A
Acetylene: a gas (formula C2H2) used as a
fuel, for example in the oxy-acetylene torch
Acid rain: rain that is acidic because gases
such as sulfur dioxide are dissolved in it
(from burning fossil fuels)
Acidic solution: has a pH less than 7; an
acidic solution contains H+ ions
Acid fermentation: the process in which
bacteria convert ethanol to ethanoic acid
Addition reaction: where a molecule adds
onto an alkene, and the C ” C double bond
of the alkene changes to a single bond
Addition polymerisation: where small
molecules join to form a very large molecule,
by adding on at double bonds
Alcohols: a family of organic compounds,
similar to the alkanes but with the OH
functional group; ethanol is an example
Alkali: a soluble base; for example sodium
hydroxide
Alkali metals: the Group I elements of the
Periodic Table
Alkaline earth: metals the Group II
elements of the Periodic Table
Alkaline solution: has a pH above 7;
alkaline solutions contain OH # ions
Alkanes: a family of saturated hydrocarbons
with the general formula CnH2n+2;
‘saturated’ means they have only single C–C
bonds
Alkenes: a family of unsaturated hydrocarbons
with the general formula CnH2n ;
their molecules contain a carbon ” carbon
double bond
Allotropes: different forms of an element;
diamond and graphite are allotropes of
carbon
Alloy: a mixture where at least one other
substance is added to a metal, to improve its
properties; the other substance is often a
metal too (but not always)
Amphoteric: can be both acidic and basic in
its reactions; for example aluminium oxide
is an amphoteric oxide
Anion: another name for a negative ion
anode the positive electrode of a cell
Aquifer: underground rocks holding a large
volume of water; it can be pumped out to
give a water supply
Atmosphere: the layer of gases around the
Earth; here at the Earth’s surface, we call it
air
Atoms: elements are made up of atoms,
which contain protons, neutrons, and
electrons
Avogadro constant: the number of particles
in one mole of an element or compound; it
is 6.02 $ 1023
B
Backward reaction: the reaction in which the
product breaks down again, in a reversible
reaction
Bacteria: tiny organisms, some of which can
cause disease; others break down dead plant
and animal material
Balanced equation: a chemical equation in
which the number of each type of atom is
the same on both sides of the arrow
Base: a metal oxide or hydroxide; a base will
neutralise an acid, to form a salt and water
Battery: a portable electrical cell; for
example a torch battery
Biodegradable: will decay naturally in the
soil, with the help of bacteria
Biopolymer: a polymer made by bacteria
Blast furnace: the chemical plant in which
iron is extracted from its ore, iron(III) oxide
Boiling: the change from a liquid to a gas,
which takes place at the boiling point
Boiling Point: the temperature at which a
substance boils
Bond energy: the energy needed to break a
bond, or released when the bond is formed;
it is given in kilojoules (kJ) per mole
Bonding: how the atoms are held together
in an element or compound; there are three
types of bonds: ionic, covalent, and metallic
Brittle: breaks up easily when struck
Brine: the industrial name for a
concentrated solution of sodium chloride in
water; it can be made by dissolving rock salt
Burette: a piece of laboratory equipment for
delivering a measured volume of liquid
Burning: an exothermic chemical reaction
in which the reactant combines with oxygen
to form an oxide; also called combustion
C
Carbon cycle: the way carbon moves nonstop
between the atmosphere, living things,
the land, and the ocean; it moves in the form
of carbon dioxide
Carboxylic acids: a family of organic acids,
which have the COOH functional
group; ethanoic acid is an example
Cast iron: iron from the blast furnace that is
run into molds to harden; it contains a high
% of carbon, which makes it brittle
Catalyst: a substance that speeds up a
chemical reaction, without itself being used
up in the process
Catalytic converter: a device in a car
exhaust, in which catalysts are used to
convert harmful gases to harmless ones
Catalytic cracking: where large molecules
of hydrocarbons are split up into smaller
ones, with the help of a catalyst
Cathode: the negative electrode of an
electrolysis cell
Cation: another name for a positive ion
cell (biological) the building blocks for
animals and plants
Cell: (electrical) a device that converts
chemical energy to electrical energy
Cement: a substance used in building, made
from limestone and clay
Ceramic: a hard, ureactive material that can
withstand high temperatures, made by
baking clay in a kiln; ceramics are nonconductors
Chalk: a rock made of calcium carbonate
Change of state: a change in the physical
state of a substance – for example from solid
to liquid, or liquid to gas
Chemical change: a change in which a new
chemical substance forms
Chemical equation: uses chemical symbols
to describe a chemical reaction in a short
way
Chemical reaction: a process in which
chemical change takes place
Chromatogram: the paper showing the
