Glossary

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Glossary Entries
Word(s)	Definition	Image	Caption	Link	Source
Accuracy	how closely a measurement aligns with a correct value
Acid anhydride	compound that reacts with water to form an acid or acidic solution
Acid ionization	reaction involving the transfer of a proton from an acid to water, yielding hydronium ions and the conjugate base of the acid
Acid ionization constant (Ka)	equilibrium constant for the ionization of a weak acid
Acid-base indicator	organic acid or base whose color changes depending on the pH of the solution it is in
Acidic	describes a solution in which [H3O+] > [OH?]
Actinide	inner transition metal in the bottom of the bottom two rows of the periodic table
Actinide series	(also, actinoid series) actinium and the elements in the second row or the f-block, atomic numbers 89–103
Activated complex	(also, transition state) unstable combination of reactant species representing the highest energy state of a reaction system
Activation energy (Ea)	energy necessary in order for a reaction to take place
Active electrode	electrode that participates in the oxidation-reduction reaction of an electrochemical cell; the mass of an active electrode changes during the oxidation-reduction reaction
Actual yield	amount of product formed in a reaction
Addition reaction	reaction in which a double carbon-carbon bond forms a single carbon-carbon bond by the addition of a reactant. Typical reaction for an alkene.
Adhesive force	force of attraction between molecules of different chemical identities
Alcohol	organic compound with a hydroxyl group (–OH) bonded to a carbon atom
Alkali metal	element in group 1
Alkaline earth metal	element in group 2
Alkaline earth metal	any of the metals (beryllium, magnesium, calcium, strontium, barium, and radium) occupying group 2 of the periodic table; they are reactive, divalent metals that form basic oxides
Alkane	molecule consisting of only carbon and hydrogen atoms connected by single (?) bonds
Alkene	molecule consisting of carbon and hydrogen containing at least one carbon-carbon double bond
Alkyl group	substituent, consisting of an alkane missing one hydrogen atom, attached to a larger structure
Alkyne	molecule consisting of carbon and hydrogen containing at least one carbon-carbon triple bond
Allotropes	two or more forms of the same element, in the same physical state, with different chemical structures
Alloy	solid mixture of a metallic element and one or more additional elements
Alpha (?) decay	loss of an alpha particle during radioactive decay
Alpha particle	(? or He24He24 or ?24?24) high-energy helium nucleus; a helium atom that has lost two electrons and contains two protons and two neutrons
Alpha particle (? particle)	positively charged particle consisting of two protons and two neutrons
Amide	organic molecule that features a nitrogen atom connected to the carbon atom in a carbonyl group
Amine	organic molecule in which a nitrogen atom is bonded to one or more alkyl group
Amorphous	solid material such as a glass that does not have a regular repeating component to its three-dimensional structure; a solid but not a crystal
Amorphous solid	(also, noncrystalline solid) solid in which the particles lack an ordered internal structure
Amphiphilic	molecules possessing both hydrophobic (nonpolar) and a hydrophilic (polar) parts
Amphiprotic	species that may either gain or lose a proton in a reaction
Amphoteric	species that can act as either an acid or a base
Amplitude	extent of the displacement caused by a wave (for sinusoidal waves, it is one-half the difference from the peak height to the trough depth, and the intensity is proportional to the square of the amplitude)
Analyte	chemical species of interest
Angular momentum quantum number (l)	quantum number distinguishing the different shapes of orbitals; it is also a measure of the orbital angular momentum
Anion	negatively charged atom or molecule (contains more electrons than protons)
Anode	electrode in an electrochemical cell at which oxidation occurs; information about the anode is recorded on the left side of the salt bridge in cell notation
Antimatter	particles with the same mass but opposite properties (such as charge) of ordinary particles
Aqueous solution	solution for which water is the solvent
Aromatic hydrocarbon	cyclic molecule consisting of carbon and hydrogen with delocalized alternating carbon-carbon single and double bonds, resulting in enhanced stability
Arrhenius equation	mathematical relationship between the rate constant and the activation energy of a reaction
Atmosphere (atm)	unit of pressure; 1 atm = 101,325 Pa
Atom	smallest particle of an element that can enter into a chemical combination
Atomic mass	average mass of atoms of an element, expressed in amu
Atomic mass unit (amu)	(also, unified atomic mass unit, u, or Dalton, Da) unit of mass equal to 112112 of the mass of a 12C atom
Atomic number (Z)	number of protons in the nucleus of an atom
Atomic orbital	mathematical function that describes the behavior of an electron in an atom (also called the wavefunction), it can be used to find the probability of locating an electron in a specific region around the nucleus, as well as other dynamical variables
Aufbau principle	procedure in which the electron configuration of the elements is determined by “building” them in order of atomic numbers, adding one proton to the nucleus and one electron to the proper subshell at a time
Autoionization	reaction between identical species yielding ionic products; for water, this reaction involves transfer of protons to yield hydronium and hydroxide ions
Average rate	rate of a chemical reaction computed as the ratio of a measured change in amount or concentration of substance to the time interval over which the change occurred
Avogadro’s number (NA)	experimentally determined value of the number of entities comprising 1 mole of substance, equal to 6.022 × 1023 mol?1
Axial position	location in a trigonal bipyramidal geometry in which there is another atom at a 180° angle and the equatorial positions are at a 90° angle
Balanced equation	chemical equation with equal numbers of atoms for each element in the reactant and product
Band of stability	(also, belt of stability, zone of stability, or valley of stability) region of graph of number of protons versus number of neutrons containing stable (nonradioactive) nuclides
Bar	(bar or b) unit of pressure; 1 bar = 100,000 Pa
Barometer	device used to measure atmospheric pressure
Base anhydride	metal oxide that behaves as a base towards acids
Base ionization	reaction involving the transfer of a proton from water to a base, yielding hydroxide ions and the conjugate acid of the base
Base ionization constant (Kb)	equilibrium constant for the ionization of a weak base
Basic	describes a solution in which [H3O+] < [OH?]
Becquerel (Bq)	SI unit for rate of radioactive decay; 1 Bq = 1 disintegration/s
Beta (?) decay	breakdown of a neutron into a proton, which remains in the nucleus, and an electron, which is emitted as a beta particle
Beta particle	(?? or e?10e?10 or ??10??10) high-energy electron
Bicarbonate anion	salt of the hydrogen carbonate ion, HCO?3HCO3?
Bidentate ligand	ligand that coordinates to one central metal through coordinate bonds from two different atoms
Binary acid	compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
Binary compound	compound containing two different elements.
Binding energy per nucleon	total binding energy for the nucleus divided by the number of nucleons in the nucleus
Bismuth	heaviest member of group 15; a less reactive metal than other representative metals
Blackbody	idealized perfect absorber of all incident electromagnetic radiation; such bodies emit electromagnetic radiation in characteristic continuous spectra called blackbody radiation
Body-centered cubic (BCC) solid	crystalline structure that has a cubic unit cell with lattice points at the corners and in the center of the cell
Body-centered cubic unit cell	simplest repeating unit of a body-centered cubic crystal; it is a cube containing lattice points at each corner and in the center of the cube
Bohr’s model of the hydrogen atom	structural model in which an electron moves around the nucleus only in circular orbits, each with a specific allowed radius; the orbiting electron does not normally emit electromagnetic radiation, but does so when changing from one orbit to another.
