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absolute zero: The temperature at which all molecular motion should cease.

accuracy: The relationship between the graduations on a measuring device and the actual standard for the quantity being measured.

acid: A substance which produces hydrogen ions in water solution (Arrhenius). A proton donor (Bronsted). An electron-pair acceptor (Lewis).

acid anhydride: An oxygen containing substance which produces an acid when dissolved in water. actinide: An element whose highest energy electron is in the 5f sublevel

activated complex: The species formed when the reactants in a chemical reaction have collided with sufficient energy to meet the activation energy requirement.

activation energy: The energy required to start chemical reaction.

activity (ion): The effective concentration of a species. addition polymerization: The formation of a polymer from monomers by an addition reaction. addition reaction: The adding on of a substance to the double bond of an alkene or the triple bond of an alkyne.

adiabatic: A process taking place without interchange of energy with its surroundings.

adsorption: The process of one substance being attracted and held to the surface of another.

alcohol: A class of organic compounds characterized by the presence of the hydroxyl group, -OH.

aldehyde: A class of organic compounds characterized by the presence of the carbonyl group (X=O) on the end carbon of the chain (RCHO).

aliphatic: A subdivision of hydrocarbons characterized by open chains and nonaromatic rings.

alkali metal: An element from group IA of the periodic table.

alkaline earth metal: An element from group IIA of the periodic table.

alkane: An aliphatic compound having only single carbon-carbon bonds.

alkene: An aliphatic compound having a double carbon-carbon bond.

alkyne: An aliphatic compound having a triple carbon-carbon bond.

alloy: A mixture of two or more metals. alpha particle: Helium nucleus.

amine: An organic compound derived from ammonia by replacement of one or more hydrogen atoms by organic radicals.

amino acid: An organic compound characterized by the presence of an amino group and a carboxylic acid group on the same carbon atom.

amorphous: A solid-appearing material without crystalline structure.

ampere: The unit of electric current equal to one coulomb per second.

amphoteric: A substance which can act as either an acid or a base.

amplitude: The displacement of a wave from the average position.

anhydrous: A substance without water of hydration.

aromatic: A group of organic ring compounds having (4n + 2) pi electrons.

asymmetric: Not symmetrical.

atomic mass: The average mass of the atoms of an element. One-twelfth the mass of the carbon-

anion: A negative ion.

anode: The positive electrode. The electrode at which oxidation occurs.

antibonding orbital: In molecular orbital theory, an orbital of the molecule which represents a higher energy than the atomic orbitals from which it was formed.

asymmetric: The property of not having symmetry.

atomic radius: The radius of an atom without regard to surrounding atoms.

atomic theory: The body of knowledge concerning the existence of atoms and their characteristic structure.

Avogadro's number: The number of objects in a mole equal to 6.02 x 10²³.

Avogadro's hypothesis: The statement that equal volumes of gases at the same temperature and pressure contain the same number of molecules.

atomic number: The number of protons in the nucleus

balance: A device used to measure mass.

band: A group of extremely closely spaced energy levels occupied by free electrons in a metal crystal.

barometer: A manometer used to measure the atmospheric pressure.

baryon: A subatomic particle classified as a large hadron.

base: A substance which produces hydroxide ions in water solution (Arrhenius). A proton acceptor (Bronsted). An electron-pair donor (Lewis).

basic anhydride: An oxygen containing substance which produces a base when dissolved in water.

beta particle: An electron.

bidentate: A ligand which attaches to the central ion in two locations.

binary: A compound containing two elements.

binding energy: The energy required to split the nucleus into separate nucleons.

Bohr atom: The planetary atom.

boiling point: The temperature at which the vapor pressures of the liquid and vapor phases of a substance are equal. For an open liquid, boiling point is the temperature at which the vapor pressure equals the atmospheric pressure.

bond: OO7. Just kidding. The force holding atoms together in a compound.

bond angle: The angle between two bond axes extending from the same atom.

bond axis: The line connecting the nuclei of two bonded atoms.

bond character: The relative ionic or covalent character of a bond.

bond order: The number of electron pairs bonding two atoms as described by molecular

orbital theory: The energy required to break a bond. In molecular orbital theory, a molecular orbital which is at a lower energy level than the atomic orbitals from which it was formed.

Boyle's law: The volume of a specific amount of gas varies inversely as the pressure if the temperature remains constant.

Brownian motion: The random motion of colloidal particles due to their bombardment by the molecules of the continuous phase.

