Glossary
Glossary and
Definitions
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- Activation energy
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- The minimum energy required for a
collision to be able to result in reaction.
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- Addition
- A reaction in which two or more atoms
are joined to a compound without elimination.
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- Aliphatic
- Non-cyclic organic compounds.
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- Addition polymerisation
- The process in which two or more
molecules of the same compound combine without
elimination to form larger molecules which have the same
empirical formula but a higher molar mass.
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- amorphous
- Irregular; having no
discernible order or shape. In the context of solids, the
molecules are randomly arranged, as in glass, rather than
periodically arranged, as in a crystalline material.
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- anisotropic
- Having properties which vary
depending on the direction of measurement. In liquid
crystals, this is due to the alignment and the shape of
the molecules. See also: isotropic
- aromatic
- 1. A compound containing a
series of benzene (6 Carbon) rings; so named because many
have a distinctive odor.
2.
An organic compound that contains a benzene ring or that
has properties similar to that of benzene; often
detectable by NMR after the existence of a ring current.
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The Aufbau Principle
The construction of The Periodic Table from
electronic configuration, building up by one electron at a time.
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- Avogadro constant
- the number of specified particles in 1
mol of a substance.
L = 6.023 x 1023 mol-1
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- Bond energy
- The average or mean energy for
breaking one mol of a specified bond into gaseous
component atoms at a stated pressure and temperature. [Note:
"bond energyo is a vague term better replaced by
"mean enthalpy change of bond dissociation".]
- Bond polarity the
ionic character of a bond resulting from the
electronegativity difference between atoms.
- Bond length the
distance between a pair of atoms or ions in a compound.
- Brønsted-Lowry acid
a proton donor in the presence of a solvent
(BL base - proton acceptor)
- buffer solution a
solution of a weak acid and the salt of a weak acid (or a
weak base and the salt of a weak base) whose pH only
changes slightly on the addition of acid or base or on
dilution at a constant temperature.
- chain
polymer
- A polymer in which the
repetition of units is linear. The monomers are linked
end to end forming a single straight polymer.
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- Catalyst A substance
which when added to a reaction lowers the (general)
activation energy by providing an alternative reaction
mechanism, and can be recovered unchanged in mass at the
end of the reaction. The catalyst concentration does not
appear in the equilibrium expression.
Chiral Centre An atom in a
molecule that is attached to four different atoms or groups.
Complex ion a metal cation
surrounded by a number of ligands.
Condensation reaction A
chemical change in which two molecules combine to form a larger
molecule with elimination of a small molecule e.g. H2O.
Coupling reaction A
chemical change in which two molecules join together e.g.
formation of an azo compound by the joining together of a
diazonium compound with a phenol.
- chiral
molecule
- A molecule that is not
identical to its mirror image. This gives a chiral
substance its characteristic twisted shape, due to the
fact that its molecules do not line up when combined.
- chromophoric
groups
- Chemical groups which have
distinctive colors.
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- cis (configuration)
- A polymer configuration in
which adjacent bonds are coplanar and on the same side of
the carbon-carbon double bond.
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- colligative properties
- Are those that depend on the
number of species present rather than their kind.
Complex reaction One which
proceeds by a series of elementary steps.
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- copolymer
- Polymers that are derived
from more than one species of monomer. Polymers having
monomeric units differing in constitutional or
configurational features but derived from a single
monomer, are not regarded as copolymers.
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- Cracking The
decomposition of a chemical substance by heat; this
usually refers to mineral oils of high boiling
temperature being broken down into more volatile
components of lower molar mass; unsaturated hydrocarbons
are produced in this process.
- cross-linking
- A process in which bonds are
formed joining adjacent molecules. At low density, these
bonds add to the elasticity of the polymer and at higher
densities, eventually produce rigidity in the polymers.
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- crystallization
- the process of forming
crystals from the melt or solution.
- Delocalization The
extension of a molecular orbital over more than two atom
centres.
