The Free High School Science Texts: Textbooks for High School Students Chemistry

The Free High School Science Texts: Textbooks for High School Students Chemistry
FHSST Authors
The Free High School Science Texts:
Textbooks for High School Students
Studying the Sciences
Chemistry
Grades 10 - 12
Version 0
November 9, 2008
ii
Copyright 2007 “Free High School Science Texts”
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FHSST Core Team
Mark Horner ; Samuel Halliday ; Sarah Blyth ; Rory Adams ; Spencer Wheaton
FHSST Editors
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Whitfield
FHSST Contributors
Rory Adams ; Prashant Arora ; Richard Baxter ; Dr. Sarah Blyth ; Sebastian Bodenstein ;
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Daniels ; Sean Dobbs ; Fernando Durrell ; Dr. Dan Dwyer ; Frans van Eeden ; Giovanni
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Andrew Kubik ; Dr. Marco van Leeuwen ; Dr. Anton Machacek ; Dr. Komal Maheshwari ;
Kosma von Maltitz ; Nicole Masureik ; John Mathew ; JoEllen McBride ; Nikolai Meures ;
Riana Meyer ; Jenny Miller ; Abdul Mirza ; Asogan Moodaly ; Jothi Moodley ; Nolene Naidu ;
Tyrone Negus ; Thomas O’Donnell ; Dr. Markus Oldenburg ; Dr. Jaynie Padayachee ;
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iii
iv
Contents
I
II
Introduction
1
Matter and Materials
3
1 Classification of Matter - Grade 10
1.1
1.2
5
Mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
5
1.1.1
Heterogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
1.1.2
Homogeneous mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . .
6
1.1.3
Separating mixtures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
7
Pure Substances: Elements and Compounds . . . . . . . . . . . . . . . . . . . .
9
1.2.1
Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
1.2.2
Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
1.3
Giving names and formulae to substances . . . . . . . . . . . . . . . . . . . . . 10
1.4
Metals, Semi-metals and Non-metals . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.1
Metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
1.4.2
Non-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.4.3
Semi-metals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5
Electrical conductors, semi-conductors and insulators . . . . . . . . . . . . . . . 14
1.6
Thermal Conductors and Insulators . . . . . . . . . . . . . . . . . . . . . . . . . 15
1.7
Magnetic and Non-magnetic Materials . . . . . . . . . . . . . . . . . . . . . . . 17
1.8
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2 What are the objects around us made of? - Grade 10
21
2.1
Introduction: The atom as the building block of matter . . . . . . . . . . . . . . 21
2.2
Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.2.1
Representing molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.3
Intramolecular and intermolecular forces . . . . . . . . . . . . . . . . . . . . . . 25
2.4
The Kinetic Theory of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.5
The Properties of Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.6
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3 The Atom - Grade 10
3.1
35
Models of the Atom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.1
The Plum Pudding Model . . . . . . . . . . . . . . . . . . . . . . . . . . 35
3.1.2
Rutherford’s model of the atom
v
. . . . . . . . . . . . . . . . . . . . . . 36
CONTENTS
3.1.3
3.2
3.3
CONTENTS
The Bohr Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.1
How heavy is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.2.2
How big is an atom? . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Atomic structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
3.3.1
The Electron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.3.2
The Nucleus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.4
Atomic number and atomic mass number . . . . . . . . . . . . . . . . . . . . . 40
3.5
Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.6
3.7
3.8
3.9
3.5.1
What is an isotope? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
3.5.2
Relative atomic mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
Energy quantisation and electron configuration . . . . . . . . . . . . . . . . . . 46
3.6.1
The energy of electrons . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
3.6.2
Energy quantisation and line emission spectra . . . . . . . . . . . . . . . 47
3.6.3
Electron configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
3.6.4
Core and valence electrons . . . . . . . . . . . . . . . . . . . . . . . . . 51
3.6.5
The importance of understanding electron configuration . . . . . . . . . 51
Ionisation Energy and the Periodic Table . . . . . . . . . . . . . . . . . . . . . . 53
3.7.1
Ions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
3.7.2
Ionisation Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
The Arrangement of Atoms in the Periodic Table . . . . . . . . . . . . . . . . . 56
3.8.1
Groups in the periodic table
. . . . . . . . . . . . . . . . . . . . . . . . 56
3.8.2
Periods in the periodic table . . . . . . . . . . . . . . . . . . . . . . . . 58
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
4 Atomic Combinations - Grade 11
63
4.1
Why do atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.2
Energy and bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
4.3
What happens when atoms bond? . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.4
Covalent Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
4.4.1
The nature of the covalent bond . . . . . . . . . . . . . . . . . . . . . . 65
4.5
Lewis notation and molecular structure . . . . . . . . . . . . . . . . . . . . . . . 69
4.6
Electronegativity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
4.7
4.8
4.6.1
Non-polar and polar covalent bonds . . . . . . . . . . . . . . . . . . . . 73
4.6.2
Polar molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
Ionic Bonding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
4.7.1
The nature of the ionic bond . . . . . . . . . . . . . . . . . . . . . . . . 74
4.7.2
The crystal lattice structure of ionic compounds . . . . . . . . . . . . . . 76
4.7.3
Properties of Ionic Compounds . . . . . . . . . . . . . . . . . . . . . . . 76
Metallic bonds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
4.8.1
The nature of the metallic bond . . . . . . . . . . . . . . . . . . . . . . 76
4.8.2
The properties of metals . . . . . . . . . . . . . . . . . . . . . . . . . . 77
vi
CONTENTS
4.9
CONTENTS
Writing chemical formulae
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
4.9.1
The formulae of covalent compounds . . . . . . . . . . . . . . . . . . . . 78
4.9.2
The formulae of ionic compounds . . . . . . . . . . . . . . . . . . . . . 80
4.10 The Shape of Molecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
4.10.1 Valence Shell Electron Pair Repulsion (VSEPR) theory . . . . . . . . . . 82
4.10.2 Determining the shape of a molecule . . . . . . . . . . . . . . . . . . . . 82
4.11 Oxidation numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
4.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
5 Intermolecular Forces - Grade 11
91
5.1
Types of Intermolecular Forces . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
5.2
Understanding intermolecular forces . . . . . . . . . . . . . . . . . . . . . . . . 94
5.3
Intermolecular forces in liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 96
5.4
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97
6 Solutions and solubility - Grade 11
101
6.1
Types of solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101
6.2
Forces and solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102
6.3
Solubility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
6.4
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
7 Atomic Nuclei - Grade 11
107
7.1
Nuclear structure and stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.2
