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Absolute zero: Lowest possible temperature, 0K

Acid (Arrhenius) : A substance that increases the concentration of hydronium ions in aqueous solution.

Acid ionozation constant : The equlibrium constant for the reaction with a eak acid with water to produce hydronium ions and the conjugate base of the weak acid.

Acidic solution : An aqueous solution in which the concentration of hydronium ion exceeds the concentration of hydroxide ion.

Activation energy : The potential energy difference between reactants and activated complex; the minimum energy that reactant molecules must have to be converted to product molecules.

Actual yield : The quantity reaction product obtained; less than the theoretical yield.

Alkali metals : The Group 1A elements in the periodic table (except hydrogen).

Alkaline earth metals : The elements in Group 2A of the periodic table.

Alpha radiation : Radiation composed of alpha particles (heliun nuclei).

Anion : An ion with a negative electrical charge.

Anode : the electrode of an electrochemical cell at which oxidation occurs.

Atom : The smallest particle of an element that can be involved in chemical combination with another element.

Atomic mass units (amu) : the unit of a scale of relative atomic masses of the elements; 1 amu = 1/12 the mass of a six-proton, six-neutron carbon atom.

Atomic number : The number of protons in the nucleus of an atom of an element.

Atomic radius : One-half the distance between the nuclei centers of two like atoms in a molecule.

Atomic structure : The identity and arrangement of subatomic particles in an atom.

Average reaction rate : A reaction rate calculated from a change in concentration divided by a change in time.

Avogadro's law : The volume of a gas, at a given temperature and pressure, is directly proportional to the amount of gas.


Bar : Apressure unit equal to 100,000 Pa.

Base : A compund that dissociates, ionizes, or reacts in aqueous solution to increase the concentration of a hydroxide ion.

Base ionazation constant : The equilibrium constant for the reaction of a weak base with water to produce hydroxide ions and the conjugate acid of the weak base.

Basic solution : An aqueous solution in which the concentration of hydroxide ion is greater than the concentration of hydronium ion.

Battery (voltaic cell) : An electrochemicla cell (or group of cells) in which a product-favored oxidation-reduction reaction is used to produce an electric current.

Becquerel : A unit of radioactivity equal to 1 nuclear disintergration per second.

Beta particles : electrons ejected from certain radioactive nuclei.

Beta radiation : Radiation composed of electrons.

Bimolecular rection : An elementary reaction in which two particles must collide for products to be formed.

Binary molecular compound : A molecular compound whose molecules containatoms of only two elements.

Binding enregy : The energy required to separate all nucleons in an atomc nucleus.

Binding energy per nucleon : The energy per nuleon required to separate all nucleonsin an atomic nucleus.

Boiling point : The temperature at which the equilibrium vapor pressure of a liquid equals the external pressure on the liquid.

Boiling-point elevation : A colligative property; the difference between the normal boiling point of a pure solvent and the higher boiling point of a solution in which a nonvolatile nonelectrolyte soluteis dissolved in that solvent.

Bond : Attractive force between two atoms holding them together, for example, as part of a molecule.

Bond angle : the angle between the bonds to two atoms that are bonded to the same third atom.

Bond enthalpy ( bond energy) : The change in enthalpy when a mole of chemical bonds of a given type is broken, separating the bonded atoms; the atoms and molecules must be in the gas phase.

Bond length : The distance between the centers of the nuclei of two bonded atoms.

Bonding electrons : Electron pairs shared in covlent bonds.

Bonding molecular orbital : A lower-energy molecular orbital that can be occupied by bonding electrons.

Bonding pair : A pair of valence electrons that are shared between two atoms.

Born-Haber cycle : a stepwise thermochemical cycle in which the constituent elements are converted to ions and combined to form an ionic compound.

Boyle's law : The volume of confined ideal gas varies inversely with the applied pressure, at a constant temperature and amount of gas.

Bronsted-Lowry base : A hydrogen ion acceptor.

Buffer capacity : The quantity of acid or base a buffer can accommodate without a significant pH change ( more than one ph unit).

Buffer solution : A solution that resists changes in pH when limited amounts of acids or bases are added; it contains a weak acid and its conjugate base, or a weak base and its conjugate base, or a weak base and its conjugate acid.


calorie (cal) : A unit of energy equal to 4.184 J. Approximately 1 cal is required to raise the temperature of 1 g of liquid water by 1 degree celsius.

Calorie (Cal) : A unit of energy equal to 4.184 kJ = 1 kcal.

Calorimeter : a device for measuring the quantity of thermal energy transferred during a chemical reaction or some other process.

Capillary action : The process whereby a liquid rises in a small diameter tube due to noncovalent interactions between the liquid and the tube's material.