- dipole
- Two equal electric or
magnetic charges of opposite sign, separated by a small
distance. In the electric case, the dipole moment is
given by the product of one charge and the distance of
separation. Applies to charge and current distributions
as well. In the electric case, a displacement of charge
distribution produces a dipole moment, as in a molecule.
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dynamic equilibrium A
reversible reaction in which products are being converted into
reactants and vice-versa at a measurable rate.
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- Electron Affinity The
energy change for the process of bringing 1 mol of
electrons from infinity to 1 mol of gaseous atoms to form
1 mol of gaseous uninegative ions at a stated temperature
and pressure.
X(g)+e- = X-(g)
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Electronegativity The
power of an atom in a molecule or in a bond to attract electrons
to itself.
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- Electrophile a
positively charged species which seeks out a region of
high electron density; a Lewis acid or electron-pair
acceptor.
- Elementary reaction
One which proceeds by a single step, for which the order
and molecularity must be identical. Elementary reactions
are unlikely to be termolecular.
Elimination A reaction in
which one molecule decomposes into two, one smaller than the
other.
Empirical formula The
simplest whole number ratio of atoms in a compound.
Enantiomer One of a pair
of optical isomers
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- The Enthalpy Change of
Atomisation
The energy change at constant pressure and a stated
temperature for the process of separating a substance
into its constituent atoms in the ground state in the gas
phase.
Usually for
(i) an element, the formation of 1 mol of gaseous atoms;
(ii) a compound, the formation of gaseous atoms from 1
mol of the compound.
- The Enthalpy Change of
Combustion
The energy change at constant pressure for the process of
burning completely in oxygen (or sometimes fluorine) 1
mol of a substance at a stated temperature.
NOTE: Standard pressure is 105 Pa. There is no
internationally agreed standard of temperature, so this
must always be stated. Commonly it is 273.15K or 298K.
Definitions involving standard must include reference to
the standard of pressure. Other enthalpy change
definitions follow the pattern of the two above.
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Enthalpy change of reaction The energy
change at constant pressure and a stated temperature for
a process in which a specified amount of reactants is
converted into products.
Enthalpy change of solution The energy
change at constant pressure and a stated temperature for
the process of dissolving 1 mol of a compound in a stated
amount of water.
- Enthalpy change of hydration The
energy change at constant pressure and a stated
temperature for the process of bringing 1 mol of gaseous
ions from infinity to form a solution in a specified
volume of water containing 1 mol of hydrated ions.
Enthalpy change of neutralisation
The energy change at constant pressure and a stated
temperature for the process of reacting 1 mol of hydrated
protons with an equivalent amount of base.
NOTE: Standard pressure is 105 Pa. There is no
internationally agreed standard of
temperature, so this must always be stated. Commonly it
is 273.15K or 298K. Definitions
involving "standardo must include reference to the
temperature chosen. -
- equilibrium A
reaction in which both reactants and products are present
and are being dynamically converted into one another
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elastomers - A class of polymers that have
some degree of cross linking and are rubbery. Elastomers
possess memory, that is, they return to their original
shape after a stress is applied.
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- enantiomers
- Molecules which exist in two
nonsuperimposable mirror images, analogous to human hands.
Chiral molecules are perfect physical and chemical models
of each other with the exception of their rotation of
polarized light and those interactions that involve other
chiral systems, such as chiral molecular recognition. A
racemic mixture contains equal amounts of two enantiomers
and thus produces no rotation of the plane of
polarization of light.
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- First Ionization Energy
The energy change for the process of removing to infinity
1 mol of electrons from 1 mol of gaseous atoms to form 1
mol of gaseous unipositive ions at a stated temperature
and pressure.
M(g) = M+(g) + e-
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First Law of Thermodynamics There are
several definitions possible of which one is sometimes
called the Law of Conservation of Energy: energy cannot
be created nor destroyed, merely changed from one form to
another. -
- Fractional distillation
The separation of several liquids which have different
boiling points, by collecting the distillates (fractions)
at different temperatures.
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- free
radical
- A molecule with an unpaired
electron, making it highly reactive.