Brownian motion: The random motion of colloidal particles due to their bombardment by the molecules of the continuous phase.

buffer: A solution which can receive moderate amounts of either acid or base without significant change in its pH

bond strength: bonding orbital:

calorimeter: A device for measuring the change in enthalpy during a chemical change.

capillary rise: The tendency of a liquid to rise in a tube of small diameter due to the surface tension of the liquid.

calorimeter: A device for measuring the change in enthalpy during a chemical change.

capillary rise: The tendency of a liquid to rise in a tube of smell diameter due to the surface tension of the liquid.

carboxylic acid: A class of organic compounds containing a -COOH group.

catalyst: A substance which speeds a chemical reaction without being permanently changed itself.

catenation: The joining in chains of carbon atoms.

cathode: The negative electrode (general). The electrode at which reduction occurs (electrochemical).

cathode rays: The beam of electrons in a gas discharge tube.

cation: A positive ion.

Celsius scale: The temperature scale based on the freezing and boiling points of water.

cell potential: The voltage obtained from a voltaic cell.

cellulose: A biological polymer of glucose.

chain reaction: A reaction in which the product from each step acts as reactant for the next step.

chalcogen: An element from Group VIA of the periodic table.

Charles' law: The volume of a specific amount of gas varies directly ss the absolute temperature if the pressure remains constant.

chemical change: A change in which one or more new substances with new properties are formed.

chemical properties: The properties characteristic of a substance when it is involved in a chemical change.

chemical reaction: A chemical change.

chemistry: The study and investigation of the structure and properties of matter.

chromotography: The separation of a mixture using a technique based upon differential adsorption.

closest packing: A crystal structure particle arrangement in which the empty space between particles is minimized.

coefficient: A number placed before a formula in a balanced chemical equation to indicate the relative amount of the substance represented by the formula.

Colligative properties: Properties of solutions which depend only on the number of particles present, without regard to type.

colloid: A dispersion of particles from 1 to 100 nm in at least one dimension, in a continuous medium.

column chrometography: A chromatographic technique utilizing a glass column packed with adsorbent.

common-ion effect: An equilibrium phenomenon in which an ion common to two or more substances in a solution shifts an equilibrium away from itself.

complex ion: A central positive ion surrounded by bonded ligands.

compound: Two or more elements combined by chemical bonds.

concentrated solution: A solution in which there is high ratio between solute and solvent.

concentration: The ratio between the amount of solute and the amount of solvent in which the solute is dissolved.

condensation polymer: A polymer formed by a reaction in which a small molecule. usually water, is produced as the monomers form the polymer.

condensed state: The solid or liquid form of a substance.

conduction band: The group of extremely closely spaced energy levels in a metal which free electrons can occupy.

conductivity: A property involving the transport of electrons or heat from one point to another.

conjugate acid: The particle obtained after a base has gained a proton.

conjugate base: The particle remaining after an acid has donated a proton.

conjugated system: A series of alternating single and double bonds in an organic molecule.

contact catalyst: A catalyst which functions by adsorbing one of the reactants on its surface.

continuous phase: The dispersing medium in a colloid. control rods: Neutron absorbing materials used to control the rate of reaction in a nuclear reactor.

coordinate covalent bond: A covalent bond in which both electrons of the shared pair were donated by the same atom.

coordination number: The number of ligands surrounding the central ion.

corrosion: The gradual electrochemical destruction of a metal by substances in the environment.

coulomb: A quantity of electricity equal to 1/96 500 of a mole of electrons.

covalent bond: A bond characterized by a shared pair of electrons.

covalent radius: The radius of an atom along the bond axis.

critical pressure: The pressure needed to liquefy a gas at a critical temperature.

critical temperature: The temperature above which no amount of pressure will liquefy a gas.

crystal: A solid in which the particles are arranged in a regular, repeating pattern.

crystallization: Separating a solid from a solution by evaporating the solvent, or by cooling.

cyclic compounds: Compounds in which the atoms are bonded in a ring.

cycloalkanes: Aliphatic hydrocarbons with the carbon atoms bonded in rings.

Dalton's law: In a mixture of gases the total pressure of the mixture is the sum of the partial pressures of each component gas.

