absolute configuration
The spatial arrangement of the atoms about a chiral center.
absolute zero
The minimum possible temperature: 0 K, -273.15 °C, -459.67 °F.
absorbance
A measure of the quantity of light that does not pass through a sample. Absorbance is the negative lograrithm of the transmittance. Transmittance is the fraction of incident light that passes through a sample. In the visible region of the spectrum, absorbance occurs when a material uses the energy from light to change the energy level of the material’s electrons. Because different materials have different electronic energy states, they absorb light of different wavelengths.
absorption
Permeation of a solid by a gas or liquid, or permeation of a liquid by a gas. Absorption differs from adsorption in that the substance absorbed is found throughout the absorbent.
absorption spectrum
The quantity of light a sample absorbs (its absorbance) plotted as a function of wavelength, frequency, or energy. An absorption spectrum of a substance often can help to identify the substance.
accuracy
The extent to which an experimental value agrees with true value for a quantity.
acid
In Arrhenius theory, a substance that produces hydrogen ions (hydronium ions) in aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) donor. In Lewis theory, a species that accepts a pair of electrons to form a covalent bond.
acid ionization constant
The equilibrium constant for the ionization of a weak acid to form its conjugate base and hydrogen (hydronium) ions. Also called acid dissociation constant.
acid rain
Rain with pH less than 5.6 (the pH of unpolluted rainwater). Acid rain is caused by sulfur and nitrogen oxides formed by combustion of fossil fuels.
acid precipitation
Any form of precipitation from the atmosphere (rain, snow, frost, etc.) that produces water with a pH below 5.6. Usually the acidity comes from sulfur and nitrogen oxides formed by combustion of fossil fuels.
acid-base indicator
A substance that changes color depending on the concentration of hydrogen ions (hydronium ions) in solution. An acid-base indicator is an acid (or a base) whose color is different when protonated from the color when not protonated.
acidic anhydride
A substance (often a non-metal oxide) that reacts with water to form an acid. Also called acid anhydride.
actinide
An element in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103); also called actinoid. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.
actinoid
An element in the periodic table from actinium (atomic number 89) to lawrencium (atomic number 103); also called actinide. Sometimes actinium itself is not included in this series; sometimes lawrencium is not.
activated complex
In the mechanism of a reaction, a species that lies at an energy peak and that can change either into products or into reactants; also called a transition state.
activation energy
The energy barrier over which a reaction must progress in order for reactants to form products; the minimum energy that reactants must have if they are to be converted to products.
active metal
A highly reactive metal, usually an element in the first or second column of the periodic table.
active site
The location where catalysis occurs in an enzyme or other catalyst.
activity series
A sequence of species arranged according to their reactivity; often used to describe metals and the ease with which they can be oxidized.
actual yield
The quantity of a product found to be formed in a chemical reaction (distinguished from theoretical yield).
acyl group
The functional group RC(=O)-, formally derived from a carboxylic acid by the removal of the hydroxyl group.
addition polymer
The kind of polymer that is formed by the combination of monomers without the release of a small molecule at each point where monomers are joined.
addition reaction
A reaction in which two moleular-scale species combine to form a single molecular-scale species (distinguished from a substitution reaction).
adduct
A species formed by the union of two molecular-scale species held together by a coordinate covalent bond.
adhesive force
An intermolecular force between unlike molecules, usually occurring where two phases meet.
adsorption
Formation of a layer of gas, liquid, or solid on the surface of a solid; the adsorbed substance is held by either covalent bonds or by non-covalent (intermolecular) forces. Adsorption differ from absorption in that the adsorbed substance is on the surface only.
alcohol
An organic compound containing the functional group -OH.
aldehyde
An organic compound containing the functional group -CHO.
alicyclic
An aliphatic compound containing one or more rings of carbon atoms.
aliphatic
A hydrocarbon whose molecules contain no aromatic rings; for example, an alkane, alkene, or alkyne.
alkali
Any substance in aqueous solution that is bitter, irritating to the skin, and has a pH value greater than 7.0.
alkali metal
One of the metals appearing in the first column of the periodic table.
alkaline earth
One of the metals appearing in the second column of the periodic table.
alkaloid
A naturally occurring organic base containing nitrogen.
alkane
A hydrocarbon containing only single bonds between carbon atoms.
alkene
A hydrocarbon containing one or more double bonds between carbon atoms. Also called olefin.
alkyl group
A functional group formally derived from an alkane by the removal of a hydrogen atom.
alkyne
A hydrocarbon containing one or more triple bonds between carbon atoms.
allotrope
One of two or more different structural forms for an element that exist in the same physical state at the same temperature and pressure.
alloy
A solid that has metallic properties and is made up of two or more elements.
alpha particle
A species consisting of two protons and two neutrons and formed by radioactive decay or nuclear bombardment; identical in composition to the nucleus of a helium-4 atom.
amalgam
An alloy (metallic solution) containing mercury.
amide
An organic compound formally derived from a carboxylic acid by the replacement of the hydroxyl group by -NH2, -NHR, or -NR2.
amide linkage
A chemical bond linkage formed when a carboxylic acid reacts with an amine, often found in polymers such as nylon and proteins; in proteins also called a peptide bond.
amine
An organic compound formally derived from ammonia by the replacement of one or more hydrogen atoms by alkyl groups. Examples are primary amine: RNH2; secondary amine: R2NH; tertiary amine: R3N.
amino acid
A carboxylic acid containing an amino group (-NH2). In an alpha amino acid, the amino group is attached to the carbon atom adjacent to the carboxyl group.
amino group
The functional group of a nitrogen atom bonded to two hydrogen atoms, -NH2; found in amines and amino acids.
amorphous
A solid in which the constituent atoms, molecules, or ions have no long-range repeating structure.
amphiprotic
A molecule or ion that can both gain a proton and lose a proton; that is, a species that can serve as either an Bronsted-Lowry acid or a Bronsted-Lowry base.
amphoteric
A substance that can behave as either an acid or a base. Examples are aluminum metal, aluminum hydroxide, and zinc hydroxide.
amu
Abbreviation for atomic mass unit, a unit for expressing the relative masses of atoms. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662×10-24 g.
angstrom
A unit of length equal to 100 pm or 10-10 m.
anhydride
A substance that reacts with water to form an acid or a base. A substance from which water has been removed.
anhydrous
Free of water. Often used to describe a solid having no water of crystallization or a solvent from which traces of water have been removed.
anion
A negatively charged ion. An ion that is attracted toward the anode in an electrolytic cell.
anode
The electrode in an electrochemical cell where oxidation occurs. The positively charged electrode in a vacuum tube.
anodizing
The electrolytic deposition of a metal oxide film to serve as a protective or decorative layer; the object to be coated is made the anode in an electrolytic cell and its surface is oxidized.
antibonding molecular orbital
An orbital formed by the overlap of out-of-phase orbitals from two different atoms; higher in energy than the corresponding bonding molecular orbital.
aqueous
Describing a solution in which the solvent is water.
aromatic
Referring to a hydrocarbon containing benzene-like rings and exhibiting characteristic stability and patterns of reactivity.
