Cambridge IGCSE Chemistry 3rd Edition

Chemistry

Third Edition

Bryan Earl
Doug Wilford

COMPANION @ 1/. HODDER
EDUCATION
CD

Chemistry

Third Edition

Br yan Earl
Doug Wilford

L1 ~o'a~R1~~
AN HACHETTE UK COMPANY

Internation al hazard warning symbols
You w ill need to be fam ili ar w it h these symbo ls when undertaking practica l experiments in the laboratory.

Corrosive Oxidising
Thesesubstancesattackordestroylivingtissues, These substances provide oxygen which allows other
including eyes and skin . materials to burn more fiercely.

Harmful Toxic
Thesesubstancesa resimilartotoxicsubstancesbut These substances can cause death.
less dangerous.

Irritant Highly flammable
Thesesubstancesarenotcorrosivebutcancause red - These substances can easily catch fire .
dening orblisteringoftheskin.

Teachers and students should note that a new system for labelling hazards is being introduced between 2010 and 2015 and, in due
course, you will need to become familiar with these new symbols:

Physical Hazards ~

~~~0
Explosives Flammable Liquids Oxidizing Liquids Compr~d Gases Corrosive to Metals

Health Hazards Environmental
Hazards
~~~ ~
Skinlrration CMRHSTOTH ~
Acute Skin Corrosion Hazardous to the
Taxi city
Aspiration Hazard Aquatic Environment

® ! GCSE is the registered trademark of Cambridge Imemational Exami nations. The questions, example answers, marks
awarded and/or comments that appear in this book/CD were written by the authors. In examination the way marks
would be awarded to answers like these may be different. Questions from the Cambridge !GCSE Chemistry papers are
reprcxluced by permission of Cambridge Imernational Examinations.

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© Bryan Earl and Doug Wilford 2002

First published in2002 by

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Thisthirdeditionpublished2014

Impres.sionnumber 5 4 3 2 I

Year 2018 2017 2016 2015 2014

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Primedinlraly

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ISBN 978 l 44417644 5

Contents

Acknowledgements vii
Preface to the reader ix

Chapter 1 The particulate nature of matter 10
So lids, liquids and gases 10
Th e kinetic theory o f m atter 13
C hanges o f state 16
Diffusio n - evidence fo r m oving particles 17
Ch ccklist 25
Additio nal qu r:stio ns 26
28
Chapter 2 Elements, compounds and experimental techniques 29
Elements 31
Com po L1nds
Mi xtures 33
Separating mixtures 33
Accuracy in experimental wo rk in the labo ratory 37
Gd s, sols, foa m s and emulsio n s 38
Mixtures fo r streng th 45
Ch ccklist 54
Additio nal qu estio ns 55
56
Chapter 3 Atomic structure and bonding 58
Inside atom s
Th e arrangem ent o f electro ns in atom s 59
Io nic bo ndin g 59
Covalent bonding 59
Glasses and ceramics 61
Metallic bo nding 64
Ch ccklist 66
Additio nal questio ns 69
71
Chapter 4 Stoichiometry - chemical calculations

Relative ato mic mass
Reacting m asses
Calculating m o les
Calculating formub.c
Mo les and chemical equatio ns
Ch ecklist
Additio nal qu estio ns

Chapter 5 Electricity and chemistry 72
73
Electrolysis ofkad(11 ) bromide 74
Electrolysis ofaluminium oxide 77
Electrolysis ofaqueous solutio ns 80
Electro lysis of concentrated hydrochl oric acid 80
Electro lysis of coppcr(11) sulfatc solutio n 83
Electrolysis g uidelines 83
Electroplating 85
Chccklist 86
Additi o nal questions
88
Chapter 6 Chemical energetics 88
Substances from oil 90
Fossilfuds 92
What is a foci? 93
Alternative sources of en ergy 95
Chemical energy 97
C hanges of state 98
Cells and batteries 100
Chccklist 10 1
Additional qu estio ns
104
Chapter 7 Chemical reactions 105
Factors that affect the rate o f a reactio n 111
Enzymes 11 4
C h cc kli st 11 5
Additional questions
117
Chapter 8 Acids, bases and salts 11 7
Acids and alkalis 122
Formatio n o f salts 127
Crystal hydrates 129
Solubility of salts in water 129
Titratio n 132
C h cckli st 133
Additional questions
135
Chapter 9 The Periodic Table 135
Development of the Periodic Table 138
Electro nic stru cture and th e Periodic Table 138
Group I - the alkali metals 140
Group II - th e alkaline earth metals 14 1
Group VII - the hal ogens 143
Group O- th e noble gases 144
Transiti o n elements 146
The position of hyd rogen 146
C h eckli st 147
Additional questions

Chapter 10 Metals 149

Mt:tal reactions 150
Decompositio n of m etal nitrates, carbo nates, oxides and hyd roxid es 152
Reactivity o f metals and their uses 153
ldcntif)1ing metal io ns 155
Discovery o f metals and th eir extracti on 157
Metal waste 161
Rusting of iron 161
Alloys 165
C h cc kli st 168
Additional qu estio n s 169

Chapter 11 Air and wa ter 171
Th e air 17 1
174
H ow do we get the u scfol gases we need fr om the air? 176
Ammonia - an impo rtant nitrogen-containing ch emical 180
Artificial fertilisers 182
Atmospheric pollutio n 184
Water 186
The water cycle 18 7
H;1rdncss in water 190
Water pollution and treatment 193
C h cc kli st 194
Additional questions
197
Chapter 12 Sulfur 197
198
Sulfur - the clement 199
Sulfur di oxide 203
Sulfuric acid 204
C h cc kli st
Additional questions 206
206
Chapter 13 Inorganic carbon chemistry 211
Lim esto n e 212
Carbo nate s 215
Carbon di oxide 216
C h ec kli st
Additional questio ns 218
218
Chapter 14 Organic chemistry 1 220
Alkanes 222
Th e chemical behaviour of alkanes 224
Alkenes 22 6
Th e chemical behaviour of alkenes 230
A special addition reaction of alkene mo lecules 231
C h ec kli st
Additional questions

Chapter 15 Organic chemistry 2 233
Alcohols (R-OH ) 233
Biotechnology 236
Carboxylic acids 237
Soaps and detergents 239
Conden satio n polymers 24 1
Some biopolymcrs 242
P h a r m a c e u t i c als 246
C h cckli st 247
Additi o nal questions 249

Chapter 16 Experimental chemistry 251
Objectives fo r experim ental skills and investigatio ns 25 1
Suggestio ns for practical work and assessment 25 1
Notes o n qualitative analysis 26 1

Revision and exam-style questions 264

Alternative to practical paper 264
Theory 274

The Periodic Table of the elements 294
295
Index

Acknowledgements

The authors would like to thank Irene , Katharine, Michael and Barbara for their never-ending patience and encouragement throughout the pnxluction
of this textbook. Also to Lis, Phillipa, Nina, Eleanor, Will and the publishing ream at H odder Education.

Examination questions

Past examination questions reproduced by permission of University of Cambridge Imemational Examinations.

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•

Preface to the reader

This textbook has been written to help you in your Yo u will sec fro m the b ox at the foot o f this page
study of chemistry to C ambrid ge !GCSE. Th e that the b oo k is divid ed into four different areas
different chapters in this b ook arc split up into o f chemistry: Starter, Ph ysical , Inorganic and Org anic
sh o rt to pi cs . At the end o f many o f these to pics arc ch emistry. We fed , h owever, that some to pics lead
qu esti on s to t est w h eth er you have und e rst ood w hat n aturally o n to oth er topics n ot in th e sam e area. So
you have read. At the end of each chapter there arc you can , o f cou rse, read and study th e chapters in
larger study questio ns. Try to answer as many o f your own preferred ord er and the co lo ur coding will
the questio ns as you c m as you come across them help you with this.
bccau st: asking and answerin g qu estio n s is at the
heart o f your study o f chemistry. The accompanying Revision CD -ROM provid es
invaluable exam preparatio n and practice. We want to
Some questio ns in the style o f C ambrid ge !GCSE test your kno wl ed ge with interactive questi o ns that
examinati on papers arc includ ed at the end o f the cover b o th th e Core and E xtend ed curriculum. Th ese
b ook . In many cases they arc d esig ned to test your arc organised by syllabus to pic.
ability to apply your ch emical knowkd gc. The
qu estion s may provid e certain facts and ask you to Togeth er, th e textbook and C D-R01Vl will p ro,,ide
make an interpretati on o f th em. In su ch cases, the you with the information you need for the Cambridge
fa ctual informati o n may no t be covered in the text . IG CSE syllabus. We hope you enjoy using them.

To help draw attention to the more important Bryan Earl and Do ug Wilford
word s, scientific terms arc printed in bold the fir st
time th ey arc used. There arc also ch ecklists at the
end o f each chapter summarising the impo rtant
points covered.

As you read throu gh th e book, you will no tice
three sorts o f shaded area in th e text.

Material highlighted in green is for the Cambridge
!GCSE Extended curriculum.

Areas hi ghlig hted in yellow contain material that
is n ot part o f the Cam bridge !GCSE syllabus. It is
exten sion work and will no t be examin ed.

Questions are highlighted by a box like this.

We u se different colo urs to defin e diffCrent areas o f ch emistry:

• 'starter' chapters - basic principles
• physical ch emistry
• in o rg anic chemistry
• organic ch emistry and th e living wo rld.

•

This page intentionally left blank

G) The particulate nature of matter

Solids, liquids and gases Diffusion - evidence for moving particles
Brownian motion
The kinetic theory of matter
Explaining the states of matter Check li st

Changes o f state Addit ional questions
Anunusualstateofmatter
An unusual change of state
Heat ing and cooling curves

C hemistry is abo ut what matter is like and how it
be haves, and o ur explanatio ns and predi ctio ns o f
its b ehavio ur. What is matter? This word is u sed to
cover all th e substan ces and materials fr o m w hich
the physical universe is composed. Th ere arc man y
milli o ns o f different substances known , and all of
them can be categorised as solid s, liquid s o r gases
( Fig ure 1.1 ). These arc what we call th e three states
of matter.

a solid c gas
Fi gure 1.1 Waterinthreedifferentstates.
0

THE PARTICULATE NATURE OF MATTER

• Solids, liquids and gases The main points of the theory arc:

A solid, at a g iven temperature, has a definite volume • All matter is mad e up o f tiny, m oving particles,
and shape which may be affected by changes in invisible to the naked eye . Different substances
temperature. Solids usually in crease slightly in size have different types o f particles (atoms, m o lecules
when heated (expansion ) ( Figure 1.2 ) and usually or ion s) which have different sizes.
decrease in size ifcoo led (contraction).
• The particles move all th e time. The high er the
A liquid, at a given temperature, has a temperature, the fa ster they m ove o n average.
fix ed volume and will take up the shape of any
container into which it is p o ured. Like a solid , a • H eavier particles move more slowly than lig hter
liquid 's volume is slig htly affected by changes in on es at a given temperature .
te mp eratur e.
The kin etic theory can be used as a scientific model
A gas, at a given temperature, has neither a d efinite to explain how th e arrangement o f particles relates to
shape no r a definite volume. It will take up the shape the properties of the three states o f matter.
of any container into which it is placed and will
spread o ut evenly within it. Un like th ose o f so lid s Explaining the states of matter
and liquids, th e volumes o f gases arc affected quite
markedly by changes in temperature. In a solid the particles attract o ne another. There
arc attractive forces between th e particl es whi ch
Liquids and gases, unlike solids, arc relatively h o ld the m close t ogeth er. The particles have little
compressibl e. This m ean s that their volum e can be fr eed o m o f m ovem e nt and can o nly vibrate abou t
reduced by the application o f pressure. Gases arc a fi xed position. Th ey arc arranged in a regular
much more compressible than liquids. manne r, whi ch exp lains w h y man y so lid s form
cr ystal s.

It is possible to m odel su ch crystals by using
spheres to represent the particles ( Fig ure 1. 3a ). If th e
spheres arc built up in a regular way then the shape
compares very closely with that o f a part o f a chrome
alum crystal ( Fig ure 1. 3b).

• The kinetic theory a Amodei of a chrome alum crystal. b An actual chrome alum crystal.
of matter Figure 1.3

The kinetic theory helps to explain the way in which Studies using X-ray crystall ography (Figure 1.4) have
matter behaves. The evidence is consistent with the confirmed how the particles arc arranged in crystal
idea that all matter is made up of tiny particles. This stru ctures. VVhc n crystals o f a pure substance form
theory explains the physical properties of matter in under a g iven set o f conditions, the particles present
arc always packed in th e sam e way. H owever, th e
•term s o f the m ovem ent o f its constitu ent particles. particles may b e packed in different ways in crystals
o f different substances. For example , comm on salt
(sodium chl oride) has its particles arranged to give
cubic crystals as sh own in Fig ure 1.5.

