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Unformatted text preview: Glossary A
The minimum amount of combined total kinetic energy
a colliding pair of ions, atoms or molecules require for a
chemical reaction to occur. It may be thought of as the
size of the energy barrier that has to be overcome to form
t he transition state.
The region of an enzyme, usually a pocket or groove, that
binds the substrate molecule(s) and catalyses a reaction.
An energy-requiring process that involves the transport
of ions or molecules across a cell membrane, usually in
t he direction of increasing concentration (that is, against
a concentration gradient).
Molecules that have an open-chain molecular structure
rather than a ring-shaped structure.
A group of atoms fitting the general formula, RCO-,
where R is typically a benzene ring or alkyl group.
The introduction of an acyl group into an organic
A reaction in which two (or more) molecules combine
together to form a single molecule. Alkenes undergo
addition reactions which involve atoms and/or groups of
atoms adding to opposite faces of a carbon-carbon double
bond. They are characteristic of unsaturated compounds,
such as the alkenes and carbonyl compounds.
A type of polymerisation which occurs when alkenebased monomers undergo repeated addition reactions to
form a single molecule.
The accumulation, usually temporarily, of gases, liquids,
or solutes on the surface of a solid or liquid through the
formation of weak intermolecular interactions.
Containing or requiring molecular oxygen.
a substance present in sufficient concentration in the air
to produce a harmful effect on humans or other animals,
vegetation or materials Alcohols (monohydric)
A homologous series of organic compounds containing
t he functional group –OH and the general formula
A homologous series of compounds with the general
formula, RCHO, where the –CHO group (the aldehyde
group) consists of a carbonyl group attached to a
hydrogen atom. R is an alkyl or aryl group.
Rapid growth of algae on the surface of freshwaters in
response to a supply of nitrogen and/or phosphorus,
leading to depletion of light and oxygen below the water
Salts of alginic acid, a hydrophilic colloidal carbohydrate
which is extracted from marine kelp.
An alkali is a strong base which is soluble in water.
A lkalis are Group 1 metal hydroxides, aqueous solution
of ammonia, aqueous solution of amines and barium
The group of very reactive metals in Group 1 of the
Periodic Table. They react with water to release hydrogen
gas and form strongly alkaline solutions:
Alkaline earth metals
The group of reactive metals in Group 2 of the Periodic
Table. They all react with water to give suspensions of
t heir hydroxides.
An alkaline solution is an aqueous solution that has an
excess of hydroxide ions.
nitrogen containing organic compound of plant origin
whose structure consists of a tertiary amine group
heterocyclic rings such as cocaine, codeine, caffeine and
A homologous series of compounds with the general
formula, RCHO, where the –CHO group (the aldehyde
or alkanal group) consists of a carbonyl group attached
to a hydrogen atom.
Saturated hydrocarbons which have the general formula
CnH2n+2(if acyclic). 513
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Alkanoic (carboxylic) acids
A homologous series of organic compounds with the
general formula RCOOH. They can be formed by the
oxidation of a primary alcohol or alkanal (aldehyde). Amine
Organic compounds derived by replacing one or more of
t he hydrogen atoms in ammonia by alkyl groups. All are
basic and react with acids to form amine salts. Alkanones (ketones)
A homologous series of compounds with the general
formula RCOR’, having two alkyl groups bonded to a
carbonyl group. α-Amino acid
A group of soluble organic compounds that possess a
carboxylic acid group (-COOH) and a primary amine
group (-NH2) bonded to a common carbon atom. αamino acids are the monomers of proteins. They are also
k nown as 2-amino acids. Alkenes
Unsaturated hydrocarbons a carbon-carbon double
bond and with the general formula CnH2n (if acyclic).
The introduction of an alkyl group into an organic
A group, with the general formula CnH2n+1, obtained by
removing a hydrogen atom from an alkane, and usually
represented by R.
Unsaturated hydrocarbons with a carbon-carbon triple
bond and with the general formula CnH2n-2 (if acyclic).
The ability of an element to exist in different crystalline
forms or allotropes.
A mixture which is made up of two or more metals, or
which contains metals and carbon.
A right-handed helical conformation of a protein chain,
held together by intra-molecular hydrogen bonding. It is
a common protein secondary structure.
Alpha decay is the emission of an alpha particle from the
nucleus of a radioactive atom. Alpha decay results in a
decrease of the atomic number by two and an increase in
t he mass number by four.
An alpha particle (4 He2+) is a helium nucleus or ion
emitted by an atom undergoing alpha decay.
An alloy which contains mercury. They may be solid or
liquid depending on their composition.
A homologous series of organic compounds with the
general formula RCONH2. Amino group
The –NH2 f unctional group found in primary amines
and amino acids.
Amino-terminal residue (N-terminus)
The amino acid residue at one end of a polypeptide chain
t hat contains a free amino group.
A complex ion in which ammonia molecules act as
ligands and are coordinated to a metal ion.
A physical quantity indicating the number of moles of a
substance present in a sample.
Synthetic amines which stimulate the central nervous
system (brain and spinal cord) and make people feel
Molecules containinf non-polar tails and polar heads.
A solvent, for example, water, which undergoes selfionisation and can act as both a proton donor and proton
A chemical species capable of accepting and donating
protons, thus able to behave as both as an acid and a
An oxide of a metal that will react and dissolve in a
solution of an acid and a solution of a strong base (alkali).
They can react as both acidic and basic oxides.
The water-soluble component of starch. It consists of
highly branched chains of glucose molecules.
The water-insoluble component of starch. It consists
of between 100 and 1000 linear chains of glucose
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A group of synthetic hormones that promote the storage
of protein and the growth of tissue, sometimes used by
athletes to increase muscle size and strength.
Lacking or not requiring molecular oxygen.
A sample component whose concentration is being
measured (i.e. analyzes).
The qualitative and quantitative analysis of a sample to
determine its chemical composition and structure.
A substance which reduces or removes the feeling of
A drug used to alleviate the sensation of pain.
A negatively charged ion which migrates to the anode
(positive electrode) during electrolysis.
The anode is where oxidation (the loss of electrons)
occurs during an electrochemical process. In an
electrolytic cell the anode is the positive electrode. In an
electrochemical cell the anode supplies electrons since
oxidation has occurred in that half cell. It is therefore the
negative electrode of the cell. Antifoulant coating
coating to hulls of ships below the water line to stop
plants and marine life forms attaching to the hull
A chemical compound or substance that inhibits
a drug that reduces fever
Natural or synthetic substance that kills viruses directly
or prevents their replication.
Transition and aluminium metal ions in aqueous
solution are bonded to six molecules of water to form
octahedral complex ions. The bonds are co-ordinate
(dative) covalent bonds from the water ligands.
A solution in which the water is the solvent.
A compound containing one (or more) benzene rings in
its structure and typified by its propensity to undergo
A constant that appears in the Arrhenius equation in
front of the exponential term. It is a term which includes
t he frequency of collisions and their orientation in
A process for protecting aluminium with a thin oxide
layer formed in an electrolytic cell containing dilute
sulfuric acid where the aluminium object is the anode.. Arrhenius equation
An equation that relates the rate constants for a reaction
obtained at different absolute temperatures to the
activation energy of the reaction. Anomers (of a sugar)
Two stereoisomers which differ only in the configuration
about the carbonyl carbon atom. Arrhenius plot
A plot of the natural logarithm of the rate constant (yaxis) against 1/(absolute temperature) (x-axis). A straight
line will be obtained with a gradient of - R . The value of
t he activation energy, Ea, will be in J mol-1. Antacids
Substances, basic in nature, used to reduce the pH of the
gastric juice in the stomach with the aim of relieving
A substance or a semi-synthetic substance derived
from a microorganism, usually a bacterium or fungus,
and able in dilute solution to inhibit or kill another
microorganism, usually a bacterium.
A defence protein synthesised by the immune system. a Arrhenius temperature dependence
A rise in temperature results in an increase in the rate
constant, thereby increasing the rate of reaction. For
many reactions (with an activation energy ~50 kJ mol-1)
a rise in temperature of ten degrees Celsius leads to an
approximate doubling of the initial rate. Reactions that
follow this dependence are said to exhibit Arrhenius
The theory of acidity and alkalinity that defines an acid as
a solution containing hydrogen ions as the positive ions
and an alkali as a solution as one containing hydroxide
ions as the only negative ions. 515
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A group derived by removing a hydrogen atom from a
benzene ring, or other aromatic structure.
Asymmetric carbon atom
A common term for a carbon atom that is attached to
four different atoms or groups of atoms.
Molecules with no centres, axes or planes of symmetry.
Asymmetric molecules are chiral and can exist as a pair
of enantiomers or optical isomers.
A polymer chain in which the substituents, or side
chains, are randomly distributed along the chain.
The pressure exerted by the atmosphere on the surface of
t he Earth due to the weight of the atmosphere.
The smallest particle of an element that can take part in
a chemical reaction. All atoms of the same element have
t he same number of protons in the nucleus.
The number of atoms in a molecule.
The weighted average mass (according to relative
abundances) of all the naturally occurring isotopes of
an element compared with an atom of the 6C carbon
isotope which has a mass of exactly 12.
The number of protons in the nucleus of an atom.
Half the distance of the closest approach of atoms in
t he crystal or molecule of a chemical element (for a
The theory that all substances are composed of atoms
(that cannot be created or destroyed).
The process in which an element or compound is
converted into gaseous atoms.
The unit atmosphere is used to measure pressure. 1 atm
= 101,325 Pa. It is, however, not an SI unit.
A principle that the order in which orbitals are filled
with electrons is the order of increasing energy. Autocatalysis
Autocatalysis occurs when the product of a reaction
acts as a catalyst in the reaction and causes its rate to
The direct combination of a substance with molecular
oxygen at ordinary temperature.
Avogadro constant, NA
The Avogadro constant (6.02 × 1023) is the number of
atoms in exactly 12 grams of carbon-12. It has units of
per mol (mol-1).
A mixture of liquids that will distil without changing in
composition. When a mixture that forms a low-boiling
point is distilled, the vapour has the composition of the
The law states that at a specified temperature and pressure,
equal volumes of (ideal) gases contain equal numbers of
moles of particles. There is a directly relationship between
t he volume of gas, V, and the amount of particles, n: V
α n. B
A back titration typically consists of two consecutive
acid-base titrations and is performed when an insoluble
and slowly reacting reagent is treated with an excess of
an acid or base. The excess acid or base is then titrated
w ith base or acid solution of a primary standard.
The backward reaction refers to the conversion of
products into reactants in an equilibrium reaction.
A virus capable of replicating in a bacterial cell.
A single celled organism lacking a nucleus.
infections caused by bacteria include tetanus, tuberculosis
(TB), cholera, typhoid fever, syphilis, gonorrhea.
A summary of a chemical reaction using chemical
formulas. The total number of any of the atoms or ions
involved is the same on the reactant and product sides of
t he equation. 516
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A series of lines in the emission spectrum of visible light
emitted by excited hydrogen atoms. The lines correspond
to the electrons falling down into the second lowest
energy level, emitting visible light.
drugs which depress the central nervous system.
Base (DNA or RNA)
One of the nitrogen-containing compounds that occurs
attached to the sugar component of DNA or RNA.
A substance which neutralises an acid, producing a
salt and water as the only products. Common bases
are aqueous ammonia, amines, carbonate ions and the
oxides and hydroxides of metals. In the Brønsted-Lowry
t heory a base is a proton acceptor; a Lewis base is an
Base dissociation constant
The equilibrium constant for the reaction in which base
reacts with water to produce the conjugate acid and
hydroxide ions. It is a measure of the extent to which
weak bases accept hydrogen ions in solution.
t wo nucleotides in nucleic acid chains that are paired
together by intermolecular hydrogen bonding between
t he bases.
An ionic oxide, usually an oxide of a metal, that reacts
with acids to form salts and water. Some basic oxides
react with water to form alkaline or basic solutions.
Basic oxygen convertor
In the basic oxygen process scrap steel and a small
amount of limestone are dissolved in molten iron. Pure
oxygen is then blown into the molten mixture to remove
Two nucleotides in nucleic acid chains that are paired
together by intermolecular hydrogen bonding between
t he bases.
A process which produces a specified amount of a
product in a single operation.
A group of galvanic or electrochemical cells connected
in series or in parallel. Beer-Lambert law
The concentration of a substance in moles is proportional
to the absorbance of a given wavelength of light by a
solution of the substance (provided the solution is dilute).
A=εcl, where c is the concentration of the substance and
l is the length of the radiation through the substance. T
A process formerly used for making hydrocarbon fuels
from coal. A powdered mixture of coal, heavy oil and a
catalyst was heated with hydrogen at high pressure.
A high speed electron ejected from the nucleus following
t he decay of a neutron into a proton.
heteroatomic four-membered ring structure consisting
of one nitrogen atom and three carbon atoms
An extended, zigzag arrangement of a protein chain;
a common secondary structure held together by
intramolecular hydrogen bonding.
A ligand able to form two coordinate (dative) covalent
bonds with a central metal atom or ion.
An elementary step in a reaction involving the collision
between two reactant species to form one large particle
or two particles.
A structure, such as a cell membrane, consisting of two
A compound that contains only two elements.
Binary liquid mixture
A mixture that consists of two miscible liquids which
mutally dissolve in each other.