Arrhenius acid
A substance that increases the concentration of hydrogen (hydronium) ions in aqueous solution.
Arrhenius acid-base theory
The idea that in aqueous solution acids ionize to produce hydrogen ions and bases ionize to produce hydroxide ions.
Arrhenius base
A substance that increases the concentration of hydroxide ions in aqueous solution.
Arrhenius equation
An equation that expresses the logarithmic relationship between the rate constant of a reaction and the reciprocal of the absolute temperature; ln k = exp(Ea/RT).
atactic
Having no regularly repeating structural units; said of a polymer.
atm
Abbreviation for atmosphere, a unit of pressure equal to 101.325 kPa or 760 mmHg.
atmosphere
A unit of pressure equal to 101.325 kPa or 760 mmHg; abbreviated atm. Also, the mixture of gases surrounding the earth.
atom
The smallest particle of an element that can be involved in chemical combination with another element; an atom consists of protons and neutrons in a tiny, very dense nucleus, surrounded by electrons, which occupy most of its volume.
atomic force microscope
A type of microscope in which a tiny diamond-chip probe is held on a cantilever in contact with a sample’s surface; the probe is scanned slowly across the surface and the force between probe and surfaces is measured and kept constant by adjusting the height of the probe tip. Gives a picture of the surface with molecular-scale resolution.
atomic mass
The average mass of the naturally occurring isotopes of an element, taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic weight.
atomic mass unit
A unit for expressing the relative masses of atoms; abbreviated amu. An atom of carbon-12 has a mass of 12 amu. 1 amu corresponds to 1.662×10-24 g.
atomic number
The number of protons in the nucleus of an atom; used to define the position of an element in the periodic table; represented by the letter Z.
atomic orbital
A mathematical function from which electron density around an atom can be calculated. A region in an atom within which there is a high probability that a particular electron will be found.
atomic spectrum
The quantity of light absorbed or emitted from a sample containing atoms measured as a function of wavelength, frequency, or energy. An atomic spectrum can be used to identify an element, even in a distant star.
atomic weight
The average mass of the naturally occurring isotopes of an element, taking into account the different natural abundances of the isotopes. Expressed relative to the value of exactly 12 for carbon-12; also called atomic mass.
aufbau
A scheme for accounting for the electron configurations of elements in which the electron configuration of one element is determined by adding one electron to the electron configuration of the previous element in the periodic table.
autoionization
The ionization of the molecules of a solvent; for example, water autoionizes to form hydrogen (hydronium) and hydroxide ions.
Avogadro’s hypothesis
The idea that equal volumes of two gases at the same temperature and pressure contain equal numbers of molecules.
Avogadro’s constant
The number of atoms, molecules, ions, or other species per mole, defined by the number of carbon atoms in 12 g of carbon-12 and numerically equal to 6.0220 x 1023 mol-1.
Avogadro’s number
The number of units in a mole of substance, defined by the number of carbon atoms in exactly 12 g of carbon-12 and numerically equal to 6.0220 x 1023.
axial
Oriented along an axis; in a trigonal bipyramidal structure, lying above or below the trigonal plane; in chair cyclohexane, bonds perpendicular to the rough plane of the carbon atoms.
azeotrope
A solution of two more substances, usually liquids, that remains unchanged in composition as it boils because the vapor has the same composition as the liquid.
balanced equation
A representation of a chemical reaction that has values of the stoichiometric coefficients of reactants and products such that the number of atoms of each element is the same before and after the reaction.
balancing an equation
Determining those values of the stoichiometric coefficients of reactants and products in a chemical equation that make the number of atoms of each element the same before and after the reaction.
band theory
A description of the electronic structure in metals and semiconductors using molecular orbital theory. In an energy band, there are a great many molecular orbitals and the differences between their energies are very small so that a continuous band of energies is possible.
barometer
A device for measuring the pressure of the atmosphere.
base
In Arrhenius theory, a substance that increases the concentration of hydroxide ions in an aqueous solution. In Bronsted-Lowry theory, a hydrogen-ion (proton) acceptor. In Lewis theory, a species that donates a pair of electrons to form a covalent bond.
base ionization constant
The equilibrium constant for the ionization of a weak base to form its conjugate acid and hydroxide ions. Also called base dissociation constant.
basic anhydride
A species (often a metal oxide) that reacts with water to form a base. Also called base anhydride.
battery
A series of voltaic cells connected together, used to produce electricity. Also, a single voltaic cell for commercial use.
bcc
Abbreviation for body-centered cubic; a crystal lattice structure whose cubic unit cell has one atom in the center and one atom at each corner (only 1/8 of each corner atom is within the unit cell).
becquerel
The SI unit of radioactive disintegration; one disintegration per second; abbreviated Bq.
beta particle
A particle equivalent to an electron formed by radioactive decay or nuclear bombardment.
bidentate
Referring to a ligand for which two separate atoms form coordinate covalent bonds to a central metal ion or atom in a coordination complex.
bimolecular process
In a reaction mechanism, an elementary step in which two atoms, molecules, or ions must collide in order for a reaction to occur.
binary acid
An acid that contains hydrogen and only one other element.
binary compound
A compound containing two elements.
binding energy
The energy released as particles are brought together to form an atomic nucleus; also called nuclear binding energy.
body-centered cubic
A crystal lattice structure whose cubic unit cell has one atom in the center and one atom at each corner (only 1/8 of each corner atom is within the unit cell); abbreviated bcc.
boiling
The process of a liquid becoming vapor in which bubbles of vapor form beneath the surface of the liquid; at the boiling temperature the vapor pressure of the liquid equals the pressure of the gas in contact with the liquid.
boiling point
The temperature at which the vapor pressure of a liquid equals the pressure of the gas in contact with the liquid; usually this is atmospheric pressure.
boiling point elevation
The increase in the boiling point of a liquid as a result of the presence of a solute. Boiling-point elevation is proportional to the concentation of solute particles.
bomb calorimeter
A sturdy, rigid container (bomb) and associated device for measuring the heat energy transferred out of or into a chemical system in which a reaction occurs; the sturdy bomb maintains constant volume.
bond angle
The angle formed by lines drawn between the centers of atomic nuclei for two atoms joined by bonds to a third atom.
bond dissociation energy
The change in energy when a mole of chemical bonds are broken; the molecules whose bonds are broken must be in the gas phase.
bond energy
The change in energy when a mole of chemical bonds of a particular type are broken; the molecules whose bonds are broken must be in the gas phase. Closely related to bond enthalpy.
bond enthalpy
The change in enthalpy when a mole of chemical bonds of a particular type are broken; the molecules whose bonds are broken must be in the gas phase. Closely related to bond energy.
bond length
The distance between the nuclei of two bonded atoms.
bond order
An indication of the bond strength expressed in terms of molecular orbital theory; half the difference between the number of electrons in antibonding molecular orbitals and the number of electrons in bonding molecular orbitals. A single bond has a bond order of one; a double bond, two; and a triple bond three.
bonding molecular orbital
An orbital formed by the overlap of atomic orbitals that are in phase and therefore reinforce each other; lower in energy than an anti-bonding molecular orbital and lower in energy than the average energy of the atomic orbitals from which it is formed.
bonding pair
A pair of electrons between atoms joined by a covalent bond.