The kinetic theory of matter

ln a liquid the particl es arc still cl ose togeth er but
they m ove around in a rando m way and o ft en collide
with o ne ano ther. The fo rces o f attractio n between
the particles in a liquid arc weaker than th ose in a
solid. Particles in the liquid form o f a substance have
m ore energy o n average than the particles in the solid
fo rm o f th e sam e substan ce .

In a gas the particles are relatively fur apart. They arc
frt..: to move anywhere \\~thin the container in which they
arc held. They move randomly at very high velocities,
much more rapidly than those in a liquid. They collide
with t.-ach other, but less o ften than in a liquid, and they
also collide with the walls of the container. They exert
virtually no forces o f attraction on each other because
they arc relatively fur apart. Such forces, however, arc very
significant. lfthcy did not exist we could no t have solids
or liquids (sec Changes of state, p. 4 ).

The arran gem ent o f particles in solids, liquids and
gases is sh own in Figure I .6 .

solid
Particles o nly vibrate abo ut fixed positi ons.
Regular stru cture.

Figure 1.4 A modem X-r<11 crystallography instrument, used for stU(fying liquid
crystalstruc:ture. Particl es have some fre edom and can move
aro und each othe r. Co llide often.

Figure 1.5 Sodium chloride crystals. gas
Particles move freely and at random in all
th e space availabl e. Collide less often than
in liquid.

Figure 1.6 Thearrangementofparticlesinsolids, liquids and gases.

Questions

1 VV'hen a metal such as copper is heated it expands. Explain
what happens to the metal particles as the solid metal expands.

2 Use your research skills on the Internet to find out about
the technique of X-ray crystallography and how this
technique can be used to determine the crystalline structure
of solid substances such as sodium chloride.

0

THE PARTICULATE NATURE OF MATTER

• Changes of state call ed the boiling point o f the substance. At the
bo iling po int the pressure o f the gas created above
The kinetic th eory m odel can b e used to explain the liquid equals that in the air - atmospheric
h ow a substance changcs fro m o n e state t o pressure.
an o the r. If a solid is h eated th e particles vibrate
faster as they g ain en ergy. This m akes th em ' push ' Liquids with hig h boiling points have stronger
th cir neig hbo uring particles forth cr away fr o m fo rct:s between their particles than liquid s with low
th em selves . This cau ses an increase in th e volum e bo iling po ints.
o f the solid , and th e solid ex pands. Expansio n ha s
taken place. Wh en a gas is cooled tht: avcr.i.gt: energy o f the
particles decreases and the particles m ove closer
E ventually, the heat e n e rgy cau ses th e fo rces together. The fo rces o f attraction between the
o f attrac tio n to weaken. Th e regular pattern o f particles n ow becom e significant and cause the gas
the stru cture breaks d own. The particles can n ow to condense into a liquid. When a liquid is cooled
m ove a round eac h o the r. Th e solid has melted . it freezes to fo rm a so lid. In each o f these changes
Th e tcmpnaturc at w hi ch thi s takes place is energy is g iven o ut.
called th e melting point o f th e substa nce. Th e
temperature o f a pure melting solid will n o t ri se C han ges o f state arc examples o f physical changes.
until it has all m elted. Wh en th e substance has \..Yh cn cvcr a physical ch ange o f state occurs, th e
becom e a liquid th ere arc still very sig nificant temperature remains constant during the change
fo rces o f attractio n between the particles, which is (sec H eating and cooling curves, p . 5 ). During a
why it is a liquid ;md n o t a g as. physical chan ge no new substance is fo rmed.

Solid s which have high melting po ints have An unusua l st at e of matter
st ronger fo rces o f attractio n between their particles
than th ose which have low melting points. A list of Liqu id crystals arc an unu sual state o f matter
som e substances with their corresp o nding melting (Fig ure 1.7 ). Th ese substan ces look like liquid s
and b oiling points is shown in Table 1.1. and fl ow like liquids but have som e o rder in th e
arrangem ent o f the particles, and so in som e ways
Table 1 1 Meltingpointl°C Bo ilingpointl°C th ey behave like crystals.
Substance 661 2467
Aluminium
Et hanol -117 79
Magnesium oxide 827 3627
Mercury -30
Methane -182 357
Oxygen -218 -164
Sodium chloride 801 -183
Sulfur 113 1413
Water
445
100

If the liquid is heated the particles will m ove aro und Figure 1.7 A polarised light micrograph of liquid crystals.
even fa ster as their average energy increases . Som e
particles at the surface o f th e liquid have en o ug h Liquid crystal s are n ow part o f o ur everyday
en ergy to overcom e the fo rces o f attr.i.ctio n between life . Th ey arc w idely used in displays for di gital
them selves and the o ther particl es in the liquid and watch es , calculato rs and lap -to p computers, and
they cscapt: to fo rm a gas. The liquid begins to in televisio ns (Figure 1.8 ). They arc also useful
evaporate as a gas is form ed . in thermo m eters because liquid crystals change
colo ur as the temperature rises and fall s.
Eventu ally, a tempcr.i.turc is reach ed at which
the particles arc trying to escape fr om the liquid so
quickly that bubbles o f gas actually start to fo rm

•inside the bulk of th e liquid. This temperature is

Changes of state

solid liquid gas

Figure1.10 Summaryofthechangesofstate.

Heating and cooling curves

Figure 1.8 Liquid crystals are used in this TV screen. Th e g raph sh ow n in Fi g ure 1.11 was dra w n

An unusual change of state by pl o ttin g th e te mp e rature o f wat er as it was
he ated ste adil y fr o m - 15 °C t o 110 °C. Yo u can
There arc a few substances that change directly fr om sec fro m th e cur ve that chan ges o f state ha ve
a solid to a gas when they arc heated with out ever
becoming a liquid. This rapid spreadin g o ut o f the taken place. \¥hen the temperature was first
particles is called sublimation. C ooling cau ses a
change fr om a gas directly back to a solid. Examples m easured o nl y ic e was present. After a sh o rt tim e
o f substances that behave in this way arc carbo n
dioxide ( Fig ure 1.9) and io dine. th e curve flatt e n s, sh ow in g that eve n th o u g h
heat en ergy is being put in , the tempe rature