Biological oxygen demand (BOD)
This is the amount of oxygen taken up by bacteria
t hat decompose organic waste in water. The BOD is
calculated by keeping a sample of water containing
a k nown amount of oxygen for five days at 20 ºC. The
oxygen content is then measured again after this time. A
high BOD value indicates the presence of a large number
of micro-organisms, which suggests a high level of
pollution. Unpolluted water has a very low BOD value.
Methane gas produced by the action of bacteria on
animal and plant wastes under anaerobic conditions
(absence of oxygen). 517
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The use of microorganisms, such as bacteria or yeasts,
or biological substances, such as enzymes, to perform
specific industrial or manufacturing processes.
A furnace in which iron oxide is reduced to iron by
tradiationally using a very strong blast of air to produce
carbon monoxide from coke, and then using this gas as
t he active reducing agent for the iron.
A substance used to decolourise materials by a process of
oxidation or reduction.
A classical model of atomic structure with energy levels
The change of a liquid into a gas at constant temperature.
This occurs when the vapour pressure of the liquid is
equal to the external pressure exerted on the liquid. It
is characterised by the appearance of bubbles of vapour
t hroughout the liquid.
The temperature at which a liquid is converted to a gas
at the same temperature; a liquid boils when the vapour
pressure of the liquid equals the surrounding pressure.
A device used to measure energy changes (at constant
volume) that occur when substances, for example,
a lcohols or hydrocarbons, are burnt in excess oxygen in
a sealed container.
An angle formed by the location of three atoms or two
covalent bonds in space. They are used to describe the
shapes of molecules.
The bond enthalpy is the amount of energy (in kiloJoules)
required to break one mole of a particular covalent bond
in the gaseous state into gaseous atoms (under standard
t hermodynamic conditions). It is a measure of the
strength of the bond.
The equilibrium distance between the nuclei of two
atoms linked by a covalent bond or bonds. Bond order
A theoretical index of the degree of bonding between
t wo atoms relative to that of a normal single bond, that
is, the bond provided by one localised electron pair.
In the valence-bond theory it is a weighted average of
t he bond numbers between the respective atoms in the
A pair of electrons (with opposite spins) located in the
space between the nuclei of two adjacent atoms.
An energy or enthalpy cycle commonly used in
calculating the lattice energies of ionic solids. It is a series
of reactions (and the accompanying enthalpy changes)
which, when summed, represents the hypothetical onestep reaction in which elements in their standard states
are converted into crystals of the ionic compound (and
t he accompanying enthalpy changes) under standard
t hermodynamic conditions.
The gas law stating that the product of pressure and
volume (for a fixed mass of ideal gas at constant
temperature) is a constant.
A solution of 2,4-dinitrophenylhydrazine in either
hydrochloric or phosphoric acid. It is used to test for the
carbonyl group in aldehydes or ketones and to identify
t he aldehyde or ketone via the formation of a 2,4dinitrophenylhdrazone derivative with a characteristic
An instrument for estimating the concentration of
a lcohol in the blood by measuring the concentration of
ethanol in a sample of the air from the lungs.
A nuclear reactor in which fissionable fuel is produced
while the reactor runs.
A concentrated aqueous solution of sodium chloride. It is
used to make sodium hydroxide and sodium chlorate(I),
Broad spectrum antibiotic
An antibiotic that is effective against a wide range of
strains of bacteria.
A reaction in which a bromine atom or a pair of bromine
atoms is introduced into a molecule of benzene, alkane
or alkene. 518
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An aqueous solution of bromine that contains hydrated
bromine molecules and bromic(I) acid. It is commonly
used to test for the presence of a carbon-carbon
double bond, which turns the yellow/orange solution
A theory of acidity that describes an acid as a proton or
hydrogen ion donor, and a base as a proton or hydrogen
A buffer is an aqueous solution consisting of a weak base
and its conjugate acid that resists a change in pH when
small amounts of either hydroxide ions (from a base) or
hydrogen ions (from an acid) are added. Buffers typically
consist of a weak acid and its corresponding salt (an
acidic buffer) or a weak base and its corresponding salt
(a basic buffer).
The ability of a buffer to absorb hydrogen ions or
hydroxide ions without a significant change in pH. It is
determined by the concentrations of the weak acid and
its conjugate base.
Unwanted products of a chemical synthesis or
manufacturing process. C
A drug that exerts its central nervous system stimulant
action by working inside nerve cells to increase their
rates of cellular metabolism.
A quantitative procedure performed in order to relate
t he known concentration of standard solutions of the
analyte to the detector signal which is generated from
t he analyte in the unknown solutions.
The relationship of instrument response (absorbance)
as a function of concentration. Ideally, this should be
a linear relationship, under conditions that obey Beer’s
Law, where absorbance = (slope × concentration) +
A calorie is notionally the energy required to raise the
temperature of 1 g of water by 1 °C. Calorific value
The amount of heat released by a unit mass of a substance,
for example, a food, (or of a unit volume of gas) being
A piece of insulated apparatus for measuring the energy
released or absorbed during a chemical reaction.
Capacity (of a galvanic cell)
The capacity of a cell or battery is measured by the
number of amp-hours (Ah) of charge it can deliver.
Caramelisation is the oxidation of sugar, a process used
extensively in cooking for the resulting nutty flavour and
brown colour. Caramelisation is a type of non-enzymatic
browning reaction and as the process occurs, volatile
chemicals are released producing the characteristic
caramel flavour. Caramelisation is a complex, poorly
understood process that produces hundreds of
chemicals. The reactions occurring include: inversion,
condensation, dehydration and fragmentation.
A carbocation is an organic ion with a positive charge on
an electron deficient carbon atom. They are intermediates
during nucleophilic substitution via an SN1 mechanism
or electrophilic addition to alkenes.
Carbohydrates are organic compounds that contain
t he elements carbon, hydrogen and oxygen. The ratio
of hydrogen to oxygen atoms is usually 2:1 and their
formulas are of the form Cx(H2O)y.
The combined processes, including photosynthesis,
combustion and respiration (including that in
decomposition), by which carbon as a component
of various compounds alternates between its major
reservoirs the atmosphere, oceans, and living
The functional group, >C=O, which occurs in aldehydes,
ketones, amides and carboxylic acids. However, the
characteristic properties of carbonyl compounds, for
example, condensation reactions, are only exhibited in
a ldehydes and ketones
(See alkanoic acid).
The only amino acid residue at one end of a polypeptide
chain that contains a free carboxyl group. 519
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A substance that causes or induces cancer.
The inert gas used to carry the sample in gas
The solidified iron direct from the blast furnace. It is
brittle, but very hard.
A substance which, when present in relatively small
amounts, increases the rate of a chemical reaction but
which is not consumed during the overall process.
The function of a catalyst is to provide a new reaction
pathway with a lower activation energy.
A reaction process accelerated by the presence of a
substance (a catalyst) which is neither consumed nor
produced during the overall reaction.
Part of the exhaust system of a modern car running
on unleaded petrol. It consists of a platinum/rhodium
catalyst in a honeycomb structure which converts
carbon monoxide, nitrogen monoxide and unburnt
hydrocarbons into carbon dioxide, nitrogen and
Cracking carried out in the presence of a heated catalyst,
for example, aluminium oxide (alumina) or silicon
Methanation is used to remove residual carbon monoxide
and carbon dioxide from synthesis gas. It involves
passing the pressurised gas over a heated nickel catalyst.
The cathode is where reduction (the gain of electrons)
occurs during an electrochemical process. In an
electrolytic cell the anode is the negative electrode. In
an electrochemical cell the cathode consumes electrons
since reduction has occurred in that half cell. It is
t herefore the positive terminal or pole of the cell.
A positively charged ion attracted to the cathode during
The process by which a cation in a liquid phase exchanges
with another cation present as the counter-ion of a
negatively charged solid polymer (cation exchanger). Cation exchange capacity
The cation exchange capacity (CEC) is a value given on a
soil analysis report to indicate its capacity to hold cation
A shorthand form of summarising the electrodes and
electrolytes present in an electrochemical cell. The cell
diagram traces the path of the electrons. The reduced
form of the metal to be oxidised at the anode is written
first, followed by its oxidised form, then the oxidised
form of the metal to be reduced at the cathode, and
finally the reduced form of the metal at the cathode.
The cell potential is the potential difference between
t he two electrodes (in their standard states) of an
Celsius scale (of temperature)
This scale of temperature is based on a one hundred
degree range between the normal melting point of pure
ice (0 °C) and the normal boiling point of pure water
Chain reaction (chemical)
A chain reaction occurs when a reaction intermediate
generated in one step reacts in such a way that this
intermediate is regenerated.
Change of state
The inter-conversion of a substance between the solid,
liquid and gaseous states.
Charge density (of a metal ion)
The ratio of the charge of a metal ion to its radius. The
higher the charge density the greater its polarising power
on neighbouring water molecules and the lower the pH
of the resulting solution.
The gas law stating that the volume of a fixed mass (at
constant pressure) of an ideal gas is directly proportional
to absolute temperature.
A substance formed by the chemical combination of two
or more chemical elements in fixed proportions.
A substance which cannot be decomposed or broken
down into simpler substances by chemical methods; all
t he atoms of an element contain the same number of
The chemical environment refers to the number and
t ypes of atoms a particular atom within a molecule is
bonded to. 520
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The raw materials required for an industrial process.
A large collection of molecules prepared by conventional
chemical synthesis or, more usually, combinatorial
A change in which a new substance or substances are
Chemical shift (δ)
The position of a resonance in the NMR spectrum
relative to a standard such as TMS (tetramethylsilane).
A chemical symbol consists of one or two letters used to
represent each element. The first (or only) letter is always
a capital letter, the second a lower case.
The use of chemical agents in the treatment or control of
disease, particularly cancer, or mental illness.
Chiral (asymmetric) centre
An atom, usually a carbon atom, in a molecule that
is attached to four different atoms and/or functional
A molecule that is non-superimposable on its mirror
A chiral auxiliary is a chiral compound that is covalently
attached to the substrate as a controlling factor in a
diastereo-selective reaction and is subsequently cleaved
from the product.
cisUsed to describe geometric isomers of 1,2-disubstituted
a lkenes with functional groups or atoms which are on
t he same side of the molecule as each other.
Cis-trans isomerism is a form of stereo-isomerism and
describes the orientation of functional groups at the
ends of a bond around which no rotation is possible.
The chlor-alkali industry refers to the industrial
electrolysis of brine which results in the production of
sodium hydroxide and chlorine.
The addition of chlorine to drinking water in order to
k ill harmful bacteria. It also refers to a reaction in which
a hydrogen atom in an organic molecule is replaced with
a chlorine atom. Chlorofluorocarbons (CFC)
Chloroflurocarbons are a group of compounds in which
some or all of the hydrogen atoms of an alkane have been
replaced (substituted) by chlorine and fluorine atoms.
They are involved in ozone depletion.
An important steroid; a key component of cell membranes
and precursor for other steroids
A technique for analysing or separating mixtures of
gases, liquids, or dissolved substances based upon
differential solubility in two phases.
A record obtained from chromatography.
A group of atoms responsible for absorbing
electromagnetic radiation. They usually have delocalised
One of a group of conjugated proteins, consisting of a
combination of pigment (that is, a coloured prosthetic
group) with a protein.
A closed system is one in which matter and energy cannot
be lost or gained from the system. It is a pre-requisite for
t he establishment of an equilibrium.
A brown or black deposit composed largely of carbon. It
is a fossil fuel formed by the action of heat and pressure
on the remains of plants buried under sediments.
Coal gasification is a process for converting coal partially
or completely to combustible gases. After purification,
t hese gases - carbon monoxide, carbon dioxide, hydrogen,
methane, and nitrogen - can be used as fuels.
Coal liquification is a process for converting coal into
liquid fuels. The basic process of liquification is that
pulverised coal is mixed with a liquid to form a slurry
mix which is combined with hydrogen in a reactor. This
is treated with heat, pressure and chemical catalysts to
produce liquids and gases which can be made into a
variety of synthetic fuels.
The coefficients are the numbers that appear to the left of
chemical formulas in a balanced equation.
An organic co-factor required for the action of certain
enzymes; often contains a vitamin as the component. 521
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The inorganic complement of an enzyme reaction,
usually a metal ion.
The material left behind when volatile components in
coal have been removed by heating. It contains a very
high percentage of carbon.
A colligative property is a physical property that depends
on the number of solute species present, but not on their
A colloid is a dispersion of small particles (less than 500
nm in diameter) of one material in another.
Collision theory is a simple model that accounts for the
variation in the rate of reaction with temperature and
concentration. It considers particles to be hard spheres
t hat react with each other when they collide with
sufficient kinetic energy.
A device for measuring the concentration of coloured
substances in solution by passing visible light through
t he solution.
the automated, parallel synthesis of a ibrary of chemical
structures, usually drug leads. This is in contrast to the
traditional approach of synthesising different compounds
one at a time, manually.
Combined gas law
The gas law that combines absolute temperature, pressure
and volume, but not the amount of gas.
A highly exothermic and rapid chemical reaction in
which a substance reacts with oxygen during burning.
Combustion analysis is a method for determining
t he empirical formula of a compound via a series of
weighings before and after complete combustion.