Catalyst : a substance that increases the rate of a reaction but is not consumed in the overall reaction.

Cathode : The electrode of an electrochemical cell at which reduction occurs.

Cation : An ion with a positive electrical charge.

Cell voltage : The electromtive force of an electrochemical cell; the quantity of work a cell can produce per coulomb of charge that a chemical reaction produces.

Celsius temperature scale : A scale defined by the freezing ( 0 degree celsius) and boiling (100 degrees celsius) points of pure water, at 1 atm.

Change of state : A physical process in which one state of matter is changed into another (such as melting a solid to form a liquid).

Charle's law : the volume of an ideal gas at constant pressure and amount of gas varies directly with its absolute temperature.

Chelating ligand : A ligand that uses more than one atom to bind to the same metal ion in a complex ion.

Chemical compound : A pure substance (e.g. , sucrose or water) that can be decomposed into two or more pure substances; homogeneous, constant-composition matter that consists of two or more chemically combined elements.

Chemical element (element) : A substance ( e.g. , carbon, hydrogen, or oxygen) that can't be decomposed into two or more new substances by chemical or physical means.

Chemical Equilibrium: A state in which the concentrations of reactants and products remain constant because the rates of forward and reverse reactions are equal.

Chemical kinetics: The study of the speeds of chemical reactions and the nanoscale pathways or rearrangements by which atoms, ions, and molecules are converted from reactants to products.

Chemical periodicity, law of: Law stating that the properties of the element are periodic functions of atomic number.

Chemistry: The study of matter and the changes it can undergo.

Clausius-Clapeyron equation: Equation that gives the relationship between vapor pressure and temperature.

Colligative properties: Properties of solutions that depend only on the concentration of solute particles on the solution, not on the nature of the soulute particles.

Combination reaction: A reaction in which two rectants combine to give a single product.

Combining volumes, law of: At constant temperature and pressure, the volumes of reacting gases are always in the ratios of small whole numbers.

Combustion reaction: A reaction in which an elementor compound burns in air or oxygen.

Common ion effect: Shift in equilibrium position that results from addition of an ion identical to one in the equilibrium.

Complex ion: An ion with several molecules or ions connected to a central metal ion by coordinate covalent bonds.

Compressibility: The propert of a gas that allows it to be compacted into a smaller volume by application of pressure.

Concentration: The relative quantities of solute and solvent in a solution.

Condenstion reaction: A chemical reaction in which two (or more) molecules combine to form a larger molecule, simultaneously producing a small molecule such as water.

Conjugate acid-base pair: A pair of molecules or ions related to on another by the loss and gain of a single hydrogen ion.

Conservation of mass, law of: Law stating that there is no detectable change in mass in an ordinary chemical reaction.

Constant composition, law of: Law stating that a chemical compund always contains the same elements in the same proportions by mass.

Coordinate covalent bond: A chemical bond in which both of the two electrons forming the bond were originally associated with the same one of the two bonded atoms.

Coordination compound: A compound in which complex ions are combined with oppositely charged ions to form a neutral compund.

Coordination number: The number of coordinate covalent bonds between igands and a central metal ion in a complex ion.

Coulomb: The unit of electrical charge equal to the quantity of charge that passes a fixed point in an electrical circuit when a current of one ampere flows for one second.

Coulomb's law: Law that represents the force of attraction between two charged particles.

Critical pressure: The pressure above which there is no distinction between liquid and vapor phases.

Critical temperature: The temperature above which there is no distinction between liquid and vapor phases.

Crystal-field splitting energy: Energy difference betweensets of d orbitals on the central metal ion in coordination compund.

Crystal-field theory: Theory that predicts spectra and magnetism of coordination compounds based on electrostatic bonding between ligands and a metal ion.

Crystal lattice: The ordered, repeating arrangement of ions, molecules, or atoms in a crystalline solid.

Crystalline solids: Solids with an ordered arrangement of atoms, molecules, or ions that results in planar faces and sharp angles of the crystals.

Crystallization: The process in which mobile atoms molecules, milecules, or ions in a liquid convert into a crystalline solid.

Cubic close packing: The three dimensional structure that results when atoms or ions are stacked in the abcabc arrangement.

Cubic unit cell : A unit cell with equal-length edges that meet at 90 degree angles.



Dalton's law of partial pressures: The total pressure exerted by a mixture of gases is the sum of the partial presures of the individual gases in the mixture.

Decomposition reaction: A reaction in which a compound breaks down chemically to form two or more simpler substances.

Delocalized electrons: Electrons, such as in benzene, that are spread over several atoms in a molecule or polyatomic ion.

Density: The ratio of the mass of an object to its volume.