- free radical polymerization
- The synthesis of a polymer
involving the chain reaction of free radicals with
monomers.
Functional group a set of
bonded atoms with characteristic chemical reactions.
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- glass
transition temperature
- Tg, can be defined as the
temperature at which the specific volume vs temperature
plot has a change in slope. Chain motion and other local
molecular motions are greatly reduced below this
temperature, which is also dependant on the rate of
cooling.
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Geometrical isomerism a
type of stereoisomerism which can arise from restricted rotation
about a C=C double bond; cis-trans isomerism.
Hess' Law The enthalpy
change accompanying a chemical change is independent of the route
by which the chemical change takes place, all measurements being
made at the same temperature and pressure.
Heterogeneous catalyst is
one which is not in the same phase as the reactants
Heterolytic fission the
breaking of a covalent bond in which the pair of electrons in the
bond are transferred to the most electronegative atom, sometimes
forming an ion.
- homogeneous
- An uniform structure or composition
throughout. Having or possessing the same properties.
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Homogeneous catalyst is
one which is in the same phase as reactants: it is consumed by an
early step, and regenerated in a later step of the complex
mechanism; the concentration of the catalyst appears in the rate
equation.
Homologous series A set of
organic compounds with similar chemical properties and a regular
gradation of physical properties and for which a general formula
can be written.
Homolytic fission the
breaking of a covalent bond in which one electron returns to each
atom, often resulting in the formation of a pair of radicals.
Hydrocarbon A compound of
carbon and hydrogen only.
Hydrolysis A chemical reaction with water in
which the
water itself is decomposed ( cf hydration)
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- hybridization
- The combination of atomic
orbitals on the same atom. (Example: sp2, the composite
of the "s" and two "p" orbitals.)
- hydrogen
bond
- The force of attraction between a
hydrogen atom bonded to an electronegative species such
as a N,O or F atom and another electronegative species
such as a N,O or F atom.
- hypertext
- Text that includes pointers
to other text, pictures, movies, etc. "Clicking"
on these links takes the reader to the object that it is
pointed to. Links may point to documents on other
computers connected on the Internet.
Inductive Effect A shift
of electron density in a molecule arising
from polarization of a bond; (+I) is pushing
electrons away.
- initiation
reaction
- The first step in chain polymerization.
Initiation involves the formation of a free radical.
- initiator
- A relatively unstable molecule that
decomposes into a free
radical. Used to "initiate"
a polymer growth reaction.
- Isoelectric pH the
value of the pH at which a substance (often a colloid or
a protein) has zero net electric
charge
- isomer
- A molecule which has an identical
molecular formula to another molecule, but has a
different structure.
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- Isotope One of two or
more atoms or elements with the same proton number but
different mass numbers: each isotope differs in the
number of neutrons.
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Lattice Enthalpy The
energy change at constant pressure and a stated temperature for
the process of bringing 1 mol of gaseous component ions from
infinity to their positions in the lattice.
Example:
M+(g)+X-(g) = MX(s)
Le Chatelier's Principle
"When a closed system,
at dynamic equilibrium, is subjected to a change in an
independent variable (temperature, pressure, or concentration),
the position of equilibrium changes so as to oppose the effect of
the imposed change."
'Tout système en équilibre
chimique stable soumis à l'influence d'une cause extérieure qui
tend à faire varier soit sa température, soit sa condensation (pression,
concentration, nombre de molécules dans l'unité de volume) dans
sa totalité ou seulement dans quelques-unes de ses parties, ne
peut éprouver que des modifications intérieures, qui, si elles
se produisaient seules, amèneraient un changement de température
ou de condensation de signe contraire à celui resultant de la
cause extérieure.'
(the only true and exact version according to Le Chatelier)
Translated: Any system
in stable chemical equilibrium, when subjected to the influence
of an external cause which tends to change either its temperature
or condensation (pressure, concentration, number of molecules in
unit volume), throughout or in only some of its parts, can
undergo only such internal modifications which, if they occurred
on their own, would bring about a change of temperature or of
condensation of a sign contrary to that resulting from the
external cause.