separated coloured substances, after paper
chromatography has been carried out
Climate change: how climates around the
Earth are changing, because of the rise in
average air temperatures
Coagulant: a substance that will make small
particles stick together; coagulants are used
in cleaning up water, ready for piping to
homes
Coke: a form of carbon made by heating
coal
Combination: where two or more
substances react to form a single substance
Combustible: can catch fire and burn very
easily
Combustion: another name for burning
compound fertiliser it provides
nitrogen, potassium, and phosphorus
for plants
Compound ion: an ion containing more
than one element; for example the nitrate
ion NO3
Compound: a substance in which two or
more elements are chemically combined
Concentration: tells you how much of one
substance is dissolved in another; usually
given as grams or moles per dm3
Condensation: the physical change in which
a gas turns into a liquid on cooling
Condensation polymerisation: where
molecules join to make very large molecules,
by eliminating small molecules (such as
water molecules)
condenser a piece of laboratory equipment
used to cool a gas rapidly, and turn it into a
liquid
conductor a substance that allows heat or
electricity to pass through it easily
Contact process the industrial process for
making sulfuric acid
corrosion where a substance is attacked by
air or water, from the surface inwards; the
corrosion of iron is called rusting
covalent bond the chemical bond formed
when two atoms share electrons
covalent compound a compound made of
atoms joined by covalent bonds
cracking reactions in which long-chain
hydrocarbon molecules are broken down to
shorter, more useful molecules
cross-linking the chemical bonds between
the long-chain molecules in some polymers,
that hold the chains together
crude oil the fossil fuel formed over millions
of years from the remains of tiny sea plants
and animals; it is also called petroleum
crystallisation the process in which
crystals form, as a saturated solution cools
D
decomposition reaction where a substance
breaks down to give two or more products
denature to destroy the structure of an
enzyme by heat, or a change in pH
degradeable will break down naturally
(for example through the action of
bacteria)
density tells you how ‘heavy’ something is;
the density of a substance is its mass per
unit volume; for water it is 1g/cm3
diatomic a substance is called diatomic if
its molecules contain two atoms joined by a
covalent bond
diffusion the process in which particles
mix by colliding randomly with each other,
and bouncing off in all directions
displacement reaction a reaction in
which a more reactive element takes the
place of a less reactive one, in a compound
dissolving the process in which a soluble
substance forms a solution
distillation separating a liquid from a
mixture by boiling it off, then condensing it
double bond a covalent bond in which two
atoms share two pairs of electrons
ductile can be drawn out into a wire; for
example copper is ductile
dynamic equilibrium where forward and
back reactions take place at the same rate,
so there is no overall change
E
electrodes the conductors used to carry
current into and out of an electrolyte; they
could be graphite rods, for example.
electrolysis the process of breaking down
a compound by passing a current through it
electrolyte the liquid through which the
current is passed, in electrolysis; the current
is carried by ions in the electrolyte
electron distribution how the electrons in
an atom are arranged in shells (2 ! 8 ! …)
electron shells the different energy levels
which electrons occupy, around the nucleus
electronic configuration another term for
electron distribution
electrons the particles with a charge of 1–
and almost no mass, in an atom
electroplating coating one metal with
another, using electrolysis
element a substance that cannot be split
into anything simpler, in a chemical reaction
empirical found by experiment
empirical formula shows the simplest
ratio in which the atoms in a compound
are combined
endothermic takes in energy from the
surroundings
enzymes proteins made by living cells, that
act as biological catalysts
equilibrium the state where the forward
and back reactions are taking place at the
same rate, in a reversible reaction; so there
is no overall change
ester a compound formed when an alcohol
reacts with a carboxylic acid; esters often
smell of fruit or flowers
evaporation the physical change where a
liquid turns to a gas at a temperature below
its boiling point
exothermic gives out energy
extract to remove a metal from its ore
F
fermentation the process in which the
enzymes in yeast break down sugars, to
form ethanol and carbon dioxide
fertilisers substances added to soil to help
crops grow well
filtering separating solids from liquids by
pouring the mixture through filter paper
filtrate the liquid obtained from filtration
(after the solid has been removed)
flammable burns easily
flue gas desulfurisation the removal of
sulfur dioxide from the waste gases at power