The Discovery of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107
7.3
Radioactivity and Types of Radiation . . . . . . . . . . . . . . . . . . . . . . . . 108
7.4
7.3.1
Alpha (α) particles and alpha decay . . . . . . . . . . . . . . . . . . . . 109
7.3.2
Beta (β) particles and beta decay . . . . . . . . . . . . . . . . . . . . . 109
7.3.3
Gamma (γ) rays and gamma decay . . . . . . . . . . . . . . . . . . . . . 110
Sources of radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112
7.4.1
Natural background radiation . . . . . . . . . . . . . . . . . . . . . . . . 112
7.4.2
Man-made sources of radiation . . . . . . . . . . . . . . . . . . . . . . . 113
7.5
The ’half-life’ of an element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
7.6
The Dangers of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
7.7
The Uses of Radiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117
7.8
Nuclear Fission
7.9
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118
7.8.1
The Atomic bomb - an abuse of nuclear fission . . . . . . . . . . . . . . 119
7.8.2
Nuclear power - harnessing energy . . . . . . . . . . . . . . . . . . . . . 120
Nuclear Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120
7.10 Nucleosynthesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
7.10.1 Age of Nucleosynthesis (225 s - 103 s) . . . . . . . . . . . . . . . . . . . 121
7.10.2 Age of Ions (103 s - 1013 s) . . . . . . . . . . . . . . . . . . . . . . . . . 122
7.10.3 Age of Atoms (1013 s - 1015 s) . . . . . . . . . . . . . . . . . . . . . . . 122
7.10.4 Age of Stars and Galaxies (the universe today) . . . . . . . . . . . . . . 122
7.11 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122
vii
CONTENTS
CONTENTS
8 Thermal Properties and Ideal Gases - Grade 11
125
8.1
A review of the kinetic theory of matter . . . . . . . . . . . . . . . . . . . . . . 125
8.2
Boyle’s Law: Pressure and volume of an enclosed gas . . . . . . . . . . . . . . . 126
8.3
Charles’s Law: Volume and Temperature of an enclosed gas . . . . . . . . . . . 132
8.4
The relationship between temperature and pressure . . . . . . . . . . . . . . . . 136
8.5
The general gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
8.6
The ideal gas equation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
8.7
Molar volume of gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
8.8
Ideal gases and non-ideal gas behaviour . . . . . . . . . . . . . . . . . . . . . . 146
8.9
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
9 Organic Molecules - Grade 12
151
9.1
What is organic chemistry? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
9.2
Sources of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
9.3
Unique properties of carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4
Representing organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4.1
Molecular formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
9.4.2
Structural formula . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
9.4.3
Condensed structural formula . . . . . . . . . . . . . . . . . . . . . . . . 153
9.5
Isomerism in organic compounds . . . . . . . . . . . . . . . . . . . . . . . . . . 154
9.6
Functional groups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
9.7
The Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
9.7.1
The Alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
9.7.2
Naming the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
9.7.3
Properties of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.7.4
Reactions of the alkanes . . . . . . . . . . . . . . . . . . . . . . . . . . 163
9.7.5
The alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
9.7.6
Naming the alkenes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
9.7.7
The properties of the alkenes . . . . . . . . . . . . . . . . . . . . . . . . 169
9.7.8
Reactions of the alkenes
9.7.9
The Alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
. . . . . . . . . . . . . . . . . . . . . . . . . . 169
9.7.10 Naming the alkynes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
9.8
9.9
The Alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
9.8.1
Naming the alcohols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
9.8.2
Physical and chemical properties of the alcohols . . . . . . . . . . . . . . 175
Carboxylic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
9.9.1
Physical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177
9.9.2
Derivatives of carboxylic acids: The esters . . . . . . . . . . . . . . . . . 178
9.10 The Amino Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
9.11 The Carbonyl Group . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178
9.12 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
viii
CONTENTS
CONTENTS
10 Organic Macromolecules - Grade 12
185
10.1 Polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
10.2 How do polymers form? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.2.1 Addition polymerisation . . . . . . . . . . . . . . . . . . . . . . . . . . . 186
10.2.2 Condensation polymerisation . . . . . . . . . . . . . . . . . . . . . . . . 188
10.3 The chemical properties of polymers . . . . . . . . . . . . . . . . . . . . . . . . 190
10.4 Types of polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5 Plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
10.5.1 The uses of plastics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
10.5.2 Thermoplastics and thermosetting plastics . . . . . . . . . . . . . . . . . 194
10.5.3 Plastics and the environment . . . . . . . . . . . . . . . . . . . . . . . . 195
10.6 Biological Macromolecules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196
10.6.1 Carbohydrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
10.6.2 Proteins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
10.6.3 Nucleic Acids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
10.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
III
Chemical Change
209
11 Physical and Chemical Change - Grade 10
211
11.1 Physical changes in matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 211
11.2 Chemical Changes in Matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . 212
11.2.1 Decomposition reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 213
11.2.2 Synthesis reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214
11.3 Energy changes in chemical reactions . . . . . . . . . . . . . . . . . . . . . . . . 217
11.4 Conservation of atoms and mass in reactions . . . . . . . . . . . . . . . . . . . . 217
11.5 Law of constant composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.6 Volume relationships in gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
11.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
12 Representing Chemical Change - Grade 10
223
12.1 Chemical symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
12.2 Writing chemical formulae
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.3 Balancing chemical equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
12.3.1 The law of conservation of mass . . . . . . . . . . . . . . . . . . . . . . 224
12.3.2 Steps to balance a chemical equation
. . . . . . . . . . . . . . . . . . . 226
12.4 State symbols and other information . . . . . . . . . . . . . . . . . . . . . . . . 230
12.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
13 Quantitative Aspects of Chemical Change - Grade 11
233
13.1 The Mole . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233
13.2 Molar Mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
13.3 An equation to calculate moles and mass in chemical reactions . . . . . . . . . . 237
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CONTENTS
13.4 Molecules and compounds
CONTENTS
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
13.5 The Composition of Substances . . . . . . . . . . . . . . . . . . . . . . . . . . . 242
13.6 Molar Volumes of Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246