Common ion effect
The common ion effect is an application of Le Chatelier’s
Principle. According to Le Chatelier’s Principle the
equilibrium will respond so as to counteract the effect of
t he added common ion. This means that the equilibria
will shift so that the common ion will be reduced which
means a shift to the left thus reducing the solubility of
t he slightly soluble salt system. Competitive inhibition
A competitive inhibitor generally competes with the
substrate for the enzyme’s active site. The percentage of
competitive inhibition at fixed inhibitor concentration
can be decreased by increasing the substrate
concentration. At high concentrations of the substrate
it is possible to reach Vmax even in the presence of the
inhibitor; however, the value of KM is decreased.
One of two colours so related to each other that when
blended together they produce white light; so-called
because each colour makes up to the other what it lacks
to make it white.
A protein that provides all of the essential amino acids.
Complete consumption of at least one of the reactants in
a chemical reaction. A reaction goes to completion if its
limiting reactant or reagent is consumed.
A chemical species typically consisting of a metal ion,
usually a transition metal ion, surrounded by a fixed
number of ligands which form dative or coordinate
covalent bonds with vacant orbitals in the metal ion.
A concentrated solution contains a relatively high
concentration of solute.
The ratio of the amount (or mass) of a substance dissolved
in a given volume of solution. Concentrations of solution
are typically expressed in g dm-3 or mol dm-3.
An addition reaction immediately followed by an
Overall two or more molecules react or link together
w ith the elimination of a small molecule, usually water.
The change of a vapour into a liquid (at constant
temperature); during this process latent heat is released
to the surroundings.
The spatial arrangement of atoms or functional groups
w ithin a molecule.
The chemical species formed when a proton or hydrogen
ion is accepted by a base. 522
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Conjugate acid-base pair
Two chemical species related to each other by the loss or
gain of a single proton or hydrogen ion. Corrosion
The process by which a metal undergoes oxidation by air
and water. Conjugate base
The chemical species formed when an acid loses a proton
or hydrogen ion. Coulomb
The SI unit of electrical charge. One coulomb of charge
is passed around a circuit when a current of one Ampere
is allowed to flow for one second. Conjugated molecules
Conjugated molecules have double or triple bonds that
are separated by one single bond. There is delocalisation
of electrons in the π orbitals between the carbon atoms
linked by the single bond.
An industrial process for the manufacture of sulfuric
acid. Sulfur dioxide and air are passed over a heated
vanadium(V) oxide catalyst to produce sulfur trioxide
which is then dissolved in sulfuric acid to form disulfuric
acid which is diluted to produce sulfuric acid.
An emission spectrum that exhibits all the wavelengths
or frequencies of visible light.
Rods of materials such as cadmium or boron steel that
act as neutron absorbers and are used in nuclear reactors
to control neutron flows and therefore rates of fission.
Convergence occurs as the lines in an emission spectrum
become progressively closer to each other (at higher
frequency or smaller wavelength) and finally merge.
A plot of temperature against time for a substance where
heat energy is being lost to the surroundings.
Coordinate (dative) bond
A dative covalent bond is formed when one of the atoms
supplies both electrons of the shared pair.
The number of ligands surrounding a central metal ion,
or the number of nearest neighbours an atom, molecule
or ion has in a crystal structure.
A polymer formed from two or more different
An inner electron in an atom; an electron not in the
outer or valence shell. Covalent bonding
A chemical bond formed by the sharing of one or more
pairs of electrons (with paired spins) between two
atoms. Covalent bonds are typically formed between
t wo or more non-metals in molecules and giant covalent
structures. The strength of the bond stems from the
electron density located between the two nuclei.
The covalent radius is half of the inter-nuclear distance
between two covalently bonded atoms. If the two atoms
in the covalent bond are identical, then the covalent
radius is equivalent to half the covalent bond length.
The process of breaking down long chain alkanes into
smaller alkanes and alkenes using heat, usually in the
presence of a catalyst.
The temperature and pressure at which the liquid
and gaseous phases of a pure stable substance are in
equilibrium. A liquid does not exist above the critical
temperature, and heating a liquid in a container to a
temperature above its critical point will result in the
disappearance of the physical surface between the two
The existence of covalent bonds between adjacent chains
in a polymer, thus strengthening the material.
Crude oil or petroleum
A mixture of hydrocarbons formed originally from
marine animals, found beneath the ground trapped
between layers of sedimentary rock. It is obtained by
An arrow used to show the notional movement of a pair
of electrons in a reaction mechanism. The tail of the
arrow shows where the electrons come from and the
head where they go to.
The rate of flow of electric charge or electrons through
a conductor. It is measured in coulombs per second or
071211 Chem Glossary FINAL.indd 523 11/12/2007 3:01:57 PM Glossary
Molecules having atoms arranged in a ring or closedchain structure.
The formation of a cyclic compound from a straight
An alkane containing a ring.
A molecule resulting from the enzyme-controlled
oxidation reaction between the sulfhydryl ( –SH) groups
of two adjacent cysteine molecules. Dehydration
The removal of water or elements of water (that is,
hydrogen and oxygen in a 2:1 ratio) to form a new
The property shown by some salts of absorbing sufficient
water from the atmosphere to form a solution.
Delocalisation (of electrons)
Molecules or ions that have p orbitals extending over
t hree or more atoms. Metallic bonding involves the
delocalisation of valence electrons between all the ions
w ithin a crystal. D Denaturation
Partial or complete unfolding of a protein chain (or
nucleic acid). The process is usually reversible and is
brought about by heat and a variety of chemicals. Dalton’s law of partial pressures
The total pressure a mixture of ideal gases exerts is the
sum of the partial pressures of all the component gases. Density
Density is defined as mass per unit volume.
Density = mass . Daniell cell
A voltaic or galvanic cell consisting of a copper cathode
immersed in 1 mol dm-3 copper(II) sulfate solution and
a zinc anode immersed in 1 mol dm-3 zinc sulfate. They
are connected via as salt bridge and an external circuit.
It has a standard potential of 1.10 V and is named after JF
Daniell, who first constructed the first cell of this type. Deoxyribonucleic acid
A large nucleotide polymer having a double helical
structure with complementary bases on the two strands.
Its major functions are protein synthesis and the storage
and transport of genetic information. Dative covalent bond
A dative covalent bond is formed when one of the atoms
supplies both electrons of the shared pair.
A group of transition metals located between groups
2 and 3/13 of the Periodic table. The majority of the dblock metals have two s electrons and d-electrons in the
An electronic transition between two d-orbitals. Such
transitions are responsible for the colours of many
transition metal ions.
In Organic chemistry, it is a substituent that when
present in a benzene ring makes the resulting molecule
undergo electrophilic substitution at a slower rate than
benzene itself. volume Depressant
A drug that reduces excitability and calms a person
by producing functional slowing of the brain or spinal
The loss of a proton from a chemical species.
The removal of dissolved salts from an aqueous
A drug with properties and effects similar to a known
hallucinogen, steroid or narcotic but having a slightly
a ltered chemical structure, created in order to evade
restrictions against illegal substances.
The minimum amount of an analyte that can be detected
reliably. Degenerate orbitals
A group of orbitals with the same energy. Detergent
Water-soluble mixtures that can emulsify grease and via
t his action remove dirt. Dehydrating agent
A substance that removes water or the elements of water
from a compound. Deuterium
The isotope of hydrogen having a single neutron in the
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An industrial electrolytic cell in which a porous
diaphragm is used to separate the electrodes thereby
a llowing electrolysis of sodium chloride solution,
without allowing the products to react. Diprotic
An acid which contains two replaceable hydrogen atoms
per molecule. (Also known as dibasic). Diatomic molecule
A molecule containing two atoms of the same element
covalently bonded together. Directing effect
In Aromatic Chemistry, this is the ability of substituent
f unctional groups to direct further substitution to certain
positions on the benzene ring during the electrophilic
substitution of benzene derivatives. Dietary fibre
Mainly plant material that is found in fruit, grains and
vegetables that humans cannot digest Disaccharide
A carbohydrate consisting of two covalently joined
monosaccharide units. Diffusion
The spontaneous movement of gas or liquid particles
from a region where they are at high concentration to a
region where they are at low concentration. Discharge
the conversion of ions to atoms or molecules during
A dilute solution contains a relatively low concentration
The process of adding more solvent, usually water, to a
solution to lower the concentration.
A molecule formed by the bonding of two identical
monomers. The bonds will be relatively strong hydrogen
bonds or covalent bonds.
The linking together of two molecules.
An electronic device that allows electricity to flow in
only one direction.
Toxic chemicals formed during the high temperature
combustion of chloro-organic matter. They persist in
t he environment and contain chlorine atoms bonded to
An ion whose positive and negative charges are separated
from each other
A pair of separated opposite electrical charges located on
a pair of atoms within a molecule.
The weak intermolecular forces that exist between nonpolar molecules when they are arranged so that the
positive and negative ends can interact. Displacement reaction
A redox reaction in which a more reactive element
displaces a less reactive element from a solution of its
ions or salt, often in aqueous solution.
Displacement Reactions (halogens)
A redox reaction in which a more reactive halogen
displaces a less reactive halogen in the form of its halide
The simultaneous oxidation and reduction of a single
chemical element to produce two products.
The splitting of a molecule into two or more smaller
fragments, which could be atoms, molecules, ions of
Dissociation (of an acid)
The breakdown of an acid molecule into ions in the
presence of water.
The process of boiling a liquid and condensing the
A covalent bond (-S-S-) formed (in the presence of an
enzyme) between two protein adjacent chains by the
reaction between sulfhydryl groups (-SH) of two cysteine
A substance that leads to an increase in the discharge of
071211 Chem Glossary FINAL.indd 525 11/12/2007 3:01:58 PM Glossary
The distinctive pattern of fragments of DNA obtained
by restriction enzyme digestion and electrophoretic
separation of minisatellite DNA from individual
The incorporation of impurities within the crystal lattice
of silicon so as to increase its conductivity.
There are five d orbitals (each of a different shape) in
every shell beginning with the third shell.
A splitting caused by the ligands of the d orbitals of the
transition metal ion in a complex ion.
A covalent bond in which two pairs of bonding electrons
are shared by a pair of adjacent atoms. One of the bonds
is a pi bond; the other is a sigma bond.
The coiled structure of double-stranded DNA in which
strands linked by hydrogen bonds form a spiral or helical
configuration, with the two strands oriented in opposite
Double reciprocal plot
(see Lineweaver-Burke plot)
A substance intended for use in the diagnosis, cure,
mitigation, treatment, or prevention of disease. They
affect natural chemical processes occurring within the
A battery in which the electrolyte is in the form of a
The ability of metals to be drawn out under tension and
stretched into wires.
A physical or chemical equilibrium is described as
dynamic because although there is no change in
macroscopic properties the forward and backward
reactions are occurring (at equal rates). E
Effective nuclear charge
The actual nuclear charge exerted on a particular
electron, equal to the actual nuclear charge minus the
effect of electron-electron repulsion.
The process where water of crystallisation is lost by a
hydrated salt stored in an open container.
A measure of the ability of a substance to conduct an
electric current due to the presence of charged particles,
either ions or delocalised valence electrons, which are
free to move.
Electrochemical cells include galvanic and electrolytic
cells. They produce a potential difference (voltage) from
a redox reaction.
A ‘reactivity series’ for metals based on standard
electrode potential data, which is a measure of the
energetic tendency of a metal to form positive ions. The
elements are arranged in order of increasingly negative
electrode potentials, that is, increasing reducing power.
The study of electrolysis, electrochemical cells and the
properties of ionic solutions.
A conductor which dips into the electrolyte of an
electrolytic or voltaic cell and allows the current
(electrons) to flow to and from the electrodes. Electrodes
may be inert, functioning only to transfer electrons, or
may be active and be involved in the cell reactions.
A process in which chemical decomposition of a
substance, known as the electrolyte, is caused by the
passage of an electric current.
An electrolyte is an ionic compound, a salt, alkali or
acid, which will conduct electricity when it is melted
or dissolved in water. An electrolyte will not conduct
electricity when solid.
A wave of oscillating electric and magnetic fields that
can move through space. 526
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The entire range of electromagnetic radiation or waves
including, in order of decreasing frequency, cosmicray photons, gamma rays, x-rays, ultraviolet radiation,
v isible light, infrared radiation, microwaves, and radio
Negatively charged particle present in all atoms and
located in shells, or energy levels, located outside the
Electron affinity (first)
The enthalpy change when one mole of gaseous atoms
accepts a mole of gaseous electrons under standard
t hermodynamic conditions.
The process of forming positive ions from atoms (and
molecules) in a mass spectrometer by bombarding them
with electrons of high kinetic energy. The colliding
electron ejects a valence electron and both electrons
leave the atom.
A protein that can reversibly lose or gain electrons;
involved in the transfer of electrons from glucose to
A short hand method for describing the arrangement of
electrons in the shells or main energy levels of an atom.
Electron deficient compound
A molecule or ion where some atoms do not have filled
outer or valence shells.
A measure of the tendency of an atom in a molecule
to attract a pair of shared electrons towards itself.
The difference in electronegativities of two atoms in a
covalent bond gives an indication of the bond’s polarity.
The movement of electrons from one orbital to another.
A notation system in which atomic orbitals are regarded
as boxes into which electrons are placed.
Electron transfer chain
The movement of electrons from the break down
products of glucose to oxygen via the respiratory
(electron transfer) chain.