De Broglie's hypothesis: Particles may have the properties of waves.

decomposition: A reaction in which a compound breaks into two or more simpler substances.

defect: An imperfection in a crystal lattice.

degenerate: Having the same energy.

dehydrating agent: A substance which can absorb water from other substances.

deliquescence: The absorption of water from the air by a solid to form a liquid solution.

delocalized electrons: Electrons which are free to move through the electron cloud of p orbitals as in benzene.

density: Mass per unit volume.

desiccant: A dehydrating agent.

diagonal rule: A system for predicting the order of filling energy sublevels with electrons.

diffusion: The spreading of gas molecules throughout a given volume.

dipole-induced dipole force: An attraction between a dipole and a nonpolar molecule which has been induced to become a dipole.

dilute solution: A solution with a low ratio of solute to solvent.

dipole: A polar molecule.

dipole-dipole force: An attraction between dipoles.

dipole moment: The strength of a dipole expressed as charge multiplied by distance.

dislocation: A crystal defect.

dispersed phase: Colloidal particles distributed throughout the continuous phase.

dispersion force: The force between two particles due to the attraction of instantaneous separations of their charge centers.

dissociation: The separation of ions in solution.

distillation: The process of evaporating a liquid and condensing its vapor.

doping: Deliberate introduction of impurities into a crystal.

dot diagram: A pictorial representation of the location of outer level electrons in an atom, ion, or molecule. double bond:

double bond: A covalent bond in which two atoms share two pairs of electrons.

double displacement: A reaction in which the positive part of one compound combines with the negative part of another compound, and vice versa.

ductility: The property of a substance which enables it to be drawn into a fine wire.

dynamic equilibrium: An equilibrium in which two or more changes are taking place simultaneously, but at the same rate.

edge dislocation: A crystal defect in which a layer of atoms extends into the lattice between layers of unit cells.

efflorescence: The release of water molecules to the air by a hydrate.

effusion: The passage of gas molecules through small
openings.

elastic: Collisions in which kinetic energy is conserved.

electrochemistry: The study of the interaction of electric current and atoms, ions, and molecules.

electrode potential: The reduction potential in volts of a half-reaction compared to the potential of the hydrogen half-reaction at 0.0000 V.

electrolysis: A chemical change produced by an electric current.

electrolyte: A substance whose aqueous solution conducts electricity.

electrolytic cell: A cell in which an electrolysis reaction is taking place.

electron: A subatomic particle representing the unit of negative charge.

electron affinity: The attraction of an atom for an electron expressed as the energy needed to remove an electron from a negative ion to restore neutrality.

electron cloud: The space effectively occupied by an electron in an atom.

electron configuration: A description of the energy level and sublevel for all the electrons in an atom.

electronegativity: The relative attraction of an atom for a shared pair of electrons.

electrophoresis: The migration of colloidal particles under the influence of an electric field.

element: A substance whose atoms have the same number of protons in the nucleus.

elimination reaction: An organic reaction in which a small molecule is removed from a larger molecule leaving a double bond in the larger molecule.

empirical formula: The formula giving the simplest ratio between the atoms of the elements present in a compound.

endothermic: A change which takes place with the absorption of heat.

endpoint: The point in a titration where equivalent numbers of moles of reactants are present.

energy: A property of matter which may be converted to work under the proper circumstances.

energy level: A specific amount of energy or group of energies which may be possessed by electrons in an atom.

energy sublevel: A specific energy which may be possessed by an electron in an atom.

enthalpy: That part of the energy of a substance which is due to the motion of its particles.

entropy: The degree of disorder in a system.

enzyme: A biological catalyst.

equation: A shorthand representation of a chemical change using symbols and formulas.

equilibrium: A state in which no net change takes place in a system.

equilibrium constant: A mathematical expression giving the ratio of the product of the concentrations of the substances produced to the product of the concentration of the reactants for a reaction.

ester: A class of organic compounds derived by the action of an acid plus an alcohol.

esterification reaction: The production of an ester by the reaction of an alcohol with an acid.

ether: A class of organic compounds characterized by the presence of a double bonded oxygen separating two hydrocarbon radicals.

evaporation: The process by which a molecule leaves the surface of a liquid or solid and enters the gaseous state.

exclusion principle: No two electrons in an atom may have the same set of quantum numbers.

exothermic: A change which produces heat.

factor-label method: A problem solving method in which units (labels) are treated as factors.

fat: A biological ester of glycerol and a fatty acid.

fission: The splitting of a nucleus into two approximately equal parts.

fluid: A material which flows (liquid or gas).

forbidden zone: The energy gap between the outer level band and the conduction band in crystals.

