Unit 1 Module 3 The Periodic Table - Pearson Schools

Glossary
periodicity A regular periodic variation of properties of
elements with atomic number and position in the Periodic
Table.
permanent dipole A small charge difference across a bond
resulting from a difference in electronegativities of the
bonded atoms.
permanant dipole–dipole force An attractive force between
permanent dipoles in neighbouring polar molecules.
pi-bond (p-bond) The reactive part of a double bond
formed above and below the plane of the bonded atoms by
sideways overlap of p-orbitals.
polar covalent bond A bond with a permanent dipole.
polar molecule A molecule with an overall dipole, taking into
account any dipoles across bonds.
polymer A long molecular chain built up from monomer
units.
precipitation reaction The formation of a solid from a
solution during a chemical reaction. Precipitates are often
formed when two aqueous solutions are mixed together.
principal quantum number, n A number representing the
relative overall energy of each orbital, which increases with
distance from the nucleus. The sets of orbitals with the same
n value are referred to as electron shells or energy levels.
propagation The two repeated steps in radical substitution
that build up the products in a chain reaction.
radical A species with an unpaired electron.
radical substitution A type of substitution reaction in which
a radical replaces a different atom or group of atoms.
rate of reaction The change in concentration of a reactant
or a product in a given time.
redox reaction A reaction in which both reduction and
oxidation take place.
reducing agent A reagent that reduces (adds electrons to)
another species.
reduction Gain of electrons or a decrease in oxidation
number.
reflux The continual boiling and condensing of a reaction
mixture to ensure that the reaction takes place without the
contents of the flask boiling dry.
relative atomic mass, A r The weighted mean mass of an
atom of an element compared with one-twelfth of the mass
of an atom of carbon-12.
relative formula mass The weighted mean mass of a
formula unit compared with one-twelfth of the mass of an
atom of carbon-12.
relative isotopic mass The mass of an atom of an isotope
compared with one-twelfth of the mass of an atom of
carbon-12.
relative molecular mass, M r The weighted mean mass of a
molecule compared with one-twelfth of the mass of an
atom of carbon-12.
repeat unit A specific arrangement of atoms that occurs in
the structure over and over again. Repeat units are included
in brackets, outside of which is the symbol n.
salt A chemical compound formed from an acid, when a H +
ion from the acid has been replaced by a metal ion or
another positive ion, such as the ammonium ion, NH 4+ .
saturated hydrocarbon A hydrocarbon with single bonds
only.
shell A group of atomic orbitals with the same principal
quantum number, n. Also known as a main energy level.
simple molecular lattice A three-dimensional structure of
molecules, bonded together by weak intermolecular forces.
skeletal formula A simplified organic formula, with hydrogen
atoms removed from alkyl chains, leaving just a carbon
skeleton and associated functional groups.
species Any type of particle that takes part in a chemical
reaction.
specific heat capacity, c The energy required to raise the
temperature of 1 g of a substance by 1 °C.
spectator ions Ions that are present but take no part in a
chemical reaction.
standard conditions A pressure of 100 kPa (1 atmosphere),
a stated temperature, usually 298 K (25 °C), and a
concentration of 1 mol dm –3 (for reactions with aqueous
solutions).
standard enthalpies see enthalpy.
standard solution A solution of known concentration.
Standard solutions are normally used in titrations to
determine unknown information about another substance.
standard state The physical state of a substance under the
standard conditions of 100 kPa (1 atmosphere) and 298 K
(25 °C).
stereoisomers Compounds with the same structural formula
but with a different arrangement of the atoms in space.
stoichiometry The molar relationship between the relative
quantities of substances taking part in a reaction.
stratosphere The second layer of the Earth’s atmosphere,
containing the ‘ozone layer’, about 10 km to 50 km above
the Earth’s surface.
structural formula A formula showing the minimal detail for
the arrangement of atoms in a molecule.
structural isomers Molecules with the same molecular
formula but with different structural arrangements of atoms.
sub-shell A group of the same type of atomic orbitals (s, p,
d or f) within a shell.
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