- Ligand a group,
charged or uncharged, or an ion which bonds by a
coordinate bond to a metal cation to form a complex ion:
a electron-pair donor (Lewis base / nucleophile) which
bonds by a coordinate bond to a metal cation to form a
complex ion.
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- macromolecule
- A very large molecule. Many polymers
are composed of hundreds of thousands of atoms, and are
thus characterized as macromolecules.
Markownikoff's Rule The
negative part of the addendum adds to the least hydrogenated
carbon atom. ( cf. questions expecting stability of primary and
secondary carbocations)
Molecular formula A multiple of the empirical
formula giving the number of atoms of each type in a molecule
Monomer A molecule that
joins with others in forming a polymer.
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- melting transition temperature
- The temperature at which the substance
loses its translational and orientational order, changing
from a solid phase to a liquid phase.
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- molar mass
- M, is the mass divided by the amount
of the substance. Molar mass is usually expressed in g/mol
or kg/mol units. The g/mol unit is recommended in polymer
science.
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mole The unit of amount of
substance One mole is that amount of substance which contains as
many specified elementary particles as there are atoms in 0.012
kg of the Carbon-12 isotope.
Molecularity The number of
particles participating in an elementary reaction.
- molecular
weight
- The ratio of the average mass per
formula unit of a substance to 1/12 of the mass of an
atom of nuclide 12C.
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- monochromatic
light
- Light composed of only one specific
wavelength.
- monomer
- The simple chemical unit which, when
many are joined together, form a polymer.
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Nucleophile A species (ion
or molecule) that can donate a pair of electrons; a Lewis base.
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- optical
activity
- The plane of vibration of linearly
polarized light rotates as it propagates through a medium.
This rotation can occur in either a right or left handed
direction. Since linearly polarized light can be regarded
as the sum of right and left hand circularly polarized
components, this optical activity corresponds to
different indices of refraction for the two circular
components(circular birefringence).
Order The power to which
to the concentration of a species in the experimental rate
equation is raised.
Overall order The sum of the powers to which
each concentration is raised in the experimental rate equation.
- p-bond a molecular
orbital consisting of regions of electron density above
and below the line of centres between a pair of bonded
atoms.
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- Periodic Law The
physical and chemical properties of the elements are in
periodic dependence upon their atomic numbers.
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- perturbations
- Disturbances from an equilibrium
condition.
pH
pH = -log10[H3O+]/moldm-3
(you need to supply units, because you can only take a logarithm
of a number)
- plastics
- A large group of polymers that has
properties between elastomers and fibers. As such,
plastics have a wide range of properties such as
flexibility and hardness and can be synthsized to have
almost any combination of desired properties.
- plasticizer
- Material added to a polymer to improve
its processability and/or flexibility. These are low
molecular weight substances which, when mixed with a
polymer, lower its glass transition temperature, Tg.
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- polarizer (linear)
- A device, which in the transmission of
electro-magnetic radiation, confines the vibration of the
electric and magnetic field vectors to one plane.
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- polymers
- 1. A large molecule which consits of
repeating units (the monomers). 2. Long chains of
covalently bonded atoms.
- polymerization
- The act of joining simple molecules(monomers)into
giant ones (polymers) to form plastics, fibers,
elastomers and non-structural resins.
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- propagation
reaction
- The middle step in chain
polymerization where successive monomers are attached to
the growing chain.
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- propagation (in
polymer growth)
- The irreversible repetitive addition
of monomers to the growing chain.
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- Proton A sub-atomic
elementary particle, with unit positive charge and unit
mass, expressed in relative atomic mass units (The actual
mass is approximately 1.66 x 10-24 g).
- racemic mixture
- See enantiomers
- Rate equation an
experimentally-determined expression relating the rate of
reaction to the concentrations of reactants.
Rate constant The constant of proportionality in
the experimental rate equation relating the rate to the
concentration of the species raised to their appropriate orders.
Rate determining step The
slowest elementary reaction in a complex reaction.