formula: A combination of atomic symbols and numbers indicating the elements and their proportions in a compound.

formula mass: The sum of the atomic masses of the atoms in a formula.

formula unit: The amount of a substance represented by its formula.

fractional crystallization: The separation of a mixture into its components through differences in solubility.

fractional distillation: The separation of a mixture into its components through differences in boiling points.

fractionation: Separating a whole into its parts.

free electrons: Electrons not bound to one atom or associated with one bond.

free energy: The chemical potential energy of a substance or system.

freezing point: The temperature at which the vapor pressures of the solid and liquid are equal.

frequency: The number of complete wave cycles per unit of time.

functional isomers: Organic compounds with the same formula, but with the nonhydrocarbons part of the molecule bonded in different ways.

galvanometer: An instrument used to detect an electric current.

gamma ray: A quanta of energy of very high frequency and very small wavelength.

gas: A physical state characterized by random motion of the particles which are far apart compared to their diameters.

gas chromatography: A chromatographic method in which a carrier gas (inert) distributes the vapor being analyzed in a packed column.

geometric isomers: Compounds with the same formula but different arrangement of substituents around a double bond.

gluon: A theoretical massless particle exchanged by quarks.

glycogen: A biological polymer of glucose.

Graham's law: The ratio of the relative rates of diffusion of gases is equal to the square root of the inverse ratio of their molecular masses.

ground state: All electrons in the lowest possible energy sublevels.

group: The members of a vertical column in the periodic table.

hadrons: A class of heavy subatomic particles.

half-cell: The part of an electrochemical cell in which either the oxidation or reduction reaction is taking place.

half-life: The length of time necessary for one-half an amount of a radioactive nuclide to disintegrate.

half-reaction: The oxidation or reduction reaction in a chemical reaction.

halogen: An element from Group VIIA of the periodic table.

heat: The form of energy due to motion of particles.

heat content: Enthalpy.

heat of formation: The amount of heat produced or consumed when a mole of a compound is formed from its elements.

heat of fusion: The heat required to change 1 gram of a substance from solid to liquid.

heat of reaction: The heat produced or consumed when a chemical change takes place in the amounts indicated by the equation involved.

heat of solution: The amount of heat produced or consumed when a substance is dissolved in water. heat of vaporization: The heat needed to change 1 gram of a substance from liquid to gas.

Henry's law: The mass of a gas which will dissolve in a specific amount of a liquid varies directly with the pressure.

heterogeneous: Composed of different parts not uniformly dispersed.

homogeneous: Uniform throughout.

homologous series: A series of organic compounds which differ from each other by a specific structural unit.

hybrid orbitals: Equivalent orbitals formed from orbitals of different energies.

hydration: The adhering of water molecules to dissolved ions.

hydrate: A compound (crystalline) in which the ions are hydrated.

hydrocarbons: Compounds composed solely of carbon and hydrogen.

hydrogen bonding: An exceptionally strong type of dipole-dipole interaction due to the strong positive center in molecules in which hydrogen is bonded to a highly electronegative element.

hydrolysis: Reaction with water to form a weak acid or base.

hygoscopic: Absorbing water from the air.

ideal gas: A model in which gas molecules are treated as though they were geometric points exerting no force on each other.

ideal gas equation: PV=nRT .

idea solution: A solution obeying Raoult's law.

immiscible: Two liquids which will not dissolve in each other.

indicator: A weak organic acid whose conjugate base differs in color. Used to indicate the pH of a solution.

inertia: The tendency of an object to resist any change in its velocity.

infrared spectroscopy: A spectroscopic method useful in investigating the bonding in molecules.

inhibitor: A substance which prevents a reaction from taking place by forming a complex to tie up one of the reactants.

insulator: A substance having a large forbidden zone and which does not conduct.

intensive properties: Those properties of a substance which are independent of the amount of matter present.

interface: The area of contact between two phases.

ion: A particle with an electric charge.

ionic bond: The electrostatic attraction between ions of opposite charge.

ionic radius: The radius of an ion.

ionization constant: The equilibrium constant for the ionization of a weak electrolyte.

ionization energy: The energy required to remove an electron from an atom.

ion-product constant for water: The product of the hydronium and hydroxide ion concentrations, equal to 10^-14 .

irreversible thermodynamic change: A change in volume or pressure in which some energy is lost to an entropy change.

isobaric: At constant pressure.

isomers: Two compounds having the same formula but different structures.

isomorphism: Two or more compounds having the same crystalline structure.

isothermal: At constant temperature.

isotope: Two or more atoms of an element having the same number of protons but different numbers of neutrons.

joule: The SI unit of energy equal to 1 kg•m²/s².