------remains constant.
110
100 - - - - - - - - - - - -
U I liquid and I all

)ro : !~st~:~~~ : gas

.;= water

1 vapour) 1

1

[ all = ,-01"1"a'",'",a'" 1"iq'u""17a ,' a11 1
so 1d liquid 1
E (ice) l(ice and liquid I
~~~~ :
-2:! 0 I
-15

lwater) 1

time/minutes

Figure 1.11 Graph of temperature against time for the change from ice
at -15 •c to water to steam.

Figure 1.9 Dry ice (solid carbon dioxide) sublimes on heating and can be ln ice the particles o f water arc close together and arc
usedtocreatespecialeffectson stage. attracted to o ne an other. Fo r ice to melt the particles
must o btain sufficient energy to overcom e th e fo rces
C arbon dio xid e is a white solid called dry ice at o f attractio n between the water particles to allow
temperatures below - 78 °C. \¥ h en heated to just relative m ovem ent to take place. This is wh ere the
above -78 °C it changes into carbo n dioxide gas. The heat energy is going.
changes o f state arc summarised in Figure 1.10.
The temperature will begin to ri se ag ain o nly after
all th e ice has melted. G enerally, th e heatin g curve
fo r a pure solid always sto ps ri sin g at its meltin g
p o int and gives rise to a sharp melting po int. A
sharp melting po int indicates a pure sample . Th e
additio n o r presence o f impurities lowers the
melting po int. Yo u can try to find the melting

•po int o f a substance using the apparatus shown in

Fig ure 1.1 2 .

THE PARTICULATE NATURE OF MATTER All gases diffu se to fill th e space available. In
the rmo meter Fig ure 1.1 3, afte r a d ay the brown- red fum es o f
gaseous b romine have spread evenly thro ug ho ut
ru bber band melting point b o th gas jars fro m th e li q uid present in th e lowe r
o il tube gas ja r.

s o lid

Fi gure 1. 12 Apparatus shown here if heated slowly c.an be used Figure 1.13 After 24 hours the bromine fumes have diffused throughout
to find the melting point of a substance such as the solid in the melting both gas jars.
point tube.
Gases diffi.1sc at diffe re nt rates . If o n e piece o f
In the s:um: way, if you want t o b o il a liquid su ch cotto n wool is soa ked in con centrated amm onia
as water you have t o g ive it som e extra e n e rgy. This soluti o n and an o ther is soaked in concentrated
can be seen o n the graph (Fig ure 1.11 ) where the hyd rochl oric acid and these arc put at o pposite
cur ve levels o ut at 100 °C - th e bo iling po int of e nds of a dry gla ss tube, the n afte r a few minutes
wa te r. a white cloud o f amm o nium chloride appears
( Fig ure 1.14). This sh ows th e p ositio n a t w hi ch
Solid s and liquid s can be identified fro m th eir th e two gases meet and react . The white cloud
characteristic melting and bo iling po ints. fo rms in the positi o n sh own b ecau se the a mm o nia
particles arc lig hte r a nd have a sm alle r rela tive
The reverse processes o f conde n sing and freezing m olecular m ass ( C h apter 4 , p. 62 ) than the
occur on cooling . This tim e, h owever, e ne rgy is g iven hyd rogen chlo ride particles ( released fro m th e
o ut when the gas cond enses to the liq uid and the hyd rochl oric acid ) and so m ove fa st e r.
li q uid freezes to give the solid.

Questions

1 Write down as many uses as you can for liquid crystals.
2 Why do gases expand more than solids for the same

increase in temperature?
3 Ice on a car windscreen will disappear as you drive

along, even without the heater on. Explain why this
happens.
4 When salt is placed on ice the ice melts. Explain why.
5 Draw and label the graph you would expect to produce if
water at 100°( was allowed to cool to -S 0 C.

• Diffusion - evidence for Diffu sio n also takes pl ace in liq uid s ( Fi gure 1.1 5)
moving particles but it is a mu ch slower process than in gases. This
is becau se the particles o f a liq uid m ove much m ore
VVh en you walk past a cosm e tics counter in a slowly.
department st o re you can u su ally smell th e perfi.unes.
Fo r this to happe n gas particles must be leaving o pen W hen diffi.1sion takes place between a liquid and a gas
pcrfomc bottles and be spreading o ut th rough th e it is known as intimate mixing . The kinetic theory can
air in the sto re. This spreading out o f a gas is called be used to explain this process. It states that collisions
dif fusio n and it takes place in a h aph azard and arc taking place rando mly between particles in a liquid
rando m way. or a gas and that there is sufficient space between the
particles o f one substance for the particles o f the o ther
substance to move into .

0

Diffusion - evidence for moving particles

Questions

1 When a jar of coffee is opened, people in all parts of the
room soon notice the smell. Use the kinetic theory to
explain how this happens.

2 Describe, with the aid of diagrams, the diffusion of
nickel(u) sulfate solution.

3 Explain why d iffusion is faster in gases than in liquids.

Brownian motion

Evidence fo r th e m ovem ent o f particles in liquids
cam e to li ght in 1827 wh en a botanist, Ro bert
Brown, o bserved that fin e po llen g rains o n the
surface o f water were no t stationary. Throug h his
microscope h e n oticed th at the g rains were m m'ing
abo ut in a rando m way. It was 9 6 years later, in
19 2 3, that ano ther scientist called N orbert Wien er
explained wh at Brown had o bserved. H e said that
the po llen grains were m oving becau se the mu ch
sm aller and fa ster-moving water particles were
constantly colliding with them (Fig ure 1.1 6a ).

1l1is random motion o f visible particles (pollen grains)
caused by much sm aller, invisible o nes (water particles )
is ea.lied Brownian m o tion (Figu re 1.16b ), after the
scientist who first observed this plu.110menon. It was used
as evidence fo r the kinetic particle modd of matter (p. 3).

Figure 1.14 Hydrochloric acid (left) and ammonia (right) diffuse at Figure 1.16a Pollen particle being bombarded by water molecules.
differentrate5.
•
G!

I

ab Figure 1.16b Brownian motion causes the random motion of the visible
Figure 1.15 Diffusion within nickel(1)sulfatesolutioncantakedaysto
•particle.
reachthestageshownontheright.

THE PARTICULATE NATURE OF MATTER

Checklist • Evaporation A process occurring at the surface of a liquid
involving the change of state of a liquid into a vapour at a
After studying Chapter 1 you should know and understand the temperature below the boiling point.
following terms. Kinetic theory A theory which accounts for the bulk
• Atmospheric pressure The pressure exerted by the properties of matter in terms of the constituent particles.
Matter Anything which occupies space and has a mass.
atmosphere on the surface of the Earth due to the weight Melting point The temperature at which a solid begins to
of the air. liquefy. Pure substances have a sharp melting point.
• Boiling point The temperature at which the pressure of Solids, liquids and gases The three states of matter to
the gas created above a liquid equals atmospheric pressure. which all substances belong.
• Condensation The change of a vapour or a gas into a
liquid. This process is accompanied by the evolut ion of heat. • Sublimation The direct change of state from solid to gas
• Diffusion The process by which different substances mix and the reverse process.
as a result of the random motions of their particles.

•

Q The particulate nature of matter

• Additional questions c The white clo ud fo rmed furth er fro m the cotton
wool soaked in ammo nia.
1 a Draw diagram s to show the arrangem ent o f
particles in: d Cooling the concentrated ammo nia and
( i) solid lead hydrochlo ric acid before carrying o ut the
( ii) molten lead experim ent increased the time taken fo r the
(iii) gaseous lead. white clo ud to fo rm.

b E xplain how the particles m ove in these three 6 The fo llowing diagram sh ows th e three states o f
states o f m atte r. matter and h ow they can be interchanged.

c E xplain , u sing the kinetic theory, what happens
to the particles in oxygen as it is cooled d own.

2 E xplain the m eanin g o f each o f the fo llowing

terms. In your an swer includ e an example to help

with your explanatio n .

a E xpansio n . d Sublimation.

b Contractio n. e Diffusio n.

c Physical change. f Rando m m o ti on. a Na.me the changes A to E .
b Name a substance which will undergo change E .
3 :i Why d o solids no t diffuse? c Name a substance which will undergo changes from
b Give two examples of diffu sio n of gases and
liquids found in the ho use. solid to liquid to gas between 0 °C and 100 °C.
d D escribe what happen s to the particles o f the
4 U se th e kinetic th eory to explain th e followin g:
:i When you take a block o f butter o ut o f solid during ch ange E.
th e frid ge, it is quite hard. H owever, after e Which o f th e changes A to E will involve:
15 minutes it is soft en ou gh to spread.
b W hen you com e h o me fro m school and op en th e (i) an input o f h eat en ergy?
d oor you can smell your tea being coo ked. (ii) an o utput o f heat energy?
c A fo otball is blown up until it is hard o n a ho t
summer's day. In th e evening the football feel s 7 Some ni ckd(11 ) sulfate solutio n was carefull y placed
s o ft e r. in the b otto m o f a b eaker o f water. Th e beaker was
d When a person wearing perfume enters a roo m then covered and left fo r several days .
it takes several minutes fo r the sm ell to reach th e
back of the room. beaker
e A windy day is a good drying day.

5 The apparatu s shown below was set up.

glass tube nick e l(n)

~----~--:~:~~nI Pll
cotton w ool soaked cotto n w ool soaked a D escribe what you would sec after:
in co ncentrated in concentrated (i) a few h o urs
hydrochlo ric ac id ammo nia solutio n (ii) several days .

Give explanatio n s fo r th e followin g o b servatio ns. b E xplain your answer to a u sing your ideas o f th e
:i The fo rmatio n o f a white cloud . kinetic theo ry o f particles.
b It took a fe w minutes before the white clo ud
c What is the nam e o f the physical process that
fo rmed. takes place in this experiment?

0

® Elements, compounds and
experimental techniques

Elements Separating solidr'solid mixtures
Atoms - the smallest particles Criteria for purity
Molecules
Accuracy in experimental work in the laboratory
Compounds Apparatus used for measurement in chemistry
More about formulae
Balancing chemical equations Gels, sols, foams and emulsions
Instrumental techniques
Mixtures for strength
Mixtures Composite materials
What is the difference between mixtures and compounds?
Checklist
Separating mixtures
Separating solid,1iquid mixtures Additional questions
Separating liquid/liquid mixtures

The universe is m ad e u p o f a very large number o f
substances (Fig ure 2. 1), and o ur own world is n o
nccption. If this vast array of substances is namincd
m ore closely, it is fo und that they arc mad e u p o f some
basic substances which wcn: given the nam e elements
in 166 1 by Robert Boyle.

Figure 2.1 The planets in the universe are made of millions of • Elements
substances. These are made up mainly from just 91 elements w hich occur
naturally on the Earth. Robert Boyle used the nam e clement fo r an y
su bstan ce that cann o t be broken d own furth er, into a
In 1803, Jo hn D alto n ( Figure 2.2 ) su ggested that simpler su bstance. This definiti o n can be ex tended to
each clem ent was composed o f its own ki nd o f includ e the fac t that each clement is mad e up o f o nly
particles, whi ch he called ato m s. Ato m s arc mu ch too o ne kind o f ato m. The word ato m comes fr o m the
sm all to be see n. We n ow know that about 20 x 106 G reek word atomos meaning ' unsplittable' .
o f them wo uld st retch over a len gth of o nly 1cm.

Elements

For c.xamplt: , aluminium is an clement whi ch is aGoldisverydecorative.
mad e up of o nly aluminium atoms. It is no t possible b Alumin ium has many uses in the aerospace industry.
to obtain a simpler substan ce chemi cally from
the aluminium atoms. You can o nly make m ore
compli cated substances fr om it, su ch as aluminium
ox ide, aluminium nitrate o r aluminium sulfatc.

There are 118 ele ments which have now been
identified . T wenty-seven o f these do n ot occur in
nature and have been made artificially by scientists.
They includ e elem ents such as curium and
unnilpentium . Ninety-one of the elements occur
naturally and range fro m some very reactive gases,
su ch as flu orine and chlo rine, to gold and platinum,
which arc unreactive elem ents.

All elements can be classified according to their
vari o us properties. A simple way to d o thi s is to
classify them as met:ils or non -metals (Fig ures 2.3
and 2.4, p. 12 ). Table 2.1 sh ows the physical data for
some comm on metallic and no n -m etallic elem ents.

You will no tice that many metals have hig h
densities, hig h melting points and hig h boiling
points, and that m ost no n -m etals have low de nsities,
low melting points and low boiling points. Table 2.2
summarises the diftCrent properties o f metals and
n on -m etals.

A discussio n o f the chemical properties o f metals is
given in C hapters 9 and 10. The chemical properties
of certain n on -m etals are discussed in Chapters 9, 12
and 13.

Table 2.1 Physical data for some metallic and non-metallic elements at
room temperature and pressure.

Element Metal or Den sity/ Melt ing Bo ili n g
non-metal gcm-l po in t! ° ( p o in t! ° (
Aluminium Metal
Copper Metal 2.70 660 2580
Gold Metal 8.92
Iron Metal 19.29 1083 2567
L~d Metal 7.87
Magnesium Metal 11.34 1065 2807 cThesecoinscontainnickel.
Nickel Metal 1.74 Figure2 .3 Somemetals.
Silver Metal 8.90 1535 2750 Tab le 2.2 How the properties of metals and non-metals compare.
Zinc Metal 10.50
Carbon Non-metal 7.14 328 1740