Born-Haber cycle
A description of the relationship among the lattice energy, ionization energy, electron affinity, and heats of atomization of ionic compounds; used to calculate any one of these quantities from the others.
Boyle’s law
The statement that the volume of a sample of gas is inversely proportional to the pressure of the gas (at constant temperature and constant amount of gas).
Bq
Abbreviation for becquerel; the SI unit of radioactive disintegration; one disintegration per second.
breeder reactor
A nuclear reactor designed to produce nuclear fuel as it produces energy.
Bronsted-Lowry acid
A molecule or ion that donates a hydrogen ion (proton) to another molecule or ion.
Bronsted-Lowry acid-base theory
The idea that acids can be described as proton donors and bases as proton acceptors.
Bronsted-Lowry base
A molecule or ion that accepts a hydrogen ion (proton) from another ion or molecule.
buffer
A solution to which strong acid or strong base can be added without significant change in pH; a solution containing a weak acid and its conjugate base or a weak base and its conjugate acid.
buffer capacity
The quantity of acid or base that a buffer solution can absorb without significant change in pH.
buffer solution
A solution to which strong acid or strong base can be added without significant change in pH; a solution containing a weak acid and its conjugate base or a weak base and its conjugate acid.
by-product
A product of a chemical reaction other than the intended or desired one(s).
cal
Abbreviation for calorie, a unit of energy equal to 4.184 J.
Cal
Abbreviation for Calorie; a nutritional calorie, equal to 1000 cal = 1 kcal; a unit of energy equal to 4184 J.
calcination
The heating of a solid below its melting point to decompose it, such as the heating of calcium carbonate to drive off carbon dioxide gas and form solid calcium oxide.
calorie
A unit of energy equal to 4.184 J; abbreviated cal.
calorimeter
A device for measuring the heat energy transferred into or out of a chemical system during a reaction.
capillary action
The spontaneous movement of a liquid into thin tubes (capillary tubes); the extent of capillary action is determined by adhesive forces, cohesive forces, and surface tension.
carbohydrate
A compound containing carbon, hydrogen, and oxygen, with twice as many hydrogen atoms as oxygen atoms; examples are sugar and starch.
carbonyl
The functional group consisting of a carbon atom doubly bonded to an oxygen atom; found in aldehydes and ketones.
carboxyl
The functional group consisting of a carbon atom bonded to a hydroxyl group and doubly bonded to an oxygen atom; found in carboxylic acids: -C(=O)OH.
carboxylic acid
An organic compound containing the functional group -C(=O)OH.
catalysis
The increase in rate of a reaction due to the presence of a substance that undergoes no net change during the reaction.
catalyst
A substance that increases the rate of a chemical reaction but that undergoes no net change during the reaction.
cathode
The electrode in an electrochemical cell where reduction occurs; the negatively charged electrode in a vacuum tube.
cathode rays
Electrons emitted from the surface of a cathode in a vacuum tube.
cathodic protection
The attachment of a more active metal to a less active metal to prevent corrosion. The more active metal serves as the anode, making the less active metal a cathode.
cation
A positively charged ion, attracted toward the cathode in an electrolytic cell.
ccp
Abbreviation for cubic closest packed; one of two schemes for closest packing of spheres; described as “abca” to indicate that the atoms of the second and third layers do not lie directly above the atoms of the first layer, but the atoms of the fourth layer are directly above the atoms of the first layer.
cell potential
The electrical potential difference between two electrodes of an electrochemical cell; the larger the cell potential, the greater the extent of reaction when equilibrium is reached.
Celsius
The temperature scale defined by the values 0 °C for the freezing point of water and 100 °C for the boiling point of water; a °C is the same size as a kelvin.
central atom
In a small molecule or ion, the atom to which the other atoms are bonded. The central atom is surrounded by the other atoms.
central metal
The metal ion or atom at the center of a coordination complex to which the ligands are attached.
chain reaction
A reaction mechanism that contains a sequence of steps in which a product of one step reacts in a second step and a product of the second step is a reactant in the first step; such steps can repeat many times before the chain is broken. Chain reactions often involve free radicals.
chalcogen
One of the elements in the same column of the periodic table as oxygen.
Charles’s law
The statement that the volume of a sample of gas is directly proportional to the temperature of the gas (at constant pressure and constant amount of gas).
Chelate
In coordination chemistry, a ligand that can attach to a central metal through two or more coordinate covalent bonds; a complex consisting of at least one such ligand together with a central metal.
chelating agent
In coordination chemistry, a ligand that can attach to a central metal through two or more coordinate covalent bonds; a molecule or ion that can occupy more than one site in the coordination sphere of a metal ion.
chemical change
A process in which one or more substances, the reactant or reactants, change into one or more different substances, the products; chemical change involves rearrangement, combination, or separation of atoms. Also referred to as chemical reaction.
chemical compound
A substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances.
chemical equation
A representation of a chemical reaction in which chemical symbols represent reactants on the left side and products on the right side.
chemical formula
A represention of the elemental composition of a substance; subscripts are used to indicate the relative numbers of atoms of each kind of element present.
chemical property
A characteristic of a material that describes the material’s chemical composition or reactions.
chemical reaction
A process in which one or more substances, the reactant or reactants, change into one or more different substances, the products; chemical change involves rearrangement, combination, or separation of atoms. Also called chemical change.
chemical symbol
A one- or two-letter abbreviation for an individual element.
chiral
Refers to an ion or molecule that cannot be superimposed on its mirror image.
chromatography
The separation of a mixture into its components by taking advantage of each components’ different affinities for a stationary phase and a mobile phase.
Ci
Abbreviation for curie, a unit of radioactive decay; equal to 3.70 x 1010 disintegrations per second.
cis
Describes the relationship between two atoms or groups of atoms, each attached to one of two doubly bonded carbon atoms and located on the same side of the double bond. Also refers to groups located adjacent to each other in an octahedral or square planar coordination complex.
codon
A three-base sequence in a molecule of messenger RNA; a codon contains genetic information that specifies which amino acid will be incorporated into a protein at a specific point.
cohesive force
An intermolecular force between like molecules, important in the phenomenon of surface tension.
colligative property
A characteristic of a solution that depends upon the concentration of atomic-scale particles in the solution, but not on the nature of the particles.
collision frequency
The rate at which chemical species collide; used in theories of chemical kinetics. Also, the frequency with which gaseous molecules collide.
collision theory
In chemical kinetics the idea that for a reaction to occur molecules must collide and the corresponding mathematical description of the number of collisions between molecules in a sample of matter per unit time.