Electroplating is the electrolytic process of coating a
metal with a thin layer of another metal by electrolysis. Electrophile
An electrophile is a chemical species that can act as an
electron pair acceptor or Lewis acid.
Electrophilic addition (in alkenes)
An addition reaction initiated by the rate determining
attack of an electrophile on the pi electrons of the
carbon-carbon double bond.
A reaction involving the substitution of an atom or group
of atoms in benzene (or derivative) with an electrophile
as the attacking species.
Movement of charged ions in response to an electrical
field. It is often used to separate mixtures of ions,
proteins, or nucleic acids.
Electrostatic forces of attraction
A usually strong force of attraction between particles
w ith opposite charges.
The removal of very fine particles suspended in a gas by
electrostatic charging and subsequent precipitation onto
a collector in a strong electric field.
Most reactions occur in a series of steps each of which
involves one or two reacting particles (atoms, ions or
molecules). They are reactions in which no reaction
intermediates (other than transition species) have been
A reaction in which atoms or small molecules are
removed from a single molecule, usually to give a double
bond, or between two molecules.
Diagrams that explain how standard free energies of
formation of metal oxides vary with temperature. They
a llow prediction of the conditions required for metal
extraction from oxide ores.
The process of removing an absorbed material (the
adsorbate) from an adsorbent by washing it with a liquid
(the eluent). The solution consisting of the adsorbate
dissolved in the eluent is the eluate.
The study of spectra produced by excited gaseous atoms
A formula for a compound which shows the simplest
ratio of atoms present. 527
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A compound whose molecular structure is not superimposable on its mirror image.
Groups of cells specialised to synthesise hormones and
release them into the blood stream.
A reaction in which heat energy is absorbed from the
surroundings when a reaction occurs. There is a fall in
temperature when the reaction occurs or heat energy has
to be continually supplied to make the reaction occur.
In endothermic reactions, there is more enthalpy or
potential energy in the bonds of the products than there
were in the bonds of the reactants.
The end point is where the indicator changes colour
The allowed energies of electrons in an atom (and
molecules), which correspond to the shells. Electrons fill
t he energy levels, or shells, starting with the one closest
to the nucleus.
The amount of heat energy possessed by a chemical
substance. It is stored in the chemical bonds as potential
energy. When substances react, the difference in the
enthalpy between the reactants and products (at constant
pressure) can be measured.
Enthalpy change of combustion
The enthalpy change that occurs when one mole of a
compound is completely combusted (burned) in excess
oxygen under standard thermodynamic conditions
(with no change in volume).
Enthalpy change of formation
The enthalpy change that occurs when one mole of a
compound is formed under standard thermodynamic
conditions from its elements in their standard states.
Enthalpy change of neutralisation
The enthalpy change that occurs when one mole of acid
undergoes complete neutralisation with a base under
standard thermodynamic conditions.
Enthalpy change of solution
The enthalpy change when one mole of a substance is
dissolved in a solvent to infinite dilution (in practice, to
form a dilute solution) under standard conditions.
Enthalpy level diagram
A diagram that traces the relative changes in the enthalpy
or potential energy of a chemical system during the
course of a reaction. Enthalpy of atomisation
The enthalpy change when a substance is dissociated
into one mole of gaseous atoms under standard
t hermodynamic conditions.
Enthalpy of hydrogenation
The enthalpy change when hydrogen is added across a
Enthalpy of vaporization
The enthalpy change that occurs when one mole of a
pure liquid is vaporised at its boiling point.
A thermodynamic function that measures randomness
or disorderness in a chemical system and can be used to
predict the direction of physical and chemical changes. It
can also be interpreted as corresponding to the number
of ways of arranging particles in a chemical system or a
measure of how energy is distributed among particles. It
is defined as the heat absorbed divided by the absolute
The change in entropy that accompanies a physical or
chemical change is given by the sum of the entropies
of the products minus the sum of the entropies of the
A globular protein that catalyses a specific biochemical
Equilibrium is said to occur for a reversible reaction
when the rate of the forward reaction is equal to the rate
of the back ward reaction and consequently there are no
changes in the concentrations of reactants and products.
It is also where the Gibbs free energy, of the system is
minimised with the system maintained at constant
temperature and pressure.
The value obtained when equilibrium concentrations of
t he chemical species are substituted in the equilibrium
expression. The value indicates the equilibrium
The expression obtained by multiplying the product
concentrations and dividing by the multiplied reactant
concentrations, with each concentration raised to the
power by the coefficient in the balanced equation.
A particular set of equilibrium concentrations of
reactants and products. 528
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The point in an acid-base titration where the acid and
base have been added in stoichiometric amounts, so
t hat neither is present in excess. If a suitable indicator is
chosen it will correspond to the end point.
Essential amino acids
Amino acids that cannot be synthesised by humans and
must be obtained from the diet.
Essential fatty acids
These are two fatty acids (linoleic and linolenic) that
humans cannot make and must be present in the diet in
order for the body to function properly.
Organic compounds formed by the condensation
reaction between alcohols and acids. Esters formed from
carboxylic acids have the general formula RCOOR’. Faraday’s laws of electrolysis
The amount of a chemical product formed is directly
proportional to the quantity of electrons passed. The
amount of chemical product formed (for a constant
quantity of electricity) is proportional to the relative
atomic mass of the ion and its charge.
Fat A solid ester composed of glycerol (propane-1,2,3-triol)
and fatty acids. Fatty acid
A long chain carboxylic acid which is chemically
combined with glycerol (propane-1,2,3-triol) to form
fats and oils.
The raw material(s) for a process in the chemical
The reaction between an acid and alcohol to form an
ester and water. Fermentation
The conversion of sugars to ethanol and carbon dioxide
by yeast under anaerobic conditions. Ether
An organic compound containing the group -O-. Fertilisers
A group of chemicals that supply plants with the mineral
salts they need for growth. Evaporation
Evaporation occurs at the surface of the liquid and
involves a liquid changing into a gas at a temperature
below the boiling point of the liquid.
A reactant is said to be present in excess when after
t he reaction is complete, some of that reactant remains
The state of an atom or molecule when one ore more of
its electrons is raised to a higher energy level above the
stable ground state.
A reaction in which heat energy is released to the
surroundings from the reactants. The bonds of the
products contain less enthalpy or potential energy than
t he bonds of the reactants. F
A unit of electrical charge (in Coulombs) equal to the
charge required to discharge one mole of a unipositive
ion. It is the charge carried by one mole of electrons. Fibrous protein
Insoluble proteins that serve in a protective or structural
The region of the infrared spectrum of a substance
between 910 and 1430 cm-1 where the pattern of peaks
is characteristic of that compound, even though all the
peaks may not be known.
First order reaction
A reaction in which the initial rate of reaction is directly
proportional to the concentration of one of the reacting
The catalytic hydrogenation of carbon monoxide in
t he ratio 2:1 hydrogen to carbon monoxide at 200 °C to
produce hydrocarbons, especially motor fuel.
The splitting of a nucleus of an element with a high
atomic number into two or more smaller atoms with
lower atomic numbers. Faraday constant
The quantity of electricity (in coulombs) transferred by
one mole of electrons. 529
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An analytical technique in which a small sample of a
metal salt is introduced into a hot Bunsen flame on a
clean platinum or nichrome wire. The flame vaporises
part of the sample which excites some of the atoms,
which emit light at wavelengths characteristic of the
metal ion in the salt.
The process of aggregating suspended solids in water
into larger insoluble clumps.
The formula mass is the sum of the atomic masses of the
elements in the formula of an ionic compound.
The symbols used in equations and calculations
to represent elements and compounds with giant
The forward reaction refers to the conversion of the
reactant into products in an equilibrium reaction.
Non-renewable fuels, such as coal, oil and natural gas,
formed underground over geological periods of time
from the decaying remains of plants and animals.
A mixture of liquids with similar boiling points collected
by fractional distillation.
Distillation to separate volatile chemical substances in
which the products are collected in a series of separate
fractions, each with a higher boiling point than the
The change of a liquid into a solid at constant
The temperature at which a liquid turns to a solid.
A species with one or more unpaired electrons, often
produced by photolysis. They act as highly reactive
intermediates in atmospheric chemistry.
The number of complete waves passing a point per
second. Friedel-Crafts reaction
A method for substituting an alkyl or acyl group into a
benzene ring and forming a C-C bond. It involves the
reaction between benzene (or other aromatic compound)
w ith a halogenoalkane or acyl chloride in the presence of
a so-called halogen carrier.
A device which converts chemical energy directly into
electrical energy. A gaseous fuel, usually hydrogen or
a hydrocarbon, and oxygen are passed over porous
electrodes where combustion occurs This is accompanied
by the production of an electric current.
Chemicals that burn in air or oxygen and release heat
A group of cage-like hollow molecules composed of
hexagonal and pentagonal groups of an even number of
A functional group is an atom or group of atoms (other
t han hydrogen) that imparts specific physical and
chemical properties of a homologous series of organic
Functional group isomerism
Functional group isomerism is a form of structural
isomerism where molecules with the same molecular
formula have different functional groups.
The forming of a nucleus from two nuclei of lower atomic
number. The process releases large amounts of energy
and only takes place at very high temperatures. G
(See voltaic cell).
Gamma waves/radiation (or rays)
High energy electromagnetic radiation of high frequency
and extremely short wavelength emitted by changes in
t he nuclei of atoms.
A state of matter in which there are little attractive forces
operating between the particles. The individual particles
move at high velocity in straight lines (until they collide
w ith each other or the walls of the container).
A technique for separating or analysing mixtures in the
gaseous phase using a carrier gas as an eluent. 530
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A form of partition or adsorption chromatography in
which the mobile phase is a gas and the stationary phase
a liquid. Solid and liquid samples are vaporized before
being introduced to the column.
The various laws that describe the physical behaviour of
gases. Global warming
The increase in the temperature of the Earth’s
atmosphere since the Industrial Revolution. It is believed
to be a consequence of rising levels of greenhouse gases,
especially carbon dioxide which are enhancing the
Soluble proteins with a globular or rounded shape. Gateway drug
A habit-forming substance whose use may lead to
t he abuse of drugs that are more addictive or more
dangerous. Glycosidic bond
The covalent bond, -O-, formed between two reacting
sugar molecules, or the bond between the sugar and base
in a nucleotide, in the presence of enzymes. Gene
A segment of a DNA molecule that contains the genetic
code for a protein molecule. Graham’s law of diffusion
Gases diffuse at a rate that is inversely proportional to the
square root of their density or molar mass (at constant
temperature and pressure). General anaesthetic
An anesthetic that affects the entire body and causes loss
of consciousness and insensitivity to pain.
Geometric isomerism occurs in alkenes when there is
restricted rotation about a carbon-carbon double bond.
It can also occur in ring system where there is restricted
rotation about a carbon-carbon single bond.
The use of hot water or steam located deep underground,
often under pressure, to generate electricity.
Giant covalent structure
A regular arrangement, usually three dimensional, of
covalently bonded atoms that extends throughout the
A lattice, usually three-dimensional, of ions or atoms in
which the bonding (ionic, covalent or metallic) extends
t hroughout the substance.
Gibbs free energy
A thermodynamic function equal to the enthalpy minus
t he product of the entropy and the absolute temperature.
A negative sign indicates that the reaction is spontaneous
under standard conditions. It is the energy available to
Gibbs free energy of reaction
The Gibbs free energy of a reaction is defined as the sum
of the Gibbs free energies of formation of the products
minus the sum of the Gibbs free energies of formation
of the reactants. Gravimetric analysis
A method of quantitative analysis for finding the
composition and formulas of compounds based on
accurate weighing of reactants and products.
A heating effect occurring in the atmosphere because of
t he presence of greenhouse gases that absorb infrared
Greenhouse gases are molecules that contribute to the
greenhouse effect and global warming by absorbing
infrared energy emitted or reflected from the surface of
t he Earth.
A column of the Periodic table which contains elements
w ith similar chemical properties. Atoms of elements in
t he same group have the same number of electrons in
t heir outer or valence shell. H
The industrial manufacture of ammonia from nitrogen
and hydrogen, carried out at high pressure and moderate
temperature in the presence of an iron catalyst.
An iron complex found in the protein hemoglobin.
A quaternary protein composed of four polypeptide
chains combined with a haem group. It can bond and
transport oxygen molecules from the lungs to body
071211 Chem Glossary FINAL.indd 531 11/12/2007 3:02:00 PM Glossary
An electrode in contact with a solution of ions.
The two parts of a redox reaction, one describing the
oxidation and the other reduction.
Half life (of a chemical reaction)
The time taken for the reactant concentration (in a
chemical reaction) of the reactants to reach a value which
is the mean or average of its initial and final values.
Half life (of a radioactive sample)
The time take for the radioactivity emitted by a sample
of a radioactive isotope to fall to half its original value.
The value will be constant for a particular isotope and
unaffected by changes in temperature or pressure.
The halide ions are chloride (Cl-), fluoride (F-) bromide
(Br-) and iodide (I-). The halides are salts that contain a
metal ion combined with the halide ions. Heavy metals
Heavy metals are toxic and metals, such as cadmium,
mercury and lead, which have relatively high relative
Heavy water is the common name for deuterium oxide,
D2O or 1H2O.
A substance designed to kill plants.
