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Chemistry Glossary


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Accuracy: Freedom from error. How close a measured quantity is to the true value.
Acid: A substance that produces H3O+ (H+) when it is dissolved in water. A proton donor. An electron pair acceptor.
Acid Ionization Constant Ka: Ka = [H+][A-]/[HA] for the equilibrium, HA <=> H+ + A-.
Acid Rain: Rain made acidic by dissolved sulfur and nitrogen oxides.
Acid Salt: A salt of a partially neutralized polyprotic acid; for example NaSO4 and NaHCO3.
Acid Base Indicator: A dye with one color below a narrow pH range on the acid side and a different color for the range on the basic side.
Acidic Solution: A aqueous solution in which [H+] > [OH-]
Actinide Elements (Actinide Series): Elements 90-103.
Activated Complex: The chemical species that exists with partly broken and partly formed bonds in the transistion state.
Activation Energy: the minimum kinetic energy that must be possessed by the reactants in order to give an effective collision (one that produces the products).
Addition Polymer: A polymer that forms from monomers by an addition process without the monomers losing any of their structural parts.
Addition Reaction: An organic reaction in which a molecule of one reactant (e.g., H-H) adds to a double (or triple) bond of another reactant.
Alcohol: An organic compound whose molecules have the -OH group attached to a carbon having only single bonds.
Aldehyde: An organic compound with the -COH group attached to a carbon having only single bonds.
Alkali Earth Metals (Alkalis): Elements in Group IIA.
Alkane: A hydrocarbon whose molecules have only single bonds.
Alkene: A hydrocarbon whose molecules have one or more double bonds.
Alkyl Group: An organic group of atoms consisting of an alkane less one of its hydrogen atoms( e.g., CH3-, Methyl; CH3CH2-, ethyl).
Allotrope: One of the two or more forms of an element.
Alpha-Amino Acid: One of about 20 monomers of polypeptides all having the general structure: (+NH3--CH--CO2-, where G is bonded to the C in CH (alpha po

sition)) where G is a sidechain group (or H).
Alpha-Helix: A secondary structure of polypeptides in which the chain is twisted in a right-handed coil that is stabilized by hydrogen bonds.
Alpha Particle: The nucleus of a helium atom--two protons and two neutrons--emitted by radioactive decay. Its symbol is 42He
Alpha Radiation: A stream of alpha particles produced by radioactive decay.
Alum: A double salt with the general formula: M+M3+(SO4)2 12H2O; for example, KAl(SO4)2 12H2O.
Amalgam: A solution of a metal in mercury.
Amide: An organic compound whose molecules have a carbonyl-nitrogen group: -CON-
Amine: An organic compound with one, two, or three hydrogen carbon groups joined by single bonds to a nitrogen atom.
Amorphous Solid: A noncrystalline solid. It lacks the long-range order found in crystals. A glass.
Ampere (A): The SI unit for electric current; one coulomb per second.
Amphoteric Compound: A compound that can react either as an acid or as a base.
Amphoteric Oxide: An oxide that will neutralize either an acid or a base.
ngstrom (): A = 10-10 m = 100 pm = 0.1 nm.
Anion: A negative ion.
Anode: The electrode where oxidation occurs during an electrochemical change.
Antibonding Molecular Orbital: A MO that removes electron density from between nuclei and destabilizes a molecule.
Antimatter: A particle that is the counterpart of a particle of ordinary matter (as the positron is antimatter to the electron) and with which it undergoes mutual annihilation when the two collide to give gamma radiation.
Aqua Regia: One part concentrated HNO3 and three parts concentrated HCl by volume.
Aqueous Solution: Any solution having water as the solvent.
Aromatic Compound: Any organic compound with flat rings having delocalized pi-electron networks and which give substitution reactions (like benzene) rather than addition reactions.
Atmosphere, Standard: The pressure that supports a column of mercury 760 mm high at 0 C.
Atomic Mass Unit (amu): 1 mau = 1.6606 x 10-24 g, 1/12 of the mass of a carbon-12 atom.
Atomic Number: The number of protons in a nucleus.
Atomic Spectrum: The line spectrum produced when energized or excited atoms emit light.
Atomic Weight: The average relative mass of an element's atoms on a scale using atoms of carbon-12 as the reference. Also called the atomic mass.
Avogadro's Law: Equal volumes of gases contain equal numbers of molecules (provided they are compared at identical temperatures and pressures).
Avogadro's Number: 6.02 x 1023; the number of things in 1 mole of things.
Background Radiation: The radiation to which all people are exposed caused by the presence of nautral radionuclides in the soil and other parts of the environment, radioactive pollutants, and by cosmic radiations.
Balance: Apparatus used to measure mass by comparing an unknown mass with known masses.
Balanced Equation: A chemical equation having the same number of atoms and the same net charge on both sides of the arrow.
Band of Stability: An envelope enclosing all stable nuclides when all known nuclides are given locations on a plot of number of neutrons versus number of protons.
Barometer: A device for measuring pressure.
Base: A substance that produces OH- when it is dissolved in water (Arrhenius). A proton acceptor (Brnsted). An electron-pair donor (Lewis).
Base Ionization Constant, Kb: Kb=[BH+][OH-]/[B] for the equilibrium: B + H2O <=> BH+ + OH-.
Base Units: Fundamental units of the SI.
Basic Oxygen Process: A relatively fast method used to convert pig iron into steel.
Basic Solution: An aqueous solution in which [H+] < [OH-].
Battery: One or more galvanic cells arranged to serve as a practical source of electricity.
Becquerel (Bq): The SI unit for activity in nuclear chemistry. 1 Bq = 1 disintegration/sec.
Beta Particle: An electron emitted in radioactive decay. Its symbol is 0-1e.
Beta Radiation: A stream of electrons produced by radioactive decay.
Bidentate Ligand: A ligand that has two atoms that can become simultaneously attached to the same metal ion.
Binary Acid: An acid with the general formula HnX, where X is a nonmetal.
Binary Compound: A compound composed of two different elements (e.g., HCl and Al2O3).
Binding Energy, Nuclear: the energy equivalent of the difference in mass between an atomic nucleus and the sum of the masses of its nucleons.
Blast Furnace: An apparatus that is used to reduce iron ore to metallic iron.
Body-Centered Cubic (bcc) Unit Cell: A cubic unit cell having atoms, molecules, or ions at the corners plus one in the center of the cell.
Boiling Point: The temperature at which the vapor pressure of a liquid is equal to the atmospheric pressure.
Bond Angle: When one atom forms a bond to each of two other atoms, the angle between the two bonds is the bond angle.
Bond Distance: See Bond Length.
Bond Energy: The amount of energy needed to separate two bonded atoms to give electrically neutral particles.
Bond Length: The distance between two nuclei that are joined by a chemical bond.
Bond Order: (number of bonding e- - number anti-bonding e-)/2: the net number of pairs of bonding electrons.
Bonding Molecular Orbital: A MO that gives a buildup of electron density between nuclei and helps stabilize a molecule.
Boyle's Law: See Pressure-Volume Law.
Bragg Equation: n(lambda) = 2dsin(theta). The equation is used to analyze X-ray diffraction data obtained from crystals.
Branched Chain Compound: An organic compound in whose molecules the carbon atoms do not all occur in a continuous sequence.
Branching Step: A step in a chain reaction that produces more free radicals than it consumes.
Breeder Reactor: An atomic reactor in which a fissile isotope is continuously made ("bred") from a fertile isotope.
Brine: An aqueous sodium chloride solution.
Brnsted Acid: A donor of H+.
Brnsted Base: A acceptor of H+.
Brownian Movement: The random, erratic motions of colloidally dispersed particles in a fluid medium and that can be observed by using a microscope.
Buffer: (a) A pair of solutes that, together in water, keep the pH of the solution almost constant despite any addition of acids or bases. (b) A solution containing this pair of salts.