13.7 Molar concentrations in liquids . . . . . . . . . . . . . . . . . . . . . . . . . . . 247
13.8 Stoichiometric calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
13.9 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
14 Energy Changes In Chemical Reactions - Grade 11
255
14.1 What causes the energy changes in chemical reactions? . . . . . . . . . . . . . . 255
14.2 Exothermic and endothermic reactions . . . . . . . . . . . . . . . . . . . . . . . 255
14.3 The heat of reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
14.4 Examples of endothermic and exothermic reactions . . . . . . . . . . . . . . . . 259
14.5 Spontaneous and non-spontaneous reactions . . . . . . . . . . . . . . . . . . . . 260
14.6 Activation energy and the activated complex . . . . . . . . . . . . . . . . . . . . 261
14.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
15 Types of Reactions - Grade 11
267
15.1 Acid-base reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.1 What are acids and bases? . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.2 Defining acids and bases . . . . . . . . . . . . . . . . . . . . . . . . . . 267
15.1.3 Conjugate acid-base pairs . . . . . . . . . . . . . . . . . . . . . . . . . . 269
15.1.4 Acid-base reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270
15.1.5 Acid-carbonate reactions . . . . . . . . . . . . . . . . . . . . . . . . . . 274
15.2 Redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
15.2.1 Oxidation and reduction
. . . . . . . . . . . . . . . . . . . . . . . . . . 277
15.2.2 Redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 278
15.3 Addition, substitution and elimination reactions . . . . . . . . . . . . . . . . . . 280
15.3.1 Addition reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280
15.3.2 Elimination reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 281
15.3.3 Substitution reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
15.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 283
16 Reaction Rates - Grade 12
287
16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
16.2 Factors affecting reaction rates . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
16.3 Reaction rates and collision theory . . . . . . . . . . . . . . . . . . . . . . . . . 293
16.4 Measuring Rates of Reaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
16.5 Mechanism of reaction and catalysis . . . . . . . . . . . . . . . . . . . . . . . . 297
16.6 Chemical equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300
16.6.1 Open and closed systems . . . . . . . . . . . . . . . . . . . . . . . . . . 302
16.6.2 Reversible reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
16.6.3 Chemical equilibrium . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
16.7 The equilibrium constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
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CONTENTS
CONTENTS
16.7.1 Calculating the equilibrium constant . . . . . . . . . . . . . . . . . . . . 305
16.7.2 The meaning of kc values . . . . . . . . . . . . . . . . . . . . . . . . . . 306
16.8 Le Chatelier’s principle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
16.8.1 The effect of concentration on equilibrium . . . . . . . . . . . . . . . . . 310
16.8.2 The effect of temperature on equilibrium . . . . . . . . . . . . . . . . . . 310
16.8.3 The effect of pressure on equilibrium . . . . . . . . . . . . . . . . . . . . 312
16.9 Industrial applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 315
16.10Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
17 Electrochemical Reactions - Grade 12
319
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
17.2 The Galvanic Cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
17.2.1 Half-cell reactions in the Zn-Cu cell . . . . . . . . . . . . . . . . . . . . 321
17.2.2 Components of the Zn-Cu cell . . . . . . . . . . . . . . . . . . . . . . . 322
17.2.3 The Galvanic cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
17.2.4 Uses and applications of the galvanic cell . . . . . . . . . . . . . . . . . 324
17.3 The Electrolytic cell . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325
17.3.1 The electrolysis of copper sulphate . . . . . . . . . . . . . . . . . . . . . 326
17.3.2 The electrolysis of water . . . . . . . . . . . . . . . . . . . . . . . . . . 327
17.3.3 A comparison of galvanic and electrolytic cells . . . . . . . . . . . . . . . 328
17.4 Standard Electrode Potentials . . . . . . . . . . . . . . . . . . . . . . . . . . . . 328
17.4.1 The different reactivities of metals . . . . . . . . . . . . . . . . . . . . . 329
17.4.2 Equilibrium reactions in half cells . . . . . . . . . . . . . . . . . . . . . . 329
17.4.3 Measuring electrode potential . . . . . . . . . . . . . . . . . . . . . . . . 330
17.4.4 The standard hydrogen electrode . . . . . . . . . . . . . . . . . . . . . . 330
17.4.5 Standard electrode potentials . . . . . . . . . . . . . . . . . . . . . . . . 333
17.4.6 Combining half cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
17.4.7 Uses of standard electrode potential . . . . . . . . . . . . . . . . . . . . 338
17.5 Balancing redox reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
17.6 Applications of electrochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.6.1 Electroplating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 347
17.6.2 The production of chlorine . . . . . . . . . . . . . . . . . . . . . . . . . 348
17.6.3 Extraction of aluminium
. . . . . . . . . . . . . . . . . . . . . . . . . . 349
17.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349
IV
Chemical Systems
353
18 The Water Cycle - Grade 10
355
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
18.2 The importance of water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
18.3 The movement of water through the water cycle . . . . . . . . . . . . . . . . . . 356
18.4 The microscopic structure of water . . . . . . . . . . . . . . . . . . . . . . . . . 359
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18.4.1 The polar nature of water . . . . . . . . . . . . . . . . . . . . . . . . . . 359
18.4.2 Hydrogen bonding in water molecules . . . . . . . . . . . . . . . . . . . 359
18.5 The unique properties of water . . . . . . . . . . . . . . . . . . . . . . . . . . . 360
18.6 Water conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363
18.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
19 Global Cycles: The Nitrogen Cycle - Grade 10
369
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
19.2 Nitrogen fixation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
19.3 Nitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
19.4 Denitrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 372
19.5 Human Influences on the Nitrogen Cycle . . . . . . . . . . . . . . . . . . . . . . 372
19.6 The industrial fixation of nitrogen . . . . . . . . . . . . . . . . . . . . . . . . . 373
19.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 374
20 The Hydrosphere - Grade 10
377
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
20.2 Interactions of the hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
20.3 Exploring the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 378
20.4 The Importance of the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . 379
20.5 Ions in aqueous solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 379
20.5.1 Dissociation in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . 380
20.5.2 Ions and water hardness . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
20.5.3 The pH scale . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 382
20.5.4 Acid rain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 384
20.6 Electrolytes, ionisation and conductivity . . . . . . . . . . . . . . . . . . . . . . 386
20.6.1 Electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
20.6.2 Non-electrolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