Joule-Thompson effect: The cooling effect achieved by allowing a highly compressed gas to expand rapidly after passing through a small opening.

kelvin: The SI unit of temperature equal to 1/273.16 the thermodynamic temperature of the triple point of water.

ketone: A class of organic compounds characterized by the presence of the carbonyl group (-C=O) between hydrocarbon radicals.

kilogram: The SI unit of mass.

kinetic energy: Energy due to motion.

kinetic theory: The group of ideas treating the interaction of matter and heat.

lanthanide: An element whose highest energy electron is in the 4f sublevel.

law of conservation of energy: Energy is conserved in all changes except nuclear reactions.

law of conservation of mass: Mass is conserved in all changes except nuclear reactions.

law of conservation of mass and energy: The total amount of mass and energy in the universe is constant.

law of definite proportions: The elements composing a compound are always present in the same proportions by mass.

law of multiple proportions: The masses of one element which combine with a specific mass of another element in a series of compounds. These masses are in the ratio of small whole numbers.

Le Chatelier's principle: If a stress is placed on a system at equilibrium, the system will shift so as to offset the stress.

leptons: A class of light subatomic particles.

ligand: A negative ion or polar molecule attached to a central ion in a complex.

limiting reactant: The reactant which is used completely in a reaction.

linear accelerator: A device for imparting a high energy to atomic or subatomic particles traveling in a straight line.

lipid: A biological molecule which is soluble in nonpolar solvents.

liquefaction: Changing a gas to a liquid. liquid: A state characterized by particles in such close proximity that their random motion appears to be a vibration about a moving point.

liquid crystal: A substance which has order in the arrangement of its particles in only one or two dimensions.

liter: A unit of volume equal to 1 dm³.

London forces: see dispersion forces

macromolecule: A crystal which consists of a single molecule with all component atoms bonded in a network fashion.

magnetohydrodynamics: The study of plasmas.

malleability: The property of a substance which allows it to be hammered into thin sheets.

manometer: A device for measuring gas pressure.

mass: The measure of the amount of matter.

mass defect: The difference between the mass of a nucleus and the sum of the masses of the particles from which it was formed.

mass number: The number of nucleons in an atom.

mass spectrometry: The separation of atoms or radicals on the basis of the varied effects of electric and magnetic fields on different masses.

matter: Anything which exhibits the property of inertia.

mean free path: The average distance a molecule travels between collisions.

melting point: The temperature at which the vapor pressures of the solid and liquid phases of a substance are equal.

meson: A subatomic particle classed as a hadron.

metal: An element which tends to lose electrons in chemical reactions.

metallic bond: A force holding metal atoms together and characterized by free electrons.

metalloid: An element which has properties characteristic of a metal and a nonmetal.

miscible: Two liquids which are mutually soluble in all proportions.

mixture: A combination of two or more substances.

mobile phase: The fluid containing the mixture to be analyzed in chromatography.

moderator: A substance used to slow neutrons in a nuclear reactor.

molal boiling point constant: A value characteristic of a solvent indicating the rise in the boiling point of 1 kilogram of the solvent if it contains 1 mole of particles.

molal freezing point constant: A value characteristic of a solvent indicating the drop in the freezing point of 1 kilogram of the solvent if it contains 1 mole of particles.

molality: A unit of concentration equal to the number of moles of solute in 1 kilogram of solvent.

molar heat capacity: The amount of heat required to change the temperature of 1 mole of a substance by 1 Celsius degree.

molar volume: The volume occupied by 1 mole of gas molecules at standard temperature and pressure and equal to 22.4 dm³.

molarity: A unit of concentration equal to the number of moles of solute in 1 dm³ of solution.

mole: Avogadro's number of objects = 6.02 x 10²³.

mole fraction: A unit of concentration equal to the number of moles of solute in a mole of solution.

molecular formula: A formula indicating the actual number of each kind of atom contained in a molecule.

molecular mass: The mass of a molecule found by adding the atomic masses of the atoms comprising the molecule.

molecular orbital theory: A model of molecular structure based upon the formation of molecular orbitals from corresponding atomic orbitals.

molecule: A particle in which the constituent atoms are held together by covalent bonds.

