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Word Power ii
Contents
Keywords v 4.7 Appreciating the Existence of Elements and
Their Compounds 98
FORM 4 SPM Exam Practice 4 100
CHAPTER 1 1 CHAPTER 25 107
2 108
Introduction to Chemistry 5 Chemical Bonds 109
1.1 Chemistry and Its Importance 5.1 Formation of Compounds 114
1.2 Scientific Method 7 5.2 Formation of Ionic Bonds
1.3 Scientific Attitudes and Values in 9 5.3 Formation of Covalent Bonds 121
5.4 The Properties of Ionic Compounds and 128
Conducting Scientific Investigations
SPM Exam Practice 1 Covalent Compounds
SPM Exam Practice 5
CHAPTER 2 14
15 CHAPTER 26
The Structure of the Atom 23
2.1 Matter 26 Electrochemistry 134
2.2 The Atomic Structure 29
2.3 Isotopes and Their Importance 6.1 Electrolytes and Non-electrolytes 135
2.4 The Electronic Structure of an Atom 32
2.5 Appreciating the Orderliness and 33 6.2 Electrolysis of Molten Compounds 137
Uniqueness of the Atomic Structure 6.3 Electrolysis of Aqueous Solutions 142
SPM Exam Practice 2
6.4 Electrolysis in Industries 152
CHAPTER 32 6.5 Voltaic Cells 158
Chemical Formulae and Equations 6.6 The Electrochemical Series 165
3.1 Relative Atomic Mass and Relative
39 6.7 Developing Awareness and Responsible
Molecular Mass
3.2 Relationship between the Number of 40 Practices when Handling Chemicals used in
Moles and the Number of Particles 43 the Electrochemical Industries 172
3.3 Relationship between the Number of
45 SPM Exam Practice 6 173
Moles of a Substance and Its Mass
3.4 Relationship between the Number of 48 CHAPTER 27
51
Moles of a Gas and Its Volume 57 Acids and Bases 181
3.5 Chemical Formulae
3.6 Chemical Equations 60 7.1 Characteristics and Properties of Acids and
3.7 Scientific Attitudes and Values in 62
Bases 182
Investigating Matter
SPM Exam Practice 3 7.2 The Strength of Acids and Alkalis 192
7.3 Concentration of Acids and Alkalis 196
7.4 Neutralisation 203
SPM Exam Practice 7 211
CHAPTER 24 67 CHAPTER 28
Periodic Table of Elements 68 Salts 218
4.1 Periodic Table of Elements 74 8.1 Salts
4.2 Group 18 Elements 219
4.3 Group 1 Elements
4.4 Group 17 Elements 75 8.2 Qualitative Analysis of Salts 240
4.5 Elements in a Period
4.6 Transition Elements 82 8.3 Practising Systematic and Meticulous
89 Methods when Carrying Out Activities 255
93 SPM Exam Practice 8 256
iii
CHAPTER 92 CHAPTER 23
Manufactured Substances in Industry 262 Oxidation and Reduction 384
9.1 Sulphuric Acid 263 3.1 Redox Reactions 385
9.2 Ammonia and Its Salts 266 3.2 Rusting as a Redox Reaction 412
9.3 Alloys 272 3.3 The Reactivity Series of Metals and
9.4 Synthetic Polymers 278 Its Applications 418
9.5 Glass and Ceramics 281 3.4 Redox Reactions in Electrolytic Cell and
9.6 Composite Materials 284 Chemical Cell 430
9.7 Appreciating Various Synthetic Industrial 3.5 Appreciating the Ability of the Elements to
Materials 288 Change their Oxidation Numbers 441
SPM Exam Practice 9 289 SPM Exam Practice 3 444
FORM 5 CHAPTER 42
CHAPTER 1 Thermochemistry 452
Rate of Reaction 295 4.1 Energy Changes in Chemical Reactions 453
1.1 Rate of Reaction 296 4.2 Heat of Precipitation 463
1.2 Factors that Affect the Rate of Reaction 305 4.3 Heat of Displacement 469
1.3 The Collision Theory 322 4.4 Heat of Neutralisation 474
1.4 Practising Scientific Knowledge to 4.5 Heat of Combustion 482
Enhance Quality of Life 328 4.6 Appreciating the Existence of Various
SPM Exam Practice 1 329 Energy Sources 489
SPM Exam Practice 4 492
CHAPTER 2 CHAPTER 25
Carbon Compounds 340 Chemicals for Consumers 499
2.1 Carbon Compounds 341 5.1 Soaps and Detergents 500
2.2 Alkanes 343 5.2 Uses of Food Additives 510
2.3 Alkenes 346 5.3 Medicine 515
2.4 Isomerism 352 5.4 Appreciating the Existence of Chemicals 519
2.5 Alcohols 357 SPM Exam Practice 5 521
2.6 Carboxylic Acids 362
2.7 Esters 366 SPM Model Test 526
2.8 Oils and Fats 370
2.9 Natural Rubber 371 Answers 537
2 .10 Order in Homologous Series 376 Glossary 592
2.11 The Variety of Organic Materials in Nature 376
SPM Exam Practice 2 378
iv
Key Words
FORM 4 denominator – penyebut decomposition – penguraian KEY WORDS
element – unsur discharge – nyahcas
1 Introduction to Chemistry empirical formula – formula empirik displacement reaction – tindak balas
ionic compound – sebatian ion
conclusion – kesimpulan mass – jisim penyesaran
constant variable – pembolehubah molar volume – isipadu molar dry cell – sel kering
molecular formula – formula molekul electrochemical series – siri
yang dimalarkan numerator – pengangka
manipulated variable product – hasil tindak balas elektrokimia
reactant – bahan tindak balas electrochemistry – elektrokimia
– pembolehubah yang reduced – diturunkan electrode – elektrod
dimanipulasikan relative atomic mass – jisim atom electrolysis – elektrolisis
procedure – kaedah/prosedur electrolyte – elektrolit
responding variable – pembolehubah relatif electroplating – saduran elektrik
yang bergerakbalas half-reaction – tindak balas setengah
scientific attitudes – sikap saintifik 4 Periodic Table of Elements non-electrolyte – bukan elektrolit
variable – pembolehubah non-rechargeable cell – sel yang tidak
boiling point – takat didih
2 The Structure of the Atom chemical bonding – ikatan kimia boleh dicas semula
covalent bond – ikatan kovalen potential difference – beza
charged particles – zarah bercas double bond – ikatan ganda dua
chemical reaction – tindakbalas kimia electrical conductivity – kekonduksian keupayaan
collision – perlanggaran primary cell – sel primer
compressibility – kemampatan elektrik rechargeable cell – sel yang boleh
condensation – kondensasi electrostatic force of attraction – daya
diffusion – peresapan dicas semula
duplet – duplet tarikan elektrostatik secondary cell – sel sekunder
electronic configuration – susunan inert gas – gas adi
ionic bond – ikatan ion 7 Acids and Bases
elektron Lewis structure – struktur Lewis
electron shells – petala elektron non-polar – tidak berkutub basicity – kebesan
forces of attraction – daya tarikan organic solvent – pelarut organik degree of dissociation – darjah
freezing point – takat beku polar – berkutub
half-life – setengah hayat shell – petala penceraian
isotope – isotop single bond – ikatan tunggal dilution – pencairan
matter – jirim solubility – kelarutan diprotic acid – asid dwibes
melting point – takat lebur triple bond – ikatan ganda tiga end point – takat akhir
non-renewable – tidak boleh valence electron – electron valens molarity – kemolaran
volatility – kemeruapan monoprotic acid – asid monobes
diperbaharui hydroxide ion – ion hidroksida
nucleon number – n ombor nukleon 5 Chemical Bonds hydroxonium ion – ion hidroksonium
octet – oktet neutralisation – peneutralan
aqueous solution – larutan akueus partial dissociation – penceraian
3 Chemical Formulae and giant molecules – molekul raksasa
Equations intermolecular force – daya tarikan separa
standard solution – larutan piawai
anion (negatively-charged ion) antara molekul titration – pentitratan
– anion (ion bercas negatif) noble gas – gas adi triprotic acid – asid tribes
universal indicator – penunjuk
cation (positively-charged ion) 6 Electrochemistry
– kation (ion bercas positif) semesta
alkaline cell – sel alkali
compound – sebatian anode – anod 8 Salts
crucible – mangkuk pijar cathode – katod
covalent compound – sebatian concentration – kepekatan brown ring test – ujian cincin perang
confirmatory test – ujian pengesahan
kovalen continuous variation – perubahan
berterusan
crystal – hablur
v Key Words
KEY WORDS decolourised – nyahwarna energy profile diagram – rajah profil metal displacement – penyesaran
double decomposition – penguraian tenaga logam
ganda dua observable change – perubahan yang oxidation state – keadaan
evaporation – sejatan dapat diperhatikan pengoksidaan
filtrate – hasil turasan
impurities – benda asing rate of reaction – kadar tindak balas oxidising agent – a gen pengoksidaan
insoluble salts – garam tak terlarutan reactivity series – siri kereaktifan
precipitate – mendakan 2 Carbon Compounds reducing agent – agen penurunan
qualitative analysis – analisa kualitatif sacrificial metal – logam korban
recrystallisation – penghabluran addition – penambahan
alkanes – alkana 4 Thermochemistry
semula alkenes – alkena
residue – baki alkynes – alkuna bond energy – tenaga ikatan
soluble salts – garam terlarutan combustion – pembakaran endothermic reaction – tindak balas
solution – larutan fractionating column – turus
endotermik
9 Manufactured Substances in pemeringkat energy content – kandungan tenaga
Industry functional group – kumpulan energy level diagram – gambar rajah
alloy – aloi berfungsi aras tenaga
biodegradable – terbiodegradasikan general formula – formula am exothermic reaction – tindak balas
borosilicate glass – kaca borosilikat homologous series – siri homolog
brass – loyang hydration – penghidratan eksotermik
bronze – gangsa hydrogenation – penghidrogenan fuel value – nilai haba bahan api
catalyst – mangkin IUPAC nomenclature – sistem heat of combustion – h aba
ceramic – seramik
coagulation – penggumpalan penamaan IUPAC pembakaran
Contact process – proses sentuh saturated – tepu heat of displacement – haba
corrosion – kakisan sootiness – kejelagaan
density – ketumpatan straight chain – rantai lurus penyesaran
ductility – kemuluran structural formula – formula struktur heat of formation – haba
explosive – bahan letupan substitution – penukargantian
fibre optic – gentian optik unsaturated – tak tepu pembentukan
fused glass – kaca silika terlakur carboxylic acid – asid karboksilik heat of neutralisation – haba
lead glass – kaca plumbum coagulation – penggumpalan
malleability – kebolehtempaan dehydration – pendehidratan peneutralan
photochromic glass – kaca fotokromik distillation – penyulingan law of conservation of energy
polymerisation – pempolimeran drying agent – agen pengontangan
refrigerant – bahan penyejuk elasticity – kekenyalan – hukum keabadian tenaga
rust – karat esterification – pengesteran precipitation – pemendakan
soda glass – kaca soda kapur extraction – pengekstrakan reversible reaction – tindak balas
solder – pateri fatty acid – asid lemak
stainless steel – keluli nirkarat fermentation – penapaian berbalik
superconductor – superkonduktor hydroxonium ion – ion hidroksonium specific heat capacity – muatan haba
synthetic fibre – gentian sintetik hydroxyl group – kumpulan hidroksil
polyunsaturated fats – lemak poli tak tentu
FORM 5 thermal dissociation – penceraian
tepu
1 Rate of Reaction volatility – kemeruapan terma
vulcanised – tervulkan thermochemical equation –
activation energy – tenaga
pengaktifan 3 Oxidation and Reduction persamaan termokimia
average rate – kadar purata blast furnace – relau bagas 5 Chemicals for Consumers
catalyst – mangkin cast iron – besi tuangan
collision frequency – frekuensi chemical cell – sel kimia additive – bahan tambahan
displacement reaction – tindak balas analgesic – analgesik
perlanggaran antioxidant – pengantioksida/
collision theory – teori perlanggaran penyesaran
effective collision – perlanggaran electrolytic cell – sel elektrolisis antipengoksida
extraction – pengekstrakan antipsychotic – antipsikotik
berkesan impurity – bendasing biodegradable – terbiodegradasikan
energy barrier – rintangan tenaga biological enzyme – enzim biologi
codeine – kodeina
detergent – detergen
flavouring agent – agen perisa
preservative – pengawet
saponification – saponifikasi
soap – sabun
stabiliser – pengstabil
thickening agent – agen pemekat
Key Words vi
1CHAPTER FORM 4
THEME: Introducing Chemistry
Introduction to Chemistry
SPM Topical Analysis
Year 2008 2009 2010 2011
Paper 1 2 31 2 31 2 31 2 3
Section ABC ABC ABC ABC
Number of questions – – – – – – – – – – – – – – – – – – – –
ONCEPT MAP
INTRODUCTION TO CHEMISTRY
History of chemistry Importance of chemistry Methodology in chemistry
Meaning of chemistry The scientific method Scientific attitudes
and values
Science that studies the • Observe a situation • Attitudes
properties, composition and • Identify all variables • Avoid wastage
structure of substances and • Suggest a problem • Maintain cleanliness
the changes they undergo • Avoid accidents
statement
In the fields of: Careers that need • Form a hypothesis
• Food processing knowledge of chemistry: • Select suitable apparatus
• Medicine • Medicine and Dentistry • Carry out an experiment
• Agriculture • Pharmacy • Collect and tabulate data
• Transportation • Geology • Interpret the data
• Telecommunications • Biochemistry • Write a report
• Daily usage of • Engineering
chemical products
1 1.1 Chemistry and Its (a) Medicine: to fight diseases and prolong life.
Importance Medicine
1 Human beings used chemical processes before (b) Fertilisers and pesticides: increase crop
500 BC to extract metals such as copper and yields.
iron for making ornaments. They also found
ways to make ceramics from clay. However, (c) Preservatives: prolong the storage of food.
they could not explain the chemical processes Food preservative
that took place.
