C
or 0K) at which the volume and pressure of an ideal
gas extrapolate to zero.
| The Glossary |
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Absolute zero - The temperature
(-273.15C
or 0K) at which the volume and pressure of an ideal
gas extrapolate to zero.
Absorption spectrum - The spectrum of dark lines against a light background that results from the absorption of selected frequencies of the electromagnetic radiation by an atom or molecule.
Accuracy - The extent to which a measurement agrees with the true value of the quantity being measured.
Acid-base complex - The product of a reaction between a Lewis acid and a Lewis base. It contains a covalent bond formed by the donating pair of nonbonding electrons from the Lewis base to the Lewis acid.
Acid-base indicator - A weak acid or weak base which changes color when it gains or loses an H+ ion.
Acid-dissociation equilibrium constant (Ka)
- A measure of the relative strength of an acid. For a generic acid
HA, Ka is represented as: 
Acidic buffer - A mixture of a weak acid and its conjugate base that has a pH less than 7 that resists changes in pH when relatively small amounts of acid or base are added.
Activation Energy (Ea) - The energy level that must be overcome by the reactants in a chemical reaction in order for the reaction to occur.
Active metal - A metal that is unusually reactive.
Activity - A measure of the number of disintegrations of a radioactive nuclide per unit time; reported in unites of curries or becquerels.
Acyl chloride - A compound in which a chlorine atom is bound to the carbon atom of a C=O (carbonyl) group.
Addition polymer - A polymer formed without the loss of any atoms in the monomer.
Addition reaction - A reaction in which a molecule adds across a C=C or C=O double bond.
Adhesion - The force of attraction between different substances.
Alcohol - Compounds with an -OH group attached to a carbon atom.
Aldehyde - An alcohol that has by dehydrogenated. Compounds with at least one hydrogen atom attached to a C=O (carbonyl) group.
Algorithm - A set of rules for calculating something that can be taught to a reasonably intelligent system, such as a computer.
Alkali metal - A metal in Group IA. Li, Na, K, Rb, Cs, and Fr
Alkali earth metal - A metal in Group IIA. Be, Mg, Ca, Sr, Ba, and Ra
Alkaloid - A class of organic compounds that contains nitrogen, isolated form plants.
Alkane - A hydrocarbon with the generic formula CnH2n+2 that contains only C-C and C-H bonds. Aka saturated hydrocarbon.
Alkene - A hydrocarbon with the generic formula CnH2n that contains on or more C=C double bonds. Alkenes are unsaturated hydrocarbons.
Alkoxide - The conjugate base of an alcohol.
Alkyl halide - A derivative of an alkane in which a hydrogen atom is replaced by a halogen.
Alkyne - A hydrocarbon
with the generic formula CnH2n-2 that contains one or
more C
C triple bonds. Alkynes are unsaturated hydrocarbons.
Allotropes - Forms of an element with different structures and consequently different chemical and physical properties.
Alloy - A mixture of two or more elements that acts like a metal.
Alpha particle (
)
- A positively charged particle consisting of two protons and two neutrons emitted
by one of the radioactive elements. An alpha particle is equivalent to
an He2+ ion.
Amide - A compound that can be thought of as the product of the reaction between a carboxylic acid (RCO2H) and an amine, such as CH3CONH2. This term is also used to describe the NH2- ion.
Amine - Compound with an -NH2, -NHR, or -NR2 substituent attached to a carbon atom.
Amino acid - One of the essential building blocks from which proteins are made. Amino acids have the generic formula H3N+CHRCO2-.
Amonton's Law -
The Pressure of a gas is directly proportional to the Temperature (Kelvin) at
constant Volume and moles of gas: P 
V
Amorphous - "Without form or shape" Describes substances that are solids but not crystals.
Amphoteric - Description for a compound that can act as either an acid or a base.
Amplitude - The height of a wave. The difference between the center of gravity of the wave and the highest (or lowest) point on the wave.
Amu - Atomic mass unit. The unit in which the relative masses of atoms are expressed.
Angular momentum - For a particle in a spherical orbit, the product of the mass of the particle times its velocity times the radiums of the orbit: mvr
Angular quantum number (l) - The quantum number that describes the shape of an atomic orbital:
Anhydrous - "Without water," A hydrated salt without the water molecules.
Anion - An ion with a negative charge, e.g. Cl-
Anode - The positive end of an electric field. Also the electrode in an electrochemical cell toward which the anions flow and the electrode where oxidation occurs.
Antibonding molecular orbital - A molecular orbital in which electrons are held in a region of space that does not lie between the atoms.
Approximation methods - A technique for obtaining approximate answers to calculations that are difficult, of not impossible to solve exactly.
Aqueous - "Watery," Solutions of substances dissolved in water.
Aromatic compound - A compound that seems to contain C=C double bonds but does not react as an alkene does.
Arrhenius acid - A substance that dissociates when it dissolves in water to give the H+ ion.
Arrhenius base - A substance that dissociates when it dissolves in water to give the OH- ion.
Arrhenius equation
- Describes the relationship between temperature ad the rate constant
for a reaction:
Atactic - Polymers in which the side chains are randomly distributed on either side of the polymer backbone.
Atom - The smallest particle of an element that retains any of the properties of the element.
Atomic mass unit - See Amu
Atomic number (Z) - The number of protons in the nucleus of an atom.
Atomic orbital - A region in space where electrons on an atom can be found.
Atomic weight - The weighted average of the atomic isotopes of an element.
Aufbau principle - The principle that atomic orbitals are filled one at a tim, starting with the orbital at the lowest energy level.
Avogadro's number - The number of particles in a mole: 6.0220 X 1023
Avogadro's hypothesis
- The hypothesis that equal volumes of different gases at the same temperature
and pressure contain the same number of particles: V
n
Axial - The two positions in a trigonal bipyramid that lie above and below the trigonal plane. See equatorial.
Balanced equation - A symbolic representation of a chemical reaction in which both sides of the equation contain equivalent numbers of atoms of each element. Charge and mass are both conserved in a balanced equation.
Band of stability - A narrow band of neutron-to-proton ratios that correspond to stable nuclides.
Base-ionization equilibrium constant (Kb)
- A measure of the relative strength of a base. For the generic base B,
Kb is represented as:
Basic buffer - A mixture of a weak base and its conjugate acid that has a pH greater than 7 that can resist changes in pH when relatively small amounts of acid or base are added.
Battery - Describes a set of electrochemical cells connected in a series.
Beta decay (
)
- A nuclear reaction in which beta particles (electrons
or positrons) are absorbed by or emitted from the nucleus of an atom.
Bidendate - A ligand that binds twice. See chelating ligand.
Bimolecular - A step in a chemical reaction in which two molecules are consumed.
Binding energy - The energy released when the nucleus of an atom is formed by combining neutrons and protons.
Bohr model - A model of the distribution of electrons in an atom based on the assumption that the electron in a hydrogen atom is in one of a limited number of circular orbits. See Bohr model notes.
Boiling point - The temperature at which the vapor pressure of a liquid is equal to the pressure on the liquid (usually atmospheric pressure).
Boiling point elevation - The increase in the boiling point of a solvent that occurs when a solute is added to form a solution.
Bond-dissociation enthalpy - The energy needed to break an X—Y bond to get X and Y atoms in the gas phase.
Bond order - The number of bonds between a pair of atoms.
Bonding electrons - A pair of electrons used to form a covalent bond between adjacent atoms.
Bonding molecular orbital - A molecular orbital in which the electrons reside in the region in space between the atoms.
Boundary - In thermodynamics, the boundary separates the system from its surroundings.
Boyle's Law - The Pressure
(P) of a gas is inversely proportional to Volume (V) at constant Temperature
(T) and moles of gas (n): P
1/V
Breeder reactor - A nuclear reactor that produces more fuel than it consumes.