momentum: The product of mass and velocity.

nematic substance: A liquid crystal with order in one dimension only.

net ionic equation: A chemical equation indicating only those substances taking part in the reaction and omitting spectator ions.

neutral: Neither acidic nor basic (electrolytes). Neither positive nor negative (electricity).

neutralization: The combining of an acid and a base until the amounts present correspond to the proportions shown by the equation for their reaction.

neutron: A neutral particle found in the nucleus of an atom and having a mass of approximately one atomic mass unit.

nitrile: A class of organic compounds characterized by the presence of the --CN group.

nitro: A class of organic compounds characterized by the presence of the --NO₂ group.

noble gas: Any element from Group VIIIA of the periodic table.

nonmetal: An element which tends to gain electrons in chemical reactions.

nonvolatile: A substance which has a high boiling point, strong intermolecular forces, and a low vapor pressure at room temperature.

nuclear magnetic resonance spectroscopy: A spectroscopic method based on the energy required to reorient a nucleus with a magnetic field with respect to an external magnetic field.

nucleic acid: A biological polymer involved in genetic transfer and cell metabolism.

nucleon: A particle found in the nucleus of an atom. A proton or neutron.

nuclide: An element containing a specific number of protons and a specific number of neutrons.

octahedral: A molecular or ionic shape in which six particles are clustered about a central particle at the vertices of a regular octahedron.

octane rating: A system of rating gasoline based upon the proportions of heptane and 2,2,4-trimethylpentane in the mixture.

octet rule: The tendency of atoms to react in such a way that they acquire eight electrons in their outer level. He with 2 electrons also conforms.

ohm: The unit of electric resistance. One volt will force 1 ampere through 1 ohm.

olefln: Another name for an alkene.

optical isomers: Mirror image molecules which rotate a plane of polarized light in opposite directions.

optically active: A property of substances characterized by their ability to rotate a plane of polarized light.

orbital: The space which can be occupied by O, 1, or 2 electrons with the same energy level, energy sublevel, and special orientation.

orbital theory. The energy required to break a bond. In molecular orbital theory, a molecular orbital which is at a lower energy level than the atomic orbitals from which it was formed.

organic: Related to carbon compounds.

organic oxidation reaction: The combustion of an organic compound to produce carbon dioxide and water.

osmotic pressure: The pressure developed across a semipermeable membrane by differential diffusion through the membrane.

oxidation: The loss of electrons.

oxidation number: The charge on an atom if the electrons in a compound are assigned in an arbitrary manner according to established rules.

oxidizing agent: A substance which tends to gain electrons.

packing: An adsorbent used in columns for column and gas chromatography.

pair repulsion: A model for molecular shape based upon the assumption that electron clouds will repel each other and be as far away from each other as possible.

paper chromatography: A chromatographic method based upon the movement of a solvent through paper by capillary action.

parent chain: The longest continuous chain of carbon atoms used for naming organic molecules.

partially miscible: Two liquids which are soluble in each other to a limited extent.

pascal: The SI unit of pressure equal to 1 N/m².

percentage composition: The proportion of an element present in a compound found by dividing the mass of the element present by the mass of the whole compound and multiplying by a hundred.

periodic law: The properties of the elements are a periodic function of their atomic numbers.

periodic table: A pictorial arrangement of the elements based upon their electron configurations.

petroleum: A natural mixture of organic compounds found in liquid form.

pH: The negative logarithm of the hydronium ion concentration.

phase: A physically distinct section of matter set off from the surrounding matter by physical boundaries.

phase diagram: A graphical representation of the vapor pressures of the solid and liquid forms of a substance.

photoelectric effect: The ejection of electrons from a surface which is exposed to light.

physical change: A change in which the substance or substances present after the change are the same chemically.

physical properties: The characteristics of a material as it is subjected to physical changes.

pi bond: A bond formed by the sideways overlap of p orbitals.

plasma: A high temperature physical state characterized by the separation of atoms into electrons and nuclei.

pOH: The negative logarithm of the hydroxide ion concentration.

polarimeter: A device for measuring the rotation of plane polarized light.

polarity: Unsymmetrical charge distribution.

polarized light: Light in which the field variations are all in the same plane.

polyatomic ion: A group of atoms bonded to each other covalently put possessing an overall charge. A very large molecule made from simple units
repeated many times.

polymerization: The reaction producing a polymer from monomers.

polymorphism: The property of existing in more than one crystalline form.