2 The next 1700 years of chemical history were
dominated by a pseudo-science called alchemy
(pseudo means not genuine or false). The word
alchemy originated from the Arabic word ‘al-
kimiya’ (al === the; kimiya === art of changing).
The alchemists in Egypt believed they could
change cheap metals like lead into gold. Their
efforts were unsuccessful but along the way they
(a) discovered other substances like mercury,
sulphur, antimony and phosphorus,
(b) developed some reliable techniques of
chemical manipulation,
(c) learned to prepare some mineral acids such
as sulphuric, hydrochloric and nitric acids.
A chemist carrying out research (d) Materials used for making clothing such as
cotton, silk and nylon.
3 Modern chemistry originated from an
Englishman named Robert Boyle. In 1661, Nylon
he wrote a book called The Sceptical Chymist
which introduced the modern concept of (e) Building materials such as cement,
chemical elements. An element is a substance concrete and glass.
that cannot be broken down into simpler
substances by chemical means. In the Building
centuries that followed, many elements were
discovered.
The Importance of Chemistry
1 Chemistry is the science concerned with the
composition of substances, the basic forms of
matter and the interactions between them.
2 Chemical substances or chemicals are very
important in our lives. The following are a
few examples of chemicals.
Introduction to Chemistry 2
(f) Components of automobiles and computers. (b) how chemicals interact among each other,
and
(g) Consumer products such as soap and
detergents. (c) how to use the knowledge of the properties of
these chemicals to produce new substances.
1
Chemistry Related Careers
1 Many careers require knowledge of chemistry.
For example, a dentist uses hydrogen peroxide
gel (H2O2) to bleach teeth (making it whiter).
For extraction of a tooth, the dentist will
administer a local anaesthetic (procaine)
before extracting the tooth of a patient. To fill
a tooth, he/she will use amalgam which is an
alloy of mercury and silver. Hydrogen peroxide,
procaine and amalgam are all chemicals.
Consumer products
3 Table 1.1 shows the uses of some chemical A dentist at work
substances in our daily life.
4 In chemistry, we study
(a) the basic units that make up these
materials,
Name of substance Table 1.1 Uses
Chemical formula
Oxygen O2 Respiration and combustion
Nitrogen N2 Manufacture of ammonia
Carbon dioxide CO2 In photosynthesis and in making carbonated drinks
Sodium chloride NaCl Food preservation, for example, salted fish
Iron(II) sulphate FeSO4 Iron pills to treat anaemia
CH3COOC6H4COOH
Aspirin An analgesic drug to treat pain and fever
2CaSO4. H2O
Calcium sulphate Used as a cast to support broken bones of accident
hemihydrate victims
Copper-nickel alloy 25% Nickel + 75% Copper To make coins
Urea CO(NH2)2 A nitrogenous fertiliser
Sulphuric acid H2SO4
Ethanol C2H5OH As an electrolyte in a lead-acid accumulator
Sodium stearate
Ethanoic acid (acetic acid) C17H35COONa As a solvent and manufacture of industrial chemicals
CH3COOH
Soap
Preservation of fruits and manufacture of food
flavourings
Calcium carbonate CaCO3 Calcium supplement
3 Introduction to Chemistry
2 A medical doctor needs a knowledge of
chemistry to administer the correct amount of
medicine to a patient. Categories of medicine
include antibiotics, hormones, psychiatric
medicine, analgesics, alkaloids and fungal
creams. All these medicine are chemicals.
1 A doctor Food processing
administering 6 A farmer uses fertilisers to increase the yield of
an injection
his crops. Pesticides, herbicides and fungicides
3 Pharmacy is a branch of science which deals are used to control pests. Therefore, even the
with the interaction of medicine with the farmer is required to have a knowledge of
human body. It also finds ways to synthesise chemistry.
new drugs. Most medicine are organic
compounds. Therefore a pharmacist must A farmer spraying
have an understanding of organic chemistry. pesticides
Pharmacist Chemical-based Industries in Malaysia and
4 The expertise of forensic chemists can help their Contributions
the police to solve crimes. The analyses and Local chemical industries have contributed
identification of samples of blood, drugs, greatly to Malaysia’s economy. These industries
semen, poison, weapons and a host of other not only provide job opportunities but also
items collected from the crime scene are used earn foreign exchange for the country when
as evidence to convict criminals. the chemicals produced are exported. Some
notable chemical industries in Malaysia are:
Analysis of DNA 1 Plants in Pasir Gudang, Johor and Gebeng,
5 Many types of chemicals, namely, preservatives,
Pahang produce chemicals such as
colourings, antioxidants, flavour enhancers, polyethylene. Polyethylene and polypropylene
food stabilisers and artificial flavourings are are used to make many household items
used in the food processing industry. Thus, food such as chairs, raincoats, pails and basins.
technologists require knowledge of chemistry to Table 1.2 shows the chemicals produced by
ensure the correct mixture of these chemicals. the petrochemical plants.
Table 1.2 Chemicals produced by petrochemical
plants in Malaysia
Petrochemical plant Product
BASF Petronas Acrylic polymers
Chemicals Sdn Bhd
Titan Petrochemicals Polyethylene
(M) Sdn Bhd
Petrochemicals (M) Expandable polystyrene
Sdn Bhd
Introduction to Chemistry 4
2 The Asean Bintulu Fertiliser (ABF) plant of the water affect the solubility of
in Sarawak produces urea. This is a project sugar in water.
undertaken by some Asean countries. Urea (ii) A constant variable is the factor
is a nitrogenous fertiliser. Lack of nitrogen which is kept the same throughout
in plants will cause chlorosis whereby the the experiment.
leaves of the plants turn yellowish. To study the effect of temperature
on the solubility of sugar in water,
3 Composite Technology Research of Malaysia the volume of the water used in the
(CTRM) in Malacca produces fibreglass used experiment must be kept constant.
in the making of aircraft and boats. The volume of water is called the
constant variable.
1.1 (iii) A variable which is changed during the
experiment is called the manipulated
1 Name two examples of chemicals used in each of variable. 1
the following fields. An experiment can be carried out by
heating the water to temperatures of
Field Chemicals used 30 °C, 40 °C, 50 °C, 60 °C and 70 °C.
Agriculture The mass of sugar that dissolves at
Medicine different temperatures of water is then
Food processing measured. The temperature of water
is called the manipulated variable.
1.2 Scientific Method (iv) A responding variable is the variable
that responds to the change made
1 Chemistry is an experimental science similar by the manipulated variable. The
to Biology and Physics and requires scientific amount of sugar that dissolves in
research. water at different temperatures is
called the responding variable.
2 There are some basic guidelines in approaching Thus the variables are:
any scientific research. These guidelines are Manipulated variable: Temperature
known as the scientific method. of the water
Responding variable: Amount
3 The scientific method is a systematic approach of sugar that dissolves in water at
to research. It consists of the following steps: different temperatures
(a) Making an observation about a situation Constant variable: Volume of water
A scientific research starts with an (c) Suggesting a problem statement
observation. For example, a student would This is a question which identifies the
have observed a situation as follows: problem related to the observation.
For example,
When he adds 20 g of sugar to 100 cm3 Does the solubility of sugar increase
of hot water and stirred, all the sugar proportionally with the increase in the
dissolved. However, when 20 g of sugar temperature of water?
is added to 100 cm3 of water at room
temperature and stirred, some sugar This will lead to the forming of a
remains undissolved in the water. hypothesis.
(d) Forming a hypothesis
(b) Identifying variables A hypothesis is a proposition, idea, theory
(i) A variable is a factor which affects the or any other statement used as a starting
point for discussion, investigation or study.
results of the experiment. The factors For example, to study the effect of the
that affect the solubility of sugar in temperature of water on the amount of
water are called variables. It is found sugar that dissolves, a probable hypothesis
that the temperature and volume would be:
5 Introduction to Chemistry
Experiment 1.1 The higher the temperature of the the scientist needs to draw a conclusion
1 water, the greater the amount of sugar based on the experimental results.
that can dissolve in it. (j) Writing a report
Lastly, the scientist has to write a report of
(e) Apparatus and materials his/her work. This will enable him/her to
When planning an experiment, suitable communicate with other scientists.
apparatus and materials that are required The general format of a report:
to carry out the experiment are selected.
Title:
(f) Listing a work procedure Aim:
The procedure is the list of steps that needs Problem statement:
to be taken to carry out an experiment. Hypothesis:
It is advisable to list the steps in point Variables:
form. (a) Manipulated variable:
(b) Responding variable:
(g) Carrying out the experiment (c) Constant variable(s):
After planning the experiment, a scientist Materials:
will carry out the experiment according to Apparatus:
the procedure. Procedure:
(h) Data collection Data and observation:
The scientist will then record the results Interpreting data:
of the experiment accurately. He or she Discussion:
should not change the results of the Conclusion:
experiment and must be honest.
4 The following is an example of an experimental
(i) Data interpretation and conclusion report.
After collecting the data, the scientist will
analyse the results of his/her experiment. The
results can be presented in various forms,
such as a table, graph or calculation. Then,
1.1
To investigate the effect of the temperature of water on the solubility of sugar
Problem statement Procedure
Does the amount of sugar that dissolves in water increase 1 100 cm3 of water is
when the temperature of the water increases? measured using a
measuring cylinder and
Hypothesis is poured into a 250
cm3 beaker.
The higher the temperature of the water, the greater
the mass of sugar that dissolves in it. 2 The temperature of the
water is recorded using
Variables
• Manipulated variable: Temperature of water a thermometer.
• Responding variable: Amount of sugar that
3 A 100 cm3 beaker is
dissolves at different temperatures
• Constant variable: Volume of water and size of filled with sugar. The Figure 1.1
beaker and its contents
sugar
are then weighed and recorded as a gram.
Materials Sugar and water. 4 The sugar is added a little at a time to the water
Apparatus
in the beaker using a spatula. The mixture is then
stirred using a glass rod.
100 cm3 measuring cylinder, 250 cm3 beaker, 100 5 The process is continued until no sugar can
cm3 beaker, electronic balance, Bunsen burner,
tripod stand, wire gauze, spatula, thermometer and further dissolve in the water.
glass rod.
6 The beaker and its contents (sugar) are weighed
again and recorded as b gram.
Introduction to Chemistry 6
7 The amount of sugar that dissolved in the water Interpreting data
at room temperature is (a – b) gram.
Figure 1.2 Graph of mass of sugar dissolved
8 The experiment is repeated by heating the water against temperature
to temperatures of 40 °C, 50 °C, 60 °C and 70 °C
respectively. A graph of the mass of sugar dissolved against
temperature is plotted as shown in Figure 1.2.
9 The results are recorded in Table 1.3. (Note: Both axes must be labelled with their units
Results and the title of the graph must be stated)
Temperature Table 1.3 Conclusion 1
(°C) Room 40 50 60 70 The amount of sugar that dissolves in the water
temperature increases when the temperature of the water increases.
Initial mass of The hypothesis is accepted.
beaker and its a bcde
contents (g)
b cde f
Final mass of
beaker and its (a – b) (b – c) (c – d) (d – e) (e – f)
contents (g)
Mass of sugar
dissolved (g)
(Note: The unit of each reading must be
stated:temperature in °C and mass in gram)
1.2 (iii) the constant variable of the experiment.
(c) List the materials and apparatus needed to carry
1 You are required to investigate whether table salt
dissolves in water and kerosene. out the experiment.
(a) State a hypothesis for the experiment. (d) Give a brief procedure of the experiment.
(b) State (e) Tabulate your results.
(i) the manipulated variable,
(ii) the responding variable,
1.3 Scientific Attitudes and 1 A student must develop the following good
Values in Conducting laboratory practices.
Scientific Investigations (a) Positive attitudes
A student should
Scientific Attitudes and Values
(i) have an enquiring outlook,
Students carrying out an experiment (ii) cooperate with other students while
carrying out an experiment,
(iii) be honest and not alter the results of
an experiment.
(b) Safety
(i) Do not carry out an experiment
without the supervision of the
teacher.
(ii) Do not taste any chemicals.
(iii) Do not use burning paper to light a
Bunsen burner.
(iv) Always check the label of the chemical
before using it.
7 Introduction to Chemistry
1 (v) Dispose of all toxic waste in a proper (e) Accidents
container. (i) Any chemical spilled on the body,
(vi) Do not play with electrical clothing or eyes must be washed
appliances. immediately with plenty of water.
(ii) Anychemicalunintentionallyingested
(c) Wastage must be spat out immediately and
(i) Do not waste chemicals. Take only the mouth must be washed with plenty
of water.
whatever is necessary.
(ii) Switch off the gas supply or electricity 1.3
when it is not required. 1 What are the safety precautions that must be taken
(d) Cleanliness when carrying out the following experiments?
(a) Diluting concentrated acid.
After carrying out an experiment, (b) Heating a solution in a test tube.
(i) the apparatus must be cleaned and (c) Carrying out an experiment that involves the
release of a poisonous gas.
returned to the same place,
(ii) the table must be wiped dry with a
towel or rag,
(iii) all solid waste must be thrown into
the dustbin and not into the sink.
1 The scientific method is a systematic approach to (b) Responding variable: A variable that responds
to the change of the manipulated variable.
research.
2 The scientific approach begins with a hypothesis. (c) Constant variable: The factor that is kept
constant throughout the experiment.
A hypothesis is an intelligent guess relating a
5 After carrying out the experiment, you have to write
manipulated variable with a responding variable. a report which includes the following:
3 A variable is a factor that affects the result of a (a) Write the aim or problem statement
(b) State the hypothesis
reaction. (c) List all the variables
(d) List the chemicals and apparatus used in the
For example, the mass of salt that can dissolve in experiment
(e) Tabulation of your data
water depends on the volume and the temperature (f) Interpret your result
(g) Make a conclusion
of the water. Volume and temperature are called
variables.