colloid
A situation intermediate between a solution and a suspension in which particles between one nanometer and one micrometer in size are dispersed in a solid, liquid, or gaseous medium; particles of this size are large enough to scatter light but small enough not to settle out of the medium.
colloidal dispersion
A mixture containing particles larger than those found in a solution but small enough to remain suspended for a very long time; a colloid.
combustion
Vigorous combination of a material with oxygen gas, usually resulting in a flame.
combustion analysis
A method for determining the chemical composition of a compound by burning the compound under controlled conditions. Can be used to determine the relative amounts of carbon, hydrogen, and (by difference) oxygen in a compound.
common ion effect
A shift in a chemical equilibrium caused by adding a substance that contains ions that participate in the equilibrium.
complex
A central metal and the ligands surrounding it; also called coordination complex.
complex ion
An ion formed by the combination of a central metal ion and ligands; a complex that is electrically charged.
compound
A substance made up of two or more elements and having those elements present in definite proportions; a compound can be decomposed into two or more different substances.
concentrated
Increased the concentration of a mixture or solution (verb). Having a large concentration (adjective).
concentration
A measure of the ratio of the quantity of a substance to the quantity of solvent, solution, or ore. Also, the process of making something more concentrated.
concentration cell
An voltaic (galvanic) cell in which the anode and cathode compartments contain the same solutions, but at different concentrations.
condensation
The process in which a liquid forms from gas or vapor of the same substance. A chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants.
condensation polymer
A polymer formed by condensation reactions between monomers and the growing polymer chain; in a condensation polymerization a small molecule each time a monomer becomes bonded to the polymer chain.
condensation reaction
A chemical reaction in which two molecules combine to form a very small molecule and a larger molecule than either of the two reactants. An example is formation of an ester from a carboxylic acid and an alcohol.
condensed formula
A notation for representing which atoms are bonded to which others in a chemical compound without showing the bonds between atoms. For example, CH3CH2OH is the condensed formula for ethanol.
conduction band
In the band theory of solids, a band that is partially occupied; electrons in a conduction band are mobile and their movement corresponds with conduction of electricity through the solid.
configuration
The 3-D arrangement of atoms about a chiral center in a molecule.
conformation
In an ion or molecule, one of many spatial arrangements of atoms that differ by rotation about single bonds, but that do not differ in which atoms are attached to each other.
conjugate acid
The acid formed when a base accepts a hydrogen ion (proton).
conjugate base
The base formed when an acid releases a hydrogen ion (proton).
constitutional isomer
One of two or more compounds having the same molecular formula but differing in how the atoms are connected together; for example, butane and 2-methyl propane are constitutional isomers.
continuous spectrum
A spectrum in which there is significant absorbance or emission over a broad range of wavelengths; distinguished from a line spectrum in which absorbance or emission occurs at only a few specific wavelengths.
control rod
A rod made of a neutron-absorbing material that can be moved into or out of a nuclear reactorr to control the rate of nuclear fission.
conversion factor
A relationship between two units of measure that is derived from the proportionality of one quantity to another; for example, the mass of a substances is proportional to its volume and the conversion factor from volume to mass is density.
coordinate covalent bond
A bond between two atoms in which the shared electrons are considered to be contributed by only one of the atoms.
coordination complex
An ion or molecule that consists of ligands bonded to a central metal ion or atom.
coordination compound
A compound that contains one or more coordination complexes.
coordination isomer
One of two or more coordination complexes having the same chemical composition but differing in which ligands are attached to which metal ion(s) or atom(s).
coordination number
The number of atoms to which a particular atom is bonded; in a coordination complex, the number of positions where ligands are attached to the central metal; in a ionic compound, the number of ions of opposite charge surrounding an ion.
coordination sphere
In a coordination complex the region around a central metal where the ligands are attached to the metal.
core electrons
Any electrons in filled subshells within inner shells of an atom.
corrosion
Chemical or electrochemical oxidation of the surface of a metal or alloy; corrosion can cause structural damage, as in the case of rusting.
Coulomb’s Law
The generalization that the force of attraction between two charged particles is proportional to the product of their electric charges divided by the square of the distance between the centers of the particles.
covalent bond
The attractive force between one atom (nucleus and core electrons) and another atom as a result of sharing electrons.
covalent compound
A compound that consists of molecules in which atoms are attached to one another by covalent bonds; a compound where the solid is soft, that has low melting and boiling points, and with low electrical conductivity in solid and liquid states.
covalent radius
An indication of the size of an atom in a covalent compound; often measured as half the internuclear distance between like atoms bonded to each other.
critical mass
The minimum mass of a fissionable nucleus necessary for a sustained chain reaction to occur.
critical point
The temperature and pressure above which no distinction exists between a liquid and its vapor.
critical pressure
The pressure required to convert a gas to a liquid at the critical temperature of a substance.
critical temperature
The highest temperature at which the vapor of a substance can be converted to a liquid.
cryogenics
The study of the behavior of matter at temperatures below -200°C.
crystal
A solid with a regular polyhedral shape; for example, in sodium chloride (table salt) the crystal faces are all at 90° angles. A solid in which the atoms, molecules, or ions are arranged in a regular, repeating lattice structure.
crystal field theory
A theory that explains properties of coordination complexes in terms of electrostatic attractions between the ligands and the central metal and electrostatic effects that result in different energies of metal d orbitals.
crystal lattice
An orderly, repeating arrangement of points in 3-D space in which each p;oint has surroundings identical to every other point. A crystal’s constituent atoms, molecules, and ions are arranged about each lattice point.
cubic closest packed
One of two schemes for closest packing of spheres; described as “abca” to indicate that the atoms of the second and third layers do not lie directly above the atoms of the first layer, but the atoms of the fourth layer are directly above the atoms of the first layer. Abbreviated ccp.
curie
A unit of radioactive decay; equal to 3.70 x 1010 disintegrations per second; abbreviated Ci.
cuvette
A vessel used to hold a liquid sample within a spectrophotometer.
cycloalkane
A hydrocarbon containing no multiple bonds between carbon atoms and containing at least one ring of carbon atoms.
d block
Columns 3 through 12 of the periodic table, containing elements in which the d atomic orbitals are being filled.
