Glossary for Chemistry 115/116 courtesy of the General Chemistry site at Purdue University
absolute entropy: represents the entropy change of a substance taken from absolute zero to a given temperature.
absolute zero: the temperature at which all possible heat has been removed from an object.
acid: a compound that donates a hydrogen ion (H+) to another compound.
acid-base reaction: reaction occurring when a hydrogen atom is transferred from a Bronsted acid to a Bronsted base.
activated complex: an unstable combination of reacting molecules that is intermediate between reactants and products.
activation energy: the minimum energy necessary to form an activated complex in a reaction.
addition reaction: reaction of two or more substances to give another substance.
alpha decay: the loss of an alpha particle during radioactive decay.
alpha particle: a helium nucleus; i.e., a helium atom that has lost two electrons.
amino acid: a substance containing both an amine group and a carboxylic acid group. Proteins are composed of amino acids.
amorphous solid: a solid that lacks a crystalline structure.
amphiprotic: a species that may either gain or lose a proton in reaction.
anion: a negative ion.
anaerobic decomposition: the decomposition of organic matter in the absence of oxygen.
anode: the electrode at which oxidation takes place in an electrochemical cell.
antibonding orbital: molecular orbital located outside of the region between two nuclei. Electrons in an antibonding orbital destabilize the molecule.
Arrhenius equation: expresses the relationship between the rate constant and the activation energy of a reaction.
Aufbau process: process by which chemists illustrate the electronic structures of the elements by "building" them in atomic order, adding one proton to the nucleus and one electron to the proper subshell at a time.
Avogadro's law: equal volumes of all gases, measured under the same conditions of temperature and pressure, contain the same number of molecules.
Avogadro's number: the number of atoms contained in exactly 12 grams of 12C, equal to 6.022 x 1023 atoms.
azeotropic mixture: a solution that forms a vapor with the same concentration as the solution, distilling without a change in concentration.
azimuthal quantum number (l): a quantum number distinguishing the different shapes of orbitals.
band: the orbitals, or energy levels, that extend through a crystal. The way in which these bands are filled or not filled with electrons determines whether the substance is a metal, a semiconductor or an insulator.
barometer: a device used to measure air pressure.
base: a compound that accepts a hydrogen ion (H+).
beta decay: the breakdown of a neutron into a proton, which remains in the nucleus, and an electron, which is emitted as a beta particle.
bimolecular reaction: the collision and combination of two reactants to give an activated complex in an elementary reaction.
boiling point: the temperature at which the vapor pressure of a liquid equals the pressure of the gas above it.
binary compound: a compound containing two different elements.
boiling-point elevation: the elevation of the boiling point of a liquid by addition of a solute.
body-centered cubic structure: a crystalline structure that has a cubic unit cell with lattice points at the corners and in the center of the cell.
bond angle: the angle between any two covalent bonds that include a common atom.
bond distance: the distance between the nuclei of two bonded atoms.
bond energy: the energy required to break a covalent bond in a gaseous substance.
bonding orbital: molecular orbital located between two nuclei. Electrons in a bonding orbital stabilize a molecule.
bond order: in a Lewis formula, the number of bonding pairs of electrons between two atoms. The molecular- orbital bond order is the net number of pairs of bonding electrons, or the difference between the number of bonding and anti-bonding electrons divided by two.
Born-Haber cycle: cyclic process used to relate the enthalpy of formation of a compound to its lattice energy, the ionization energy, the electron affinity, the enthalpy of sublimation, and the bond dissociation energy of its constituents.
Boyle's law: the volume of a given mass of gas held at constant temperature is inversely proportional to the pressure under which it is measured. PV = k.
Bronsted acid: a compound that donates a hydrogen ion (H+) to another compound.
Bragg equation: an equation which relates the angles at which X-rays are scattered by planes with a separation d.