The SI unit of frequency (units of s-1 or Hz).
It states that the total enthalpy change for a reaction is
independent of the route taken.
Heterogeneous catalysis occurs when the catalyst and
t he reactants are in different phases (or states). Hallucinogens
Drugs which affect the brain and cause people to
experience hallucinations. Heterogenous equilibrium
An equilibrium system where the reactants and products
are in more than one phase. Halogen carrier
An electron deficient metal halide that acts as a Lewis
acid during electrophilic substitution. Heterolytic fission
The cleavage of a covalent bond so that one of the atoms
or groups separates with both bonding electrons and
becomes negatively charged, leaving the other atom or
group positively charged. Halogenoalkane
A homologous series of organic compounds in which
one or more of the hydrogen atoms of an alkane have
been replaced by halogen atoms.
Halogenoarenes are compounds formed by replacing
one or more hydrogen atoms in an arene with halogen
A group of reactive non-metals in Group 7 of the Periodic
Table. They are composed of diatomic molecules.
The heat capacity is the amount of heat energy required
to raise the temperature of a substance by one degree
kelvin (or Celsius).
The energy transferred between two objects due to a
temperature difference between them. The source of heat
energy is the movement of atoms, ions and molecules,
t hat is their kinetic energy.
A plot of temperature against time for a substance where
heat energy is added at a constant rate. High-pressure liquid chromatography
A technique in which the sample is forced through the
chromatography column under pressure. It is sometimes
k nown as High Performance Liquid Chromatography.
Heterogeneous catalysis occurs when the catalyst and
t he reactants are in the same phase (or states).
An equilibrium system where the reactants and products
are in the same phase.
A homologous series of organic compounds follow a
regular structural pattern and have the same general
molecular formula and differ only by the addition of
The breaking of a covalent bond so that one electron
from the bond is left on each fragment. It results in the
formation of two free radicals. 532
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A chemical substance produced in small amounts by
endocrine glands and then carried in the blood to a
target organ or tissue.
A rule that states that the electronic configuration in
orbitals of the same energy will have the minimum
number of paired electrons. Electrons with parallel
spins are lower in energy than a corresponding pair with
A salt associated with a definite number of molecules of
Ions dissolve in water and attract the polar molecules of
water and become associated with a definite number of
A reaction where an unsaturated molecule adds a
molecule of water, or where water molecules interact
with ions in aqueous solution.
A compound of hydrogen and one other element.
Organic compounds containing only hydrogen and
A process by which the hydrocarbon molecules of crude
oil or petroleum are broken into simpler molecules, by
t he addition of hydrogen under high pressure and in the
presence of a catalyst.
Hydrofluorocarbons (HFCs) are compounds containing
carbon, hydrogen, and fluorine and because they contain
no chlorine atoms they do not directly affect stratospheric
ozone. However, they are efficient absorbers of infrared
The addition of hydrogen across a multiple bond.
An unusually strong dipole-dipole force that occurs
among molecules in which hydrogen is bonded to
nitrogen, fluorine and oxygen.
A chemical reaction involving the reaction of a molecular
compound with water. Covalent bonds are broken during
t he reaction and the elements of water are added to the
chemical fragments. Hydrophobic
Used to describe molecules or functional groups that are
poorly soluble or insoluble in water.
Hydrophic interactions (of a protein)
The association of the non-polar groups within the
center of a folding protein, driven by the tendency of
t he surrounding water molecules to maximise their
Used to describe molecules or functional groups that are
soluble in water.
The –OH group covalently bonded in a molecular
structure. Found in alcohols, alkanoic acids and some
An ideal gas is a hypothetical substance that consists of
molecules or atoms that occupy almost no space and have
v irtually no attractive forces operating between them, or
between themselves and the walls of the container. All
collisions between the molecules or atoms are perfectly
elastic. An ideal gas obeys the gas laws exactly under all
Ideal gas constant
The ideal gas constant is the constant that appears in
t he ideal gas equation. It is formed by combining all
t he constants from Boyle’s Law, Charles’s Law and
Ideal gas equation
It is an equation relating the temperature, pressure,
volume and amount of an ideal gas. It is frequently used
in experimental work to determine the molar masses of
Immiscible liquids are liquids which do not mix (e.g. oil
A protein that does not provides all of the essential
A substance which changes colour over a particular
pH range. They are used to detect the end point during
The pH range – usually 2 pH units – over which an acidbase indicator changes colour completely. 533
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A force induced in one molecule by the approach of
another molecule which has a dipole, whether temporary
or permanent. Ion
An ion is charged particle formed by the loss or gain of
electrons from an atom (simple ion), or a group of atoms
(polyatomic ions). Inductive effect
The effect of a functional group or atom in an organic
molecule in attracting sigma electrons towards itself,
or in repelling them. This results in the formation of a
dipole in the molecule. Ion channel
A membrane-bound protein that provides a path for
t he regulated transport of a specific ion across a cell
A chemical is described as inert if it has little or no
tendency to react under given circumstances.
A substance that slows down the rate of a reaction.
Initial rate method
An experimental method for determining the order of a
chemical reactions and its rate equation.
The first elementary step in a free radical reaction. It
involves the homolytic cleavage of a bond, typically by
ultraviolet radiation or high temperature, to generate
A group of naturally occurring anti-viral compounds.
A covalent compound formed by the reaction between
t wo different halogens. A molecule containing atoms of
A chemical species that is neither a reactant nor a
product but is formed and consumed during the overall
chemical reaction. Intermediates never appear in a rate
The weak attractive
molecules. forces operating between Internal resistance
The resistance of a cell or a battery.
Forces operating within molecules. They are usually
covalent bonds, though hydrogen bonding can occur
intra-molecularly. They do not normally break during
melting or boiling.
Iodine number (or index)
The amount of iodine in grams which 100 grams of a fat
or oil can absorb; it is inversely related to the amount of
unsaturated fatty acids present in the fat or oil. Ion exchange
The exchange of ions of the same charge between an
aqueous solution and a solid (in the form of a resin) in
contact with it.
Ion exchange chromatography
In ion exchange chromatography, charged substances are
separated via column materials that carry an opposite
A bond formed when electrons are transferred from a
metal atom to one or more non-metal atoms. It is the
result of electrostatic forces of attraction between
oppositely charged ions.
A strong electrostatic force of attraction between
oppositely charged ions arranged into a lattice. Ionic
bonding typically involves the transfer of one, or more
electrons, between a metal atom and one ore more nonmetal atoms.
The simplified equation for a reaction involving ionic
substances. Only those ions that actually participate in
t he reaction are included in the ionic equation; spectator
ions are not included.
Ionic product constant of water
The product of the concentrations of hydrogen and
hydroxide ions in water under standard thermodynamic
A measure of the radius of an ion in the crystalline form
of a compound.
Ionisation energy (first)
The energy required to remove one mole of electrons
from one mole of isolated gaseous atoms to form one
mole of unipositive ions under standard thermodynamic
Isoelectric point (of an amino acid)
The pH at which an amino acid in solution has no overall
electrical charge. At this pH the amino acid does not
move when placed in an electric field. 534
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Two atoms or ions that have the same number of electrons
are described as isoelectronic. Knocking
A knocking noise made by a petrol engine in car, as a
result of premature fuel combustion. Isomers
Isomers are compounds with the same molecular
formula but different molecular structures and physical
and/or chemical properties. Latent heat
The heat needed to bring about a change in state. Isomerism
Isomerism is the existence of two or more molecules
having the same molecular formula, but with different
bonding arrangements of atoms or orientation of their
atoms in space.
A polymer chain in which the substituents, or side
chains, are distributed on the same side of the chain.
Two or more atoms of the same element with different
numbers of neutrons (and therefore different relative
The proportions of the different isotopes of an element.
The SI unit for energy. Symbol J.
A representation of a hypothetical localised structure of
benzene or a benzene derivative in which there is a sixmembered ring with alternate double and single bonds.
A temperature scale starting from absolute zero (-273
C) using degrees the same size or magnitude as degrees
Kinetic energy (of particles in a gas)
The energy due to the motion of gas particles; it depends
on the mass of the gas particle (atom or molecule) and
t he square of its velocity (speed in a specified direction).
The quantitative study of the dependence of reaction
rate on variables, such as concentration, pressure and
If two chemicals react relatively slowly because the
activation energy is relatively high, then the system
shows kinetic stability.
A theory which explains the physical properties of solids,
liquids and gases in terms of the movement of particles
(atoms, ions or molecules). The theory also accounts for
t he changes that occur during a change in state. Lattice
A regular, repeating three dimensional arrangement of
atoms, molecules or ions within a crystal.
The amount of energy required to dissociate one mole of
an ionic compound to its gaseous ions (under standard
t hermodynamic conditions).
Law of conservation of mass
Mass is not lost or gained during a chemical reaction
– t he total mass of the reactants equals the total mass of
t he products.
LD stands for “Lethal Dose”. LD50 is the amount of a
substance, given all at once, which causes the death of
50% (one half) of a group of test animals. The LD50 is
one way to measure the short-term poisoning potential
(acute toxicity) of a material.
Lead acid battery
A battery (used in cars) in which the anode is lead,
t he cathode is lead coated with lead(IV) oxide and the
electrolyte is sulfuric acid.
Lean burn engine
Lean combustion engines were designed to enhance fuel
efficiency without sacrificing power or drive-ability. All
engines burn a mixture of air and fuel, but a lean-burn
engine has a higher air-to-fuel ratio than conventional
engines. This can mean significant savings in petrol, and
t hus in emissions, such as carbon dioxide.
An atom or group of atoms which breaks away from
a molecule during a substitution or an elimination
Le Chatelier’s principle
Le Chatelier’s principle states that if a change is
imposed on a reaction at equilibrium, the position of
t he equilibrium will shift in a direction that reduces the
effect of that change.
The size of dosage that will typically cause death.
A chemical species that can accept an electron pair to
form a dative or coordinate covalent bond. 535
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A chemical species that can donate an electron pair to
form a dative or coordinate covalent bond.
Lewis (electron dot) structure
A diagram of a molecule showing how the valence
electrons are arranged among the atoms in the
A molecule or negative ion that donates a pair of electrons
to a central metal ion to form a dative or coordinate
covalent bond. Ligands are Lewis acids.
The process where one or more ligands in a complex ion
are replaced, often reversibly, by one another.
An emission spectrum that has only certain wavelengths
or frequencies of visible light. The lines arise from excited
electrons falling back to lower energy levels within the
The reactant that is completely consumed, or used up,
when a reaction goes to completion.
An algebraic rearrangement of the Michealis-Menten
equation which allows its maximum rate, Vmax and the
Michaelis-Menten constant, K m, by extrapolating the
substrate concentration, [S], to infinity.
A state of matter in which particles are loosely attracted
by intermolecular forces. A liquid always take up the
shape of the walls of its container and its particles are
not arranged into a lattice.
Biological compounds, for example, fats, oils and
steroids, which are soluble in organic solvent, but
essentially insoluble in water.
An anesthetic that numbs a local area of the body whilst
t he patient remains conscious.
Electron pairs forming covalent bonds between two
atoms. They are not free to move through a structure.
A model for the mechanism of enzyme activity
postulating that the shapes of the substrate and the
enzyme are such that they fit together as a key fits into a
specific lock. Lone pair (of electrons)
A lone or non-bonding pair of electrons are pairs of
outer or valence shell electrons which are not used to
form covalent bonds within the molecule. Lone pairs
affect the shape of a molecule and can be used to form
dative or coordinate covalent bonds.
Low level radioactive waste
Radioactive waste which, because of its low radioactivity,
does not require shielding during normal transport or
Lyotropic liquid crystal
A solution that shows liquid crystal state at certain
Lysergic acid diethylaminde (LSD)
a drug that is a powerful hallucinogen
Destruction of a cell’s cell membrane or of a bacterial
cell wall, releasing the cellular contents and killing the
cell. This often occurs during viral infections. M
A very large molecule, usually with a molar mass in the
tens of thousands.
Chemical substances required in relativley large amounts
in the diet for metabolism.
Macroscopic properties are properties of substances in
bulk that can be observed, for example, colour, or easily
measured, for example, pressure of a gas.
Magnetic resonance imaging (MRI)
The use of a nuclear magnetic resonance spectrometer
to produce electronic images of specific atoms and
molecular structures in solids, especially human cells,
tissues, and organs. Because it uses radio frequencies the
technique is non invasive.
The ability of metals to be bent and beaten into thin
A rule that predicts the major and minor products when
a hydrogen halide or interhalogen adds across the double
bond in an unsymmetrical alkene. The rule states that
t he major product will be the one in which the hydrogen
atom (or less electronegative atom of the interhalogen)
attaches itself to the carbon atom with the larger number
of hydrogen atoms. 536
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The amount by which the mass of an atomic nucleus
is less than the sum of the masses of its constituent
The mass number is the sum of the protons and neutrons
in the nucleus of the atom or ion.
An instrument in which gaseous atoms are ionised and
t hen accelerated into a magnetic field where the ions are
separated according to their mass.
Analysis of individual molecules according to their
elemental composition and usually giving information
about molar mass, as well as structures of component
parts of the molecules.
The output plot from the mass spectrometer, which is a
bar graph of abundance against mass/charge ratio.