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Calibration: A check on the accuracy and the precision of the stated capacity of a volumetric flask or pipet, or of the stated mass of some weight. Any check on the accuracy and precision of a state value associated with any instrument of measureme nt.
Calorie (cal): The calorie is the energy that will raise the temperature of 1.00 g of water from 14.5 to 15.5 C. The Calorie is 1000 cal (or 1 kilocalorie), and is the term used to describe the energy content of foods. 1 cal = 4.184 J.
Carbohydrate: A substance in animals or plants consisting of a polyhydroxyaldehyde or polyhydroxyketone or molecules that can be hydrolyzed to these.
Carbon Family: Group IVA in the periodic table; carbon, silicon, germanium, tin, and lead.
Carboxylic Acid: A compound having the carboxyl group, -COOH
Carbonyl Group: The carbon-oxygen double bond: -CO
Catalysis: The phenomenon of rate-enhancement brought about by a catalyst.
Catalyst: A substance that in a relatively small proportion will accelerate the rate of a reaction without itself being permanently changed, chemically.
Cathode: The electrode where reduction occurs during an electrochemical change.
Cation: A positive ion.
Cell Potential, Ecell: The emf that can be produced by any particular galvanic cell when no current is drawn from the cell.
Cell Reaction: The overall chemical change that takes place in an electrolytic cell or a galvanic cell.
Celsius Scale: Temperature scale on which water freezes at 0 C and boils at 100C at a pressure of 1 atm.
Centimeter (cm): 0.01 m = 1 cm; 100 cm = 1 m.
Chain Reaction: A self-sustaining reaction in which the products from one event cause on or more new events.
Change of State: Transformation of matter from one state to another, for example, from liquid to solid.
Charles' Law: See Temperature-Volume Law.
Chelate: A complex ion containing rings formed by polydentate ligands.
Chelate Effect: The extra stability found for complexes that contain chelate rings.
Chemical Bond: Force of attraction that holds atoms together in compounds.
Chemical Equation: A before-and-after description of a chemical reaction.
Chemical Property: Property relating to how a substance interacts with others to form new substances.
Chemical Reaction: The interaction of substances causing them to form new substances.
Chemistry: The study of the composition of substances and the way their properties are related to their composition.
Chiral Carbon: A carbon holding four different atoms or groups.
Chirality: The handedness of a molecular structure such that it cannot pass the test of superimposability with the model of the mirror image of this structure.
Cholesteric Liquid Crystals: Rodlike molecules similar in structure to cholesterol arranged in layers in which the parallel rods in one layer are oriented in a different direction that the parallel rods in an adjoining layer.
Codon: An individual unit of hereditary instruction that consists of three amine sidechains, side by side, on an mRNA molecule.
Coefficients: Numbers in front of formulas in a chemical equation.
Coenzyme: A nonprotein, organic substance that forms part of an enzyme.
Coinage Metals: Copper, silver, and gold.
Coke: Coal that has had its volatile components driven off at high temperature. It is mostly carbon.
Colligative Property: A property whose physical value depends only on the ration of the numbers of solute and solvent particles and not on their chemical identities; vapor pressure lowering, boiling point elevation, freezing point depression, osmot ic pressure.
Collision Theory: A theory of reaction rates that posulates that the rate of a reaction is proportional to the number of collisions that occur each second between the reactants.
Colloidal Disperision: A mixture in which the particles of one (or more) substance are smaller than those in suspensions but larger than those in solutions and that have one dimension in the range of 1 to 10 nm.
Colloidal Osmotic Pressure: That part of the osmotic pressure caused by colloids.
Common Ion: An ion that is common to more than one salt. Na+ is the common ion in NaCl and NaNO3.
Common Ion Effect: The solubility of a salt is less in a solution containing one of its ions than it is in pure water.
Complex Ion (or simply a Complex): A substance formed when on e or more anions or neutral molecules become bonded to a metal ion.
Compound: Substance formed from two or more different elements always combined in a fixed ratio.
Compound Nucleus: An atomic nucleus carrying excess energy following the capture of some bombarding particle.
Concentrated Solution: Any solution with a large ratio of the amounts of solute to solvent.
Concentration: The ratio of the quantity of solute to the volume of the solution. See Molar Concentration; Percent Concentration.
Condensation Copolymer: A polymer whose formation involves the splitting out of small molecules from the functional groups of the monomers.
Conformations: The different possible relative orientations of the atoms in a molecule.
Conjugate Acid-Base Pair: Two substances, ions or molecules, whose formulas differ only by one H+. (The acid is the species with this H+ and the base is the species without this H+.)
Conservation of Energy, Law of: The energy of the universe is constant; it can be neither created nor destroyed but only transferred and transformed.
Conservation of Mass-Energy, Law of: The sum of all the mass in the universe and of all the energy, expressed as an equivalent in mass, is a constant.
Contact Process: An industrial synthesis of sulfuric acid from sulfur in which one stage, the oxidation of sulfur dioxide to sulfur trioxide, is catalyzed by contact with vanadium pentoxide.
Conversion Factor: Fraction constructed from a relationship between units; for example, 2.54 cm/1.00 in.
Coordinate Covalent Bond: A covalent bond in which both electrons are contributed by only one of the two joined atoms. Once formed, it is no different than any other covalent bond.
Coordination Compound: A complex ion or its salt.
Coordination Number: The number of donor atoms that surround a metal ion.
Copolymer: A polymer made from two or more different monomers.
Coulomb (C): The SI unit for electrical charge; the charge on 6.25 x 1018 electrons, the amount of charge that passes a fixed point along a wire when a current of 1 A flows for 1 s.
Covalent Bond: A chemical bond formed by the sharing of electrons between two atoms.
Covalent Crystal: A crystal in which lattice positions are occupied by atoms covalently bonded to other atoms at neighboring lattice sites.
Critical Pressure, Pc: The vapor pressure of a substance at its critical temperature.
Critical Temperature Tc: The temperature above which a substance cannot exist as a separate liquid phase, regardless of the pressure.
Crystal Field Splitting, Delta: A theory that considers the effects of the polar or ionic ligands of a complex on the energies of the d orbitals of the central metal ion.
Crystal Field Theory: A theory that considers the effects of the polar or ionic ligands of a complex on the energies of the d orbitals of the central metal ion.
Crystal Lattice: The repeating symmetrical pattern of atoms, molecules, or ions that occurs in a crystal.
Curie (Ci): A unit of activity for radioactive substances. 1 Ci = 3.7 x 1010 disintegrations/sec.
Dalton's Atomic Theory: A theory that matter consists of tiny, indestructible particles called atoms; that all atoms of one element are identical; that atoms of differnt elements have different masses; and that atoms combine in definite ratios b y atoms when they form compounds.
Dalton's Law of Partial Pressures: See Partial Pressures, Law of.
Data: The information (often numbers) obtained in an experiment.
Decimal Multipliers: Factors that modify the size of SI units.
Deliquescence: Absorbtion of moisture by a solid to the extent that the solid dissolves in the absorbed water.
Delocalized Molecular Orbital: A MO that spreads over more than two nuclei.
DeltaG: See Standard Free Energy Change.
DeltaH: See Enthalpy Charge, Standard.
DeltaHfusion: See Molar Heat of Fusion.
DeltaHsublimation: See Molar Heat of Sublimation.
DeltaHvaporization: See Molar Heat of Vaporization.
Denaturation: The loss of biological function by a protein brought about by any action that disorganizes the molecular shape.
Density: An object's mass divided by its volume.
Derived Units: SI units defined in terms of the base units.
Desiccant: A chemical drying agent.
Deuterium: Hydrogen-2; 21H (sometimes 21d); an isotope of hydrogen.
Deuterium Isotope Effect: The reduction in the rate of a reaction caused by the substitution of a deuterium atom for a hydrogen atom at a molecular site undergoing the reaction.
Dialysis: The passage of small molecules and ions through a semipermeable membrane, one that prevents the passage of large molecules or ions in the colloidal state.
Diatomic: A molecule is diatomic if it is composed of two atoms (e.g., N2, HCL).
Diffraction: Constructive and destructive interference by waves.
Diffraction Pattern: The image formed on a screen or on film by diffraction of visible light or X rays.
Dilute Solution: Any solution with a small ratio of the quantities of solute to solvent.
Dipeptide: A dimer of two alpha-amino acids joined by a peptide bond.
Dipole: A molecule having partial positive and negative charges separated by a distance.
Dipole Moment: The product of the partial charge on either end of a dipole multiplied by the distance between the partial charges. It is a measure of the extent of polarity of a molecule.
Dipole-Dipole Attractions: Attractions between molecules that are dipoles.
Diprotic Acid: An acid that can furnish two H+ per molecule.
Disaccharide: A carbohydrate whose molecules can be hydrolyzed to two monosaccharides.
Disproportionation: A redox reaction in which a portion of a substance is oxidized while the rest is reduced. The same species undergoes both oxidation and reduction.
DNA: Deoxyribonucleic acid; nucleic acid that, when hydrolyzed, gives deoxyribose, phosphate ion, and chiefly four heterocyclic amines--adenine, thymine, guanine, and cytosine; the carrier of the genetic messages of an organism.
Double Bond: A covalent bond in which two pairs of electrons are shared.
Double Replacement Reaction (Metathesis Reaction): A reaction between two salts in which cations and anions exchange partners, for example AgNO3 + NaCl => AgCl + NaNO3.
Double Salt: Crystals that contain the components of two different salts in a definite ratio.
Ductility: A metal's ability to be drawn (stretched) into wire.
Dynamic Equilibrium: An equilibrium in which two opposing processes are occurring at equal rates.