Diamagnetic: Describes atoms or ions in which all the electrons are paired in filled shells so their magnetic fields effectively can cancel each other

Diffusion: Spread of gas molecules of one type through those of another type.

Dimensional analyis: A method of using units in calculations to check for correctness.

Dipole moment: The product of the magnitude of the partial charges of a molecule between times the distance of separation between the charges.

Dipole-dipole attraction: The noncovalent force of attraction between any two polar molecules or polar regions in the same large molecule.

Dynamic equilibrium: A balance between opposing reactions occuring at equal rates.



Effective nuclear charge: The nuclear positive charge experienced by outer-shell electrons in a many-electron atom.

Effusion: Escape of gas molecules from a container through a tiny hole into a vacuum.

Electrochemical cell: A combination of anode, cathode, aand other materials arranged so that a product-favored oxidation-reduction reaction can cause a current to flow or an electrical current can cause a reactant-favored redox reaction to occur.

Electrochemistry: The study of the relationship between electron flow and oxidation-reduction reactions.

Electrode: A device such as a metal plate or wire that conducts electrons into and out of a system.

Electrolysis: The use of electrical energy to produe a chemical change.

Electrolyte: A substance that ionizes or dissociates in water to form an electrically conducting solution.

Electromagnetic radiation: Radiation that consists of oscillating electric and magnetic fields that travel through space at the same rate.

Electron: A negatively charged subatomic particle that occupies most of the volume of an atom.

Electron affinity: The energy change when a mole of electrons is added to a mole of atoms in th gas phase.

Electron capture: A radioactive decay process in which one of n atom's innershell electrons is captured by the nucleus, which decreases the atomic number by 1.

Electron configuration: The complex description of the orbitals occupied by all the electrons in an atom or ion.

Electron-pair geometry: The geometry around a central atom including the spatial positions bonding and lone electron pairs.

Electonegativity: A measure of the ability of an atom in a molecule to attract bonding electrons to itself.on

Elementary reaction: A nanoscale reaction whose equation indicates exactly which atoms, ions, or molecules collide or change as the reaction occurs.

Emprical formula: A formula showing the simplest possible ratio of atoms of elements in a compound.

Endergonic: Refers to a reaction that requires input of Gibbs free energy; applies to biochemical reactions that are reactant favored at body temperature.

Endothernic (process): A process in which thermal energy must be transferred into a thermodynamic system in order to maintain constant temperture. c

Enthalpy change: The quantity of thernal energy transferred when a process takes place at constant temperature andha pressure.

Enthalpy of a solution: The quantity of thermal energy transferred when a solution is formed.

Entropy: A measure of the dispersal of energy in a system.

Enzyme: A highly efficient biochemical catalyst for one or more reactions in a living system.

Enyme-substrate complex: The combination formed by the binding of an enzyme with a substrate.

Equatorial position: Position lying on the equator of an imaginary sphere around a triangular bipyramidal molecular or ionic structures .

Equilibrium constant : The concentration of a substance ( generally expressed as molarity) in a system that has a constant value for a given reaction.

Equilibrium constanet expression: The mathmatical expression associated with an equilibrium constant.

Equilibrium vapor pressure: Pressure of the vapor of a substance in equilibrium with its liquid or solid in a closed container.

Equivalence point: The point in a tirration at which a stiochiometrically equivalent amount of one substance bvavaeen added to another substance.

Evaporation: The process of conversion of a liquid to a gas.

Exchange reacton: A reaction in which cations and anions that were partners in the reacants are interchanged in the products.

Excited state: The unstable state of an atom or molecule in which at least one electron does not have its lowest possible energy.

Exergonic: Refers to a reaction that releases Gibbs free energy; applies to biochemical recation that are product-favored at body temperature.

Exothermic: Refers to a process in which thermal energy must be transferred out of a thermodynamic system in order to maintain a constant temperature.




Faraday constant: The quantity of electric charge on one mole of electrons.

Ferromagnetic: A substance that contains clusters of atoms with unpaired electrons whose magnetic spins become aligned, caused pemenant magnetism.

First law of thermodynamics (law of conservation of energy): Energy can neither be created or destroyed - the total energy of the universe its constant.

Formal charge: The charge a bonded atom would have if its electron where shared equally.

Formal Constant: The equilibrium constant for the formation of a complex ion.

Formula Weight: The sum of atomic weights in amu of all the atoms in a compound's formula.

Freezing-point lowering: A colligative property; the difference between the freezing point of a pure solvent and the freezing point of a solution in which a nonvolatile nonelectrolyte solute is dissolved in the solvent.

Frequency: The number of complete waves passing a point in a given period of time (cycles per second).

Frequency factor: The factor (A) in the Arrhenius equation that depends on how often molecules collide when all concentrations are 1 mol/L and on whether the molecules are properly oriented when they collide.


