Regents Examination in Physical Setting / Chemistry: Glossary of Important Terms

Glossary of Important Terms
 

Absolute zero The lowest possible temperature, written as 0 K or −273°C.
Accuracy The closeness of a measurement to an accepted value; see also precision.
Acid See Arrhenius acid; Brønsted-Lowry acid.
Activated complex The intermediate state between reactants and products in a chemical reaction; the peak of the potential energy diagram.
Activation energy The minimum energy needed to initiate a reaction.
Addition polymerization The joining of unsaturated monomers by a series of addition reactions.
Addition reaction The process in which a substance reacts across a double or triple bond in an organic compound.
Alcohol An organic compound containing a hydroxyl (—OH) group.
Aldehyde An organic compound containing a carbonyl group with at least one hydrogen atom attached to the carbonyl carbon.
Alkali metal Any Group 1 element, excluding hydrogen.
Alkaline earth element Any Group 2 element.
Alkane A hydrocarbon containing only single bonds between adjacent carbon atoms.
Alkene A hydrocarbon containing one double bond between two adjacent carbon atoms.
Alkyl group An open-chained hydrocarbon less one hydrogen atom; for example, CH3 = methyl group, C2H5 = ethyl group. Unspecified alkyl groups are designed by the letter R.
Alkyne A hydrocarbon containing one triple bond between two adjacent carbon atoms.
Allotrope A specific form of an element that can exist in more than one form; graphite and diamond are allotropes of the element carbon.
Alloy A solid metallic solution.
Alpha decay The radioactive process in which an alpha particle is emitted.
Alpha particle (α) A helium-4 nucleus.
Amide An organic compound containing the CONH2 functional group.
Amine A hydrocarbon derivative containing an amino group.
Amino acid An organic compound containing at least one amino group and one carboxyl group.
Amino group An ammonia molecule less one hydrogen atom; —NH2.
Anhydrous Pertaining to a compound from which the water of crystallization has been removed.
Anode The electrode at which oxidation occurs.
Aqueous Pertaining to a solution in which water is the solvent.
Aromatic hydrocarbon Any ring hydrocarbon whose electronic structure is related to that of benzene.
Arrhenius acid Any substance that releases H+ ions in water.
Arrhenius base Any substance that releases OH− ions in water.
Atmospheric pressure 1 standard atmosphere (atm) = 101.3 kilopascals.
Atom The basic unit of an element.
Atomic mass The weighted average of the masses of the isotopes of an element.
Atomic mass unit (u) One-twelfth the mass of a carbon-12 atom.
Atomic number The number of protons in the nucleus of an atom; the atomic number defines the element.
Atomic radius A measure of the size of an atom.
Avogadro’s hypothesis Equal volumes of gases, measured at the same temperature and pressure, contain equal numbers of particles.
Avogadro’s number (NA)  The number of particles in 1 mole; 6.02 × 1023.
Battery A commercial voltaic cell.
Benzene C6H6; the parent hydrocarbon of all aromatic compounds.
Beta decay The radioactive process in which a beta particle is emitted.
Beta (−) particle (β−) An electron.
Beta (+) particle (β+) A positron.
Binary compound A compound containing two elements.
Binding energy The energy released when a nucleus is assembled from its nucleons.
Boiling The transition of liquid to gas; boiling occurs when the vapor pressure of a liquid equals the atmospheric pressure above the liquid.
Boiling point The temperature at which boiling occurs; the temperature at which the liquid and vapor phases of a substance are in equilibrium.
Boiling point elevation The increase in the boiling point of a solvent due to the presence of solute particles.
Bond energy The energy needed to break a chemical bond.
Boyle’s law At constant temperature and mass, the pressure of an ideal gas is inversely proportional to its volume; P1V1 = P2V2.
Breeder reactor A fission reactor that generates its own nuclear fuel.
Bright-line spectrum The lines of visible light emitted by elements as electrons fall to lower energy levels.
Brønsted-Lowry acid A substance that can donate H+ ions.
Brønsted-Lowry base A substance that can accept H+ ions.
Carbonyl group The functional group characteristic of aldehydes and ketones; > C=O.
Carboxyl group The functional group characteristic of organic acids; —COOH.
Catalyst A substance that speeds a chemical reaction by lowering the activation energy of the reaction.
Cathode The electrode at which reduction occurs.
Celsius (C) scale The temperature scale on which the freezing and boiling points of water (at 1 atm) are set at 0 and 100, respectively.
Chain reaction A chemical or nuclear reaction in which one step supplies energy or reactants for the next step.
Charles’s law At constant pressure and mass, the volume of an ideal gas is directly proportional to the Kelvin temperature;