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Effusion: The movement of a gas through a very tiny opening into a region of lower pressure.
Effusion, Law of (Graham's Law): The rate of effusion of a gas is inversely proportional to the square root of its density when the pressure and temperature are constant.
Einstein Equation: DeltaE = Deltamc2 where DeltaE is the energy obtained when a quantity of mass, Deltam, is destroyed, or the energy lost when this quantity of mass is created.
Elastomer: A polymer with elastic properties.
Electrochemical Change: A chemical change that is caused by or that produces electricity.
Electrochemistry: The study of electrochemical changes.
Electrolysis: A chemical change caused by the passage of electricity through a molten ionic compound or through a solution that contains ions.
Electrolysis Cell: An electrolysis apparatus.
Electrolyte: A compound that either in the molten state or in solution conducts electricity.
Electrolytic Cell: An electrolysis apparatus.
Electromagnetic Energy: The energy transmitted by wave-like oscillations in the strengths of electrical and magnetic fields; light energy.
Electromagnetic Radiation: The successive series of oscillations in the strengths of electrical and magnetic fields associated with ligh, microwaves, gamma rays, and the like.
Electromagnetic Spectrum: The distribution of frequencies of electromagnetic radiation among various classifications such as microwave, infrared, visible, ultraviolet, X-ray, and gamma-ray bands of radiation.
Electromotive Force (emf): The voltage produced by a galvanic cell.
Electron: A subatomic particle with a charge of 1- and a mass of 0.0005486 amu (9.109534 x 10-28g) that occurs outside the nucleus. The particle that moves when an electric current flows. Its symbol is e- in discussions of chemical changes or 0-1e in discussions of nuclear changes.
Electron Affinity (EA): The energy change that occurs when an electron is added to an isolated gaseous atom or ion (usually expressed in kJ/mol).
Electron Capture: A nuclear reaction in which a nucleus captures an orbital electrons that changes a nuclear proton into a neutron.
Electron Cloud: Because of its wave properties, the electron is spread out like a cloud around the nucleus.
Electron Configuration: The distribution of electrons in an atom's orbitals.
Electron Density: The concentration of the electron's charge within a given volume.
Electron Spin: A property that the electron appears to have because it behaves like a tiny magnet.
Electronegativity: The relative attraction that an atom has for the electrons in a bond.
Electronic Structure: The distribution of electrons in an atom's orbitals.
Electron-Pair Bond: A covalent bond.
Electron Volt (eV): The energy an electron receives when it is accelerated under the influece of 1 V; eV = 1.6 x 10-19J.
Electroplating: Depositing a thin metallic coating on an object by electrolysis.
Element: Simplest substance ever obtained in a chemical reaction.
Elementary Process: One of the individual steps in a reaction mechanism.
Empirical Facts: Facts discovered by performing experiments.
Empirical Formula: A chemical formula in which the subscripts are the smallest whole numbers that will express the proportions of the atoms of the different elements present.
Emulsifying Agent: Any substance that stabilizes an emulsion.
Emulsion: A colloidal dispersion of one liquid in another.
Enantiomers: Stereoisomers whose molecular structures are related as an object to its mirror image and that cannot be superimposed.
End Point: The step in a titration when the indicator changes color and the titration is ended.
Endergonic: A change that occurs with a free energy increase.
Endothermic: Descriptive of a change in which energy leaves the surroundings and enters a system.
Energy: Something that matter possesses if it is able to do work.
Energy Level: A particular energy that an electron can have in an atom or molecule.
Energy Source: Any natural change or any material that can be induced to undergo a change that people can use to make their own tasks easier.
Enthalpy, H: The heat content of a system.
Enthalpy Change, Standard, DeltaH: The heat of reaction at constant pressure measured under standard conditions (25 C and 760 torr).
Enthalpy of Solution: The enthalpy change accompanying the formation of a solution when a solute dissolves in a solvent.
Entropy: The thermodynamic quantity that describes the degree of randomness of a system. The greater the disorder or randomness, the higher is the statistical probablility of the state snad the higher is the entropy.
Enzyme: A catalyst in a living organism; a protein that catalyzes biochemical reactions.
Enzyme-Substrate Complex: A molecular association of enzyme and substrate molecules that forms as the enzyme catalyzes a reation of the substrate.
Equation, Thermochemical: A balanced chemical equation accompanied by the value of DeltaH for the mole quantities actually given by the coefficients.
Equilibrium Constant: The value that th emass action expression has when a chemical system is at equilibrium.
Equilibrium Law: An equation that sets the mass action expression equal to the equilibrium constant.
Equilibrium Vapor Pressure: The pressure exerted by a vapor in equilibrium with its liquid.
Equilibrium Vapor Pressure of a Solid: The pressure exerted by a vapor that is in dynamic equilibrium with a solid.
Equivalence Point: The point in a titration when the number of equivalents of one reactant (e.g., an acid) equals the number of equivalents of a second reactant (e.g., a base).
Equivalent (Eq): The grams of an acid that provide 1 mole of H+ or the grams of a base that neutralize 1 mole of H+. In a redox reaction, one equivalent of reducing agent loses 1 mole of electrons, and one equivalent of oxidiz ing agen gains 1 mole of electrons.
Equivalent Weight: If an acid, the mass that provides one mole of H+. If a base, the mass that neutralizes one mole of H+. In a redox reaction, the mass of reactant that either gains or loses 1 mole of electrons.
Ester Group: A compound with the carbonyl-oxygen-carbon group: -COOC-
Ether: An organic compound with two hydrocarbon groups attached to one oxygen atom.
Exact Numbers: Numbers that come from a direct count or that result from definitions. They have an infinite number of significant figures.
Exergonic: A change that occurs with a free energy decrease.
Exothermic: Descriptive of a change in which energy leaves a system and enters the surroundings.
Exponential Notation: See Scientific Notation.
Face-Centered Cubic (fcc) Unit Cell: A cubic unit cell having atoms, molecules, or ions at the corners and in the center of each face.
Factor-Label Method: Problem-solving method that uses the cancellation of units to aid in settin up the proper arithmetic in a problem.
Fahrenheit Scale: Temperature scale on which water freezes at 32 F and boils at 212 F.
Family of Elements: See Group.
Faraday (F): One mole of electrons; 96,500 coulombs.
Fatty Acid: One of several long-chain carboxylic acids produced by the hydrolysis of a lipid.
Fertile Isotope: An isotope that can be converted by nuclear reactions into a fissile isotope.
Filler: A substance added during polymerization or casting to prevent shrinkage of the substance a s the polymer forms or takes its shape.
First Law of Thermodynamics: A formal statement of the law of conservation of energy--the basis for Hess's law.
Fissile Isotope: An isotope capable of undergoing fission following neutron capture.
Fission: The breaking apart of atomic nuclei and the source of energy in nuclear reactors.
Flame Test: Using the color produced by an ion such as sodium when the ion is introduced into a flame. Sodium gives a yellow color.
Flotation: A method for concentrating sulfid ores of copper and lead. Air is bubbled through a slurry of oil coated ore particles, which stick to rising air bubbles and collect in the foam at the surface.
Fluid: Any material whose shape adjusts spontaneously and rather quickly to the shape of its container. (Both ordinary liquids and gases are fluids.)
Force: Anything that will cause an object to change its motion or direction.
Formula: Shorthand way of representing the composition of a substance using chemical symbols.
Formula Unit: A particle having the composition given by the chemical formula.
Formula Weight: The sum of the atomic weights of all the atoms represented in the chemical formula of a compound (or element).
Fossil Fuels: Coal, oil, and natural gas.
Free Energy: See Gibbs Free Energy.
Free Radical: An extremely reactive chemical species that contains an unpaired electron.
Frequency, v: The number of cycles per second of electromagnetic radiation.
Functional Group: A small part of an organic molecule or organic ion that enters into a set of charactoristic reactions.
Fusion: The formation of atomic nuclei by the fusing together of the nuclei of lighter isotopes.
Galvanic Cell: An electrochemical cell in which a spontaneous redox reaction produces electricity.
Galvanizing: Coating a steel object with zinc.
Gamma Radiation: A stream of very high energy photons emitted from atomic nuclei when they undergo energy transitions from higher nuclear energy levels to lower ones.
Gangue: The unwanted rock and sand that is separated from an ore.
Gas Constant, Universal (R): R = 0.0821 liter atm/mol K = PV/nT.
Gas Law, Combined: For a given mass of gas, the product of its pressure and volume divided by its Kelvin temperature is a constant. P1V1/T1 = P2V2/T2
Gay-Lussac's Law: See Pressure-Temperature Law.
Generalization: Summary statement of behavior based on data collected in experiments.
Geometric Isomers: Isomers in which the atoms are arranged in different relative orientations. Among organic compounds, they are isonmers with differences in the directions or geometries with which groups ping at a double bond or at the carbons of a ring.
Gibbs Free Energy, G: A thermodynamic quantity that relates energy (enthalpy, H) and entropy, S. G = H - TS.
Graham's Law: See Effusion, Law of
Gram (g): 1 g = 0.001 kg.
Gray (Gy): The SI unit of radiation-absorbed-dose. 1 Gy = 1 J/kg.
Ground State: Lowest energy state of an atom or molecule
Group: Vertical column of elements in the periodic table.