Dalton’s law
The statement that the total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases.
decay constant
A rate constant for radioactive decay or other first-order decomposition reaction.
degenerate orbital
One of two or more orbitals having the same energy.
degree of ionization
The extent to which a species in solution ionizes. Often applied to the ionization reactions of acids and bases.
deionized water
Water that has been passed through ion exchange resin to remove impurities that consist of ions.
deliquescent
Able to absorb moisture from the air so readily as to dissolve in the absorbed water to form a concentrated solution.
delocalization
Spreading of electrons over more than two atoms because the electrons occupy a molecular orbital that encompasses more than two atoms.
delocalized molecular orbital
A molecular orbital that encompasses more than two atoms.
denaturation
Chemical or physical factors that disrupt a protein’s secondary and tertiary structure so that the biological activity of the protein is lost.
density
The ratio of the mass of a sample of a material to its volume.
deoxyribonucleic acid
The polymer of nucleotides that constitutes the genetic material of chromosomes; abbreviated DNA.
deposition
The process of forming a solid from a gas.
deuterium
The isotope of hydrogen having one neutron in its nucleus.
dextrorotatory
Describes a substance that rotates the plane of polarized light to the right.
diagonal relationship
In the periodic table, similarities in chemical or physical properties of two elements (or their compounds); the second element is either above and to the left or below and to the right of the first element (on a diagonal in the periodic table).
dialysis
A process in which ions or small molecules in a solution pass through a semipermeable membrane while larger molecules remain behind.
diamagnetic
Describes a substance that is repelled very weakly by a magnetic field; a diamagnetic substance has no unpaired electrons.
diastereomer
One of two or more compounds that have the same molecular formula, have the same atoms joined to each other, but are not identical and are not mirror images of each other.
diatomic
Containing two atoms per molecule.
differential rate equation
An equation that describes the rate of a reaction as a function of the concentrations of reactants (and products), also called rate law.
differentiating solvent
A solvent that is a sufficiently weak base or acid that the acid or base strength of a pair of substances may differentiated in that solvent.
diffusion
The spreading of one substance into another (usually involves gases or liquids).
dilution
The addition of solvent to a solution (or mixture) to decrease the concentration of a solute (or component).
dimensional analysis
A technique in which the cancelling of units is used as a tool to check the correctness of a calculation.
dimer
A molecule formed by the combination of two smaller identical units.
dipole
In an electrically neutral species, separated, equal positive and negative charges that consitute a positive and a negative pole; such a species tends to assume certain orientations more than others in an electric field.
dipole force
The attraction between polar molecules as a result of the partially positively charged portion of one molecule being oriented toward the partially negatively charged portion of another molecule.
dipole moment
The magnitude of the separation of electrical charge in a molecule that makes the molecule polar; the partial positive charge times the partial negative charge divided by the distance by which the charges are separated.
diprotic
Describes an acid that can donate two hydrogen ions (protons) to a base.
disintegration
The event of a nuclear transformation caused by radioactive decay or nuclear bombardment.
dispersion force
Intermolecular forces arising from an instantaneous dipole in one molecule inducing a dipole in another molecule; the second dipole is always oriented in such a way as to attract the first. Also called London force.
disproportionation
A reaction in which a single species (molecule or ion) undergoes both oxidation and reduction.
dissociation
The breaking apart of one species into two or more smaller species; often applied to ions in a crystal lattice, which dissociate when the ionic solid dissolves in water. Dissociation refers to separation of particles that already exist; ionization refers to the formation of ions from neutral species, as in the ionization of a weak acid in aqueous solutoin.
distillation
A technique for separating the components of a liquid mixture or solution by vaporizing a portion of the liquid and condensing its vapor in a separate container.
DNA
Abbreviation for deoxyribonucleic acid; the polymer of nucleotides that constitutes the genetic material of chromosomes.
double bond
Attraction between two atoms (nuclei and core electrons) that results from sharing two pairs of electrons between the atoms; a bond with bond order = 2.
dry ice
Solid carbon dioxide; called dry because of its tendency to sublime (form a gas without first forming a liquid). At standard pressure carbon dioxide sublimes at -78 °C.
ductile
Able to be drawn into a wire; usually applied to metals, of which ductility is a characteristic property.
dynamic equilibrium
A self-establishing state in which the concentrations of reactant and product species remains constant forever; called dynamic because it is reached when opposing processes occur at the same rate; if a change in conditions causes a system not to be at equilibrium, the system will return to equilibrium in a way that partially counteracts the change in conditions.
effective nuclear charge
In a multi-electron atom, the positive charge that a particular electron experiences; depends on the positive charge on the nucleus, the negative charges on all other electrons, and the locations of those electrons relative to the electron in question.
effusion
The escape of a gas through an orifice.
electrochemical cell
A system containing an oxidation-reduction reaction in which oxidation and reduction reactions are physically separated and the transferred electrons pass through an electrical circuit. Voltaic (galvanic) cells produce and electic current; electrolyic cells use electric current to force a reaction to occur.
electrochemical equivalent
The chemical amount of a substance that reacts in an electrochemical cell as one mole of electrons passes through its circuit.
electrode
In an electrochemical cell, a surface on which oxidation or reduction occurs; an electrode conducts electric current into or out of a cell.
electrode potential
In electrochemistry, the electrical potential difference measured for a cell in which the electrode in question is connected to a standard hydrogen electrode. See also standard electrode potential.
electrolysis
A process in which a reaction that would otherwise be non-spontaneous (reactant-favored) is forced to occur by passage of electric current.
electrolyte
A substance that dissolves to produce a solution containing ions, which cause the solution to conduct electricity.
electrolytic cell
An electrochemical cell used to drive a reaction that would otherwise be non-spontaneous (reactant-favored).
electromagnetic radiation
Energy in the form of oscillating, mutually perpendicular electric and magnetic fields. The energy is quantized in units called photons.
electromotive force
The electrical potential difference that can develop across a voltaic (galvanic) cell, used as a measure of the spontaneity of a reaction.
electron
A negatively charged, sub-atomic particle with charge of 1.602 x 10-19 coulombs and mass of9.109 x 1023 kilograms; electrons have both wave and particle properties; electrons occupy most of the volume of an atom but represent only a tiny fraction of an atom’s mass.
electron affinity
The energy change that occurs as an atom or negative ion accepts an electron. The first electron affinity applies to a neutral atom combining with an electron; the second electron affinity applies to a minus-one ion accepting an electron; etc. Sometimes defined as negative when the negative ion is more stable than the neutral atom and sometimes defined as positive for the same circumstance; check the definition in any source of data.
electron capture
A type of radioactive decay in which an electron from an inner shell of an atom is absorbed by the nucleus. In the process a proton is converted into a neutron and the atomic number of the element decreases by one. Also called K capture, because the electron comes from the 1s orbital (K shell).
electron configuration
A representation of the number of electrons of an atom or ion and the orbitals in which they lie. For example, the electron configuration of oxygen is 1s22s22p4.
electron dot structure
A representation of the structure of a covalent molecule that uses dots to indicate for each atom how many electrons ae shared with other atoms (form bonds) and how many are unshared; also called Lewis structure.
electronegativity
The tendency of an atom (nucleus and core electrons) within a molecule to attract electrons in bonds.
electrophile
A species that in its reactions seeks negative charge; Lewis acids are typically electrophiles.
electrostatic attraction
The attraction between opposite electric charges that holds ions together in a crystal lattice and causes electrons to be attracted to atomic nuclei. The attractive force can be calculated using Coulomb’s law.
element
A substance containing only one kind of atom and that therefore cannot be broken down into component substances by chemical means.
elementary process
In chemical kinetics, a reaction that takes place when a single molecule breaks apart or when two molecules collide; the rate law for an elementary process can be determined from the coefficients in the chemical equation; reaction mechanisms must consist only of elementary processes. Also called elemenary reaction.
elementary reaction
In chemical kinetics, a reaction that takes place when a single molecule breaks apart or when two molecules collide; the rate law for an elementary reaction can be determined from the coefficients in the chemical equation; reaction mechanisms must consist only of elementary reactions. Also called elemenary process.
elimination reaction
A reaction in which a larger molecule forms two other molecules; often one of the other molecules is much smaller than the reactant.
empirical formula
The chemical formula of a substance written using the smallest possible integer subscripts that reflect the elemental composition.
enantiomer
Molecular structures that are mirror images and are not superimposable. The molecules are said to be optical isomers and are optically active.
end point
In a titration, the minimum volume of titrant that must be added to cause a sudden change in a physical property (such as color of an indicator, pH, conductivity, or absorbance). The end point should match the equivalence point as closely as possible
endothermic
In chemical thermodynamics, describes a process in which energy is transferred from the surroundings to the system as a result of a temperature difference.
energy
A system’s capacity to do work.