Chemical bond The stabilizing of two atoms by sharing or transferring electrons.
Chemical equation A shorthand listing of reactants, products, and molar quantities in a chemical reaction.
Chemical equilibrium The state in which the rates of the forward and reverse reactions are equal.
Chemical family See group.
Coefficient A number in a chemical equation that indicates how many particles of a reactant or product are required or formed in the reaction.
Colligative property A property that depends on the number of particles present rather than the type of particle; see also boiling point elevation; freezing point depression.
 

Combined (ideal) gas law At constant mass, the product of the pressure and volume divided by the Kelvin temperature is a constant;

 

Compound A combination of two or more elements with a fixed composition by mass.
Concentrated Pertaining to a solution that contains a relatively large quantity of solute.
Concentration The “strength” of a solution; the quantity of solute relative to the quantity of solvent.
Condensation The change from gas to liquid.
Condensation polymerization The joining of monomers by a series of dehydration reactions.
Control rod The part of a fission reactor that controls the rate of fission by absorbing neutrons.
Coordinate covalent bond A single covalent bond in which the pair of electrons is supplied by one atom.
Covalent bond A chemical bond formed by the sharing of electrons.
Cracking The process of breaking large hydrocarbon molecules into smaller ones in order to increase the yield of compounds such as gasoline.
Crystal A solid whose particles are arranged in a regularly repeating pattern.
Decomposition A reaction in which a compound forms two or more simpler substances.
 

Density Mass per unit volume;

 