Gamma radiation: Radiation composed of highly energetic photons.

Gibbs free energy: A thermodynamic function that decreases for any product-favored system. For a process at constant temperature and pressure.

Global warming: Increase in temperature at Earth's surface as a result of the greenhouse effect enhanced by increasing concentrations of carbon dioxide and other green house gases.

Greenhouse effect: Atmospheric warming caused by absorption by atmospheric carbon dioxide, water vapor, methane, ozone, and other greenhouse gases of infrared radiation reradiated from earth.


Haber-Bosch process: The process developed by Fritz Haber and Carl Bosch for the direct synthesis of ammonia from its elements.

Half-life: The time required for the concentration of one reactant to reach half its original value; radioactivity-the time required for the activity of a radioactive sample to reach half of its original value.

Half-reaction: A reaction that represents either an oxidation or a reduction process.

Halide ion: A monatomic ion (1-) of a halogen.

Halogens: The elements in Group 7A of the periodic table.

Heat (heating): The energy-transfer process between two samples of matter at different temperatures.

Heat capacity: The quantity of energy that must be transferred to an object to raise its temperature by 1 degree C.

Heat of fusion: The enthalpy change when a solid sublimes; the quantity of energy that subsance melts; the quantity of energy that must be transferred when a substance melts at constant temperature and pressure.

Heat of sublimation: The enthalpy change when a solid sublimes; the quantity of energy, at constant pressure, that must be transferred to cause a solid to vaporize.

Heat of vaporization: The enthalpy change when a substance vaporizes: the quantity of energy that must be transferred when a liquid vaporizes at constant temperature and pressure.

Heating curve: A polt of the temperature of a substance versus the quantity of energy transferred to it by heating.

Henry's law: A mathematical expression for the relationship of gas pressure and solubility

Hess's law: If two or more chemical equations can be combined to give another equation, the enthalpy change for that equation will be the sum of the enthalpy changes for the equations that were combined.

Heterogeneous catalyst: A catalyst that is in a different phase from that of the reaction mixture.

Heterogeneous mixture: A mixture in which components remain separate and can be observed as individual substances, hases, or entites.

Heterogeneous reaction: A reaction that takes place at an interface between two phases, solid and gas for example.

High-spin complex: A complex ion that has the maximum possible number of unpaired electrons.

Homogeneous catalyst: A catalyst that is in the same phase as that of the reaction mixture.

Homogeneous mixture: A mixture of two or more substances in a single phase that is uniform throughout.

Homogeneous reaction:A reacton in which the reactants and products are all in the same phase.

Hund's rule: Electrons pair only after each orbital in a subshell is occupied by a single electron.

Hybrid orbitals: Orbitals formed by combining atomic orbitals of appropriate energy and orientation.

Hybridized: Refers to atomic orbitals of proper energ and orientation that have combined to form hybrid orbitals.

Hydration: The binding of one or more water molecules to an ion or molecule within a solution or within a crystal lattice.

Hydrocarbon: An organic compound composed only of carbon and hydrogen.

Hydrophilic: "Water-loving", a term describing the polar part of a molecule that is strongly attracted to water molecules.

Hydrophobic: "Water-fearing", a term describing the nonpolar part of a molecule that is not attracted to water molecules.

Hypertonic: Refers to a solution having a higher concentration of nanoscale particles and therefore a higher osmotic pressure than another solution.

Hypotonic: Refers to a solution having a lower solute concentration of nanoscale particles and therefore a lower osmotic pressure than another solution.



Ideal gas: A gas that behaves exactly as described by the ideal gas law, and by Boyle's, Charles's, and Avogadro's laws.

Ideal gas law: A law that relates pressure, volume, amount(moles), and temperature for ideal gas; the relationships expressed by the equation PV=nRT.

Immiscible: Describes two liquids that form two separate phases when mixed.

Iinduced dipole : A temporary dipole created by a momentary uneven distribution of electrons in a molecule or atom.

Induced fit : The change in the shape of an enzyme, its substrate, or both when they bind.

Inhibitor : A molecule or ion other than the substrate that occupies the active site of an enzymecausing a decrease in enzymatic reactivity.

Initial rate : The instantaneous rate of reaction determined at the beginning of the reaction.

Inorganic compound : A chemical compound that is not a hydrocarbon or derived from a hydrocarbon.

Insoluble : Describes a solute, almost all of which dissolves in a solvent.

Instantaneous reaction rate : The rate at a particular time after a reaction has begun.

Intermolecular forces : Noncovalent attractions between separate molecules.

Internal energy : The sum of the individual energies (kinetic and potential) of all of the nanoscale particles (atoms, molecules, or ions) in a sample of matter.