Hydrogen Non-metal 2.25
Nitrogen Non-metal 0.07° 649 1107 Property Metal Non-metal
Oxygen Non-metal 0.88b
Sulfur Non-metal 1.15c 1453 2732 Physical state at room Usually solid Solid, liquid or gas
2.07
962 2212 temperature (occasionally liquid)

420 907 Malleability Good Poor-usuallysoftor

Sublimesat3642 t -- - - - - - - t - - - - - - - - 1 brittle
Ductility Good

-259 -253 Appearance(solids) Shiny(lustrous) Dull

-210 -196 Melting point Usually high Usually low

-218 -183 Boiling point Usually high Usually low

113 445 Density Usually high Usually low

So urce: Earl B., Wilford L.D.R. Chemistry data book. Nelson Blackie, Conductivity(thermal Good Very poor •
1991 • At-254°C bAt-197 °C ' At-184'C. and electrical)

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

a A premature baby needs oxygen. Atoms - the smallest particles

b Artists often use charcoal {carbon) to produce an initial sketch. Ever ything is mad e up o f billi o ns o f ato m s. Th e
ato ms o f all elements arc extremely sm all ; in
c Neon is used in advertising signs fa ct th ey arc t oo sm all t o be seen. The sm allest
Figure 2.4 Some non-metals. ato m known is hydrogen, with each ato m being
represented as a sphere having a diam eter o f
0.00000007 mm (or 7 x 10-8 mm ) (Table 2.3 ).
Ato m s o f diffe re nt ele m e nts have diffCrc nt diam e t e rs
as well as diffe re nt masses . H ow many a t o m s o f
hyd rogen would have to be placed side by sid e
alo n g the ed ge o f your ruler t o fill ju st on e o f th e
I mm division s1

Table 2.3 Sizes of atoms.

Atom Diameter of atom/mm
Hydrogen ] X JQ---11
Oxygen 12 X 10---8
Sulfur 20.B x 10---11

C he mist s u se sh orthand symbo ls t o label th e
ele m ents and their ato m s. Th e symbo l con sist s o f
o ne, two or three letters, th e first o f w hich must be a
capital. W he re several ele m ents have the sam e initial
letter, a second letter o f th e nam e o r subsequ ent
lette r is added. For example, C is used fo r carbon ,
Ca fo r calcium and Cl fo r chlorine. So me symbo ls
seem t o have no rela tio nship t o the n am e o f the
cle m ent, fo r example Na fo r s odium and Pb fo r
lead. These sym bols com e fro m their Latin nam es,
n atrium fo r sodium and plumbum for lead. A list o f
som e comm on eleme nts a nd their symbo ls is given in
Table 2.4.

Molecules

The ato m s o f som e elem ents arc jo ined together in
sm all groups. These small groups o f ato m s arc ca ll ed
molecules. Fo r example, the ato m s o f the elem ents
hyd rogen , oxygen , nitrogen , flu o rin e, chlo rine,
b romin e and io din e are each jo in ed in pairs and they
arc kn own as dia t o mic molecules. In the case o f
phosph o ru s and sulfor th e ato ms are jo in ed in larger
numbe rs, fo ur a nd eig ht respectively ( P4 , S8 ) . In
ch emical sh orthand the m o lecule o f chlorine sh own
in Fi g ure 2.5 is w ritte n as C l2 .

Compounds

Table 2.4 Some common elements and their symbols. The Latin names Cl - Cl
ofsomeoftheelementsaregiven in brackets. a As a letter-and-stick model.

Element Symbo l Phy sical st at e at room b As a space-filling model.
temperature and pres sure Figure2.S Achlorinemolecule.
Aluminium
Argon Al Solid M olecules arc no t always fo rmed by ato m s o f th e
Barium A, Gas sam e type jo ining together. For example, water exists
Soroa Ba Solid as m olecules containing oxygen and hyd rogen ato ms.
Bromine
Calcium ,, Solid Questions
Carbon Liquid
Chlorine Ca Solid 1 How would you use a similar chemical shorthand to write a
Chromium representation of the molecules of iodine and fluorine?
Copper (Cuprum) Solid
Fluorine Cl Gas 2 Using the Periodic Table on p . 294 write down the symbols
German ium for the following elements and give t heir physical states at
Gold(Aurum) c, Solid room temperat ure:
Helium c, Solid a chromium b krypton c osmium.
Hydrogen
Iodine Gas • Compounds
lron(Ferrum) Ge Solid
Lead(Plumbum) A, Solid Compm mds arc pure substanccs which arc formed when
Magnesium He Gas two or more elements chemically combine together.
Mercury(Hydragyrum) Water is a simple compound fo rmed from the elements
Nroa Gas hydrogen and oxygen ( Figure 2 .6 ). This combining of
Nitrogen Solid the elements can be represented by a word equatio n:
Oxygen Fe Solid
Phosphorus Pb Solid hyd rogen + oxygen ---,. water
Potassium(Kalium) Mg Solid
Silicon Hg Liquid Hydrogen Oxygen Hydrogen and Water
Silver(Argentum) Ne Gas a pure a pure oxygen mixed a pure
Sodium {Natrium) Gas element element t ogether compo und
Sulfur Gas formed from
Tin(Stannum) Solid hydrogen
Zinc Solid burning in
Solid oxygen
Ag Solid
Na Solid
Solid
Sa Solid
Za Solid

The co mplet e list of the elements w ith their co rrespo nding symbo ls
is shown in the Periodic Tabl e on p. 294.

The gaseous elem ents helium , neon , argon ,
krypto n , xen o n and rad o n arc composed o f separate
and individu al ato m s. W h en an clem ent ex ists
as se parate ato m s, then th e m o lecules arc said
to be monatomic . In ch emi cal sh o rth and these
m o nato mi c m o lecules arc written as H e, N e, Ar, Kr,
Xc and Rn resp ectively.

Fi gure 2.6 The element hydrogen reacts with the element oxygen to
produce the compound water.

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

\..Yater m o lecules co ntain two ato ms o f hyd rogen A redox reactio n is o ne whi ch involves the two
and on e atom o f o xygen , and hence water has
the chemical fonnula H 20 . Elemen ts o ther than processes o f redu ctio n and oxidati o n. Fo r example ,
h yd rogen will also react with oxygen to form
compo und s called oxid es . Fo r example, m agm:sium the o xygen has to b e rem oved in th e extracti on
reacts vio lently with oxygen gas to fo rm th e white
powder magnesium oxid e (Fi g ure 2.7). This reactio n o f iron fro m iron( m ) ox ide . This can be d o ne in a
is accompanied by a release o f energy as new ch emical
b ond s arc fo rmed. blast furnace with carbon mo noxide. The iron( m )

o xide loses o xygen to the carbon m on o xide and is

reduced to iron. C arbo n m on oxide is the reducing

agent. A reducin g agent is a substance that reduces

an o ther substance during a red o x reactio n. C arbo n

m o n oxid e is o xidised to carbon dio xide by the

iron( m ) oxid e. 1l1c iron(m ) o xide is the oxidising

agent. An oxidi sing agent is a substance which

o xidises ano ther substance during a rcd o x reacti on.

iron (m ) + carbo n ---> iron + carbo n

oxide m on ox ide d i o xid e

Fo r a furth er discussion o f o xidatio n and reduction
sec C hapter 3 (p. 39 ) and C hapter 5 (p. 73 ).

Bo th reduction and oxidation have taken place in
this chemical process, and so this is known as a redox
reactio n.

More about formulae

Th e fo rmula of a compound is ma.d e up fr om the
symbols of the elements present and numbers to sh ow
the ratio in which the different ato m s arc present.
Car bon dioxid e has the formula C 0 2 . This tells you
that it contains on e carbo n ato m fo r every two oxygen
ato ms. The 2 in th e fo rmula tells you that there arc
two oxygen ato m s present in each m o lecule o f carbon
dioxide. Fo r furth er discussion sec p. 4 3 .

Table 2. 5 sh ows the names and fo rmulae of som e
comm o n compounds whi ch you will m eet in your
study o f chemistry.

Tabl e 2.5 Names and formulae of some common compounds.

Figure 2.7 Magnesium burns brightly in oxygen to produce magnesium Compound Formula
oxide. Ammonia NH
Calcium hydroxide Ca(OH)2
Wh en a new substan ce is fo rmed during a chemical Carbon dioxide
reactio n , a chemic.-.1 change has taken place. Copper sulfate co,
Ethanol(alcohol)
m agnesium + oxygen ----> mag nesium ox id e Gltx:ose HCI
Hydrochloric acid
\iVh cn substances such as hyd rogen and m agnesium Nitric acid NaOH
combin e with oxygen in this way they are said to have Sodium carbonate
been oxidised. Th e p rocess is kn own as oxidation. Sodium hydroxide
Sulfuricacid
Reduction is th e o pposite o f oxidatio n. In this

•p rocess oxygen is rem oved instead o f being add ed .

Compounds

The ratio o f ato m s within a chemical compound There are now t wo ato m s o f mag nesium o n the
is usually con stant. Compo und s an:: mad e up o f right-h and side and o nly o ne o n the left. By placing a
fi xed proportion s o f elemen ts: they have a fi xed 2 in fro nt o f the magn esium , we o btain th e following
compositio n. C hemi sts call this the Law of co n stant balanced chemical equatio n:
composition.
2M g(, ) + 0 2(g) ----""--. 2Mg0 (, )
Balancing chem ica l equat io ns
This balanced chemical equatio n now shows u s that
Wo rd equatio n s are a useful way o f representing two ato m s o f mag nesium react with o ne m o lecule
chemical reacti o ns but a better and m o re u seful o f o xygen gas when heated to produ ce two units o f
method is to produ ce a balanced chemic."11 equation. magn esium oxid e.
This type o f equatio n gives the formulae o f the
reactants and th e produ cts as well as sh owing the Instru ment al t echniq ues
relative numbers o f each particle involved.
Elements and compo unds can be de tected and
Balan ced equati o ns o ften include th e physical state id entifie d by a vari et y o f instrum ental m etho d s.
sy m b o ls: Scientist s have deve lo p e d in strum ental t echniqu es
that all ow u s to pr o b e and di scover w hi ch
(s) =solid, (!) = liquid, (g) = gas, (aq) = aqueous solution el em e nts are prese nt in the substan ce as well
as how the atom s are arranged within the
The wo rd equatio n to represent th e reaction between sub st a n ce .
iron and sulfur is:
Many o f the in strumental me th o d s that have
iron + sulfor ~ iron (11 ) sulfide been d evelo ped arc quite sophisticated. So m e
m eth o d s arc suited t o id enti fy in g e lem ents . Fo r
\.Yh en we replace the words with symbo ls fo r the example , ato mi c ab sorpti o n spect roscopy all ows
reactants and th e produ cts and include their physical the clem e nt to b e id entified and also all ows the
state symbo ls, we o btain: quantity o f th e cle m ent that is present t o be fo und
( Fi g ure 2.8 ).
Fc(s) + S(s) ----""--. FcS(s)

Since there is the sam e number o f each type o f atom
o n b oth sid es o f the equatio n this is a balanced
chemical equati o n.

In the case o f magn esium reactin g with o xygen ,
the word equatio n was:

magn esium + o xygen ~ magn esium oxide

\.Yh cn we repl ace the word s with symbo ls fo r the
reactants and th e produ cts and includ e their physical
state symbo ls, it is impo rtant to rem ember that
oxygen is a diato mic mo lecule:

Mg(s) + 0 2 (g) ----""--. MgO(s) Figure2.8 Thisinstrumentallowsthequantityofaparticular element
to be found. It is used extensively throughout industry for this purpose.
ln the equatio n there are two o xygen ato m s It will allow even tiny amoun ts of a particular element to be found.
o n the left-hand side ( 0 2 ) but o nly o ne o n the
rig ht ( M g O ). We cann o t change th e fo rmula o f So me metho d s arc particularly suited to the
mag nesium o xide, so to produ ce th e necessary two identificatio n o f compo unds. For example, infrared
oxygen atom s o n the rig ht-hand side we will need spect roscopy is u sed to id entif)1 compounds by
2Mg0 - this means 2 x MgO. The equatio n now sh owing th e presen ce o f particular gro upings o f
b ecomes: ato m s ( Fi gure 2 .9 ).

Mg(, ) + 0 2 (g) ----""--. 2M g0 (, )

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

• Mixtures

M any everyday things arc n ot pure substan ces,
they arc mixtures. A mixture contains m ore than
o ne substance ( elements and/or com po unds).
An example o f a commo n mixture is sea watt:r
( Figure 2 .10).

Fi gure 2.9 This is a modem infrared spectrometer. It is used in analysis
to obtain a so-called fingerprint spectrum of a substance that will allow
thesubstancetobeidentified.

lnfrarcd spect roscopy is used by the pharmaceutical Figure 2.10 Sea water is a common mixture.
industry to identify and discriminate between dru gs
that arc similar in stru cture, fo r example penicillin- Other mixtures include the air, which is a mixture
type drugs. U sed b o th with organic and in organic o f elements su ch as oxygen , nitrogen and neon and
m o lecules, this m ethod assumes that each compound compo unds such as carbon dioxid e (sec C hapter 11 ,
has a uniqu e infrarcd sp ectrum. Samples can be so lid , p. 173 ), and alloys such as brass, which is a mixture
liquid or gas and arc u sually tin y. H owever, N e, H e, o f copper and zinc ( fo ra furth er discu ssio n o f all oys
0 2 , N 2 o r H 2 canno t be used. sec C h apter l 0 , p. 165 ).

This m ethod is also used to m onitor en viro nmental Wh at is t he d iffere nce between
po llutio n , and has bi ological uses in m o nitoring mixtures a nd compo unds?
tissue physio logy includin g oxygenation , respiratory
stah1s and blood fl ow damage . Th ere arc differen ces between compo unds and
mixtures. This can be sh own by con sidering the
Fo ren sic scientists make u se o f b o th th ese reactio n between iron filin gs and sulfur. A mixture
techniqu es b eca u se they arc very accurate but they o f iron filin gs and sulfur looks different fr o m the
o nl y require tin y am o unts o f sample - o fte n o nl y individu al elem ents (Figure 2 . 1 1). This mixture has
sm all am o unt s o f sample arc fo und at crim e sce n es. the prop erti es o f both iron and sulfur; fo r example , a
Othe r tec hniques utilised arc nucl ear m agnetic magn et can be u sed to separate the iron filin gs fro m
resonan ce spect rosco py and ultravio let /visibl e the sulfur ( Fig ure 2 . 12 ).
spec t roscopy.
Substances in a mixture have no t undergon e
Questions a ch emical reactio n and it is possible to separate