- Reforming the
rearrangement of carbon chains in compounds using a
combination of high temperature, high pressure and
catalysts to give more useful molecules containing
branches or rings.
Relative atomic mass The
ratio of the average mass per atom of an element relative to 1/12
the mass of an atom of Carbon-12 (obsolete but in syllabus; use
molar mass).
Relative molecular mass
The sum of the relative atomic masses of the elements in a
compound.
resonance
- A method of stabilizing a bond by
delocalizating the electrons around the molecule.
reversible reaction A
reaction which can be made to proceed either forwards or
backwards under suitable conditions; a reaction in which both
products and reactants are present at equilibrium
s-bond a molecular orbital
generally of low energy whose region of electron density lies
along the line of centres between a pair of bonded atoms.
- Saturated compound An
organic compound containing no carbon-carbon multiple
bonds.
saturated solution a
solution in which no more solute can dissolve without
causing precipitation; a solution in which the ionic product
equals the solubility product.
stability
- A measure of the reactivity of a given
molecule.
standard cell potential is
the difference between the standard electrode potentials of the
right- and left-hand electrodes in a specified cell at a stated
temperature; = VR - VL
The Standard Enthalpy Change
of Formation
The energy change at constant pressure for the formation of 1 mol
of a compound from its constituent elements in their standard
states (stable forms at 105 Pa and a stated
temperature).
standard electrode potential
is the value of the standard emf of a cell in which molecular
hydrogen is oxidised to to solvated protons at the left hand
electrode at a stated temperature.
[Note: standard conditions as above, with concentration of
solvated protons being 1 mol dm-3]
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- stereoisomers
- 1. Isomers that differ only in the way
their atoms are oriented. 2. A compound which differs
from another in the arrangements in space of the atoms or
groups of atoms about a particular atom.
Steric effect Manifests
itself where the kinetics of a reaction are found to be dependent
upon the size or shape of a molecule
- steric
hindrance
- A condition when the rotation of a
given group is restricted due to the size of neighboring
groups.
Structural formula A
representation of the sequence in which the atoms in a molecule
are linked; often referred to as a displayed formula.
Structural isomer One of
two or more substances with the same molecular formulae but
different structural formulae. Chain, positional, functional
group isomerism should be recognised.
Substitution A reaction in
which one atom or group of atoms is exchanged for another.
- surfactants
- Surface active agents. Organic
compounds consisting of two parts: a water-attracting (hydrophilic)
portion and a water-resistant (hydrophobic) portion.
Detergents may contain more than one kind of surfactant.
The hydrophobic ends attach themselves to the soil
particles or to the fabrics being washed while the
hydrophilic ends are attracted to the water. The
surfactant molecules surround the soil particles, break
them up, force them away from the surface of the fabric,
then suspend the soil particles in the wash water.
Surfactants are classsified by their ionic (electrical
charge) properties in water.
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- symmetry
- The invariance of some properties of
the object being investigated with respect to all the
transformations considered.
- termination
reaction
- The final step in chain polymerization
where the growth of a polymer is stopped.
- thermoplastics
- Linear plastics of finite molecular
weight that can be fabricated into complex shapes by
melting and injection molding.
- thermosets
- A type of plastic that must be cured,
forming network-like structures that do not soften at
high temperatures.
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- torsion
- The rotation about a single bond which
joins two atoms.
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Transition element a d-block
element forming one or more stable ions which have incompletely
filled d-orbitals.
Trouton's Rule An empirical observation that a wide range of
liquids give approximately the asame standard molar entropy of
vaporization (about 85 JK-1mol-1)
- unit cell
- van
der Waal's forces
- Forces which act between molecules
that are caused by small random fluctuations in the
polarity of the molecules.
- viscosity
- The internal resistance to flow
existing between two liquid layers when they are moved
relative to each other. This internal resistance is a
result of interaction between liquid molecules in motion.
- vulcanization
- A process by which a network of
crosslinks is introduced into an elastomer to strengthen
it.
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Zwitterion An ion that has
both a negative and a positive charge on the same group of atoms;
a dipolar ion ( esp . amino acids).