20.6.3 Factors that affect the conductivity of water . . . . . . . . . . . . . . . . 387
20.7 Precipitation reactions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
20.8 Testing for common anions in solution . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.1 Test for a chloride . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.2 Test for a sulphate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 391
20.8.3 Test for a carbonate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
20.8.4 Test for bromides and iodides . . . . . . . . . . . . . . . . . . . . . . . . 392
20.9 Threats to the Hydrosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393
20.10Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 394
21 The Lithosphere - Grade 11
397
21.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
21.2 The chemistry of the earth’s crust . . . . . . . . . . . . . . . . . . . . . . . . . 398
21.3 A brief history of mineral use . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
21.4 Energy resources and their uses . . . . . . . . . . . . . . . . . . . . . . . . . . . 400
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CONTENTS
21.5 Mining and Mineral Processing: Gold . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.2 Mining the Gold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.3 Processing the gold ore . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
21.5.4 Characteristics and uses of gold . . . . . . . . . . . . . . . . . . . . . . . 402
21.5.5 Environmental impacts of gold mining . . . . . . . . . . . . . . . . . . . 404
21.6 Mining and mineral processing: Iron . . . . . . . . . . . . . . . . . . . . . . . . 406
21.6.1 Iron mining and iron ore processing . . . . . . . . . . . . . . . . . . . . . 406
21.6.2 Types of iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 407
21.6.3 Iron in South Africa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
21.7 Mining and mineral processing: Phosphates . . . . . . . . . . . . . . . . . . . . 409
21.7.1 Mining phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
21.7.2 Uses of phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 409
21.8 Energy resources and their uses: Coal . . . . . . . . . . . . . . . . . . . . . . . 411
21.8.1 The formation of coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
21.8.2 How coal is removed from the ground . . . . . . . . . . . . . . . . . . . 411
21.8.3 The uses of coal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
21.8.4 Coal and the South African economy . . . . . . . . . . . . . . . . . . . . 412
21.8.5 The environmental impacts of coal mining . . . . . . . . . . . . . . . . . 413
21.9 Energy resources and their uses: Oil . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.1 How oil is formed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.2 Extracting oil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 414
21.9.3 Other oil products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
21.9.4 The environmental impacts of oil extraction and use . . . . . . . . . . . 415
21.10Alternative energy resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 415
21.11Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 417
22 The Atmosphere - Grade 11
421
22.1 The composition of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . . 421
22.2 The structure of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.1 The troposphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.2 The stratosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 422
22.2.3 The mesosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.2.4 The thermosphere . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
22.3 Greenhouse gases and global warming . . . . . . . . . . . . . . . . . . . . . . . 426
22.3.1 The heating of the atmosphere . . . . . . . . . . . . . . . . . . . . . . . 426
22.3.2 The greenhouse gases and global warming . . . . . . . . . . . . . . . . . 426
22.3.3 The consequences of global warming . . . . . . . . . . . . . . . . . . . . 429
22.3.4 Taking action to combat global warming . . . . . . . . . . . . . . . . . . 430
22.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 431
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23 The Chemical Industry - Grade 12
435
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2 Sasol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 435
23.2.1 Sasol today: Technology and production . . . . . . . . . . . . . . . . . . 436
23.2.2 Sasol and the environment . . . . . . . . . . . . . . . . . . . . . . . . . 440
23.3 The Chloralkali Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 442
23.3.1 The Industrial Production of Chlorine and Sodium Hydroxide . . . . . . . 442
23.3.2 Soaps and Detergents . . . . . . . . . . . . . . . . . . . . . . . . . . . . 446
23.4 The Fertiliser Industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.1 The value of nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.2 The Role of fertilisers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
23.4.3 The Industrial Production of Fertilisers . . . . . . . . . . . . . . . . . . . 451
23.4.4 Fertilisers and the Environment: Eutrophication . . . . . . . . . . . . . . 454
23.5 Electrochemistry and batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.1 How batteries work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 456
23.5.2 Battery capacity and energy . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.3 Lead-acid batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 457
23.5.4 The zinc-carbon dry cell . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
23.5.5 Environmental considerations . . . . . . . . . . . . . . . . . . . . . . . . 460
23.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
A GNU Free Documentation License
467
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Chapter 2
What are the objects around us
made of? - Grade 10
2.1
Introduction: The atom as the building block of matter
We have now seen that different materials have different properties. Some materials are metals
and some are non-metals; some are electrical or thermal conductors, while others are not. Depending on the properties of these materials, they can be used in lots of useful applications. But
what is it exactly that makes up these materials? In other words, if we were to break down a
material into the parts that make it up, what would we find? And how is it that a material’s
microscopic structure is able to give it all these different properties?
The answer lies in the smallest building block of matter: the atom. It is the type of atoms, and
the way in which they are arranged in a material, that affects the properties of that substance.
It is not often that substances are found in atomic form. Normally, atoms are bonded to other
atoms to form compounds or molecules. It is only in the noble gases (e.g. helium, neon and
argon) that atoms are found individually and are not bonded to other atoms. We will look at
the reasons for this in a later chapter.
2.2
Molecules
Definition: Molecule
A molecule is a group of two or more atoms that are attracted to each other by relatively
strong forces or bonds
Almost everything around us is made up of molecules. Water is made up of molecules, each of
which has two hydrogen atoms joined to one oxygen atom. Oxygen is a molecule that is made
up of two oxygen atoms that are joined to one another. Even the food that we eat is made
up of molecules that contain atoms of elements such as carbon, hydrogen and oxygen that are
joined to one another in different ways. All of these are known as small molecules because
there are only a few atoms in each molecule. Giant molecules are those where there may be
millions of atoms per molecule. Examples of giant molecules are diamonds, which are made up
of millions of carbon atoms bonded to each other, and metals, which are made up of millions of
metal atoms bonded to each other.