4 There are three types of variables:
(a) Manipulated variable: A variable that is changed
during the experiment.
Introduction to Chemistry 8
1
Multiple-choice Questions
1.1 Chemistry and Its 7 Which of the following chemicals 11 What is the manipulated variable
Importance of the experiment?
is synthetic? A Magnesium oxide and
1 The chemical used to neutralise A Neon manganese(IV) oxide 1
acidity in soil is B Protein B Mass of magnesium oxide
A potassium nitrate C Sodium hydroxide and manganese(IV) oxide
B calcium hydroxide D Citric acid C Temperature of hydrogen
C copper(II) oxide peroxide solution
D sodium carbonate 8 DDT is a chemical used as D Concentration of hydrogen
peroxide solution
pesticide. It is made up of carbon,
12 What is the constant variable of
2 The chemical used in raising flour chlorine and hydrogen atoms. the experiment?
is
A calcium carbonate The molecular formula of DDT is I Volume of oxygen released
B sodium nitrate II Mass of magnesium oxide
C magnesium sulphate CCl3CH(C6H4Cl)2.
D sodium bicarbonate What is the total number of and manganese(IV) oxide
III Temperature of hydrogen
atoms in a DDT molecule?
peroxide solution
A 3 C 18 IV Concentration of hydrogen
B 17 D 28 peroxide solution
A I, II and III only
3 Which of the following careers 9 Chemical X is used as electrolyte B I, III and IV only
below do not need a knowledge in the accumulator. C II, III and IV only
of chemistry? Chemical Y is used in soap making. D I, II, III and IV
A Geologist What is chemical X and Y?
B Forensic scientist 13 The responding variable for the
C Meteorologist XY experiment is
D Pharmacist A the rate of release of oxygen gas.
A Sulphuric Sodium B the decreasing rate in volume
4 The branch of chemistry that acid hydroxide of hydrogen peroxide.
studies carbon compounds is C the rate of increase in
A organic chemistry B Sodium Sulphuric concentration of hydrogen
B polymer chemistry hydroxide acid peroxide.
C inorganic chemistry D the decreasing rate in mass of
D industrial chemistry C Hydrochloric Sodium the metal oxide.
acid hydroxide
14 Magnesium ribbon reacts with
5 Chloroform has the formula of D Sodium Hydrochloric hydrochloric acid as shown.
CstHatCelm3. eWnhtsicahreoftrtuhee following hydroxide acid Mg + 2HCl → MgCl2 + H2
about the If you are required to study
the effect of concentration of
chloroform molecule? 1.2 Scientific Method hydrochloric acid on the rate of
reaction above, what variables
I It is made up of three elements. must be constant?
II It is made up of five elements. 10 The factor that affects the result I Time of reaction
II Temperature of hydrochloric acid
III The molecule consists of five of an experiment is called a III Size of beaker
IV Length of magnesium ribbon
atoms. A solute C result
A IV only
IV The molecule consists of four B solution D variable B II and IV only
C I, II and IV only
atoms. For questions 11 – 13, use the D II, III and IV only
A I and III only information given below:
B I and IV only
C II and III only Hydrogen peroxide decomposes as
D II and IV only
represented by the equation:
6 The substance that cannot be 2H2O2 → 2H2O + O2
broken down into simpler form is
called A student is required to study the
A compound C molecule effect of magnesium oxide and
B element D particle manganese(IV) oxide on the rate of
decomposition of hydrogen peroxide.
9 Introduction to Chemistry
15 “The greater the quantity of sodium chloride added to ice, the lower its 20 Q Analyse data
melting point”. If you are required to study the above hypothesis, what is the R Observe a situation
manipulated variable? S Make a hypothesis
A Mass of ice
B Types of salt added T Carry out the experiment
C Mass of salt added
D Temperature of ice U Collect data
16 “Without water iron will not rust”. Which of the following is correct in carrying The steps above are the steps
out the experiment to prove the statement above? taken to carry out a scientific
investigation. The correct order in
1 Manipulated variable Constant variable carrying out the investigation is
A Presence or absence of water Rusting of iron A S, R, T, U, Q
B Presence or absence of water Presence or absence of air B R, S, T, U, Q
C Presence or absence of water Presence of air C R, T, U, Q, S
D Presence or absence of air Presence of water D R, T, U, S, Q
17 A student wants to find out the effect of temperature on the solubility of 21 During electrolysis, the mass of
sugar in water. Which of the following is correct? metal deposited at the cathode
is dependent on the time and
Manipulated variable Responding variable Constant variable the amount of current passed
through the electrolyte. If you are
A Temperature of Mass of sugar Volume of water required to show that the mass of
water dissolved metal deposited is proportional
to the current passed through the
electrolyte, what are the variables
in this experiment?
B Volume of water Mass of sugar Temperature of water Manipulated Constant
dissolved variable variable
C Mass of sugar Temperature of Volume of water A Time Types of
dissolved water electrodes
B Time used
D Temperature of Mass of sugar Humidity of the air
water dissolved C Amount of Amount of
current current
18 An experiment is carried out to study the solubility of sodium chloride in
water and in benzene. What is the (i) manipulated variable (ii) constant D Amount of Types of
variable of the experiment? current electrodes
used
Manipulated variable Constant variable
A Solvent Rate of stirring Time
B Solvent Mass of sodium chloride
C Solute Volume of solvent 1.3 Scientific Attitudes and
D Solute Rate of stirring Values
19 A hypothesis 22 What precautions must you take
when storing concentrated nitric
I is a law of science. acid?
A Store it in a dark place
II can be a true or false statement. B Store it in a fume cupboard
C Store it in a locked cupboard
III is a conclusion derived from the result of the experiment. D Store it away from any
Bunsen burner
IV is a statement that relates the manipulated variable and the responding
23 What precaution must you take
variable. when diluting concentrated
A I and III only sulphuric acid?
B II and IV only A Add the concentrated
C I, II and III only sulphuric acid to water
D II, III and IV only
Introduction to Chemistry 10
B Add water to the concentrated 25 27 An experiment should be carried 1
sulphuric acid out in the fume cupboard if it
A bottle of chemical has a label involves
C Mix equal volumes of the shown in the diagram. What does A the release of poisonous gas.
concentrated sulphuric acid this label represents? B the release of flammable gas.
and water together A Flammable chemical C the use of corrosive
B Corrosive chemical chemicals.
D Mix one volume of C Radioactive chemical D the use of oxidising
concentrated sulphuric acid D Oxidising chemical chemicals.
to three volumes of water
together 26 When heating a solution in a 28 Why is it important to understand
boiling tube, what precaution the experimental procedures
24 must you take? before carrying out the
A Never heat the solution too experiment?
A bottle of chemical has a label strongly
as shown in the diagram. What B Never hold the boiling tube I To prevent wastage of
precaution must be taken when vertically chemicals
storing this chemical? C Never use a Pyrex boiling tube
A Store it in a dark place to heat the solution II To prevent accidents from
B Store it in a fume cupboard D Never direct the mouth happening
C Store it in a locked cupboard of the boiling tube at your
D Store it away from any classmates III To prevent repetition of the
experiment
Bunsen burner
IV To know what apparatus
is needed to carry out the
experiments
A I, II and III only
B I, III and IV only
C II, III and IV only
D I, II, III and IV
Structured Questions
1 Table 1 shows the time taken for a 5 cm length of seconds. From the graph in (i), determine
magnesium ribbon to dissolve in 50 cm3 of dilute
hydrochloric acid of different concentrations. the concentration of the hydrochloric acid
solution. [1 mark]
Concentration of 0.1 0.2 0.3 0.4 0.5 2 Table 2 shows the mass of two salts P and Q that
hydrochloric acid (mol dm–3) dissolved in 100 cm3 of water at different temperatures.
Time taken for a 5 cm 30 26 22 18 14 Temperature Solubility of salt (mass of salt
magnesium ribbon to (°C) soluble in 100 cm3 of water)
dissolve (s)
Salt P (g) Salt Q (g)
Table 1 30 5 7
40 10 14
(a) State 50 15 21
60 20 28
(i) the manipulated variable, 70 25 35
(ii) the responding variable and
(iii) the constant variable of the experiment
above. [3 marks]
(b) State a hypothesis for this experiment. [1 mark] Table 2
(c) (i) Plot a graph of concentration of hydrochloric (a) State one other variable, besides temperature,
acid against time taken for the magnesium that affects the solubility of salt. [1 mark]
to dissolve. [5 marks]
(ii) If a 5 cm length of magnesium ribbon is (b) In the experiment above, state
(i) the manipulated variable
added to a hydrochloric acid solution of (ii) the constant variable
(iii) the responding variable
unknown concentration, the time taken for
the magnesium ribbon to dissolve is 17 [3 marks]
11 Introduction to Chemistry
1 (c) Plot a graph of the solubility of salts P and Q (a) State a hypothesis for the experiment above.
against temperature on the same axis. [4 marks] [1 mark]
(d) What can you conclude from the graphs in (c)? (b) What is the
[2 marks] (i) manipulated variable
(ii) responding variable
3 The procedure below shows the sequence in (iii) constant variable when carrying out the
carrying out an experiment to study the effect of the
temperature of water on the mass of sugar that can experiment? [3 marks]
dissolve.
(c) Calculate the mass of sugar that dissolved in water
Procedure: at various temperatures and write your answer in
• Initial mass of beaker P and sugar is taken (a gram). the right column of the table. [2 marks]
• 50 cm3 of water is poured into a separate 100 cm3
(d) Plot a graph of the mass of sugar that dissolved
beaker. The water is heated to 30 °C. against the temperature of water. [3 marks]
• Sugar is added to the 50 cm3 of water at 30 °C
(e) From your graph, estimate the mass of sugar that
a little at a time while stirring the mixture until no can dissolve in water at 45 °C. [1 mark]
more sugar can further dissolve.
• The final mass of beaker P and sugar is taken (b 4 (a) Name four chemicals used in food processing.
gram). The mass of sugar that dissolved is (a – b) [4 marks]
gram.
• The experiment is repeated by dissolving the sugar (b) Name six careers that need a knowledge of
in water heated to 40 °C, 50 °C, 60 °C and 70 °C.
chemistry. [6 marks]
The results are tabulated in Table 3.
(c) Name three contributions of chemical industries
Initial mass Final mass Mass of to the country. [3 marks]
Temperature of beaker P of beaker P sugar
of water (°C) and contents and contents dissolved (d) Name five scientific values that must be observed
when carrying out scientific research. [5 marks]
(g) (g) (g)
(e) Name two types of chemicals that can increase
30 92.50 87.50
the yield of crops. [2 marks]
40 87.50 77.50
50 77.50 62.50
60 62.50 42.50
70 42.50 17.50
Table 3
Essay Questions
1 ‘Without air, an iron nail will not rust’. You are required (b) The list below shows the steps involved in carrying
to plan an experiment to verify the statement. out scientific research:
(a) List the apparatus and materials needed to carry Making a hypothesis, making a conclusion, collecting data,
out the experiment. [3 marks] making an inference, making an observation, carrying out
an experiment, interpreting data, identifying variables and
(b) State (i) the manipulated variable, (ii) the planning the procedure of the experiment.
responding variable and (iii) the constant variable
of the experiment above. [3 marks]
(c) Briefly write the procedure for the experiment. (i) Arrange the steps in the correct order.
[10 marks]
[8 marks]
(d) Tabulate your results. [4 marks] (ii) Explain the difference between inference
and hypothesis. [4 marks]
2 (a) Explain the meaning of the scientific method. (iii) State three ways of presenting the
[2 marks] experimental results. [6 marks]
Introduction to Chemistry 12
Experiments
1 ‘The greater the volume of water, the higher the solubility of salt’. Plan an experiment to prove the [3 marks]
statement. Your answer should include the following items: [3 marks]
(a) Aim of experiment [3 marks]
(b) Statement of hypothesis [3 marks]
(c) All variables [3 marks]
(d) List of materials and apparatus [3 marks]
(e) Procedure
(f) Tabulation of data
2 The table shows the pH values of 25 cm3 sodium hydroxide solutions of different concentrations
measured by a student using a pH meter.
Concentration of sodium hydroxide solution 0.1 0.2 0.3 0.4 0.5 1
(mol dm–3)
pH value 13.0 13.3 13.5 13.6 13.7
(a) State the variables of this experiment. [3 marks]
(b) Suggest a hypothesis for the experiment. [3 marks]
(c) Plot a graph of pH value against concentration of the NaOH solution. [3 marks]
(d) Using the graph that you have plotted, determine [3 marks]
(i) the pH value of a sodium hydroxide solution with a concentration of 0.35 mol dm–3.
(ii) the concentration of NaOH solution with a pH value of 13.4.
3 Manganese(IV) oxide is a catalyst that speeds up the decomposition of hydrogen peroxide (H2O2) to form
water and oxygen gas as represented by the equation:
2H2O2(l) → 2H2O(l) + O2(g)
A student carried out an experiment by adding different amounts of manganese(IV) oxide to 50 cm3 of 0.2
mol dm–3 hydrogen peroxide solution.
The table shows the results obtained by the student.
Quantity of manganese(IV) oxide (g) 0.2 0.4 0.6 0.8 1.0
Time taken to collect 50 cm3 of oxygen (s) 30 25 20 15 10
(a) State the [3 marks]
(i) manipulated variable, [3 marks]
(ii) responding variable,
(iii) constant variable of the experiment.
(b) What can you conclude from the results of the experiment?
13 Introduction to Chemistry
2CHAPTER FORM 4
THEME: Matter Around Us
The Structure of the Atom
SPM Topical Analysis
Year 2008 2009 2010 2011
Paper 123 123 123 123
Section
ABC ABC ABC ABC
Number of questions 5 —21 – – – 6 —21 – – –
2 1–– – 3 1–– –
ONCEPT MAP
MATTER
Kinetic theory of matter Atomic structure
Changes in states of Diffusion in a solid, liquid Particles in matter: atom, molecule and ion
matter and gas
Subatomic particles: proton, electron and neutron
Determination of the Electron arrangement in atoms
melting and freezing and valence electrons
points of naphthalene
Symbols of elements
A X
Z
Isotopes
2.1 Matter SPM (b) When the gas tap in the laboratory is turned
on, the smell of the gas is immediately
’08/P1 detected. This shows that the gas is also
made up of particles in motion.