polyprotic acid: An acid with more than one ionizable hydrogen atom.

position isomers: Two molecules having the same formula but differing in the position to which a substituent is attached to the parent chain.

positron: A subatomic particle identical to an electron except possessing a positive charge. The antiparticle of the electron.

potential difference: The difference in potential energy of electrons located at different points.

potential energy: Energy of an object due to its position.

precipitate: A solid produced from a reaction occurring in aqueous solution.

precision: The possible error in a measurement

pressure: The force per unit area.

protein: A biological polymer of amino acids.

proton: A positive particle found in nuclei and having a mass of approximately 1 atomic mass unit.

quadridentate: A ligand which attaches to a central ion in four locations.

quantum number: A number describing a property of an electron in an atom.

quantum theory: The concept that energy is transferred in discrete units.

quark: A theoretical particle believed to be a constituent of a hadron.

radiant energy: Energy in transit between two objects.

radical: A fragment of a molecule. It is neutral yet at least one atom is lacking its octet of electrons.

radioactivity: The spontaneous disintegration of nuclei.

Raoult's law: The vapor pressure of a solution of a nonvolatile solute is the product of the vapor pressure of the pure solvent and the mole fractions of the solvent.

reaction mechanism: The actual step-by-step description of the interaction of atoms, ions, and molecules in a reaction.

reaction rate: The rate of disappearance of a reactant or the rate of appearance of a product.

redox reaction: A reaction involving the transfer of electrons.

reducing agent: A substance that tends to donate electrons.

reduction: The gain of electrons.

Refraction: The bending of a beam of light as it passes from one medium into another.

refractometer: A device for measuring the refraction of light.

resonance: The phenomenon in which several equally valid dot diagrams can be drawn for a substance. The actual substance is an average of all the possible arrangements.

reversible chemical change: Products can be changed back into the original reactants, under the proper conditions.

reversible thermodynamic change: An ideal change in which the difference in pressure causing the change is infinitesimal.

salt: A compound formed from the positive ion of a base and the negative ion of an acid.

saponification reaction: The reaction of an ester with a strong base to form a soap and glycerol.

saturated hydrocarbon: A hydrocarbon in which all carbon-carbon bonds are single bonds.

saturated solution: A solution in which undissolved solute is in equilibrium with dissolved solute.

scientific notation: Expression of numbers in the form M x 10ⁿ .

screw dislocation: A crystal defect in which the unit cells are improperly aligned.

semiconductor: A device in which the electrons are involved in bonding, but which may be made to conduct under the proper conditions.

shielding effect: The decrease in the force between outer electrons and the nucleus due to the presence of other electrons between them.

SI units: The internationally accepted set of standards for measurement.

side chain: A hydrocarbon radical attached to the parent chain of an organic molecule.

sigma bond: A bond formed by the end-to-end overlap of atomic orbitals.

significant digits: Digits in the value of a measurement indicating the quantity to a precision justified by the measuring device and technique used to make the measurement.

single displacement: A reaction in which one element replaces another in a compound.

smectic substance: A liquid crystal having order in two dimensions.

solid: A physical state characterized by particles in such close proximity that their random motion appears to be vibration about a fixed point.

solubility: The quantity of a solute which will dissolve in a specific quantity of solvent at a specific temperature.

solubility product constant: The equilibrium constant for the dissolving of a slightly soluble salt.

solute: The substance present in lesser quantity in a solution.

solution: A homogeneous mixture composed of solute and solvent.

solution equilibrium: Solute is dissolving and crystallizing at the same rate.

solvation: The attaching of solvent particles to solute particles.

solvent: The substance present in the greater amount in a solution.

space lattice: The theoretical arrangement pattern of the unit cells in a crystal.

specific heat capacity: The amount of heat required to raise the temperature of 1 gram of a substance by 1 Celsius degree.

specific rate constant: A constant used to determine the rate of a reaction from the concentration of the reactants.

spectator ion: An ion present in a solution but not taking part in the reaction.

spin: A property of subatomic particles which corresponds most closely with our concept of rotation about an axis.

spontaneous: Occurring without outside influence.

square planar: An arrangement of particles in a complex ion in which the ligands are arranged in a plane with the central ion and form a square with the central ion in the center.

stability: The tendency (or lack of it) for a compound to disintegrate or decompose.

standard solution: A solution whose concentration is known with precision.