Ion : An atom or group of atoms that has lost or gained one or more electrons so that it is no longer electrically neutral.

Ionic compound : A compound that consists of negative and positive ions.

Ionic hydrate : Ionic compounds that incorporate water molecules in the ionic crystal lattice.

Ionic radius : Radius of an anion or a cation in an ionic compound.

Ionization energy : The energy needed to remove a mole of electrons from a mole of atoms in the gas phase.

Isoelectronic : Refers to atoms and ions that have identical electron configuration.

Isomers : Compounds that have the same molecular formula but different arrangements of atoms.

Isotonic : Refers to a solution having the same concentration of nanoscale particles and therefore the same osmotic pressure as another solution.

Isotopes: Forms of an element composed of atoms with the same atomic number but different mass numbers owing to a difference in the number of neutrons.


Joule(J): A unit of energy equal to 1 kg. The kinetic energy of a 2-kg object traveling at a speed of 1m/s.


Kinetic-Molecular Theory: The theory that matter consists of nanoscale particles that are in constant, random motion.


Lanthanides: The elements after lanthanum in the sixth period in which the 4f subshell is being filled.

Lattice energy: Enthalpy of formation of 1 mol of an ionic solid from its separated gaseous ions.

Law of conservation of mass: Law stating that there is no detectable change in mass in an ordinary chemical reaction.

Law of constant composition: Law stating that a chemical compound always contains the same elements in the same proportions by mass.

Law of multiple proportions: When two elements can combine in two or more ways, the mass ratio A : B in one compound is a small-whole-number multiple of the mass ratio A : B in the other compund.

Le Chatelier's principle: If a system is at equilibrium and the conditions are changed so that it is no longer at equilibrium, the system will react to give a new equilibrium in a way that partially counteracts the change.

Lewis acid: A molecule or ion that can accept an electron pair from another atom, molecule, or ion to form a new bond.

Lewis base: A molecule or ion that can donate an electron pair to another atom, molecule or ion to form a new bond.

Lewis structure: Structural formula for a molecule that shows all valence electrons as dots or lines that represent covalent bonds.

Ligands: Atoms, molecules, or ions bonded to a central atom, such as the central metal ion in a coordination complex.

Limiting reactant: The reactant present in limited supply that controls the amount of product formed in a reaction.

Liquid: A phase of matter in which a substance has no definite shape but a definite volume.

London forces: Forces resulting from the attraction between positive and negative regions of momentary (induced) dipoles in neighboring molecules.

Lone-pair electrons: Paired valence electrons unused in bond formation; also called nonbonding pairs.


Mass: A measure of an object's resistance to acceleration.

Mass fraction: The ratio of the mass of one component to the total mass of a sample.

Mass number: The number of protons plus neutrons in the nucleus of an atom of an element.

Mass percent: The mass fraction multiplied by 100%.

Matter: Anything that has mass and occupies space.

Melting point: The temperature at which the structure of a solid collapses and the solid changes to a liquid.

Meniscus: A concave or convex surface that forms on a liquid as a result of the balance of noncovalent forces in a narrow container.

Metal: An element that is malleable, ductile, forms alloy, and conducts an electric current.

Metal activity series: A ranking of realtive reactivity of metals in displacement and other kinds of reactions.

Metallic bonding: In solid metals, the nondirrectional attraction between positive metal ions and the sorrounding sea of negatively charged electrons.

Metalloid: An element that has some typically metallic properties and other properties that are more characteristic of nonmetals.

Metric system: A decimalized measurement system.

Miscible: Describes two liquids that will dissolve in each other in any proportion.

Molality (m): A concentration term equal to the moles of solute per kilogram of solvent.

Molar heat capacity: The quantity of energy that must be transferred to 1 mol of a substance to increase its temperature by 1 degree C.

Molar heat of fussion: The energy transfer required to melt 1 mol of a pure solid.

Molar mass: The mass in grams of 1 mol of atoms, molecules, or formula units of one kind, numerically equal to the atomic or molecular weight in amu.

Molar solubility: The solubility of a solute in a solvent, expressed in moles per liter.

Molarity(M): Solute concentration expressed as the moles of solute per liter of solution.

Molar heat capacity : The quantity of energy transferred to 1 mol of a substance to increase its temperature by 1 degree celsius.

Molar heat of fusion : The energy tranfer required to melt 1 mol of a pure solid.

Molar mass : The mass in grams of 1 mol of atoms, molecules, or formula units of one kind, numerically equal to the atomic or molecular weight in amu.

Molar solubulity : The solubility of a solute in a solvent, expressed in moles per liter.

Molarity (M) : Solute concentration expressed as the moles of solute per liter of solution.