Bronsted base: a compound that accepts a hydrogen ion (H+).
buffer capacity: the amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly.
buffer solution: a mixture of a weak acid or weak base and its salt. The pH of a buffer resists change when small amounts of acid or base are added.
calorie: a non-SI unit representing the amount of heat or other energy necessary to raise the temperature of one gram of water one degree Celsius. 1 cal = 4.184 J.
calorimetry: the process of measuring the amount of heat involved in a chemical or physical change.
catalysis: the increase in the speed of a chemical reaction caused by a catalyst.
catalyst: a substance that changes the speed of a chemical reaction without affecting the yield or undergoing permanent chemical change
cathode: the electrode at which reduction takes place in an electrochemical cell.
cathode ray: stream of particles (electrons) emanating from the negative electrode in an evacuated glass tube.
cathodic protection: method of preventing corrosion of iron or steel by suspending stainless steel anodes in the tank and passing a small current continuously through the system.
cation: a positive ion.
cell potential: the difference in potential between the two electrodes of a cell.
chain mechanism: a series of elementary reactions that repeat over and over to produce a product.
chain reaction: repeated fission caused when the neutrons released in fission bombard other atoms.
Charles's law: the volume of a given mass of gas is directly proportional to its Kelvin temperature when the pressure is held constant. V/T = k.
chelating ligand: a ligand that is attached to a central metal ion by bonds from two or more donor atoms.
chemical thermodynamics: the chemical science that deals with the energy transfers and transformations that accompany chemical and physical changes.
cis configuration: configuration of a geometrical isomer in which two groups are on the same side of an imaginary reference line on the molecule.
colligative properties: properties of a solution that depend only on the concentration of a solute species.
colloid: insoluble particles (larger than single molecules) in a stable suspension.
combination reaction: reaction of two or more substances to give another substance.
common ion effect: the shift in equilibrium caused by the addition of a substance with an ion in common with the substances in equilibrium.
compound: a pure substance with an invariant composition that can be decomposed, producing either elements or other compounds, by chemical change.
concentration: the relative amounts of solute and solvent present in a solution.
condensation: the change from a vapor to a condensed state (solid or liquid).
conjugate acid: substance formed when a base gains a hydrogen ion. Considered an acid because it can lose a hydrogen ion to reform the base.
conjugate base: substance formed when an acid loses a hydrogen ion. Considered a base because it can gain a hydrogen ion to reform the acid.
constant boiling solution: a solution that forms a vapor with the same concentration as the solution, distilling without a change in concentration.
coordinate covalent bond: a bond formed when one atom provides both electrons in a shared pair.
coordination compound: a molecule or ion formed by the bonding of a metal atom or ion to two or more ligands by coordinate covalent bonds
coordination number: the number of atoms closest to any given atom in a crystal.
coordination sphere: the central metal ion plus the attached ligands of a coordination compound.
coulomb: the quantity of electricity involved when a current of one ampere flows for one second.
covalent bond: bond formed when pairs of electrons are shared between atoms.
covalent radius: half the distance between the nuclei of two identical atoms when they are joined by a single covalent bond.
critical pressure: the pressure required to liquefy a gas at its critical temperature.
critical temperature: the temperature above which a gas cannot be liquefied, no matter how much pressure is applied.
crystal defect: a variation in the regular arrangement of the atoms or molecules of a crystal.
crystalline solid: a homogeneous solid in which the atoms, ions or molecules assume ordered positions.
cubic closest packed structure: a crystalline structure in which planes of closest packed atoms or ions are stacked ABCABC.
Dalton's law: the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of the component gases.
daughter nuclide: a nuclide produced by the radioactive decay of another nuclide. May be stable or may decay further.
decomposition reaction: reaction in which one compound breaks down into two or more substances.
degenerate orbitals: orbitals having the same energy.
density: mass per unit volume of a substance.
diamagnetic substance: substance that contains no unpaired electrons. Diamagnetic substances tend to move out of a magnetic field.
diffusion: the movement of gas molecules through the gas.
dipole: the separation of charge in a bond or a molecule with a positively charged end and a negatively charged end.
dipole-dipole attraction: the intermolecular attraction of two dipoles.
diprotic acid: an acid containing two ionizable hydrogen atoms per molecule. A diprotic acid ionizes in two steps.
disproportionation: oxidation-reduction reaction in which the same element is both oxidized and reduced.
dissociation constant: the equilibrium constant for the decomposition of a complex ion into its components in solution.
double bond: a bond in which two pairs of electrons are shared between two atoms.