2.2.1
Representing molecules
The structure of a molecule can be shown in many different ways. Sometimes it is easiest to
show what a molecule looks like by using different types of diagrams, but at other times, we
may decide to simply represent a molecule using its chemical formula or its written name.
21
2.2
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
1. Using formulae to show the structure of a molecule
A chemical formula is an abbreviated (shortened) way of describing a molecule, or some
other chemical substance. In chapter 1, we saw how chemical compounds can be represented using element symbols from the Periodic Table. A chemical formula can also tell
us the number of atoms of each element that are in a molecule, and their ratio in that
molecule.
For example, the chemical formula for a molecule of carbon dioxide is:
CO2
The formula above is called the molecular formula of that compound. The formula tells
us that in one molecule of carbon dioxide, there is one atom of carbon and two atoms of
oxygen. The ratio of carbon atoms to oxygen atoms is 1:2.
Definition: Molecular formula
A concise way of expressing information about the atoms that make up a particular chemical
compound. The molecular formula gives the exact number of each type of atom in the
molecule.
A molecule of glucose has the molecular formula:
C6 H12 O6
In each glucose molecule, there are six carbon atoms, twelve hydrogen atoms and six oxygen atoms. The ratio of carbon:hydrogen:oxygen is 6:12:6. We can simplify this ratio to
write 1:2:1, or if we were to use the element symbols, the formula would be written as
CH2 O. This is called the empirical formula of the molecule.
Definition: Empirical formula
This is a way of expressing the relative number of each type of atom in a chemical compound.
In most cases, the empirical formula does not show the exact number of atoms, but rather
the simplest ratio of the atoms in the compound.
The empirical formula is useful when we want to write the formula for a giant molecule.
Since giant molecules may consist of millions of atoms, it is impossible to say exactly how
many atoms are in each molecule. It makes sense then to represent these molecules using
their empirical formula. So, in the case of a metal such as copper, we would simply write
Cu, or if we were to represent a molecule of sodium chloride, we would simply write NaCl.
Chemical formulae therefore tell us something about the types of atoms that are in a
molecule and the ratio in which these atoms occur in the molecule, but they don’t give us
any idea of what the molecule actually looks like, in other words its shape. Another useful
way of representing molecules is to use diagrams.
Another type of formula that can be used to describe a molecule is its structural formula.
A structural formula uses a graphical representation to show a molecule’s structure (figure
2.1).
2. Using diagrams to show the structure of a molecule
Diagrams of molecules are very useful because they give us an idea of the space that is
occupied by the molecule, and they also help us to picture how the atoms are arranged in
the molecule. There are two types of diagrams that are commonly used:
22
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
CH3
(a) C4 H10
(b) C2 H5
2.2
CH
CH3
CH3
Figure 2.1: Diagram showing (a) the molecular, (b) the empirical and (c) the structural formula
of isobutane
• Ball and stick models
This is a 3-dimensional molecular model that uses ’balls’ to represent atoms and
’sticks’ to represent the bonds between them. The centres of the atoms (the balls)
are connected by straight lines which represent the bonds between them. A simplified
example is shown in figure 2.2.
oxygen atom
hydrogen atom
Figure 2.2: A ball and stick model of a water molecule
• Space-filling model
This is also a 3-dimensional molecular model. The atoms are represented by multicoloured spheres. Space-filling models of water and ammonia are shown in figures
2.3 and 2.4.
Figures 2.3 and 2.4 are some examples of simple molecules that are represented in different ways.
oxygen atom
O
hydrogen atoms
H
H
Figure 2.3: A space-filling model and structural formula of a water molecule. Each molecule
is made up of two hydrogen atoms that are attached to one oxygen atom. This is a simple
molecule.
Figure 2.5 shows the bonds between the carbon atoms in diamond, which is a giant
molecule. Each carbon atom is joined to four others, and this pattern repeats itself until
a complex lattice structure is formed. Each black ball in the diagram represents a carbon
atom, and each line represents the bond between two carbon atoms.
teresting Diamonds are most often thought of in terms of their use in the jewellery industry.
Interesting
Fact
Fact
However, about 80% of mined diamonds are unsuitable for use as gemstones and
are therefore used in industry because of their strength and hardness. These
23
2.2
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
nitrogen atom
hydrogen atom
N
H
H
H
Figure 2.4: A space-filling model and structural formula of a molecule of ammonia. Each
molecule is made up of one nitrogen atom and three hydrogen atoms. This is a simple molecule.
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
b
Figure 2.5: Diagrams showing the microscopic structure of diamond. The diagram on the left
shows part of a diamond lattice, made up of numerous carbon atoms. The diagram on the right
shows how each carbon atom in the lattice is joined to four others. This forms the basis of the
lattice structure. Diamond is a giant molecule.
properties of diamonds are due to the strong covalent bonds betwene the carbon
atoms in diamond. The most common uses for diamonds in industry are in
cutting, drilling, grinding, and polishing.
Exercise: Atoms and molecules
1. In each of the following, say whether the chemical substance is made up of
single atoms, simple molecules or giant molecules.
(a) ammonia gas (NH3 )
(b) zinc metal (Zn)
(c) graphite (C)
(d) nitric acid (HNO3 )
(e) neon gas (Ne2 )
2. Refer to the diagram below and then answer the questions that follow:
24
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
O
C
2.3
O
(a) Identify the molecule.
(b) Write the molecular formula for the molecule.
(c) Is the molecule a simple or giant molecule?
3. Represent each of the following molecules using its chemical formula, structural
formula and ball and stick model.
(a) H2
(b) NH3
(c) sulfur dioxide
2.3
Intramolecular and intermolecular forces
When atoms join to form molecules, they are held together by chemical bonds. The type of
bond, and the strength of the bond, depends on the atoms that are involved. These bonds are
called intramolecular forces because they are bonding forces inside a molecule (’intra’ means
’within’ or ’inside’). Sometimes we simply call these intramolecular forces chemical bonds.
Definition: Intramolecular force
The force between the atoms of a molecule, which holds them together.
Examples of the types of chemical bonds that can exist between atoms inside a molecule are
shown below. These will be looked at in more detail in chapter 4.
• Covalent bond
Covalent bonds exist between non-metal atoms e.g. There are covalent bonds between
the carbon and oxygen atoms in a molecule of carbon dioxide.