Deposition The direct transition from gas to solid.
Deuterium The isotope of hydrogen with a mass number of 2.
Diatomic molecule A neutral particle consisting of two atoms; Br2 and CO are diatomic molecules.
Diffusion The movement of one substance through another.
Dihydroxy alcohol An organic compound with two hydroxyl groups.
Dilute (adjective) Pertaining to a solution that contains a relatively small quantity of solute; (verb) to reduce the concentration of a solution by adding solvent.
Dipole An unsymmetrical charge distribution in a neutral molecule.
Dipole–dipole attraction The attractive force between two oppositely charged dipoles of neighboring polar molecules.
Dissociation The separation of an ionic compound in solution into positive and negative ions.
Distillation The simultaneous boiling of a liquid and condensation of its vapor.
Double bond A covalent bond in which two pairs of electrons are shared by two adjacent atoms.
Ductility The property of a substance that allows it to be drawn into a wire; metallic substances possess ductility.
Dynamic equilibrium The state in which the rates of opposing processes are equal; see also chemical equilibrium; phase equilibrium; solution equilibrium.
Electrochemical cell—either a voltaic cell or an electrolytic cell A device that produces usable electrical energy from a spontaneous redox reaction; see also battery.
Electrode A conductor in an electrochemical or electrolytic cell that serves as the site of oxidation or reduction.
Electrolysis A nonspontaneous redox reaction driven by an external source of electricity.
Electrolyte A substance whose aqueous solution conducts electricity.
Electrolytic cell A device for carrying out electrolysis.
Electron The elementary unit of negative charge.
Electron-dot diagram See Lewis structure.
Electronegativity The measure of an atom’s attraction for a bonded pair of electrons.
Electroplating The use of an electric current to deposit a layer of metal on a negatively charged object.
Element A substance all of whose atoms have the same atomic number.
Empirical formula A formula in which the elements are present in the smallest whole-number ratio; NO2 is an empirical formula, but C2H4 is not.
Endothermic reaction A reaction that absorbs energy; ΔH is positive for an endothermic reaction.
End point The point in a titration that signals that equivalent quantities of reactants have been added.
Energy A quantity related to an object’s capacity to do work.
Enthalpy change (ΔH) The heat energy absorbed or released by a system at constant pressure.
Entropy (S) The measure of the randomness or disorder of a system.
Entropy change (ΔS) An increase or decrease in the randomness of a system.
Equilibrium See dynamic equilibrium.
Ester The organic product of esterification.
Esterification The reaction of an acid with an alcohol to produce an ester and water.
Ethanoic acid CH3COOH; acetic acid.
Ethanol CH3CH2OH; ethyl (grain) alcohol.
Ethene C2H4; ethylene; the parent of the alkene family of hydrocarbons.
Ether An organic compound containing the arrangement R—O—R.
Ethyne C2H2; acetylene; the parent of the alkyne family of hydrocarbons.
Evaporation The surface transition of liquid to gas.
Excited state A condition in which one or more electrons in an atom are no longer in the lowest possible energy state.
Exothermic reaction A reaction that releases energy; ΔH is negative for an exothermic reaction.
Fermentation The (anaerobic) oxidation of a sugar such as glucose to produce ethanol and carbon dioxide; the reaction is catalyzed by enzymes.
Filtration A method of separating a liquid from the particles suspended in it.
First ionization energy The quantity of energy needed to remove the most loosely held electron from an isolated neutral atom.
Fission A nuclear reaction in which a heavy nuclide splits to form lighter nuclides and energy.
Fission reactor A device for producing electrical energy by means of a controlled fission reaction.
Formula mass The sum of the masses of the atoms in a formula; units are atomic mass units (u) or grams per mole (g/mol).
Fractional distillation The separation of organic substances based on differences in their boiling points.
Freezing The transition from liquid to solid.
Freezing point The temperature at which freezing occurs.
Freezing point depression (lowering) The decrease in the freezing point of a solvent due to the presence of solute particles.
Fuel rod The part of a nuclear reactor that contains the fissionable material.
Functional group An atom or group of atoms that confers specific properties on an organic molecule.
Fusion A synonym for melting; also, a nuclear process in which light nuclides join to form heavier nuclides and produce radiant energy.
Fusion reactor An experimental device for producing a controlled fusion reaction and generating electrical energy from it.
Gas The phase in which matter has neither definite shape nor definite volume.
Gram-atomic mass The molar mass of an element expressed in grams per mole (g/mol).
Gram-formula mass See molar mass.
Gram-molecular mass The molar mass of a molecule.
Ground state The electron configuration of an atom in the lowest energy state.
Group The elements within a single vertical column of the Periodic Table.
Half-cell The part of an electrochemical cell in which oxidation or reduction occurs.
Half-life The time needed for a substance to decay to one-half its initial mass.
Half-reaction The oxidation or reduction portion of a redox reaction.
Halogen An element in Group 17 of the Periodic Table; F, Cl, Br, I, At.
Heat energy The energy released or absorbed by a system undergoing a change in temperature, in phase, or in composition.
Heat of fusion (Hf) The heat energy absorbed when a unit mass of solid changes to liquid at its melting point; Hf(ice) = 80 calories per gram.
