GLOSSARY 455equilibrium constant (Kc) A ratio (defined by the reac-
tion equation) involving the concentrations of reactants
and products in an equilibrium reaction.equivalence point In a titration, the point when exactly
enough solution has been added from a burette to
completely react with the solution in the flask.error The difference between the measured value and the
true value.ester One of a series of organic compounds which contain
the–COOR group, e.g. CH 3 COOC 2 H 5.excited state An energy state other than the ground state.exothermic reaction A reaction in which heat is given
out.explosion A violent increase in gas pressure in a confined
space.extensive property A property of a substance that de-
pends on the amount of substance present, e.g. volume.first-order reaction (decay) A reaction which follows
first-order kinetics.fissile Having the ability to undergo fission by slow
neutrons; uranium-235 is fissile, uranium-238 is not.fluorescence The emission of light from a substance.frequency The number of waves of light passing a fixed
point per second.fusion (1) solidification; (2) in nuclear science, the forma-
tion of heavy nuclei from lighter nuclei (as in the sun).ground state The lowest energy state of the atom,
molecule or an ion.half-life (t (^1) ⁄ 2 ) The time taken for the concentration of a
reactant to fall to half its original value.
hard water Water that contains dissolved magnesium or
calcium salts, and which does not lather well with soap.
halogen A Group 17 element.
Henry’s law This states that ‘the solubility of a gas is pro-
portional to the pressure of the gas above the liquid’.
hydration of ions The attachment of water molecules to a
central ion.
hydrogen bond A hydrogen atom bridging two strongly
electronegative atoms (N, F, Cl or O).
hydrolysis The reaction of a substance with water.
hydrophilic Water-attracting.
hydrophobic Water-repelling.
ideal gas A gas whose pressure, volume, and temperature
may be predicted with perfect accuracy by the ideal gas
equation.
immiscible liquids Liquids which do not dissolve in each
other (i.e. they do not mix).
inert pair A pair of electrons that form part of the outer (or
valence) shell of electrons in an atom, but do not take
part in bond formation.
intensive property A property of a substance that does
not depend on the amount of substance present, e.g.
temperature.
intermolecular forces Forces between molecules.
ion An atom or group of atoms that possess a positive or
negative charge.
ion exchange The exchange of one type of ion in solution
with another.
ionic product constant (Kw) The product of the hydro-
nium and hydroxide ion concentrations for any aqueous
solution; the product varies with temperature.
ionization The formation of an ion
ionization energy (or enthalpy) The standard energy
change when one electron is removed from a gaseous
atom, molecule or ion.
isomers Compounds that have the same molecular for-
mula, but different structures.
isotopes Atoms with the same number of protons but dif-
ferent numbers of neutrons.
isotopic mass The mass of one atom of an isotope in
atomic mass units; symbolized m(isotope).
kelvin (K) The SI unit of temperature. 0 °C is equivalent to
273.15 K.
ketone Compounds that contain the carbonyl group
(–C=O) between organic groups, e.g. CH 3 COCH 3.
lattice enthalpy (H^ —L) The standard enthalpy change
when 1 mol of a crystal lattice is broken into isolated
gaseous particles.
Le Chatelier’s principle States that the concentrations
of reactants and products in an equilibrium mixture
will alter so as to counteract any changes in pressure,
temperature or concentration.
ligand A molecule or anion that attaches itself to the
central metal ion in a complex.
light A wave that travels at 3.00 108 metres per second.
London dispersion forces Weak attractive intermolec-
ular or interatomic forces.
lone pair A pair of electrons in the outer (valence) shell of
an atom not shared with another atom.
mass number (A) The number of protons added to the
number of neutrons.
mass spectrum When a molecule or atom is ionised, a
characteristic group of ions with different masses are
made. A plot of the relative abundance of these ions
against their mass by charge ratio (m/e) is called a mass
spectrum.
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