Einstein equation: equation for determining the amount of energy resulting from the conversion of matter to energy.
electrode: a conductor that delivers electricity into a cell without necessarily entering into the cell reaction. Also, a system in which a conductor is in contact with a mixture of oxidized and reduced forms of some chemical species.
electrode potential: the difference between the charge on an electrode and the charge in the solution.
electrolysis: the input of electrical energy as a direct current to force a nonspontaneous reaction to occur.
electrolyte: ionic or covalent compounds that melt to give liquids that contain ions or that dissolve to give solutions that contain ions.
electrolytic conduction: the movement of ions through a molten substance, a solution, or occasionally, a solid.
electromotive force: the difference in potential between two half-cells.
electron affinity: a measure of the energy involved when an electron is added to a gaseous atom to form a negative ion.
electron capture: capture of an electron by an unstable nucleus. The electron converts a proton to a neutron in the nucleus.
electron configuration: electronic structure of an atom.
electronegativity: the attraction of an atom for the electrons in a covalent bond.
element: a substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change.
elementary reaction: a reaction that cannot be broken down into smaller steps.
empirical formula: a formula showing the composition of a compound given as the simplest whole-number ratio of atoms.
end point: the point during a titration when an indicator shows that the amount of reactant necessary for a complete reaction has been added to a solution.
endothermic reaction: a chemical reaction or physical change
enthalpy change: the heat lost or absorbed by a system under constant pressure during a reaction.
entropy: the randomness, or amount of disorder, of a system.
entropy change: the change in entropy that accompanies a chemical or physical change. The entropy change is given by the sum of the entropies of the products of a chemical change minus the sum of the entropies of the reactants.
equilibrium: the state at which the conversion of reactants into products and the conversion of products back into reactants occur simultaneously at the same rate.
equilibrium constant: the value of the reaction quotient for a system at equilibrium.
equivalent: an equivalent of an acid is the mass of acid required to provide one mole of hydrogen ions in a reaction; an equivalent of a base is the mass of base required to react with one mole of hydrogen ions. An equivalent of an oxidizing agent or of a reducing agent is the mass of the agent that combines with or releases one mole of electrons, respectively.
evaporation: the change of a liquid into a gas.
excited state: state in which an atom or molecule picks up outside energy, causing an electron to move into a higher-energy orbital.
exothermic reaction: a chemical reaction or physical change that produces heat.
expansion work: work transferred between a system and its surroundings as the system expands or contracts against a constant pressure.
face-centered cubic structure: a crystalline structure with a cubic unit cell with lattice points on the comers and in the center of each face.
Faraday: the charge on one mole of electrons. 1 F = 96,487 coulombs
Faraday's law: the amount of a substance undergoing a chemical change at each electrode during electrolysis is directly proportional to the quantity of electricity that passes through the electrolytic cell.
first ionization energy: the energy required to remove the most loosely bound electron from a gaseous atom.
first law of thermodynamics: the total amount of energy in the universe is constant.
fission: the splitting of a heavier nucleus into two or more lighter nuclei, usually accompanied by the conversion of mass into large amounts of energy.
formation constant: the equilibrium constant for the formation of a complex ion from its components in solution.
formula weight: the sum of the atomic weights of the atoms found in one formula unit of an ionic compound.
free energy change: a predictor of the spontaneity of a chemical reaction at constant temperature.
freezing point: the temperature at which the solid and liquid phases of a substance are in equilibrium.
freezing-point depression: the lowering of the freezing point of a liquid by addition of a solute.
frequency factor: in the Arrhenius equation, a constant indicating how many collisions have the correct orientation to lead to products
fusion: the combining of very light nuclei into heavier nuclei, accompanied by the conversion of mass into large amounts of e
gamma ray: high energy electromagnetic radiation.
gas: the state in which matter has neither definite volume nor shape.
gas constant: constant derived from the ideal gas equation, PV = nRT. R = 8.314 L kPa/mol K.