Boiling point	temperature at which the vapor pressure of a liquid equals the pressure of the gas above it
Boiling point elevation	elevation of the boiling point of a liquid by addition of a solute
Boiling point elevation constant	the proportionality constant in the equation relating boiling point elevation to solute molality; also known as the ebullioscopic constant
Bomb calorimeter	device designed to measure the energy change for processes occurring under conditions of constant volume; commonly used for reactions involving solid and gaseous reactants or products
Bond angle	angle between any two covalent bonds that share a common atom
Bond dipole moment	separation of charge in a bond that depends on the difference in electronegativity and the bond distance represented by partial charges or a vector
Bond distance	(also, bond length) distance between the nuclei of two bonded atoms
Bond energy	(also, bond dissociation energy) energy required to break a covalent bond in a gaseous substance
Bond length	distance between the nuclei of two bonded atoms at which the lowest potential energy is achieved
Borate	compound containing boron-oxygen bonds, typically with clusters or chains as a part of the chemical structure
Born-Haber cycle	thermochemical cycle relating the various energetic steps involved in the formation of an ionic solid from the relevant elements
Bragg equation	equation that relates the angles at which X-rays are diffracted by the atoms within a crystal
Brønsted-Lowry acid	proton donor
Brønsted-Lowry base	proton acceptor
Buffer	mixture of a weak acid or a weak base and the salt of its conjugate; the pH of a buffer resists change when small amounts of acid or base are added
Buffer capacity	amount of an acid or base that can be added to a volume of a buffer solution before its pH changes significantly (usually by one pH unit)
Buret	device used for the precise delivery of variable liquid volumes, such as in a titration analysis
Calorie (cal)	unit of heat or other energy; the amount of energy required to raise 1 gram of water by 1 degree Celsius; 1 cal is defined as 4.184 J
Calorimeter	device used to measure the amount of heat absorbed or released in a chemical or physical process
Calorimetry	process of measuring the amount of heat involved in a chemical or physical process
Capillary action	flow of liquid within a porous material due to the attraction of the liquid molecules to the surface of the material and to other liquid molecules
Carbonate	salt of the anion CO2?3CO32?; often formed by the reaction of carbon dioxide with bases
Catalyst	substance that increases the rate of a reaction without itself being consumed by the reaction
Cathode	electrode in an electrochemical cell at which reduction occurs; information about the cathode is recorded on the right side of the salt bridge in cell notation
Cathodic protection	method of protecting metal by using a sacrificial anode and effectively making the metal that needs protecting the cathode, thus preventing its oxidation
Cation	positively charged atom or molecule (contains fewer electrons than protons)
Cell notation	shorthand way to represent the reactions in an electrochemical cell
Cell potential	difference in electrical potential that arises when dissimilar metals are connected; the driving force for the flow of charge (current) in oxidation-reduction reactions
Celsius (°C)	unit of temperature; water freezes at 0 °C and boils at 100 °C on this scale
Central metal	ion or atom to which one or more ligands is attached through coordinate covalent bonds
Chain reaction	repeated fission caused when the neutrons released in fission bombard other atoms
Chalcogen	element in group 16
Chelate	complex formed from a polydentate ligand attached to a central metal
Chelating ligand	ligand that attaches to a central metal ion by bonds from two or more donor atoms
Chemical change	change producing a different kind of matter from the original kind of matter
Chemical equation	symbolic representation of a chemical reaction
Chemical property	behavior that is related to the change of one kind of matter into another kind of matter
Chemical reduction	method of preparing a representative metal using a reducing agent
Chemical symbol	one-, two-, or three-letter abbreviation used to represent an element or its atoms
Chemical thermodynamics	area of science that deals with the relationships between heat, work, and all forms of energy associated with chemical and physical processes
Chemistry	study of the composition, properties, and interactions of matter
Chemotherapy	similar to internal radiation therapy, but chemical rather than radioactive substances are introduced into the body to kill cancer cells
Chlor-alkali process	electrolysis process for the synthesis of chlorine and sodium hydroxide
Circuit	path taken by a current as it flows because of an electrical potential difference
cis configuration	configuration of a geometrical isomer in which two similar groups are on the same side of an imaginary reference line on the molecule
Clausius-Clapeyron equation	mathematical relationship between the temperature, vapor pressure, and enthalpy of vaporization for a substance
Coefficient	number placed in front of symbols or formulas in a chemical equation to indicate their relative amount
Cohesive force	force of attraction between identical molecules
Colligative property	property of a solution that depends only on the concentration of a solute species
Collision theory	model that emphasizes the energy and orientation of molecular collisions to explain and predict reaction kinetics
Colloid	(also, colloidal dispersion) mixture in which relatively large solid or liquid particles are dispersed uniformly throughout a gas, liquid, or solid
Color-change interval	range in pH over which the color change of an indicator takes place
Combustion analysis	gravimetric technique used to determine the elemental composition of a compound via the collection and weighing of its gaseous combustion products
Common ion effect	effect on equilibrium when a substance with an ion in common with the dissolved species is added to the solution; causes a decrease in the solubility of an ionic species, or a decrease in the ionization of a weak acid or base
Complete ionic equation	chemical equation in which all dissolved ionic reactants and products, including spectator ions, are explicitly represented by formulas for their dissociated ions
Compound	pure substance that can be decomposed into two or more elements
Compressibility factor (Z)	ratio of the experimentally measured molar volume for a gas to its molar volume as computed from the ideal gas equation
Concentrated	qualitative term for a solution containing solute at a relatively high concentration
Concentration	quantitative measure of the relative amounts of solute and solvent present in a solution
Concentration cell	galvanic cell in which the two half-cells are the same except for the concentration of the solutes; spontaneous when the overall reaction is the dilution of the solute
Condensation	change from a gaseous to a liquid state
Conjugate acid	substance formed when a base gains a proton
Conjugate base	substance formed when an acid loses a proton
Containment system	(also, shield) a three-part structure of materials that protects the exterior of a nuclear fission reactor and operating personnel from the high temperatures, pressures, and radiation levels inside the reactor
Continuous spectrum	electromagnetic radiation given off in an unbroken series of wavelengths (e.g., white light from the sun)
Control rod	material inserted into the fuel assembly that absorbs neutrons and can be raised or lowered to adjust the rate of a fission reaction
Coordination compound	stable compound in which the central metal atom or ion acts as a Lewis acid and accepts one or more pairs of electrons
Coordination compound	substance consisting of atoms, molecules, or ions attached to a central atom through Lewis acid-base interactions
Coordination number	number of atoms closest to any given atom in a crystal or to the central metal atom in a complex
Coordination number	number of coordinate covalent bonds to the central metal atom in a complex or the number of closest contacts to an atom in a crystalline form
Coordination sphere	central metal atom or ion plus the attached ligands of a complex
Core electron	electron in an atom that occupies the orbitals of the inner shells
Corrosion	degradation of metal through an electrochemical process
Covalent bond	attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms
Covalent bond	bond formed when electrons are shared between atoms
Covalent compound	(also, molecular compound) composed of molecules formed by atoms of two or more different elements
Covalent network solid	solid whose particles are held together by covalent bonds
Covalent radius	one-half the distance between the nuclei of two identical atoms when they are joined by a covalent bond
Crenation	process whereby biological cells become shriveled due to loss of water by osmosis
Critical mass	amount of fissionable material that will support a self-sustaining (nuclear fission) chain reaction
Critical point	temperature and pressure above which a gas cannot be condensed into a liquid
Crystal field splitting (?oct)	difference in energy between the t2g and eg sets or t and e sets of orbitals