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Haber Process: The industrial synthesis of ammonia from nitrogen and hydrogen under pressure and heat in the presence of a catalyst.
Half-Cell: That part of a galvanic cell in which either oxidation or reduction takes place.
Half-Life, t1/2: The time required for a reactant concentration or the mass of a radionnuclide to be reduced by half.
Half-Reaction: An individual oxidation or reduction reaction that include the correct formulas for all species taking part in the reaction; for example, 2H2O(l) => O2(g) + 4H+(aq) + 4e-.
Halogen Family: Group VIIA in the periodic table; fluorine, chlorine, bromine, iodine, and astatine.
Hard Water: Water with dissolved Mg2+, Ca2+, Fe2+, or Fe3+ ions at a concentration (above 25 mg/liter) high enough to interfere with the use of soap.
Heat Capacity: The quantity of heat needed to raise the temperature of an object by 1 C. Its units are cal/C or J/C, where C = the change in temperature.
Heat of Combustion, Standard, DeltaHcombustion: The enthalpy of combustion for 1 mole of a compound under standard conditions.
Heat of Formation, Standard, DeltaHf: The enthalpy change for the formation of 1 mole of a compound from its elements, all in their standard states.
Heat of Reaction, Standard, DeltaH: The value of DeltaH for a reaction conducted so as to maintain the pressure at 1 atm and the temperature at 25 C.
Henderson-Hasselbalch Equation: pH = pKa + log ([anion]/[acid]).
Henry's Law: See Pressure-Solubility Law.
Hertz (Hz): 1 Hz = 1 cycle/second; the SI unit of frequency.
Hess Law Equation: For the change: aA + bB + ... => nN + mM + ..., DeltaH = [nDeltaHf(N) + mDeltaHf(M) + ...] - [aDeltaHf(A) + bDeltaHf(B) + ...].
Heterocyclic Compound: An organic ring compound in which one (or more) or the ring atoms is from a nonmetal other than carbon.
Heterogeneous: Two or more phases with different properties.
Heterogeneous Catalyst: A catalyst that is in a different phase than the reactants. The reactants are adsorbed on the the catalytic surface where the reaaction occurs.
Heterogeneous Reaction: A reaction in which all of the reactants and products are in the same phase.
Hund's Rule: The lowest energy electron configuration results when electrons that occupy orbitals of equal energy are spread out over the orbitals as much as possible with spins unpaired.
Hybrid Atomic Orbitals: Orbitals formed by mixing the basic atomic orbitals of an atom. They are more effective at overlap than ordinary atomic orbitals.
Hydrate: A compound holding molecules of water usually in a stoichiometric ratio.
Hydration: The development of a solvent cage of water molecules about polar molecules or ions disolved in water.
Hydride: (1) A binary compound of hydrogen. (2) A compound containing the H- (hydride) ion.
Hydrocarbon: A compound whose molecules consists entirely of carbon and hydrogen.
Hydrogen Bond: An extra strong dipole-dipole attraction that occurs between molecules in which hydrogen is covalently bonded to nitrogen, oxygen, or fluorine.
Hydrogen Electrode: The standard of comparison for reduction portentials, 2H+(aq) + 2e- <=> H2(g), EH+ = 0.00 V at 25 C, 1 atm, and 1 M H +.
Hydrolysis of Salts: The reaction of a salt with water to affect the pH of the solution.
Hydronium Ion: H3O+.
Hydrophilic Group: Any polar organic group that cannot be involved in hydrogen bonds with water.
Hypertonic Solution: A solution whose osmotic pressure is greater than a reference solution.
Hypothesis: Tenetative explanation of the results of experiments.
Hypotonic Solution: A solution whose osmotic pressure is less than a reference solution.
Ideal Gas: A hypothetical gas that obeys the gas laws exactly.
Ideal Gas Law: PV = nRT.
Ideal Solution: The hypothetical solution that would obey the vapor pressure-concentration law (Raoult's law) exactly.
Induced Dipole: A dipole created when the electron cloud of an atom or a molecule is distorted by a neighboring dipole or by an ion.
Inert Gases: The noble gases.
Initiation Step: The first step in a chain reaction in which a reactant molecule is converted to one or more free radicals.
Initiator: A substance that, like a catalyst, promotes a reaction, but is used up during the reaction.
Inner Transition Elements: The two long rows of elements below the main body of the periodic table. They include elements 58-71 and 90-103.
Instantaneous Dipole: A momentary dipole caused by the erratic movement of electrons.
Intermolecular Attractions: Attractions between neighboring molecules.
Inverse Square Law: In the science of atomic radiations, the relationship between radiation intensity and distance: radiation intensity is proportional to 1/d2.
Ion: An electrically charged particle.
Ion Product: A product of ion concentrations, each of which is raised to a power that is equal to the number of ions of that kind obtained from one formula unit of the salt. The mass action expression for a solubility equilibrium.
Ion-Electron Method: A method for balancing redox reactions that uses half-reactions.
Ionic Bond: The attractions between ions that hold them together in ionic compounds.
Ionic Compound:A compound composed of positive and negative ions.
Ionic Crystal: A crystal that has ions located at the lattice points.
Ionization Energy (IE): The energy needed to remove an electron from an isolated gaseous atom, ion, or molecule (usually expressed in units of kJ/mol).
Ionizing Radiation: Radiation arising from radioactivity or other nuclear reactions that generates ions as it passes through matter.
Ion-Product Constant of Water: [H+][OH-] = Kw.
Isomer: ONe of a set of compounds having identical molecular formulas but different structures.
Isomerism: The phenomenonof the existence of sets of compounds having the same moelcular formular but different structures.
Isotonic Solution: A solution whose concentration is such that it has the same osmotic pressure as a reference solution.
Isotope Dilution Analysis: An analytic technique for measuring volumes by studying the extent to which the specific activity of a sample of radioactive material is reduced by its being biluted into the larger volume.
Isotopes: Atoms of the same element having different mass numbers caused by differences in their numbers of neutrons.
IUPAC Rules: The formal rules for naming compounds as developed by the International Union of Pure and Applied Chemisty.
Joule (J): The SI unit of energy. 1 J = 1 kg m2/s2; 4.184 J = 1 cal.
Ka: See Acid Ionization Constant.
Kb: See Base Ionization Constant.
Kw: See Ion-Product Constant of Water.
Kelvin Scale: Absolute temperature scale having degree units called kelvins (K). Degree size is the same as the Celsius degree. K = C + 273.15.
Ketone: An organic compound with the -CCC- with an O double bonded to the middle C group.
Kilogram (kg): 1 kg = 1000 g; the base unit for mass in the SI.
Kinetic Energy: Energy of motion: KE = 1/2mv2
Kinetic Theory of Gases: A set of postulates about gases used to explain the gas laws. A gas consists of an extremely large number of very tiny, hard particles in constant random motion. They have negligible volume and, between collisions, they mov e in straight lines.
Lanthanide Contraction: The decrease in siz experienced by elements 58-71 that causes the elements that follow the lanthanides to have unusually small sizes.
Lanthanide Elements: Elements 58-71.
Lattice Energy: Energy released by the imaginary process in which isolated ions come together to form a crystal of an ionic compound.
Law: Statement of behavior based on the results of many experiments. Laws do not offer explanations of behavior.
Law of Conservation of Mas: Mass is neither gained nor lost in a chemical change; mass is conserved.
Law of Constant Heat Summation (Hess's Law): For any reaction that can be written in steps, the standard heat of reaction is the sum of the standard heats of reaction for the steps.
Law of Definite Proportions: In a given chemical compound, the elements are always combined in the same proportion by mass.
Law of Multiple Proportions: Whenever two elements form more than one compound, the different masses of one that combines with the same mass of the other are in the ratio of small whole numbers.
Le Chtelier's Principle:
Lewis Acid: An electron-pair acceptor.
Lewis Base: An electron-pair donor.
Lewis Structure: Also called Lewis formula. A structural formula drawn with Lewis symbols that shows the valence electrons using dots and dashes.
Lewis Symbol: The symbol of an element surrounded by dots that represent the valence electrons of an atom of that element.
Ligand: A molecule or anion that can bind to a metal ion to form a complex.
Lipid: Any substance found in plants or animals that can be dissolved in nonpolar solvents.
Liquid Crystal: A substance that is able to flow like a liquid but that has some physical properties normally associated with crystals.
Liter: 1 liter = 1 dm3 = 1000 cm3 = 1000 ml.
London Forces: Weak attractive forces caused by instantaneous dipole-induced dipole attractions.
Lone Pair: A pair of electrons in the valence shell of an atom that is not shared with another atom. an unshared pair of electrons.