Mole (mol) : The amount of substance that contains as manyb elementary particles as there are atoms in exactly 0.012 kg of carbon-12 isotope.

Mole fraction (X) : The ratio of moles of one component to the total number of moles in a mixture of substances.

Molecular compound : A compound of atoms of two or more elements chemically combined in molcules.

Molecualar formula : A formula that expresses the number of atoms of each type within one molecule of a compound.

Molecular geometry : The three- dimensonal arrangement of atoms in a molecule.

Molecular orbitals : Orbitals extending over an entire molecule generated by combining atomic orbitals.

Molecular weight : The sum of the atomic weights (in amu) of all the atoms in a compound's formula.

Molecule : The smallest part of an element or compound that exists independently, and retains the chemical properties of that element or compound.



Nernst equation : The equation relating the potential of an electrochemical cell to the concentrations of the chemical species involved in the oxidation-reduction reactions occurring in the cell.

Net ionic equation : A chemical equation in which only those ions undergoing chemical changes in the course of the reaction are represented.

Network solid : A solid consisting of one huge molecule in which all atoms are connected via a network of covalent bonds.

Neutron : An electrically neutral subatomic particle found in the nucleus.

Noble gas notation : An abbreviated electron configuration of an element in which filled inner shells are represented by the symbol of the preceding noble gas in brackets.

Noble gases : Gaseous elements in Group 8A; the least reactive elements.

Noncovalent interactions : All forces of attraction other than covalent, ionic, or metallic bonding.

Nonelectrolyte : A substance that dissolves in water to form an electrically nonconductiong solution.

Nonpolar molecule : A molecule that is not polar because it has no polar bonds or because its polar bonds are oriented symmectrically so that they cancel each other.

Normal boiling point : The temperature at which the vapor pressure of a liquid equals 1 atm.

Nuclear fusion : The highly exothermic process by which comparatively light nuclei combine to form hevier nuclei.

Nuclear reaction : Spontaneous emission of radiation by an unstable nucleus that is converted into a more stable nucleus of a different element.

Nucleon : A nuclear particle, either a neutron or a proton.




Octet rule : In forming bonds, many main group elements gain, lose, or share electrons to achieve a stable electron configuration characterized by eight valence elctrons.

Orbital: A region of an atom or molecule within which there is a significant probability that an electron will be found.

Order of reaction: The reaction rate dependency on the concentration of a reactant or product, expressed as an exponent of a concentration term in the same equation.

Osmosis: The movement of a solvent (water) through a semipermeable membranc from a region of lower solute concentration to a region of higher solute concentration.

Osmotic pressure (II): The pressure that must be applied to a solution to stop osmosis from a sample of pure solvent.

Overall reaction order: The sum of the exponents for all concentration terms in the rate equation.

Oxidation: The loss of electrons by an atom, ion, or molecules, leading to an increase in oxidation number.

Oxidation number (oxidation state): A comparison of the charge of an uncombined atom with its actual charge or its relative charge in a compound.

Oxidizing agent: The substance that accepts electron(s) and is reduced in an oxidation-reduction reaction.



p- block elements: Main- group elements in group 3A throught 8A whose valence electrons consist of outermost s and p electrons.

Paramagnetic: Refers to atoms, molecules, or ions that are attracted to a magnetic field because they have unpaired electrons in incompletely filled electron subshells.

Partial pressure: The pressure that one gas in a mixture of gas in a mixture of gases would exert it if it occupied the same volume at the same temperature as the mixture.

Parts per billion (ppb): One part in one billion parts.

Parts per million (ppm): One part in one million parts.

Pauli exclusion principle: An atomic principle that states that, at most, two electrons can be assigned to the same orbital in the same atom or molecule , and these two electrons must have opposite spins.

Percent abundance: The percentage of atoms of a natural sample of the pure element that consists of a particular isotope.

Percent composition by mass: The percentage of the mass of a compound represented by each of its constituent elements.

Percent yield: The ratio of actual yield to theoretical yield, multiplied by 100%.

Periodic table: A table of elements arranged in order of increasing atomic number so that those with similar chemical and physical properties fall in the same vertical groups.

Periods: The horizontal rows of the periodic table of elements.

pH: The negative logarithm of the hydronium ion concentration.

Phase: Any of the three states of matter: gas, liquid, solid. Also one of several solid-state structures of the same subtance.

Phase change: A physical process in which one state or phase of matter is changed into another( such as melting a solid to form a liquid).

Phase diagram: A diagram showing the relationships among the three phases of a substance (solid, liquid, and gas), at different temperatures and pressures.

Photoelectric effect: The emitting of electrons by some metals when illuminated by light of certain wavelengths.

Photon: A massless particle of light whose energy is given by hv, where v is the frequency of the light and h is Planck's constant.