Crystal field theory	model that explains the energies of the orbitals in transition metals in terms of electrostatic interactions with the ligands but does not include metal ligand bonding
Crystalline solid	solid in which the particles are arranged in a definite repeating pattern
Cubic centimeter (cm3 or cc)	volume of a cube with an edge length of exactly 1 cm
Cubic closest packing (CCP)	crystalline structure in which planes of closely packed atoms or ions are stacked as a series of three alternating layers of different relative orientations (ABC)
Cubic meter (m3)	SI unit of volume
Curie (Ci)	larger unit for rate of radioactive decay frequently used in medicine; 1 Ci = 3.7 × 1010 disintegrations/s
Current	flow of electrical charge; the SI unit of charge is the coulomb (C) and current is measured in amperes (1A=1Cs)(1A=1Cs)
d orbital	region of space with high electron density that is either four lobed or contains a dumbbell and torus shape; describes orbitals with l = 2. An electron in this orbital is called a d electron
d-block element	one of the elements in groups 3–11 with valence electrons in d orbitals
Dalton (Da)	alternative unit equivalent to the atomic mass unit
Dalton’s atomic theory	set of postulates that established the fundamental properties of atoms
Daughter nuclide	nuclide produced by the radioactive decay of another nuclide; may be stable or may decay further
Density	ratio of mass to volume for a substance or object
Deposition	change from a gaseous state directly to a solid state
Diffraction	redirection of electromagnetic radiation that occurs when it encounters a physical barrier of appropriate dimensions
Dilute	qualitative term for a solution containing solute at a relatively low concentration
Dilution	process of adding solvent to a solution in order to lower the concentration of solutes
Dimensional analysis	(also, factor-label method) versatile mathematical approach that can be applied to computations ranging from simple unit conversions to more complex, multi-step calculations involving several different quantities
Dipole moment	property of a molecule that describes the separation of charge determined by the sum of the individual bond moments based on the molecular structure
Dipole-dipole attraction	intermolecular attraction between two permanent dipoles
Diprotic acid	acid containing two ionizable hydrogen atoms per molecule. A diprotic acid ionizes in two steps
Diprotic base	base capable of accepting two protons. The protons are accepted in two steps
Dispersed phase	substance present as relatively large solid or liquid particles in a colloid
Dispersion force	(also, London dispersion force) attraction between two rapidly fluctuating, temporary dipoles; significant only when particles are very close together
Dispersion medium	solid, liquid, or gas in which colloidal particles are dispersed
Disproportionation reaction	chemical reaction where a single reactant is simultaneously reduced and oxidized; it is both the reducing agent and the oxidizing agent
Dissociation	physical process accompanying the dissolution of an ionic compound in which the compound’s constituent ions are solvated and dispersed throughout the solution
Dissolved	describes the process by which solute components are dispersed in a solvent
Donor atom	atom in a ligand with a lone pair of electrons that forms a coordinate covalent bond to a central metal
Double bond	covalent bond in which two pairs of electrons are shared between two atoms
Downs cell	electrochemical cell used for the commercial preparation of metallic sodium (and chlorine) from molten sodium chloride
Dynamic equilibrium	state of a system in which reciprocal processes are occurring at equal rates
Effective nuclear charge	charge that leads to the Coulomb force exerted by the nucleus on an electron, calculated as the nuclear charge minus shielding
eg orbitals	set of two d orbitals that are oriented on the Cartesian axes for coordination complexes; in octahedral complexes, they are higher in energy than the t2g orbitals
Electrical potential	energy per charge; in electrochemical systems, it depends on the way the charges are distributed within the system; the SI unit of electrical potential is the volt (1V=1JC)(1V=1JC)
Electrical work (wele)	negative of total charge times the cell potential; equal to wmax for the system, and so equals the free energy change (?G)
Electrolyte	substance that produces ions when dissolved in water
Electromagnetic radiation	energy transmitted by waves that have an electric-field component and a magnetic-field component
Electromagnetic spectrum	range of energies that electromagnetic radiation can comprise, including radio, microwaves, infrared, visible, ultraviolet, X-rays, and gamma rays; since electromagnetic radiation energy is proportional to the frequency and inversely proportional to the wavelength, the spectrum can also be specified by ranges of frequencies or wavelengths
Electron	negatively charged, subatomic particle of relatively low mass located outside the nucleus
Electron affinity	energy required to add an electron to a gaseous atom to form an anion
Electron capture	combination of a core electron with a proton to yield a neutron within the nucleus
Electron configuration	electronic structure of an atom in its ground state given as a listing of the orbitals occupied by the electrons
Electron density	a measure of the probability of locating an electron in a particular region of space, it is equal to the squared absolute value of the wave function ?
Electron volt (eV)	measurement unit of nuclear binding energies, with 1 eV equaling the amount energy due to the moving an electron across an electric potential difference of 1 volt
Electron-pair geometry	arrangement around a central atom of all regions of electron density (bonds, lone pairs, or unpaired electrons)
Electronegativity	tendency of an atom to attract electrons in a bond to itself
Element	substance that is composed of a single type of atom; a substance that cannot be decomposed by a chemical change
Empirical formula	formula showing the composition of a compound given as the simplest whole-number ratio of atoms
Empirical formula mass	sum of average atomic masses for all atoms represented in an empirical formula
Emulsifying agent	amphiphilic substance used to stabilize the particles of some emulsions
Emulsion	colloid formed from immiscible liquids
End point	measured volume of titrant solution that yields the change in sample solution appearance or other property expected for stoichiometric equivalence (see equivalence point)
Endothermic process	chemical reaction or physical change that absorbs heat
Energy	capacity to supply heat or do work
Enthalpy (H)	sum of a system’s internal energy and the mathematical product of its pressure and volume
Enthalpy change (?H)	heat released or absorbed by a system under constant pressure during a chemical or physical process
Entropy (S)	state function that is a measure of the matter and/or energy dispersal within a system, determined by the number of system microstates often described as a measure of the disorder of the system
Equatorial position	one of the three positions in a trigonal bipyramidal geometry with 120° angles between them; the axial positions are located at a 90° angle
Equilibrium	in chemical reactions, the state in which the conversion of reactants into products and the conversion of products back into reactants occur simultaneously at the same rate; state of balance
Equilibrium constant (K)	value of the reaction quotient for a system at equilibrium
Equivalence point	volume of titrant solution required to react completely with the analyte in a titration analysis; provides a stoichiometric amount of titrant for the sample’s analyte according to the titration reaction
Ether	organic compound with an oxygen atom that is bonded to two carbon atoms
Exact number	number derived by counting or by definition
Excess reactant	reactant present in an amount greater than required by the reaction stoichiometry
Excited state	state having an energy greater than the ground-state energy
Exothermic process	chemical reaction or physical change that releases heat
Expansion work (pressure-volume work)	work done as a system expands or contracts against external pressure
Extensive property	property of a substance that depends on the amount of the substance
External beam radiation therapy	radiation delivered by a machine outside the body
f orbital	multilobed region of space with high electron density, describes orbitals with l = 3. An electron in this orbital is called an f electron
f-block element	(also, inner transition element) one of the elements with atomic numbers 58–71 or 90–103 that have valence electrons in f orbitals; they are frequently shown offset below the periodic table
Face-centered cubic (FCC) solid	crystalline structure consisting of a cubic unit cell with lattice points on the corners and in the center of each face
Face-centered cubic unit cell	simplest repeating unit of a face-centered cubic crystal; it is a cube containing lattice points at each corner and in the center of each face
Fahrenheit	unit of temperature; water freezes at 32 °F and boils at 212 °F on this scale
Faraday’s constant (F)	charge on 1 mol of electrons; F = 96,485 C/mol e?