Maxwell-Boltzmann energy distribution curve
A curve describing the distribution of velocities (‘speeds’)
or kinetic energies among the atoms or molecules of
an ideal gas. It is often used to explain the effects of a
temperature change or the presence of a catalyst on the
rate of a chemical reaction.
A detailed description in terms of bond breaking, bond
making and intermediate formation that occurs during
t he series of elementary steps by which an overall
chemical reaction occurs.
A substance or preparation used in treating disease or
to give relief from the symptoms of the disease. It also
refers to the practice and study of disease treatment.
The change of a solid into a liquid at constant
The temperature at which a solid is converted to a liquid
at the same temperature.
Mercury cathode cell
An electrolytic cell with a flowing mercury cathode
used in the industrial production of chlorine from
concentrated sodium chloride solution.
All of the chemical reactions that occur in living
Chemical elements which are shiny solids and are good
conductors of heat and electricity when solid. They form
positive ions (cations). They are located on the left hand
side of the Periodic Table and possess one, two or three
electrons in the outer shell which take part in chemical
Metallic bonding, found in metals and mixtures of
metals (known as alloys), consists of a lattice of cations
surrounded by delocalised or mobile valence electrons.
Elements which show some of the physical properties of
metals, but the chemical properties of non-metals.
A protein that possesses one or more metal ions.
The substrate concentration at which an enzymecatalysed reaction occurs at one half of its maximum
The equation describing the relationship of the initial rate
of an enzyme-controlled reaction and the concentration
of the substrate. It takes the form of a hyperbolic curve.
Kinetic behaviour, exhibited by enzymes, in which the
initial rate of an en enzyme-catalysed reaction shows a
hyperbolic dependence on substrate concentration.
A substance required in small amounts in the diet for
proper cell and body function.
A microscopic and usually single celled organism capable
of independent existence.
A naturally occurring inorganic chemical (element
or compound) which is used as a raw material in the
Liquids that mix in all proportions, for example, ethanol
A liquid or gas which percolates through or along the
stationary phase during chromatography.
A substance, such as water or graphite, that is used in
a nuclear reactor to decrease the speed of fast neutrons
and increase the likelihood of fission. 537
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Molar extinction coefficient
Absorbance of light per unit path length (usually the
centimetre) and per unit concentration (moles per cubic
decimetre). Mole fraction
This is the number of moles of a substance divided by the
total number of moles of all the components present in
t he mixture. Molar gas volume
One mole of an ideal gas occupies 22.4 cubic decimetres
at 0 °C (273 K) and one atmosphere pressure. Molecular mass
The molecular mass is the sum of the atomic masses of
t he elements in the formula of a covalent compound. Molar mass
The mass in grams of one mole of molecules or the
formula units of an ionic compound. It is numerically
equal to the relative molecular or atomic mass of a
substance, but has units of g mol-1. Molecule
A group of atoms held together by covalent bonds. Molarity
The amount in moles of solute per volume of solution in
cubic decimetres. Monodentate ligand
A ligand that forms one dative covalent bond to a central
metal ion. Mole
The measure of the amount of a substance. One mole of a
substance has a mass equal to its formula mass in grams.
One mole of a substance contains 6.02 × 1023 (Avogadro’s
constant) of atoms, ions or molecules. Monomer
A small molecule, a large number of which can be
polymerised via the formation of covalent bonds to form
a polymer. Molecular ion
The unipositive ion formed by the unfragmented molecule
losing one electron following electron bombardment.
The molecularity indicates the number of chemical
species or particles participating in the rate determining
step of the mechanism.
Molecular orbitals are formed in molecules when atomic
orbitals combine and merge when atoms bond together.
Sigma and pi bonds are molecular orbitals.
A measure of the amount of a component in a mixture.
The mole fraction of a component is the ratio of the
amount of a particular substance over the total amount
of all the substances in a mixture.
Molecular covalent (simple molecular)
A substance consisting of molecules arranged into a
lattice held together by intermolecular forces.
An equation representing a reaction in solution showing
t he reactants and products in undissociated or unionised
form, whether they are strong or weak electrolytes and
(acids, salts and bases.
A chemical formula which shows the actual number of
atoms of each element present in a molecule of a covalent
compound. Monochromatic radiation
Electromagnetic radiation with a single wavelength. Monoprotic
An acid which contains one replaceable hydrogen atom
per molecule, sometimes also known as monobasic.
A sugar that cannot be hydrolysed to simpler sugars.
A double or triple covalent bond between atoms in a
A change in the nucleotide sequence of a gene. N
Research, development and use of technology in the size
range of about 1-100 nm.
A general term used to describe a light hydrocarbon
fraction from crude oil distillation with a boiling point
between 40 °C and 150 °C. It is an important feedstock
used to manufacture other substances.
A drug that doses dulls the senses, relieves pain, and
induces profound sleep but in excessive doses causes
stupor, coma, or convulsions.
Narrow spectrum antibiotic
An antibiotic that is only effective against a small number
of bacterial strains. 538
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Gas obtained from underground deposits and often
associated with crude oil or petroleum. It contains a
high percentage of methane.
A chemical reaction between an acid and a base to
produce a salt and water only.
An aqueous solution that is neutral has a pH of seven
and contains the same concentrations of hydrogen and
A neutral particle found in the nucleus of all atoms
(except that of the most abundant isotope of hydrogen).
It has approximately the same mass as the proton.
A type of reaction in which a nitro group (-NO2) is
introduced into an aromatic compound, usually via the
use of a nitrating mixture.
A 1:2 molar mixture of concentrated nitric and sulfuric
acids used to nitrate some aromatic organic compounds.
The mixture produces the electrophilic nitronium cation,
NO2+, via an acid-base reaction.
A compound of the form RCN, where R is an alkyl group
or aryl group. Nitriles can be hydrolysed to carboxylic
The nitronium ion, NO2+, is formed in a nitrating mixture
and used to nitrate aromatic compounds. It is a powerful
A group of organic compounds which contain the
f unctional group NNO and some of which are powerful
Noble gas configuration
An octet of electrons in the valence shell or a pair of
electrons in the first shell.
A group of very unreactive gases found in Group 0, 8 or
18 of the Periodic Table. They exist as single atoms and
a ll have filled outer or valence shells.
Naming rules for compounds.
A type of enzyme inhibition not reversed by increasing
t he substrate concentration. Non-electrolyte
A substance which, when dissolved in water, gives a nonconducting solution due to the absence of ions.
Chemical elements that are typically poor conductors
of heat and electricity. They form covalent bonds and/or
form negative ions (anions).
A non-polar molecule is a symmetrical molecule whose
individual dipoles sum or cancel to zero.
Normal boiling point
The temperature at which the vapour pressure of a liquid
is exactly one atmosphere.
A n-type semiconductor is formed when the impurities
added to silicon donate electrons which enter the
unoccupied energy level.
Nuclear binding energy
The net energy required to decompose a molecule, an
atom, or a nucleus into its component protons, neutrons
The nuclear charge is the total charge of all the protons
in the nucleus.
The energy released during nuclear fusion or fission.
Nuclear magnetic resonance
The absorption of radio waves by nuclei with an odd
A particle in a nucleus, either a neutron or proton.
A nucleophile is a species which contains a lone pair of
electrons that can be donated to an electron deficient
A type of reaction in which the rate determining step is
t he attachment of a nucleophile to a positive (electrondeficient) part of the molecule (often a C=O bond in a
A reaction involving the substitution of an atom or group
of atoms with as the attacking species.
A compound consisting of a purine or pyrimidine base
covalently bonded to ribose or deoxyribose. 539
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A monomer of the nucleic acids composed of a fivecarbon sugar (a pentose), a nitrogen-containing base,
and phosphoric(V) acid
The central part of an atom containing protons and
frequently neutrons. Optically active
A compound that is able to rotate plane-polarised light.
Optimum pH and temperature
The characteristic pH and temperature at which an
enzyme has maximum activity. Nuclide
The general term for a unique atom. Oral contraceptive
A pill, typically containing estrogen or progesterone,
t hat inhibits ovulation and thereby prevents conception.
A lso called the birth control pill. Nutrients
Food components which provide growth, energy and
replacement for body tissues. Orbit
The circular path of an electron around the nucleus (in
t he Bohr theory). Nylon
A polymer with a long chain of carbon atoms to which
amide groups (-NH-CO-) are combined at regular
intervals. There is extensive hydrogen bonding between
t he chains. Orbital
A region in space in which an electron may be found in
an atom or molecule. Each atomic orbital can hold up to
a maximum of two electrons with opposite spins. O
Excess body mass which often leads to health problems
A numerical representation of the antiknock properties
of motor fuel, compared with a standard reference fuel,
such as iso-octane (2,2,4-trimethylpentane), which has
an octane number of 100.
A set of eight electrons in the valence shell.
Atoms (other than hydrogen) typically fill their valence
or electron shell with eight electrons (an octet) when
t hey form compounds.
Oil A liquid ester composed of glycerol (propane-1,2,3-triol)
and fatty acids. Opiates
A drug, hormone, or other chemical substance having
sedative or narcotic effects similar to those containing
opium or its derivatives.
Optical isomerism typically occurs when a molecule has
no plane of symmetry and can exist in left- and righthanded forms that are non-superimposable mirror
images of each other. The molecule must possess a chiral
centre. Optical isomers rotate plane-polarised light. Order of a reaction (individual)
The order of a reaction, with respect to a particular
reactant, indicates how the rate of a chemical reaction is
affected by the changes of concentration in a particular
reactant. It is the exponent in the rate expression with
respect to a particular reactant. The order can only be
determined experimentally; it cannot be deduced from
t he stoichiometric equation.
A naturally occurring mineral from which a metal can
Organic Chemistry is the study of carbon containing
compounds with the exception of the elements itself and
The sum of the individual orders with respect to each of
t he reactants in the rate expression.
(see oxidising agent).
Oxidation involves an increase in oxidation number or
loss of electrons.
A number (usually an integer), positive or negative,
given to indicate whether an element has been reduced
or oxidised during a redox reaction.
A compound of oxygen with another element where the
oxygen has the oxidation number (-2). 540
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A chemical or substance that brings about oxidation;
it accepts electrons from the reactant or one of the
reactants. In the reaction the oxidising agent itself is
Particulates are any type of solid particle or droplet in
t he air in the form of haze, smoke or dust, which can
remain suspended in the air or atmosphere for extended
periods. Oxy acid
An acid in which the acidic proton, or replaceable
hydrogen, is covalently bonded to an oxygen atom. Partition
The distribution of a solute between two immiscible
A colourless and toxic gas with the chemical formula
O3. It is produced in the stratosphere by the action of
high-energy ultra-violet radiation on oxygen molecules,
producing oxygen atoms. These oxygen atoms then react
with oxygen molecules to form ozone. It is also produced
in the lower atmosphere by the action of ultraviolet
radiation on nitrogen dioxide, to produce oxygen atoms
which can then react with oxygen molecules to give
The SI unit of pressure, abbreviated to Pa. One pascal
is equivalent to a force of one newton on one square
metre. Ozone depletion
The production of a region of lower concentration (‘hole’)
in the ozone layer by the action of chlorine atoms released
from chlorofluorocarbons (CFC’s), which destroy ozone
by reactions on the surface of ice crystals.
A layer of ozone in the stratosphere (between 15 – 30
k m) which prevents harmful ultra-violet radiation from
reaching the earth’s surface.
Chromatography carried out using a special grade of
fi lter paper as the stationary phase.
A single-batch method that uses a mixture of reagents
at each step of a synthesis to generate a large number of
A drug taken into the body or administered in a manner
other than through the digestive tract, as by intravenous,
subcutaneous or intra-muscular injection.
The pressure a gas in a mixture of gases would exert on
t he container if it were the only gas in the container. It
is equal to the mole fraction of the gas multiplied by the
The term particle (in the context of kinetic theory) refers
to atoms, molecules or ions. Pauling scale
A common measure of electronegativity which runs
from 0 (least electronegative or most electropositive) to
4 (most electronegative or least electropositive).
An element where the valence electrons are in the pshell. P-block elements are in groups 3, 4, 5, 6, 7 and 8 in
t he Periodic Table.
An antibiotic derived from the mould Pencillium
notatum. They produce their effects by disrupting
synthesis of the bacterial cell wall.
A bond formed between the amino group of an amino
acid and the carboxyl group of another (in the presence
of enzymes), with the elimination of water.
An amide bond resulting from the condensation reaction
between the amine group of one amino acid and the
carboxylic acid group of another.
The percentage by mass of each of the elements in a
The actual or experimental yield as a percentage of the
t heoretical yield.
A row in the Periodic Table which contains elements with
same number of shells, but with an increasing number of
electrons in the outer or valence shell.
The regular repetition of chemical and physical properties
as you move across and down the Periodic Table. 541
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A table of the chemical elements arranged in order of
increasing atomic (proton) number to show the similar
chemical properties of elements with similar electron
Peroxyacetyl nitrate (PAN)
Peroxyacetyl nitrate is an important by-product in
t he photochemical production of ozone, and acts as a
reservoir for nitrogen dioxide.
Organic compounds found in, or derived from petroleum
t hat are used in the manufacture of products other than
a drug which leads to an improvement in health;
t he scientific study of the interactions of drugs with the
different cells found in the body.
A physically or chemically distinct part of a chemical
equilibrium. A phase is homogenous throughout and is
separated from other phases by a phase boundary.