1 Chemistry is the study of matter, its
composition and the changes it undergoes. 7 An element is a substance that cannot be
made into anything simpler by means of a
2 Matter is anything that occupies space and chemical reaction.
has mass. In other words, matter is anything
8 The particles in some elements are made
that has volume and mass. up of atoms. For example, metals like gold,
3 Examples of matter are books, pens, chairs, copper, iron, zinc are all made up of atoms.
water, air and plants. Examples of non-matter 2
are electricity and light.
4 The particle theory of matter states that matter
is made of very tiny discrete particles. The
particulate nature of matter is investigated in
Activity 2.1.
5 Elementary particles that make up matter may
be atoms, molecules or ions.
1 ’04
Substance Chemical formula Figure 2.1 Copper foil is made up of atoms
Naphthalene C10H8
Iron Fe 9 A compound is a substance that can be
Sodium chloride NaCl
made into something smaller by means of a
chemical reaction.
State the particles present in each of the above 10 Compounds contain more than one element.
substances.
The elements in a compound are not just mixed
Solution Naphthalene – molecules, iron – atoms,
sodium chloride – ions. together. They are joined by strong forces called
chemical bonds. Compounds do not have the
same properties as the elements they contain.
Compounds are
(a) formed by chemical reactions, and
(b) they have different properties from the
elements they contain.
All metals and noble gases are made up of atoms. 11 The particles in compounds may be molecules
A compound formed between non-metallic elements
(example: naphthalene, C10H8), is made up of molecules. or ions. Molecules are made up of two or
A compound formed between a metal and a non-metal
(example: sodium chloride, NaCl) is made up of ions. more atoms held together by chemical bonds.
Molecules are particles that are not charged.
12 A molecule may consists of atoms of the same
element, for example, oxygen molecules (O2),
6 The existence of these particles is supported nitrogen molecules (N2), hydrogen molecules
13 (AH2m) oanledcusulelphmuarymaollseoculceosn(sSi8s)t (Figure 2.2(a)).
by some observations. Some examples are: of dissimilar
(a) When a drop of atoms of two or more elements. For
ink falls into a example, a water molecule (H2O) consists of
one oxygen and two hydrogen atoms, and a
glass of water,
the colour of carbon dioxide molecule (CO2) consists of
one carbon and two oxygen atoms (Figure
the ink spreads
throughout the 2.2(b)).
water. This shows 14 Some molecules can be very large. For example,
that ink is made quinine which is a drug used to treat malaria
up of particles in Dropping ink into a patients has the formula C20H24N2O2.
motion. glass of water
15 The Structure of the Atom
2 (a) Model of nitrogen, oxygen and sulphur (a) The particles (atoms, molecules or
molecules
ions) possess kinetic energy. They are in
(b) Model of carbon dioxide and water molecules constant motion and constantly collide
Figure 2.2
with each other.
15 However, some compounds consist of atoms or (b) The velocities of the particles in the three
a group of atoms that carry positive or negative
charges. These charged particles are called physical states of matter—solid, liquid
ions. For example, table salt, NaCl, consists and gas—are different.
of sodium ions (Na+) and chloride ions (Cl–) (c) The higher the temperature, the higher
(Figure 2.3). The rust on an iron nail consists of the kinetic energy, as the velocity of the
iron(III) ions (Fe3+) and oxide ions (O2–).
particles increases.
(d) At a given temperature, the lighter particles
move faster than the heavier ones.
2 In 1827, Robert Brown (a botanist) made an
observation through a microscope. He found
that pollen grains on the surface of water are
in constant motion. He explained that the
pollen grains are moving because the moving
water molecules are constantly colliding
with the pollen grains. The visible motion
of these pollen grains is called the Brownian
motion.
3 The Brownian motion gives the evidence that
a liquid consists of particles in constant
movement.
Figure 2.3 Model of sodium chloride crystal
16 Ions which are positively-charged are called Figure 2.4 Pollen grain being bombarded by water
cations. For example, sodium ions (Na+) and molecules
iron(III) ions (Fe3+) are cations. 4 Another evidence of the movement of particles
17 Ions which are negatively-charged are called is diffusion. Diffusion is the random
movement of particles from a region of high
anions. For example, chloride ions (Cl–) and concentration to a region of low concentration.
oxide ions (O2–) are anions. You can smell perfume
18 Generally, metals form positive ions and non- while you walk past
cosmetic counters.The
metals form negative ions. Some examples of perfume particles have
left the open perfume
cations and anions are given in Table 2.1. bottles and spread
out through the air by
Table 2.1 diffusion.
Examples of positive H+, K+, Cu2+, Al3+, NH4+, 5 There are three states of matter, namely,
ions (cations) Mg2+, Ca2+, Zn2+, Pb2+ and Ag+ solid, liquid and gas. Table 2.2 shows the
comparison between the three states of matter.
Examples of negative Br–, I–, OH–, NO3–, SO42–,
ions (anions) CO32–, PO43–, O2–, S2–
and S2O32–
The Kinetic Theory of Matter
1 The kinetic theory is an extension of the
particle theory of matter. According to the
kinetic theory:
The Structure of the Atom 16
Table 2.2 Comparison between the three states of matter SPM
solid liquid
’11/P2
States of matter gas
Arrangement The particles are very closely The particles are closely The particles are very far
of particles packed. packed but there are more apart from each other.
empty spaces between them
Forces of The very strong forces compared to the solid state. The forces of attraction are 2
very weak. The particles
attraction of attraction restrict the The forces of attraction are move randomly in all
weaker than in the solid state. directions at great speed.
between particles movement of the particles. The particles are no longer
held in fixed positions. Gases do not have fixed
The particles in a solid are shapes or volumes.
Liquids have fixed volumes.
held in fixed positions. However, they do not have Vibration, rotation and
fixed shapes but take the translation
Volume and Solids have fixed volumes shapes of the containers. The kinetic energy of the
shape and shapes. particles are very high and
Vibration, rotation and they move at high speed.
Types of Vibration and rotation translation Easily compressed because
movement the particles are very far
The kinetic energy of the The kinetic energy of apart
Kinetic energy particles are low. the particles are high, on
of particles average. Very high
Compressibility Very difficult to be Not easily compressed
compressed because the because the particles are
particles are packed closely packed quite closely
Rate of diffusion Very low Average
Diffusion SPM
1 Diffusion refers to the process by which particles ’08/P2
intermingle as a result of their kinetic energy
of random motion.
2 Figure 2.5(a) shows a container that consists
of gases A and B. The two gases are separated
by a partition. The particles of both gases
are in constant motion and make numerous
collisions with the partition.
3 If the partition is removed as in Figure 2.5(b),
the gases will mix because of the random
motion of their particles.
In time, a uniform mixture of gases A and B
particles will be produced in the container.
4 The rate of diffusion depends on the
temperature and the molecular mass of the
particles. The higher the molecular mass, the
lower the rate of diffusion.
17 The Structure of the Atom
To investigate the diffusion of particles in a gas, liquid SPM
and solid
’09/P1
Apparatus Two gas jars with plastic covers, beaker, teat pipette, boiling tube, spatula and rubber stopper.
Materials Liquid bromine, potassium manganate(VII), KMnO4 crystals, water and hot jelly solution.
Procedure
Activity 2.1 (A) Diffusion in a gas 1 A few drops of liquid bromine are dropped into a gas jar using a teat
2 pipette.
Figure 2.6
(B) Diffusion in a liquid 2 The gas jar is covered with a gas jar cover.
3 An empty gas jar is placed upside down on top of the first jar.
Figure 2.7 4 The cover is removed and any colour change is recorded. The time
(C) Diffusion in a solid
taken for the brown bromine vapour to spread into the second gas jar is
Figure 2.8 recorded.
1 A beaker is —32 filled with water.
2 A few potassium manganate(VII) crystals are placed at the bottom of
the water using a spatula.
3 Any colour change is recorded. The time taken for the purple
manganate(VII) ions to spread throughout the water is recorded.
1 Some freshly cooked jelly solution is poured into a boiling tube until it
is almost full.
2 The jelly is allowed to set.
3 A small potassium manganate(VII) crystal is placed on top of the jelly.
4 The boiling tube is then stoppered using a rubber stopper.
5 Any colour change is recorded. The time taken for the purple
manganate(VII) ions to spread throughout the solid jelly is recorded.
Results Observation
Experiment
A The brown bromine vapour spreads out into the upper gas jar. The time taken is very short.
B
After about 10 minutes, the purple colour of the manganate(VII) ions had spread throughout
C the water.
After a week, the purple colour of the manganate(VII) ions had spread throughout the solid
jelly.
The Structure of the Atom 18
Discussion
1 Diffusion has taken place in the gas (air in experiment A), liquid (water in experiment B) and solid (jelly
in experiment C).
2 The rates of diffusion of the particles in the solid, liquid and gaseous states are different. It is highest in
gases, lower in liquids and lowest in solids.
3 This shows that there are more and bigger spaces between particles in the gas. The spaces between liquid particles
are smaller. The particles in the solid state are very close with little space between them.
4 The occurence of diffusion proves that matter (bromine and potassium manganate(VII)) consist of particles
in constant motion.
5 The diffusion experiments show that because particles possess kinetic energy, they are in constant motion.
2
The Changes in the States of Matter SPM
1 A substance can be changed from one state into another when it is heated or cooled. ’10/P2
2 The changes in the state of the substance can be explained using the kinetic theory model.
Heating Heating
Solid Liquid Gas
1 The particles in a solid are 1 When a liquid is continuously 1 When a gas is cooled,
packed closely in a fixed heated, the partic les receive more the particles lose kinetic
pattern. energy and move even faster. They energy. The movement of
2 When the solid is heated, collide with each other more often. the particles slows down.
the particles receive heat 2 At the boiling point, the particles 2 The forces of attraction
energy. The kinetic energy receive enough energy to between the particles are
of the particles increases overcome the forces of attraction formed which hold the
and the particles vibrate holding them together. The particles particles together in the
faster. in the liquid state break loose to liquid state.
3 At the melting point, the become the gaseous state. 3 The process whereby the
particles vibrate so much 3 When the liquid is cooled, the gas changes into a liquid
that they break away from movement of the particles slows is called condensation.
their fixed positions. The down. Stronger forces of attraction 4 The temperature at which
solid becomes a liquid. between the particles are formed. the gas condenses to the
4 The temperature at which 4 The particles are arranged in an liquid state is the
the solid changes into the orderly mann er in the solid state. The same as the boiling point.
liquid state is called the process whereby the liquid changes
melting point. into a solid is called solidification.
The temperature at which this process
occurs is called the freezing point.
5 The melting point and the freezing
point of a substance have the same
value.
Cooling Cooling
19 The Structure of the Atom
Activity 2.2 When a state of matter gains or loses heat, it undergoes 3 Examples of substances that undergo sublima
2 a change. tion are iodine, ammonium chloride and
A gain in heat is called an endothermic change. A loss solid carbon dioxide (dry ice).
in heat is called an exothermic change.
The process in which substances change
Sublimation directly from the gaseous to the solid state is
also called sublimation.
1 Certain substances do not melt when heated.
SPM They change directly from the solid to the Melting Point and Boiling Point
’11/P1 gaseous state.
2 This process is called sublimation. 1 No two substances have the same melting
and boiling points. We can thus identify a
substance by its melting and boiling points.
2 The melting and boiling points of a substance
will change when there is a small amount of
impurity in it. For example, the melting point
of pure water is 0 °C and its boiling point is
100 °C. A small amount of salt added to the
water will decrease its melting point to –2 °C
and increase its boiling point to 102 °C.
3 As the melting and boiling points of an
impure substance will deviate slightly from its
standard values, we can determine the purity
of a substance by the melting and boiling
points of the substance.
To determine the melting and freezing points of
naphthalene
Apparatus (A) Heating of naphthalene
1 3 spatulas of naphthalene powder are placed in a
Boiling tube, retort stand and clamp, tripod stand,
Bunsen burner, wire gauze, thermometer (0 – 110 °C), boiling tube.
500 cm3 beaker, 250 cm3 conical flask, test tube 2 A 500 cm3 beaker is filled with water until it is
holder and stopwatch. about —43 full. It is then placed on a tripod stand.
3 The boiling tube containing naphthalene is clamped
Materials Naphthalene and water.
in the beaker of water, making sure the naphthalene
Procedure powder is below the water level of the water bath.
4 The water bath is heated until it reaches a
Figure 2.9 temperature of about 65 °C as shown in Figure
Heating of 2.9. The water is then heated with a low flame.
naphthalene 5 A stopwatch is started and the temperature of the
naphthalene is recorded at 30-second intervals until
Figure 2.10 the temperature reaches 90 °C. The naphthalene is
Cooling of stirred continuously during the experiment.
naphthalene 6 The results are recorded in a table.
(B) Cooling of naphthalene
1 The boiling tube containing the molten naphthalene
is removed from the hot water bath using a test
tube holder.
2 It is immediately transferred into a conical flask
to be cooled slowly as shown in Figure 2.10.
The Structure of the Atom 20
3 The stopwatch is started and the temperature of Discussion
the naphthalene is recorded at 30-second intervals
until it drops to about 70 °C. The naphthalene is 1 In the heating of naphthalene, a water bath is
stirred continuously during the experiment. used instead of direct heating. This is to ensure
that an even heating process is carried out.
4 The results are recorded in a table.
2 In the cooling of naphthalene, the boiling tube
Results containing the liquid naphthalene is cooled
inside a conical flask. This is to ensure that an
(A) Heating of naphthalene even cooling process is carried out.