First law of thermodynamics	internal energy of a system changes due to heat flow in or out of the system or work done on or by the system
First transition series	transition elements in the fourth period of the periodic table (first row of the d-block), atomic numbers 21–29
Fissile (or fissionable)	when a material is capable of sustaining a nuclear fission reaction
Fission	splitting of a heavier nucleus into two or more lighter nuclei, usually accompanied by the conversion of mass into large amounts of energy
Formal charge	charge that would result on an atom by taking the number of valence electrons on the neutral atom and subtracting the nonbonding electrons and the number of bonds (one-half of the bonding electrons)
Formula mass	sum of the average masses for all atoms represented in a chemical formula; for covalent compounds, this is also the molecular mass
Fourth transition series	transition elements in the seventh period of the periodic table (fourth row of the d-block), atomic numbers 89 and 104–111
Frasch process	important in the mining of free sulfur from enormous underground deposits
Free radical	molecule that contains an odd number of electrons
Freezing	change from a liquid state to a solid state
Freezing point	temperature at which the solid and liquid phases of a substance are in equilibrium; see also melting point
Freezing point depression	lowering of the freezing point of a liquid by addition of a solute
Freezing point depression constant	(also, cryoscopic constant) proportionality constant in the equation relating freezing point depression to solute molality
Frequency (??)	number of wave cycles (peaks or troughs) that pass a specified point in space per unit time
Frequency factor (A)	proportionality constant in the Arrhenius equation, related to the relative number of collisions having an orientation capable of leading to product formation
Functional group	part of an organic molecule that imparts a specific chemical reactivity to the molecule
Fundamental unit of charge	(also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 ×× 10?19 C
Fusion	combination of very light nuclei into heavier nuclei, accompanied by the conversion of mass into large amounts of energy
Fusion reactor	nuclear reactor in which fusion reactions of light nuclei are controlled
Galvanic cell	electrochemical cell that involves a spontaneous oxidation-reduction reaction; electrochemical cells with positive cell potentials; also called a voltaic cell
Galvanized iron	method for protecting iron by covering it with zinc, which will oxidize before the iron; zinc-plated iron
Gamma (?) emission	decay of an excited-state nuclide accompanied by emission of a gamma ray
Gamma ray	(? or ?00?00) short wavelength, high-energy electromagnetic radiation that exhibits wave-particle duality
Gas	state in which matter has neither definite volume nor shape
Geiger counter	instrument that detects and measures radiation via the ionization produced in a Geiger-Müller tube
Gel	colloidal dispersion of a liquid in a solid
Geometric isomers	isomers that differ in the way in which atoms are oriented in space relative to each other, leading to different physical and chemical properties
Gibbs free energy change (G)	thermodynamic property defined in terms of system enthalpy and entropy; all spontaneous processes involve a decrease in G
Gravimetric analysis	quantitative chemical analysis method involving the separation of an analyte from a sample by a physical or chemical process and subsequent mass measurements of the analyte, reaction product, and/or sample
Gray (Gy)	SI unit for measuring radiation dose; 1 Gy = 1 J absorbed/kg tissue
Ground state	state in which the electrons in an atom, ion, or molecule have the lowest energy possible
Group	vertical column of the periodic table
Haber process	main industrial process used to produce ammonia from nitrogen and hydrogen; involves the use of an iron catalyst and elevated temperatures and pressures
Half-life (t1/2)	time required for half of the atoms in a radioactive sample to decay
Half-life of a reaction (tl/2)	time required for half of a given amount of reactant to be consumed
Half-reaction method	method that produces a balanced overall oxidation-reduction reaction by splitting the reaction into an oxidation “half” and reduction “half,” balancing the two half-reactions, and then combining the oxidation half-reaction and reduction half-reaction in such a way that the number of electrons generated by the oxidation is exactly canceled by the number of electrons required by the reduction
Halide	compound containing an anion of a group 17 element in the 1? oxidation state (fluoride, F?; chloride, Cl?; bromide, Br?; and iodide, I?)
Hall–Héroult cell	electrolysis apparatus used to isolate pure aluminum metal from a solution of alumina in molten cryolite
Halogen	element in group 17
Heat (q)	transfer of thermal energy between two bodies
Heat capacity (C)	extensive property of a body of matter that represents the quantity of heat required to increase its temperature by 1 degree Celsius (or 1 kelvin)
Heisenberg uncertainty principle	rule stating that it is impossible to exactly determine both certain conjugate dynamical properties such as the momentum and the position of a particle at the same time. The uncertainty principle is a consequence of quantum particles exhibiting wave–particle duality
Hemolysis	rupture of red blood cells due to the accumulation of excess water by osmosis
Henderson-Hasselbalch equation	equation used to calculate the pH of buffer solutions
Henry’s law	law stating the proportional relationship between the concentration of dissolved gas in a solution and the partial pressure of the gas in contact with the solution
Hertz (Hz)	the unit of frequency, which is the number of cycles per second, s?1
Hess’s law	if a process can be represented as the sum of several steps, the enthalpy change of the process equals the sum of the enthalpy changes of the steps
Heterogeneous catalyst	catalyst present in a different phase from the reactants, furnishing a surface at which a reaction can occur
Heterogeneous equilibria	equilibria between reactants and products in different phases
Heterogeneous mixture	combination of substances with a composition that varies from point to point
Hexagonal closest packing (HCP)	crystalline structure in which close packed layers of atoms or ions are stacked as a series of two alternating layers of different relative orientations (AB)
High-spin complex	complex in which the electrons maximize the total electron spin by singly populating all of the orbitals before pairing two electrons into the lower-energy orbitals
Hole	(also, interstice) space between atoms within a crystal
Homogeneous catalyst	catalyst present in the same phase as the reactants
Homogeneous equilibria	equilibria within a single phase
Homogeneous mixture	(also, solution) combination of substances with a composition that is uniform throughout
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
Hydrocarbon	compound composed only of hydrogen and carbon; the major component of fossil fuels
Hydrogen bonding	occurs when exceptionally strong dipoles attract; bonding that exists when hydrogen is bonded to one of the three most electronegative elements: F, O, or N
Hydrogen carbonate	salt of carbonic acid, H2CO3 (containing the anion HCO?3HCO3?) in which one hydrogen atom has been replaced; an acid carbonate; also known as bicarbonate ion
Hydrogen halide	binary compound formed between hydrogen and the halogens: HF, HCl, HBr, and HI
Hydrogen sulfate	HSO?4HSO4? ion
Hydrogen sulfite	HSO?3HSO3? ion
Hydrogenation	addition of hydrogen (H2) to reduce a compound
Hydrometallurgy	process in which a metal is separated from a mixture by first converting it into soluble ions, extracting the ions, and then reducing the ions to precipitate the pure metal
Hydrostatic pressure	pressure exerted by a fluid due to gravity
Hydroxide	compound of a metal with the hydroxide ion OH? or the group ?OH
Hypertonic	of greater osmotic pressure
Hypervalent molecule	molecule containing at least one main group element that has more than eight electrons in its valence shell
Hypothesis	tentative explanation of observations that acts as a guide for gathering and checking information
Hypotonic	of less osmotic pressure
Ideal solution	solution that forms with no accompanying energy change
Immiscible	of negligible mutual solubility; typically refers to liquid substances
Indicator	substance added to the sample in a titration analysis to permit visual detection of the end point
Induced dipole	temporary dipole formed when the electrons of an atom or molecule are distorted by the instantaneous dipole of a neighboring atom or molecule
Inert electrode	electrode that allows current to flow, but that does not otherwise participate in the oxidation-reduction reaction in an electrochemical cell; the mass of an inert electrode does not change during the oxidation-reduction reaction; inert electrodes are often made of platinum or gold because these metals are chemically unreactive.