An equilibrium in which the amounts of the phases are
fi xed, with transfer from one phase to another feasible.
A group of organic compounds in which a hydroxyl
group is bonded directly to one of the carbon atoms of a
A common acid-base indicator, used for strong acid/
strong base and weak acid.strong base titrations. It is
colourless in acid solution, pink in alkaline solution.
The group –C6H5.
Lipids that contain the phosphate group.
A reaction initiated by light.
A form of local atmospheric pollution found in large cities
in which oxides of nitrogen and unburnt hydrocarbons
react in the presence of light to produce a range of
harmful products including ozone and PAN. Photolysis
The splitting of molecules into fragments (often free
radicals) by light, usually ultraviolet radiation.
A ‘packet’ or quantum of light, or other electromagnetic
pH The pH of a solution is the negative logarithm (to the
base 10) of the hydrogen ion or proton concentration (in
mol dm-3). pH probe
An electrode that can be used to accurately measure (via
voltage) the pH of an aqueous solution.
The pH scale runs from 0 to 14 and is used to describe
t he acidity or alkalinity of an aqueous solution.
A bond formed by the sideways overlap of two p-orbitals.
In a pi bond the electron density is concentrated on either
side of the line between the nuclei of the two joined by
t he bond.
An improvement in the condition of an ill person that
occurs in response to treatment but that cannot be
considered due to the specific treatment used.
The constant relating the change in energy for a system to
t he frequency of the electromagnetic radiation absorbed
Plane polarised light
Electromagnetic radiation in which both components
of the wave oscillate in a single plane. It is used for the
detection of optical activity.
Materials that can be shaped by applying heat or
A substance added to a synthetic (man-made) plastic to
make it flexible.
Polar covalent bond
A bond formed when electrons are shared unequally
between two atoms due to a difference in electronegativity.
One atom has a partial positive charge, and the other
atom has an equal but opposite partial negative charge.
A device used to study optically active substances. 542
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Polarisability or polarising power
The extent to which the electron distribution in a
molecule, ion or an atom can be distorted by an externally
applied electric field.
The dipole possessed by a bond as a consequence of
a difference in electronegativity values between the
A polar molecule is an unsymmetrical molecule whose
individual dipoles do not sum to zero or cancel.
Solvents composed of polar molecules.
A polymer in which the monomer molecules are linked
by amide bonds.
A synthetic polymer formed by reacting alcohols with
acids, so that the monomers are linked by the group, O-CO-.
A compound containing very large molecules composed
of repeating units called monomers.
A chemical reaction in which small molecules called
monomers are joined together covalently to form a
A long linear chain of between 10 and 100 amino acids
linked via peptide bonds.
An acid with more than one acidic proton or replaceable
hydrogen. It dissociates in a stepwise manner , one
proton or hydrogen ion at a time.
Carbohydrates whose molecules contain chains of
A dumb bell-shaped atomic orbital; there are three per
shell, beginning with the second.
Potential difference (‘voltage’)
A measure of the force pushing electrons around a
circuit. If the potential difference between two points is
1 volt, then the passage of 1 coulomb of charge between
t hese points involves 1 joule of energy. Power (of a galvanic cell)
The power of a cell (measured in watts (W)) is given by
t he product of the voltage and the current.
A precipitate is an insoluble substance formed by a
chemical reaction in solution. It occurs when two soluble
salts react to give one soluble and one insoluble salt.
A measure of the force pressing onto an object’s surface.
The pressure that a gas exerts upon its container is caused
by the particles colliding with the walls of the container.
Pressure is defined as force per unit area.
Pressure = force
area Pressure law
The gas law stating that the pressure of a fixed mass (at
constant volume) of an ideal gas is directly proportional
to absolute temperature.
An alcohol containing the –CH2OH group.
An amine of the form RNH2, where R is an alkyl or aryl
Primary air pollution
Primary pollutants enter the atmosphere directly from
A device which produces a flow of electric current. A
primary cell cannot be recharged.
A chemical which can be weighed out accurately to
prepare a standard solution for volumetric analysis.
Primary structure (of a protein)
The order or sequence of the amino acids in a polypeptide
A substance produced during a chemical reaction.
The movement of an electron from a low energy level to a
higher energy level further away from the nucleus.
An elementary reaction involving one radical causing
t he formation of another radical.
A group of organic compounds derived from essential
fatty acids and causing a range of actions, including
071211 Chem Glossary FINAL.indd 543 11/12/2007 3:02:04 PM Glossary
A molecule composed of one or more polypeptide
chains, each with a characteristic sequence of amino
acids linked via peptide bonds.
Positively charged particle found in the nuclei of all
atoms. It has approximately the same mass as the
An order of a chemical reaction that appears to be
less than the true order because of the experimental
conditions used. Pseudo orders occur when one reactant
is present in large excess.
Pseudo order constant
If the rate equation takes the form, rate = k [A] [B] then k
[A] is the pseudo first-order rate constant with respect to
B. Similarly, k [B] is the pseudo first-order with respect
(or psychotomimetics or hallucinogens) mind-altering
drugs produce a qualitative change in thought, perception
or mood and can cause vivid illusions and fantasies
A p-type semiconductor is formed when the impurities
added to silicon withdraw electrons from the occupied
energy level leaving positive ‘holes’ which allow
conduction to occur.
A nitrogen containing base found in nucleotides and
nucleic acids. It contains one six membered ring fused
with a five-membered ring.
The breaking up of larger hydrocarbons into shorter
chain ones using heat.
A nitrogen containing base found in nucleotides and
nucleic acids. It contains one six membered ring. Q
Analysis used to determine the nature of the constituents
of a material or substance.
Analysis used to determine the amount of each
component in a material or substance. Quantisation
The concept that energy can only be obtained in the form
of small ‘packets’ called quanta.
Quantum (plural quanta)
A packet of energy.
The overall three-dimensional structure of a protein
composed of two or more polypeptide chains. R
An equimolar mixture of two enantiomers of the same
compound. As their rotation of plane-polarised light is
equal but opposite, the mixture is not optically active.
The transmission of energy by means of an
electromagnetic wave; or the emission of particles from
t he nucleus of a decaying atom.
(See free radical).
The decay of a radioactive nucleus to form the nucleus
of another element by alpha decay or bet decay. Gamma
rays may also be emitted.
A series of isotopes produced one from the other in a
sequence of spontaneous radioactive disintegrations.
An irregular arrangement of a polypeptide chain in
The constant in a rate expression. The rate constant
is unaffected by changes in the concentrations of
t he reactants, but is only affected by changes in
Rate determining step
The slowest elementary step in a reaction mechanism
t hat controls the rate of the overall reaction.
A rate expression is the experimentally determined
relationship between the rate of a reaction and the
concentrations of the chemical species that occur in the
overall chemical reaction.
Rate of decay
The change in the number of radioactive nuclides in a
sample per unit time. 544
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Rate of reaction
The rate of reaction indicates how fast reactants are
being converted to products during a chemical reaction.
It is the rate of formation of a product, or the rate of
consumption of a reactant, divided by the corresponding
coefficient in the stoichiometric equation. The rate has
units of mol dm-3 s-1. Reductant
(See reducing agent).
Reduction involves a decrease in oxidation number or
gain of electrons. Reactant
A substance that is consumed during a chemical
reaction. Reducing agent
A chemical or substance that brings about reduction; it
donates electrons to the reactant or one of the reactants.
In the reaction the reducing agent itself is oxidised. Reacting masses
The masses of elements and compounds which take part
in a chemical reaction. Reducing smog
A smog containing soot particles and aqueous sulfur
dioxide from the combustion of coal in power stations. Reaction mechanism
A description of the changes in electronic structure that
occur during a reaction. The movement of electron pairs
is shown by means of curly arrows. Refining
The processes which separate, convert and purify
chemicals in crude oil in oil refinery, or the removal of
impurities from metals. Reaction quotient
A quotient obtained by applying the equilibrium law
to initial concentrations, rather than to equilibrium
The process of boiling a liquid in a flask fitted with a
condenser so that the condensed liquid runs back into
t he flask. Reactivity series
An order of metal reactivity based on the relative rates
of reactions of metals with oxygen, water, dilute aqueous
acid and solutions of metal ions or salts. Reforming
Processes occurring where molecules obtained from
crude oil or petroleum are converted into more useful
products. The reactions involved are rearrangements
and do not involve a change in the molar mass of the
molecule. Reactor core
The part of a nuclear reactor where the fission reaction
A real gas does not obey the gas laws and exhibits nonideal behaviour. Its molecules have a finite size and there
are intermolecular or inter-atomic forces of attraction
operating between the molecules or atoms.
A technique for the purification of solid crystalline
substances. The procedure is based on the fact that
solutes are much more soluble in a hot solvent and much
less soluble when the solvent is cold.
An equation constructed by combining two half
equations so the numbers of electrons on both sides of
t he equation and cancel.
A reaction involving reduction and oxidation and which
results in one or more electrons being transferred.
A titration used to determine the concentration of a
solution of an oxidising agent or of a reducing agent. Relative abundance
The relative abundance is the percentage of a particular
isotope of an element relative to other isotopes of the
same element in a naturally occurring sample.
Relative atomic mass
The weighted average (according to relative abundances)
of the isotopic masses of the atoms in a naturally
occurring sample of that element.
Relative isotopic mass
The mass of a particular isotope of an element compared
to the mass of one twelfth of a carbon-12 atom. They are
measured using a mass spectrometer.
The unit of a polymer chain that originates from a single
monomer, in the case of addition polymers, or from the
pair of molecules usually used to make condensation
Residue (amino acid)
A single amino acid within a polypeptide chain.
A measure of an electrical component’s opposition to the
flow of an electric current. It is measured in ohms (Ω). 545
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The separation of a racemic mixture into its two
enantiomers (optical isomers).
The phenomenon where bonded atoms cannot rotate
relative to one another because either the bond between
t hem prevents it, or because the two atoms are part of a
ring that restricts rotation.
Enzymes that cause cleavage of both strands of doublestranded DNA at or near specific base sequences.
Retention factor (Rf value)
The retention factor, or Rf, is defined as the distance
travelled by the compound divided by the distance
travelled by the eluent.
An RNA virus containing reverse transcriptase.
A method for removing dissolved salts from water, for
example, in the desalination of sea water, by the use of a
semi-permeable membrane and high pressure.
A reversible reaction is a physical or chemical reaction
t hat can go either backwards or forwards depending
on the conditions. When a reversible reaction has equal
forward and reverse rates the reaction is at equilibrium.
A monosaccharide and a component of RNA.
The corrosion of iron or steel. Saturated
A term used to describe an organic molecule that
contains no carbon-carbon multiple bonds and contains
only carbon-carbon single bonds.
A fatty acid containing only fully saturated alkyl
A solution which contains as much of the dissolved
solute as possible at a particular temperature.
A vapour that is in equilibrium with a liquid. A saturated
vapour is at the maximum pressure (the saturated vapour
pressure) at a particular temperature. If the saturated
vapour pressure of a liquid is equal to atmospheric
pressure, then the temperature is the boiling point of
t hat liquid.
Elements where the valence electrons are in an s-orbital.
The s-block comprises groups 1 and 2.
Secondary air pollution
Secondary pollutants, are formed when primary
pollutants react with each other or with other compounds
present in the atmosphere.
An alcohol where the carbon bearing the –OH group
is attached to two other carbon atoms in alkyl or aryl
An amine where the nitrogen atom bears two alkyl or
aryl groups. S Secondary cell
A secondary cell can be recharged by passing an electric
current through it in the opposite direction. Salt
A ionic compound formed by the reaction of an acid
with a base, in which the hydrogen of the acid has been
replaced by a metal ion. They are usually prepared via
neutralisation, precipitation or direct synthesis. Secondary structure (of a protein)
The three-dimensional conformation of sections of
polypeptide chains. Common protein secondary
structures include the alpha-helix, the beta sheet and the
random coil. Salt bridge
An ionic connection made between two half cells that
contains an electrolyte with ions that do not cause
precipitation of the ions in the two half cells. It allows
ions to flow while preventing the two solutions from
mixing. It prevents a build up of charge which would
stop the flow of current. Second order
A reaction in which the rate of reaction is proportional
to the product of the concentrations of two of the
reactants or to the square of the concentration of one of
t he reactants.
A crystalline material with a conductivity intermediate
between that of a conductor and an insulator. Its
conductivity rises with increasing temperature. 546
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Various hormones, such as oestrogen, progesterone and
testosterone, affecting the growth or function of the
reproductive organs, the development of secondary sex
characteristics, and the behavioral patterns of animals. SN2 (halogenoalkanes)
A nucleophilic substitution where a concerted reaction
occurs in which the nucleophile begins to bond with
t he carbon bearing the halogen as the halogen begins to
leave the molecule. Shells
The main energy levels of an atom where the electrons
are located. Soap
A sodium or potassium salt of a long-chain organic
acid. Shielding (of electrons)
Shielding electrons are the electrons in the energy levels
between the nucleus and the outer or valence electrons.
They are described as ‘shielding’ electrons because they
‘shield’ the valence electrons from the nuclear charge and
reduce the pull on them by the protons in the nucleus. Solid
A state of matter whose particles are in fixed positions
and are not able to move from one location to another.
