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