Inert gas	(also, noble gas) element in group 18
Inert pair effect	tendency of heavy atoms to form ions in which their valence s electrons are not lost
Initial rate	instantaneous rate of a chemical reaction at t = 0 s (immediately after the reaction has begun)
Inner transition metal	(also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide
Instantaneous dipole	temporary dipole that occurs for a brief moment in time when the electrons of an atom or molecule are distributed asymmetrically
Instantaneous rate	rate of a chemical reaction at any instant in time, determined by the slope of the line tangential to a graph of concentration as a function of time
Integrated rate law	equation that relates the concentration of a reactant to elapsed time of reaction
Intensity	property of wave-propagated energy related to the amplitude of the wave, such as brightness of light or loudness of sound
Intensive property	property of a substance that is independent of the amount of the substance
Interference pattern	pattern typically consisting of alternating bright and dark fringes; it results from constructive and destructive interference of waves
Interhalogen	compound formed from two or more different halogens
Intermolecular force	noncovalent attractive force between atoms, molecules, and/or ions
Internal energy (U)	total of all possible kinds of energy present in a substance or substances
Internal radiation therapy	(also, brachytherapy) radiation from a radioactive substance introduced into the body to kill cancer cells
Interstitial sites	spaces between the regular particle positions in any array of atoms or ions
Ion	electrically charged atom or molecule (contains unequal numbers of protons and electrons)
Ion pair	solvated anion/cation pair held together by moderate electrostatic attraction
Ion-dipole attraction	electrostatic attraction between an ion and a polar molecule
Ion-product constant for water (Kw)	equilibrium constant for the autoionization of water
Ionic bond	electrostatic forces of attraction between the oppositely charged ions of an ionic compound
Ionic bond	strong electrostatic force of attraction between cations and anions in an ionic compound
Ionic compound	compound composed of cations and anions combined in ratios, yielding an electrically neutral substance
Ionic solid	solid composed of positive and negative ions held together by strong electrostatic attractions
Ionization energy	energy required to remove an electron from a gaseous atom or ion. The associated number (e.g., second ionization energy) corresponds to the charge of the ion produced (X2+)
Ionization isomer	(or coordination isomer) isomer in which an anionic ligand is replaced by the counter ion in the inner coordination sphere
Ionizing radiation	radiation that can cause a molecule to lose an electron and form an ion
Isoelectronic	group of ions or atoms that have identical electron configurations
Isomers	compounds with the same chemical formula but different structures
Isomorphous	possessing the same crystalline structure
Isotonic	of equal osmotic pressure
Isotopes	atoms that contain the same number of protons but different numbers of neutrons
Joule (J)	SI unit of energy; 1 joule is the kinetic energy of an object with a mass of 2 kilograms moving with a velocity of 1 meter per second, 1 J = 1 kg m2/s and 4.184 J = 1 cal
Kc	equilibrium constant for reactions based on concentrations of reactants and products
Kelvin (K)	SI unit of temperature; 273.15 K = 0 ºC
Kilogram (kg)	standard SI unit of mass; 1 kg = approximately 2.2 pounds
Kinetic energy	energy of a moving body, in joules, equal to 12mv212mv2 (where m = mass and v = velocity)
KP	equilibrium constant for gas-phase reactions based on partial pressures of reactants and products
Lanthanide	inner transition metal in the top of the bottom two rows of the periodic table
Lanthanide series	(also, lanthanoid series) lanthanum and the elements in the first row or the f-block, atomic numbers 57–71
Lattice energy (?Hlattice)	energy required to separate one mole of an ionic solid into its component gaseous ions
Law	statement that summarizes a vast number of experimental observations, and describes or predicts some aspect of the natural world
Law of conservation of matter	when matter converts from one type to another or changes form, there is no detectable change in the total amount of matter present
Law of constant composition	(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
Law of definite proportions	(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
Law of mass action	when a reversible reaction has attained equilibrium at a given temperature, the reaction quotient remains constant
Law of multiple proportions	when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers
Le Chatelier's principle	when a chemical system at equilibrium is disturbed, it returns to equilibrium by counteracting the disturbance
Length	measure of one dimension of an object
Leveling effect of water	any acid stronger than H3O+H3O+, or any base stronger than OH? will react with water to form H3O+H3O+, or OH?, respectively; water acts as a base to make all strong acids appear equally strong, and it acts as an acid to make all strong bases appear equally strong
Lewis structure	diagram showing lone pairs and bonding pairs of electrons in a molecule or an ion
Lewis symbol	symbol for an element or monatomic ion that uses a dot to represent each valence electron in the element or ion
Ligand	ion or neutral molecule attached to the central metal ion in a coordination compound
Limiting reactant	reactant present in an amount lower than required by the reaction stoichiometry, thus limiting the amount of product generated
Line spectrum	electromagnetic radiation emitted at discrete wavelengths by a specific atom (or atoms) in an excited state
Linear	shape in which two outside groups are placed on opposite sides of a central atom
Linkage isomer	coordination compound that possesses a ligand that can bind to the transition metal in two different ways (CN? vs. NC?)
Liquid	state of matter that has a definite volume but indefinite shape
Liter (L)	(also, cubic decimeter) unit of volume; 1 L = 1,000 cm3
Lone pair	two (a pair of) valence electrons that are not used to form a covalent bond
Low-spin complex	complex in which the electrons minimize the total electron spin by pairing in the lower-energy orbitals before populating the higher-energy orbitals
Macroscopic domain	realm of everyday things that are large enough to sense directly by human sight and touch
Magic number	nuclei with specific numbers of nucleons that are within the band of stability
Magnetic quantum number (ml)	quantum number signifying the orientation of an atomic orbital around the nucleus; orbitals having different values of ml but the same subshell value of l have the same energy (are degenerate), but this degeneracy can be removed by application of an external magnetic field
Main-group element	(also, representative element) element in columns 1, 2, and 12–18
Manometer	device used to measure the pressure of a gas trapped in a container
Mass	fundamental property indicating amount of matter
Mass defect	difference between the mass of an atom and the summed mass of its constituent subatomic particles (or the mass “lost” when nucleons are brought together to form a nucleus)
Mass number (A)	sum of the numbers of neutrons and protons in the nucleus of an atom
Mass percentage	ratio of solute-to-solution mass expressed as a percentage
Mass-energy equivalence equation	Albert Einstein’s relationship showing that mass and energy are equivalent
Mass-volume percent	ratio of solute mass to solution volume, expressed as a percentage
Matter	anything that occupies space and has mass
Melting	change from a solid state to a liquid state
Melting point	temperature at which the solid and liquid phases of a substance are in equilibrium; see also freezing point
Metal	element that is shiny, malleable, good conductor of heat and electricity
Metal (representative)	atoms of the metallic elements of groups 1, 2, 12, 13, 14, 15, and 16, which form ionic compounds by losing electrons from their outer s or p orbitals
Metallic solid	solid composed of metal atoms
Metalloid	element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals
Metalloid	element that has properties that are between those of metals and nonmetals; these elements are typically semiconductors
Meter (m)	standard metric and SI unit of length; 1 m = approximately 1.094 yards
Method of initial rates	use of a more explicit algebraic method to determine the orders in a rate law
Microscopic domain	realm of things that are much too small to be sensed directly
Microstate (W)	possible configuration or arrangement of matter and energy within a system
Millicurie (mCi)	larger unit for rate of radioactive decay frequently used in medicine; 1 Ci = 3.7 × 1010 disintegrations/s
Milliliter (mL)	1/1,000 of a liter; equal to 1 cm3
Miscible	mutually soluble in all proportions; typically refers to liquid substances
Mixture	matter that can be separated into its components by physical means
Molality (m)	a concentration unit defined as the ratio of the numbers of moles of solute to the mass of the solvent in kilograms
Molar mass	mass in grams of 1 mole of a substance
Molar solubility	solubility of a compound expressed in units of moles per liter (mol/L)
Molarity (M)	unit of concentration, defined as the number of moles of solute dissolved in 1 liter of solution
Mole	amount of substance containing the same number of atoms, molecules, ions, or other entities as the number of atoms in exactly 12 grams of 12C
Molecular compound	(also, covalent compound) composed of molecules formed by atoms of two or more different elements
Molecular equation	chemical equation in which all reactants and products are represented as neutral substances
Molecular formula	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 solid	solid composed of neutral molecules held together by intermolecular forces of attraction
Molecular structure	arrangement of atoms in a molecule or ion
Molecular structure	structure that includes only the placement of the atoms in the molecule
Molecule	bonded collection of two or more atoms of the same or different elements
Monatomic ion	ion composed of a single atom
Monodentate	ligand that attaches to a central metal through just one coordinate covalent bond
Monoprotic acid	acid containing one ionizable hydrogen atom per molecule
Multiple equilibrium	system characterized by more than one state of balance between a slightly soluble ionic solid and an aqueous solution of ions working simultaneously
Nernst equation	equation that relates the logarithm of the reaction quotient (Q) to nonstandard cell potentials; can be used to relate equilibrium constants to standard cell potentials
Net ionic equation	chemical equation in which only those dissolved ionic reactants and products that undergo a chemical or physical change are represented (excludes spectator ions)
Neutral	describes a solution in which [H3O+] = [OH?]