them p rovided that there is a suitabl e difference
1 Write the word and balanced ch emical equat ions for t he in their physical p roperties . If the mixture o f iron
react ions which take place between: and sulfor is heated a chemical reacti on occurs and
a new substance is fo rmed called iron (n ) sulfid e
a calcium and oxygen b copper and oxygen. ( Figure 2 .11 ). Th e word equation fo r this reactio n is:

2 Write down the ratio of t he atoms present in t he formula iron+ sulfur ~ iron (11 ) sulfide
for each of the compounds shown in Table 2 .5.

3 Iron is extracted from iron(111) oxide in a blast furnace by a
redox reaction. What does the term 'redox reaction' mean?

4 Identify the oxidising and reducing agents in the following
reac ti ons :

a copper(n) oxide + hydrogen --+ copper + water

b tin(u) oxide + carbon --+ tin + carbon dioxide

c PbO(~) + Hi{g) --+ Pb(s) + H20(1)

•

Separating mixtures

Tabl e 2.7 The major differences between mixtures and compounds.

Mixture Compound

It contains two or more substances It is a single substance

The composition can vary The composition is always the same

No chemical change takes place When the new substance is formed

when a mixture is formed it involves chem ical change

Thepropertiesarethoseofthe Thepropertiesareverydifferentto
individual elements/compounds those of the component elements

The components may be The components can only be

separated quite easily by physical separated by one or more chemical

reactions

Figure 2.11 The elements sulfur and iron at the top of the photograph, In iron( n ) sulfide, FcS, o ne ato m o f iron has
and (below) black iron(II) sulfide on the left and a mixture of the two combined with o ne ato m o f sulfur. N o such ratio
elements on the right. exists in a mixture o f iro n and sulfur, because the
atoms have n o t chemically co mbined. Table 2.7
summarises how mixtures and compo unds compare.

Some commo n mixtures arc discussed in
C hapter I O (p. 165) and C hapter 11 ( p. 173).

Question

1 Make a list of some other common mixtures, stating what
they are mixtures of.

Figure 2.12 A magnet will separate the iron from the mixture. Many mixtures contain useful substances mixed
with un wanted material. ln o rd er to obtain these
Durin g the reactio n hea t en ergy is g iven o ut as useful substances, chemists o ften have to separate
n ew ch emical bonds arc fo rm ed. This is ca lled an them fr om the impurities. Chemists have d eveloped
exothermic reactio n and accompanies a ch emi ca l man y different m eth ods o f separatio n , particularly
ch an ge (Chapter 6 , pp. 92 and 95 ). The iron( n ) for separating compo unds fr o m complex mixtures.
sulfid e formed has to tally differe nt p ro perties t o Which separati o n meth od th ey use depends o n what
the mixture o f iron and sulfur (Table 2.6 ). l ro n( n ) is in the mixture and the properties o f the substances
sulfid c, fo r example, would n o t be attracted present. It also depends o n wh eth er the substances to
towards a magnet. be separated arc so lid s, liquids or gases.

Tabl e 2.6 Different properties of iron, sulfur, an iron/sulfur mixture and Separating solid/liquid mixtures
iron(1)sulfide.
If a solid substance is added to a liquid it may
Substance Appearance Effect of a Effect of dilute dissolve to fo rm a solution. In thi s case the solid is
magnet hydrochloric acid said to be soluble and is called the solute. The liquid
it has dissolved in is called the solvent. An example o f
Iron Dark grey Attracted Very little action when this type o f process is wh en sugar is added to tea or
coffee. What o ther examples can you think o f where
powder toil cold.Whenwarm, agas this type o f process takes place?

is produced with a lot of Sometimes the solid docs not dissolve in the liquid.
This solid is said to be insoluble. For example, tea
bubbling(effervescence) leaves them selves d o not dissolve in boiling water when
tea is made from them , although the soluble materials
Sulfur Yellow None No effect when hot fro m which tea is made arc seen to dissolve from them.
powder or cold

lron/sulfur Dirty yellow Iron powder Iron powder reacts

mixture powder attracted to it asalx>ve

Iron(•) Black solid No effect Afoul-smelling gas is
sulfide produced with some
effervescence

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

Filtration Centrifuging

Wh en a cup o f tea is po ured throu gh a tea strain er A n o th e r way t o separat e a so lid fr o m a liquid is
you arc carrying o ut a filtering process. Filtratio n to u se a centrifuge. This techniqu e is som etim es
is a commo n separatio n techniq ue u sed in chemist ry u sed inst ead o f filtratio n. It is u sually u sed w h e n
laborat ories through o ut the world. It is u sed w he n th e solid particles a rc so sm all th at th ey spread o ut
a so lid needs t o be separated fr om a liquid . Fo r (di sperse ) th ro ug h o ut th e liquid and rem ain in
example, sand can be separated fr om a mixture w ith su spensio n . They d o no t settle t o the botto m o f
water by filtering th roug h filter paper as sh own in the container, as heavier particles would d o, und er
Fi gure 2. 13. th e fo rce o f g ravity. The t echniqu e o f centrifuging
o r centrifugation invo lves the su sp e n sio n being
spun ro und ver y fa st in a centrifu ge so that
th e solid gets flung to th e b o tto m o f th e tube
(Fig ure 2. 14a and b ).

The filt er paper contains ho les that , altho ug h too
sm all to be seen , arc large en o ugh t o allow the
m o lecules o f water throu gh but not the sand particles .
It acts like a sieve. The sand gets trapped in the filter
paper a nd the wate r passes th ro ug h it. The sand is
called the residue and the wat er is called the filtrate .

Decanting b Anopencentrifuge.
Figure 2.14
Vcgcta bks d o n o t dissolve in wate r. W he n you h ave
b oil ed som e vegeta bles it is easy t o separate them
fro m the wate r by pouring it o ff. This process is
called decanting . This t echnique is u sed quite o ften
to separate an in soluble solid , which has settled at the
b ottom o f a flask, fr o m a liquid.

Separating mixtures

The pure liquid can be decanted after the solid has Evaporation
been fo rced to the botto m o f the tube. This metho d
o f separatio n is used extensively to separate blood cells If th e solid has dissolved in the liquid it canno t be
from blood plasma (Figure 2.15 ). In this case, the separated b y filterin g or centrifu g ing. Instead , the
solid particles (the blood cells) arc flun g to the botto m solutio n can be heated so that the liquid evaporates
o f the tu be, allowing the liquid plasm a to be d ecanted . compl etely and leaves the so lid behind. Th e simplest
way to o btain salt fr om its solutio n is by slow
evaporation as sh own in Figure 2.16.

Figure 2.16 Apparatus used t o slowly evaporate a solvent.

Crystallisation
In many par ts o f th e world salt is o btained fro m
sea water o n a vast scak . This is d o n e b y usin g
th e heat o f th e sun to evapo rate the water to lea ve
a saturated solutio n o f salt kn own as brine. A
saturated solution is defin ed as on e that contains
as much solute as ca n be dissolved at a particular
temperature . When th e so luti o n is saturated the salt
begins to crystallise , and it is rem oved using large
scoops (Fig ure 2 . 17).

Figure 2.15 Whole blood {top) is separated by centrifuging into blood Figure 2.17 Salt is obtained in north-eastern Brazil by evaporation
cellsandplasma(bottom). of seawater.

•

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

Simple distillation
If we want to obtain the solvent fro m a solutio n,
then th e process o f dis tillation ca n be carri ed o ut.
The apparatus used in this process is sh own in
Figure 2. 18 .

Separating liquid/liquid mixtures

ln recent years there have been many o il tanker
disasters, jll st like the o ne shown in Fig ure 2 .20.
Th ese have resulted in millio ns o flitr cs o f oil being
wash ed into the sea. Oil and water do no t mix easily.
They arc said to be immiscible. Wh en cleaning llp
disasters o f this typ e, a range o f ch emicals can be
add ed to the o il to ma.kc it m o re soluble. This results
in the o il and water mixing with each other. Th ey arc
n ow said to be miscible . The following techniqu es
can be used to separate mixtures o f liqllid s.

•heat

Figure 2.18 Water can be obtained from salt water by distillation. Figure 2.20 Millions of litres of oil are spilt in tanker disasters and
cleaningupis a slowandcostlyprocess.
Water can be o btained fr o m salt water using this
m eth od. The solutio n is heated in the fl ask until it Liquids which are immiscible
b oils. The steam rises into th e Liebi g cond en ser, lf two liquids a.re immiscible th ey can be separated
wh ere it conden ses back into water. The salt is left u sing a separating funnel. The mixture is po ured
behind in th e fl ask. In h o t and arid countries such into th e funnel and the layers allowed to separate.
as Saudi Arabia this sort o f technique is u sed o n a
much larger scale to o btain pun: water for drinking
( Fig ure 2. 19 ). This process is carri ed o ut in a
desalinatio n plant.

Separating mixtures

Figure2 .21 The pink liquid ismoredensethantheclearoilandsosinks
to the bottom of the separati ng funnel. When the tap is opened the pink
liquid can be run off.

Li quids which are miscib le flask

If miscible liquid s arc to b e separated, then this can support
be d o ne by fractional distillation. The apparatus
u sed fo r thi s process is shown in th e photo and Figure2.22 Typicalfractionaldistillationapparatus.
diag ram in Fig ure 2 .2 2, and could b e used to
separate a mixture o f ethan o l and water. steadily to I 00 °C, sh owing that the steam is now
enterin g the conden ser. At this po int the receiver can
Fracti onal distillatio n relics upon th e liquids be ch an ged and th e conden sing water can now be
ha,,in g different bo iling po ints. W hen an eth an o l and c o ll e c t e d.
water mixture is h eated th e vapours o f ethano l and
water boil o ff at different temperatures and can be
condensed and collected separately.

Ethano l b oils at 7 8 °C wh ereas water bo ils at
I 00 °C . When the mixture is heated the vapo ur
produced is mainly ethan ol with som e steam.
Because water has the high er boiling po int o f the
two, it cond enses o ut fro m the mixture with ethan o l.
This is what takes place in th e fra ctio natin g column.
The water cond en ses and drips back into th e fla sk
while th e ethano l vapo ur m oves up the co lumn and
into the conden ser, where it condenses into liquid
ethano l and is collected in th e receivin g flask as the
distillate. W h en all the ethano l has distilled over,
the temperature reading on the th ermo m eter rises

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

Fractio n al di stillatio n is ll scd to separate miscible
liquid s such as those in crud t: o il (st:c Figure 2 .2 3a
and p. 90 ), and the technique can also separate
individual gases, su ch as nitrogen , fro m th e mixture
we call air (sec Fig ure 2.23b and p. 174 ).

Figure 2.24 Magnetic separation of iron-containing materials.

It is essential that when separating solid/solid mixtures
you pay particular attention to the individual physical
properties of the components. If, for example, you wish
to separate two solids, one o f which sublimes, then this
property should dictate the method you employ.

In the case o f an iodin e/salt mixture the iodin e
sublimes but salt d ocs n o t. Io dine can be separated
by heatin g the mixture in a fume cupboard as shown
in Figure 2 .25. The io dine sublimes and re-fo rm s o n
the cool inverted fi.mn el.

Figure2.23

Separating solid/solid mixtures Figure2.25 Apparatusused toseparatean iodinelsaltmixture.
Theiodinesublimesonheating.
Yo u saw earlier in this chapter ( p. 16 ) that it was
possible to separate iron fro m sulfur u sing a magn et.
ln that case we were using o ne o f the physical
p roperties o f iron , that is, the fa ct that it is mag netic.
ln a similar way, it is possible to separate scrap iron
fro m o ther m etals by using a large elect romagnet like
the o ne sh own in Fig ure 2 .24.

Separating mixtures

Chro mat og ra ph y As the solvent m oves up th e paper, the d yes arc
carried with it and b egin to separate . They separate
Wh at h appen s if you have to separate two o r mo re b ecau se the substances have different solubilitics in
solids that arc soluble? This t yp e o f problem is the solvent and arc ab sorbed to different degrees
en countered when you have mixtures o f colo ured by the ch romatography paper. As a result, th ey arc
materials such as in ks and d yes . A techniqu e called separated g radually as the solvent m oves up the paper.
chromatography is widely u sed to separate these The chroma togram in Fig ure 2.26b shows h ow the
materials so that they can be id entified . ink co ntains three dyes, P, Q and R.

There arc several types o f chromatography; however, Num eri cal m easurem ents ( re tardatio n fa ct o rs)
they all follow the same basic principles. The simplest kn own as Rf val ues can b e o btain ed fr o m
kind is paper ch romatography. To separate the different- ch romatogram s. An Rf valu e is d e fin ed as th e
coloured dyes in a sample of black ink, a spo t of the ink ratio o f the distan ce tra velled by the solute ( for
is put on to a piece of chromatography paper. 1l1is paper example P, Q o r R) to the di stance travelled b y
is then set in a suitable solvent as shown in Figure 2 .2 6. the solvent.

~ - C h romatography and elect ropho resis (separatio n
according to electrical charge) arc used exten sively in