British thermal unit - See Btu.
Brønsted acid - Any substance that can donate an H+ ion to a base. Brønsted acids are H+ ion/proton donors.
Brønsted base- Any substance that can accept an H+ ion from an acid. Brønsted bases are H+ ion/proton acceptors.
Btu (British thermal unit)
- The heat needed to raise the temperature of 1 lb of water by 1F
Buffer - A mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. Buffers resist a change in the pH of a solution when small amounts of acid or base are added.
Buffer capacity - The amount of acid or base a buffer solution can absorb without significant changes in pH.
Calcining - A process in which an ore loses a gas while being heated.
Caloric theory - An obsolete theory which assumed that heat (or caloric) is a fluid that is conserved.
Calorie - The amount
of heat required to raise the temperature of 1 gram of water by 1C.
The specific
heat of water.
Calorimeter - An apparatus used to measure the heat given off or absorbed in a chemical reaction.
Calx - The powder formed when metals react with air.
Canal rays - The positively charged particles formed when electrons are removed from the gas particles in a cathode-ray tube. Because they carry a positive charge, canal rays move in the opposite direction from the cathode rays.
14C dating - A technique for estimating the age of a sample that assumes that the half life of 14C is 5730 years.
Carbanion - A compound that contains a negatively charged carbon atom.
Carbohydrate - "A hydrate of carbon" Polyhydroxy aldehydes or ketones. Includes sugars and starches. See monosaccharide and polysaccharide.
Carbonium ion - A compound that contains a positively charged carbon atom.
Carbonyl - In organic chemistry, the C=O functional group. In inorganic chemistry, a complex formed when a carbon monoxide (CO)binds to a metal.
Carboxylic acid - A compound that contains the -CO2H functional group.
Carboxylic acid ester - A compound that can be thought of as the product of the reaction between a carboxylic acid (RCO2H) and an alcohol (R'OH). Any compound that contains the RCO2HR' functional group.
Catalyst - A substance that increases the rate of a chemical reaction without being consumed in the reaction by lowering the activation energy (Ea) for the reaction.
Cantenation - The tendency of an element to form bonds to itself.
Cathode - The negative end of an electric field. The electrode in an electrochemical cell toward which the cations flow and the electrode at which reduction occurs.
Cathode rays - The negatively charged particles (now known as electrons) that travel from the cathode toward the anode in a cathode-ray tube.
Cathodic protection - The process in which a structural metal, such as iron, is protected from corrosion by connecting it to a metal that has a more negative reduction potential.
Cation - An ion with a positive charge.
Cell potential - A measure of the driving force behind an electrochemical reaction which is reported in the units of volts.
Chain reaction - A reaction in which one of the starting materials is regenerated in the last step of the reaction.
Chain-reaction mechanism - A mechanism for a chain reaction that consists of chain-initiating, chain-propagating, and chain-terminating steps.
Charles' Law - The Volume of a gas is directly proportional to the Temperature (Kelvin) at constant P and n:
T
Chelating ligand - A ligand that can coordinate to a metal atom more than once.
Chemical equation - A symbolic representation or the relationship between the reactants and the products of a chemical reaction.
Chemical kinetics - The study of the rates of chemical reactions.
Chemiluminescence - A chemical reaction that gives off energy in the form of light instead of heat.
Chiral - An object whose image is not the same as itself. Compounds with four different substituents on a carbon atom.
Chromatography - A technique for separating the components of a mixture on the basis of differences in their affinity for a stationary and mobile phase.
Cis - "On the same side", describes isomers in which similar substituents are on the same side of a C=C double bond or in adjacent coordination sites on a transition metal. See trans.
Coal gas - A gas which is rich in methane (CH4) produced when coal is heated in the absence of air.
Codon - A sequence of three nucleotides on a strand of mRNA that codes for an amino acid.
Cohesion - The force or attraction between molecules of the same substance. See adhesion.
Colligative property - Any property that depends on the number of solute particles in a solution but not their identity.
Collision theory model - A model used to explain the rates of chemical reactions which assumes that molecules must collide in order to react.
Column chromatography - Chromatography that uses a solid support in a vertical column or tube.
Combined equilibria - Two or more equilibria that occur simultaneously and involve the same ion or molecule.
Common-ion effect - The decrease in the solubility of a salt that occurs when the salt is dissolved in a solution that contains another source of one of its ions.
Complex-dissociation equilibrium constant
(Kd) - The equilibrium constant for the reaction in
which a complex dissociates, e.g.: Cu(NH3)42+(aq)
Cu2+(aq) + 4 NH3(aq)
Complex-formation equilibrium constant (Kf)
- The equilibrium constant for the reaction in which a complex is formed, e.g.:
Cu2+(aq) + 4 NH3(aq) Cu(NH3)42+(aq)
Complex ion - An ion in which a ligand is covalently bound to a metal.
Compound - A substance with a constant composition that contains two or more elements.
Compressibility - The ability to be compressed. A characteristic of substances that can be compressed to fit into smaller containers, such as gases.
Concentration - A measure of the ratio of the amount of solute in a solution to the amount of either solvent or solution. Frequently expressed in unites of moles of solute per liter of solution. See molarity.
Condensation polymer - A polymer that is formed when a small molecule is condensed out or lost during polymerization. See addition polymer.
Conduction band - An energy band in a solid in which electrons are free to move, producing a net transfer of charge.
Conductivity apparatus - An instrument used to determine whether a substance or solution can conduct an electric current.
Conjugate acid-base pair - Two substances related by the gain or loss of a proton. Every Brønsted acid has a conjugate Brønsted base. e.g. HCl - acid, Cl- - conjugate base; OH- - base, H2O - conjugate acid.
Conjugate oxidizing and reducing agents - Two substances related by the gain or loss of electrons.
Constitutional isomers - Two compounds that have the same formula but different constituents. See sterioisomers.
Coordination compound - A compound in which one or more ligands are coordinated to a metal atom.
Coordination number - The number of atoms, ions, or molecules to which bonds can be formed.
Copolymer - A polymer formed from two or more different monomers.
Corrosion - A process in which a metal is destroyed by a chemical reaction.
Covalent bond - A bond between two atoms formed by the sharing of a pair of electrons.
Covalent compound - A compound composed of neutral atoms in which the atoms are held together by covalent bonds.
Covalent radius - The radius of an atom in a covalent bond.
Covalent solid - A solid in which every atom is covalently bonded to its nearest neighbors to form an extended array of atoms rather than individual molecules.
Critical point - The temperature and pressure at which two phases of a substance in equilibrium become identical, forming a single phase.
Crystal - A three-dimensional solid formed by regular repetition of the packing of atoms, ions, or molecules.
Crystalline - Materials that behave as if they are made of regular crystals.
Crystal-field theory - An extension of the valence-bond theory used to explain transition metal compounds.
Curie - A unit for measuring the activity of a radioactive nuclide. 1 Ci = 3.700 x 1010 disintegrations per second.
Cycloalkane - An alkane that contains a ring of carbon atoms. Aka cyclic hydrocarbon.
Dalton's law of partial pressures - The total pressure of a mixture of gases is equal to the sum of the partial pressures of the various components: PT = P1 + P2 + P3 + . . . .
deBrogliae equation -
The wavelength (
)
of a particle is inversely proportional to its momentum (p):
Degenerate orbitals - Orbitals that are at the same energy level. e.g. 2px, 2py and 2pz orbitals in a single atom.
Dehydrating agent - A reagent used to remove water.
Denaturation - A process that changes the three-dimensional structure of a protein.
Density - An intensive property of a substance equal to the mass of a sample divided by the volume of the sample.
Diamagnetic - A substance in which all the electrons are paired. An object will not be affected by a magnetic field if it is diamagnetic. See paramagnetic.