stations, to stop it getting into the
atmosphere
formula uses symbols and numbers to tell
you what elements are in a compound, and
the ratio in which they are combined
forward reaction the reaction in which
the product is made, in a reversible reaction
fossil fuels petroleum (crude oil), natural
gas, and coal; they are called the fossil fuels
because they were formed from the remains
of living things, millions of years ago
fractional distillation a method used to
separate two or more liquids that have
different boiling points
fractions the different groups of
compounds that a mixture is separated into,
by fractional distillation; fractions are
collected one by one
freezing the change from liquid to solid,
that occurs at the freezing point (” melting
point)
fuel a substance we use to provide energy;
most fuels are burned to release their energy
(but nuclear fuels are not)
fuel cell a cell in which a chemical reaction
provides electricity (to light homes and so
on)
functional group the part of the molecule
of an organic compound, that largely
dictates how it reacts; for example the OH
group in molecules of the alcohol family
G
galvanising coating iron with zinc, to
prevent the iron from rusting
giant structure where a very large number
of atoms or ions are held in a lattice by
strong bonds; metals, diamond and ionic
solids such as sodium chloride are all giant
structures
global warming the rise in average
temperatures taking place around the world;
many scientists believe that carbon dioxide
(from burning fossil fuels) is the main cause of it
greenhouse gas a gas in the atmosphere
that traps heat, preventing its escape into
space; carbon dioxide and methane are
examples
group a column of the Periodic Table;
elements in a group have similar properties
H
Haber process the process for making
ammonia from nitrogen and hydrogen, in
industry
half-equation an equation that shows the
reaction taking place at an electrode
halogens the Group VII elements of the
Periodic Table
heating curve a graph showing how the
temperature of a substance changes on
heating, while it goes from solid to liquid to
gas
homologous series a family of organic
compounds, that share the same general
formula and have similar properties
hydrated has water molecules built into its
crystal structure; for example copper(II)
sulfate: CuSO4.5H2O
hydrocarbon a compound containing only
carbon and hydrogen
hydrogenation adding hydrogen
hydrogen fuel cell it uses the reaction
between hydrogen (from a tank), and
oxygen (from the air), to give an electric
current
hydrolysis the breaking down of
a compound by reaction with water
hypothesis a statement you can test by
doing an experiment and taking
measurements
I
incomplete combustion the burning of
fuels in a limited supply of oxygen; it gives
carbon monoxide instead of carbon dioxide
indicator a chemical that shows by its
colour whether a substance is acidic or
alkaline
inert does not react (except under extreme
conditions)
inert electrode is not changed during
electrolysis; all it does is conduct the current
in excess more than is needed for a
reaction; some will be left at the end
insoluble does not dissolve in a solvent
insulator a poor conductor of heat or
electricity
intermolecular forces forces between
molecules
ion a charged atom or group of atoms
formed by the gain or loss of electrons
ionic bond the bond formed between ions
of opposite charge
ionic compound a compound made up of
ions, joined by ionic bonds
ionic equation shows only the ions that
actually take part in a reaction, and ignores
any other ions present; the other ions are
called spectator ions
isomers compounds that have the same
formula, but a different arrangement of
atoms
isotopes atoms of the same element, that
have a different numbers of neutrons
L
lattice a regular arrangement of particles
lime the common name for calcium oxide
limewater a solution of the slightly soluble
compound calcium hydroxide, which is used
to test for carbon dioxide
locating agent used to show up colourless
substances, in chromatography; it reacts
with them to give coloured substances
M
macromolecule a very large molecule; for
example a molecule in a polymer
malleable can be bent or hammered into
shape
mass spectrometer an instrument used to
find the masses of atoms and molecules
melting point the temperature at which a
solid substance melts
melting the physical change from a solid to
a liquid
metal an element that shows metallic
properties (for example conducts
electricity, and forms positive ions)
metallic bond the bond that holds the
atoms together in a metal
metalloid an element that has properties of
both a metal and a non-metal
microbe a microscopic (very tiny) living
organism, such as a bacterium or virus
minerals compounds that occur naturally in
the Earth; rocks contain different minerals
mixture contains two or more substances
that are not chemically combined
molar solution contains one mole of a
substance in 1 dm3 (1 litre) of water
mole the amount of a substance that
contains the same number of elementary