--- ~ ~1s medical research and fo rensic scien ce laborato ri es to
,l,i ' sep arate a variety o fmixtun:s ( Figure 2 .2 7 ).
"
,r .~
--t~ .;~- - ;\.
!.r -~ ~-- -,.'\

'" ~---....= ~ e : # . ~
__.,..- ,

a Chromatographic separation of black ink.

U, h,omatog,aphy
paper

black ink
spo t
b efo re
Iisolvent soaks '"'"
• Fi gure 2.27 Protein samples are separated by electrophoresis in medical
up the paper research laboratories.
so l v e n t
Th e substan ccs to be separated d o n o t havc to
d urin g be colo ured . Co lo urless substances can be mad e
visible by spraying the chromatogram with a
dye R~ locating agent. The locating agent will react
dye Q with the colo urless substances to fo rm a colo ured
dye P p roduct. In o ther situati o n s the positio n o f the
substances o n the chromatogram may be located
after u sing ultravio let light.

b The black ink separates into three dyes: P. Q and R. So lve nt extracti o n

Fi gure2 .26 Sugar can be o btain ed fr om crush ed sug ar can e b y
adding water. The water dissolves thc su gar fro m
the sugar cane (Figure 2.2 8 ). This is an example

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

o f solven t extraction . In a similar way som e o f the Th roug h o ut the ch emical, pharmace utical and
green substances can be rem oved fro m ground -up food indu stries it is essential that the substances used
grass u sing ethan ol. The substances arc extracted arc pure. The purity o f a substance can be gau ged by:
fro m a mixture by using a solvent which dissolves
o nly those substances required. • its melting point - if it is a pure solid it will have a
sharp m elting po int. If an impurity is present then
melting takes place over a range o f temperatures.

• its boiling point - ifit is a pure liquid the
temperature will remain steady at its boiling p oint.
If the substance is impure then the mixture will
boil over a temperature range.

• chromatography - ifit is a pure substance it
will prod uce only on e well-defin ed sp o t on a
chromatogram. If impurities arc present then
several sp ots will b e seen o n the ch romatogram
(sec Fig ure 2 .26, p . 23 ).

- Aspirin-

- . . . ,000,,S

Fi gure 2.28 Cutting sugar cane, from which sugar can be extracted by
using a suitable solvent .

Criteri a for purity

Drugs arc manufactured to a very hig h dcgn:c of
purity (Figu re 2 .29). To ensure that the highest
possible purity is o btained , the drugs arc dissolved
in a suitable solvent and subjected to fra ctio nal
cr ystallisati o n.

Figure 2.30 These pharmaceuticals must have been through a lot of
testing before they can be sold in a chemist's shop.

Questions

1 Use your research techniques (including the Internet) to

obtain as many examples as you can in which a centrifuge

is used.

2 What is the difference between simple distillation and

fractional distillation?

3 Describe how you would use chromatography to show

whether blue ink contains a single pure dye or a mixture

Fi gure 2.29 Drugs are manufactured t o a high degree of purity by of dyes.
fractional crystall isation.
4 Explain the follow ing terms, with the aid of examples:
It is illegal to put anythin g harmful into fo o d.
Al so , governm ent legislatio n requires that a lo t o f a miscible b immiscible
testin g takes place befo re a n ew pharmaceutical is
marketed. c evaporation d condensa t ion

• e solvent extraction .

5 Devise a method for obtaining salt (sodium chloride) from

sea water in the school laboratory.

6 What criteria can be used to test the purity of a substance?

Accuracy in experimental work in the laboratory

• Accuracy in Th e m ost co mm o nl y u sed th erm o m eters in a
experimental work in labo rato ry arc alc o h o l-in- g lass . H owever, me rcur y
the laboratory in-g lass therm o m eters ca n be u sed but sh o uld
be handled with great care . The mercury inside
Scientists find o ut ab o ut the nature o f materials b y the m is po ison o u s and sh o uld n o t b e handled if a
carrying o ut experiments in a labo rato ry. M any o f the rmo m ete r breaks. Th e units o f temperature arc
these ex periments require apparatus that you have th ose o f th e C el siu s scale. Thi s scale is ba sed o n
used in your study o f ch emistry to date. Certainly the temperature at which wa ter fr eezes a nd b o il s,
a kno wledge and understanding o f the use o f that is:
this scientific apparatu s is required fo r successful
experimentatio n and investigatio ns that you may carry the freezing po int o f water is O°C whilst
o ut in your furth er study o f ch emistry. Much o f the the bo iling po int o f water is 100 °C.
work in volves :1ccurate m easurem ents with particular
pieces o f apparatu s in parti cular experiments, many o f For accuracy the thermometer should be capable o f
which arc sh own in the secti on below. being read to a tenth o f a degree Celsius. The usual
thermometer usr..-d is that shown in the photograph that
Apparatus used for measurement measures accurately between -10 ° and l 10°C. \¥ hen
in chemistry reading the thermometer always ensure that your eye is at
the same level as the liquid meniscus in the thermo meter
Measurement of time to ensure there an: no parallax effects. 111c meniscus is
the way that the liquid curves at the edges of the CJ.pilbry
in which the liquid is held in the thermometer.

Measurement of mass

Figure 2.31 This stopwa tch can be used to measure the time passed in a
chemical reaction.

Experiments in volvin g rates o f reactio n will require
the u se o f an accurate sto pwatch - o ne that m easures
to a hundredth of a second. The units of time arc
h ou rs ( h ), minutes (min ) and second s (s) .

Figure 2.32 A thermometer can be used to measure temperature. There arc man y different electro nic balan ces whi ch
can b e used . The important detail with any o f th em
is that they arc accurate to o ne hundredth o f a gram.

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

The units fo r measuring mass arc g ram s (g ) and Generally collo id s cannot be separated by filtratio n
kilograms (kg ). sin ce the size o f the di sp ersed particles is smaller
than that o f the pores found in the filt er paper.
lkg 0 lOOO g Look closely at the substances sh own in Fig ure 2 .35
to see examples o f these mixtures.
Wh en u sing an elect roni c balance you sh ould wait
until the reading is steady befo re taking it.

Measure ment of vo lume

a These jelly-likemixturesofsolid b Emulsionpaintisan
andliquidinfruit jellyandcold exampleofa'sol'.
custard are examples of 'gels'.

Fi gure 2.34 The apparatus sho'Nfl in the photograph is generally used in c These foams have been formed by d Emulsionsareformedby
different experiments to measure vo lume accu rately. trappingbubblesofga s inliquidsor mixing immiscible liquids.
solids.
Different experiments involving liquid s will require
o ne o r o ther o r all the vari ou s measurin g apparatus Fi gure2.35
for volume . Tlu: volum e o f a liquid is a m easure o f
the amo unt o f space th at it takes up. Th e units o f \Vh en you mix a solid with a liquid you som etimes
volume arc litres (I) and cubic ccntimctn:s (cm 3 ) . get a gel. A gel is a semi -solid which can m ove
around but n o t as freely as a liquid. Within a gel the
I litre= 1000 cm3 solid m akes a kind o f network which traps the liquid
and makes it unable to fl ow fr eely (Figure 2 .36 ).
H owever, som e o f the manL1fac turcrs o f apparatu s
u sed for measuring volume u se millilitres ( ml ). This is network of water mo lecules trapped
n ot a pro blem , h owever, since 1 cm 3 = 1 ml. gelatine molecules ina network of gelatine

Wht:n reading the volume u sing o ne o f the pieces I
o f apparatu s it is impo rtant to en sure that the
apparatus is vertical and that your eye is tc ,,el with the
top o f th e meniscu s o f th e liquid being measured.

• Gels, sols, foams and Figure2.36 The network w ithinagel.
emulsions

Gels, sols, foam s and emulsio ns are all examples
o f mixtures which are formed by mixing two
substances (or phases) whi ch canno t mix . Th ese
mixtures are o ften referr ed to as colloids. Collo id s
are form ed if the su spend ed particle s arc between
lnm and lOOOnmin size( lnm = l x I0-9 m ).

Gels, sols, foams and emulsions

A gelatine gd is mad e with warm water. Gelatine is a When you pour o ut a g lass of fi zzy drink, the fro thy
protein. Proteins arc natural p olymers (Chapter 15, part at th e top o f the drink is a gas/liquid mixture
p. 243 ) and the m olecu les of protein arc very large. called a foam . The gas, carbon dioxide, has fo rmed
The large molecu les disperse in water to fo rm a gd . tiny bubbles in the liquid but h as not dissolved in
As the gelatine-in-water mixture cools, the gelatine it. lfldi: to stand, foams like this o ne collapse as the
molecules are attracted to each o ther and fo rm a tiny bubbles jo in together to fo rm bigger bubbles
continuo us network. ln this way, the jelly you eat as a which then escape. It is possible to fo rm solid foa m s
pudding is formed. The kind of gel which you put into wh ere the gases are trapped in a solid stru cture. This
your hair is made fro m water and an oil (Figure 2. 37). happens in foam rubber and bread (Figure 2.38 ).

A sol is similar to a gel; h owever, the mixture will Emulsions arc mi xtures o fliquid s which arc
fl ow, fo r example emulsio n paint, o r PVA glu e. immiscible. Earlier in this chapter you fo und out that
wh en two liquids arc immiscible they d o no t mix but
Figure 2.37 Hair gel is a mixture of water and an oil plus a perfume. fo rm two different layers . Oil and water are like this
but if you sh ake the mixture it becomes cl o ud y.

The apparent mixing that you sec is du e to the
fact that on e o f the liquid s has been broken into tiny
droplets which fl oat suspend ed in the o ther li quid. If
the mixture of oil and water is now left to stand the
two layers will re-fo rm. To make emulsio ns, such as
mayonnaise, an emulsifier is used to sto p the d roplets
joining back together again to form a separate layer.
The emulsifier used when making mayonnaise is egg
yolk. In m any countries of the world , if you examine
the ingredients on the side o f many packets fo und in
kitchen cup boards you will find that emulsifiers have
' E-numbers' in the range E32 2 to E494. Fo r example,
ammo nium phosphatidc E442 is used as the emulsifier
in cocoa and chocolate. O ther food additives such as
colourings and preservatives are also g iven E-numbers
but in different ran ges to that o f the emulsifiers .

It is worth noting that gels, foa ms and emul sio ns
arc all examples o f diftCrent kinds o f solutio ns. In true
solutions the two phases completely mix together but
in these system s the two phases arc separate .

Figure2.38 Examplesofsolidfoams. •

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

T o produce a stable colloid, the particles dispersed fibres o f glass in a matrix o f plastic. The glass fibre s
must no t only be of the rig ht si ze ( 1- lOOOnm ) give the plastic extra strength so that it d ocs no t break
but al so be prevented fr o m jo ining back togeth er when it is bent or mo ulded into shape. The fini shed
(coagulating ). One way o f do ing this is to ensure that product has the lightness of plastic as wdl as the
all the particles possess the same electrical charge. streng th and flexibility of the glass fibres (Figure 2 .40 ).
This causes the particles to repel o ne ano ther.

A colloidal suspen sion can be dest royed by bringing
the dispersed particles together. 1l1is process is known
as flocculation. A m etho d of d o ing this involves
addin g ionic substan ces such as aluminium chloride
or aluminium sulfatc to the particular coll o id. The
dispersed particles interact with the added highly
charged io ns and form particles which are large
en oug h either to settle o ut under the fo rce o f gravity
or simply be filtered o ut. During the treatment o f
water, aluminium sulfu.tc is added to water prio r to
filtering to rem ove su spended solids ( Figure 2 .39 ).

Figure 2.40 GRPconsists of glass fibres (rod shapes) embedded in
plastic, in thiscase polyester.

Figure2 .39 Wateristreatedtoremovesuspendedsolidsbythe
additionof aluminiumsulfate.

Questi ons

1 Explain the following terms:

a colloid c foam e sol.

b emulsifier d 'E' number

2 Use your research skills (including the Internet) to obtain

information about as many common gels, sols, foams

and emulsions as you can, other than those given in the Figure 2.41 The glass-reinforced plastic used to make boats like this is a
composite material.
text.
W ith a little investig atio n you will find that many
• Mixtures for strength composite materials arc fo und in the natural world.
Our b o nes, for example, arc a composite material
Composite mat er ials form ed fr om strands o f the p rotein collagen and
the min eral calcium ph osphate ( Fi gure 2.42 ). The
Composite materials arc those that combin e the calcium phosphate is hard and tl1creforc gives
p roperties o f two constitu ents in order to get the streng tl1 to the bo ne . An o tl1cr example is wood.
exact properties n eed ed for a particular jo b. Wood consists o f cellulose fibres mixed with lignin
( Figure 2.43 ), which is largely respo nsible for the
Glass-reinfo rced plastic (GRP) is an example o fa streng tl1 o f th e wood .
composite material combining the properties o f two

•ditlcrcnt materials. It is made by embedding sho rt

C h e c k lis t

Figure 2.42 Bone is a composite material. Questions

1 Why are composite materials often used instead of
single materials?

2 Using the information in the text and any other
information available to you, give a use other than those
