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absolute temperature scale
A temperature scale that uses the absolute zero of temperature as the lowest temperature.
absolute zero
Theoretically the lowest attainable temperature.
acceptor impurity
An impurity that can accept electrons from a semiconductor.
accuracy
The closeness of a measurement to the true value of the quantity that is measured.
acid
A substance that yields hydrogen ions (H+) when dissolved in water.
acid ionization constant (Ka)
The equilibrium constant for the acid ionization.
actinoid series
Elements that have incompletely filled 5f subshells or readily give rise to cations that have incompletely filled 5f subshells.
activated complex
The species temporarily formed by the reactant molecules as a result of the collision before they form the product.
activation energy (Ea)
The minimum amount of energy required to initiate a chemical reaction.
activity series
A summary of the results of many possible displacement reactions.
actual yield
The amount of product actually obtained in a reaction.
addition reaction
A reaction in which one molecule adds to another.
adhesion
Attraction between unlike molecules.
alcohol
An organic compound containing the hydroxyl group —OH.
aldehydes
Compounds with a carbonyl functional group and the general formula RCHO.
aliphatic hydrocarbons
Hydrocarbons that do not contain the benzene group or ring.
alkali metals
The Group 1A elements (Li, Na, K, Rb, Cs, and Fr).
alkaline earth metals
The Group 2A elements (Be, Mg, Ca, Sr, Ba, and Ra).
alkanes
Hydrocarbons having the general formula CnH2n+2.
alkenes
Hydrocarbons that contain one or more carbon-carbon double bonds.
alkynes
Hydrocarbons that contain one or more carbon-carbon triple bonds.
allotropes
Two or more forms of the same element that differ significantly in chemical and physical properties.
alloy
A solid solution composed of two or more metals, or of a metal with one or more nonmetals.
alpha (α) rays
Helium ions with a positive charge of +2.
alpha decay
A radioactive process in which an alpha particle is emitted from a nucleus.
alpha particles
See alpha rays.
amalgam
An alloy of mercury with another metal or metals.
amines
Organic bases that have the functional group —NR2, where R may be H, an alkyl group, or an aromatic group.
amino acids
Compounds that contain at least one amino group and at least one carboxyl group.
amorphous solid
A solid that lacks a regular three-dimensional arrangement of atoms or molecules.
amphoteric oxide
An oxide that exhibits both acidic and basic properties.
amplitude
The vertical distance from the middle of a wave to the peak or trough.
anion
An ion with a net negative charge.
anode
The electrode at which oxidation occurs.
antibonding molecular orbital
A molecular orbital that is of higher energy and lower stability than the atomic orbitals from which it was formed.
aqueous solution
A solution in which the solvent is water.
aromatic hydrocarbon
A hydrocarbon that contains one or more benzene rings.
atmospheric pressure
The pressure exerted by Earth’s atmosphere.
atom
The basic unit of an element that can enter into chemical combination.
atom economy
A measure of the overall efficiency of converting reactants into useful products.
atomic mass
The mass of an atom in atomic mass units.
atomic mass unit (amu)
A mass exactly equal to the mass of one carbon-12 atom.
atomic number (Z)
The number of protons in the nucleus of an atom.
atomic orbital
The wave function (Ψ) of an electron in an atom.
atomic radius
One-half the distance between the two nuclei in two adjacent atoms of the same element.
Aufbau principle
As protons are added to the nucleus, electrons similarly are added to the atomic orbitals.
Avogadro’s law
At constant pressure and temperature, the volume of a gas is directly proportional to the number of moles of the gas.
Avogadro’s number (NA)
6.022 × 1023; the number of particles in a mole.
band theory
Delocalized electrons move freely through 'bands' formed by overlapping molecular orbitals.
barometer
An instrument that measures atmospheric pressure.
base
A substance that yields hydroxide ions (OH−) when dissolved in water.
base ionization constant (Kb)
The equilibrium constant for the base ionization.
battery
A galvanic cell, or a series of combined galvanic cells, used as a source of direct electric current.
beta (β) rays
Electrons.
beta particles
See beta rays.
bimolecular reaction
An elementary step that involves two molecules.
binary compounds
Compounds formed from just two elements.
boiling point
The temperature at which the vapor pressure of a liquid is equal to the external atmospheric pressure.
boiling-point elevation (ΔTb)
The boiling point of the solution minus the boiling point of the pure solvent.
bond enthalpy
The enthalpy change required to break a bond in 1 mole of gaseous molecules.
bond length
The distance between the nuclei of two bonded atoms in a molecule.
bond order
The difference between the numbers of electrons in bonding and antibonding molecular orbitals, divided by two.
bonding molecular orbital
A molecular orbital that is of lower energy and greater stability than the atomic orbitals from which it was formed.
Born-Haber cycle
The cycle that relates lattice energies of ionic compounds to various thermodynamic quantities.
boundary surface diagram
Diagram of the region containing a substantial amount of the electron density in an orbital.
Boyle’s law
The volume of a fixed amount of gas maintained at constant temperature is inversely proportional to the gas pressure.
breeder reactor
A nuclear reactor that produces more fissionable materials than it uses.
Brønsted acid
A substance capable of donating a proton.
Brønsted base
A substance capable of accepting a proton.
buffer solution
A solution of a weak acid or base and its salt that resists changes in pH.
calorimetry
The measurement of heat changes.
carbides
Ionic compounds containing the C4− ion.
carboxylic acids
Acids that contain the carboxyl group —COOH.
catalyst
A substance that increases the rate of a chemical reaction without being consumed.
catenation
The ability of atoms to form bonds with one another.
cathode
The electrode at which reduction occurs.
cation
An ion with a net positive charge.
cell voltage
Difference in electrical potential between the anode and the cathode of a galvanic cell.
Charles’s and Gay-Lussac’s law
The volume of a fixed amount of gas maintained at constant pressure is directly proportional to the absolute temperature.
Charles’s law
The volume of a fixed amount of gas maintained at constant pressure is directly proportional to the absolute temperature.
chelating agent
A substance that forms complex ions with metal ions in solution.
chemical energy
Energy stored within the structural units of chemical substances.
chemical equation
An equation that uses chemical symbols to show what happens during a reaction.
chemical equilibrium
A state in which the rates of the forward and reverse reactions are equal.
chemical formula
An expression showing the chemical composition of a compound.
chemical kinetics
The area of chemistry concerned with the rates at which chemical reactions occur.
chemical property
Any property of a substance that cannot be studied without converting the substance into something else.
chemical reaction
A process in which a substance is changed into one or more new substances.
chemistry
The study of matter and the changes it undergoes.
chiral
Compounds or ions that are not superimposable with their mirror images.
chlor-alkali process
The production of chlorine gas by the electrolysis of aqueous NaCl solution.
closed system
A system that enables the exchange of energy but not mass with its surroundings.
closest packing
The most efficient arrangements for packing atoms, molecules, or ions in a crystal.
cohesion
The intermolecular attraction between like molecules.
colligative properties
Properties of solutions that depend on the number of solute particles in solution.
colloid
A dispersion of particles of one substance throughout another.
combination reaction
A reaction in which two or more substances combine to form a single product.
combustion reaction
A reaction in which a substance reacts with oxygen to produce heat and light.
common ion effect
The shift in equilibrium caused by adding a compound with an ion in common.
complex ion
An ion containing a central metal cation bonded to one or more molecules or ions.