Diatomic atom - Atoms which are found paired with themselves in their elemental form, such as O2 or F2.
Diatomic molecule - A molecule that contains two atoms.
Diffusion - The movement of atoms, ions, or molecules through a gas, liquid, or solid
Dilution - The process by which more solvent is added to decrease the concentration of a solution.
Dimensional analysis - An approach to solving problems that focuses on the way the units of the problem are used to set up the problem.
Dimer - "Two parts", A compound that is produced by combining two of the same smaller molecules.
2 NO2 
N2O4
Dipole - Anything with two equal but opposite electrical charges, e.g. the positive and negative ends of a polar bond or molecule.
Diprotic acid - An acid that has the potential to lose two H+ ions. e.g. H2SO4
Diprotic base - A base that has the potential to gain two H+ ions. e.g. H2CO3
Disorder - A measure of the extent to which a system differs from a perfect crystal at 0 K where there is no disorder.
Disproportionation - A reaction in which an element or compound simultaneously undergoes both oxidation and reduction.
Br2
Br- + BrO3
Disaccharide - A carbohydrate formed by lining a pair of monosaccharides.
Dissociation - The process by which salts dissolve in water to give solutions that contain the corresponding ions.
Dissolve - "To loosen", The process in which one substance mixes with another. When a solid dissolves in a liquid, the particles that for the solid are released into solution.
Distillation - A technique used to separate liquids with different boiling points.
Disulfide linkage - The -S-S- linkage that can form between the -SH side chains on adjacent cysteine residues in a protein.
DNA - Deoxyribonucleic acid, the nucleic acid used to store the genetic information that cods for the synthesis of proteins.
Ductile - Capable of being drawn into thin sheets or wires without breaking.
Effusion - The process by which a gas escapes through a pinhole into a vacuum.
Elastic collision - A collision in which no kinetic energy is lost.
Elastomer - A polymer that snaps back to its original shape after being stretched to at lest twice its original length.
Electrolysis - A process in which an electric current is used to decompose a compound into its elements.
Electrolytic cell - An electrochemical cell in which electrolysis is done.
Electromagnetic radiation - Radiation that contains both electric and magnetic components and travels at the speed of light.
Electron - A subatomic particle with a charge of -1 and a mass of 0.0005486 amu.
Electron affinity (EA) - The energy given off when a neutral atom in the gas phase picks up an electron to form a negatively charged ion.
Electron capture - A reaction in which the nucleus of an atom captures an electron in the 1s orbital.
Electron configuration - The arrangement of electrons in atomic orbitals.
Electron emission -
A nuclear reaction in which electrons (-)
particles are ejected from the nucleus.
Electron-pair acceptor - See Lewis acid.
Electron-pair donor - See Lewis base.
Electronegativity (EN) - The tendency of an atom to draw the electrons in a bond toward itself.
Electrophile - Something that loves electrons. A Lewis acid that attacks a site rich in electron density.
Element - A substance that cannot be decomposed into a simpler substance by a chemical reaction. A substance composed of only one kind of atom.
Elemental analysis - The process by which the percent-by-mass of the elements in a compound is determined.
Emission spectrum - The spectrum of bright lines against a dark background obtained when an atom or molecule emits radiation when excited by heat or an electric discharge.
Empirical formula - The simplest formula for a compound. The ratio of the number of atoms of each element in the compound.
Empirical weight - The sum of the masses of the atoms in an empirical formula.
Endergonic - A process that leads to an increase in the free energy of a system and is therefore not spontaneous.
Endothermic - A process in which the system absorbs heat from the surroundings. See exothermic.
Endpoint - The point at which the indicator of an acid-base titration changes color. See equivalence point.
Enthalpy (H) - The sum of the internal energy plus the product of the pressure times the volume of the gas ina a system:
Enthalpy of formation (
Hf)
- The change in the enthalpy that occurs during a chemical reaction that
leads to the formation of a compound from its elements in there most thermodynamically
stable states at 1 MPa.
Enthalpy of reaction (H)
- The change in the enthalpy that occurs during a chemical reaction. The
difference between the sum of the enthalpies of the reactants and the products
of the reaction.
H
= 
Hproducts
- Hreactants
Entropy (S) - A measure of the disorder in a system.
Enzyme - A protein that catalyzes a biochemical reaction.
Equality - A symbolic representation of two quantities that are equivalent.
Equation - A symbolic statement that can be used to do a calculation.
Equation of state - An equation which relates two or more of the quantities that describe the state of a system.
Equatorial - The three positions in a trigonal bipyramidal that lie in the trigonal plane. See axial
Equilibrium - The point at which there is no longer a change in the concentrations of the reactants and the products of a chemical reaction. The point at which the rates of the forward and reverse reactions are equal.
Equilibrium constant (Kc or Kp) - The product of the concentrations (or partial pressures) of the products of a reaction divided by the product of the concentrations (or partial pressures) of the reactants.
Equilibrium constant expression - The expression used to calculate the equilibrium constant for a reaction.
Equilibrium region - The portion of a plot of the concentrations of a substance versus time in which the concentration does not change. The portion of this plot in which the reaction is at equilibrium.
Equivalence point - The point in an acid-base titration at which equivalent amounts of acid and base have been added to the solution. See endpoint.
Error - The difference between a measurement and the true value of the quantity being measured.
Ester - See carboxylic acid ester.
Ether - A compound in which an oxygen atom is attached to two carbon atoms.
Excess reactant - In a limiting reactant problem, this is the reactant present in excess. The reaction will stop before all of the excess reactant is consumed.
Excluded volume - The fraction of the volume of a gas that is not empty space. The volume of the gas actually occupied by gas particles.
Exergonic - A process that leads to a decrease in the free energy of the system and is therefore spontaneous.
Exothermic - A process in which a system gives off heat to the surroundings. See endothermic.
Expandability - A measure of the ability to expand. A characteristic of substances, such as gases, that can expand to fill their containers.
Extensive property - A quantity that depends on the size of the sample. See intensive property.
Extraction - A method of separating mixture based on differences in the solubility of their components in polar versus nonpolar solvents.
Family - A vertical column of elements in the periodic table such as H, Li, Na, K, Rb, Cs, and Fr.
Faraday's constant - The charge on a mole of electrons: 96,484.56 Coulombs.
Faraday's law - The amount of any substance consumed or produced at one of the electrodes in an electrolytic cell is directly proportional to the amount of electricity that passes through the cell.
Fat - A solid triester of glycerol and fatty acids. See oil.
Fatty acid - A carboxylic acid that contains a long hydrophobic hydrocarbon chain.
Fertile Nuclide - A nuclide that can be converted into one that undergoes spontaneous fission.
Filled-shell configuration - An electron configuration in which a shell of atomic orbitals is filled.
First-ionization energy (IE) - The energy needed to remove the outermost, highest energy electron from a neutral atom in the gas phase.
First law of thermodynamics (Law
of conservation of energy) - Energy cannot be created or destroyed:
Euniverse
= Esystem
+ Esurroundings
= 0
First-order reaction - A reaction whose rate is proportional to the concentration of a single reactant raised to the first power: rate = k[X].
Fission - A nuclear reaction in which a nuclide splits into two smaller nuclides. See Fusion.
Fluoresce - A process in which a compound emits light at one wavelength being excited by radiation with a shorter wavelength.
Force - The product of the mass of an object times its acceleration.
Formal charge - The charge on an atom in its Lewis structure. Formal charge is calculated by dividing the electrons in each covalent bond between the atoms in the bond, and then comparing the number of electrons that can be formally assigned to each atom with the number of electrons on a neutral atom of the element.