Gay-Lussac's law: the volume of gases involved in a reaction, at constant temperature and pressure, can be expressed as a ratio of small whole numbers.
geometrical isomers: isomers that differ only in the way that atoms are oriented in space relative to each other.
glass: an amorphous solid.
Graham's law: the rates of diffusion of gases are inversely proportional to the square roots of their densities (or their molecular weights).
ground state: state in which the electrons in an atom, ion, or molecule are in the lowest energy orbitals possible.
half-cell: an electrode containing both an oxidized and a reduced species.
half-life: the time required for half of the atoms in a radioactive sample to decay.
half-life of a reaction: the time required for half of the original concentration of the limiting reactant to be consumed.
half-reaction: one of the two parts (oxidation or reduction) of an oxidation-reduction reaction.
hard water: water containing dissolved calcium, magnesium, and/or iron salts.
heat: the form of energy that moves spontaneously from a warmer object to a cooler one.
heat capacity: a property of a body of matter that represents the quantity of heat required to increase its temperature by one degree Celsius.
heat of fusion: the energy needed to change a given quantity of a substance from the solid state to the liquid state at a constant temperature.
heat of reaction: the heat lost or absorbed by a system in a reaction.
heat of vaporization: the energy needed to evaporate a given quantity of liquid at a constant specified temperature.
Heisenberg uncertainty principle: it is impossible to determine accurately both the momentum and the position of a particle simultaneously.
Henry's law: the mass of a gas that dissolves in a definite volume of liquid is directly proportional to the pressure of the gas provided the gas does not react with the solvent.
Hess's law: if a process can be written as the sum of several stepwise processes, the enthalpy change of the total process equals the sum of the enthalpy changes of the various steps.
heteronuclear diatomic molecule: diatomic molecules composed of two different elements.
heterogeneous catalyst: a catalyst present in a different phase than the reactants, furnishing a surface at which a reaction can occur.
heterogeneous equilibrium: an equilibrium between two or more different phases, involving a boundary surface between the two phases.
hexagonal closest packed structure: a crystalline structure in which close packed layers of atoms or ions are stacked ABABAB; the unit
homogeneous catalyst: a catalyst present in the same phase as the reactants.
homogeneous equilibrium: an equilibrium within a single phase.
homonuclear diatomic molecule: molecules composed of two identical atoms.
Hund's rule: every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin.
hybridization: a model that describes the changes in the atomic orbitals of an atom when it forms a covalent compound.
hydrocarbon: a compound composed only of hydrogen and carbon. The major component of fossil fuels.
hydrogen bond: the strong electrostatic attraction that occurs between molecules in which hydrogen is in a covalent bond with a highly
hydrogen salt: a salt in which only part of the acidic hydrogens of a polyprotic acid are replaced by a cation.
hydronium ion: a water molecule with an added hydrogen ion.
ideal gas: a gas that follows Boyle's Law, Charles's Law, and Avogadro's Law perfectly.
ideal solution: a solution formed with no accompanying energy change, when the intermolecular attractive forces between the molecules of the solvent are the same as those between the molecules in the separate components.
insulator: a crystal that has bands that are completely filled or completely empty, with large energy gaps between them. An insulator does not conduct electricity.
intermolecular force: the attractive force between two molecules.
internal energy: the total of all possible kinds of energy present in a substance or substances.
interstitial site: a position between the regular positions in an array of atoms or ions that can be occupied by other atoms or ions.
intramolecular force: the attractive force between the atoms making up a molecule.
ion: charged particle resulting from the loss or gain of one or more electrons from an atom or molecule.
ion activity: the effective concentration of any particular kind of ion in solution. It is less than indicated by the actual concentration of a solution.
ion-dipole attraction: the electrostatic attraction between an ion and the dipole of a molecule.
ion exchange: a method of softening water by filtering it through layers of sodium aluminosilicates (zeolites), which exchange sodium or hydrogen ions for Ca2+, Mg2+, or Fe2+ in the water.
