The valence el
Valence Shell Electron Pair Repulsion Theory: A model that explains the shapes of molecules by assuming that electron pairs arrange themselves aro
Van Der Waals Equation: A semiempirical equation that describes the relationship between pressure (P), volume (V), temperatu
Van Der Waals Force: A force acting between nonbonded atoms or molecules. Includes dipole-dipole, dipole-induced dipole,
Van Der Waals Radius: One half the distance between two nonbonded atoms, when attractive and repulsive forces between the
Vapor Pressure: The partial pressure of a gas in equilibrium with a condensed form (solid or liquid) of the same sub
Vapor Pressure Lowering: A colligative property of solutions. The vapor pressure of a solution is always lower than the vapor
Variable: A quantity that can have many possible values. In designing experiments, variables that affect measu
Vertical Ionization Energy: The energy required to remove an electron from an atom, molecule, or ion in the gas phase without mo
Vinyl: A polymer made by linking ethylene (CH2=CH2) or substituted ethylene molecules together.
Viscosity: The resistance a liquid exhibits to flow. Experimentally, the frictional force between two liquid la
Visible Light: Visible light is electromagnetic radiation with a wavelength between 400 and 750 nm.
Vitamin: A substance that is critical for proper functioning of a living organism that the organism is unable
Volatile: A solid or liquid material that easily vaporizes. A material with a significant vapor pressure.
Volt: The SI unit of electrical potential. One volt equals one joule per coulomb.
Voltage: A measured electric potential, in volts.
Voltaic Cell: An electrochemical cell that spontaneously generates electrical energy.
Voltaic Pile: An early battery consisting of disks of dissimilar metals (usually zinc and copper) separated by moi
Voltammeter: An instrument for measuring voltages and amperages.
Volume: 1. The amount of space an object takes up. 2. The amount of space a container can hold. The SI unit
Volume Percentage: Volume percentages express the concentration of a component in a mixture or an element in a compound
Vulcanization: A process of combining rubber with sulfur or other substances that causes the polymer chains to cros
Water: A colorless, tasteless liquid with some very peculiar properties that stem from the bent H-O-H struc
Water Gas: A fuel gas used in industrial synthesis of organic chemicals, and in welding, glassmaking, and other
Water Hardness: Hard water is water contaminated with compounds of calcium and magnesium. Dissolved iron, manganese,
Water Of Crystallization: Water that is stoichiometrically bound in a crystal; for example, the waters in copper sulfate penta
Water Softener: A material that lowers water hardness when dissolved in water. For example, sodium carbonate ('washi
Water Softening: Removal of Ca2+ and Mg2+ from water to prevent undesirable precipitation reactions from occurring in
Wave: An oscillating motion that moves outward from the source of some disturbance (ripples running away f
Wavefunction: A mathematical function that gives the amplitude of a wave as a function of position (and sometimes,
Wavelength: The distance between adjacent peaks (or adjacent troughs) on a wave. Varying the wavelength of light
Wavenumber: The number of wave crests per unit distance. Wavenumber is the reciprocal of wavelength. Wavenumbers
Wax: An ester formed from long-chain fatty acids and alcohols that is usually solid at room temperature.
Weak Acid: An acid that only partially dissociates into hydrogen ions and anions in solution. Weak acids are we
Weak Base: A base that only partially dissociates into ions in solution. Weak bases are weak electrolytes. Ammo
Weak Electrolyte: A weak electrolyte is a solute that incompletely dissociates into ions in solution. For example, ace
Weak Ligand: A ligand that causes a small crystal field splitting which results in a high-spin complex.
Weight: Weight is the force exerted by an object in a gravitational field. The weight of an object (W) arise
Wetting: Covering with a surface with thin film of liquid. Liquid beads up on a surface if it cannot wet it.
Work: Work is the energy required to move an object against an opposing force. Work is usually expressed a
X-Ray: A very high energy form of electromagnetic radiation (though not as high energy as gamma rays). X-ra
X-Ray Crystallography: Determination of three dimensional arrangement of atoms in a crystal by analysis of x-ray diffractio
X-Ray Diffraction Pattern: Interference patterns created by x-rays as they pass through a solid material. Studying x-ray diffra
X-Ray Spectrum: A set of characteristic x-ray frequencies or wavelengths produced by a substance used as a target in
X-Ray Tube: A cathode ray tube that focuses energetic streams of electrons on a metal target, causing the metal
Xenobiotic: A substance which is not normally found in a living thing.
Xenon: Element 54, a colorless, inert gas used to fill cathode ray tubes.
Yield: The amount of product actually obtained in a chemical reaction.
Ytterbium: Element 70, atomic weight 173.04, a very rare, malleable metal used in special alloys for X-ray sour
Yttrium: Element 39, atomic weight 88.90585, a dark gray metal that is used in alloys and nuclear technology
Zeeman Effect: The splitting of spectral lines when an external magnetic field is applied.
Zeolite: Addition compounds of the type Na2OÂ·Al2O3Â·n sio2Â·m H2O, with calcium sometimes replacing or prese
Zero Order Reaction: A reaction with a reaction rate that does not change when reactant concentrations change.
Zero Point Energy: A minimum possible energy for an atom or molecule predicted by quantum mechanics. Electrons stay in
Zeta Potential: Electric potential across all phase boundaries between solids and liquids. In colloids, the zeta pot
Zinc: Element 30, atomic weight 65.37, a reactive gray metal that dissolves in acids, used to galvanize me
Zincography: Process of etching unprotected parts of a zinc plate with strong acids to produce a printing surface
Zirconium: Element 40, atomic weight 91.22, a hard, grayish, highly flammable crystalline metal that dissolves
Zone Refining: A method for purifying solids based on the fact that solutes tend to concentrate in the liquid when
Zwitterion: A particle that contains both positively charged and negatively charged groups. For example, amino a
Zymase: Enzymes present in yeast that catalyze fermentation of sugar into alcohol and carbon dioxide.
Zymogen: A protein that may be converted into an enzyme.