Time (s) Temperature (°C) 3 Stirring the naphthalene continuously also
ensures even heating or cooling.
0 2
30 4 A water bath is suitable in this experiment
60 because the melting point of naphthalene is
90 below 100 °C, the maximum temperature that
120 can be attained by the water bath.
150
180 5 If the melting point of the substance is above
210 100 °C, the water bath will have to be replaced
by an oil bath or a sand bath.
(B) Cooling of naphthalene
6 Besides naphthalene, the other substance that is
Time (s) Temperature (°C) suitable for heating by water bath is acetamide.
7 The heating curve of naphthalene consists of
three regions: AB, BC and CD as in Figure 2.11.
0 Region in State of substance and the
30 the graph energy change
60 Region AB
90 Naphthalene is in the solid state. As
120 SPM napthalene is heated, heat energy is
150 converted to kinetic energy. Kinetic
180 ’04/07 energy increases and the molecules
210 P2 vibrate faster about their fixed
positions. Temperature increases as the
Analysis of data Point B molecules receive more heat energy.
1 A graph of temperature Region BC As the kinetic energy of the molecules
increases, the molecules vibrate
SPM against time is plotted SPM faster. At point B, some molecules
’10/P1 for the heating of vibrate so much that they break away
’11/P1 from their fixed positions. The solid
naphthalene. The graph naphthalene begins to melt.
is shown in Figure 2.11. Naphthalene now consists of a
mixture of solid and liquid. At
2 A graph of temperature this region the temperature remains
constant because the heat energy
against time is plotted Figure 2.11 Heating curve supplied by the water bath is the
for the cooling of same amount as the heat energy
of naphthalene absorbed. Heat energy is absorbed to
naphthalene. The graph overcome the forces of attraction
holding the naphthalene molecules
is shown in Figure 2.12. together in the solid state. The heat
absorbed to overcome the forces of
3 When plotting a graph, attraction is called the latent heat
of fusion. Latent heat of fusion of
make sure that:
(a) The axes are
labelled with their
units.
(b) The points are
transferred
correctly. Figure 2.12 Cooling curve
(c) The curve is smooth. of naphthalene
21 The Structure of the Atom
Region in State of substance and the Region in State of substance and the
the graph energy change the graph energy change
a substance is the heat required to moving except for small vibrations.
convert a solid into a liquid without
a change in temperature. At point Q, the liquid naphthalene
begins to solidify or freeze.
Point C All the naphthalene has completely Region QR Naphthalene now consists of a
melted. mixture of liquid and solid. At
this region the temperature remains
2 Region CD Naphthalene is in the liquid state. As constant because the heat energy
the liquid naphthalene is heated, the lost to the environment is the same
molecules gain more heat energy. The amount as the heat energy released.
temperature continues to increase. Latent heat of fusion is released when
forces of attraction are formed
8 The cooling curve of naphthalene consists of between the molecules as the liquid
three regions: PQ, QR and RS as in Figure 2.12. naphthalene solidify (or freezes).
Region in State of substance and the Point R All the naphthalene has completely
the graph energy change solidified.
Region PQ Naphthalene is in the liquid state. Region RS Naphthalene is in the solid state. The
solid naphthalene continues to lose
The liquid naphthalene loses heat to heat to the environment and hence
the environment. The kinetic energy the temperature drops down to room
of the molecules decreases as the temperature.
temperature decreases.
Point Q As the kinetic energy of the molecules Conclusion
decreases, the molecules move slower.
At point Q, some molecules stop The melting point and the freezing point of
naphthalene is 80 °C.
2 ’09
A I and III only C I, II and III only
B II and IV only D I, II and IV only
Comment
From time 0 to t1 the substance loses heat to the
surroundings. Hence the temperature decreases.
(Statement I is incorrect)
From time t1 to t2 condensation takes place and heat
energy is released. The kinetic energy of particles
becomes lower and the forces of attraction become
stronger. (Statement II is correct)
The graph shows the cooling curve for gas X. From time t2 to t3 the particles continue to lose heat to
Which of the following statements are true? the surroundings. Hence the kinetic energy of particles
I From time 0 to t1 heat energy is absorbed. decreases. (Statement III is incorrect)
II From time t1 to t2 forces of attraction between
From time t3 to t4 freezing takes place. The temperature
particles become stronger. of the substance remains constant because during
III From time t2 to t3 the kinetic energy of particles freezing, heat energy released is equal to the heat lost
to the surroundings. (Statement IV is correct)
increases.
IV From time t3 to t4 heat energy released is equal to Answer B
the heat lost to the surroundings.
The Structure of the Atom 22
2.1
1 State the type of particles (atoms, molecules or
ions) that make up the substances below.
(a) Ammonia gas (d) Potassium iodide
(b) Sodium chloride (e) Copper wires
(c) Iron nail (f) Cooking oil
2 The graph shows the heating curve for Figure 2.13 John Dalton and his model
naphthalene.
3 However, Dalton’s atomic model had its
weakness. It was found that: 2
(a) The atom is not the smallest particle in
(a) State the melting point of naphthalene. an element. There are subatomic particles
(proton, electron and neutron) in an atom.
(b) What is the physical state of naphthalene at (b) A radioactive atom decomposes spon
taneously, which means that an atom can
time t second? be destroyed. A new atom can also be
created by a process called transmutation.
(c) Why does the temperature remain constant at (c) Not all atoms of an element are alike. They
may differ in atomic mass. For example,
region BC although heating is carried on?
4 In 18h9yd7roJ.geJ.nThhaosmthsroeenisdoitsocpoevser11eHd, n21Hegaantidve31Hly.-
(d) Draw the cooling curve obtained when the charged particles which he called electrons.
Thomson then suggested that an atom is
molten naphthalene is cooled from T3 to a positively-charged sphere with electrons
room temperature. embedded in it like a raisin pudding.
2.2 The Atomic Structure
The Historical Development of the Figure 2.14 J. J. Thomson and his model
Atomic Model 5 In 1911, Ernest Rutherford bombarded a thin
1 The concept of the atom originated from gold foil with alpha particles (helium nuclei,
Democritus, a Greek philosopher. He proposed He2+).
that if a piece of gold is divided repeatedly, it (a) It was found that most of the alpha particles
will reach a state whereby the smallest particle,
which is indivisible, is obtained. He called passed directly through the gold foil without
the smallest indivisible particle atomos, which deflection. Rutherford then suggested that
means ‘indivisible’ in Greek. most of the atom must be empty space.
2 In 1808, John Dalton proposed the atomic Figure 2.15(a) Rutherford’s experiment
theory. In this theory, Dalton proposed that:
(a) All elements are made up of small
indivisible particles called atoms.
(b) Atoms are neither created nor destroyed
in chemical reactions.
(c) The atoms of an element are alike, but
differ from the atoms of other elements.
(d) When atoms combine, they do so in a
simple ratio.
(e) All chemical reactions result from the
combination or separation of atoms.
23 The Structure of the Atom
Figure 2.15(b) Magnified view showing alpha 7 In 1932, James Chadwick discovered rays of
particles deflected by the electrically neutral subatomic particles which
nuclei of gold atoms he called neutrons. The neutron has a mass
almost the same as that of a proton. Chadwick
(b) However, some of the alpha particles were suggested that the nucleus of the atom contains
deflected at very acute angles. To explain protons and neutrons, and the nucleus is
the deflection of the alpha particles, surrounded by a cloud of electrons.
Rutherford proposed that all the positive
2 charge of an atom is concentrated in the
nucleus, which repelled the positively-
charged alpha particles in the opposite Figure 2.18 James Chadwick and his model
direction. Further experimental studies
led to the discovery of positive particles 8 The atomic model in the present day is based
in the nucleus. Rutherford called the on the contributions of the above scientists.
positively-charged particles protons. In this atomic model:
(a) The nucleus of an atom consists of
(c) Rutherford proposed that an atom protons and neutrons occupying a small
consists of a positively-charged nucleus space in the centre of the atom.
with a cloud of electrons surrounding the (b) Electrons are moving around the nucleus
nucleus. in permissible orbits or electron shells
(also known as quantum shells).
SPM
Subatomic Particles of an Atom
’08/P1
An atom is made up of three smaller particles
Figure 2.16 Ernest Rutherford and his model which are called protons, neutrons and electrons.
6 In 1913, Niels Bohr proposed that the These particles are called subatomic particles.
Table 2.3 shows the relative masses and charges of
electrons in the atom are arranged in permitted these particles.
orbits called electron shells surrounding the
nucleus. Table 2.3 The symbols, relative masses and the
charges of subatomic particles
Figure 2.17 Niels Bohr and his model
Subatomic Symbol Relative Charge
particle mass
Proton p 1 +1
Electron e —1—8—14—0 –1
Neutron n 10
The Structure of the Atom 24
3 ’05 that the number of neutrons in phosphorus is
31 – 15 = 16.
The diagram shows a model of an atom. 6 The relative masses of the proton and neutron
are almost similar. However, the relative mass
Who introduced this model? of the electron is very small. So the mass of an
A Niels Bohr atom is determined by the number of protons
B J. J. Thomson and neutrons in the atom.
C John Dalton 7 The nucleon number and proton number of
D Rutherford SPM an element is written in the following way:
Answer A ’09/P2
Niels Bohr. He proposed that electrons are arranged
in shells surrounding the nucleus.
2
Proton Number and Nucleon Number A student need not memorise the proton number and
nucleon number. It will be given in the examination.
1 Protons and neutrons are located in the The proton number is smaller than the nucleon number.
nucleus and the electrons are arranged in
electron shells surrounding the nucleus. 4 ’03
2 The nucleus is positively-charged because State the number of protons, electrons and neutrons
it contains protons, each of which carry a in a chlorine atom, 1377Cl.
positive charge. Solution 17 protons, 17 electrons and 20 neutrons
3 The proton number of an element is the (37 – 17 = 20)
number of protons in its atom. The proton
number is also known as the atomic number. Symbols of Elements
Each element has its own proton number.
No two different elements can have the same 1 Each element is represented by a symbol,
proton number. For example, sodium, with consisting of either one letter or two letters of
a proton number of 11 means that it has 11 the alphabet.
protons in its nucleus and an element with 11
protons in its nucleus must be sodium. 2 Some elements are represented by the first letter
of its name. Examples are in the following table.
4 In a neutral atom, the proton number
also tells us the number of electrons. For Name of element Symbol
example, the proton number of magnesium Hydrogen H
is 12. Therefore, a magnesium atom has 12 Nitrogen N
protons and 12 electrons. The proton number Oxygen O
of nitrogen is 7 and hence a nitrogen atom Fluorine F
has 7 protons and 7 electrons. Sulphur S
5 The nucleon number (also known as the 3 The names of some elements start with the same
SPM mass number) of an element is the sum of the letter. For example, the names of the elements
’11/P2 number of protons and neutrons in its atom. Nitrogen, Neon, Nickel and Nobium start
with the letter ‘N’. Therefore, a second letter is
nNuumclbeoern = Npurmotboenrso f + Nnuemutbroernos f added to differentiate between these elements.
The second letter used is always a small letter.
OR Examples are in the following table.
nNuumclbeoern = nPuromtobner + Nnuemutbroernos f
For example, a sodium atom has 11 protons
and 12 neutrons; hence the nucleon number
of sodium is 23.
The proton number of phosphorus is 15
while its nucleon number is 31. This means
25 The Structure of the Atom
Name of element Symbol and 53 stand for? How many protons, electrons
Silicon Si and neutrons are there in an iodine atom?
Neon Ne
Chlorine Cl 2 (a) A list of elements are represented by the letters
Calcium Ca given below:
Bromine Br
Magnesium Mg 11 A, 12 B, 24 C, 23 D, 14 E and 14 F
5 6 12 11 6 7
4 Some elements are represented by the letters Which two letters represent the same
of their Latin names. For example,
element? Explain your answer.
(b) State four facts that you can derive from the
nuclear symbol, 2173Al.
2 Name of Latin Name Symbol 2.3 Isotopes and Their
element Argentum Ag Importance
Silver
Copper Cuprum Cu Isotopes
Iron Ferrum Fe
Gold Aurum Au 1 Isotopes are atoms of the same element with
Lead Plumbum Pb SPM the same proton number but different nucleon
Tin Stannum Sn ’10/P1 numbers. Alternatively, isotopes can be defined
Potassium Kalium K
Sodium Natrium Na as atoms of an element with the same number
Mercury Hydrargyrum Hg of protons but different numbers of neutrons.
2 Many elements exhibit the phenomenon of
2.2 isotropy, whereby an element can have more
1 (a) An atom of uranium (U) has 92 protons and than one type of isotope.
3 The isotopes of an element have the same
143 neutrons. What is the proton number and
chemical properties because they have the
nucleon number? Write its atomic symbol. same electron arrangement but their physical
properties such as densities and melting
(b) Seaweed is rich in the element iodine,
points differ.
rceapnrecsaeunsteedgobiyte1r.2573Wl. hLaatckdoof iodine in our diet 4 Table 2.4 shows examples of isotopes of some
the numbers 127
elements.
Table 2.4 Examples of isotopes of some elements SPM
’07/P2
Element Proton Nucleon Number of Number of Percentage
number number protons neutrons abundance
Hydrogen, 11H 1 1 1 0 99.985%
Deuterium, 12H 1 2 1 1 0.015%
Tritium, 13H 13 1 2 Man-made isotope
Carbon-12, 126C 6 12 6 6 98.1%
Carbon-13, 136C 6 13 6 7 1.1%
Carbon-14, 146C 6 14 6 8 Trace amount
Chlorine-35, 1375Cl 17 35 17 18 75.5%
Chlorine-37, 1377Cl 17 37 17 20 24.5%
Oxygen-16, 168O 8 16 8 8 99.757%
Oxygen-17, 178O 8 17 8 9 0.038%
Oxygen-18, 188O 8 18 8 10 0.205%
Same Different Same Different
Nucleon number = Number of protons + Number of neutrons
The Structure of the Atom 26
5 Some elements, such as fluorine, F, have only number and nucleon number of the isotope 2
one isotope. However, most elements have may change.