Neutron	uncharged, subatomic particle located in the nucleus
Nitrate	NO?3NO3? ion; salt of nitric acid
Nitrogen fixation	formation of nitrogen compounds from molecular nitrogen
Noble gas	(also, inert gas) element in group 18
Node	any point of a standing wave with zero amplitude
Node	plane separating different lobes of orbitals, where the probability of finding an electron is zero
Nomenclature	system of rules for naming objects of interest
Nonelectrolyte	substance that does not produce ions when dissolved in water
Nonionizing radiation	radiation that speeds up the movement of atoms and molecules; it is equivalent to heating a sample, but is not energetic enough to cause the ionization of molecules
Nonmetal	element that appears dull, poor conductor of heat and electricity
Nonspontaneous process	process that requires continual input of energy from an external source
Normal boiling point	temperature at which a liquid’s vapor pressure equals 1 atm (760 torr)
Nuclear binding energy	energy lost when an atom’s nucleons are bound together (or the energy needed to break a nucleus into its constituent protons and neutrons)
Nuclear chemistry	study of the structure of atomic nuclei and processes that change nuclear structure
Nuclear fuel	fissionable isotope present in sufficient quantities to provide a self-sustaining chain reaction in a nuclear reactor
Nuclear moderator	substance that slows neutrons to a speed low enough to cause fission
Nuclear reaction	change to a nucleus resulting in changes in the atomic number, mass number, or energy state
Nuclear reactor	environment that produces energy via nuclear fission in which the chain reaction is controlled and sustained without explosion
Nuclear transmutation	conversion of one nuclide into another nuclide
Nucleon	collective term for protons and neutrons in a nucleus
Nucleus	massive, positively charged center of an atom made up of protons and neutrons
Nuclide	nucleus of a particular isotope
Nutritional calorie (Calorie)	unit used for quantifying energy provided by digestion of foods, defined as 1000 cal or 1 kcal
Octahedral	shape in which six outside groups are placed around a central atom such that a three-dimensional shape is generated with four groups forming a square and the other two forming the apex of two pyramids, one above and one below the square plane
Octahedral hole	open space in a crystal at the center of six particles located at the corners of an octahedron
Octet rule	guideline that states main group atoms will form structures in which eight valence electrons interact with each nucleus, counting bonding electrons as interacting with both atoms connected by the bond
Optical isomer	(also, enantiomer) molecule that is a nonsuperimposable mirror image with identical chemical and physical properties, except when it reacts with other optical isomers
Orbital diagram	pictorial representation of the electron configuration showing each orbital as a box and each electron as an arrow
Organic compound	natural or synthetic compound that contains carbon
Osmosis	diffusion of solvent molecules through a semipermeable membrane
Osmotic pressure (?)	opposing pressure required to prevent bulk transfer of solvent molecules through a semipermeable membrane
Ostwald process	industrial process used to convert ammonia into nitric acid
Overall reaction order	sum of the reaction orders for each substance represented in the rate law
Overlap	coexistence of orbitals from two different atoms sharing the same region of space, leading to the formation of a covalent bond
Oxidation half-reaction	the “half” of an oxidation-reduction reaction involving oxidation; the half-reaction in which electrons appear as products; balanced when each atom type, as well as the charge, is balanced
Oxide	binary compound of oxygen with another element or group, typically containing O2? ions or the group –O– or =O
Oxyacid	compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H+ ions when dissolved in water)
Oxyacid	compound containing a nonmetal and one or more hydroxyl groups
Oxyanion	polyatomic anion composed of a central atom bonded to oxygen atoms
Ozone	allotrope of oxygen; O3
p orbital	dumbbell-shaped region of space with high electron density, describes orbitals with l = 1. An electron in this orbital is called a p electron
Pairing energy (P)	energy required to place two electrons with opposite spins into a single orbital
Parent nuclide	unstable nuclide that changes spontaneously into another (daughter) nuclide
Partially miscible	of moderate mutual solubility; typically refers to liquid substances
Particle accelerator	device that uses electric and magnetic fields to increase the kinetic energy of nuclei used in transmutation reactions
Parts per billion (ppb)	ratio of solute-to-solution mass multiplied by 109
Parts per million (ppm)	ratio of solute-to-solution mass multiplied by 106
Pascal (Pa)	SI unit of pressure; 1 Pa = 1 N/m2
Passivation	metals with a protective nonreactive film of oxide or other compound that creates a barrier for chemical reactions; physical or chemical removal of the passivating film allows the metals to demonstrate their expected chemical reactivity
Pauli exclusion principle	specifies that no two electrons in an atom can have the same value for all four quantum numbers
Percent composition	percentage by mass of the various elements in a compound
Percent ionization	ratio of the concentration of the ionized acid to the initial acid concentration, times 100
Percent yield	measure of the efficiency of a reaction, expressed as a percentage of the theoretical yield
Period	(also, series) horizontal row of the periodic table
Periodic law	properties of the elements are periodic function of their atomic numbers.
Periodic table	table of the elements that places elements with similar chemical properties close together
Peroxide	molecule containing two oxygen atoms bonded together or as the anion, O2?2O22?
PH	logarithmic measure of the concentration of hydronium ions in a solution
Phase diagram	pressure-temperature graph summarizing conditions under which the phases of a substance can exist
Photon	smallest possible packet of electromagnetic radiation, a particle of light
Photosynthesis	process whereby light energy promotes the reaction of water and carbon dioxide to form carbohydrates and oxygen; this allows photosynthetic organisms to store energy
Physical change	change in the state or properties of matter that does not involve a change in its chemical composition
Physical property	characteristic of matter that is not associated with any change in its chemical composition
Pi bond (? bond)	covalent bond formed by side-by-side overlap of atomic orbitals; the electron density is found on opposite sides of the internuclear axis
Pidgeon process	chemical reduction process used to produce magnesium through the thermal reaction of magnesium oxide with silicon
Plasma	gaseous state of matter containing a large number of electrically charged atoms and/or molecules
Platinum metals	group of six transition metals consisting of ruthenium, osmium, rhodium, iridium, palladium, and platinum that tend to occur in the same minerals and demonstrate similar chemical properties
Pnictogen	element in group 15
POH	logarithmic measure of the concentration of hydroxide ions in a solution
Polar covalent bond	covalent bond between atoms of different electronegativities; a covalent bond with a positive end and a negative end
Polar molecule	(also, dipole) molecule with an overall dipole moment
Polarizability	measure of the ability of a charge to distort a molecule’s charge distribution (electron cloud)
Polyatomic ion	ion composed of more than one atom
Polydentate ligand	ligand that is attached to a central metal ion by bonds from two or more donor atoms, named with prefixes specifying how many donors are present (e.g., hexadentate = six coordinate bonds formed)
Polymorph	variation in crystalline structure that results in different physical properties for the resulting compound
Position of equilibrium	concentrations or partial pressures of components of a reaction at equilibrium (commonly used to describe conditions before a disturbance)
Positron (?+10?+10 or e+10e+10)	antiparticle to the electron; it has identical properties to an electron, except for having the opposite (positive) charge
Positron emission	(also, ?+ decay) conversion of a proton into a neutron, which remains in the nucleus, and a positron, which is emitted
Potential energy	energy of a particle or system of particles derived from relative position, composition, or condition
Pounds per square inch (psi)	unit of pressure common in the US
Precision	how closely a measurement matches the same measurement when repeated
Pressure	force exerted per unit area
Principal quantum number (n)	quantum number specifying the shell an electron occupies in an atom
Product	substance formed by a chemical or physical change; shown on the right side of the arrow in a chemical equation
Proton	positively charged, subatomic particle located in the nucleus
Pure covalent bond	(also, nonpolar covalent bond) covalent bond between atoms of identical electronegativities
Pure substance	homogeneous substance that has a constant composition
Quantitative analysis	the determination of the amount or concentration of a substance in a sample
Quantization	occurring only in specific discrete values, not continuous
Quantum mechanics	field of study that includes quantization of energy, wave-particle duality, and the Heisenberg uncertainty principle to describe matter
Quantum number	integer number having only specific allowed values and used to characterize the arrangement of electrons in an atom
Radiation absorbed dose (rad)	SI unit for measuring radiation dose, frequently used in medical applications; 1 rad = 0.01 Gy