already mentioned for each of the following composite
materials:
a reinforced concrete
b glass-reinforced plastic
c laminate
d glassfibre.

Checklist • Colloid System in which there are two or more phases,
with one (the dispersed phase) distributed in the other (the
After studying Chapter 2 you should know and understand the continuous phase). One of the phases has particles in the
following terms. range1 to1000nm(1nm=1 x 10-9m).

• Accuracy in experimental work The accuracy of each • Composite materials Materials which combine the
measurement. It depends on the quality of the measuring properties of two substances in order to get the exact
apparatus (e.g. the thermometer or electronic balance) and properties required for a particular job.
on the skill of the scientists taking the measurement.
• Compound A substance formed by the combination of
• Atom The smallest part of an element that can exist as a two or more elements in fixed proportions.
stable entity.
• Crystallisation The process of forming crystals from a
• Centrifuging The separation of the components of a liquid.
mixture by rapid spinning. The denser particles are flung to
the bottom of the containing tubes. The liquid can then be • Decanting The process of removing a liquid from a solid
decanted off. which has settled or from an immiscible heavier liquid by
pouring.
• Chemical change A permanent change in which a new
substance is formed. • Diatomic molecule A molecule containing two atoms, for
example hydrogen, H2, and oxygen,02.
• Chemical formula A shorthand method of representing
chemical elements and compounds. • Distillate The condensed vapour produced from a mixture
of liquids on distillation .
• Chromatography A technique employed for the
separation of mixtures of dissolved substances. •

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

• Distillation The process of boiling a liquid and then • Locating agent A substance used to locate, on a
condensing the vapour produced back into a liquid. It is chromatogram, the separated parts of a mixture in
used to purify liquids and to separate mixtures of liquids. chromatography.

• Element A substance which cannot be further divided into • Metals A class of chemical elements which have a
simpler substances by chemical methods. characteristic lustrous appearance and which are good
conductors of heat and electricity.
• Emulsifier A substance used to stop the droplets that
make up an emulsion joining back together again to form a • Miscible When two liquids form a homogeneous layer
separate layer. when mixed together, they are said to be miscible.
Emulsion The apparent mixing of two immiscible liquids
by the use of an emulsifier which breaks down one of the • Mixture A system of two or more substances that can be
liquids into tiny droplets. The droplets of this liquid float separated by physical means.
suspended in the other liquid so that they do not separate
out into different layers. • Molecule A group of atoms chemically bonded together.
• Monatomic molecule A molecule which consists of only
• Evaporation When a solution is heated the solvent
evaporates and leaves the solute behind. one atom, for example neon and argon.
• Non-metals A class of chemical elements that are typically
• Exothermic reaction A chemical reaction in which heat
energy is produced. poor conductors of heat and electricity.
Filtrate The liquid which passes through the filter paper • Oxidation The process of combining with oxygen.
during filtration. • Oxidising agent A substance which oxidises another
Filtration The process of separating a solid from a liquid
using a fine fi lter paper which does not allow t he solid to substance during a redox reaction.
pass through. • Redox reaction A reaction which involves the two
Flocculation The destruction of a colloidal suspension by
bringing the dispersed particles together. processes of reduction and oxidation.
Foam A mixture formed between a gas and a liquid. The • Reducing agent A substance which reduces another
gas forms tiny bubbles in the liquid but has not dissolved in
it. substance during a redox reaction.
Fractional distillation A distillation technique used to • Reduction The process of removing oxygen.
separate a mixture of liquids that have different boiling • Residue The solid left behind in the filter paper after
points.
filtration has taken place.
• Gel A mixture formed between a solid and a liquid in • R1value The ra t io of the distance travelled by the solute
which the solid forms a network which traps the liquid so
that it cannot flow freely. to the distance travelled by the solvent in chromatography.
• Saturated solution A solution which contains as much
• Immiscible When two liquids form two layers when mixed
together, they are said to be immiscible. dissolved solute as it can at a particular temperature.
• Sol A mixture formed between a solid and a liquid, which
• Insoluble If the solute does not dissolve in the solvent it is
said to be insoluble. then forms a network that can flow.
• Soluble If the solute dissolves in the solvent it is said to be
• Instrumental te chniques Instrumental methods of
analysis that are particularly useful when the amount soluble.
of sample is very small. Examples are atomic absorption • Solute The substance that dissolves (disappears) in(to) the
spectroscopy and infrared spectroscopy.
solvent.
• Law of constant composition Compounds always have • Solution The liquid formed when a substance (solute)
the same elements joined together in the same proportions:..,
disappears (dissolves) into another substance (solvent).

Solvent The liquid that the solute has dissolved in.

solute+solvent ~ solution

0 Elements, compounds and
experimental techniques
-----"---------'-----

• Additional questions 5 Name th e method which is m ost suitable for
separating the fo llowing:
1 D efin e the followin g terms using specific examples a oxygen fr o m liquid air
b red blood cells fr om plasma
to help with your explanation : c pet rol and kerosene fro m crud e oil
d coffo e grains fr om coffee solution
:i clement g fl occulatio n e pieces o f steel fro m eng ine o il
f amino acids fr om fruit juice soluti on
b metal h gd g ethano l and water.

c non-metal i foam 6 The table belo w shows the melting po ints, b oiling
po ints and d ensities o f substances A to D.
d compound j emulsio n

e m olecule k sol.

f mixture

2 W hich o f the substances listed below arc: Substance Melt ing point/" ( Boiling point/"( Density/gcm -3
a m etallic elements? 1110
b no n-metallic elements? -266 26 06 9.1
c compo unds?
d mixtures? 40 -252 0.07
Silicon , sea water, calcium , argon , water, air, -14
carbon m o n o xide, iron , sodium chlo ride, diamo nd , 94 1.6
brass, copper, dilute sulfuric acid, sulfur, o il ,
nitrogen, ammo nia. 60 0.9

3 At room te mperature and pressure (rtp ), which o f a Which substan ce is a gas at room temperature?
the su bstanccs listed below is: b Which substance is a liquid at room temperature?
a a solid clement? c \iVhich substan ces arc solids at room
b a liquid clement?
c a gaseou s mixture? t e m p er a t u re?
d a solid mixture? d Which substan ce is most likely to be a metal?
e a liquid compound ? e Which substan ce will be a liquid at - 260 °0
f a solid compound? f What is the melting po int o f th e least d en se n o n -
Bromine, carbon diox idt:, helium , steel , air, o il,
m arble , copper, water, sand , tin, bro nze, mercury, metal1
salt. g Which substan ces are gases at 72 °C?

4 A stud ent heated a mixture o f iron filin gs and 7 a H ow m any ato m s o f th e different elem ents are
sulfur stro ng ly. H e saw a red g low spread throug h there in the formulae o f the compounds given
the mixture as the reacti on continued. At the end bel ow1
o f the experiment a black solid had been fo rmed. (i) nitric acid, HN03
a E xplain what the red glo w indicates. (ii) methane, C H 4
b Give the chemical name o f th e black solid. (iii) copper nitrate, C u ( N03 )2
c Write a wo rd equati on and a balanced ch emical (iv) ethan o ic acid, C H 3C OOH
equatio n to represent the reactio n which has (v) su gar, C 12 H 220 11
taken place. (vi) phenol, C6H 50H
d The black solid is a co mpound. Explain the (vii) ammo nium sulfate, ( NH 4 )2S04
difference b etween th e mixture o f sulfur and
iron and th e compound formed by the chemical b Balance the fo ll owing equatio n s:
reactio n between them.
(i) Zn(s) + 0 2(g) - ZnO(s)
(ii) Fc(s) + C l2(g) - FcCl3(s)
(iii) Li(s) + 0 2 (g) - Li20 (s)
(iv) H2(g) + 0 2(g) - H,O(g)
(v) Mg(s) + C0 2(g) - MgO(s) + C(s)

2 ELEMENTS, COMPOUNDS AND EXPERIMENTAL TECHNIQUES

8 Carbo n -fibre-rein fo rced plastic (C RP) is used in
th e m anufu.chm:: o f golf clubs and tennis rackets.
:i W hat arc composite m at erials?
b W hich t wo substances arc u sed to m anufacture
this composite matcrial1
Co nsider the data in the tabk .

Material Strength/ Stiffn e ss/ De nsit y / g c m -J Re la t ive
GPa GPa
2 .7 I=
Alumin ium 0 .2 75 7 .8 I=
200 1.6 high
Steel 1.1 195

CRP 1.8

c Discuss the ad vantages and disadvantages
o f u sing the three materials above in the
manufac ture o f golf c!L1bs.

@ Atomic structure and bonding

Inside atoms Covalent bonding
Proton number and nucleon number Other covalent compounds
Ions Covalent structures
Isotopes Properties of covalent compounds
The mass spectrometer Allotropy
Relative atomic mass Allotropes of carbon

The arrangement of electrons in atoms Glasses and ceramics
Glasses
Ionic bonding Ceramics
Ionic structures
Properties of ionic co mpounds Metallic bonding
Formulae of ionic substances Properties of metals
Oxidation states
Checklist
We have alread y seen in C h apter 2 that everything
yo ll sec around you is m ade out o f tiny particles Additional questions
call ed ato m s (Figure 3 .1 ). W hen Jo hn D alto n
developed his ato mic th eory, about 20 0 years ago • Inside atoms
( 1807/ 1808 ), h e stated that th e ato ms of any o ne
clem ent were id entical and that each ato m was The three sub-atomic particles arc fo und in distin ct
' ind ivisible'. Scientists in those d ays believed that and separate regio ns. The p roto ns and neutron s arc
atom s were solid particles like marb les. fo und in the centre o f th e ato m , whi ch is called th e
nucleus. The neutro ns have no charge and pro to ns
arc p ositively charged . The nu cleu s occupies o nly a
very sm all volume o f the ato m but is very d ense.

Th e rest of the atom surrounding the nucleu s is
wh ere elect ron s arc m ost likely to be fo und . The
elect ron s arc negatively charged and m ove around
very quickly in electron sh ells or energy levels . The
elect ron s arc held within the ato m by an electrostatic
fo rce o f attractio n between them selves and the
positive charge of proto ns in the nucleu s (Fig ure 3 .2 ).

- .,~ -- -- nucleus, con t aining
neutrons and p rot o ns

Figure 3.1 A mk:rograph of atoms. region w here electro ns
are fo und
H owever, in the last hund red years o r so it has been
proved by great scien tists, such as N ids Bohr, Albert Figure 3.2 Diagram of an atom.
Einstein , H enry M oseley, Joseph Tho m son , Ernest
Rutherfo rd an d Jam es C h adwick, that ato m s arc in About 1837 elect rons arc equ al in mass to the mass
fact m ade up o f even sm aller 'su b -atomic' particles . o f o ne p ro to n o r o n e neutron . A summary o f each
The m ost im portant o f th ese arc electro n s, pro to n s type o f particle, its m ass and relative ch arge is sh own
and neutrons , althou gh 70 sub-ato mic particles have in Tabl e 3 .1 . You will n o tice that th e m asses o f all
now been discovered. these particles arc m easured in ato mic mass units
( a.mu) . This is because th ey arc so lig ht th at their
m asses cann o t be measured usefull y in gram s.

3 ATOMIC STRUCTURE AND BONDING

Tabl e 3.1 Characteristics of a proton, a neutron and an electron. H en ce, in the example shown in Figure 3.3 th e
helium ato m has a nucleon number o f 4 , since it h as
Particle Symbol Relative mass/amu Re lative charge two p roto ns and two neutrons in its nucleus. If wc
Proton +1 conside r the me tallic clem e nt lithium , it h as three
Neutron prot o ns and four ne utron s in its nucleu s. It the refore
Electron 1/1837 -1 has a nucl eon num ber o f 7 .

Althou gh at o m s co ntain electrically charged pa rticles, The proton number and nucleon number o f
the atom s the m selves arc electri cally n e utral (they an cle m ent arc u su all y writte n in the fo ll owing
have no overall electric ch arge ). This is becau se at o m s sh o rthand way:
contain equ al num bers o f elect ron s and prot o n s. For
example, the diagram in Fig ure 3 .3 re presents the nucleon numbe r (A )-....,.
atom o f the n on-me tallic cleme nt helium. The atom j H c +---- symbo l o f the cle m e nt
o f helium possesses two proto n s, two neutron s and
two el ectro ns. The electri cal cha rge o f the prot o n s proto n num ber (Z )'"'"
in the nucleu s is, therefore, balanced by the o pposite
charge o f th e two electro ns. The number o f neutrons present can be calculated
by rearranging the relatio nship between the proto n
nucleus which ho lds num ber, nucleon number and number of neutro ns
the 2proto nsand to give:
2 neutrons
number of= nucleon number - proton number

neutrons (A) (Z )

II-- - - ~"-' 2 electrons circling Fo r example, the number o f neutrons in o ne ato m of
tiM g is:
th e nucleus
24- 12 ~ 12
Figure 3.3 An atom of helium has two protons, two electrons and two (A) (Z )

and th e numbe r o f neutron s in o ne ato m o f 2i~ Pb is:

207 - 82 ~ 125
(A) (Z)

Table 3 .2 shows th e number o f proto ns, neutrons
and elec tro n s in the ato ms o f som e commo n
eleme nts.