Free energy (G) - The energy associated with a chemical reaction that can be used to do work. The free energy of a system is the sum of its enthalpy plus the product of the temperature (Kelvin) and the entropy of the system: G = H - TS
Free radical - A neutral atom or molecule that contains an unpaired electron.
Freezing point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure. See melting point.
Freezing point depression - The decrease in the freezing point of a solvent that occurs when a solute is added to form a solution.
Frequency ()
- The number of wave crests or troughs that pass a fixed point per unit time.
Functional group - An atom or group of atoms in an organic compound that gives the compound some of its characteristic properties.
Galvanic cell - An electrochemical cell that uses a spontaneous chemical reaction to do work. Aka: Voltaic cell.
Galvanic corrosion - Corrosion that occurs when two metals are in contact with each other and water.
Gamma ray (
)
- A high-energy, short-wavelength form of electromagnetic radiation emitted
by the nucleus of an atom that carries off some of the energy released ina nuclear
reaction.
Gas - A substance that flows freely, expands to fill its container, and can be compressed to fit into a smaller container.
Gas-phase chromatography - Chromatography in which the components of a gas are separated as the pass over a solid support.
Gas-phase reaction - A reaction in which the reactants and products are all gases.
Gay-Lussac's law - The ratio of the volumes of gases consumed or produced in a chemical reaction is equal to the ratio of simple whole numbers (coefficients in the balanced equation).
Gibbs free energy - The thermodynamic function defined by the equation: G = H - TS. See free energy.
Graham's law - The rate at which a gas diffuses or effuses is inversely proportional to the square root of its molecular mass.
Gram - The basic unit of mass in the metric system.
Group - A vertical column, or family, of elements in the periodic table.
Group number - A number that identifies a group of elements in the periodic table.
Haber process - Industrial process used to make ammonia from nitrogen and hydrogen gases.
N2(g) + 3 H2(g)
2
NH3(g)
Half-cell - One half of a galvanic cell.
Half-life - The time required for the amount of a reactant to decrease to half its initial value.
Halide - A F-, Cl-, Br-, or I- ion.
Halogen - F2, Cl2, Br2, or I2.
Hard water - Water with a high concentration of the Ca2+, Mg2+, and/or Fe3+ ions.
Heat (q) - A form of energy associated with the random motion of elementary particles in matter.
Heat of fusion - The heat that must be absorbed to melt a mole of a solid.
Heat of reaction - The change in the enthalpy of the system that occurs when a reaction is run at constant pressure.
Heat of vaporization - The heat that must be absorbed to boil a mole of a liquid.
Heat capacity - The amount of heat required to raise the temperature or a defined amount of a pure substance by one degree. See Btu, calorie, molar heat capacity, and specific heat.
Hess's law - The heat given off or absorbed in a chemical reaction is the same regardless of whether the reaction occurs in a single step or in many steps.
Hexadendate - A ligand that can bind to a transition metal six times. See chelating ligand.
High-spin complex - A transitional metal in which the difference between the energies of the t2g and eg sets of orbitals is smaller than the energy it takes to pair two electrons. As a result, the valence-shell d electrons on the metal are placed in both the t2g and eg sets of orbitals. See low-spin complex.
Homonuclear diatomic molecule - See diatomic atom.
Hund's rule - Electrons occupy equal-energy, (degenerate) orbitals so that a maximum number of unpaired electrons results.
Hybrid atomic orbitals - Orbitals formed by mixing two or more atomic orbitals.
Hybridization - A process in which things are mixed. A resonance hybrid is a mixture, or average, or two or more Lewis structures. Hybrid orbitals are formed by mixing two or more atomic orbitals.
Hydrocarbon - A compound that contains only carbon and hydrogen.
Hydrogen bond - The bond formed when the positive end of one polar molecule is attracted to the negative end of another polar molecule.
Hydrophillic - "Water loving" Polar groups that are attracted to water.
Hydrophobic - "Water hating" Nonpolar groups that repel water.
Hydroxide - A compound that contains an -OH group.
Ideal gas - A gas that obeys all the postulates of the kinetic molecular theory. Real gases deviate from ideal gas behavior because:
Ideal gas equation - PV = nRT where P is pressure, V is volume (Liters), n is amount (moles), R is a constant, and T is temperature (Kelvin).
Immiscible - Liquids that are not soluble in each other.
Indicator - A compound that changes color at the endpoint of a titration.
Induced dipole - A short-lived separation of charge created by polarization of a nonpolar atom or molecule.
Induced fission - Fission of a nuclide that occurs after the nuclide has absorbed another particle. See spontaneous fission.
Inelastic collision - A collision in which at least a portion of the kinetic energy of the colliding particles is lost.
Inert - Unreactive. Describes compounds that do not undergo chemical reactions.
Initial concentration - The concentration of a reactant before it reacts with either the solvent or another reactant.
Initial rate of reaction - The rate of a chemical reaction extrapolated back to the instant the reactants were mixed.
Inorganic - Compounds that do not contain C-H bonds.
Insoluble - A substance that does not dissolve in a solvent to give a reasonable concentration.
Instantaneous rate of reaction - The rate of a chemical reaction at an instant in time. The infinitesimally small change in the concentration of one of the reactants (or products) that occurs over an infinitesimally small length of time: d(X)/dt.
Integrated form of the rate law - An alternative form of the rate law for a chemical reaction that can be used to predict the concentrations of the reactants (or products) at some moment in time.
| First-order reaction: |
 |
Second-order reaction: |
 |
Intensive property - A property that does not depend on the amount of a sample. See extensive property.
Intermetallic compound - A compound with a fixed composition that results from the combination of two or more metals.
Intermolecular bonds - The weak bonds between molecules ina liquid or solid. e.g. the hydrogen bonds between water molecules. See intramolecular bonds.
Internal energy (E) - The sum of the kinetic and potential energies of the particles in a system. The internal energy of a system is proportional to its temperature.
Interstitial solution - A solid solution formed when solute atoms are packed in the holes, or interstices, between solvent atoms.
Intramolecular bonds - The bonds that hold a molecule together.
Ion product (Qsp) - The product of the concentrations of the ions in a solution at any moment in time
Ionic bond - The bond between two ions that results from the force of attraction between particles of opposite charge.
Ionic compound - A compound that contains ions.
Ionic radius - The radius of one of the ions in an ionic compound.
Ionic solid - A solid composed of ions. Aka salt.
Ionization - A process in which an ion is created from a neutral atom or molecule by adding or subtracting one or more electrons.
Ionization energy - See first ionization energy or second ionization energy.
Ionize - A process in which ions are created.
Ionizing radiation - Radiation with enough energy to remove an electron from a neutral atom or molecule to produce free radicals. See nonionizing radiation.
Isobars - Nuclides with the same mass number.
Isoelectronic - Atoms or ions that have the same number of electrons and therefore the same electron configuration.
Isomers - Compounds with the same chemical formulas but different structures, and therefore different chemical and physical properties. See cis or trans.
Isotones - Nuclides with the same number of neutrons.
Isotopes - Nuclides with the same number of protons.
Isotropic - "Same in all directions" Describes the pressure of a gas.
Joule - A unit of measurement for both heat and work in the SI system. 1 J = 4.184 cal.
Ketone - A compound in which a C=O (carbonyl) functional group is bound to two carbon atoms.
Kinetic control - A chemical reaction in which the products are determined by the rate of the reaction. See thermodynamic control.
Kinetic energy
- The energy of motion. The kinetic energy of an object is equal to one-half
the product of its mass times its velocity squared: KE = ![[Image]](../../media/Chem/img/half.gif){kind=small}
mv2
Kinetic molecular theory - The theory that heat is associated with the thermal motion of particles. In the kinetic theory, heat is not conserved---an inexhaustible amount of heat can be created by doing work on a system. See kinetic molecular theory notes.