9 There are many uses of radioisotopes, namely,
more than one isotope. in the field of medicine, agriculture, industry,
6 The relative atomic mass of an element is archaeology, food preservation and electricity
generation.
based on the average mass of all the isotopes
Isotopes are atoms of an element with the same
of the element. For example, the relative number of protons but different numbers of neutrons.
Alternatively, isotopes can be defined as atoms of an
atomic mass of chlorine is 35.5 because element with the same proton number but different
nucleon numbers.
chlorine has 75% of 3157Cl and 25% of 3177Cl.
7 In an element, some isotopes are stable
while the rest are unstable isotopes. Unstable
isotopes are radioactive isotopes.
8 Radioactive isotopes will undergo spontaneous
decay to emit radioactive rays: alpha, beta
and gamma. After radioactive decay, the proton
Uses of Isotopes in Daily Life SPM
’05/P2
Medicine
1 Cobalt-60 is a radioactive isotope of cobalt. to the thyroid gland. The radiation given
It decays by giving out gamma radiation. In out by the radioactive iodide ions will kill
radiotherapy, malignant cancer cells are the malignant cancer cells without affecting
killed by directing a beam of gamma rays the other parts of the body.
towards the cancer cells.
SPM
’09/P1
Radiotherapy is used to kill cancer cells Patient suffering from thyroid cancer
2 Patients suffering from thyroid cancer are 3 Some medicine, surgical gloves, bandages,
given a drink containing sodium iodide, plastic hypodermic syringes are sterilised
(NaI) containing radioactive iodide ions. The by using gamma radiation. These materials
radioactive iodide ions move preferentially cannot be sterilised by boiling.
Agriculture
1 Using the radioactive carbon-14 (14C) in pests are then exposed to gamma radiation
which can cause genetic mutation to the
carbon dioxide, the path of carbon during the gametes (sperms). The male pests are then
released to be allowed to mate with the females.
photosynthesis process can be determined. The offsprings produced will have physical
defects such as undeveloped digestive
The rate of absorption of phosphorus by the organs and wings. This will terminate the
survival of the following generation.
plant can be determined by adding radioactive
phosphate ions (32PO34–) to the ground. using
2 Male pests can be attracted into traps
female hormones (pheromone). The male
27 The Structure of the Atom
Industry
1 Beta radiation is used to control the thickness partially filled in which case a higher reading
of paper, plastic, metals and rubber made in will be recorded.
industry. A radioactive source is located at the
bottom of the material being produced. A
detector is located on top of the material. Any
change in the reading of the recorder signifies
a change in thickness of the material.
2 Figure 2.20 Using radiation to detect if a container
is fully filled
Figure 2.19 Using radiation to control the
thickness of materials 3 Radioisotopes are used to detect leaks
in pipes carrying gas. A radioisotope (for
2 Gamma radiation is used to detect whether example, sodium-24) is added to the gas
canned food or bottled drink is completely so that it will be carried along by the gas
filled or only partially filled. A radioactive flowing through the pipe. A detector is then
source emitting gamma radiation is directed moved along the external wall of the pipe.
to the bottled or canned food. More radiation The detection of a high radioactive reading
will pass through if the container is only will signify the location of the leakage.
Figure 2.21 Using radiation to detect a leak
Archaeology SPM
Carbon-14 is used to determine the age ’08/P1
of archaeological artifacts. Plants take in
carbon-14 in the form of carbon dioxide (14CO2) The age of bones dug
during photosynthesis. Carbon-14 is incorpo out from a historical site
rated into animals or human beings when the can be estimated using
plants are eaten. As long as the organism is alive, carbon-14 dating. For
the amount of carbon-14 in it remains constant. very old bones, much
This is because the intake of carbon-14 through of the C-14 would have
food is offset by its spontaneous decay. However, decayed. The minute
when the organism dies, the intake of carbon-14 amount of C-14 left will
is stopped. The amount of C-14 ‘locked’ in the show little radioa ctivity.
body will continue to decay. The amount of A recent archaeological
C-14 remaining (measured by its activity) is sample will have a high
inversely proportional to the age of the artifacts. reading of C-14.
Source: Jabatan Muzium Malaysia
The Structure of the Atom 28
Food preservation Radiation can be used to delay rotting of
fruits and vegetables
1 Food such as vegetables, fruits and meat rot due to the
activity of fungus and bacteria. These microorganisms can
be killed by irradiating the food with gamma radiation of
cobalt-60. The shelf-life of the food can be extended using
this method. Irradiation is better than chemical preserva
tives because it does not have adverse effects on health.
2 Irradiation can also slow down budding in potatoes and
onions, thus extending their shelf-life. Gamma radiation
can also slow the ripening of fruits to be exported.
Generation of electricity 2
Nuclear energy is an alternative source of This causes the uranium nuclei to split,
energy to replace fossil fuels such as petroleum, producing heat energy. The heat energy released
natural gas or coal. The nuclear fuel used is is used to produce steam from water. The steam
uranium-235. The uranium atoms become drives the turbine of the generator, producing
unstable when bombarded with fast neutrons. electricity.
5 ’05 2.4 The Electronic Structure
of an Atom
Name an isotope and state its purpose for each of
Electron Arrangement in an Atom
the following fields:
1 Niels Bohr suggested that the electrons in an
(a) Medicine (c) Archaeology atom occupy orbits with definite energy levels.
Each of these orbits or energy levels can hold
(b) Industry (d) Food preservation a certain number of electrons. The electrons
are not static but are moving around.
Solution
(a) Cobalt-60 (gamma radiation from decay of 2 The electron orbits are also known as quantum
Co-60 is used to kill cancer cells) shells. The shells are labelled first shell, second
(b) Sodium-24 (beta radiation from decay of shell, third shell and so on, away from the
Na-24 is used to detect leakages in pipes) nucleus.
(c) Carbon-14 (it is used to estimate the age of
archaeological artifacts) 3 The first shell is the one nearest to the nucleus
(d) Cobalt-60 (gamma radiation from decay of and is filled first. It can hold a maximum of
Co-60 is used to kill fungus or bacteria that two electrons.
can cause food to rot)
4 After the first shell is full, the remaining electrons
2.3 are filled into the second shell. The second shell
can hold a maximum of eight electrons.
1 Uranium has three isotopes: 23942U, U235 and 23982U.
92 Figure 2.22 The electron shells of an atom is
labelled away from the nucleus
What do you understand by the term isotopes?
5 After the first and second shells are full, the
State the differences between these isotopes. remaining electrons are filled into the third shell.
The third shell can take a maximum of eight or
2 A list of elements are represented by letters of the 18 electrons. If the number of electrons of an
alphabet as given below. Choose a pair of isotopes
from these elements. Explain your answer.
2131A, 12573B, 7394C, 13515D, 13513E, F55
25
3 Give an example of a radioactive isotope of
carbon. What is meant by radioisotope? Give a
use of the isotope given in your example.
29 The Structure of the Atom
atom is more than 20, the third shell will hold Eight electrons are filled in the second shell.
Eight electrons are filled in the third shell.
18 electrons. If the number of electrons is 20 or Two electrons are filled in the fourth shell.
The electron arrangement of calcium is 2.8.8.2.
less, the third shell will hold 8 electrons.
6 Table 2.5 shows the maximum number of 9 The electrons in the outermost occupied shell
are called the valence electrons. Therefore,
electrons permitted in each shell. carbon atom has four valence electrons,
7 The way in which the electrons are distributed chlorine atom has seven valence electrons and
calcium atom has two valence electrons.
in the shells of an atom is called the electron
arrangem ent or electronic configuration of 10 Elements with the same number of valence
electrons have the same chemical properties.
the atom. For example, lithium, sodium and potassium
of Group 1 of the Periodic Table have the
SPM Table 2.5 Maximum number of electrons same chemical properties because each atom
’11/P2 permitted in each shell of an atom has one valence electron.
Shell Maximum number of electrons
2 First 2
Second 8
Third 8 or 18
Fourth 32
8 The examples below show the electron Group 1 Electron Number of
arrangement of some elements: element arrangement valence electrons
1 Lithium 2.1 1
Sodium 2.8.1 1
The carbon atom, 126C has six protons. Potassium 2.8.8.1 1
In a neutral atom, the number of electrons =
the number of protons. 11 Group 17 elements have the same chemical
Hence there are six electrons and are arranged as properties because each element has seven
follows: valence electrons.
Two electrons are filled in the first shell.
Four electrons are filled in the second shell. Group 17 Electron Number of
The electron arrangement of carbon is 2.4. element arrangement valence electrons
2 Fluorine 2.7 7
Chlorine 2.8.7 7
The chlorine atom, 3157Cl has 17 protons. Bromine 2.8.18.7 7
In a neutral atom, the number of electrons = Iodine 2.8.18.18.7 7
the number of protons.
The 17 electrons are arranged as follows: 12 The inert or noble gases of Group 18 of the
Two electrons are filled in the first shell. Periodic Table are very stable. They have filled
Eight electrons are filled in the second shell.
Seven electrons are filled in the third shell. outer shells of electrons.
The electron arrangement of chloride is 2.8.7.
Group 18 Electron Number of
3 element arrangement valence electrons
The calcium atom, 4200Ca has 20 protons. Helium 2 2
In a neutral atom, the number of electrons = Neon 2.8 8
the number of protons. Argon 2.8.8 8
The 20 electrons are arranged as follows:
Two electrons are filled in the first shell. 13 Helium has exactly two electrons in the first
shell. It has attained the duplet electron
arrangement which is stable. Neon and argon
each has eight electrons in the outermost
shell. It has attained the octet electron
arrangement which is stable.
The Structure of the Atom 30
14 Table 2.6 shows the diagrammatic electronic structures and the electron arrangements of elements
with proton numbers 1 to 20.
Table 2.6 The diagrammatic electronic structure of elements with proton numbers 1 to 20 SPM
’04,05
06/P1
’08/P1
2
6 ’04 2131X, 3157Y, 162Z. Write the electronic configuration of
each of these elements.
The atomic symbol of element X is 199X. Which of
the following is true about the subatomic particles Solution
of element X? Proton Number Number Electronic
number of of configuration
Proton Nucleon Electronic
number number configuration protons electrons
A9 19 2.7 X 11 11 11 2.8.1
B9
C 19 19 2.8.8.1 Y 17 17 17 2.8.7
D 19
9 2.7 Z6 6 6 2.4
9 2.8.8.1
Comment 2.4
The proton number of X is 9. Hence it has 9 protons
and 9 electrons. The 9 electrons are arranged as 1 Write the electron arrangement and draw the
follows: atomic structures of carbon and magnesium
Two electrons in the first shell and the remaining atoms. [Proton number: C, 6; Mg, 12]
seven electrons are arranged in the second shell.
Its electronic configuration is 2.7. 2 The diagram shows the atomic
structure of an element X.
Answer A (a) In an atom of X, how
many of the following
7 ’04 are there?
The chemical symbols of three elements X, Y and Z (i) Valence electrons
are shown as follows: (ii) Protons
(b) What is the nucleon number of X if it has 16
neutrons?
(c) Write the atomic symbol of element X.
31 The Structure of the Atom
2.5 Appreciating the Rutherford discovered the proton in 1911 and
Orderliness and James Chadwick discovered the neutron in
Uniqueness of the 1932. Niels Bohr explained the arrangement
Atomic Structure of the electrons in an atom.
3 We now know that the protons and neutrons
1 John Dalton proposed the atomic theory are located at the center of the atom called the
about 200 years ago in 1807. Before that nucleus. The electrons are arranged in orbits
scientists thought that atoms were solid around the nucleus.
particles like marbles. 4 The atomic structure of an atom can help us
understand the chemical properties of the
2 About 100 years later, other scientists discovered elements better and how they are bonded
the subatomic particles. J.J. Thomson together to form compounds.
discovered the electron in 1897. Ernest
2
1 There are three states of matter: solid, liquid and 5 During freezing, the temperature remains constant
gas.
because heat energy is released and the energy
2 When a substance is heated or cooled it will change
released is equals to the heat lost to the surrounding
state.
3 The table shows the energy involved during the during cooling.
change in state: 6 The proton number is the number of protons in
the nucleus of an atom.
Change of Change in 7 The nucleon number is the total number of
state energy
Process protons and neutrons in the nucleus of an atom.
Solid to liquid Melting Heat energy is
absorbed 8 Isotopes are atoms of the same element which
Liquid to gas Boiling/
evaporation Heat energy is contain the same number of protons but different
Solid to gas Sublimation absorbed
numbers of neutrons.
Liquid to solid Freezing Heat energy is
absorbed 9 The protons and neutrons are enclosed in the
Gas to liquid Condensation
Heat energy is nucleus whereas the electrons are arranged in shells
Gas to solid Sublimation released
surrounding the nucleus.
Heat energy is
released (a) The first shell can hold a maximum of two
Heat energy is electrons.
released
(b) The second shell can hold a maximum of
eight or 18 electrons.
(c) The third shell can hold a maximum of 18
electrons.
However for atoms with proton numbers
1 – 20, the atom attains stability when its third
shell has eight electrons.
(d) The valence electron is the electron in the
outermost shell of the atom.
4 During melting the temperature remains constant For example, the electronic configuration of the
because heat energy absorbed is used to overcome cTahleciucmalciautmoma,to4200mCahaiss
the forces of attraction between the molecules. 2.8.8.2. electrons.
two valence
The Structure of the Atom 32
2
Multiple-choice Questions
2.1 Matter 4 An inflated balloon will shrink D The air particles diffuse out of
faster at higher temperature than the balloon at a faster rate at
1 What process and change in heat at lower temperature. higher temperature.
energy takes place when iodine
5 Carbon dioxide(CO2), sulphur 2
’11 crystals are heated at room
temperature and pressure?