Proton number and nucleon number Ions

The number o f proto ns in the nucleus o f an ato m An io n is a n electrically cha rged pa rticle. W he n
is called the proto n number ( or atomic numbe r ) an atom loses on e o r m o re electro n s it becom es
and is given the symbo l Z. H e n ce in th e diag ram a positively charged io n. Fo r exampl e, during the
sh own in Figure 3 .3, the helium atom has a p roton che mical reaction s o f po tassium, each a to m loses an
number o f 2 , since it has two proto n s in its nucleu s. elec tro n to fo rm a p ositive io n, K+.
Each cle me nt has its own prot on numbe r a nd n o two
differe nt ele m ents have the sam e prot on numbe r. Fo r 19 K+ 19 p roto n s = 19+
example, a diffe rent cle m ent, lithium, has a p rot o n 18 electrons = 18-
number o f 3, since it has three proto n s in its nucleu s.
0 vcrall charge = 1+
N eutrons and proto ns have a similar m ass. Elect ron s
possess ver y little mass. So the m ass o f any at om \-Vh cn a n a to m gains o ne o r m o re elect ron s it
de pe nds o n the num ber o f proto ns and n eutrons in its becom es a negatively cha rged io n. For example,
nucleus. The total number o f proto ns and neutrons during som e o f th e c he mical reaction s o f oxygen it
fo und in the nucle us o f an ato m is called the nucleon gains t wo elect ron s t o fo rm a negative io n, 0 2-
number (or mass number ) and is given the symbol A .
8 protons = 8+
nucleon num ber= pro to n number + number o f
(A ) (Z ) neutrons 80 2- 10 elect ron s = l 0-

0 verall c harge = 2 -

Inside atoms

Tabl e 3.2 Number of protons, neutrons and electrons in some elements.

Element Symbol Proton number Number of electrons Number of protons Number of neutrons Nucleon number
Hydrogen H
Helium He 10 10 10 12
Carbon 11 11 11 14
Nitrogen Ne 12 12 12 16
Oxygen Na 16 16 16 10 19
Fluorine Mg 19 19 19 10 20
Nroo 20 20 20 12 23
Sodium c, 26 26 26 12 24
Magnesium 30 30 30 16 32
Sulfur Fe 20 39
Potas.sium 2o 20 40
Calcium 30 56
lroo 35 65
Zinc

Table 3.3 sh ows som e commo n io ns. You will n otice Isotopes
fro m Table 3.3 that :
Not all o f th e atoms in a sample o f chlo rine, for
• some io n s contain m ore than o ne type o f atom, fo r example, will be id entical. Som e atoms o f the sa me
example N03- clem ent can contain diffe rent numbers o f n eutron s
and so have different nucleo n numbers. Atoms
• an ion may possess m o re than o n e unit o f charge o f the sam e clem ent w hich have the sam e proton
(either n egative o r positive), fo r example AJ3+, 0 2- number but different n eutro n numbers arc called
isotopes. The two isoto pes of chlorine arc shown in
or soi-. Figure 3.4 (p. 36 ).

Table 3.3 Some common ions. Formula Generally, isoto pe s behave in the same way during
LC ch emical reactio n s becau se they have the same
Name number of electrons o n their o uter shell (sec p. 38 ).
Lithium ion ,.Na'
Sodium ion The o nly effect of the extra neutron is to alter the
Potassium ion MgH mass o f the atom and properties which d epend o n it,
Magnesium ion ca2+ su ch as d ensity. Som e oth er examples o f atoms with
Calcium ion Al3.. isotopes arc sh own in Table 3.4.
Aluminium ion Zn2+
Zinc ion There arc two types o f isotopes: th ose which arc
Ammonium ion ,-NH/ stable and those which arc unstable . Th e isotopes
Fluoride ion which arc un stable, as a result o f the extra neutro ns
Chloride ion Cc in their nuclei, arc radioactive and arc call ed
Bromide ion radioisotopes. For example, uranium-235 , which
Hydroxide ion Be is used as a source o f power in nuclear reactors
Oxide ion (p. 93), and co balt-60, which is u sed in radio therapy
Sulfideion ow treatment ( Fig ure 3.5 ), arc both radio isotopes .
Carbonate ion o'-
Nitrate ion
Sulfate ion 5,-

c o /-

N03-

sol-

3 ATOMIC STRUCTURE AND BONDING

~;c1 The mass spectromet e r

17proto ns . H ow do we kn ow isotopes exist? They were fi rst
discovered by scientists u sin g apparatus call ed a
Q18 n eu t ro ns m ass spectro meter ( Fig ure 3.6 ). 1l1c first mass
spect rom eter was built by the British scit:ntist
Fi gure 3.4 The t,yo isotopes of chlorine. Fran cis Asto n in 19 19 and en abled scientists to
compare th e relative m asses of ato m s accurately fo r
the first tim e.

~~ Cl sa m p l e vac uum chamber
17 protons . inl et
20neut ro ns Q --.- - .... , - -.

Table 3.4 Some atoms and thei r isotopes. ionisati o n accelerati on drift region

Element Symbo l Particles prese nt fli g htpath
Hydrogen 1 e, 1 p,On tim e m easurement
{Deuterium) iH 1 e, 1 p, 1 n
(Tritium} jH 1 e, 1 p, 2 n Figure 3.6 A diagram of a mass spectrometer.
Carbon 6e,6p,6n
1H 6e,6p, 7 n A vacuum exists inside the mass spectro meter. A
Oxygen 6e,6p,8n sample o f the vapour o f the clement is injected into
'!c 8e,8p,8n the ionisatio n cham ber where it is bombard ed by
Strontium 'le 8e,8p,9n electron s. The collisio ns which take place between
iic 8e,8p, 10n these electron s and the injected ato ms cau se an
Uran iu m 1io 38e, 38p, 48n electron to be lost fro m the ato m, which becomes a
1io 38e, 38p, son positive ion with a + l charge . These positive ions arc
'~o 38e,38p, 52 n then accelerated towards a negatively ch arged plate,
92e,92 p, 143n in th e acceleratio n area . The spectrom eter is set up
~Sr 92e,92 p, 146n to ensu re that when the ion s leave the acceleratio n
area they all h ave the sam e kinetic energy, regardless
~s, o f the mass o f the io ns. This mean s that t he lighter
li!S, ions travel faster than the heavier ones, and effectively
separates the ion s according to their mass. H aving left
~~u the acceleratio n area, the time for the io ns to reach
the detector is recorded . The d etecto r counts the
'~U number o f each of the ion s which fall upon it and so a
m easure o f the percentage abundance of each isotope
is obtained . A typical mass spectrum for chlorine is
shown in Figure 3 .7.

100

75 35(1(75 %)
37(1(2 5%)
i1'

1~ so
25

Fi gure 3.5 Cobalt-60 is used in radiotherapy treatment. 10 20 30 40 50
Fi gure3 .7 Themassspectrumforchlorine.

The arrangement of electrons in atoms

Relative atomic mass It is n o t possible to g ive the exact positio n o f an
electro n in an en ergy level. H owever, we can st at e
The average mass o f a large num ber o f at o m s o f an tha t electro ns can only occupy certain, d efinite e ne rgy
clem ent is called its relative ato mic mass (symbol levels and that they canno t exist between the m. Each
A,.). This qu antity takes into account th e percentage o f the elect ron en e rgy levels can h o ld o nly a certain
abund ance o f all th e isot opes o f an clem ent w hich num ber of electrons.
exist .
• First e ne rgy level h o ld s up t o two elect ron s.
In 196 1 the Internatio nal U ni on of Pure and • Second e ne rgy level ho ld s up to eight electro ns.
Appli ed Chemistry (IU PAC) recomm ended that • Third energy level h o ld s up to 18 elect rons.
the st anda rd u sed fo r th e Ar scale was carbon-1 2 .
An ato m o f carbo n-1 2 was taken t o have a m ass of The re arc furth er en e rgy levels w hich contain
12 :mm . The A , o f a n clem e nt is the average mass inc reasing num bers o f elect ron s.
o f the n aturally occurrin g at o m s of an clem e nt on a
scale w h ere 12 C has a mass o f exactly 12 uni ts: The third e ne rgy level can be occu pi ed by a
m aximum o f 18 electro ns. H owever, wh en eig ht
average mass o f isot opes o f th e clem ent elect rons have occupied this level a certain st ability is
given t o the at o m and the n ext t wo el ect ron s go into
-fIA, x mass o f 1 ato m o f carbon -1 2 the fo urth e ne rgy level, and th e n the re m aining te n
elect rons complet e the third en e rgy level.
Not e: _!_ o f the m ass o f o ne carbon-1 2 at o m = l ;mm.
The electron s fill the e ne rgy levels sta rtin g fr om
For biampk , chlorine has two isot opes: the e ne rgy level nearest t o the nu cleus, w hich has the
lowest en ergy. W h en this is foll (w ith two elect rons )
I%abundance the next elect ron goes into the second en e rgy level.
Wh e n this e n ergy level is full with eig ht elect ron s,
H en ce the 'average m ass' or Ar o f a c hlo rine a to m is: the n the elect ron s begin to fill the third and fo urth
e ne rgy levels as st ated above.
(75 X 35 ) + (2 5 X 37)
35 .5 Fo r example, a 1~0 ato m h as a p rot o n numbe r
o f 8 and therefore h as eight elect rons. T wo o f the
100 eig ht elect ron s e nte r the first e ne rgy level, leaving
six t o occupy the second e ne rgy level , as sh own in
35 .5 Figure 3 .8 . The electron config uratio n fo r oxygen
A ~-- can be written in a sho rthand way as 2,6.

'l

= 35.Samu

Questions

1 Calculate the number of neutrons in the following atoms:

a HAI b HP c f83Uns d 1~os

2 Given that the percentage abundance of i8Ne is 90% and
that of l~Ne is 10%, calculate the A, of neon.

• The arrangement of Figure3.8 Arrangementofelectrons inanoxygenatom.
electrons in atoms
The re arc 11 8 elem e nts, and Ta bl e 3 .5 sh ows the
The nu cleus of an atom contains the heavier sub- way in w hich the elect ro ns arc a rran ged in the fir st
at omic particles - the prot on s a nd the ne utron s. The 20 o f these elemen ts . The way in w hich th e electro ns
elect rons , the lig htest o f the sub-a to mic pa rticles, arc distributed is called th e electronic structure
m ove aro und the nu cleus at great dist ances fr om the ( or elect ron config ura tio n ). Figure 3.9 shows the
nu cleu s relative to th eir size. They m ove ver y fast in elect ronic structure of a selection o f at o m s.
elect ron e n ergy levels ver y mu ch as the plane t s o rbit
the Sun.

3 ATOMIC STRUCTURE AND BONDING

Tabl e 3.5 Electronicstructureofthefirst20elements.

Element Symbol Proton Number of Ele c t r o n
number e le ctrons
Hydrogen He 2,1 hydrogen
Helium 10 10 2,2 lithium
Lithium ,, 11 11 2,3 sod i u m
Beryllium 12 12 2,4 argon
Boron Ne 13 13 2,5
Carbon Na 14 14 2,6
Nitrogen Mg 15 15 2,7
Oxygen AJ 16 16 2,8
Fluorine 17 17 2,8,1
Nroo ,,Cl 18 1B 2,8,2
Sodium 19 19 2,8,3
Magnesium Ca 20 20 2,8.4
Aluminium 2,8,5
Silicon 2,8,6
Ph05phorus 2,8,7
Sulfur 2,8,8
Chlorine 2,8,8,1
Argon 2,8,8,2
Potassium
Calcium

Yo u will no tice fr o m T able 3.5 that the elem en ts
helium, n eo n an d argo n have com pletely full o uter
shells. In C hapter 9 you will sec that these elements
arc kn own as the n o ble o r in ert gases and that they
arc generally vr:ry st;1bk: and unrcactivc (p . 143). This
is linked to the full o uter shells that they p ossess .
It wo uld seem that wh en elem ents react to fo rm
compo und s they d o so to achieve full electro n energy
levels. This idea forms th e basis o f the elect ronic
theory o f ch emical b onding .

Questions

1 How many electrons may be accommodated in the first
three energy levels?

2 What is the same about the electron structures of:
a lithium, sodium and potassium?
b beryllium, magnesium and calcium?

• Ionic bonding p ot assium

Ionic bonds are LJ su ally fo und in compounds that Figure 3.9 Electron arrangements of hydrogen, lithium, sodium, argon
contain m etals com bin ed with no n-m etals. VVh en this and potassium.
type o f b ond is fo rmed , electro ns are transferred fro m
the metal atoms to the non-metal atoms during the

Ionic bonding

chemical reacti o n . In d o ing this, the ato m s becom e the outer electron o f each sodium ato m is transferred to
m ore stable by getting full o uter energy levels. For the outer energy kvel of a chlorine ato m (Figure 3.11 ).
example , consider what h appens wh en sodium and
chl orine react together and combine to m ake sodium ln this way both the ato m s o btain full o uter energy
chl orid e (Fig ure 3.1 0). levels and becom e ' like' the nearest n o ble gas. The
sodium ato m has becom e a sodium ion and the
sodium + chlo rine -----+ sodium chloride process is known as ionisa tion . This sod ium io n has
an elect ron config uratio n like n eon.

sodium ato m -----+ sodium io n + elect ron

N,(g) N,+(s) +

To lo se elect rons in this way is called oxidation .

The chl orine atom has becom e a chl orid e io n with an
elect ron configuratio n like argon .

chlo rine ato m + elect ron -----+ chlo rid e io n

C l(g) + 0 -(g)

To gain electrons in this way is called reduction.
ln the chemical process producing sodium chloride

both o xidation and redu ction have taken place and
so this is known as a redox re.1ction. A further
discu ssio n o f oxidation and reductio n in terms of
electron transfer takes place in C hapter 5 (p. 73 ).

Figure 3.10 The properties of salt are very different from those of the Only the o uter elect rons arc impo rtant in bo nding,
sodium and chlorine it was made from. To get you r salt you would not so we can simplify th e diag ram s b y missin g o ut the
eatsodiumor inhalechlorine! inner energy levels (Fig ure 3. 12, p. 40 ).

Sodium has just one electron in its outer energy level The charges o n the sodium and chloride io ns arc
( 11 Na 2,8, l ). Chlorine has seven electro ns in its outer equal but opposite. They balance each other and
energy kvel (17CI 2 ,8,7). When these two elements react, th e resulting formula fo r sodium chlo ride is NaCl.
These oppositely charged io ns attract each other and
arc pulled , or bonded, to o ne another by st rong
electrostatic fo rces. This type of bonding is called
ionic bonding. The alternative name, electrovalent
bonding, is d erived fro m the fact that there arc
electrical charges o n the atom s involved in the bonding.

sodium atom chlorine atom sodium Ion chlo rid e ion
(Na) (Cl) (N a+ ) (c1- J

11 proto ns = 11+ 17prot o ns = 17+ •
10electrons = 10-
=::r::18 electrons = 18-
0verall charge = ±L
0verall charg e =

Figure 3.11 Ionic bonding in sodium chloride.