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M-O

Macromolecule: A molecule with hundreds to thousands of atoms such as found in polymers.
Magic Numbers: In nuclear chemistry, the numbers 2, 8, 20, 50, 82, and 126, and whose significance is that nuclides are expected to be particularly stable when the number of protons or neutrons (and especially both) equals on of these numbers.
Magnetic Quantum Number: m, which can have integer values from -l to +l.
Malleability: A metal's ability to be hammered or rolled into thin sheets.
Manganese Nodules: Lumps the size of an orange that contain large concentrations of manganese and iron. They are found on the ocean floor.
Mass: A measure of the amount of matter that there is in a given sample.
Mass Action Expression: A fraction in which the numerator is the product of the molar concentrations of the producets raised to powers equal to their coefficients and the denominator is the product of the molar concentrations of the reactants raise d to powers equal to their coefficients. For gaseous reactions, parital pressures can be used in place of molar concentrations.
Mass Number: The numerical sum of the protons and neutrons in an atom of a given isotope.
Matter: Anything that has mass and occupies space.
Mechanism: The series of individual steps in a chemical reaction that gives the net overall change.
Metallic Crystal: A solid having positive ions at the lattice positions that are attracted to a "sea of electrons" that extends throughout the entire crystal.
Metalloids: Elements with properties that lie between those of metals and nonmetals. They are located around the diagonal line running from boron (B) to astatine (At) in the periodic table.
Metallurgy: The science and technology of metals; it is concerned with the procedures and chemical reactions that are used to separate metals from their ores and make them ready for pratical uses.
Metathesis Reaction: See Double Replacement Reaction.
Meter (m): SI base unit for length.
Metric System: A decimal system of units.
Milliliter (ml): 0.001 liter = 1 ml; 1000 ml = 1 liter.
Millimeter (mm): 0.001 m = 1 mm; 1000 mm = 1 m.
Millimeter of Mercury (mm Hg): A unit of presure equal to 1/760 atm. 760 mm Hg = 1 atm.
Mineral: A specific solid in the earth's crust having a more or less definite chemical formula.
Mixture: Any matter consisting of two or more substances physically combined in no particular proportion by mass.
Model, Scientific: A picture or a mental construction derived from a set of ideas and assumptions that we imagine to be true because they enable us to explain certain observations and measurements (e.g., the model of an ideal gass; Bohr's atomic mo del).
Molal Concentration (m): The number of moles of solute in 1000 g of solvent; the molality of a solution.
Molality: See Molal Concentration.
Molar Concentration (M): The number of moles of solute per liter of solution.
Molar Heat of Fusion: Heat absorbed when 1 mol of a solid melts to give 1 mol of liquid at constant temperature and pressure.
Molar Heat of Sublimation: Heat absorbed when 1 mol of solid sublimes to give 1 mol of vapor at constant temperature and pressure.
Molar Heat of Vaporization: Heat absorbed when 1 mol of liquid is converted to 1 mol of vapor at constant tmemperature and pressure.
Molar Mass: The number of grams per mole of a compound or element.
Molar Solubility: The number of moles of solute required to give 1 liter of a saturated solution of the solute.
Molar Volume, Standard: The volume of 1 mol of gas at STP; 22.4 liter/mol.
Molarity: See Molar Concentration.
Mole (mol): The SI unit for amount of substance; the formula weight in grams; a quantity of chemical substance containing 6.02 x 1023 formula units.
Mole Fraction: The ratio of the number of moles of one component of a mixture to the total number of moles of all components.
Mole Percent: The mole fraction of a component expressed as a percent.
Molecular Crystal: A crystal that has molecules or individual atoms at the lattice points.
Molecular Equation: A chemical equation giving the full formulas of all the reactants and products that will be involved in an actual experiment.
Molecular Formula: A chemical formula that gives the actual composition of one molecule.
Molecular Orbital Theory: Theory of covalent bonding that views a molecule as a collection of positive nuclei surrounded by electrons distributed among a set of bonding and antibonding molecular orbitals of different energies.
Molecular Orbitals: Orbitals that extend over two or more atomic nuclei.
Molecular Weight: See Formula Weight.
Molecule: A neutral particle composed of two or more atoms.
Monodentate Ligand: A ligand that can attach itself to a metal ion by only one atom.
Monomer: A substance of low formula weight used to make a polymer.
Monoprotic Acid: An acid that can furnish one H+ per molecule.
Monosaccharide: A carbohydrate that cannot be hydrolyzed.
Nematic Liquid Crystal: Composed of long, rodlike molecules packed like short pieces of uncooked spaghetti.
Nernst Equation: Ecell = Ecell - 0.0592/n x log Q.
Net Ionic Equation: A chemical equation having no spectator ions or molecules and that satisfies both a material and an electrical balance.
Neutral Solution: A solution in which [H+] = [OH-].
Neutralization, Acid-Base: The destruction of an acid by a base or of a base by an acid.
Neutron: A subatomic particle with a charge of zero and a mass of 1.008665 amu (1.674954 x 10-24 g) that exists in all atomic nuclei except those of the hydrogen-1 isotope, its symbol is n or 10n in nu clear equations.
Neutron Activation Analysis: A technique for analyzinag for trace impurities by rendering them radioactive through neutron bombardment and then studying the frequencies and intensities of the gamma radiations they emit.
Neutron Emission: A nuclear reaction in which a neutron is ejected.
Nitrogen Family: Gourp VA in the periodic table; nitrogen, phosphorus, arsenic, antimony, and bismuth.
Nitrogen Fixation: The conversion of atmospheric nitrogen into chemical forms used by plants and accomplished soil microorganisms with the assistance of plants.
Noble Gases: Elements of group 0 in the periodic table; helium, neon, argon, krypton, xenon, radon.
Node: A place where the amplitude or intensity of a wave is zero.
Nonelectrolyte: A compound that in its molten state or in solution will not conduct electricity.
Nonstoichiometric Compound: A substance in which the elements are combined in a not quite whole number ratio by moles.
Nonvolatile: Describing a substance with a high boiling point, a low vapor pressure, and that does not evaporate.
Normal Boiling Point: The temperature at which the vapor pressure of a liquid equals 1 atm.
Normality (N): The number of equivalents per liter of an acid or a base or other reactant.
Nuclear Equation: A shorthand expression of a nuclear reaction that is balanced when the sums of the atomic numbers on either side of the arrow are equal and the sums of the mass numbers are equal.
Nucleic Acids: Polymers in plants and animals that are involved in the chemistry of heredity and whose molecules when hydrolyzed, give a sugar unit, a phospate ion, and a set of four or five nitrogen-containing, basic hetercyclic compounds.
Nucleon: A general name for protons or neutrons.
Nucleus: The hard, dense core at the center of an atom that contains all of the atom's protons and neutrons.
Octet Rule: An atom tends to gain or lose electrons its outer shell consists of eight electrons.
Odd-Even Rule: In nuclear chemistry, a rule that says when the numbers of protons and neutrons in a nucleus are both even, the isotope is far more likely to be stable that when both even, the isotope is far more likely to be stable that when both n umbers are odd.
Open Hearth Furnace: A furnace used to convert pig iron into steel.
Optical Isomers: Stereo isomers other that geometric isomers.
Orbital: A particular electron waveform with a particluar energy. In an atom, each orbital has s pecific set of values for (n), (l), and (m).
Orbital Diagram: A diagram showing an atom's orbitals in which the electrons are represented by arrows to indicate paired and unpaired spins.
Order (of Reaction): The sum of the exponents in the rate law is the overall order of the reaction. Each exponent gives the order with respect to a specific reactant.
Ore: A mineral that can be extracted from the earth's crust and processed at a profit.
Organic Compound: Any compound of carbon other that a carbonate, bicarbonate, cyanide, cyanate, carbide or gaseous oxide.
Osmolality: The molal concentration of all particles of solutes--molecules or separated ions--that contribute to the osmotic pressure of a solution.
Osmolarity: The molar concentration of all particles of solutes--molecules or separated ions--that contribute to the osmotic pressure of a solution.
Osmosis: The passage of solbent molecules, but not those of solutes, through a semipermeable membrane; the limiting case of dialysis.
Ostwald Process: An industrial synthesis of nitric acid from ammonia.
Overlap: A portion of two orbitals from different atoms sharing the same space.
Oxidation: Loss os electrons; increase in oxidation number.
Oxidation Number: The charge an atom in a compound would have if all of the electrons in the bonds belonged entirely to the more electronegative atoms.
Oxidation State: Means the same as oxidation number.
Oxidation-Reduction Reaction: A reaction involving the transfer of electrons from one species to another.
Oxidizing Agent: Substance that causes oxidation; it is reduced
Oxoacid: An acid containing hydrogen, oxygen, and another element. (e.g., HNO3, H3PO4, H2SO4).
Oxygen Family: Group VIA in the periodic table: oxygen, sulfur, selenium, tellurium and polonium.