ionic bond: the electrostatic attraction between positive and negative ions in an ionic compound.
ionic compound: a compound composed of ions.
ionic radius: the radius of an ion.
ionization constant: the equilibrium constant for the ionization of a weak acid or base.
ionization energy: the amount of energy required to remove an electron from the valence shell of a gaseous atom.
ion product for water: the equilibrium constant for the autoionization of water. At 25oC, Kw = 1.00 x 10-14 (mol/L)2 .
isoelectronic species: a group of ions, atoms, or molecules that have the same arrangement of electrons.
isomorphous structures: two elements or compounds that crystallize with the same structure.
isotopes: atoms with the same atomic number and different numbers of neutrons.
joule: the SI unit of energy. One joule is the kinetic energy of an object with a mass of 2 kilograms moving with a velocity of one meter per second. 1 J = 1 kg m2 s-2. 4.184 J = 1 cal.
Ka: the equilibrium constant for the reaction of an acid with water.
Kb: the equilibrium constant for the reaction of an base with water.
Kelvin: the SI unit of temperature. 273.15 K = 0 Celsius.
kinetic energy: the kinetic energy of a moving body, in joules, is equal to 1/2mv2 (m = mass in kilograms; v = speed in meters per second).
kilogram: standard SI unit of mass. Approximately 2.2 pounds.
kinetic molecular theory: theory that explains the properties of an ideal gas and assumes that such a gas consists of continuously moving molecules of negligible size.
lattice energy: the energy required to separate the ions or molecules in a mole of a compound by infinite distances.
lattice point: a point in a space lattice.
law of definite proportion: all samples of a pure compound contain the same elements in the same proportion by mass.
law of mass action: when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant.
Le Châtelier's principle: if a stress is applied to a system in equilibrium, the equilibrium shifts in a way that tends to undo the effect of the stress.
lewis acid: any species that can accept a pair of electrons and form a coordinate covalent bond.
lewis base: any species that can donate a pair of electrons and form a coordinate covalent bond.
Lewis structure: diagram showing shared and unshared pairs of electrons in an atom, molecule, or ion.
Lewis symbol: the symbol for an element showing a dot for each valence electron in the element or ion.
ligand: an ion or neutral molecule attached to the central metal ion in a coordination compound.
ligand field splitting: the difference in energy between the metal's eg and t2g orbitals in a coordination complex.
ligand field stabilization energy: a measure of the increased stability of a complex showing ligand field splitting.
limiting reagent: the reactant completely consumed by a chemical reaction. The amount of the limiting reagent limits the amount of product that can be formed.
liquid: the state in which matter takes the shape of its container, assumes a horizontal upper surface, and has a fairly definite volume.
liter: unit of volume. 1 L = 1000 cm3.
London force: the attraction between two rapidly fluctuating, temporary dipoles. Of significance only if atoms are very close together.
magnetic quantum number: quantum number signifying the orientation of an orbital around the nucleus.
mass defect: the difference between the calculated and experimental mass of a nucleus.
mass number: the sum of the number of neutrons and protons in the nucleus of an atom.
matter: anything that occupies space and has mass.
melting point: the temperature at which the solid and liquid phases of a substance are in equilibrium.
metal: a substance that is malleable and ductile, has a characteristic luster, and is generally a good conductor of heat and electricity. The bands of a metal are partially filled.
metallic conduction: the movement of electrons through a metal, with no changes in the metal and no movement of the metal atoms.
metathetical reaction: a reaction in which two or more compounds exchange parts.
meter: standard metric and SI unit of length. Approximately 1.094 yards.
misciblity: the ability of a liquid to mix with another liquid.
mixture: matter that can be separated into its components by physical means.
molality: the number of moles of solute dissolved in exactly one kilogram of solvent.
molarity: the number of moles of solute dissolved in one liter of solution.
molar mass: mass in grams of one mole of an element or compound. Numerically equal to the molecular weight of a molecule or the atomic weight of an atom.