units as the number of carbon atoms in 12g
of carbon-12; you obtain it by weighing out
the Ar or Mr of the substance, in grams
molecular made up of molecules
molecule a unit of two or more atoms held
together by covalent bonds
monatomic made up of single atoms; for
example neon is a monatomic element
monomers small molecules that join
together to form polymers
N
native describes a metal that is found in the
Earth as the element
negative electrode another name for the
cathode, in an electrolysis cell
negative ion an ion with a negative charge
neutral (electrical) has no charge
neutral (oxide) is neither acidic nor basic;
carbon monoxide is a neutral oxide
neutral (solutions) neither acidic nor
alkaline; neutral solutions have a pH of 7
neutralisation the chemical reaction
between an acid and a base or a carbonate,
giving a salt and water
neutron a particle with no charge and a mass
of 1 unit, found in the nucleus of an atom
nitrogenous fertiliser it provides nitrogen
for plants, in the form of nitrate ions or
ammonium ions
noble gases the Group 0 elements of the
Periodic Table; they are called ‘noble’
because they are so unreactive
non-metal an element that does not show
metallic properties: the non-metals lie to the
right of the zig-zag line in the Periodic Table,
(except for hydrogen, which sits alone)
non-renewable resource a resource such
as petroleum that we are using up, and
which will run out one day
non-toxic not harmful health
nucleon number the number of protons
plus neutrons in an atom of an element
nuclear fuel contains radioisotopes such
as uranium-235; these are forced to break
down, giving out energy
nucleus the centre part of the atom, made
up of protons and neutrons
O
ore rock containing a metal, or metal
compounds, from which the metal is
extracted
organic chemistry the study of organic
compounds
organic compound a compound containing
carbon, and usually hydrogen; petroleum is a
mixture of many organic compounds
oxidation a chemical reaction in which a
substance gains oxygen, or loses electrons
oxidation state- every atom in a formula
can be given a number that describes its
oxidation state; for example in NaCl, the
oxidation states are +I for sodium, and – I
for chlorine
oxide a compound formed between oxygen
and an other element
oxidising agent a substance that brings
about the oxidation of another substance
ozone a gas with the formula O3
ozone layer the layer of ozone up in the
atmosphere, which protects us from harmful
UV radiation from the sun
P
paper chromatography a way to separate
the substances in a mixture, using a solvent
and special paper; the substances separate
because they travel over the paper at
different speeds
percentage composition it tells you which
elements are in a compound, and what % of
each is present by mass
period a horizontal row of the Periodic
Table; its number tells you how many
electron shells there are
periodicity the pattern of repeating
properties that shows up when elements are
arranged in order of proton number; you
can see it in the groups in the Periodic Table
Periodic Table the table showing the
elements in order of increasing proton
number; similar elements are arranged in
columns called groups
petroleum a fossil fuel formed over millions
of years from the remains of tiny sea plants
and animals; it is also called crude oil
pH scale a scale that tells you how acidic or
alkaline a solution is; it is numbered 0 to 14
photochemical reaction a reaction that
depends on light energy; photosynthesis is
an example
photodegradeable can be broken down by
light
photosynthesis the process in which plants
convert carbon dioxide and water to glucose
and oxygen
physical change a change in which no new
chemical substance forms; melting and
boiling are physical changes
physical properties properties such as
density and melting point (that are not
about chemical behaviour)
pipette a piece of laboratory equipment
used to deliver a known volume of liquid,
accurately
plastics a term used for synthetic polymers
(made in factories)
pollutant a substance that causes harm if it
gets into the air or water
pollution when harmful substances are
released into the environment
polymer a compound containing very large
molecules, formed by polymerisation
polymerisation a chemical reaction in
which many small molecules join to form
very large molecules; the product is called a
polymer
positive ion an ion with a positive charge
precipitate an insoluble chemical
produced during a chemical reaction
precipitation reaction a reaction in which
a precipitate forms
product a chemical made in a chemical
reaction
protein a polymer made up of many
different amino acid units joined together
proton number the number of protons in
the atoms of an element; it is sometimes
called the atomic number
proton a particle with a charge of 1+ and a
mass of 1 unit, found in the nucleus of an
atom
pure there is only one kind of atoms in a substance
Q
quicklime another name for calcium oxide
R
radioactive isotopes (radioisotopes)
unstable atoms that break down, giving out