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P-R

Paramagnetism: Weak magnetism that a substance has when it contains unpaired electrons.
Partial Charge: Charges at opposite ends of a dipole that are less than 1 + or 1 - charges.
Partial Pressure: The pressure contributed by an individual gas in a mixture of gases.
Partial Pressures, Law of (Dalton's Law of Partial Pressures):The total pressure of a mixture of gases equals the sum of their partial pressures. Pt = Pa + Pb + Pc + . . .
Pascal (Pa): The SI unit of pressure; 133.3224 Pa = 1 torr.
Pauli Exclusion Principle: No two electrons in the same atom can have the same values for all four of their quantum numbers.
Peptide Bond: The amide linkage in protein chemistry: -CON-
Percent Concentration:

Weight/weight (w/w)

The grams of solute in 100g of solution

Volume/volume (v/v)

The number of volumes of solute in 100 v of solution.

Weight/volume (w/v)

The grams of solute in 100 ml of solution.

Milligram percent (mg %)

The milligrams of solute in 100 ml of solution.

Percentage by Weight: The number of grams iof an element combined in 100 g of a compound.
Percentage Compostion: A complete list of the percentages by weight of a compounds elements.
Period: Horizontal row of elements in the periodic table.
Peroxide: A compound whose molecules have two oxygen atoms joined by a single bond.
pH: pH = -log [H+].
Phase: A homogeneous region within a sample.
Phase Diagram: A pressure-temperature graph on which are plotted temperatures and pressures at which equilibrium exists between the states of a substance. It defined T - P regions in which the solid, liquid and gaseous states of the substance can exist.
Photon: "Packet" of energy in electromagnetic radiation; its energy, E = h(nu) where nu is the frequency and h is Planck's constant.
Photosynthesis: The use of solar energy by a plant to synthesize high-energy molecules from simpler, low-energy molecules of CO2 and H2O. The primary products are carbohydrates. The plant's chlorophyll is the solar energy ab osorber.
Physical Property: Property that can be specified without reference to another substance, for example, color or volume.
Pi Bond (pi Bond): A bond formed by the sideways overlap of a pair of p orbitals. Electron density is concentrated in two separate regions that lie on opposite sides of the imaginary line joining the nuclei.
Pig Iron: The impure iron that comes from the blast furnace.
pKa: pKa = -log Ka.
pKb: pKb = -log Kb.
Plastic: A finished or semifinished article made by molding, casting, extruding, drawing, or laminating a resin.
Plasticizer: An oily organic material added to a resin to reduce hardness and brittleness in the final plastic article.
pOH: pOH = -log [OH-].
Polar Covalent Bond (Polar Bond): A covalent bond in which more that half of the bon's negativ charge is concentrated around one of the two atoms.
Polyatomic Ion: An ion composed of two or more atoms.
Poludentate Ligand: A ligand that has two or more atoms that can become simutaneously attached to a metal ion.
Polymer: A substance consisting of macromulecules having repeating structural units.
Polymerization: A chemical reaction that converts a monomer into a polymer.
Polyolefin: A polymer of any member of the alkene ("olefin") family.
Polypeptide: A polymer of alpha-amino acids that makes up all or most of a protein.
Polyprotic Acid: An acid that can furnish more that one H+ per molecule.
Polysaccharide: A carbohydrate whose molecules can by hydrolyzed to hundreds of monosaccharide molecules.
Positron: A positively charged particle with the mass of an electron. Its symbol if 01p.
Post-Transition Metal: A metal that occurs in the periodic table immediately
Potential Energy: Stored energy
Precipitate: A solid that separates from a solution usually as the result of a chemical reaction.
Precipitation: In chemistry, the formation of a solid that separates from a solution usually as the result of a chemical reaction.
Precision: How reproducible measurements are.
Pressure-Solubility Law (Henry's Law): The concentration of a gas dissolved in a liquid at any given temperature is directly proportional to the partial pressure of that gas on the solution.
Pressure-Temperature Law (Gay-Lussac's Law): The pressure of a given mass of gas is directly proportional to its Kelvin temperature if the volume is kept constant. P1/T1 = P2/T2
Pressure-Volume Law (Boyle's Law): The volume of a given mass of gas is inversely proportional to its pressure (at constant temperature.) P1V1 = P2V2.
Principal Quantum Number: n, which can have values of 1, 2, 3, . . . , infinity.
Products: Substances whose formulas appear on the right side of the arrow in a chemical equation. The substances produced in a chemical reaction.
Propagation Step: A step in a chain reaction in which a free radical reacts with a reactant molecule to give a product molecule and another free radical.
Property: A characteristic of matter.
Protein: A macromolecular substance found in nature consisting wholly or mostly of one or more polypeptides often combined with an organic molecule and sometimes also combined with a metal ion.
Proton: (1) A subatomic particle with a charge of 1 + and a mass of 1.007276 amu (1.672649 x 10-24 g) that exists in a atomic nuclei. (2) The name often used for the hydrogen ion and symbolized as H+ in acid-base discussions a nd either 11p or 11H in discussions of tranmutations.
Pure Substance: Element or compound.
Quantized Energy: Discrete amount of energy.
Quantun: The energy of one photon.
Quantum Mechanics: See Wave Mechanics.
Quantum Number: A number realted to the energy, shape, or orientation of an orbital. Also, a number related to the spin of the electron.
R: See Gas Constant, Universal.
Rad (rd): A unit of radiation-absorbed-dose. 1 rd = 10-5 J/g = 10-2 Gy.
Radioactive Decay: The change of a nucleus into another nucleus (or a more stable form) by the loss of an alpha or beta particle or a gamma ray photon.
Radioactive Disintegration Series: A sequence of nuclear reactions beginning with an unstable actinide and eding with a stable isotope of lower atomic number.
Radioactivity: The emission of one or more kinds of radioation from an isotope with unstable nuclei.
Radiological Dating: A technique for measuring the age of some geologic formation or ancient artifact by measuring the ratio of the concentrations of two isotopes, once radioactive and the other a stable decay product.
Radionuclide: A radioactive isotope.
Raoult's Law: See Vapor Pressure-Concentration Law.
Rare Earth Metals: The lathanides.
Rate: A ration in which units of time appear in the denominator, for example, 40 miles/hr or 3.0 mol/liter/s.
Rate Constant: The proportionality constant in the rate law; the rate of reaction when all reactant concentrations are 1 M.
Rate of Reaction: How quickly the reactants disappear and the products form, expressed in units of mol liter-1 s-1.
Rate Law: An equation that relates the rate of a reaction to the molar concentrations of the reactants raised to powers.
Rate-Determining Step (Rate Limiting Step): The slow step in a reaction mechanism.
Reactant LimitingThe reactant in a given reaction that is present in a deficient quantity according to the stoichiometry of the reaction.
Reactants: Substances whose formulas appear on the left side of the arrow in a chemical equation. The substances brought together to react.
Reaction Quotient: See Mass Action Expression.
Reagent: Any chemical, mixture of chemicals, or solution of chemicals used as part of an experimental reaction.
Redox Reaction: Oxidation-reduction reaction.
Reducing Agent: Substance that causes reduction; it is oxidized.
Reduction: Gain of electrons; decrease in oxidation number.
Reduction Potential: A measure of the tendency of a given half-reaction to occur as a reduction.
Rem: A dose in rads multiplied by a factor that takes into accoun the variations that different radiations have in their damage-causing abilities in tissue.
Replication: In nucleic acid chemistry, the reporductive duplication of DNA double helixes prior to cell division.
Representative Element: An element in one of the A-groups in the peridic table.
Resin: A raw, unfabricated polymer used to make all or most of a plastic article.
Resonance: A concept in which the actual Lewis structure of a molecule of polyatomic ion is represented as a composite or average of two or more resonance structures. The individual resonance structures themselves do not actually exist.
Resonance Hybrid: The actual structure of a molecule or polyatomic ion that is represented by two or more resonance structures.
Reversible Process: A process that occurs by an infinite number of steps during which the driving force for the change is just barely greater that the force that resists the change.
Ring Compound: A compound whose molecules include closed-chain sequences of atoms.
RNA: Ribonucleic acid; nucleic acid thatm when hydrolyzed, gives ribose, phosphate ion, and chiefly four hetercyclic amines--adenine, uracil, guanine, and cytosine. Varieties include:

mRNA

or messenger RNA made at the direction of DNA; and the carrier of genetic message (as a series of codons) from the cell nucleus to the assembly site for making polypeptides.

tRNA

or transfer RNA--amino acid carrier RNA.

Roasting: Heating an ore in air, which converts sulfides to oxides.
Rock: A complex mixture of minerals.