molar volume: the volume of one mole of an ideal gas (22.4 liters at STP).
mole: the number of atoms contained in exactly 12 grams of carbon-12 (Avogadro's number). 1 mol = 6.022 x 1023 atoms, molecules, or ions
molecule: a bonded collection of two or more atoms of the same or different elements.
molecular formula: a formula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound.
molecular orbital: the discrete energy and region of space around the nuclei of the atoms in a molecule in which an electron can be found
molecular structure: the three-dimensional, geometrical arrangement of the atoms in a molecule.
molecular weight: the sum of the atomic weights of each atom in a particular molecule.
mole fraction: the number of moles of a component of a solution divided by the total number of moles of all components.
monoprotic acid: an acid containing one ionizable hydrogen atom per molecule.
Nernst equation: used to calculate emf values at other than standard conditions.
neutralization: a reaction that occurs when stoichiometrically equivalent quantities of an acid and a base are mixed.
neutron: an uncharged subatomic particle with a mass of 1.0087 amu.
nonelectrolyte: a compound that does not ionize when dissolved in water.
nonmetal: an element that is brittle and nonductile as a solid, has no luster, and is a poor conductor of heat and electricity.
normality: the number of equivalents of solute dissolved in one liter of solution.
normal boiling point: the temperature at which a liquid's vapor pressure equals one atm.
nuclear binding energy: the energy produced by the loss of mass accompanying the formation of an atom from protons, electrons, and neutrons.
nuclear force: the force of attraction between nucleons that holds a nucleus together.
nucleon: collective term for protons and neutrons.
nucleus: the very heavy, positively charged body located at the center of an atom.
nuclide: the nucleus of a particular isotope.
octahedral hole: an octahedral space between six atoms or ions in a crystal.
optical isomers: isomers that are mirror images of each other and that are optically active.
optically active molecules: molecules that rotate the plane of vibration of plane-polarized light.
orbital: a three-dimensional region around the nucleus in which an electron moves; can hold up to two electrons.
order of a reaction: with respect to one of the reactants, the order of a reaction is equal to the power to which the concentration of that reactant is raised in the rate equation.
osmosis: the tendency of a solvent to diffuse through a semipermeable membrane from the less concentrated to the more concentrated solution
osmotic pressure: the pressure required to stop the osmosis from a pure solvent into a solution.
oxidation: the loss of electrons or an increase in oxidation number.
oxidation number: number used to keep track of the redistribution of electrons during chemical reactions. The sum of the oxidation numbers of all atoms in a neutral compound is zero.
oxidation-reduction reaction: reaction in which oxidation numbers change as electrons are lost by one atom and gained by another.
oxidizing agent: the substance in an oxidation-reduction reaction that gains electrons and whose oxidation number is reduced.
paramagnetic substance: a substance containing unpaired electrons. Paramagnetic substances tend to move into a magnetic field.
parent nuclide: an unstable nuclide which changes spontaneously into another (daughter) nuclide.
partial pressure: the pressure exerted by an individual gas in a mixture of gases.
Pauli exclusion principle: no two electrons in the same atom can have the same set of four quantum numbers.
percent yield: the actual yield of an experiment divided by the theoretical yield and multiplied by 100.
periodic law: the properties of the elements are periodic functions of their atomic numbers.
photon: a quantum of light or other electromagnetic radiation. The energy of a photon equals the product of Planck's constant and its frequency.
physical change: a change in the state or properties of a particular kind of matter that does not involve a chemical change.
physical property: characteristics of a particular kind of matter that do not involve a chemical change (i.e., color, hardness, physical state).
pi orbital: a molecular orbital formed by side-by-side overlap of atomic orbitals, in which the electron density is found above and below the bond axis.
polar covalent bond: covalent bond between atoms of different electronegativities; a covalent bond with a positive end and a negative end.
polydentate ligand: a ligand that is attached to a central metal ion by bonds from two or more donor atoms.
polymers: compounds of high molecular weight that are built up of a large number of simple molecules, or monomers.
polymorphism: the assumption of two or more crystal structures by the same substance.