English system
A system of units that includes the inch and the pound.
enthalpy
A thermodynamic state function, symbol H, that equals internal energy plus pressure x volume; the change in enthalpy corresponds to the energy transferred as a result of a temperature difference (heat transfer) when a reaction occurs at constant pressure.
enthalpy of formation
The enthalpy change that occurs during the formation of a compound from its component elements in their most stable forms. See also standard enthalpy of formation.
entropy
A thermodynamic state function, symbol S, that equals the reversible heat energy transfer divided by temperature; higher entropy corresponds to greater dispersal of energy on the molecular scale. See also standard entropy.
enzyme
A highly effective, highly specific biochemical catalyst; usually a protein, but RNA enzymes also exist.
equation of state
An equation giving the relationship among the pressure, volume, temperature, and amount of a substance; most often applied to gases.
equatorial
Oriented about an equator. In a trigonal bipyramidal structure, lying in the trigonal plane. In a cyclic organic structure, approximately in the rough plane defined by the ring of atoms.
equilibrium
A state in which no net change is occurring, that is, in which the concentrations of reactants and products remain constant; chemical equilibrium is characterized by forward and reverse reactions occurring at the same rate.
equilibrium constant
The value of the equilibrium constant expression when equilibrium concentrations are substituted; a value greater than one indicates the position of equilibrium lies toward products (product-favored), and a value less than one indicates the position of equilibrium lies toward reactants (reactant-favored).
equilibrium constant expression
The ratio of the concentrations of products in a balanced chemical equation, each concentration raised to the power of its coefficient, divided by the concentrations of reactants, each raised to the power of its coefficient; at equilibrium this ratio has the value of the equilibrium constant.
equivalence point
The point in a titration at which the amount of one reactant being added stoichiometrically matches the amount of another reactant initially present. The end point should match the equivalence point as closely as possible.
equivalent weight
The molar mass of a substance divided by the chemical combining power of the substance. For example, in the case of an acid the molar mass is divided by the number of available hydrogen ions because a triprotic acid like H3PO4 has three times the chemical combining power of a monoprotic acid like HCl.
ester
An organic compound formally derived from a carboxylic acid and an alcohol; involves the functional group -C(=O)O-R.
ether
An organic compound containing the functional group R-O-R’.
exothermic
Describes a process in which energy is transferred to the surroundings as a result of a temperature difference.
extensive property
A property for which the value depends on the amount of matter under consideration. For example, mass is an extensive property, but density is not.
f block
The lanthanides and actinides, elements in which the f atomic orbitals are being filled.
face-centered cubic
A crystal lattice structure whose cubic unit cell has one atom in the center of each face (only 1/2 of each face atom is within the unit cell) and one atom at each corner (only 1/8 of each corner atom is within the unit cell). Abbreviated fcc.
Fahrenheit
The temperature scale defined by the values 32 °F for the freezing point of water and 212 °F for the boiling point of water.
family
Those elements that comprise a single column of the periodic table. Also called group.
Faraday
The electric charge carried by one mole of electrons, 9.648 670 x 104 C mol-1; abbreviated F.
Faraday constant
The electric charge carried by one mole of electrons, 9.648 670 x 104 C mol-1; abbreviated F.
Faraday’s law
The generalization that the chemical amount of a substance produced or consumed in an electrochemical cell is directly proportional to the quantity of electric charge that passes through the electrical circuit of the cell.
fat
A substance that is an ester of glycerol and three fatty acids; a triglyceride.
fatty acid
A long-chain carboxylic acid that is formed by hydrolysis (saponification) of the triglycerides that constitute fat.
fcc
Abbreviation for face-centered cubic; a crystal lattice structure whose cubic unit cell has one atom in the center of each face (only 1/2 of each face atom is within the unit cell) and one atom at each corner (only 1/8 of each corner atom is within the unit cell).
ferromagnetic
Describes a substance in which magenetism persists after removal of an external magnetic field; able to be a permanent magnet. A ferromagnetic material contains groups of atoms within which the magnetic moments of particles are aligned; in a magnetic field the domains align and they remain aligned after the field is removed.
filtration
The process of separating a solid from a liquid by permitting the liquid to pass through a filter.
first law of thermodynamics
A formal statement that energy can neither be created nor destroyed; as applied to chemical systems, the change in internal energy is equal to the heat energy transfer into the system plus the work energy transfer into the system.
first-order reaction
A reaction for which the rate is directly proportional to the concentration of one reactant.
fission
A nuclear reaction in which large nuclei break apart to form smaller ones.
formal charge
Formal charge is the charge an atom in a molecule would have if all electrons in bonds were shared equally between the two bonded atoms. To calculate formal charge, take the number of valence electrons for an atom and subtract half the number of bonding electrons and the total number of electrons in lone pairs for the same atom in a molecule; the result indicates which atoms are more negative and which more positive, which is useful for predicting where in a molecule reactions will occur.
formation constant
An equilibrium constant for a reaction in which a product of interest is formed; often applied to the formation of a coordination complex from a central metal and ligands.
formula weight
The mass of one mole of a formula unit of a substance; molar mass.
free energy
Gibbs energy: a thermodynamic function corresponding to the tendency for spontaneous change in a system; represented by the symbol G.
freezing
The process of forming a solid from a liquid.
freezing point
The temperature at which a liquid becomes a solid; also called melting point.
freezing point depression
The decrease in the freezing point of a liquid as a result of the presence of a solute.
frequency
The rate at which a periodic event occurs; specifically, the rate at which the waves of electromagnetic radiation pass a point.
fuel cell
An electrochemical cell in which the reactants are supplied on a continuing basis.
functional group
A set of atoms in a molecule that confer on the molecule a characteristic set of physical and chemical properties.
fusion
A nuclear reaction in which small nuclei are united to form larger ones.
galvanic cell
An electrochemical cell in which a spontaneous reaction occurs. Such a cell can be used to generate electricity. Also called voltaic cell.
galvanization
A process in which iron is electrolytically coated with zinc to slow down corrosion.
gamma ray
High energy electromagnetic radiation emitted during radioactive decay.
gas
A state of matter in which a substance occupies the full volume of its container and changes shape to match the shape of the container. In a gas the distance between particles is much greater than the diameters of the particles themselves; hence the distances between particles can change as necessary so that the matter uniformly occupies its container.
gas constant
A proportionality constant between the product of the pressure and volume of a gas and the product of the chemical amount (moles) and temperature of the gas.