Process Change in cddaiioouxxsiieddeea((cNSidOOr22a))inaan.red nitrogen that
heat energy three gases
A Melting Heat energy Which of the following lists the
absorbed
molecules in order of increasing
B Melting Heat energy
released average speed?
Heat energy [Relative atomic mass: C, 12;
absorbed
C Sublimation N, 14; O, 16; S, 32]
D Sublimation Heat energy Which of the following is the Slowest Fastest
released best explanation for this
observation?
2 Which statements below are true A The air particles liquefy at A Sulphur Nitrogen Carbon
about a gas? dioxide dioxide dioxide
I They move at low speed. lower temperature.
II They are easily compressed. B The air particles react to form B Sulphur Carbon Nitrogen
III They have a higher rate of dioxide dioxide dioxide
diffusion compared to a liquid. other compounds at higher
IV They spread throughout the C Nitrogen Sulphur Carbon
vessel in which they are temperature. dioxide dioxide dioxide
contained. C The air particles come
A I, II and III only D Carbon Sulphur Nitrogen
B I, III and IV only closer together at lower dioxide dioxide dioxide
C II, III and IV only
D I, II, III and IV temperature.
3 The diagrams show the spacing 6 The table shows the changes in physical states and energies of four
of the molecules of a substance substances.
at two different temperatures.
Process Name of Change of physical Change of energy
at –110 °C at 85 °C process state
I Heat is released
II Freezing Solid to liquid Heat is absorbed
III Melting Solid to liquid Heat is absorbed
IV Boiling Solid to gas Heat is released
Condensation Gas to liquid
What is the likely melting point and Which of the following processes above are correct?
boiling point of the substance?
A I and III only C I, II and IV only
Melting point Boiling point B II and IV only D II, III and IV only
(°C) (°C)
7 Which of the following statements is true about pentane molecules when it
A –125 90
is cooled to a temperature of –129 °C? [Melting point of pentane is –135 °C
B –117 78
and its boiling point is 36 °C].
C –102 75 A The pentane molecules remain static.
B The pentane molecules move randomly.
D –98 105 C The pentane molecules are arranged closely together.
D The distance between the pentane molecules increases.
33 The Structure of the Atom
8 The graph shows the ’07 Magnesium oxide Sodium Ammonia
temperature against time of a Ions Atoms Molecules
substance X when it is heated. A Ions Molecules Molecules
B Molecules Molecules Atoms
C Ions Ions Ions
D
2.2 The Atomic Structure
11 Which of the following sets is correct? The scientists who discovered the
electron, proton and neutron are
’08
2 Which of the statements below Electron Proton Neutron
are true about X ?
I X starts to melt at Q. A Ernest Rutherford J.J. Thomson James Chadwick
II The melting point of X is
III TX1e°xCis. ts in gaseous state at B J.J. Thomson Ernest Rutherford James Chadwick
region TU. C J.J. Thomson Ernest Rutherford Niels Bohr
IV At region RS, there is a
D J.J. Thomson James Chadwick Ernest Rutherford
mixture of solid and liquid X.
A I and III only 12 What can be deduced from the I It belongs to Group 15 in the
B II and IV only 31 Periodic Table.
C I, II and III only symbol 15 P?
D I, III and IV only II It belongs to Period 3 of the
I Phosphorus atom has five Periodic Table.
9 The diagram shows the graph of
temperature against time for the valence electrons. III It forms an ion with a charge
heating of substance X. of –3.
II Phosphorus atom has 15
temperature (°C) IV It is a metal.
protons and 31 neutrons. A I, II and III only
B I, III and IV only
III Phosphorus atom has 16 C II, III and IV only
D I, II, III and IV
neutrons.
15 The diagrams show three models
IV Phosphorus atom has proton of the atom.
number of 15 and nucleon
number of 31.
A I, II and III only
B I, III and IV only
65 C II, III and IV only
D I, II, III and IV
t1 t2 time (s) 13 Two particles P and Q have the
following compositions:
Particle Electron Neutron Proton
Which statements below are true P 10 10 9
about substance X? Q 10 12 11
I It is a gas at room
temperature.
II It undergoes physical change It follows that Name the scientists who proposed
A P and Q are both negatively- these models?
at 65 °C.
charged
III It absorbs heat at time B P and Q have the same
IV Iint teexrivsatslsats1 aanmd ixt2t.ure of liquid
nucleon number. I II III
C P and Q are particles of the
and solid at time intervals t1 A James J.J. Ernest
Iaannddt2II. only same element.
D P is negatively-charged and Q Chadwick Thomson Rutherford
A is positively-charged. B Niels Bohr John Ernest
B I and III only Dalton Rutherford
C II and III only
C Niels Bohr J.J. Ernest
D II and IV only 14 An atom X has an electron
arrangement of 2.8.5. Which of Thomson Rutherford
the following statements about X
10 State the particles in magnesium are correct? D Niels Bohr Ernest J.J.
oxide, sodium and ammonia. Rutherford Thomson
The Structure of the Atom 34
16 An atom has the symbol Isotope Use 25 Which of the following 79
11 III Carbon-14 35
5 X. Which of the following To estimate the age comparisons between Br and
IV Sodium-24 of archaeological 81
statements about X are correct? artifacts 35 Br are correct?
I It has 5 valence electrons in To detect leakages Bromine-79 Bromine-81
in pipes
its atom.
II It has 6 neutrons in its atom. I Has 35 Has 35
protons protons
III It belongs to Group 13 of
the Periodic Table. A I, II and III only II Has 35 Has 35
B I, II and IV only electrons electrons
IV It belongs to Period 2 of the C II, III and IV only
D I, II, III and IV
Periodic Table.
A I, II and III only III Has 35 Has 35
neutrons neutrons
B I, II and IV only
C II, III and IV only 21 Which of the following statements IV Has 44 Has 46
are true about isotopes? neutrons neutrons
D I, II, III and IV
I They have the same chemical
2
properties.
17 The atoms 12 C and 11 B have the A I and IV only
6 5 II They have different physical B II and III only
same C I, II and IV only
properties. D I, III and IV only
A number of protons
III The have a different number
B number of neutrons
of neutrons.
C physical properties
IV They have the same number
D chemical properties 26 The radioisotope that is used to
of valence electrons.
2.3 Isotopes and Their A I, II and III only kill cancerous cells is
Importance B I, III and IV only A uranium-235
C II, III and IV only B cobalt-60
18 asTtwnadote2um39r82aeUnn.ituWsmbheiicslohowtoofipstehtseruafeore?llo239w52iUng D I, II, III and IV C carbon-14
D phosphorus-32
A The U235 atom has fewer 22 Oxygen has the isotope 16O, 17O 2.4 The Electronic Structure
92 238 of an Atom
electrons than 92 U atom. and 18O. Which of the following
U235
B The 92 atom has 92 oxygen gas has the lowest rate of
protons and 235 neutrons. diffusion? 27 Which of the following particles
C Tphroeto23n982sUaantdom14h6anse9u2trons. A 16O = 16O
B 17O = 17O have eight valence electrons?
C 18O = 18O
D Thhavee239t5h2 Ue atom annudm2b398e2Ur oaftom D 17O = 18O I 186 W III 4108 Y
same I2131aXn+d III only IV 3157 Z–
II
neutrons. 23 A
B II and IV only
19 Isotopes are different atoms with C I, II and III only
the same number of D II, III and IV only
A protons but different number
28 Which of the following particles
of neutrons.
B electrons but different X Y contains 18 electrons, 19 protons
number of protons. Which term describes the and 20 neutrons?
C protons, electrons and
particles X and Y shown above? A 39 X + C X39 –
neutrons. A Isotopes C Anions 19
D protons but different number B Isomers D Cations 18
of electrons and neutrons. B 40 X 2+ D X39
20
19
20 Which of the following pairs are 24 An element has two isotopes, 29 How many protons and neutrons
correct? are there in one tin atom with
which are represented by 127X nucleon number 119?
Isotope Use and 131X. How does 127X differ Protons Neutrons
68
I Uranium-235 To generate from 131X ? A 50 69
electricity A It has four less neutrons and B 50 71
C 50 119
II Iodine-131 To kill cancerous three less electrons. D 50
thyroid cells B It has four less neutrons.
C It has four less protons and
three less electrons.
D It has four less protons.
35 The Structure of the Atom
30 The symbol of an element X is 33 Which of the following elements Element W XYZ
40 given below have the same 6 7 12 15
X. We can deduce that an atom number of valence electrons? Proton
o18f element X number
I has eight valence electrons. 19 V ; 27 W; 35 X; 39 Y; Z40
9 13 17 19
II has 22 neutrons in its nucleus. 20
III has three electron shells. A W and Y only A Y and Z only
B X and Z only B X and Z only
IV has a total of 18 electrons in C V and X only C X and Y only
D V and Y only D W and Z only
its atom.
A I, II and III only
B I, III and IV only 34 Which of the following list are the 38 The electronic configuration of
C II, III and IV only electron arrangements of all non- arsenic is 2.8.18.5.
D I, II, III and IV metals? Which of the following
statements is true?
31 Two particles X and Y have the A 2.6 2.7 2.8.5 A Arsenic has three valence
following composition:
2 B 2 2.5 2.8.3 electrons.
Particle Electrons Neutrons Protons B Arsenic is in Group 14 of the
C 2.1 2.7 2.8.6
X 10 12 11 Periodic Table.
D 2.1 2.8.2 2.8.3 C The nucleon number of the
Y 11 12 11
35 An ahtaosm203199 Y arsenic atom is 33.
Which of the following statements I neutrons. D Arsenic is in the same group
are true about X and Y?
I Both X and Y are negatively- II has 19 protons. of the Periodic Table as an
charged. III has one valence electron. element with proton number
II Both X and Y are positively-
IV has four electron shells. 7.
charged.
III Both X and Y have the same A I, II and III only
nucleon number. B I, II and IV only 39 The electronic configuration of
IV Both X and Y are particles of
C II, III and IV only the ion X– is 2.8.18.18.8.
the same element.
A I and III only D I, II, III and IV The ion X– has 74 neutrons.
B II and IV only
C III and IV only 36 What is the number of subatomic Determine the nucleon number
D II, III and IV only 60
particles in 27 Co2+ ion? of element X.
A 127
Protons Neutrons Electrons B 128
C 129
A 27 33 27 D 130
B 27 33 25 40 The electronic configuration
32 An element X39 C 33 27 27 of the strontium ion, Sr2+ is
A has one
19 electron. D 33 27 25 2.8.18.8. The Sr2+ ion has 49
valence neutrons. Determine the nucleon
B forms a positively-charged ion 37 The table shows the proton number of strontium.
numbers of four elements. Which A 85
of charge +2. of the following pairs of elements B 86
has the same number of valence C 87
C is located in Group 17 of the electrons? D 88
Periodic Table.
D has 19 protons and 39
neutrons.
Structured Questions
1 Carbon has two isotopes as shown in Table 1 below. (ii) What is the difference between the two
Atom Proton number Nucleon number isotopes 126C and 146C? [1 mark]
126C (b) Draw the atomic structure of 146C using, x, to
represent an electron. [2 marks]
146C (c) Give one use of 146C. [1 mark]
Table 1 ’08 (d) What is the number of valence electrons in both
(a) (i) Complete Table 1 with the proton numbers of the carbon atoms above? [1 mark]
and nucleon numbers of the two different
carbon isotopes. [2 marks]
The Structure of the Atom 36
2 Diagram 1 shows a graph of temperature against time (g) (i) Explain the meaning of the term isotope.
of substance M when it is heated until it boils.
[2 marks]
(ii) State a pair of isotopes from the particles in
Table 2. [1 mark]
4 Table 3 shows four substances and their respective
formulae.
’04
Substance Chemical formula
Diagram 1 Bromine Br2
Iron Fe
(a) State the physical state of M at the region
Naphthalene C10H8
(i) PQ (iii) RS Sodium chloride NaCl
2
(ii) QR (iv) ST [3 marks] Table 3
(b) When does M begin to boil? [1 mark] (a) State two substances that consist of molecules.
[1 mark]
(c) What is the melting point of M? [1 mark]
(d) Explain why the temperature of M remains (b) Which of the following substances has the highest
melting point: bromine, iron or naphthalene?
constant from time t1 to t2. [1 mark]
[1 mark]
(e) Sketch the graph obtained when molten M is
(c) (i) State the substance that can conduct
cooled from 450 °C to room temperature. [2 marks]
electricity in the solid state. [1 mark]
3 Table 2 shows the proton numbers and nucleon numbers
of five particles represented by the letters V, W, X, Y and Z. (ii) Draw the arrangement of the particles of this
substance. [1 mark]
Particle Proton Nucleon Electron (d) Name the particles present in sodium chloride.
number number arrangement [1 mark]
V 6 12 (e) Diagram 2 shows the graph of temperature against
W 8 16 time obtained when solid naphthalene is heated.
X 8 18
Y 11 23
Z 16 32
Table 2
(a) Write the electron arrangements of all the
particles in Table 2. [2 marks]
(b) What is the number of valence electrons in Diagram 2
particle V ? [1 mark]
(c) Draw the atomic structure of particle Y. [2 marks] (i) State the melting point of naphthalene. [1 mark]
(d) State the number of electron shells in particle Z. (ii) Explain why there is no change in temperature
[1 mark]
from Q to R. [2 marks]
(e) Explain the meaning of nucleon number. [1 mark] (iii) State how the movement of naphthalene
particles changes between R and S during
(f) What is the number of neutrons in particle Y ? [1 mark] heating. [1 mark]
Essay Questions
1 (a) Compare the three physical states of matter You are given two substances X and Y. They are
either naphthol or naphthalene.
in terms of particle arrangements, forces of You are required to carry out an experiment
to identify X and Y. Design an experiment to
attraction between the particles, kinetic energy of determine X and Y.
the particles and compressibility. [8 marks] The Structure of the Atom
(b) Table 1 shows the melting points of naphthol and
naphthalene.