The particles are held in a lattice by chemical bonds or
intermolecular forces. Side effects
A secondary and usually adverse effect of a drug.
Unwanted reactions which reduce the yield of the
product being formed by the main reaction.
A bond formed by the head-on overlap between atomic
orbitals along an imaginary line joining the two
nuclei (the internuclear axis). The electron density is
concentrated along the internuclear axis. Sigma bonds
can be formed by the overlap of two s-orbitals, an sorbital and a p-orbital or two p-orbitals.
A covalent bond formed by the sharing of one pair of
A formula representing organic molecules where the
carbon and hydrogen atoms are omitted and only the
bonds between them are shown.
A mixture of molten non-metallic oxides produced
during the extraction of iron in the blast furnace. It
consists of oxide impurities that have reacted with the
calcium oxide produced from the decomposition of
A form of air pollution consisting of a combination of
smoke and fog.
Tiny particles of unburnt carbon suspended in air.
A nucleophilic substitution in which a carbocation
intermediate is formed in the rate determining step
which then reacts with the nucleophile. Solid charge
The mixture of raw materials limestone, coke and iron
ore that are fed into a blast furnace.
Solid phase chemistry
Solid phase chemistry involves carrying a synthesis with
one of the reactant molecules attached to an insoluble
material known as a solid support.
The amount of solute required to form a saturated
solution in a given volume of solvent.
A solute is the solid, liquid or gas that has been dissolved
to form a solution.
A solution is formed when a solid, liquid or gas is
dissolved into a solvent.
The process occurring when ions dissolve in a polar
solvent and become surrounded by solvent molecules.
A solvent is a liquid that dissolves solids, liquids or gases
to form a solution.
A spherically symmetrical atomic orbital; there is one
per shell. s-orbitals have the lowest energy orbital in a
Specific heat capacity
The specific heat capacity is the amount of heat energy
required to raise the temperature of one kilogram of a
substance, by one degree kelvin (or Celsius).
Arrangement of ligands in order of increasing ability to
produce d-orbital splitting. 547
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The production and analysis of spectra.
Ions present in solution that do not participate directly
in a reaction.
A particular wavelength of light emitted (or absorbed)
by an atom, ion (or molecule).
A group of related lines in the emission (or absorption)
spectrum of a substance. The lines in a spectral series
occur when all the transitions all occur between one
particular energy level and a set of different energy
An instrument for examining the different wavelengths
present in electromagnetic radiation.
A reaction which will occur when the reactants are
mixed together under standard conditions. It does not
require an input of heat energy and is accompanied by a
decrease in free energy.
A compound is described as being stable if it does
not tend to decompose into its elements or into other
Standard electrode potential
The potential difference generated by a half-cell under
standard conditions when connected by a salt bridge and
an external circuit to a standard hydrogen electrode .
Standard hydrogen electrode
The standard hydrogen electrode is a half cell used to
measure standard electrode potentials. It consists of
hydrogen gas (at a pressure of one atmosphere) bubbled
over a platinum electrode in a one molar solution of
hydrochloric acid at 298 K. It is assigned a voltage of
Standard enthalpy change of reaction
The enthalpy change when molar amounts of
substances in a balanced equation react under standard
t hermodynamic conditions.
A solution with an accurately known concentration. They
are made by dissolving a known amount of a primary
standard in water.
Standard temperature and pressure (stp)
Standard conditions of 0 °C and 1 atmosphere pressure. States of matter
Solid, liquid and gas are the three states of matter in which
a ll substances can exist, depending on the conditions of
temperature and pressure.
Symbols used in equation to describe the physical state
of the substances that are participating in the reaction.
One of the two phases forming a chromatographic
system. It may be a solid, a gel or a liquid. If a liquid,
it may be distributed on a solid. The liquid may also
be chemically bonded to the solid (bonded phase) or
immobilised onto it (immobilised phase).
Cracking out in the presence of steam at very high
The reaction of naphtha with steam over a platinum/
alumina catalyst to give a variety of branched-chain
a lkanes, cycloalkanes and aromatic compounds, used in
t he blending of fuels.
Isomerism arising from differences in the shapes of
molecules. Includes geometric and optical isomerism.
An effect in which the rate of a chemical reaction
depends on the size or shape of groups of atoms within
The prevention or slowing down of a reaction by atoms
or functional groups blocking the access of an attacking
molecule or ion.
A group of lipids with a characteristic fused carbonring structure that includes cholesterol and the sex
Two DNA molecules with short overhanging singlestranded sequences that are complementary to one
another, facilitating the sealing of the ends.
A drug that temporarily arouses or accelerates
physiological activity and prevents sleep.
The ratio in which the elements combine in a compound,
or the ratio in which compounds react in a reaction. 548
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A solution whose concentration is accurately known and
does not change with time. Sub-atomic particles
The particles, electrons, protons and neutrons, from
which all atoms are made. Standard state
A reference state for a specific element (in a particular
a llotropic form, where appropriate) according to
standard thermodynamic conditions. Sublimation
The direct change of state from solid to gas (or from gas
to solid) without melting or freezing occurring. State symbols
State symbols indicate whether a substance shown in an
equation is a solid (s), liquid (l), gas (g) or in aqueous
solution (aq), that is, dissolved in water.
A type of isomerism in which the connectivity of atoms
in the isomers is the same, but the arrangements in space
are different. Sub-critical reaction (nuclear)
A nuclear reaction in which less than one neutron causes
another fission event and the process dies out.
A sub-division of an electron shell.
An atom, radical, or group substituted for another in a
chemical compound. Stereospecific reactions
Reactions with one of the optical isomers or enantiomers
of a compound, but not the other. Substitution
A reaction in which one atom or group of atoms is
replaced by another atom or functional group. Stoichiometric quantities
A reaction where amounts of reactants are reacted
together so that all are consumed at exactly the same
The compound acted upon by an enzyme. Storage cell
An electrochemical cell that stores, in the form of
chemical energy, useful quantities of electrical energy,
for example, lead-acid battery.
Strain is present in a molecule or transition structure
if the energy is enhanced because of unfavourable
bond lengths or bond angles, relative to a standard.
It is quantitatively defined as the standard enthalpy
of a structure relative to a strainless structure (real or
hypothetical) made up from the same atoms with the
same types of bonding.
The layer of the atmosphere between 15 and 30 km,
above the troposphere.
A strong acid or strong base is completely dissociated or
ionised when dissolved in water.
The determination of the structure of a pure substance. Sugar
A sweet, crystalline and water-soluble mono- or
A chemical that protects the skin from harmful
u ltraviolet radiation from the sun.
The condition in which the result of the combined action
of two or more drugs is greater than the sum of their
separate, individual effects.
A series of reactions resulting in the production of a
A mixture of carbon monoxide and hydrogen gas
produced by the steam reforming of natural gas using
nickel oxide catalyst.
A term used to describe the material or mixture of
chemicals being studied. Everything outside the system
is the surroundings. Structural formula
A structural formula shows the connectivity of the atoms
in the molecule.
A type of isomerism in which the connectivity of atoms
in the isomeric compounds differs. 549
071211 Chem Glossary FINAL.indd 549 11/12/2007 3:02:06 PM Glossary T Thermochemistry
The study of heat changes occurring during chemical
The measure of the average kinetic energy of the particles
in a substance. Thermodynamics
The laws which govern energy transfers and the direction
of chemical and physical changes. Termination
An elementary step in a reaction involving the
combination of two radicals to form a molecule. Thermoplastics
Plastics which soften when heated and can then be remoulded. Most addition polymers are thermoplastics. Tertiary alcohol
An alcohol in which the carbon atom bearing the –OH
group is attached to three other carbon atoms, that is, to
t hree alkyl or aryl groups. Thermosetting plastics
Plastics which do not soften on heating but only char
and decompose – they cannot be re-moulded. Tertiary structure (of a protein)
The overall three-dimensional folded shape of a protein
composed of a single polypeptide chain.
A reference standard for proton nuclear magnetic
The maximum amount or mass of a particular product
t hat can be formed when the limiting reactant is
completely consumed and there are no losses or side
Cracking carried out a high temperature in the absence
of a catalyst.
The decomposition of a substance by heating.
The process whereby a substance decomposes on heating
but is regenerated on cooling. This is provided it has
been heated in a closed system and the products have
A thermal inversion occurs when cold dense air is near
t he ground, and there is a layer of warmer and therefore
lighter air above it. They often occur in valleys and trap
pollutants formed during the day in towns and cities
Industrial discharge of heated water into a river, lake, or
other body of water, causing a rise in temperature that
endangers aquatic life by decreasing the solubility of
A chemical equation that describes the reaction
occurring and gives the associated enthalpy change. Thermotropic LC
Pure substances that occur as liquid crystals over a
certial temperature range bewteen the solid and liquid
A form of chromatography in which compounds are
separated by a suitable solvent or solvent mixture on
a t hin layer of adsorbent material coated onto a flat
Tidal power utilises the twice daily variation in sea level
caused primarily by the gravitational effect of the Moon
to generate electricity.
A Chemical technique in which one solution is used to
analyse another solution and find its concentration or
A plot of the pH of the reaction mixture against the
amount of titrant added.
The capacity of the body to endure or become less
responsive to a substance (such as a drug) with repeated
use or exposure.
transA prefix typically used to describe the geometric isomer
of a 1,2-disubstituted alkene with atoms or functional
groups on opposite sides of a double bond or ring. It is
a lso used in complex ions to designate two groups located
directly across a central metal or ion from each other.
A movement of electrons between energy levels. This can
be from to a higher energy level, involving a shell further
away from the nucleus, or to a lower energy level closer
to the nucleus. 550
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(See activated complex).
A set of metals in the Periodic Table, located between
groups 2 and 3/13, in which filling of electrons in an
inner d-shell occurs.
A measure of the extent to which a sample in a
spectrometer or colorimeter absorbs electromagnetic
radiation of a particular wavelength.
A term used to describe the way in which a chemical or
physical property increases or decreases along a series of
elements or organic compounds (homologous series). V
The electrons in the outermost shell of an atom or ion.
They are typically involved in bond formation.
Valence shell electron pair repulsion theory (VSEPR)
A model which states that the shape of bonds around the
central atom of a molecule is determined by minimising
t he repulsion between the regions of high electron
density. Triple bond
A covalent bond formed by the sharing of three pairs of
electrons between two atoms. Van der Waals’ forces
Intermolecular forces, that operate between noble gas
atoms and non-polar molecules in the solid and liquid
states. They occur when the electrons within an atom or
molecule induce a temporary dipole in an adjacent atom
or molecule. They occur with increasing molecular or
atomic size. Troposphere
The layer of the atmosphere closest to the ground and
extending upwards (15 – 30 km) to the stratosphere. Vapour
A gas in contact with its liquid at a temperature below its
boiling point. U Vapour pressure
The pressure of the vapour (gas) over a liquid where the
gas and vapour are in equilibrium. Ultraviolet/Visible spectroscopy
Ultraviolet/visible spectroscopy involves the absorption
of ultraviolet/visible light by a molecule causing the
promotion of an electron from a ground electronic state
to an excited electronic state.
An elementary step involving one particle dissociating
into two or more particles.
A mixture of indicators which changes colour several
times as the pH of an aqueous solution changes.
The smallest repeating part of a lattice or crystalline
Unsaturated fatty acid
A fatty acid containing one or more carbon-carbon
A term used to describe a molecule, such as an alkene
or fat, containing one or more carbon-carbon double or
triple (multiple) bonds. Virus
A simple organism that consists essentially of a core of
R NA or DNA surrounded by a protein coat. They are
only able to replicate inside a host cell.
Various unrelated fat-soluble or water-soluble organic
substances essential in minute amounts for normal
growth and activity of the body and obtained naturally
from plant and animal foods.
Volatile organic compound (VOC)
Volatile organic compound, present in the atmosphere
from evaporation of solvents or hydrocarbon fuels (manmade) or emitted by plants (Biological), and important
precursors for photochemical formation of ozone.
A qualitative measure of the how readily a liquid or solid
is vaporised upon heating or evaporation.
Voltaic or galvanic cells contain two half cells, each of
which is composed of an electrode in contact with an
electrolyte. They are connected with a salt bridge and an
external circuit. 551
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A mixture of enzymes found in yeast involved in
fermentation. Water of crystallisation
Water molecules that are incorporated into the crystal
lattice of many inorganic salts when they crystallise
from aqueous solution.
The distance between the peaks (or troughs) of one
The reciprocal of the wavelength of a wave. It is the
number of complete waves in a particular unit of
distance, for example, 1 cm. It is commonly used in
A weak acid is only partially dissociated or ionised when
dissolved in water.
A summary of a chemical reaction using the chemical
names of the reactant and products. Z
A naturally occurring series of aluminosilicate rocks
t hat contain cations in the cavities of the aluminosilicate
framework. They are widely used in ion-exchange
A chemical reaction in which the rate of reaction is
independent of the concentration of a reactant.
A method for the manufacture of high-density
polyethene using a catalyst of titanium(IV) chloride and
triethylaluminium under slight pressure.
Zone of nuclear stability
The area encompassing the stable nuclides on a plot of
t heir positions as a function of the number of protons
and the number of neutrons in the nucleus.
A technique used to reduce the level of impurities in
semiconductors. It is based on the fact that the solubility
of an impurity may be different in the solid and liquid
(See dipolar ion). 552
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