Chemistry Definitions
Absolute alcohol 1. Ethyl alcohol
that contains no more than 1% water.
Also known as
anhydrous alcohol. 2. common name for high purity ethanol or ethyl
alcohol.
Absolute boiling point The boiling
point of a substance expressed in the unit of an absolute temperature scale.
Absolute configuration The
three-dimensional arrangement of substituents around a chiral center in a
molecule. Also known as absolute stereochemistry.
Absolute density See
absolute gravity.
Absolute error Expression of the uncertainty or
inaccuracy of a measurement.
Absolute gravity Density
or specific gravity of a fluid reduced to standard conditions; for example,
with gases, to 760 mmHg pressure and 0°C temperature. Also known as
absolute density.
Absolute temperature Temperature measured using
the Kelvin scale.
Absolute uncertainty The uncertainty of a
scientific measurement, given in the same units as the measurement.
Absolute zero The lowest possible state at
which matter can exist, 0 K or -273.15°C.
Absorbance The
common logarithm of the reciprocal of the transmittance of a pure solvent. Also
known as absorbancy; extinction.
Absorbency Penetration of one substance into
another.
Absorption The
taking up of matter in bulk by other matter, as in dissolving of a gas by a
liquid.
Absorption spectrophotometer An instrument
used to measure the relative intensity of absorption spectral lines and bands.
Also known as difference spectrophotometer.
Absorption spectroscopy An instrumental
technique for determining the concentration and structure of a substance by
measuring the intensity of electromagnetic radiation it absorbs at various
wavelengths.
Absorption spectrum A plot of how
much radiation a sample absorbs over a range of wavelengths; the spectrum can
be a plot of either absorbance or transmittance versus wavelength, frequency,
or wavenumber.
Absorptivity The constant a in the Beer’s
law relation A _ abc, where A is the absorbance, b the
path length, and c the concentration of solution. Also known as
absorptive power. Formerly known as absorbency index; absorption constant; extinction
coefficient.
Acetate dye 1. Any
of a group of water-insoluble azo or anthroquinone dyes used for dyeing acetate
fibers. 2. Any of a group of water-insoluble amino azo dyes that are
treated with formaldehyde and bisulfate to make them water-soluble.
Acid 1. Any
of a class of chemical compounds whose aqueous solutions turn blue litmus paper
red, react with and dissolve certain metals to form
salts, and react with bases to form salts. 2. A compound capable of
transferring a hydrogen ion in solution. 3. A substance that ionizes in solution to yield the
positive ion of the solvent. 4. A molecule
or ion that combines with another molecule or ion by forming a covalent bond with two electrons from the other species. 5. An acid is a proton donor. It turns
litmus red. 6. a
chemical species that accepts
electrons or donate protons or hydrogen ions.
Acid acceptor A stabilizer
compound added to plastic and resin polymersto combine with trace amounts of
acids formed by decomposition of the polymers.
Acid-base catalysis The increase in
speed of certain chemical reactions due to the presence of acids and bases.
Acid-base equilibrium The condition
when acidic and basic ions in a solution exactly neutralize each other; that
is, the pH is 7.
Acid-base indicator 1. A substance that reveals, through characteristic color changes, the
degree of acidity or basicity of solutions. 2. A weak acid or weak base that
changes color when the concentration of hydrogen or hydroxide ions changes in
an aqueous solution.
Acid-base pair A concept in
the Bro¨ nsted theory
of acids and bases; the pairconsists of the source of the proton (acid) and the
base generated by the transfer of the proton.
Acid-base titration 1. A titration in which an acid of known concentration is added to a
solution of base of unknown concentration, or the converse. 2. A procedure to find the
concentration of an acid or base by reacting a known concentration with the
unknown until the equivalence point is reached.
Acid dissociation constant - Ka A quantitative measure of
how strong an acid is.
Acid dye Any of a group
of sodium salts of sulfonic and carboxylic acidsused to dye natural and
synthetic fibers, leather, and paper.
Acid electrolyte A compound,
such as sulfuric acid, that dissociates into ions when dissolved, forming an
acidic solution that conducts an electric current.
Acidic 1. Pertaining to an acid or to its
properties. 2. Forming an acid during a chemical process.
Acidic dye An organic
anion that binds to and stains positively charged macromolecules.
Acidic group The radical
COOH, present in organic acids.
Acidic oxide An oxygen
compound of a nonmetal, for example, SO2 or P2O5,
which yields an oxyacid with water.
Acidic titrant An acid
solution of known concentration used to determine the basicity of another
solution by titration.