Kinetic region - The portion of a plot of the concentration of a compound versus time in which the concentration changes. The portion of this plot between the initial conditions and the point at which the system reaches equilibrium.
Latent heat - Heat that cannot be detected because there is no change in temperature of the system. The heat that enters the system is used to do work such as melting ice to form water. See sensible heat.
Latent heat of fusion - See heat of fusion.
Latent heat of vaporization - See heat of vaporization.
Lattice Energy - The energy given off when oppositely charged ions in the gas phase come together to form a solid.
NaCl(s)
Lattice point - A point about which an atom, ion, or molecule is free to vibrate in a crystal.
Law of combining volumes - See Gay-Lussac's Law.
Law of conservation of matter - Matter cannot be created nor destroyed.
Law of constant composition - A compound always contains the same ratio by mass of its elements, regardless of its source.
Law of definite proportions - The ration by mass of compounds consumed in a chemical reaction is always the same.
LeChâtelier's principle - A principle that describes the effect of changes in the temperature, pressure, or concentration of one of the reactants or products of a reaction at equilibrium. It states that when a system at equilibrium is subjected to stress, it will shift in the direction that minimizes the effect of this stress.
Leveling effect - The tendency of water to limit the strength of the strongest acids and bases to the strength of the H3O+ and OH- ions.
Lewis acid - An electron-pair acceptor. A substance that acts in the same way as the H+ ion to accept a pair of electrons.
Lewis base - As electron-pair donor. A substance that acts in the same way as the OH- ion to donate a pair of electrons.
Lewis structure - A symbolic description of the distribution of valence electrons in a molecule. Lewis structures use dots to represent individual electrons and lines to represent covalent bonds.
Ligand - A Lewis base that can coordinate to a metal atom.
Ligand-field theory - A molecular orbital description of the bonding in transition metal complexes.
Limiting reactant - The reactant in a chemical reaction that limits the amount of product that can be formed. The reaction will stop when all the limiting reactant is consumed.
Line notation - A system for representing electrochemical reactions.
Lipid - Biologically important molecules that are soluble in nonpolar solvents.
Liquid - A substance that flows freely, and therefore conforms to the shape of the walls of its container, but cannot expand to fill the container.
Liquid crystal - A substance that has some of the long-range order of a solid but the freedom of motion of a liquid.
Liter - The fundamental
unit of volume in the metric system. The volume of 1000 grams of water
at 4C.
Low-spin complex - A transition metal complex in which the difference between the energies of the t2g and eg orbitals is larger than the energy it takes to pair electrons. As a result, the valence-shell d electrons on the metal are all placed in the lower energy set of orbitals, the t2g set for octahedral complexes and the eg set for tetrahedral complexes. See high-spin complex.
mRNA - Messenger RNA. The polynucleotide that cones for the synthesis of a protein. mRNA is assembled during transcription of a chain of DNA.
Macroscopic - Something that is visible by the naked eye.
Magnetic quantum number (m) - The quantum number used to describe the orientation of an atomic orbital in space.
Main-group element - An element in one of the groups of the periodic table in which s and p orbitals are filled. Aka representative elements.
Malleable - Something that can be hammered, pounded, or pressed into different shapes without breaking.
Mass - A measure of the amount of matter in an object.
Mass defect - The difference between the mass of an atom and the sum of the masses of the protons, neutrons, and electrons that form the atom.
Mass number (M) An integer equal to the number of protons and neutrons in the nucleus of an atom.
Measurement - The process by which the amount or quantity of something is measured.
Mechanism - The steps by which a chemical reaction converts the reactants into products.
Melting point - The temperature at which the solid and liquid phases of a substance are in equilibrium at atmospheric pressure.
Melting point depression - See freezing point depression.
Meniscus - The curved surface of a liquid in a narrow-diameter glass tube.
Metal - An element that is solid, has a metallic luster, is malleable and ductile, and conducts both heat and electricity.
Metallic radius - Half the distance between the nuclei of adjacent atoms in a metal.
Metallic solid - A solid that has the properties of a metal.
Metastable system - A system that should undergo spontaneous change, but does not.
Metathesis reaction - A reaction in which atoms or groups of atoms are interchanged, but none of the atoms undergoes a change in oxidation number. See oxidation-reduction reaction.
Meter - The basic unit of length in both the metric and SI systems. The distance light travels in 1/299,792,458ths of a second.
Metric system - A system of units introduced in 1790 based on three fundamental quantities: the gram (mass), liter (volume) and meter (length).
Mixture - A substance that contains two or more elements or compounds that retain their chemical identity and can be separated into the individual components by a physical process.
Molality (m) -
The number of moles of solute in a solution divided by the number of kilograms
of solvent.
Molar heat capacity (C) - The number of joules of heat required to raise the temperature of one mole of a substance by 1 K. See specific heat.
Molar mass - The mass of a mole of a substance. The mass values on the periodic table are the molar masses of the elements. Aka molecular weight.
Molarity (M) -
The number of moles of a solute in a solution divided by the volume of solution
in liters.
Mole - "Small mass" The amount of any substance that contains the same number of atoms, ions, or molecules as there are 12C atoms in exactly 12 g or the 12C isotope. 6.0220 x 1023 particles (Avogadro's number).
Mole fraction - The fraction of the total number of moles in a mixture due to one component of the mixture.
Mole ratio - The ratio of the moles of one reactant or product to the moles of another reactant or product in the balanced equation for a chemical reaction.
Molecular formula - The formula of a molecule of a compound.
Molecular geometry - The shape, or geometry, of a molecule as defined by the positions of its nuclei.
Molecular orbital - A region in space within a molecule where electrons can be found. Molecular orbitals are formed by the overlap or atomic orbitals.
Molecular solid - A substance that consists of individual molecules held together in the solid by relatively weak intermolecular bonds.
Molecular weight - The weight or the molecular formula, calculated from the table of atomic weights. The weighted average of the masses of the individual molecules in the substance.
Molecularity - Number of molecules consumed in a step of a chemical reaction. See bimolecular and unimolecular.
Molecule - The smallest particle that has any of the chemical or physical properties of an element or compound.
Momentum - The product of the mass times the velocity of an object in motion.
Monodendate - "One toothed" Ligands that can coordinate to a transition metal only once.
Monomer - One of the relatively small molecules from which polymers are formed.
Monoprotic acid (HA) - An acid that can lose only one H+ ion.
Monosaccharide - A carbohydrate that cannot be hydrolyzed into a simpler carbohydrate. See disaccharide and polysaccharide.
Natural radioactivity - The radioactive decay that occurs naturally, as opposed to induced fission. Aka spontaneous fission.
Negative electrode - The electrode in an electrochemical cell that carries a negative charge. In an electrolytic cell, it is the cathode; in a galvanic cell it is the anode.
Nernst equation - Describes
the relationship between the potential of an electrochemical cell at any moment
in time and the standard-state cell potential. Used to understand what
happens to the potential of a galvanic
cell as it comes to equilibrium: 
Neutrino - A particle with no charge and little or no mass that is ejected from the nucleus at the same time as an electron or positron.
Neutron - A subatomic particle with a mass of 1.008665 amu and no charge.
Neutron-poor nuclide - A nuclide with fewer neutrons than the lightest stable isotope of the element. A nuclide that decays either by electron capture, positron emission, or the alpha decay.
Neutron-rich nuclide - A nuclide with more neutrons than the heaviest stable isotope of the element. A nuclide that decays by the emission of an electron.
Nomenclature - A systematic way of naming chemical compounds.
Nonbonding electrons - Electrons in the valence shell of an atom that are not used to form covalent bonds.
Nonbonding molecular orbital - A molecular orbital whose energy is more or less equal to the energy of the atomic orbitals from which it is formed.