• Ionic bond
Ionic bonds occur between non-metal and metal atoms e.g. There are ionic bonds between
the sodium and chlorine atoms in a molecule of sodium chloride.
• Metallic bond
Metallic bonds join metal atoms e.g. There are metallic bonds between copper atoms in
a piece of copper metal.
Intermolecular forces are those bonds that hold molecules together. A glass of water for
example, contains many molecules of water. These molecules are held together by intermolecular
forces. The strength of the intermolecular forces is important because they affect properties such
as melting point and boiling point. For example, the stronger the intermolecular forces, the higher
the melting point and boiling point for that substance. The strength of the intermolecular forces
increases as the size of the molecule increases.
25
2.4
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
Definition: Intermolecular force
A force between molecules, which holds them together.
Diagram 2.6 may help you to understand the difference between intramolecular forces and intermolecular forces.
intermolecular forces
intramolecular forces
H
O
O
H
O
O
H
O
O
Figure 2.6: Two representations showing the intermolecular and intramolecular forces in water:
space-filling model and structural formula.
It should be clearer now that there are two types of forces that hold matter together. In the case
of water, there are intramolecular forces that hold the two hydrogen atoms to the oxygen atom
in each molecule of water. There are also intramolecular forces between each of these water
molecules. As mentioned earlier, these forces are very important because they affect many of
the properties of matter such as boiling point, melting point and a number of other properties.
Before we go on to look at some of these examples, it is important that we first take a look at
the Kinetic Theory of Matter.
Exercise: Intramolecular and intermolecular forces
1. Using ammonia gas as an example...
(a) Explain what is meant by an intramolecular force or chemical bond.
(b) Explain what is meant by an intermolecular force.
2. Draw a diagram showing three molecules of carbon dioxide. On the diagram,
show where the intramolecular and intermolecular forces are.
3. Why is it important to understand the types of forces that exist between atoms
and between molecules? Try to use some practical examples in your answer.
2.4
The Kinetic Theory of Matter
The kinetic theory of matter is used to explain why matter exists in different phases (i.e. solid,
liquid and gas), and how matter can change from one phase to the next. The kinetic theory of
matter also helps us to understand other properties of matter. It is important to realise that
what we will go on to describe is only a theory. It cannot be proved beyond doubt, but the fact
that it helps us to explain our observations of changes in phase, and other properties of matter,
suggests that it probably is more than just a theory.
Broadly, the Kinetic Theory of Matter says that:
26
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
2.4
• Matter is made up of particles that are constantly moving.
• All particles have energy, but the energy varies depending on whether the substance is a
solid, liquid or gas. Solid particles have the least energy and gas particles have the most
amount of energy.
• The temperature of a substance is a measure of the average kinetic energy of the particles.
• A change in phase may occur when the energy of the particles is changed.
• There are spaces between the particles of matter.
• There are attractive forces between particles and these become stronger as the particles
move closer together. These attractive forces will either be intramolecular forces (if the
particles are atoms) or intermolecular forces (if the particles are molecules). When the
particles are extremely close, repulsive forces start to act.
Table 2.1 summarises the characteristics of the particles that are in each phase of matter.
Table 2.1: Table summarising the general features of solids, liquids and gases.
Property of matter Gas
Liquid
Gas
Particles
Atoms or molecules
Atoms or molecules
Atoms or molecules
Energy and move- Particles have high Particles have less Low energy - partiment of particles
energy and are con- energy than in the cles vibrate around a
stantly moving
gas phase
fixed point
Spaces between par- Large spaces be- Smaller spaces than Very little space
ticles
cause of high energy in gases
between particles.
Particles are tightly
packed together
Attractive forces be- Weak forces because Stronger forces than Very strong forces.
tween particles
of the large distance in gas. Liquids can Solids have a fixed
between particles
be poured.
volume.
Changes in phase
In general a gas A liquid becomes a Solids become liqbecomes a liquid gas if its tempera- uids or gases if their
or solid when it is ture is increased. It temperature is incooled.
Particles becomes a solid if creased.
have less energy its temperature deand therefore move creases.
closer together so
that the attractive forces become
stronger, and the
gas becomes a liquid
or a solid
Let’s look at an example that involves the three phases of water: ice (solid), water (liquid) and
water vapour (gas).
solid
liquid
gas
Figure 2.7: The three phases of matter
In a solid (e.g. ice), the water molecules have very little energy and can’t move away from each
other. The molecules are held close together in a regular pattern called a lattice. If the ice is
27
2.5
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
heated, the energy of the molecules increases. This means that some of the water molecules are
able to overcome the intermolecular forces that are holding them together, and the molecules
move further apart to form liquid water. This is why liquid water is able to flow, because the
molecules are more free to move than they were in the solid lattice. If the molecules are heated
further, the liquid water will become water vapour, which is a gas. Gas particles have lots of
energy and are far away from each other. That is why it is difficult to keep a gas in a specific
area! The attractive forces between the particles are very weak and they are only loosely held
together. Figure 2.8 shows the changes in phase that may occur in matter, and the names that
describe these processes.
Gas
co n
eva dens
p o a ti o
rat n
io n
on
a ti
lim o n
s u b a ti
re- blim
su
Liquid
Solid
freezing
melting
Figure 2.8: Changes in phase
2.5
The Properties of Matter
Let us now look at what we have learned about chemical bonds, intermolecular forces and the
kinetic theory of matter, and see whether this can help us to understand some of the macroscopic
properties of materials.
1. Melting point
Definition: Melting point
The temperature at which a solid changes its phase or state to become a liquid. The reverse
process (change in phase from liquid to solid) is called freezing.
In order for a solid to melt, the energy of the particles must increase enough to overcome
the bonds that are holding the particles together. It makes sense then that a solid which is
held together by strong bonds will have a higher melting point than one where the bonds
are weak, because more energy (heat) is needed to break the bonds. In the examples we
have looked at, metals, ionic solids and some atomic lattices (e.g. diamond) have high
melting points, whereas the melting points for molecular solids and other atomic lattices
(e.g. graphite) are much lower. Generally, the intermolecular forces between molecular
solids are weaker than those between ionic and metallic solids.
2. Boiling point
Definition: Boiling point
The temperature at which a liquid changes its phase to become a gas.