Radiation dosimeter	device that measures ionizing radiation and is used to determine personal radiation exposure
Radiation therapy	use of high-energy radiation to damage the DNA of cancer cells, which kills them or keeps them from dividing
Radioactive decay	spontaneous decay of an unstable nuclide into another nuclide
Radioactive decay series	chains of successive disintegrations (radioactive decays) that ultimately lead to a stable end-product
Radioactive tracer	(also, radioactive label) radioisotope used to track or follow a substance by monitoring its radioactive emissions
Radioactivity	phenomenon exhibited by an unstable nucleon that spontaneously undergoes change into a nucleon that is more stable; an unstable nucleon is said to be radioactive
Radiocarbon dating	highly accurate means of dating objects 30,000–50,000 years old that were derived from once-living matter; achieved by calculating the ratio of C614:C612C614:C612 in the object vs. the ratio of C614:C612C614:C612 in the present-day atmosphere
Radioisotope	isotope that is unstable and undergoes conversion into a different, more stable isotope
Radiometric dating	use of radioisotopes and their properties to date the formation of objects such as archeological artifacts, formerly living organisms, or geological formations
Raoult’s law	the partial pressure exerted by a solution component is equal to the product of the component’s mole fraction in the solution and its equilibrium vapor pressure in the pure state
Rare earth element	collection of 17 elements including the lanthanides, scandium, and yttrium that often occur together and have similar chemical properties, making separation difficult
Rate constant (k)	proportionality constant in the relationship between reaction rate and concentrations of reactants
Rate expression	mathematical representation relating reaction rate to changes in amount, concentration, or pressure of reactant or product species per unit time
Rate law	(also, rate equation) mathematical equation showing the dependence of reaction rate on the rate constant and the concentration of one or more reactants
Rate of reaction	measure of the speed at which a chemical reaction takes place
Reactant	substance undergoing a chemical or physical change; shown on the left side of the arrow in a chemical equation
Reaction order	value of an exponent in a rate law, expressed as an ordinal number (for example, zero order for 0, first order for 1, second order for 2, and so on)
Reaction quotient (Q)	ratio of the product of molar concentrations (or pressures) of the products to that of the reactants, each concentration (or pressure) being raised to the power equal to the coefficient in the equation
Reactor coolant	assembly used to carry the heat produced by fission in a reactor to an external boiler and turbine where it is transformed into electricity
Reduction half-reaction	the “half” of an oxidation-reduction reaction involving reduction; the half-reaction in which electrons appear as reactants; balanced when each atom type, as well as the charge, is balanced
Relative biological effectiveness (RBE)	measure of the relative damage done by radiation
Representative element	(also, main-group element) element in columns 1, 2, and 12–18
Representative element	element where the s and p orbitals are filling
Representative metal	metal among the representative elements
Resonance	situation in which one Lewis structure is insufficient to describe the bonding in a molecule and the average of multiple structures is observed
Resonance forms	two or more Lewis structures that have the same arrangement of atoms but different arrangements of electrons
Resonance hybrid	average of the resonance forms shown by the individual Lewis structures
Reversible process	process that takes place so slowly as to be capable of reversing direction in response to an infinitesimally small change in conditions; hypothetical construct that can only be approximated by real processes removed
Reversible reaction	chemical reaction that can proceed in both the forward and reverse directions under given conditions
Roentgen equivalent man (rem)	unit for radiation damage, frequently used in medicine; 1 rem = 1 Sv
Rounding	procedure used to ensure that calculated results properly reflect the uncertainty in the measurements used in the calculation
s orbital	spherical region of space with high electron density, describes orbitals with l = 0. An electron in this orbital is called an s electron
Sacrificial anode	more active, inexpensive metal used as the anode in cathodic protection; frequently made from magnesium or zinc
Saturated	of concentration equal to solubility; containing the maximum concentration of solute possible for a given temperature and pressure
Saturated hydrocarbon	molecule containing carbon and hydrogen that has only single bonds between carbon atoms
Scientific method	path of discovery that leads from question and observation to law or hypothesis to theory, combined with experimental verification of the hypothesis and any necessary modification of the theory
Scintillation counter	instrument that uses a scintillator—a material that emits light when excited by ionizing radiation—to detect and measure radiation
Second (s)	SI unit of time
Second law of thermodynamics	entropy of the universe increases for a spontaneous process
Second transition series	transition elements in the fifth period of the periodic table (second row of the d-block), atomic numbers 39–47
Selective precipitation	process in which ions are separated using differences in their solubility with a given precipitating reagent
Semipermeable membrane	a membrane that selectively permits passage of certain ions or molecules
Series	(also, period) horizontal row of the period table
Shell	set of orbitals with the same principal quantum number, n
SI units (International System of Units)	standards fixed by international agreement in the International System of Units (Le Système International d’Unités)
Sievert (Sv)	SI unit measuring tissue damage caused by radiation; takes into account energy and biological effects of radiation
Sigma bond (? bond)	covalent bond formed by overlap of atomic orbitals along the internuclear axis
Significant figures	(also, significant digits) all of the measured digits in a determination, including the uncertain last digit
Silicate	compound containing silicon-oxygen bonds, with silicate tetrahedra connected in rings, sheets, or three-dimensional networks, depending on the other elements involved in the formation of the compounds
Simple cubic structure	crystalline structure with a cubic unit cell with lattice points only at the corners
Simple cubic unit cell	(also, primitive cubic unit cell) unit cell in the simple cubic structure
Single bond	bond in which a single pair of electrons is shared between two atoms
Skeletal structure	shorthand method of drawing organic molecules in which carbon atoms are represented by the ends of lines and bends in between lines, and hydrogen atoms attached to the carbon atoms are not shown (but are understood to be present by the context of the structure)
Smelting	process of extracting a pure metal from a molten ore
Solid	state of matter that is rigid, has a definite shape, and has a fairly constant volume
Solubility	extent to which a solute may be dissolved in water, or any solvent
Solubility product (Ksp)	equilibrium constant for the dissolution of a slightly soluble electrolyte
Solute	solution component present in a concentration less than that of the solvent
Solvation	exothermic process in which intermolecular attractive forces between the solute and solvent in a solution are established
Solvent	solution component present in a concentration that is higher relative to other components
Space lattice	all points within a crystal that have identical environments
Spatial isomers	compounds in which the relative orientations of the atoms in space differ
Specific heat capacity (c)	intensive property of a substance that represents the quantity of heat required to raise the temperature of 1 gram of the substance by 1 degree Celsius (or 1 kelvin)
Spectator ion	ion that does not undergo a chemical or physical change during a reaction, but its presence is required to maintain charge neutrality
Spectrochemical series	ranking of ligands according to the magnitude of the crystal field splitting they induce
Spin quantum number (ms)	number specifying the electron spin direction, either +12+12 or ?12?12
Spontaneous change	process that takes place without a continuous input of energy from an external source
Spontaneous process	physical or chemical change that occurs without the addition of energy from an external source
Standard cell potential (E?cell)(Ecell?)	the cell potential when all reactants and products are in their standard states (1 bar or 1 atm or gases; 1 M for solutes), usually at 298.15 K; can be calculated by subtracting the standard reduction potential for the half-reaction at the anode from the standard reduction potential for the half-reaction occurring at the cathode
Standard enthalpy of combustion (?H?c?Hc?)	heat released when one mole of a compound undergoes complete combustion under standard conditions
Standard enthalpy of formation (?H?f?Hf?)	enthalpy change of a chemical reaction in which 1 mole of a pure substance is formed from its elements in their most stable states under standard state conditions
Standard entropy (S°)	entropy for a substance at 1 bar pressure; tabulated values are usually determined at 298.15 K and denoted S?298S298?
Standard entropy change (?S°)	change in entropy for a reaction calculated using the standard entropies, usually at room temperature and denoted ?S?298?S298?