Nonionizing radiation - Radiation that carries enough energy to excite an atom or molecule, but not enough energy to remove an electron from the atom or molecule. See ionizing radiation.
Nonmetal - An element that lacks the properties generally associated with metals.
Nonpolar - Compounds that do not carry a dipole moment.
Nucleic acid - A molecule of very high molecular weight used to store and process the genetic information in cells.
Nucleon - A proton or a neutron.
Nucleophile - "Something that loves nuclei" All nucleophiles are Lewis bases.
Nucleophilic substitution reaction - A reaction in which one nucleophile is substituted for another in a molecule.
Nucleotide - The smallest repeating unit out of which nucleic acids are built.
Nucleus - "Little nut" In consists of neutrons, protons, occupies an infinitesimally small fraction of the total volume of an atom, and contains almost all the mass of an atom.
Nuclide - An atom with a particular combination of protons and neutrons.
Octahedral complex - A complex in which six ligands bound to a metal atom are arranged toward the corners of an octahedron.
Octahedral geometry - A geometry in which six atoms, ions, or molecules are arranged around a central atom in opposite directions along the x, y, and z axes of a coordinate system.
Octane number - A comparison between the tendency of a gasoline to knock against the tendency of a blend of two hydrocarbons to knock.
Octet - "Eight objects" Describes the tendency of main-group elements to have eight valence-shell electrons in their compounds.
Olefin - A common name for the class of compounds know as alkenes.
Orbitals - Regions in space where electrons can reside. See atomic orbitals and molecular orbitals.
Order - The relationship between the rate of step in a chemical reaction and the concentration of one of the reactants consumed in that step. See first-order reaction, second-order reaction, and zero-order reaction.
Organic - Compounds that contain C-H bonds.
Osmosis - The process by which one component of a solution passes through a membrane to dilute the solution.
Osmotic pressure - The pressure exerted by water or other solvents flowing in to a solution through a membrane.
Ostwald process - An industrial process in which ammonia is converted into nitric acid.
Overlap - The interaction between a pair of atomic orbitals that occurs when the orbitals share space.
Overvoltage - The voltage greater than the voltage predicted from standard tables of reduction potentials that must be applied before an electrochemical reaction occurs at the expected rate.
Oxidation - Any process in which the oxidation number of an atom becomes more positive.
Oxidation number - The charge that would be present on an atom if the element or compound in which the atom is found were ionic.
Oxidation-reduction reaction (redox reaction) - Reaction in which at lest one atom undergoes a change in oxidation state. See metathesis reaction.
Oxidizing agent - An atom, ion, or molecule that gains electrons in a chemical reaction, thereby oxidizing the substance with which it reacts. An oxidizing reaction undergoes reduction.
Oxyacid - An acid in which the acidic hydrogen atoms are attached to an oxygen atom.
Oxyanion - A negatively charged ion formed when an oxyacid loses on or more H+ ions.
pH - A measure of acidity.
The negative of the logarithm of the H3O+ ion concentration:
pH = -log [H3O+]
pOH - The negative of the
logarithm of the OH- ion concentration:
pOH = -log[OH-]
Paramagnetic - A compound that is attracted to a magnetic field. A compound that contains one or more unpaired electrons. See diamagnetic.
Partial pressure - The fraction of the total pressure of a mixture of gases due to one component of the mixture.
Particle - Any object that has mass and therefore occupies space.
Peptide - A relatively small polymer of amino acids. Peptides are usually too small to have extensive secondary or tertiary characteristics.
Peptide bond - The bond between two amino acids in a peptide or protein.
Period - A horizontal row in the periodic table.
Periodic table - A matrix in which the elements are arranged across rows in order of increasing atomic number so that elements with similar chemical properties fall in the same vertical column.
Peroxide - "Compound rich in oxygen" Compounds that contain the O22- ion.
Phase diagram - A two-dimensional graph that shows the state, or phase, of a substance at any combination of temperature and pressure.
Phospholipid - A triester of glycerol with two fatty acids and one phosphate (PO43-) ion. Polar lipids found in biological membranes.
Photon - The smallest unit of electromagnetic energy.
Pi bond - A bond formed by the edge-on overlap of p atomic orbitals.
Plastic - "A material that can flow" Polymers that can be shaped, molded, or milled.
Poise - The unit of measurement for viscosity.
Polar - Compounds that have a dipole moment because they consist of molecules that have negative and positive poles.
Polar covalent bond - A bond in a molecule that is neither strictly covalent nor strictly ionic.
Polarity - The tendency of a molecule to have positive and negative poles because of the unequal sharing of a pair of electrons.
Polyamide - A polymer or protein held together by -CO-NH- bonds.
Polyatomic ion - An ion that contains more than one atom.
Polyester - A polymer held together by ester linkages between the monomers.
Polymer - A molecule with a large molecular weight formed by the linking of 30 to 100,000 (or more) repeating units.
Polynucleotide - A condensation polymer formed by the linking of nucleotides.
Polyprotic acid - An acid that can lose more than one H+ ion, or proton.
Polyprotic base - A base that can accept more than one H+ ion, or proton.
Polysaccharide - A carbohydrate made by polymerizing many monosaccharide units.
Positive electrode - The electrode in an electrochemical cell that carries a positive charge. In an electrolytic cell, it is the anode. In a galvanic cell, it is the cathode.
Positron
- The antimatter analog of an electron (+).
Positrons have the same mass as an electron but the opposite charge.
Positron emission - A nuclear reaction in which a positron is emitted. Positron emission leads to a decrease in the atomic number by one and no change in the mass number of the nuclide.
Potential - A measure of the driving force behind an electrochemical reaction that is reported in units of volts.
Precipitation - A process in which positive and negative ions combine to form a salt that separates out of the solution as a solid.
Precipitation hardening - A process by which an alloy becomes harder when an intermetallic compound is allowed to precipitate from a supersaturated solution of two metals.
Precision - A measure of the extent to which individual measurements of the same quantity agree.
Pressure - The force exerted on a surface divided by the are of the surface.
Primary battery - A battery that cannot be charged. See secondary battery.
Primary structure - The sequence of amino acids in a protein.
Primary valence - The number of negative ions needed to satisfy the charge on a metal ion.
Principal quantum number (n) - The quantum number that describes the size, and therefore the relative energy, of an orbital.
Product - A substance formed in a chemical reaction.
Protein - A relatively large polymer of amino acids. A polypeptide that is large enough to have an extensive secondary and tertiary structure.
Proton - A subatomic particle that has a charge of +1 and a mass of 1.007276 amu.
Proton acceptor - An ion or molecule that can gain an H+ ion, or proton. A Brønsted base.
Proton donor - An ion or molecule that can lose an H+ ion, or proton. A Brønsted acid.
Purine - A heterocyclic aromatic compound, containing nitrogen, found in nucleic acids.
Pyrimidine - A heterocyclic aromatic compound, containing nitrogen, found in nucleic acids.
Pyrophoric - Compounds that burst into flames in the presence of air.
Quadratic formula -
A formula for solving quadratic equations:
Quantized - "Countable"
Quantum number - An integer that describes the size, shape, and orientation in space of an atomic orbital.
Quarternary structure - The ionic or hydrophobic interactions between individual chains of amino acids in some proteins.
R process - The process by which nuclides are built up by the rapid capture of neutrons. The R process produces heavy nuclides such as 238U. It requires a large neutron flux, which occurs when a star becomes a supernova. See S process.
Rad - A unit in which the dose of radiation absorbed by an object is reported: 1 rad = 10-5 J/g.
Radioactivity - The spontaneous disintegration of an unstable nuclide by a first-order rate law.
Radius ratio - The radius of the positive ion divided by the radius of the negative ion in a salt.
Random error - A source of error that limits the precision of a measurement. An error that is equally likely to give results that are too large or too small. See systematic error.