28
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
2.5
When the temperature of a liquid increases, the average kinetic energy of the particles also
increases, and they are able to overcome the bonding forces that are holding them in the
liquid. When boiling point is reached, evaporation takes place and some particles in the
liquid become a gas. In other words, the energy of the particles is too great for them to
be held in a liquid anymore. The stronger the bonds within a liquid, the higher the boiling
point needs to be in order to break these bonds. Metallic and ionic compounds have high
boiling points while the boiling point for molecular liquids is lower.
The data in table 2.2 below may help you to understand some of the concepts we have
explained. Not all of the substances in the table are solids at room temperature, so for
now, let’s just focus on the boiling points for each of these substances. Of the substances
listed, ethanol has the weakest intermolecular forces, and sodium chloride and mercury
have the strongest. What do you notice?
Substance
Ethanol (C2 H6 O)
Water
Mercury
Sodium chloride
Melting point (0 C)
-114,3
0
-38,83
801
Boiling point (0 C)
78,4
100
356,73
1465
Table 2.2: The melting and boiling points for a number of substances
You will have seen that substances such as ethanol, with relatively weak intermolecular
forces, have the lowest boiling point, while substances with stronger intermolecular forces
such as sodium chloride and mercury, must be heated much more if the particles are to
have enough energy to overcome the forces that are holding them together in the liquid
or solid phase.
Exercise: Forces and boiling point
The table below gives the molecular formula and the boiling point for a
number of organic compounds called alkanes. Refer to the table and then
answer the questions that follow.
Organic compound Molecular formula Boiling point (0 C)
Methane
CH2
-161.6
Ethane
C2 H6
-88.6
Propane
C3 H8
-45
Butane
C4 H10
-0.5
Pentane
C5 H12
36.1
Hexane
C6 H14
69
Heptane
C7 H16
98.42
Octane
C8 H18
125.52
Data from: http://www.wikipedia.com
(a) Draw a graph to show the relationship between the number of carbon atoms
in each alkane, and its boiling point (Number of carbon atoms will go on
the x-axis and boiling point on the y-axis).
(b) Describe what you see.
(c) Suggest a reason for what you have observed.
(d) Why was it enough for us to use ’number of carbon atoms’ as a measure
of the molecular weight of the molecules?
3. Density and viscosity
Density is a measure of the mass of a substance per unit volume. The density of a solid
is generally higher than that of a liquid because the particles are hold much more closely
29
2.5
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
together and therefore there are more particles packed together in a particular volume. In
other words, there is a greater mass of the substance in a particular volume. In general,
density increases as the strength of the intermolecular forces increases. Viscosity is a
measure of how resistant a liquid is to changing its form. Viscosity is also sometimes
described as the ’thickness’ of a fluid. Think for example of syrup and how slowly it pours
from one container into another. Now compare this to how easy it is to pour water. The
viscosity of syrup is greater than the viscosity of water. Once again, the stronger the
intermolecular forces in the liquid, the greater its viscosity.
It should be clear now that we can explain a lot of the macroscopic properties of matter (i.e.
the characteristics we can see or observe) by understanding their microscopic structure and
the way in which the atoms and molecules that make up matter are held together.
Activity :: Investigation : Determining the density of liquids:
Density is a very important property because it helps us to identify different
materials. Every material, depending on the elements that make it up, and the
arrangement of its atoms, will have a different density.
The equation for density is:
Density = Mass/Volume
Discussion questions:
To calculate the density of liquids and solids, we need to be able to first determine
their mass and volume. As a group, think about the following questions:
• How would you determine the mass of a liquid?
• How would you determine the volume of an irregular solid?
Apparatus:
Laboratory mass balance, 10 ml and 100 ml graduated cylinders, thread, distilled
water, two different liquids.
Method:
Determine the density of the distilled water and two liquids as follows:
1. Measure and record the mass of a 10 ml graduated cyclinder.
2. Pour an amount of distilled water into the cylinder.
3. Measure and record the combined mass of the water and cylinder.
4. Record the volume of distilled water in the cylinder
5. Empty, clean and dry the graduated cylinder.
6. Repeat the above steps for the other two liquids you have.
7. Complete the table below.
Liquid
Distilled water
Liquid 1
Liquid 2
Mass (g)
Volume (ml)
Density (g/ml)
Activity :: Investigation : Determining the density of irregular solids:
Apparatus:
Use the same materials and equpiment as before (for the liquids). Also find a
number of solids that have an irregular shape.
Method:
Determine the density of irregular solids as follows:
30
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
2.6
1. Measure and record the mass of one of the irregular solids.
2. Tie a piece of thread around the solid.
3. Pour some water into a 100 ml graduated cylinder and record the volume.
4. Gently lower the solid into the water, keeping hold of the thread. Record the
combined volume of the solid and the water.
5. Dtermine the volume of the solid by subtracting the combined volume from the
original volume of the water only.
6. Repeat these steps for the second object.
7. Complete the table below.
Solid
Solid 1
Solid 2
Solid 3
2.6
Mass (g)
Volume (ml)
Density (g/ml)
Summary
• The smallest unit of matter is the atom. Atoms can combine to form molecules.
• A molecule is a group of two or more atoms that are attracted to each other by chemical
bonds.
• A small molecule consists of a few atoms per molecule. A giant molecule consists of
millions of atoms per molecule, for example metals and diamonds.
• The structure of a molecule can be represented in a number of ways.
• The chemical formula of a molecule is an abbreviated way of showing a molecule, using
the symbols for the elements in the molecule. There are two types of chemical formulae:
molecular and empirical formula.
• The molecular formula of a molecule gives the exact number of atoms of each element
that are in the molecule.
• The empirical formula of a molecule gives the relative number of atoms of each element
in the molecule.
• Molecules can also be represented using diagrams.
• A ball and stick diagram is a 3-dimensional molecular model that uses ’balls’ to represent
atoms and ’sticks’ to represent the bonds between them.
• A space-filling model is also a 3-dimensional molecular model. The atoms are represented
by multi-coloured spheres.
• In a molecule, atoms are held together by chemical bonds or intramolecular forces.
Covalent bonds, ionic bonds and metallic bonds are examples of chemical bonds.