polyprotic acid: an acid with more than one proton per molecule that can be given up in a reaction.
positron: an atomic particle with the same mass as an electron but with one unit of positive charge.
pressure: force exerted on a unit area. The SI unit of pressure is the pascal (Pa).
principal quantum number: quantum number specifying the shell of an electron in an atom or a monatomic ion.
proton: a nuclear particle with a mass of 1.0073 amu and carrying a charge of + 1.
quantized: a description of the discrete, or individual, values by which the energy of an electron can vary.
radioactive decay: the spontaneous change of an unstable nuclide (parent) into another nuclide (daughter).
radioactivity: the spontaneous decomposition of an unstable element, with the simultaneous emission of rays of particles.
radius ratio: in an ionic compound, the radius of the positive ion, r+, divided by the radius of the negative ion, r-.
Raoult's law: the vapor pressure of the solvent in an ideal solution is equal to the mole fraction of the solvent times the vapor pressure of the pure solvent.
rate constant: the proportionality constant in the relationship between reaction rate and concentrations of reactants.
rate-determining step: the slowest elementary reaction in a reaction path, which determines the maximum rate of the overall reaction.
rate equations: equations giving the relationship between reaction rate and concentrations of reactants.
reaction mechanism: the stepwise sequence of elementary reactions in an overall reaction.
reaction quotient: a ratio of molar concentrations of the reactants to those of the products, each concentration being raised to the power equal to the coefficient in the equation.
reducing agent: the substance in an oxidation-reduction reaction that gives up electrons, and whose oxidation number is increased.
resonance forms: two or more Lewis structures having the same arrangement of atoms but different arrangements of electrons.
resonance hybrid: the average of the resonance forms shown by the individual Lewis structures.
reversible reaction: a chemical reaction that can proceed in either direction.
salt: an ionic compound composed of cations and anions other than hydroxide or oxide ions.
saturated solution: a solution in which no more solute can be dissolved.
second law of thermodynamics: any spontaneous change that occurs in the universe must be accompanied by an increase in the entropy of the universe.
semiconductor: a substance that contains a full band and an empty band, with small energy gaps between the bands. It is a poor conductor.
semi-metal: substances possessing some of the properties of both metals and nonmetals.
shell: all of the orbitals in an atom or monatomic ion with the same value of n.
sigma orbital: a molecular orbital in which the electron density is found along the axis of the bond.
simple cubic structure: a crystalline structure with a cubic unit cell with lattice points only on the corners.
single bond: a bond in which a single pair of electrons is shared between a pair of atoms.
solid: the state in which matter is rigid, has a definite shape, and has a fairly constant volume.
solid solution: a homogeneous and stable solution of one solid substance in another.
solubility product: the equilibrium constant for the dissolution of a slightly soluble electrolyte.
solution: a homogeneous mixture of a solute in a solvent.
space lattice: all points within a crystal that have identical environments.
specific gravity: the ratio of the density of a substance to the density of a reference substance - for solids and liquids, usually water; for gases, usually air or hydrogen.
specific heat: property of a substance that represents the quantity of heat required to raise the temperature of one gram of the substance one degree Celsius (or Kelvin).
spectrum: the component colors, or wavelengths of light.
spin quantum number: number specifying the direction of the spin of an electron around its own axis.
spontaneous process: a physical or chemical change that occurs without the addition of energy.
stability curve: a plot of the number of neutrons versus the number of protons for stable nuclei.
standard conditions: 273.15 K (0oC) and one atmosphere of pressure (760 torr or 101.325 kilopascals).
standard electrode potential: potential measured with respect to a standard hydrogen electrode at 25oC with one M concentration of each ion in solution and one atm of pressure of each gas involved.
standard hydrogen electrode: assigned an electrode potential of exactly zero. The potential of all other electrodes is reported relative to the standard hydrogen electrode.
standard molar enthalpy of formation: the enthalpy change of a chemical reaction in which one mole of a pure substance is formed from the free elements in their most stable states under standard state conditions.
standard molar entropy: actual entropy content of one mole of a substance in a standard state.