Raoult's law - The vapor
pressure of the solvent escaping from a solution is equal to the mole fraction
of the solvent times the vapor pressure of the pure liquid: 
Rare gases - The last group of elements on the periodic table that all have filled valence shells. Aka noble gases and previously given the misnomer inert gases.
Rate of reaction - The change in the concentration of a compound divided by the amount of time necessary for this change to occur: rate = d(X)/dt
Rate constant (k) - The proportionality constant in the equation that describes the relationship between the rate of a step in a chemical reaction and the product of the concentrations of the reactants consumed in that step.
Rate law - An equation that describes how the rate of a chemical reaction depends of the concentrations of the reactants consumed in that reaction.
Rate-limiting step - The slowest step in a chemical reaction.
RBE - Radiation Biological Effectiveness. Used to correct for differences in the effect of equivalent doses of different forms of radiation. See rad and rem.
Reactant - One of the starting materials in a chemical reaction.
Reaction coordinate - The sequence of infinitesimally small steps that must be taken to convert the reactants into the products of a reaction.
Reaction quotient (Qc or Qp) - The quotient obtained when mathematical product of the concentrations (or partial pressures) of the products of a reaction is divided by the mathematical product of the concentrations (or partial pressures) of the reactants. The reaction quotient can have any value between zero and infinity. When the reaction is at equilibrium, the reaction quotient is equal to the equilibrium constant for the reaction.
Recrystallization - A technique for purifying solids that removes impurities when the solid is dissolved in an appropriate solvent and then allowed to recrystallize.
Redox - See oxidation-reduction reaction.
Reducing agent - An atom, ion, or molecule that loses electrons in a chemical reaction, thereby reducing the substance with which it reacts. A reducing agent undergoes oxidation.
Reduction - Any process that leads to a decrease in the oxidation number of an atom.
Rem - A unit of radiation absorbed dose equal to the product of the rads of absorbed radiation times the RBE.
Replication - The process by which DNA is duplicated in preparation for cell division.
Representative elements - See main-group elements.
Resonance - An averaging or mixing process that occurs when more than one Lewis structure can be written for a molecule.
Resonance hybrid - A mixture, or average of two or more Lewis structures.
RNA - Ribonucleic acid, the nucleic acid involved in transcribing genetic information for the synthesis of proteins stored in DNA and then translating this information into the sequence of amino acids in the protein.
Roasting - A process by which a metal ore is transformed into the corresponding oxide and SO2.
Rusting - The corrosion of iron or alloys of iron (e.g. steel).
4 Fe(s) + 3 O2(g) 
2
Fe2O3 • 3 H2O
S process - The process by which heavier nuclides are built up by the slow absorption of one neutron at a time. See R process.
Salt - See ionic compound.
Salt bridge - A tube containing a saturated solution of a salt that is used to complete the electric circuit in a galvanic cell.
Saporification - The reaction between fats and oils with KOH or NaOH to produce soap.
Saturated fatty acid - A long-chain carboxylic acid that contains no C=C double bonds. See unsaturated fatty acid.
Saturated hydrocarbon - A hydrocarbon that contains as much hydrogen as possible. See alkane.
Scientific notation - A system in which a number is expressed as a number between 1 and 10 times 10 raised to an exponent.
Second ionization energy - The energy needed to remove an electron from an ion with a +1 charge in the gas phase.
Second law of thermodynamics - The notion that natural processes that occur in an isolated system are spontaneous when they lead to an increase in entropy, disorder.
Second-order reaction - A reaction whose rate is proportional to the concentration of a single reactant raised to the second power: rate = k[X]2.
Secondary battery - A battery used to store electricity. Secondary batteries are capable of being charged and discharged. See primary battery.
Secondary structure - The hydrogen bonds between adjacent peptide linkages in a protein that stabilize the structure of the protein.
Secondary valence - The number of ions or molecules that are covalently bound to a transition metal ion.
Selective precipitation - A technique in which one ion is selectively removed from a mixture of ions by precipitation.
Semiconductor - A material whose ability to carry an electric current falls between those of metals and nonmetals.
Semimetal - An element with chemical properties that fall between the extremes associated with metals and nonmetals. Aka metalloid.
Semipermiable membrane - A thin, flexible solid that can pass small molecules such as water but not larger molecules such as sugars or alcohols.
Sensible heat - Heat that can be sensed, detected, by a change in the temperature of the system. See latent heat.
Shell - A set of orbitals that have the same principal quantum number.
SI - The International System of Units, which is based on seven fundamental quantities: the meter (length), kilogram (mass), second (time), kelvin (temperature), ampere (current), mole (amount of substance), and candela (luminous intensity). See SI system tables.
Sigma bond (
)
- A cylindrical symmetric bond formed by the overlap of s orbitals of
the head-on overlap of p orbitals.
Significant figures - The digits in a measurement that are reliable.
Sintering - A process in which a finely divided ore is heated until it collects to form larger particles.
Skeleton structure - A representation of the basic structure of a molecule in which lines are used to connect atoms held together by covalent bonds.
Smelting - A process in which a metal oxide is reduced to the corresponding metal.
Soap - The sodium or potassium salt of a fatty acid.
Solid - A substance that does not flow and therefore does not conform to the shape of its container.
Solubility - The ratio of the maximum amount of solute to the volume of solvent in which this solute can dissolve. Generally expressed in units of grams of solute per 100 g of water, or in molarity.
Solubility equilibria - Equilibria that exist in a saturated solution, in which additional solid dissolves at the same rate the particles in a solution come together to precipitate more solid.
Solubility product (Ksp) - The product of the equilibrium concentrations of the ions in a saturated solution of a salt.
Solute - The substance that dissolves in a solvent to form a solution.
Solution - A mixture of one or more solutes dissolved in a solvent.
Solvent - The substance in which a solute dissolves.
Specific heat - The
amount of heat required to raise the temperature of 1 g or a substance by 1C.
See molar heat capacity.
Spectrochemical series - A sequence of ligands arranged in order of decreasing magnitude of splitting the energies of eg and t2g orbitals in transition metal complexes.
Spin quantum number (s)
- The quantum number used to specify the electrons that occupy an orbital. The
spin quantum number can have values of 
.
Spontaneous fission - Fission of a nuclide that occurs spontaneously. See induced fission.
Spontaneous reaction
- A reaction in which the products are favored. Spontaneous reactions
have negative G.
Square-planar geometry - A geometry in which four atoms, ions, or molecules lying in the same plane are bound to a central atom and arranged toward the corners of a square.
Square-pyramidal geometry - A geometry in which a fifth atom, ion, or molecule is added to a square-planar geometry along an axis perpendicular to the plane of the other four.
Standard state - State in which all concentrations are 1 M and all partial pressures are 1MPa.
Standard-state cell potential - The potential of a cell measured under standard-state conditions.
Standard-state enthalpy of reaction - The change in the enthalpy that occurs during a chemical reaction that begins and ends under standard-state conditions. See enthalpy of reaction.
Standard-state entropy - The results of the measurements of the entropy taken under standard-state conditions.
Standard-state free energy of formation - The results of the standard-state measurements of the change in free energy that occurs when a compound is formed from its elements in their most thermodynamically stable states.
Standard-state free energy reaction - The energy associated with a chemical reaction that can be used to do work when the reaction begins and ends under standard-state conditions. See free energy of reaction.
State function
- A quantity whose value depends only on the state of the system and not its
history; X is a state function if and only if the value of X
does not depend on the path used to go from the initial to the final state of
the system.
Stepwise dissociation - The assumption that we can separate the individual steps in a dissociation reaction.
Sterioisomers - Compounds with the same chemical formula that have different three-dimensional structures. See cis and trans isomers and chiral isomers.