Heat of reaction (ΔH) The heat energy absorbed or released as a result of a chemical reaction.
Heat of vaporization (Hv) The heat energy absorbed when a unit mass of liquid changes to gas at its boiling point; Hv(water) = 540 calories per gram.
Heavy water A molecule of water in which the hydrogen atoms have a mass number of 2; deuterium oxide.
Heterogeneous mixture A nonuniform mixture.
Homogeneous mixture A mixture with a uniform distribution of particles; a solution is one example of a homogeneous mixture.
Homologous series A group of organic compounds with related structures and properties; each successive member of the series differs from the one before it by a specific number of carbon and hydrogen atoms (usually CH2).
Hydrate A crystalline compound that has water molecules incorporated into its crystal structure; common examples include CuSO4 · 5H2O and Na2SO4 · 10H2O [also written as CuSO4(H2O)5 and Na2SO4(H2O)10].
Hydration The association of water molecules with an ion or another molecule.
Hydride A binary compound of an active metal and hydrogen; the oxidation state of hydrogen is −1.
Hydrocarbon An organic compound composed of carbon and hydrogen.
Hydrogen bond An unusually strong intermolecular attraction that results when hydrogen is bonded to a small, highly electronegative atom such as F, O, or N.
Hydrolysis A reaction in which a water molecule breaks a chemical bond; the reaction between certain salts and water to produce an excess of hydronium or hydroxide ions.
Hydronium ion H3O+; the conjugate acid of H2O; responsible for acidic properties in water solutions.
Hydroxide ion OH−; the conjugate base of H2O; responsible for basic properties in water solutions.
Ideal gas A model of a gas in which the particles have no volume, do not attract or repel each other, and collide without loss of energy; real gases approximate ideal gas behavior under conditions of low pressure and high temperature.
Ideal gas law The relationship obeyed by an ideal gas; see combined (ideal) gas law.
Indicator A substance that undergoes a color change to signal a change in chemical conditions; acid–base indicators change color over specified pH ranges.
Inert (noble) gas An element in Group 18 of the Periodic Table; Ne, Ar, Kr, Xe, Rn. (He is also associated with Group 18.)
Inorganic compound A compound that is not a hydrocarbon derivative.
Ion A particle in which the numbers of protons and electrons are not equal.
Ion–dipole attraction The attractive force between an ion and the oppositely charged dipole of a neighboring polar molecule.
Ionic bond The electrostatic attraction of positive and negative ions in an ionic compound; an electronegativity difference of 1.7 or greater indicates the presence of an ionic bond.
Ionic compound A substance whose particles consist of positive and negative ions.
Ionization energyThe quantity of energy needed to remove an electron from an atom or ion; see also first ionization energy.
Isomers Different compounds that have the same molecular formula.
Isotopes Atoms having the same atomic number but different mass numbers; atoms of the same element with differing numbers of neutrons.
IUPAC International Union of Pure and Applied Chemistry; the scientific group responsible for all major policies in chemistry, including the naming of elements and compounds.
Joule (J) The unit of work and energy in the SI (metric) system.
Kelvin (K) A measure of absolute temperature; the Kelvin scale begins at 0 and is related to the Celsius scale by the equation K = C + 273; a temperature difference of 1 K is equal to a temperature difference of 1°C.
Ketone An organic compound containing a carbonyl group with no hydrogen atoms directly attached to the carbonyl carbon.
Kilo- The metric prefix signifying 1,000.
Kilojoule (kJ) 1,000 joules.
Kinetic energy The energy associated with the motion of an object.
Kinetic molecular theory (KMT) The theory that explains the structure and behavior of idealized models of gases, liquids, and solids.
Le Châtelier’s principle When a system at equilibrium is subjected to a stress, the system will shift in order to lessen the effects of the stress. Eventually, a new equilibrium point is established.
Lewis structure A shorthand notation for illustrating the ground-state valence electron configuration of an atom.
Liquid The phase in which matter has a definite volume but an indefinite shape; a liquid takes the shape of its container.
Liter (L) A unit of volume in the metric system; 1 liter = 1,000 cubic centimeters; 1 liter = 1 cubic decimeter; 1 liter is approximately equal to 1 quart.
Litmus An acid–base indicator that is red in acidic solutions and blue in basic solutions.
Macromolecule A giant molecule formed by network bonding or by polymerization.
Malleability The property by which a substance is able to be formed into various shapes; metallic substances possess malleability.
Mass number The number of nucleons in a nuclide.
Melting The transition from solid to liquid.
Melting point The temperature at which the vapor pressure of a solid equals the vapor pressure of the liquid; the temperature at which the solid and liquid phases of a substance are in equilibrium; see also freezing point.
Meniscus The curved surface of a liquid, caused by the attraction of the particles of the liquid and the container holding the liquid (e.g., water in a graduated cylinder), or by the mutual attraction of the particles of the liquid (e.g., mercury).
Metal A substance composed of atoms with low ionization energies and relatively vacant valence levels; Na, Fe, Ag, and Ba are metallic substances.
Metallic bond The delocalization of the valence electrons among the kernels of the metal atoms; “mobile valence electrons immersed in a sea of positive ions.”