Acidification Addition
of an acid to a solution until the pH falls below 7.
Acidimeter An apparatus or a standard solution used to
determine the amount of acid in a sample.
Acidimetry The titration of an acid with a standard
solution of base.
Acidity The state of being acid.
Acidity function A quantitative
scale for measuring the acidity of a solvent system; usually established over a
range of compositions.
Acid number See acid
value.
Acid value Also known as acid number. The acidity of a solution expressed in terms
of normality. A number indicating the
amount of nonesterified fatty acid present in a sample of fat or fatty oil as
determined by alkaline titration.
Activated complex 1. An intermediate
state at the maximum energy point on the reaction path that occurs as reactants
are being converted into product in a chemical reaction. 2. An
energetically excited state which is intermediate between reactants and
products in a chemical reaction. Also known as transition state.
Activation Treatment of a substance by heat, radiation,
or activating reagent to produce a more complete or rapid chemical or physical
change.
Activation energy - Ea 1. The minimum
amount of energy needed for a chemical reaction to occur. 2. The
energy, in excess over the ground state, which must be added to an atomic or
molecular system to allow a particular process to take place.
Activation energy Activator 1. A substance that increases the
effectiveness of a rubber vulcanization accelerator; for example, zinc oxide or
litharge. 2. A trace quantity of a substance that imparts luminescence
to crystals; for example, silver or copper in zinc sulfide or cadmium sulfide
pigments.
Active center 1. Any
one of the points on the surface of a catalyst at which the chemical reaction
is initiated or takes place. 2. See active site.
Active site The effective
site at which a given heterogeneous catalytic reaction can take place. Also
known as active center.
Active solid A porous solid possessing adsorptive
properties and used for chromatographic separations.
Activity A thermodynamic function that correlates
changes in the chemical potential with changes in experimentally measurable
quantities, such as concentrations or partial pressures, through relations
formally equivalent to those for ideal systems.
Activity coefficient A
characteristic of a quantity expressing the deviation of a solution from ideal
thermodynamic behavior; often used in connection with electrolytes.
Actual yield The quantity of product
experimentally obtained from a chemical reaction.
Addition agent A substance
added to a plating solution to change characteristics of the deposited
substances.
Addition polymer A polymer
formed by the chain addition of unsaturated monomer molecules, such as olefins,
with one another without the formation of a by-product, as water; examples are
polyethylene, polypropylene, and polystyrene. Also known as addition resin.
Addition polymerization A reaction
initiated by an anion, cation, or radical in which a large number of monomer
units are added rapidly (a chain reaction) until terminated by some mechanism,
forming a high-molecular-weight polymer in a very short time; an example is the
free-radical polymerization of propylene to polypropylene.
Addition reaction A type of
reaction of unsaturated hydrocarbons with hydrogen, halogens, halogen acids,
and other reagents, so that no change in valency is observed and the organic
compound forms a more complex one.
Addition resin See addition
polymer.
Adiabatic calorimeter An instrument
used to study chemical reactions which have a minimum loss of heat.
Adjective dye Any dye that
needs a mordant.
Adsorbate A solid, liquid, or gas which is adsorbed as
molecules, atoms, or ions by such substances as charcoal, silica, metals,
water, and mercury.
Adsorbent A solid or liquid that adsorbs other
substances; for example, charcoal, silica, metals, water, and mercury.
Adsorption 1. The surface retention of solid, liquid, or
gas molecules, atoms, or ions by a solid or liquid, as opposed to absorbtion,
the penetration of substances into the bulk of the solid or liquid. 2. The adhesion of a chemical
species onto a surface
Adsorption
catalysis A catalytic reaction in which the
catalyst is an adsorbent.
Adsorption chromatography Separation of a
chemical mixture (gas or liquid) by passing it over an adsorbent bed which
adsorbs different compounds at different rates.
Adsorption complex An entity
consisting of an adsorbate and that portion of the adsorbent to which it is
bound.
Adsorption indicator An indicator
used in solutions to detect slight excess of a substance or ion; precipitate
becomes colored when the indicator is adsorbed. An example is fluorescein.
Adsorption isobar A graph showing
how adsorption varies with some parameter, such as temperature, while holding
pressure constant.
Adsorption isotherm The
relationship between the gas pressure p and the amount w, in
grams, of a gas or vapor taken up per gram of solid at a constant temperature.
Adsorption potential A change in the
chemical potential that occurs as an ion moves from a gas or solution phase to
the surface of an adsorbent.