Stoichiometry - The relationship between the weights of the reactants and the products of a chemical reaction.
Strong acid - Acids that dissociate more or less completely in water.
Sublimation - A process in which a solid goes directly to the gaseous state without passing through an intermediate liquid state.
Subshell - Atomic orbitals for which the values of the n and l quantum numbers are the same.
Substitution reaction - A reaction that involves the substitution of one group for another.
Successive approximations - A technique in which the answer obtained from an approximate calculation is substituted into the original equation to yield a more accurate solution.
Superconductor - A substance that has no resistance to conducting an electric current.
Supercooled liquid - A liquid that has been cooled to a temperature below its freezing point.
Superoxide - A compound that contains the O2- ion.
Surface tension - The force that controls the shape of a liquid. Surface tension results from the force of cohesion between liquid molecules.
Surroundings - In thermodynamics, the part of the universe not included in the system.
Syndiotactic - Polymers in which the substituents alternate regularly between the two sides of the polymer backbone.
Synthesis gas - A mixture of CO and H2 produced during the gasification of coal that can be used to synthesize a wide range of materials.
System - In thermodynamics, the small portion of the universe in which we are interested.
Systematic error - A source of error that limits the accuracy of a measurement, which gives results that are always too small or too large. See random error.
tRNA - Transfer RNA. The relatively small polynucleotide that carries amino acids and recognizes the codon on mRNA that specifies the amino acid to be incorporated at a particular point on a protein chain.
T-shaped geometry - A molecular geometry whose shape resembles the letter T.
Taticity - "Arrangement or system" Describes the arrangement of substituents on a polymer chain. See atactic, isotactic, and syndiotactic.
Temperature - An intensive property that measures the extent to which an object can be labeled "hot" or "cold".
Tertiary structure - The interactions between the side chains on amino acids in a protein that help determine the structure of the protein.
Tetrahedral complex - A complex in which four ligands are bound to the metal atom and arranged toward the corners of a tetrahedron.
Tetrahedron - A geometric shape that resembles a trigonal-based pyramid.
Tetravalent - "Able to form four bonds" Carbon is tetravalent because it forms four bonds in virtually all of its compounds.
Thermal conductor - An object that conducts heat easily from one side to the other, or from one end to the other.
Thermal insulator - An object that slows down the rate at which heat is transferred from one object to another.
Thermal neutron - A slow-moving neutron.
Thermochemistry - The study of the heat given off or absorbed in a chemical reaction.
Thermodynamic control - A chemical reaction that forms the most stable product, not the product of the fastest reaction. See kinetic control.
Thermodynamics - The study of the relationship between heat, work, and other forms of energy.
Thermonuclear reaction - A nuclear reaction that only occurs at extremely high temperatures.
Thin-layer chromatography - Chromatography in which a solvent is passed over a solid support that has been applied as a thin layer to a glass or plastic plate.
Third law of thermodynamics
- The entropy of a perfect crystal is zero when the temperature of the crystal
is equal to absolute zero (0 K, -273.15C).
Titration - A technique used to determine the concentration of a solute in a solution.
Torr - A unit of pressure equal to the pressure exerted by a column of mercury 1 mm tall. 1 torr = 1 mmHg
Trans - "Across" Isomers of compounds in which similar constituents lie on opposite sides of a double bond or on opposite sides of a transition metal. See cis.
Transcription - The process by which the message encoded in DNA is copied to form a sequence of mRNA that can be used as a template to make proteins.
Transition metal - Metals in the block of elements that serve as a transition between the two columns on the left side of the periodic table, where s orbitals are filled, and the six columns on the right, where p orbitals are filled.
Translation - The process by which the information coded in a sequence of mRNA is transformed into a sequence of amino acids in a protein.
Translational motion - The net movement of an atom, ion, or molecule through a gas, liquid, or solid.
Transuranium elements - Elements with atomic numbers larger than that of uranium.
Triad - Three elements with similar chemical properties.
Trigonal bipyramidal - A geometry in which two atoms, ions, or molecules are added to a trigonal planar system along an axis perpendicular to the trigonal plane.
Trigonal planar - A geometry in which three atoms, ions, or molecules are coordinated to a central atom and arranged toward the corners of an equilateral triangle.
Triple point - The specific temperature and pressure in a phase diagram at which the substance can simultaneously exist as a solid, a liquid, and a gas.
Triprotic acid - Acids that can donate three protons.
Triprotic base - Bases that can accept three protons.
Uncertainty - The limit on the precision of a measurement. e.g. analytical balances can weigh an object with an uncertainty of "0.0001 grams.
Unimolecular - A step in a chemical reaction in which one molecule is consumed.
Unit - The basis for comparing a measurement with a standard reference.
Unit cell - The simplest repeating unit in a crystal.
Unit factor - A ratio, or factor, equal to one that is constructed form an equality. Used in dimensional analysis.
Unsaturated fatty acid - A long-chain carboxylic acid that contains one or more C=C double bonds. See saturated fatty acid.
Unsaturated hydrocarbon
- A hydrocarbon that contains C=C double bonds and/or CC
triple bonds, and therefore contains less hydrogen than a saturated hydrocarbon.
Valence band - The highest energy band in a solid that contains electrons.
Valence electrons - Electrons in the outermost or highest energy orbitals of an atom. The electrons that are gained or lost in chemical reactions.
Valence-shell electron-pair repulsion theory (VSEPR) - A model in which the repulsion between pairs of valence electrons is used to predict the shape or geometry of a molecule.
van der Waals equation - An equation that corrects for the two erroneous assumptions in the ideal gas equation:
van der Waals forces - The weak forces of attraction between atoms or molecules that explain why gases condense to form liquids and solids when cooled.
Vapor pressure - The pressure of the gas that collects above a liquid in a closed container.
Vapor pressure depression - The decrease in the vapor pressure of a solvent that occurs when a solute is added to form a solution.
Vibrational motion - The motion of a molecule that results in the stretching or bending of one or more bonds in the molecule.
Viscosity - A measure of the resistance of a liquid or gas to flow. Viscous liquids flow very slowly (e.g. molasses).
Vitamin - "Vital amines" A wide range of compounds that are either water soluble or fat soluble and are necessary components of the diet of higher organisms.
Voltaic cell - See galvanic cell.
Volume percent - The percentage of the total volume of a mixture due to a particular component.
Water-dissociation equilibrium constant
(Kw) - The product of the equilibrium concentration
of the H3O+ and OH- ions in an aqueous solution:
Kw = 1.0 X 10-14 @ 25C
Water gas - A mixture of CO, CO2, and H2 produced from the reaction of red-hot coal with steam.
Wave - A phenomenon that does not have mass and therefore does not occupy space. Waves travel through space.
Wave function - A mathematical equation that describes orbitals in which electrons reside.
Wavelength - The distance between repeating points on a wave.
Wave-particle duality - The principle that all objects in motion are simultaneously particles and waves. Most objects have a wavelength that is too small to be detected. Very light objects, such as photons and electrons, have wavelengths that are large enough to give these objects some of the properties of waves.
Weak acid - An acid that dissociates only slightly in water. An acid for which the acid-dissociation equilibrium constant is significantly smaller than one.
Weight - A measure of the gravitational force of attraction of the Earth action on an object.
Weight percent - The percent by weight of an element in a compound, or the percent by weight of one component in a mixture.
Work (w) - Mechanical energy equal to the product of the force applied to an object times the distance the object is moved.
Work of expansion - The work done when a system that consists of a gas expands against its surroundings.
X-ray - A high-energy, short wavelength form of elecromagnetic radiation.
Zero-order reaction - A reaction whose rate is not proportional to the concentration of any of the reactants.
Zeroth law of thermodynamics - Two objects in thermal equilibrium with a third object are in thermal equilibrium with each other.