• A covalent bond exists between non-metal atoms. An ionic bond exists between nonmetal and metal atoms, and a metallic bond exists between metal atoms.
• Intermolecular forces are the bonds that hold molecules together.
• The kinetic theory of matter attempts to explain the behaviour of matter in different
phases.
• The theory says that all matter is composed of particles which have a certain amount
of energy which allows them to move at different speeds depending on the temperature
(energy). There are spaces between the particles, and also attractive forces between
particles when they come close together.
31
2.6
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
• Understanding chemical bonds, intermolecular forces and the kinetic theory of matter, can
help to explain many of the macroscopic properties of matter.
• Melting point is the temperature at which a solid changes its phase to become a liquid.
The reverse process (change in phase from liquid to solid) is called freezing. The stronger
the chemical bonds and intermolecular forces in a substance, the higher the melting point
will be.
• Boiling point is the temperature at which a liquid changes phase to become a gas. The
stronger the chemical bonds and intermolecular forces in a substance, the higher the boiling
point will be.
• Density is a measure of the mass of a substance per unit volume.
• Viscosity is a measure of how resistant a liquid is to changing its form.
Exercise: Summary exercise
1. Give one word or term for each of the following descriptions.
(a) The property that determines how easily a liquid flows.
(b) The change in phase from liquid to gas.
(c) A composition of two or more atoms that act as a unit.
(d) Chemical formula that gives the relative number of atoms of each element
that are in a molecule.
2. For each of the following questions, choose the one correct answer from the
list provided.
A Ammonia, an ingredient in household cleaners, can be broken down to
form one part nitrogen (N) and three parts hydrogen (H). This means that
ammonia...
i. is a colourless gas
ii. is not a compound
iii. cannot be an element
iv. has the formula N3 H
B If one substance A has a melting point that is lower than the melting point
of substance B, this suggests that...
i. A will be a liquid at room temperature.
ii. The chemical bonds in substance A are weaker than those in substance
B.
iii. The chemical bonds in substance A are stronger than those in substance B.
iv. B will be a gas at room temperature.
3. Boiling point is an important concept to understand.
a Define ’boiling point’.
b What change in phase takes place when a liquid reaches its boiling point?
c What is the boiling point of water?
d Use the kinetic theory of matter and your knowledge of intermolecular
forces, to explain why water changes phase at this temperature.
4. Refer to the table below which gives the melting and boiling points of a
number of elements, and then answer the questions that follow. (Data from
http://www.chemicalelements.com)
Element
copper
magnesium
oxygen
carbon
helium
sulfur
Melting point
1083
650
-218.4
3500
-272
112.8
32
Boiling point (0 C)
2567
1107
-183
4827
-268.6
444.6
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
a What state of matter (i.e. solid, liquid or gas) will each of these elements
be in at room temperature?
b Which of these elements has the strongest forces between its atoms? Give
a reason for your answer.
c Which of these elements has the weakest forces between its atoms? Give
a reason for your answer.
33
2.6
2.6
CHAPTER 2. WHAT ARE THE OBJECTS AROUND US MADE OF? - GRADE 10
34
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The author(s) and publisher(s) of the Document do not by this License give permission to use
their names for publicity for or to assert or imply endorsement of any Modified Version.
COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the
terms defined in section A above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them
all as Invariant Sections of your combined work in its license notice, and that you preserve all
their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant
Sections may be replaced with a single copy. If there are multiple Invariant Sections with the
same name but different contents, make the title of each such section unique by adding at the
end of it, in parentheses, the name of the original author or publisher of that section if known,
or else a unique number. Make the same adjustment to the section titles in the list of Invariant
Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original
documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled
“Endorsements”.
470
APPENDIX A. GNU FREE DOCUMENTATION LICENSE
COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under
this License, and replace the individual copies of this License in the various documents with a
single copy that is included in the collection, provided that you follow the rules of this License
for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under
this License, provided you insert a copy of this License into the extracted document, and follow
this License in all other respects regarding verbatim copying of that document.
AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents
or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the
copyright resulting from the compilation is not used to limit the legal rights of the compilation’s
users beyond what the individual works permit. When the Document is included an aggregate,
this License does not apply to the other works in the aggregate which are not themselves derivative
works of the Document.
If the Cover Text requirement of section A is applicable to these copies of the Document, then if
the Document is less than one half of the entire aggregate, the Document’s Cover Texts may be
placed on covers that bracket the Document within the aggregate, or the electronic equivalent
of covers if the Document is in electronic form. Otherwise they must appear on printed covers
that bracket the whole aggregate.
TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section A. Replacing Invariant Sections with translations requires
special permission from their copyright holders, but you may include translations of some or
all Invariant Sections in addition to the original versions of these Invariant Sections. You may
include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and
the original versions of those notices and disclaimers. In case of a disagreement between the
translation and the original version of this License or a notice or disclaimer, the original version
will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the
requirement (section A) to Preserve its Title (section A) will typically require changing the actual
title.
TERMINATION
You may not copy, modify, sub-license, or distribute the Document except as expressly provided
for under this License. Any other attempt to copy, modify, sub-license or distribute the Document
is void, and will automatically terminate your rights under this License. However, parties who
have received copies, or rights, from you under this License will not have their licenses terminated
so long as such parties remain in full compliance.
FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation
License from time to time. Such new versions will be similar in spirit to the present version, but
may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
471
APPENDIX A. GNU FREE DOCUMENTATION LICENSE
Each version of the License is given a distinguishing version number. If the Document specifies
that a particular numbered version of this License “or any later version” applies to it, you have the
option of following the terms and conditions either of that specified version or of any later version
that has been published (not as a draft) by the Free Software Foundation. If the Document does
not specify a version number of this License, you may choose any version ever published (not as
a draft) by the Free Software Foundation.
ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document
and put the following copyright and license notices just after the title page:
c YEAR YOUR NAME. Permission is granted to copy, distribute and/or
Copyright modify this document under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the
license is included in the section entitled “GNU Free Documentation License”.
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.”
line with this:
with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts being LIST,
and with the Back-Cover Texts being LIST.
If you have Invariant Sections without Cover Texts, or some other combination of the three,
merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these
examples in parallel under your choice of free software license, such as the GNU General Public
License, to permit their use in free software.
472
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