Photosynthesis: A series of reactions in a green plant that contains carbon dioxide with water to form carbohydrate and oxygen.

Physical changes : Changes in the physical properties of a substance, such as the transformation of a solid to a liquid.

Physical properties : Properties (e.g., melting point or density) that can be observed and measured without changing the composition of a substance.

Polar covalent bond : A covalent bond between atoms with different electronegativities; bonding electrons are shared unequally between the atoms.

Polar molecule : A molecule that is polar because it has polar bonds arranged so that electron density is concentrated at one end of the molecule.

Polarization : The induction of a temporary dipole in a molecule or atom by shifting of electron distribution.

Precipitate : An insoluble product of an exchange reaction in aqueous solution.

Principal energy level : An energy level containing orbitals with the same quantum number (n = 1, 2, 3...).


Quantum : The smallest possible unit of a distinct quantity; for example, the smallest possible unit of energy for electromagnetic radiation of a given frequency.


Radioactivity : The spontaneous emission of energy and/or subatomic particles by unstable atomic nuclei; the enrgy or particles so emitted.

Raoult's law : A mathematical expression for the vapor pressure of the solvent in a solution.

Rate : The change in some measurable quantity per unit time.

Rate constant (k) : A proportionality constant relation reaction rate and reactant concentrations of reactants and other species that affect the rate of a specific reaction.

Rate law (rate equation) : A mathematical equation that summarizes the relationship between concentrations and reaction rate.

Rate-limiting step : The slowest stepin a reaction mechanism.

Reactant : A substance that is initially present and undergoes change in a chemical reaction.

Reactant-favored system : a system in which, when a reaction appears to be over, reactants predominate over products.

Reaction intermediate : An atom, molecule, or ion produced in one step and used in a later step in a reaction mechanism; doesn't appear in the equation for the overall reaction.

Reaction mechanism : a sequence of unimolecular and bimolecular elementary reactions by which an overall reaction may occur.

Reaction quotient (Q) : A value found from an expression with the smae mathematical form as the equilibrium constant espression but with the actual concentrations in the mixture not at equilibrium.

Reaction rate : The change in concentration of a reactant or product per unit time.

Redox reaction ( oxidation-reduction reaction) : A reaction involving the transfer of one or more electrons from one species to another so that oxidation numbers change.

Reduced : The result when an atom, molecule, or ion gains an electron(s).

Reducing agent : The atom, molecule, or ion that donates electron(s) and is oxidized in an oxidation-reduction reaction.

Reduction : The gain of electrons by an atom, ion, or molecule, leading to a decrease in its oxidation number.

Resonance structures : The possible structures of a molecule for which more than one Lewis structure can be written, differing by the arrangement of electrons but having the same arrangement of atomic nuclei.

Reverse osmosis : Application of pressure greater than the osmotic pressure to cause solvent to flow through a semipermeable membrane from a concentrated solution to a solution of lower soluteconcentration.

Reversible process : Aprocess for which a very small change in conditions will cause a reversal in direction.


S-block elements : Main group elemnts in Group 1A and 2A whose valence electrons are s electrons.

Salt : An ionic compound whose cations comes from an acid.

Salt bridge : A device for maintaining balance of ion charges in the compartments of an electrochemical cell.

Saturated solution: A solution in which the concentration of solute is the concentration that would be in equilibrium with undisolved solute at a given temperature.

Second law of thermodynamics: The total entropy of the universe (the system and surroundings) is continually increasing. In any product-favored system, the entropy of the universe is greater after a reaction than it was before.

Semiconductor: Material with a narrow energy gap between the valence band and the conduction band; a conductor when an electric field or a higher temperature is applied.

Semipermeable membrane: A thin layer of material through which only certain kinds of molecules can pass.

Shifting an equilibrium: Changing the conditions of an equilibrium system so that the system is no longer at equilibrium and there is a net reaction in either the forward or reverse direction until equilibrium is reestablished.

Sigma (o) bond: A bond formed by head-to-head orbital overlap along the bond axis.

Single covalent bond: A bond formed by sharing one pair of electrons between the same two atoms.

Solid: A state of matter in which a substance has a definite shape and volume.

Solubility: The maximum amount of solute that will dissolve in a given volume of solvent at a given temperature when pure solute is in equilibrium with the solution.

Solubility product constant: An equilibrium constant that is the product of concentrations of ions in a solution in equilibrium with a solid ionic compound.

Solubility product expression: Molar concentrations of a cation and anion, each raised to a power equal to its coefficient in the balanced chemical equation for the solubility equilibrium.

Solute: The material dissolved in a solution.

Solution: A homogeneous mixture of two or more substances in a single phase.