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S-T

Salt Bridge: A tube containing an electrolyte that connects the two half-cells of a galvanic cells.
Saturated Organic Compound: Any organic compound having only single bonds.
Saturated Solution: A solution in which there is an equilibrium between the dissolved and undissolved states of the solute.
Scientific Method: Observation, explanation, and testing of an explanation by additional experiments.
Scientific Notation: Numbers represented as a decimal number between 1 and 10 multiplied by 10 raised to a power; for example, 6.02 x 1023
Second Law of Thermodynamics: Whenever a spontaneous event takes place it is accompanied by an increase in the entropy of the universe.
Secondary Quantum Number: l, which can have values of 0, 1, . . . , (n - 1).
Semiconductor: A substance that conducts electricity weakly.
Shell: All orbitals of a given n.
Sigma Bond (Sigma Bond): A bond formed by the "head-to-head" overlap of two orbitals. The electron density is concentrated along the imaginary line joining the two nuclei.
Significant Figures: In a measured quantity, the number of digits known for sure plus the first one that is uncertain.
Simple Cubic Unit Cell: A cubic unit cell with atoms, molecules, or ions only at the corners.
Single Bond: A covalent bond in which a single pair of electrons are shared.
Slag: A relatively low melting mixture of impurities that forms in the blast furnace and other furnaces used in refining metals.
Smectic Liquid Crystals: Rodlike molecules in layers of parallel rods.
Sol: The colloidal dispersion of a solid in a fluid.
Solubility: The ratio of solute to solvent in a saturated solution; usually expressed as the number of grams of solute per 100 g of solvent at a specified temperature.
Solubility Product Constant, Ksp: The equilibrium constant for the solubility of a salt. For a saturated solution, Ksp is equal to the product of the molar concentrations of the ions, each raised to an appropria te exponent.
Solute: Something dissolved in a solvent to make a solution.
Solution: A homogeneours mixture in which all particles are the size of atoms, small molecules or small ions.
Solvation: The development of a cagelike network of solvent molecules about a molecule or ion of the solute.
Solvay Process: Used to prepare Na2CO3 from NaCl, CO2 and NH3.
Solvent: A medium, usually a liquid, into which something (the solute) is dissolved to make a solution.
sp Hybrid Orbitals: Hybrid orbitals formed by mixing one (s) and one (p) atomic orbitals. The angle between a pair of sp hybrids is 180
sp2 Hybrid Orbitals: Hybrid orbitals formed by mixing one (s) and two (p) atomic orbitals. The angle between any two sp2 hybrids is 120
sp3 Hybrid Orbitals: Hybrid orbitals formed by mixing one (s) and three (p) atomic orbitals. The angle between any two sp3 hybrids is 120.
Specific Heat: The quantity of heat that will raise the temperature of 1 g of a substance by 1 C. (Its units are cal/g C, where C = the change in temperature.)
Spectrochemical Series: A listing of ligands in order of their ability to produce a large crystal field splitting.
Spin Quantum Number: ms, which can have values of +1/2 and -1/2.
Spontaneous Change: A change that occurs by itself without outside assistance.
Standard Cell Potential: The potential of a galvanic cell at 25 degrees celsius and 1 atm when all ionic concentrations are exactly 1 M.
Standard Conditions of Temperature and Pressure (STP): 273 K (0 C) and 760 Torr.
Standard Enthropy, S: The entropy of 1 mol of a substance has at 25 C and 1 atm.
Standard Entropy Change, DeltaS: DeltaS = (Sum of S of products) - (Sum of S of reactants).
Standard Free Energy Change, DeltaG: DeltaG = DeltaH - TDeltaS
Standard Reduction Potential: The reduction potential of a half-reaction at 25 C and 1 atm when all ion concentrations are 1 M.
Standard Solution: Any solution whose concentration is accurately known.
Standard State: The condition in which a substance is in its most stable form at 25 C and 1 atm.
Standing Wave: A wave whose peaks and nodes do not change position.
State: Solid, liquid, or gas. In thermodynamics, a particular set of conditions of temperature, composition, and pressure.
State Function: A thermodynamic function whose value depends only on the initial and final states of the system and not on the path used to get from the initial to the final state. P, V, T, H, S, and G are all state functions.
State of a System: The specified values of the physical properties of a system--physical form, composition, concentration, temperature, and pressure.
Stereoisomers: Isomers whose structures differ only in spatial orientations (geometric iosmers; optical isomers).
Stock System: System of nomenclature that uses Roman numerals to specify oxidation states.
Stoichiometry: A description of the relative quantities by moles of the reactants and products in a reactionas given by the coefficients in the balanced equation.
STP: See Standard Conditions of Temperature and Pressure.
Straight-Chain Compound: An organic compound in whose molecules the carbon atoms are joined in one continuous open chain sequence.
Strong Acid: An acid that is essentially 100% ionized in water. A good proton donor. An acid with a very large value of Ka.
Strong Base: Any powerful proton acceptor; a base with a very large value of Kb; a metal hydroxide that ionizes almost 100% in water.
Structural Formula: A chemical formula that shows how the atoms of a molecule are arranged and to which other atoms they are bonded.
Sublimation: Conversion of a solid directly to a gas without passing through the liquid state.
Subshell: All orbitals of a given shell that have the same value of l.
Substrate: In enzyme chemistry, the substance whose reaction is catalyzed by the enzyme.
Supercooled Liquid: A liquid at a temperature below its freezing point. An amorphous solid.
Supercooling: Cooling a liquid to a temperature below its freezing point.
Supercritical Fluid: A substance at a temperature above its critical temperature.