Standard free energy change (?G°)	change in free energy for a process occurring under standard conditions (1 bar pressure for gases, 1 M concentration for solutions)
Standard free energy of formation (?G?f)(?Gf?)	change in free energy accompanying the formation of one mole of substance from its elements in their standard states
Standard hydrogen electrode (SHE)	the electrode consists of hydrogen gas bubbling through hydrochloric acid over an inert platinum electrode whose reduction at standard conditions is assigned a value of 0 V; the reference point for standard reduction potentials
Standard reduction potential (E°)	the value of the reduction under standard conditions (1 bar or 1 atm for gases; 1 M for solutes) usually at 298.15 K; tabulated values used to calculate standard cell potentials
Standard state	set of physical conditions as accepted as common reference conditions for reporting thermodynamic properties; 1 bar of pressure, and solutions at 1 molar concentrations, usually at a temperature of 298.15 K
Standing wave	(also, stationary wave) localized wave phenomenon characterized by discrete wavelengths determined by the boundary conditions used to generate the waves; standing waves are inherently quantized
State function	property depending only on the state of a system, and not the path taken to reach that state
Steel	material made from iron by removing impurities in the iron and adding substances that produce alloys with properties suitable for specific uses
Stepwise ionization	process in which an acid is ionized by losing protons sequentially
Stress	change to a reaction's conditions that may cause a shift in the equilibrium
Strong electrolyte	substance that dissociates or ionizes completely when dissolved in water
Strong nuclear force	force of attraction between nucleons that holds a nucleus together
Strong-field ligand	ligand that causes larger crystal field splittings
Structural formula	shows the atoms in a molecule and how they are connected
Structural isomer	one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently
Subcritical mass	amount of fissionable material that cannot sustain a chain reaction; less than a critical mass
Sublimation	change from solid state directly to gaseous state
Subshell	set of orbitals in an atom with the same values of n and l
Substituent	branch or functional group that replaces hydrogen atoms in a larger hydrocarbon chain
Substitution reaction	reaction in which one atom replaces another in a molecule
Sulfate	SO2?4SO42? ion
Sulfite	SO2?3SO32? ion
Superconductor	material that conducts electricity with no resistance
Supercritical fluid	substance at a temperature and pressure higher than its critical point; exhibits properties intermediate between those of gaseous and liquid states
Supercritical mass	amount of material in which there is an increasing rate of fission
Superoxide	oxide containing the anion O?2O2?
Supersaturated	of concentration that exceeds solubility; a nonequilibrium state
Surface tension	energy required to increase the area, or length, of a liquid surface by a given amount
Surroundings	all matter other than the system being studied
Symbolic domain	specialized language used to represent components of the macroscopic and microscopic domains, such as chemical symbols, chemical formulas, chemical equations, graphs, drawings, and calculations
System	portion of matter undergoing a chemical or physical change being studied
t2g orbitals	set of three d orbitals aligned between the Cartesian axes for coordination complexes; in octahedral complexes, they are lowered in energy compared to the eg orbitals according to CFT
Temperature	intensive property of matter that is a quantitative measure of “hotness” and “coldness”
Tetrahedral	shape in which four outside groups are placed around a central atom such that a three-dimensional shape is generated with four corners and 109.5° angles between each pair and the central atom
Tetrahedral hole	tetrahedral space formed by four atoms or ions in a crystal
Theoretical yield	amount of product that may be produced from a given amount of reactant(s) according to the reaction stoichiometry
Theory	well-substantiated, comprehensive, testable explanation of a particular aspect of nature
Thermal energy	kinetic energy associated with the random motion of atoms and molecules
Thermochemistry	study of measuring the amount of heat absorbed or released during a chemical reaction or a physical change
Third law of thermodynamics	entropy of a perfect crystal at absolute zero (0 K) is zero
Third transition series	transition elements in the sixth period of the periodic table (third row of the d-block), atomic numbers 57 and 72–79
Titrant	solution containing a known concentration of substance that will react with the analyte in a titration analysis
Titration analysis	quantitative chemical analysis method that involves measuring the volume of a reactant solution required to completely react with the analyte in a sample
Titration curve	plot of the pH of a solution of acid or base versus the volume of base or acid added during a titration
Torr	unit of pressure; 1torr=1760atm1torr=1760atm
trans configuration	configuration of a geometrical isomer in which two similar groups are on opposite sides of an imaginary reference line on the molecule
Transition metal	element in columns 3–11
Transmutation reaction	bombardment of one type of nuclei with other nuclei or neutrons
Transuranium element	element with an atomic number greater than 92; these elements do not occur in nature
Trigonal bipyramidal	shape in which five outside groups are placed around a central atom such that three form a flat triangle with 120° angles between each pair and the central atom, and the other two form the apex of two pyramids, one above and one below the triangular plane
Trigonal planar	shape in which three outside groups are placed in a flat triangle around a central atom with 120° angles between each pair and the central atom
Triple bond	bond in which three pairs of electrons are shared between two atoms
Triple point	temperature and pressure at which the vapor, liquid, and solid phases of a substance are in equilibrium
Triprotic acid	acid that contains three ionizable hydrogen atoms per molecule; ionization of triprotic acids occurs in three steps
Tyndall effect	scattering of visible light by a colloidal dispersion
Uncertainty	estimate of amount by which measurement differs from true value
Unified atomic mass unit (u)	alternative unit equivalent to the atomic mass unit
Unit	standard of comparison for measurements
Unit cell	smallest portion of a space lattice that is repeated in three dimensions to form the entire lattice
Unit conversion factor	ratio of equivalent quantities expressed with different units; used to convert from one unit to a different unit
Unsaturated	of concentration less than solubility
Vacancy	defect that occurs when a position that should contain an atom or ion is vacant
Valence bond theory	description of bonding that involves atomic orbitals overlapping to form ? or ? bonds, within which pairs of electrons are shared
Valence electrons	electrons in the outermost or valence shell (highest value of n) of a ground-state atom; determine how an element reacts
Valence shell	outermost shell of electrons in a ground-state atom; for main group elements, the orbitals with the highest n level (s and p subshells) are in the valence shell, while for transition metals, the highest energy s and d subshells make up the valence shell and for inner transition elements, the highest s, d, and f subshells are included
Valence shell electron-pair repulsion theory (VSEPR)	theory used to predict the bond angles in a molecule based on positioning regions of high electron density as far apart as possible to minimize electrostatic repulsion
Van der Waals equation	modified version of the ideal gas equation containing additional terms to account for non-ideal gas behavior
Van der Waals force	attractive or repulsive force between molecules, including dipole-dipole, dipole-induced dipole, and London dispersion forces; does not include forces due to covalent or ionic bonding, or the attraction between ions and molecules
Van’t Hoff factor (i)	the ratio of the number of moles of particles in a solution to the number of moles of formula units dissolved in the solution
Vapor pressure	(also, equilibrium vapor pressure) pressure exerted by a vapor in equilibrium with a solid or a liquid at a given temperature
Vaporization	change from liquid state to gaseous state
Vector	quantity having magnitude and direction
Viscosity	measure of a liquid’s resistance to flow
Voltaic cell	another name for a galvanic cell
Volume	amount of space occupied by an object
Volume percentage	ratio of solute-to-solution volume expressed as a percentage
Wave	oscillation that can transport energy from one point to another in space
Wave-particle duality	term used to describe the fact that elementary particles including matter exhibit properties of both particles (including localized position, momentum) and waves (including nonlocalization, wavelength, frequency)
Wavefunction (?)	mathematical description of an atomic orbital that describes the shape of the orbital; it can be used to calculate the probability of finding the electron at any given location in the orbital, as well as dynamical variables such as the energy and the angular momentum
Wavelength (?)	distance between two consecutive peaks or troughs in a wave
Weak electrolyte	substance that ionizes only partially when dissolved in water
Weak-field ligand	ligand that causes small crystal field splittings
Weight	force that gravity exerts on an object
Work (w)	energy transfer due to changes in external, macroscopic variables such as pressure and volume; or causing matter to move against an opposing force
X-ray crystallography	experimental technique for determining distances between atoms in a crystal by measuring the angles at which X-rays are diffracted when passing through the crystal