standard state: 298.15 K (25 degrees Celsius) and one atmosphere of pressure.
state function: a property of a system that is not dependent on the way in which the system gets to the state in which it exhibits that property.
stoichiometry: the calculation of both material balances and energy balances in a chemical system
strong acid: an acid that gives a 100% yield of hydronium ions when dissolved in water.
strong base: a base that gives a 100% yield of hydroxide ions when dissolved in water.
strong electrolyte: an electrolyte that gives a 100% yield of ions when dissolved in water.
structural isomers: two substances having the same molecular formula but different physical and chemical properties because the arrangement of their component atoms is different.
structural isomers: two substances having the same molecular formula but different physical and chemical properties because the arrangement of their component atoms is different.
subshell: a set of degenerate orbitals with the same values of n and l.
substitution reaction: a reaction in which one atom replaces another in a molecule.
supercooling: a liquid that is cooled below its freezing point.
supersaturated solution: a solution that contains more solute than it would if the dissolved solute were in equilibrium with the undissolved solute.
surface tension: the force that causes the surface of a liquid to contract, reducing its surface area to a minimum.
surroundings: the universe outside a thermodynamic system.
system: the substance or substances involved in a reaction that is being studied.
temperature: measure of the hotness or coldness of a body.
termolecular reaction: an elementary reaction involving the simultaneous collision of any combination of three molecules, ions, or atoms.
ternary compound: a compound containing three different elements.
tetrahedral hole: a tetrahedral space formed by four atoms or ions in a crystal.
theoretical yield: the calculated yield of a reaction based on the assumptions that there is only one reaction involved, that all the reactant is converted into product, and all the product is collected.
three-center bond: the bonding of three atoms by one pair of electrons in a molecular orbital formed from the overlap of three atomic orbitals.
titration: method of determining the concentration of a solution by adding a solution of a reactant to a solution of sample until an indicator changes color.
trans configuration: configuration of a geometrical isomer in which two groups are on opposite sides of an imaginary reference line on the molecule.
transition state: a combination of reacting molecules that is intermediate between reactants and products.
triple bond: a bond in which three pairs of electrons are shared between two atoms.
triple point: the point at which an equilibrium exists among the vapor, liquid, and solid phases of a substance.
triprotic acid: an acid containing three ionizable hydrogen atoms per molecule. Ionization of triprotic acids occurs in three stages.
unimolecular reaction: an elementary reaction in which the rearrangement of a single molecule produces one or more molecules of product.
unit cell: the portion of a space lattice that is repeated in order to form the entire lattice.
unsaturated solution: a solution in which more solute can be dissolved.
unshared pair: electrons not used in bonding to form a molecule.
valence electrons: electrons in the valence shell of an atom. The number of valence electrons determines how an element reacts.
valence shell: the outermost shell of electrons of a representative element; the outermost shell of electrons and the d electrons in the next inner shell of a d-block element; or the outermost shell of electrons, the d electrons in the next inner shell, and the f electrons in the next inner shell of an f-block element.
van der Waals equation: a quantitative expression of the deviations of real gases from the ideal gas laws.
vapor pressure: the pressure exerted by a gas in equilibrium with a solid or a liquid at a given temperature.
vapor-pressure lowering: the lowering of the vapor pressure of a liquid by addition of a solute.
volt: difference in electrical potential when one joule of energy is required to move 1/96,485 mole of electrons (one coulomb of charge) from a lower potential to a higher potential.
voltaic cell: any cell that generates an electric current by an oxidation-reduction reaction.
wave function: a mathematical function that describes the shape of the orbital that an electron occupies, the energy of the electron in the orbital, and the probability of finding the electron at any location in the orbital.
weak acid: an acid that gives a 10% or less yield of hydronium ions when dissolved in water.
weak base: a base that gives a 10% or less yield of hydroxide ions when dissolved in water.
weak electrolyte: an electrolyte that gives a low percentage yield of ions when dissolved in water.
work: one process for removing energy from a system or adding energy to it.
yield: the quantity of a product of a chemical reaction.