Metalloid An element that has both metallic and nonmetallic properties; examples of metalloids include B, Ge, Si, and Te.
Methanal HCHO; formaldehyde; the simplest aldehyde.
Methane CH4; the parent of the alkane family of hydrocarbons.
Methanoic acid HCOOH; formic acid; the simplest organic acid.
Methanol CH3OH; methyl (wood) alcohol; the simplest alcohol.
Milli- The metric prefix signifying 1/1,000.
Milliliter (mL) 1/1,000 liter; 1 liter = 1,000 milliliters.
Miscible A solution of liquids that is soluble in all proportions; ethanol and water are a miscible pair of liquids.
Mixture A material consisting of two or more components and having a variable composition.
Moderator A substance used to produce slow neutrons and promote nuclear fission; graphite and heavy water are used as moderators in fission reactors.
Molar mass The mass of any atom, element, ion, or compound expressed in grams per mole (g/mol).
Molarity The concentration of a solution, measured as the number of moles of solute per liter of solution.
Molar volume The volume occupied by 1 mole of an ideal gas; 22.4 liters at STP.
Mole The number of atoms contained in 12 grams of carbon-12; see also Avogadro’s number.
Molecular formula A chemical formula that lists the number of atoms present but does not show the arrangement of the atoms in space.
Molecular mass The sum of the masses of the atoms in a molecule; units are atomic mass units (u) or grams per mole (g/mol).
Molecule The smallest unit of a nonionic substance; Ar, Cl2, and NH3 are molecules.
Monatomic molecule A molecule consisting of one atom; Xe and He are monatomic molecules.
Monomer The basic unit of a polymer; the monomer of a protein is an amino acid; the monomer of starch is glucose.
Network solid A substance formed by a two- or three-dimensional web of covalent bonds to produce a macromolecule; diamond and SiO2 are network solids.
Neutralization The reaction of equivalent amounts of hydronium and hydroxide ions in aqueous solution; the principal product is water. When the water is evaporated, the spectator ions form a salt; see also spectator ion.
Neutron A neutral nuclear particle with a mass comparable to that of a proton.
Noble gas See inert (noble) gas.
Nonelectrolyte A substance whose aqueous solution does not conduct electricity; glucose is a nonelectrolyte.
Nonmetal A substance that does not have characteristic metallic properties; C and S are nonmetallic elements.
Nonpolar bond A covalent bond in which the electron pair or pairs are shared equally by both atoms.
Nonpolar molecule A molecule containing only nonpolar bonds, such as N2, or a molecule with a symmetrical charge distribution, such as CCl4 and CO2.
Normal boiling point The boiling temperature of a substance at a pressure of 1 atmosphere.
Nuclear equation A shorthand listing of reactant and product nuclides in a nuclear reaction.
Nucleon A constituent of an atomic nucleus; a proton or a neutron.
Nucleus The portion of the atom that contains more than 99.9 percent of the atom’s mass; the nucleus is small, dense, and positively charged.
Ore A native mineral from which a metal or metals can be extracted.
Organic chemistry The study of the hydrocarbons and their derivatives; the chemistry of carbon.
Organic compound A compound that is a hydrocarbon or a hydrocarbon derivative.
Oxidation The loss or apparent loss of electrons in a chemical reaction.
Oxidation number (state) The charge that an atom has or appears to have when certain arbitrary rules are applied; oxidation numbers are useful for identifying the atoms that are oxidized and reduced in a redox reaction.
Oxidizing agent The particle in a redox reaction that causes another particle to be oxidized; as a result, an oxidizing agent is reduced.
Paraffin A common name for a mixture of solid alkanes; another name for paraffin is wax.
Percent composition by mass The number of grams of an element (or group of elements) present in 100 grams of an ion or compound.
Period One of the horizontal rows of the Periodic Table; the period number indicates the valence level of an element.
Periodic law The properties of elements recur at regular intervals and depend on their nuclear charges; “The properties of elements are a periodic function of their atomic numbers.”
Peroxide A compound in which oxygen has an oxidation state of −1; H2O2 and BaO2 are peroxides.
Petroleum Crude oil containing a mixture of hydrocarbons.
pH A scale of acidity and basicity based on the hydronium ion concentration in aqueous solution; pH = −log [H3O+]. At 298 K, a pH less than 7 indicates an acidic solution; a pH greater than 7, a basic solution; a pH of 7, a neutral solution.
Phase equilibrium The state in which the rates of opposing phase changes (freezing–melting, boiling–condensation, sublimation–deposition) are equal.
Phenolphthalein An acid–base indicator that is colorless in acidic solutions and pink in basic solutions.
Photon A fundamental unit of radiant energy; a quantum of radiation.
Polar bond A covalent bond in which the electron pair or pairs are shared unequally by both atoms; the atom with the larger electronegativity has more of the electron density surrounding it.
Polar molecule A molecule with an unsymmetrical charge distribution, such as H2O; a dipole.
Polyatomic ion An ion composed of more than one atom; SO42− is a polyatomic ion.
Polymer A macromolecule consisting of a chain of simpler units; polyethylene is a polymer of ethene.
Polymerization See polymer; addition polymerization; condensation polymerization.
Positron A positively charged electron; a particle of antimatter.
Potential energy The energy associated with the position of an object; a “stored” form of energy.
Precipitate A deposit formed by the appearance of an excess of solid solute in a saturated solution.
Precision The closeness of a series of measurements to one another; see also accuracy.
 