Aeration cell An electrolytic
cell whose electromotive force is due to electrodes of the same material
located in different concentrations of dissolved air. Also known as oxygen
cell.
Aliphatic Of or pertaining to any organic compound of
hydrogen and carbon characterized by a straight chain of the carbon atoms;
three subgroups of such compounds are alkanes, alkenes, and alkynes.
Aliphatic acid Any organic
acid derived from aliphatic hydrocarbons.
Aliphatic acid ester Any organic
ester derived from aliphatic acids.
Aliphatic polycyclic hydrocarbon A
hydrocarbon compound in which at least two of the aliphatic structures are
cyclic or closed.
Aliphatic polyene compound Any unsaturated
aliphatic or alicyclic compound with more than four carbons in the chain and
with at least two double bonds; for example, hexadiene.
Aliphatic series A series of
open-chained carbon-hydrogen compounds; the two major classes are the series
with saturated bonds and with the unsaturated.
Alkali Any compound
having highly basic qualities.
Alkali-aggregate reaction The chemical
reaction of an aggregate with the alkali in a cement, resulting in a weakening
of the concrete.
Alkali alcoholate A compound
formed from an alcohol and an alkali metal base; the alkali metal replaces the
hydrogen in the hydroxyl group.
Alkalide A member of a class of crystalline salts with
an alkali metal atom.
Alkali metal Any of the
elements of group I in the periodic table: lithium, sodium, potassium,
rubidium, cesium, and francium.
Alkalimeter 1. An apparatus for measuring the
quantity of alkali in a solid or liquid. 2. An apparatus for measuring
the quantity of carbon dioxide formed in a reaction.
Alkalimetry Quantitative measurement of the concentration
of bases or the quantity of one free base in a solution; techniques include
titration and other analytical methods.
Alkaline 1. Having
properties of an alkali. 2. Having a pH greater than 7. 3. An aqueous solution with a pH
greater than 7.
Alkaline earth An oxide of an
element of group 2 in the periodic table, such as barium, calcium, and
strontium. Also known as alkaline-earth oxide.
Alkaline-earth metals The heaviest
members of group 2 in the periodic table; usually calcium, strontium, magnesium,
and barium.
Alkalinity 1. The property of having excess
hydroxide ions in solution. 2. A quantitative measure of a
solution's ability to neutralize an acid.
Alkaloid One of a group
of nitrogenous bases of plant origin, such as nicotine, cocaine, and morphine.
Alkalometry The measurement
of the quantity of alkaloids present in a substance.
Alloy Substance made by melting together two or more elements,
at least one of which must be a metal.
Alpha decay Spontaneous radioactive
decay which produces an alpha particle or helium nucleus.
Alpha radiation The ionizing radiation
released from radioactive decay emitting an alpha particle.
Amorphous Term describing a solid that does not have crystalline
structure.
Amperometric titration A titration
that involves measuring an electric current or changes in current during the
course of the titration.
Amperometry Chemical
analysis by techniques which involve measuring electric currents.
Ampholytic detergent A detergent
that is cationic in acidic solutions and anionic in basic solutions.
Amphoteric 1. Having both acidic and basic
characteristics. Also known as amphiprotic. 2. Substance capable of acting as
either an acid or a base.
Amphoteric oxide Oxide that can act as either an
acid or a base in a reaction to produce a salt and water.
Analyte 1. The sample being analyzed. 2. The
specific component that is being measured in a chemical analysis.
Analytical chemistry The branch of
chemistry dealing with techniques which yield any type of information about
chemical systems.
Angular momentum quantum number ℓ, the quantum number associated
with the angular momentum of an electron.
Anhydrous - describes a substance that does not contain water or
else is as concentrated as it can get.
Anion An
ion that is negatively charged.
Anion exchange A type of ion
exchange in which the immobilized functional groups on the solid resin are
positive.
Anionic polymerization A type of
polymerization in which Lewis bases, such as alkali metals and metallic alkyls,
act as catalysts.
Anode 1. The positive
terminal of an electrolytic cell. 2. Electron where oxidation occurs;
positive charged anode.
Anode-corrosion efficiency The ratio of
actual weight loss of an anode due to corrosion to the theoretical loss as
calculated by Faraday’s law.
Anode effect A condition
produced by polarization of the anode in the electrolysis of fused salts and
characterized by a sudden increase in voltage and a corresponding decrease in
amperage.
Anode film The portion of solution in immediate
contact with the anode.
Anodic polarization The change in
potential of an anode caused by current flow.