Solvent: The medium in which a solute is dissolved to form a solution.

sp hybrid orbitals: Orbitals of the same atom formed by the combination of one s orbital and one p orbital.

Specific heat capacity: The quantity of energy that must be transferred to 1 g of a substance to increase its temperature by 1 degree C.

Spectator ion: An ion that is present in a solution in which a reaction takes place, but is not involved in the net process.

Spectrochemical series: A list of ligands in the order of their crystal-field splitting energy.

Spectrum: A plot of the intensity of light ( photons per unit of time) as a function of the wavelegnths or frequency of light.

Standard atmosphere (atm): A unit of pressure; 1atm equals 760mm Hg exactly.

Standard enthalpy change: The enthalpy change when a process occurs with reactants and products all in their standard states.

Standard equilibrium constant: An equilibrium constant in which each concentration (or pressure) is divided by the standad-state concentration (or pressure); if concentrations are expressed in moles per liter (or pressures in bars) then the concentration (or pressure) equillibrium constant equals the standard equilibrium constant .

Standard hydrogen electrode: The electrode against which standard reduction potentials are measured, consisting of a platinum electrode at which 1 M hydronium ion is reduced to hydrogen gas at 1 bar.

Standard molar enthalpy of formation: The standard enthalpy change for forming 1 mol of a compound from its elements, with all the substances in their standard states.

Standard molar volume : The volume occupied by exactly 1 mol of an ideal gas at standard temperature (o degrees celsius) and pressure (1atm), equal to 22.414 L.

Standard reduction potential: The potential of an electrochemical cell when a given electrode is paired with a standard hydrogen electrode under standard conditons.

Standard state: The most stable form of a substance in the physical state in which it exists at 1 bar and a specified temperature.

Standard solution: A solution whose concentration is known accurately.

Standard temperature and pressure (STP): Universally accepted experimental conditions for the study of gases, defined as a temeperature of 0 degrees celsius and a pressure of 1 atm.

Standard voltages: Electrochemical cell voltages measures under standard conditions.

State functions: A property whose value is invariably the same if a system is in the same state.

Stoichiometric coefficients: The multiplying numbers assigned to the species in a chemical equation in order to balance the equation.

Stoiciometric factor ( mole ratio): A factor relating moles of a reactant or product to moles of another reactant and product.

Stoichiometry: The study of the quantative relations between amounts of reactants and products.

Strong acid : an acid that ionizes completely in aqueous solution.

Strong base : A base that ionizes completely in aqueous solution.

Strong electrolyte : An electrolyte that is completely converted to ions in aqueous solution.

Structural formula : Formulas written to show how atoms in a molecule are connected to each other.

Sublimation : Conversion of a solid directly to a gas with no formation of liquid.

Subshell : A group of atomic orbitals with the same n and l quantum numbers.

Substance : Matter of a particular kind; each substance, when pure, has a well-defined composition and a set of characteristic properties that differ from the properties of any other substance.

Substrate : A molecule or molecules whose reaction is catalyzed by an enzyme.

Superconducter : A substance that, below some temperature, offers no resistance to the flow of electric current.

Supercritical fluid : A substance above its critical temperature; has density characteristic of a liquid, but flow properties of a gas.

Supersaturated solution : a solution that temporarily contains more solute per unit volume than the saturation concentration.

Surface tension : The enrgy required to overcome the attractive forces between molecules at the surface of a liquid.

Surroundings : Everything that can exchange energy with a thermodynamic system.

System : In thermodynamics, the part of the universe that is singled out for observation and analysis. The region of primary concern.


Temperature : The physical property of matter that determines whether there can be heat energy transferred from one object to another.

Theoretical yield : The maximum quantity of product theoretically obtainable from a given quantity of reactant in a chemical reaction.

Theory : A unifying principle that explains a body of facts and the laws based on them.

Thermochemical equation : A balanced chemical equation, including specification of the states of matter of reactants and products, together with tesponding value of the enthalpy change.

Thermodynamics : The science of heat, work, and the transformation of one into the other.

Third law of thermodynamics : A perfect crystal of any substance at 0 K has minimum entropy.

Titrant : The standard solution being added to the unknown solution in the course of carrying out a titration.

Titration: A procedure wherby a substance in a standard solution reacts with a known stoichiometry with a substance whose concentration is to be determined.




Uncertainty principle : The statement that if it is impossible to determine simutaneously the exact position and the exact momentum of an electron.

Unit cell : A small portion of a crystal lattice that can replicated in each of the three directions to generate the entire lattice.

Unsaturated fats : Fats (or oils) that contain one or more carbon-carbon double bonds in their hydrocarbon chains.


Unstaurated hydrocarbon : a hydrocarbon containing double or triple carbon-carbon bonds.