Geiger counter
A device used to measure the number of radioactive disintegrations in a sample of matter.
genetic code
The rules that govern how a sequence of three-base codons in a DNA molecule can be translated into a sequence of amino acids in a protein.
geometrical isomer
One of two or more compounds that have the same chemical composition but differ in the spatial arrangements of the atoms.
Gibbs energy
A thermodynamic function corresponding to the tendency for spontaneous change in a system; represented by the symbol G.
glass
A solid material that does not have the long-range order of a crystal lattice; an amorphous solid. A glass melts over a range of temperatures instead of having the definite melting temperature characteristic of crystalline solids.
Graham’s law
The statement that the rate of effusion of a gas is inversely proportional to the square root of the molar mass of the gas.
gram
One thousandth of a kilogram.
grating
In spectroscopy, a component that disperses electromagnetic radiation so that each wavelength is separated from its neighbors; white, visible light is dispersed into a continuous spectrum (rainbow) of colors. A grating is made by ruling fine, parallel, equally spaced grooves on a surface.
group
Those elements that comprise a single column of the periodic table. Also called family.
half-life
In chemical kinetics, the time it takes for one half of the limiting reactant to be consumed. In nuclear chemistry, the time for half of a sample to undergo radioactive decay.
half-reaction
A portion of an oxidation-reduction reaction involving only oxidation or only reduction. An oxidation half-reaction can be combined with a reduction half-reaction to give an overall equation; this is useful in balancing oxidation-reduction reactions. Each half-reaction can be assigned its own standard reduction potential; cell potentials can be calculated by combining these half-reaction potentials.
halogen
One of the elements in the same column of the periodic table as fluorine.
hard water
Water containing high concentrations of cations having charge greater than +1; hardness can be removed by ion exchange.
hcp
Abbreviation for hexagonal closest packed; one of two schemes for closest packing of spheres; described as “aba” to indicate that the atoms of the third layer lie directly above the atoms of the first layer.
heat
Energy transferred as a result of a temperature difference; a form of energy stored in the movement of atomic-sized particles.
heat capacity
The quantity of heat energy transfer needed to raise the temperature of a sample of matter by one unit.
heat of formation
The heat energy transfer into a system during the formation of one mole of a compound from its component elements in their most stable forms.
heat of fusion
The heat energy transfer into a system as a substance melts.
heat of reaction
The heat energy transfer into a system as a reaction occurs.
heat of vaporization
The heat energy transfer into a system as a substance passes from a liquid to a gas.
Henry’s law
The generalization that the partial pressure of a gas in equilibrium with a solution is proportional to the concentration of the dissolved gas in the solution.
Hess’ law
The generalization that if a chemical reaction can be written as the sum of two or more other chemical reactions, then the heat of the overall reaction is the sum of the heats of reaction for the other reactions. A similar rule applies to enthalpy and Gibbs energy.
heterocyclic
Describes an organic compound with at least one ring that includes other atoms as well as carbon atoms. For example, furan contains a five-membered ring with four carbon atoms and one oxygen atom.
heterogeneous mixture
A mixture in which some regions differ in composition or state of matter from other regions.
hexagonal closest packed
One of two schemes for closest packing of spheres; described as “aba” to indicate that the atoms of the third layer lie directly above the atoms of the first layer.
homogeneous mixture
A mixture in which all regions have the same composition and state of matter.
homologous series
A sequence of molecules having the same functional group but differing in the length of the chain of carbon atoms.
Hund’s rule
The statement that electrons singly occupy all degenerate orbitals before pairing in an orbital.
hybrid orbital
An orbital formed by mathematically combining atomic orbitals (all on the same atom) to generate an equivalent set of orbitals more consistent with the observed bonding geometry.
hybridization
The process of mathematically combining atomic orbitals (all on the same atom) to generate an equivalent set of orbitals more consistent with the observed bonding geometry; a description (sp, etc.) of what orbitals were combined.
hydrate
A substance that solidifies with water included in the crystal lattice. An example is copper(II) sulfate pentahydrate, CuSO4˙5H2O where four water molecules are coordinate-covalently bonded to the copper ion and one is hydrogen bonded to the sulfate ion.
hydration energy
The heat energy transferred into the system as a substance dissolves in water.
hydrocarbon
A compound containing only the elements carbon and hydrogen.
hydrogen bond
An attractive force, either intramolecular or intermolecular, between an electronegative atom and a hydrogen atom attached to another electronegative atom.
hydrogenation
Any addition reaction of hydrogen with an organic compound; usually the organic compound has a carbon-carbon double bond or triple bond.
hydrolysis
Any reaction in which water (hydro) is split into two parts (lysis). Examples include the reaction of an anion with water to form the conjugate acid and hydroxide ion and hydrolysis of an ester or amide, in which the H from water bonds to form an alcohol or amine and the OH bonds to a carbonyl carbon to form a carboxylic acid.
hydrolyze
To react with water so that the water molecule is split into two parts.
hydrophilic
Water-loving; attracted to water molecules and polar molecules.
hydrophobic
Water-hating; not attracted to water molecules or polar molecules.
hydroxyl group
The functional group of an oxygen atom bonded to an hydrogen atom, -OH; found in alcohols.
hygroscopic
Describes a substance that absorbs moisture from the air.
ideal gas
A hypothetical gas for which the relationship among the pressure, volume, temperature, and chemical amount (moles) can be described by simple proportionalities summarized by the ideal gas equation, PV = nRT.
ideal gas equation
An equation which gives a simple relationship among the pressure, volume, temperature, and chemical amount (moles) of a well behaved gas: PV, = nRT.
ideal solution
A solution for which the pressure of solvent vapor in equilibrium with the solution is proportional to the mole fraction of solvent in the solution.
igneous
Formed by volcanic action or by great heat.
immiscible
Describes two liquids that cannot be dissolved in one another in all proportions.
indicator
A substance for which a physical property (such as color) changes abruptly when the equivalence point is reached in a titration.
induced dipole
A dipole moment in a species created as a result of a nearby ion or dipole; an induced dipole results in an attraction between the species and the nearby ion or dipole.
inert
Unreactive. Used to describe coordination complexes that exchange ligands slowly or an electrode in an electrochemical cell that serves only as a surface where reaction can occur and is neither consumed nor added to during reaction.
inert complex
A coordination complex that exchanges ligands slowly.
inert gas
One of the elements in the same column of the periodic table as helium; more correctly called noble gas.
initial rate
The rate of a reaction measured close enough to the beginning of a reaction that the reactant concentations have not yet changed appreciably.
inorganic
Pertaining to the chemistry of elements other than carbon and compounds containing at most a small amount of carbon.