37
Chemical Melting point (°C) 2 (a) Define the following terms:
(i) Proton number
Naphthol 65 (ii) Nucleon number [3 marks]
Naphthalene 80 (iii) Valence electron
Table 1 [12 marks] (b) (i) What are isotopes? [3 marks]
(ii) Give an example of a pair of isotopes. [2 marks]
(iii) Discuss six uses of isotopes. [12 marks]
2 Experiments
1 An experiment is carried out to determine the melting point of naphthalene. Solid naphthalene is heated
and its temperature is recorded every 30 seconds.
’05 Diagram 1 shows the recorded temperature readings at 30-second intervals.
Diagram 1 [3 marks]
(a) Record the temperatures in the spaces provided in Diagram 1. [3 marks]
(b) Draw a labelled diagram of the apparatus used to carry out the experiment. [3 marks]
(c) Plot a graph of temperature against time for the heating of naphthalene. [3 marks]
(d) State the melting point of naphthalene. [3 marks]
(e) What is the physical state of naphthalene at time 90 seconds? [3 marks]
(f) Explain why the temperature between time 60 s to 120 s remained constant. [3 marks]
(g) Sketch a graph you expect to obtain if the molten naphthalene is cooled to room temperature.
[3 marks]
2 ‘The melting point of a substance is lowered by the presence of impurities’. [3 marks]
Using naphthalene and a mixture of naphthalene with some acetamide, describe an experiment to prove [3 marks]
the statement above. Your answer should include the following items: [3 marks]
(a) Aim of experiment [3 marks]
(b) All variables involved
(c) List of apparatus and materials used
(d) Procedure of experiment
(e) Tabulation of results
The Structure of the Atom 38
3CHAPTER FORM 4
THEME: Matter Around Us
Chemical Formulae and
Equations
SPM Topical Analysis
Year 2008 2009 2010 2011
Paper 1 2 31 2 31 2 31 2 3
Section ABC ABC ABC ABC
Number of questions 4 —21 – – – 9 1 – – – 4 – – – – 4 – – – –
ONCEPT MAP
FORMULAE AND CHEMICAL EQUATIONS
Atom Molar mass Molecule
Mass of matter
Relative atomic mass Relative molecular mass
Relative atomic mass, Relative molecular mass,
Ar in gram Mr in gram
3 Molar mass 4 Molar mass
Volume of gas 4 Molar volume Number of moles 3 Avogadro constant Number of particles
Reactants 3 Molar volume 4 Avogadro constant
Chemical equation Products of reaction
Empirical formula Chemical formula Molecular formula
3.1 Relative Atomic Mass and Relative Molecular Mass
1 It is impossible to weigh an atom in gram. So Relative = ———M1——a—ss—m—o—fa—os—sn—o—e—fa—ot—on—me—c—oa—r—fb—tho——en—-e—1l—e2—ma—t—eo—nm—t
chemists compared how heavy one atom is to atomic mass
another atom which is taken as the standard. of an element
The comparison of the mass of an atom to 12
another is called the relative atomic mass
(r.a.m.). For example, a sodium atom, Na is 23 times
heavier than one-twelfth of the mass of one
carbon-12 atom. Thus the relative atomic mass
of Na is 23.
3 ———11—2————m——aMs—s—a—os—sf—oo—nf—e—o—nc—ae—rNb——oa—n—a-—t1o—2m—a—t—o—m— = 23
The relative atomic mass of atoms or relative (Note: the mass of one carbon-12 atom is 12
molecular mass of molecules can be determined units)
using the mass spectrometer with carbon-12 as the
standard 5 A molecule is a small group of atoms joined
together. The simplest being diatomic
2 In 1961, scientists agreed to use carbon-12 as molecules like O2, N2 and Cl2. Examples of
the standard. The mass of a carbon-12 atom triatomic molecules are CO2 and H2O. Some
is assigned a value of exactly 12 units. examples of larger molecules are ammonia
(NH3), methane (CH4), sulphur (S8),
3 Carbon is chosen as the standard because phosphorus (P4) and ethanol (C2H5OH).
(a) the abundance of carbon-12 isotope is
almost 99%. Carbon-13 and carbon-14 6 The relative molecular mass (Mr) of a
isotopes make up about only 1%. compound is defined as the number of times
Thus the mass of a carbon atom using one molecule of the compound is heavier than
carbon-12 isotope or using the average one-twelfth of the mass of a carbon-12 atom.
mass of the three isotopes of carbon is
still 12.00 units. Relative Mass of one molecule
(b) carbon is a solid at room temperature.
Unlike hydrogen and oxygen which are molecular = —————o—f—th——e—c—o—m——p—o—u—n—d———————
gases, it does not require a container with mass of a —112 mcaarbssoonf-1o2neatom
a lid to contain it. c ompound
(c) carbon is present in many organic
substances, namely, wood, natural gas and For example, a molecule of methane, CH4,
petroleum. Thus carbon is easily available. is 16 times heavier than one-twelfth of the
Carbon can be obtained by burning these mass of a carbon-12 atom. Thus the relative
organic substances in a limited supply of molecular mass of CH4 is 16.
oxygen.
A student need not memorise the relative atomic mass
4 The relative atomic mass (Ar) of an element of elements. They will be given in the examination.
SPM is defined as the number of times one atom However, one must know how to calculate the relative
’11/P1 of the element is heavier than one-twelfth of damteootmelercmicuilmnaerasmthseaosMfs erovofef rcayommatooplmoeucunpldrees,swefrneotmsiunmtthheuepAmtrhogelievrceeunlal.eti.vToe
the mass of a carbon-12 atom, that is:
Chemical Formulae and Equations 40
Apparatus Concept of relative atomic mass and relative molecular mass
using analogy
Twin-pan balance
Ball bearings, iron nails, screws and nuts.
Figure 3.1(a) Figure 3.1(b) Activity 3.1 3
1 An iron nail is put into the pan on the right of the Mass of 1 iron nail = mass of five ball bearings
balance (Figure 3.1(a)).
OR
2 Ball bearings are added to the pan on the left of
the balance until it is balanced. —M—M—a—sas—s—os—fo—of—no—en—eb—ai—lrl—o—bn—ena—ar—iinl—g = 5
3 The number of ball bearings needed to balance Hence, relative mass of one iron nail = 5
the small nail is counted. 2 If we assume that a ball bearing represents one-
4 The procedure is repeated for a screw, a nut, twelfth of the mass of carbon-12 atom and the
a screw and a nut (Figure 3.1(b)) and a screw nail, screw and nut represent the atoms of other
and two nuts. For each sample the number of ball elements, then the relative atomic mass of these
bearings required to balance the object is counted elements will be 5, 12 and 7 respectively.
and recorded in the table as follows: 3 If we assume that the screw and the nut form a
molecule, relative molecular mass of the molecule
Object Number of Relative mass = relative atomic mass of a screw +
ball bearings of object relative atomic mass of a nut
= 12 + 7 = 19
needed to (compared to 4 A total of 26 ball bearings are required to balance
balance object a ball bearing) the mass of one screw and two nuts. Hence, Mr
of a screw and two nuts
Iron nail 5 5 = r.a.m. of a screw + r.a.m. of two nuts
= 12 + 7 + 7 = 26
Screw 12 12 Therefore to determine the relative molecular
mass of a molecule, we sum up the relative atomic
Nut 7 7 mass of each atom present in the molecule.
5 In this experiment, we do not need to know the
Screw + nut 19 19 actual mass of a ball bearing to determine the
relative mass of other objects. Similarly, we do
Screw + 2 nuts 26 26 not need the actual mass of a carbon atom to
determine the relative atomic mass of an element
(Assuming the relative mass of a ball bearing is or the relative molecular mass of a molecule.
1 unit)
1 If we assume that the ball bearing has a mass of 1
unit, then the iron nail which is equivalent to five
ball bearings has a relative mass of five units.
41 Chemical Formulae and Equations
1 Solution
(a ) Z is heavier than Y by —12—64 times = 1.5 times.
Iridium is a very dense metal and was discovered in (b) Assume that n atoms of X has the same mass as
1804 by Smithson Tennant. Determine how many
carbon atoms will have the same mass as one iridium the sum of 3 atoms of Y and 2 atoms of Z.
atom.
[Relative atomic mass: C, 12; Ir, 192] 12n = 3(16) + 2(24)
Solution 12n = 96
Assuming n carbon atoms has the same mass as one
iridium atom. n = —91—62
12n = 192
n = —11—92—2 =8
3 = 16 5
2 SPM Adrenaline is produced by the adrenal gland.
’08/P1 Adrenaline has the formula C9H13NOx. If its r.m.m.
is 183, determine the value of x. Then write the
Three cobalt atoms have the same mass as fifteen molecular formula of adrenaline.
carbon atoms. Determine the relative atomic mass of [Relative atomic mass: H, 1; C, 12; N, 14; O, 16]
cobalt. [Relative atomic mass: C, 12]
Solution is
Solution Relative molecular mass of adrenaline
Assume that the relative atomic mass of Co = a C9H13NOx= 183
Co + Co + Co = 15 C 9(12) + 13(1) + 14 + x(16) = 183
108 + 13 + 14 + 16x = 183
3a = 15 12 16x = 183 – 135
a = —1—5——3——1—2 x = —14—68
x = 3
= 60
The formula of adrenaline is C9H13NO3.
3
1 ’09
The mass of a rutherfordium (Rf) atom is equal to the
sum of three sodium atoms and six sulphur atoms. The relative formula mass of X3(PO4)2 is 310.
What is the relative atomic mass of rutherfordium? Determine the relative atomic mass of element X.
[Relative atomic mass: Na, 23; S, 32] [Relative atomic mass: O, 16; P, 31]
Solution Solution
Relative atomic mass of Rf = 3(23) + 6(32) Assume that the relative atomic mass of the
element X is p.
= 69 + 192
= 261 Relative formula mass of X3(PO4)2 = 310
3(p) + 2[31 + 4(16)] = 310
4 3p + 2[31 + 64] = 310
3p + 190 = 310
The relative atomic mass of elements X, Y and Z are 3p = 310 – 190
12, 16 and 24 respectively. p = —1—320
(a) How much is an atom of Z heavier than an atom
= 40
of Y?
(b) How many atoms of X will have the same mass as
the sum of 3 atoms of Y and 2 atoms of Z?
Chemical Formulae and Equations 42
3.1 3 Let us extend the reasoning to other elements. 3
The number of atoms in a sample of any
1 (a) A platinum atom is five times heavier than a element with its relative atomic mass in grams
potassium atom. What is the relative atomic is equal to the number of atoms in 12 g of
mass of platinum? [Relative atomic mass: K, 39] carbon-12.
For example, 1 g of hydrogen, 14 g of nitrogen,
(b) Calculate the number of carbon atoms that 23 g of sodium, 56 g of iron will all contain the
has the same mass as one molybdenum same number of atoms as in 12 g of carbon-12.
atom. [Relative atomic mass: C, 12; Mo, 96]
4 Now the question that arises is: how many
(c) Five aluminium atoms have the same mass atoms are there in 4 g of helium, 1 g of
as the sum of six lithium atoms and three hydrogen, 14 g of nitrogen, 23 g of sodium,
phosphorus atoms. Determine the r.a.m. of 56 g of iron and 12 g of carbon-12?
phosphorus. [Relative atomic mass: Li, 7; Al, 27] Through several experiments scientists have
found that this number is 602 000 000 000
(d) The relative atomic mass of elements W, X, Y 000 000 000 000 or 6.02 1023.
and Z are 7, 39, 56 and 195 respectively.
5 In Chemistry, the number 6.02 1023 is called
(i) One atom of thorium (Th) has the same one mole (or mol in short).
mass as the sum of six W atoms, two
X atoms and two Y atoms. What is the Amedeo Avogadro
r.a.m. of thorium?
Amedeo Avogadro was a professor of physics at the
(ii) How many W atoms will have the same University of Turin, Italy. In 1811, he proposed the
mass as the sum of two X atoms, one Y hypothesis which states that under the same temperature
atom and one Z atom? and pressure, equal volumes of different gases contain
equal numbers of molecules. He showed that 22.4 dm3
2 Determine the relative molecular mass (or relative of any gas at a temperature of 0 °C and a pressure of 1
formula mass) of the following compounds: atmosphere contains 6.02 1023 molecules. Therefore
(a) Sodium stearate, C17H35COONa (Soap molecule) the value of 6.02 1023 is called Avogadro’s number
(b) Complex ion Cu(NH3)4SO4 or the Avogadro constant in honour of him.
[Relative atomic mass: H, 1; C, 12; N, 14; O, 16;
Na, 23; S, 32; Cu, 64] Definition of the Mole SPM
3 Borax is a compound used to kill cockroaches. ’08/P1
Its molecular formula is X2B4O7. If the relative
molecular mass of borax is 202, determine the 1 One mole is the amount of substance which
relative atomic mass of the element X. Identify the
element X from the list of elements given below. contains the same number of particles as
[Relative atomic mass: B, 11; C, 12; O, 16; F, 19;
Na, 23; Mg, 24] there are in 12 grams of carbon-12.
3.2 Relationship between 2 The number of atoms in 12 grams of
the Number of Moles
and the Number of carbon-12 is 6.02 1023.
Particles
3 This number, 6.02 1023, is called Avogadro’s
Concept of the Mole
4 number or the Avogadro constant (NA). or
1 The relative atomic mass of carbon atom is 12 The particles in matter can be atoms, ions
and the relative atomic mass of helium atom
is 4. This means that a carbon atom is three molecules.
times heavier than a helium atom.
5 For elements, the particles are atoms. For
2 Thus, a sample containing 12 grams of carbon
and four grams of helium will contain the example, 1 mol of gold contains 6.02 1023
same number of atoms, that is,
gold atoms.
number of atoms in 12 grams of carbon
= number of atoms in 4 grams of helium
43 Chemical Formulae and Equations
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