standard state: A reference set of conditions for thermodynamic measurements equal to 25^oC, 101.325 kPa, and 1M.

standard temperature and pressure: A set of reference conditions for dealing with gases equal to O^oC and 101.325 kPa.

starch: A biological polymer of glucose.

state: A physical property of a phase designating it as solid, liquid, gas, or plasma.

state function: Thermodynamic quantity which is determined solely by the conditions, not the method of arriving at those conditions.

stationary phase: The adsorbent in chromatography.

stoichiometry: The solution of problems involving specific quantities of a substance or substances.

strong acid or base: A completely ionized electrolyte.

structural isomers: Two compounds with the same formula but differing arrangements of the parent carbon chain.

sublimation: The change directly from solid to gas.

substituent: A hydrocarbon branch or nonhydrocarbon group attached to the parent chain or ring in organic compounds.

substitution reaction: A reaction in organic compounds in which a hydrogen atom or substituent is replaced by another substituent.

supercooled liquid: A liquid cooled below its normal freezing point without having changed state to the solid form. A metastable state.

supersaturated solution: A solution containing more solute than a saturated solution at the same temperature. A metastable state.

surface tension: The apparent "skin" effect on the surface of a liquid due to unbalanced forces on the surface particles.

suspension: A dispersion of particles larger than 100 nm throughout a continuous medium.

symmetry: The property of being balanced with respect to the relative positions of atoms or substituents on opposite sides of an imaginary center or axis.

synchrotron: A device for accelerating subatomic particles in a circular path.

synthesis: Formation of a compound from two or more simpler substances.

synthetic element: An element not occurring in nature produced by means of nuclear reactions.

technology: The application of scientific principles for practical use.

temperature: A measure of the average kinetic energy of molecules.

ternary: A compound formed from three elements.

tetrahedral: An arrangement in which four particles surround a central particle at angles of 109.5^o to each other.

thermodynamics: The study of the interaction of heat and matter.

thermometer: A device for measuring temperature.

thin layer chromatography: A chromatographic method utilizing an adsorbent spread over a flat surface in a thin layer.

time: The interval between two occurrences.

titration: A laboratory technique for measuring the relative strength of solutions.

tracer: A nuclide used to follow a reaction or process.

transistor: An electronic device whose operation is based upon the behavior of certain crystals with deliberate built-in defects.

transition element: An element whose highest energy electron is in a d sublevel.

transmutation: The change of one element into another.

transuranium element: An element with Z > 92.

tridentate: A ligand which attaches to the central ion in three locations.

triple bond: A covalent bond in which two atoms share three pairs of electrons.

triple point: The temperature and pressure at which all three phases of a substance are in equilibrium.

Tyndall effect: The scattering of light by colloids.

ultraviolet spectroscopy: A spectroscopic technique using light of wavelength slightly less than visible light and lending evidence to the electronic structure of atoms and molecules.

uncertainty principle: The impossibility of measuring exactly both the position and the momentum of an object at the same time.

unit cell: The simplest unit of repetition in a crystal lattice.

unsaturated molecule: An organic molecule containing at least one double or triple bond.

unsaturated solution: A solution containing less solute than a saturated solution at the same temperature.

van der Waals forces: Weak intermolecular forces of attraction between molecules.

van der Waals radii: The radius of an atom in the direction of adjacent nonbonded atoms.

vapor equilibrium: The state in which evaporation and condensation are taking place at the same rate.

vapor pressure: The pressure generated by a vapor in equilibrium with its liquid.

velocity: Speed expressed as a vector quantity.

viscosity: The resistance of a fluid to flow.

visible spectroscopy: A spectroscopic method useful in investigating the behavior of electrons in atoms.

volatile: A substance with a low boiling point, weak intermolecular forces, and a high vapor pressure at room temperature.

volt: The unit of electric potential difference.

voltaic cell: An electrochemical cell in which a chemical reaction generates an electric current.

wave: A periodic disturbance in a medium.

wave equation: A mathematical expression treating the electron as a wave and providing the amplitude of the wave at specific points in space with reference to the nucleus as the origin.

wavelength: The distance between corresponding crests or troughs in a wave.

wave-particle duality of nature: The property of particles behaving as waves as well as particles and the property of waves behaving as particles as well as waves.

weak (acids and bases): An electrolyte which is only slightly ionized.

weak forces: Attractive forces between molecules and consisting of dipole-dipole, dipole-induced dipole, and dispersion forces.

work: A force moving through a distance.

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