Anolyte The part of the electrolyte at or near the
anode that is changed in composition by the reactions at the anode.
Aqua regia Mixture of hydrochloric and nitric acids, capable of dissolving
gold, platinum, and palladium.
Aqueous solution A solution with
the solvent as water.
Aromatic 1. Pertaining to or characterized by
the presence of at least one benzene ring. 2. Describing those compounds
having physical and chemical properties resembling those of benzene.
Arrhenius acid Species that dissociates
in water to form protons or hydrogen ions.
Arrhenius base Species that increases the
number of hydroxide ions when added to water.
Aryl An organic group derived
from an aromatic hydrocarbon by removal of one hydrogen.
Aryl compound Molecules with
the six-carbon aromatic ring structure
characteristic of benzene or
compounds derived from aromatics.
Aryl diazo compound A diazo
compound bonded to the ring structure
characteristic of benzene or any
other aromatic derivative.
Arylene A radical that is bivalent and formed by
removal of hydrogen from two carbon sites on an aromatic nucleus.
Aryl halide An aromatic
derivative in which a ring hydrogen has been replaced by a halide atom.
Arylide A compound formed from a metal and an aryl
group, for example, PbR4, where R is the aryl group.
Asymmetric carbon atom A carbon atom
with four different atoms or groups of atoms bonded to it. Also known as chiral
carbon atom; stereogenic center.
Asymmetry The geometrical
design of a molecule, atom, or ion that cannot be divided into like portions by
one or more hypothetical planes. Also known as molecular asymmetry.
Atom 1. The individual structure which
constitutes the basic unit of any chemical element. 2. The defining unit of an element,
which cannot be subdivided using chemical means.
Atom cluster An assembly of
between three and a few thousand atoms
or molecules that are weakly bound
together and have properties intermediate between those of the isolated atom or
molecule and the bulk or solid-state material.
Atomic absorption spectroscopy An
instrumental technique for detecting concentrations of atoms to parts per
million by measuring the amount of light absorbed by atoms or ions vaporized in
a flame or an electrical furnace.
Atomic emission spectroscopy A form of
atomic spectroscopy in which one observes the emission of light at discrete
wavelengths by atoms which have been electronically excited by collisions with
other atoms and molecules in a hot gas.
Atomic fluorescence spectroscopy A
form of atomic spectroscopy in which the sample atoms are first excited by
absorbing radiation from an external source containing the element to be
detected, and the intensity of radiation emitted at characteristic wavelengths
during transitions of these atoms back to the ground state is observed.
Atomic heat capacity The heat
capacity of a gram-atomic weight of an element.
Atomic mass - average mass of atoms of
an element.
Atomic mass unit (amu) - 1/12th the mass of an
unbound atom of carbon-12, used to represent atomic and molecular masses.
Atomic number - the number of protons in
the nucleus of an atom of an element.
Atomic percent The number of
atoms of an element in 100 atoms representative of a substance.
Atomic radius Also known as
covalent radius.1. Half the distance between the nuclei of two like
atoms that are covalently bonded. 2. The experimentally determined
radius of an atom in a covalently bonded compound. 3. Value used to describe the size
of an atom, usually half the distance between two atoms just touching each
other.
Atomic solid Solid in which atoms are bonded
to other atoms of the same type.
Atomic spectroscopy The branch of
physics concerned with the production, measurement, and interpretation of
spectra arising from either emission or absorption of electromagnetic radiation
by atoms.
Atomic volume 1. The volume occupied by 1 gram-atom of an element in the solid
state. 2.
Volume occupied by one mole of an element at room temperature.
Atomic weight 1. The relative
mass of an atom based on a scale in which a specific carbon atom (carbon-12) is
assigned a mass value of 12. Abbreviated At. wt. Also known as relative atomic
mass. 2.
Average mass of atoms of an element.
Atomization In flame spectrometry, conversion of a
volatilized sample into free atoms. A
process in which the chemical bonds in a molecule are broken to yield separated
(free) atoms.
Avogadro's Law Relation that states equal
volumes of all gases contain the same number of molecules at the same pressure
and temperature.
Avogadro's number The number of particles in
one mole of a substance; 6.0221 x 1023
Azimuthal quantum number The quantum number
associated with the angular momentum of an electron, determining the shape of
its orbital.
Azo compound A compound
having two organic groups separated by an azo group (-N=N-).
Azo dyes Widely used
commercial dyestuffs derived from amino compounds, with the –N- chromophore
group; can be made as acid, basic, direct, or mordant dyes.