Superimposability: A test of molecular chirality in which a model of a molecule and a model of the mirror image of this molecule are compared to see if the two can be made to blend perfectly, with every part of one coinciding simultaneously with th e parts of the other.
Superoxide: An oxide containing the O2- ion.
Supersaturated Solution: Any solution containing more solute than a saturated solution would ordinarily hold at the given temperature.
Surface Tension: A measure of the amount of energy needed to expand the surface area of a liquid.
Surfactant: A substance that lowers the surface tension of a liquid and promotes wetting.
Surroundings: That part of the universe other than the system being studied and separated from the system by a real or an imaginary boundary.
Suspension: A homogeneous mixture in which the particles of one (or more) of the substances are relatively large (10 nm in one dimension) and are dispersed uniformly in some medium.
System: That part of the universe under study and separated from the rest of the universe (the surroundings) by a real or an imaginary boundary.
t1/2: See Half-Life.
Temperature-Volume Law (Charles' Law): The volume of a given mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant. V1/T1 = V2/T2
Theory: Tested explanation of the results of many experiments.
Thermite Reaction: The very exothermic reaction, 2Al + Fe2O3 => 2Fe + Al2O3.
Thermodynamics: The study of energy changes and the flow of energy from one substance to another.
Thermometer: Device used to measure temperature.
Thermotropic Substance: A substance that behaves like a liquid crystal over a limited temperature range.
Third Law of Thermodynamics: For a pure crystalline substance, S = 0 at 0 K.
Torr: A unit of pressure equal to 1 mm Hg.
Trace Element: In enzyme chemistry, any metal or nonmetal ion needed by an enzyme.
Tracer Analysis: The use of radioactivity to trace the movement of something or to locate the site of radioactivity.
Transcription: In nucleic acid chemistry, the synthesis of mRNA at the direction of DNA.
Transition Elements: Elements in the periodic table located between Groups IIA and IIIA.
Transition Metals: Transition elements.
Transition State: The brief moment during a reaction when the reactants have collided and are at the high point on the potential energy diagram for the reaction.
Translation: In nucleic acid chemistry, the synthesis of a polypeptide at the direction of a molecule of mRNA.
Transmutation: The conversion of one isotope into another.
Transuranium Elements: Elements 93 and higher.
Traveling Wave: A wave whose peaks and nodes move.
Triple Bond: A covalent bond in which three pairs of electrons are shared.
Triple Point: The temperature and pressure at which the liquid, solid, and vapor states of a substance can coexist in equilibrium.
Triprotic Acid: An acid that can furnish three H+ per molecule.
Tritium: Hydrogen-3; 31H (sometimes 31t); an isotope of hydrogen.
Tyndall Effect: The scattering of light by colloidally dispersed particles that gives a milky appearance to the mixture.

[ A-B | C-D | E-G | H-L | M-O | P-R | S-T | U-Z ]

U-Z

Uncertainty Principle: There are limits in our ability to measure a particle's speed and position simultaneously.
Unit Cell: The smallest portion of a crystal that can be repeated over and over in all directions to give the crystal lattice.
Unsaturated Solution: Any solution with a concentration less than that of a saturated solution of the same solute.
Vacuum: An enclosed space containing no matter whatsoever. A partial vacuum is an enclosed space containing a gas at a very low pressure.
Valence Bond Theory: Theory of covalent bonding that views a bond as being formed by the sharing of one pair of electrons between two overlapping atomic or hybrid orbitals.
Valence Electrons: Electrons in the valence shell.
Valence Shell: In an atom, the shell with highest n.
Valence Shell Electron Pair Repulsion Theory: A theory used to predict molecular structure. It is based on the idea that electron pairs (bonding and lone pairs) in the valence shell of an atom stay as far apart as possible.
Vapor Pressure: The pressure exerted by the vapor above a liquid. If the liquid and vapor are in equilibrium, this pressure is the equilibrium vapor pressure.
Vapor Pressure-Concentration Law (Raoult's Law): The vapor pressure of one component above a mixture of molecular compounds equals the product of its vapor pressure when pure (at the same temperature) and its mole fraction.
Vitamin: An organic compound present in trace concentration in various foods that is essential for health but that cannot be made by the body and whose absence leads to a specific vitamin-deficiency disease.
Volatile: Describing a liquid that has a low boiling point, a high vapor pressure, and, therefore, evaporates easily.
Volt (V): The SI unit of electrical potential or emf. 1 V = 1 J/C
Water of Hydration: Water molecules trapped in a solid substance, usually in a stoichiometric ratio to the other material.
Wave Mechanics: Theory of atomic structure based on the wave properties of matter.
Wavelength: The distance between crests in the wavelike oscillations of electromagnetic radiations; symbol, (lambda).
Weak Acid: A poor proton donor; an acid with a value of Ka less than 10-3; any acid with a low percentage ionization in water.
Weak Base: Any poor proton acceptor; a base with a low value of Kb; any base with a low percentage ionization in water.
Weight: The force with which a substance is attracted to the earth by gravity.
Wetting: The spreading of a liquid across a surface.
X Ray: A stream of very high-energy photons emitted by substances when they are bombarded by high-energy beams of electrons or are emitted by radionuclides that have undergone K-electron capture.
Yield, Percentage: The ratio, given as a percent, of the quantity of a product actually obtained to the theoretical yield.
Yield, Theoretical: The quantity of a product calculated by the stoichiometry of the reaction.