insoluble
Unable to dissolve appreciably in a solvent.
instantaneous dipole
A temporary dipole moment in a species created as a result of the influence of a dipole moment in another species, and resulting in an attraction between the two species.
instantaneous rate
The rate of a reaction at a particular time; evaluated from the slope of a plot of concentration vs. time.
integrated rate equation
In chemical kinetics, an equation that describes the concentrations of reactants (and products) as a function of time.
intensive property
A property for which the value does not depend on the quantity of matter under consideration. Density is an example of an intensive property; mass and volume are not intensive properties.
intermediate
In chemical kinetics, a species that is formed in an early step in a reaction mechanism and then consumed in a later step; evidence of existence of an intermediate may be important for the interpretation of a rate law.
intermolecular force
Any attraction between molecules, including dipolar attractions, hydrogen bonds, and London forces.
internal energy
A thermodynamic function corresponding to the energy of a system; represented by the symbol U or E.
internuclear distance
The distance between the nuclei of nearest-neighbor atoms or ions in an element or compound. Bond distances and ionic radii are calculated from this quantity because atoms have no discrete edges.
interstitial
Found in the holes between the atoms or ions of a metal or crystal lattice; often used to describe a non-stoichiometric compound of a metal and a non-metal in which atoms of the non-metal are located between the metal atoms.
iodine number
The number of grams of iodine that react with 100 g of an organic compound, usually a fat; indicative of the degree of unsaturation in the compound.
ion
An atom or covalently bonded set of atoms that carries an overall net charge.
ion exchange
The replacement of ions by other ions, usually on the surface of a resin designed as a reservoir for ions.
ion product
An equilibrium constant expression for a reaction in which the only products are ions and the reactants are such that their concentrations do not appear in the expression; applied to dissolution and autoionization reactions.
ionic bond
The electrostatic attraction that holds together the positive and negative ions of an ionic compound.
ionic compound
A compound containing oppositely charged ions held together by electrostatic attraction. Usually the ions are in a crystal lattice with positive ions surrounded by negative ions and negative ions surrounded by positive ions.
ionic radius
An estimate of the size of an ion in an ionic compound; found from the internuclear distance between ions in a crystal lattice.
ionization
A process in which an atom, molecule, or negative ion loses an electron; a process in which a covalent molecule reacts with a solvent to form positive and negative ions; for example, a weak acid reacting with water to form its conjugate base (an anion) and a hydrogen (hydronium) ion.
ionization energy
The quantity of energy required to remove an electron from a neutral atom or molecule or from a positive ion.
ionization isomer
One of two or more coordination complexes that have the same chemical composition but differ in which species are ligands and which are non-coordinated ions.
ionizing radiation
Electromagnetic radiation of sufficient energy to remove one or more electrons from a molecule or atom to form an ion.
isoelectronic
Having the same number of electrons. Sometimes used to describe species that have the same number of valence electrons.
isomer
One of two or more substances that have the same molecular formula (are composed of elements in the same proportion and have the same molar mass), but differ in some aspect of structure.
isotactic
In polymer chemistry, having regularly repeating, identical structural units. For example, isotactic polypropylene has each methyl group along the polymer chain oriented in the same way.
isotope
One of two or more samples of an element whose atoms differ in the number of neutrons found in the nucleus.
joule
The SI unit of energy (or heat or work); equal to 0.239 calories, or a kg m2/s2
kelvin
A unit of temperature equal to 1/273.16 of the thermodynamic temperature of the triple point of water; the kelvin is the same size as the degree Celsius. The thermodynamic temperature scale (Kelvin scale) has absolute zero as its zero point.
ketone
An organic compound containing a carbonyl group that is bonded to two other carbon atoms, R-C(=O)-R’.
kilogram
The SI unit for mass.
labile
Reactive; often used to describe coordination complexes that exchange ligands rapidly.
laboratory tissue
A laboratory tissue is a paper product which is essentially lint free. Laboratory tissues are typically used to wipe liquid off of the outside of pipets or cuvettes for a spectrophotometer.
lanthanide
An element in the periodic table from lanthanum (atomic number 57) to lutetium (atomic number 71); also called lanthanoid. Sometimes lanthanum itself is not included in this series; sometimes lutetium is not.
lanthanide contraction
The effect of increased nuclear charge and incomplete screening by filled f orbitals that results in a decrease in the size of atoms appearing after the f block in the periodic table.
lanthanoid
An element in the periodic table from lanthanum (atomic number 57) to lutetium (atomic number 71); also called lanthanide. Sometimes lanthanum itself is not included in this series; sometimes lutetium is not.
lattice
The points in space that define the ordered, repeating arrangement of atoms, ions, or molecules in a crystal.
lattice energy
The heat energy tranfer into a system as gaseous ions come together to form an ionic compound. Different textbooks define the sign of this quantity differently.
law of constant composition
The statement that the mass ratio of elements in a given substance is always the same. Also called the law of definite proportions.
law of definite proportions
The statement that the mass ratio of elements in a given substance is always the same. Also called the law of constant composition.
law of multiple proportions
The generalization that when two elements, A and B, form more than a single compound, the mass ratio A : B in one compound is a small whole number multiple of the mass ration A : B in each of the other compounds.
Le Chatelier’s principle
The idea that, if it can, a system at equilibrium will respond to a change in conditions in such a manner as to partially offset that change.
leveling effect
The situation when a basic solvent completely reacts with an acidic solute so the strength of the acid may not be distinguished from other acids with which the solvent reacts completely. The solvent may also be an acid and react with a basic solute. For example, water is a leveling solvent because it reacts completely with hydrochloric acid, nitric acid, and other strong acids for form the acid hydronium ion; consequently the strengths of these acids appear to be the same in water.
levorotatory
Descriptive of a substance that rotates the plane of polarized light to the left.
Lewis acid
A species that accepts a pair of electrons to form a covalent bond.
Lewis acid-base theory
The idea that an acid is a species that accepts a pair of electrons to form a covalent bond and a base is a species that donates a pair of electrons to form a covalent bond.
Lewis base
A species that donates a pair of electrons to form a covalent bond.
Lewis structure
A representation of the structure of a covalent molecule that uses dots to indicate for each atom how many electrons ae shared with other atoms (form bonds) and how many are unshared; also called electron dot structure.
ligand
One of the small molecules or ions attached to a central metal in a coordination complex.
ligand field theory
A theory that explains properties (such as spectra and magnetism) of coordination complexes in terms of molecular orbital theory.
limiting reactant
The reactant (of two or more reactants) present in an amount such that it would be completely consumed if the reaction proceeded to completion. Also called limiting reagent.
limiting reagent
The reactant (of two or more reactants) present in an amount such that it would be completely consumed if the reaction proceeded to completion. Also called limiting reactant.
linkage isomer
One of two or more coordination complexes that have the same chemical composition but that differ in the manner in which ligands are attached to the central metal ion. For example, thiocyanate ion, SCN-, can be bonded to a central metal through the sulfur atom or through the nitrogen atom.
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