Pressure The force exerted on an object divided by the surface area of the object;

 

Principal energy level An integer beginning with 1 that describes the approximate distance of an electron from the nucleus of an atom.
Product(s) The substance or substances that are formed in a chemical process; products are on the right side of a chemical equation.
Propanone (CH3)2CO; acetone; the simplest ketone.
Proton A nuclear particle with a positive charge equal to the negative charge on the electron; a nucleon.
Radiant energy Electromagnetic energy; visible light and X rays are examples of radiant energy.
Radioactive dating The use of radioactive isotopes to measure the age of an object.
Radioactive tracer A radioisotope used to indicate the path of an atom in a chemical reaction.
Radioactivity The spontaneous breakdown of a radioactive nuclide.
Radioisotope A radioactive isotope.
Reactant(s) The substance or substances that react in a chemical process; reactants are on the left side of a chemical equation.
Redox reaction A chemical reaction in which oxidation–reduction takes place.
Reducing agent The particle in a redox reaction that causes another particle to be reduced; as a result, a reducing agent is oxidized.
Reduction The gain or apparent gain of electrons in a chemical reaction.
Salt The spectator-ion product of a neutralization reaction; see also spectator ion.
Salt bridge A device for allowing the flow of ions in an electrochemical cell.
Saponification The reaction of an ester with a base to produce an alcohol and the sodium salt of an organic acid; soap is produced by saponifying fats with NaOH.
Saturated hydrocarbon A hydrocarbon containing only single carbon–carbon bonds.
Saturated solution A solution in which the pure solute is in equilibrium with the dissolved solute; a solution that contains the maximum amount of dissolved solute.
Significant digit(s) [figure(s)] The number or numbers that are part of a measurement. If there are two or more, all but the last figure is known; the last figure is the experimenter’s best estimate.
Single bond A covalent bond in which one pair of electrons is shared by two adjacent atoms.
Solid The phase in which matter has both definite shape and definite volume.
Solubility The amount of solute needed to produce a saturated solution with a given amount of solvent.
Solute(s) The substance or substances dissolved in a solution.
Solution A homogeneous mixture whose particles are extremely small.
Solution equilibrium The state in which the undissolved and dissolved solutes are in dynamic equilibrium; in a solid–liquid solution, the rate of dissolving equals the rate of crystallization.
Solvent The substance in which the solute is dissolved.
Spectator ion An ion that does not take part in a chemical reaction; in the (acid–base) reaction between NaOH(aq) and HCl(aq), Na+(aq) and Cl−(aq) are spectator ions; in the (redox) reaction between Zn(s) and Cu(NO3)2(aq), NO3−(aq) is the spectator ion.
Standard solution A solution whose concentration is accurately known; a standard solution is used for analyzing other substances.
Standard temperature and pressure (STP) 273 K and 1 atmosphere.
Stock system A systematic method of naming chemical compounds in which the positive oxidation number is written as a Roman numeral in parentheses after the element. For example, the Stock name of the compound Fe2O3 is iron(III) oxide.
Stoichiometry The study of quantitative relationships in substances and reactions; chemical mathematics.
Strong acid In aqueous solution, a substance that ionizes almost completely to hydronium ion.
Strong base In aqueous solution, a substance that ionizes or dissociates almost completely to hydroxide ion.
Structural formula A chemical formula that illustrates the spatial arrangement of each atom.
Sublimation The direct transition from solid to gas; CO2(s) and I2(s) sublime at atmospheric pressure.
Substance An element or a compound.
Supersaturated solution A solution that contains more dissolved solute than a saturated solution at the same temperature; supersaturation is an unstable condition.
Temperature A measure of the average kinetic energy of the particles of a substance.
Titration The addition of a known volume of a standard solution in order to determine the concentration of an unknown solution.
Toluene C7H8; methylbenzene.
Transition element An element whose atoms contain unfilled d sublevels; an element in Groups 3–11 of the Periodic Table.
Transmutation The conversion of one element to another by a nuclear process.
Triple bond A covalent bond in which three pairs of electrons are shared by two adjacent atoms.
Tritium The radioactive isotope of hydrogen with a mass number of 3.
Unsaturated hydrocarbon A hydrocarbon containing double and/or triple carbon–carbon bonds.
Unsaturated solution A solution that contains less dissolved solute than a saturated solution at the same temperature.
Valence electron An electron in the outermost principle energy level.
Voltaic cell A device that produces usable electrical energy from a spontaneous redox reaction; see also battery.
Water of hydration The water molecules that are part of the crystalline structure of certain compounds.
Weak acid In aqueous solution, a substance that is poorly ionized and produces only a small concentration of hydronium ion.
Weak base In aqueous solution, a substance that is poorly ionized or dissociated and produces only a small concentration of hydroxide ion.