radiation
random motion the zig-zag path a particle
follows as it collides with other particles and
bounces away again
rate of reaction how fast a reaction is
reactant a starting chemical for a chemical
reaction
reactive tends to react easily
reactivity how readily a substance reacts
reactivity series the metals listed in order
of their reactivity
recycling reusing resources such as scrap
metal, glass, paper and plastics
redox reaction any reaction in which
electrons are transferred; one substance is
oxidised (it loses electrons) and another is
reduced (it gains electrons)
reducing agent a substance which brings
about the reduction of another substance
reduction when a substance loses oxygen,
or gains electrons
refining (petroleum) the process of
separating petroleum (crude oil) into groups
of compounds with molecules fairly close in
size; it is carried out by fractional distillation
refining (metals) the process of purifying
a metal; copper is refined using electrolysis
relative atomic mass (Ar) the average
mass of the atoms of an element, relative to
the mass of an atom of carbon-12
relative formula mass (Mr) the mass of
one formula unit of an ionic compound; you
find it by adding together the relative atomic
masses of the atoms in the formula
relative molecular mass the mass of a
molecule; you find it by adding the relative
atomic masses of the atoms in it
renewable resource a resource that will
not run out; for example water, air, sunlight
residue the solid you obtain when you
separate a solid from a liquid by filtering
respiration the reaction between glucose
and oxygen that takes place in the cells of all
living things (including you) to provide
energy
reversible reaction a reaction that can go
both ways: a product can form, then break
down again
rusting the name given to the corrosion of
iron; oxygen and water attack the iron, and
rust forms
S
sacrificial protection allowing one metal
to corrode, in order to protect another metal
salt an ionic compound formed when an
acid reacts with a metal, a base, or a
carbonate
saturated compound an organic
compound in which all the bonds between
carbon atoms are single covalent bonds
saturated solution no more of the solute
will dissolve in it, at that temperature
single bond the bond formed when two
atoms share just one pair of electrons
slaked lime another name for calcium
hydroxide
solubility the amount of solute that will
dissolve in 100 grams of a solvent, at a given
temperature
soluble will dissolve in a solvent
solute the substance you dissolve in the
solvent, to make a solution
solution a mixture obtained when a solute
is dissolved in a solvent
solvent the liquid in which a solute is
dissolved, to make a solution
sonorous makes a ringing noise when
struck
spectator ions ions that are present in a
reaction mixture, but do not actually take
part in the reaction
state symbols these are added to an
equation to show the physical states of the
reactants and products (g ” gas, l ” liquid,
s ” solid, aq ” aqueous)
structural formula the formula of a
compound displayed to show the bonds
between the atoms as lines; we often show
organic compounds this way
T
thermal decomposition the breaking
down of a compound by heating it
thermite process the redox reaction
between iron oxide and aluminium, which
produces molten iron
titration a laboratory technique for finding
the exact volume of an acid solution that will
react with a given volume of alkaline
solution, or vice versa
toxic- poisonous
transition elements the elements in the
wide middle block of the Periodic Table; they
are all metals and include iron, tin, copper,
and gold
trend a gradual change; the groups within
the Periodic Table show trends in their
properties; for example as you go down
Group I, reactivity increases
triple bond the bond formed when two
atoms share three pairs of electrons; a
nitrogen molecule has a triple bond
U
universal indicator a paper or liquid you
can use to find the pH of a solution; it
changes colour across the whole range of pH
unreactive does not react easily
unsaturated compound an organic
compound with at least one double bond
between carbon atoms
V
valency a number that tells you how many
electrons an atom gains, loses or shares, in
forming a compound
valency electrons the electrons in the
outer shell of an atom
variable valency- an element shows
variable valency if its atoms can lose
different numbers of electrons, in forming
compounds; for example copper forms Cu+
and Cu2 + ions
viscosity a measure of how runny a liquid
is; the more runny it is, the lower its viscosity
viscous thick and sticky
volatile evaporates easily, to form a vapour
W
water of crystallisation water molecules
built into the crystal structure of a
compound; for example in copper(II) sulfate,
CuSO4.5H2O
weak acids acids in which only some of the
molecules are dissociated, to form H ! ions;
ethanoic acid is a weak acid
Y
yield the actual amount of a product
obtained in a reaction; it is often given as a
% of the theoretical yield (which you can
work out from the equation
prepIGCSE 