Chemistry Definitions
Back titration 1. A
titration to return to the end point which was passed. 2. Titration in which the analyte
concentration is determined by reacting it with a known quantity of excess
reagent.
Balanced equation Chemical equation in which the number and type of atoms
and the electric charge is the same on both the reactant and product sides of
the equation.
Balmer series The part of the hydrogen
emission spectrum for electron transitions n=2 and n>2, There are four lines
in the visible spectrum.
Barometer Instrument used to measure
atmospheric pressure.
Base 1, Any
chemical species, ionic or molecular, capable of accepting or receiving a
proton (hydrogen ion) from another substance; the other substance acts as an acid
in giving of the proton. Also known as Brønsted base. 2, chemical species that either
accepts protons or else donates electrons or hydroxide ions.
Basic solution Aqueous solution
containing more hydroxide ions than hydrogen ions; a solution with pH > 7.
Beer’s law The law which states that the absorption of
light by a solution changes exponentially with the concentration, all else
remaining the same.
Beta-ray spectrometer An instrument used to determine the energy
distribution of beta particles and secondary electrons.
Block copolymer A copolymer in
which the like monomer units occur in relatively long alternate sequences on a
chain. Also known as block polymer.
Boiling
The transition of a substance from the liquid to the gaseous phase,
taking place at a single temperature in pure substances and over a range of temperatures
in mixtures.
Boiling point Abbreviated bp.
1. The temperature at which the transition from the liquid to the gaseous phase
occurs in a pure substance at fixed pressure.
Bond The
strong attractive force that holds together atoms in molecules and crystalline
salts. Also known as chemical bond.
Bond angle The angle
between bonds sharing a common atom. Also known as valence angle.
Bond dissociation energy The change in
enthalpy that occurs with the homolytic cleavage of a chemical bond under
conditions of standard state.
Bond distance The distance
separating the two nuclei of two atoms bonded to each other in a molecule. Also
known as bond length.
Bonded-phase chromatography A type of
high-pressure liquid chromatography which employs a stable, chemically bonded
stationary phase.
Bond energy 1. The average
value of specific bond dissociation energies that have been measured from
different molecules of a given type.
Bond hybridization The linear
combination of two or more simple atomic orbitals.
Bonding electron An electron
whose orbit spans the entire molecule and so assists in holding it together.
Bonding orbital A molecular
orbital formed by a bonding electron whose energy decreases as the nuclei are
brought closer together, resulting in a net attraction and chemical bonding.
Bond length See
bond distance.
Bond strength The strength
with which a chemical bond holds two atoms together; conventionally measured in
terms of the amount of energy, in kilocalories per mole, required to break the
bond.
Born equation An equation for
determining the free energy of solvation of an ion in terms of the Avogadro
number, the ionic valency, the ion’s electronic charge, the dielectric constant
of the electrolytic, and the ionic radius.
Born-Oppenheimer approximation The
approximation, used in the Born-Oppenheimer method, that the electronic wave
functions and energy levels at any instant depend only on the positions of the
nuclei at that instant and not on the motions of the nuclei. Also known as
adiabatic approximation.
Born-Oppenheimer method A method for
calculating the force constants between atoms by assuming that the electron
motion is so fast compared with the nuclear motions that the electrons follow
the motions of the nuclei adiabatically.
Bouguer-Lambert-Beer law The
intensity of a beam of monochromatic radiation in an absorbing medium decreases
exponentially with penetration distance. Also known as Beer-Lambert-Bouguer
law; Lambert-Beer law.
Bouguer-Lambert law The
law that the change in intensity of light transmitted through an absorbing
substance is related exponentially to the thickness of the absorbing medium and
a constant which depends on the sample and the wavelength of the light. Also
known as Lambert’s law.
Boundary line On a phase
diagram, the line along which any two phase areas adjoin in a binary system, or
the line along which any two liquidus surfaces intersect in a ternary system.
Bouvealt-Blanc method A laboratory
method for preparing alcohols by reduction of esters utilizing sodium dissolved
in alcohol.
Boyle's law Ideal gas law that states
the volume of a gas is inversely proportional to its absolute pressure,
assuming constant temperature.
Branched polymer A polymer chain
having branch points that connect three or more chain segments; examples
include graft copolymers, star polymers, comb polymers, and dendritic polymers.
Brønsted acid A chemical
species which can act as a source of protons. Also known as proton acid; protonic
acid.
Brønsted base See
base.
Brønsted-Lowry theory A
theory that all acid-base reactions consist simply of the transfer of a proton
from one base to another. Also known as Brønsted theory.
Brunauer-Emmett-Teller equation An extension of the Langmuir isotherm equation in the study of
sorption; used for surface area determinations by computing the monolayer area.
Abbreviated BET equation.
Bucherer reaction A method of
preparation of polynuclear primary aromatic amines; for example, α-naphthylamine
is obtained by heating β-naphthol in an autoclave with a solution of ammonia
and ammonium sulfite.
Buffer A solution selected or prepared to
minimize changes in hydrogen ion concentration which would otherwise occur as a
result of a chemical reaction. Also known as buffer solution.
Buffer capacity The relative
ability of a buffer solution to resist pH change upon addition of an acid or a
base.
Buffer solution See
buffer.
