preliminary chemistry - sciencepress · pdf filecontents iv dot point preliminary chemistry...

Marilyn Schell

Kevin Molyneux

PRELIMINARY CHEMISTRY

© Science Press 2007First published 2007Reprinted 2007, 2008, 2010

Science PressPrivate Bag 7023 Marrickville NSW 1475 AustraliaTel: (02) 9516 1122 Fax: (02) 9550 [email protected] www.sciencepress.com.au

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Science Press. ABN 98 000 073 861

Dot Point Preliminary Chemistry iii Contents

Science Press

Contents

Introduction vVerbs to Watch vi

Dot Points

The Chemical Earth viiMetals ixWater xiEnergy xiii

Questions

The Chemical Earth 1Metals 47Water 87Energy 117

Answers

The Chemical Earth 171Metals 191Water 203Energy 215

Appendix

Data Sheet 237Periodic Table 238

Contents iv Dot Point Preliminary Chemistry

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Notes

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Introduction

What the book includes

syllabus for the following topics in the Year 11 Chemistry course:

Also included are typical experimental results for students to analyse if the third column of the syllabus indicates

Format of the book

The book has been formatted in the following way:

1. Main topic statement (column 1 of syllabus)

1.1etc Syllabus requirement from columns 2 and 3.

1.1.1

1.1.2

worth in an examination. As a rough rule, every two lines of answer might be worth one mark. Note that in

chemistry involved is worth only one mark.

How to use the book

You may have done work in addition to this with your teacher as extension work. Obviously this is not covered, but you may need to know this additional work for your school exams.

spend more time revising later, and allow you to spend your study time more productively.

Dot Point Preliminary Chemistry v Introduction

Science Press

account/account for State reasons for, report on, give an account of, narrate a series of events or transactions.

analyse Identify components and the relationships among them, draw out and relate implications.

apply Use, utilise, employ in a particular situation.

appreciate Make a judgement about the value of something.

assess

results or size.

calculate

clarify Make clear or plain.

classify Arrange into classes, groups or categories.

compare Show how things are similar or different.

construct Make, build, put together items or arguments.

contrast Show how things are different or opposite.

critically (analyse/evaluate) Add a degree or level of accuracy, depth, knowledge

deduce Draw conclusions.

demonstrate Show by example.

describe Provide characteristics and features.

discuss Identify issues and provide points for and against.

distinguish Recognise or note/indicate as being distinct or different from, note difference between things.

evaluate Make a judgement based on criteria.

examine

explain Relate cause and effect, make the relationship between things evident, provide why and/or how.

extract Choose relevant and/or appropriate details.

extrapolate Infer from what is known.

identify Recognise and name.

interpret Draw meaning from.

investigate

justify Support an argument or conclusion.

outline Sketch in general terms; indicate the main features.

predict Suggest what may happen based on available data.

propose Put forward (a point of view, idea, argument, suggestion etc) for consideration or action.

recall Present remembered ideas, facts or experiences.

recommend Provide reasons in favour.

recount Retell a series of events.

summarise Express concisely the relevant details.

synthesise Put together various elements to make a whole.

Verbs to Watch

Verbs to Watch vi Dot Point Preliminary Chemistry

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Dot Point Page

1. Mixtures of the Earth 2 and their separation

1.1 Particle theory of matter 21.2 Mixtures in the biosphere, lithosphere, 3

hydrosphere and atmosphere1.3 Separation of naturally occuring mixtures 3

Separating a mixture

1.6 Uses of gravimetric analysis 6

Gravimetric analysis of a mixture1.8 Industrial separation of a mixture 91.9 Applied Question Section 1 102. Elements – occurrence and properties 112.1 Reactivity and occurrence of elements 11

2.3 Investigation: Physical properties 12 of elements

2.4 Physical properties of 13

and the Periodic Table

2.6 Uses and properties of metals 152.7 Applied Question Section 2 163. Compounds, molecules and ions 173.1 Matter is made of moving particles 173.2 Mass number and atomic number 173.3 Energy levels of electrons 183.4 Atoms gain or lose electrons to form ions 193.5 Ion formation and the Periodic Table 20

3.7 Lewis electron dot structures 213.8 Attraction of ions and ionic compounds 223.9 Molecules 223.10 Atoms in molecules 23

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3.11 Atoms share electrons in 23 covalent molecules

3.12 Formulas of ionic and 24 molecular compounds

3.13 Models of ionic and covalent compounds 254. Energy in the extraction of elements 274.1 Physical and chemical changes 274.2 Boiling and electrolysis of water 28

Electrolysis of water

4.4 Boiling and electrolysis as physical and 30 chemical changes

Light on silver salts

Heat on carbonates

4.7 Energy changes in decomposition 32 and synthesis reactions

4.8 Energy needed to break 33 bonds in compounds

5. Bonding, structure and properties 355.1 Physical and chemical properties 35

elements and the compounds they form

5.3 Physical properties of ionic, 37 covalent molecular and covalent network compounds

metallic, ionic and covalent substances

5.7 Empirical formulas of ionic compounds 405.8 Elements as molecules or lattices 415.9 Properties, structure and 42

bonding of substances5.10 Metallic, ionic and covalent bonds 435.11 Limitations of models 45Answers to The Chemical Earth 171

The Chemical Earth

Dot Point Preliminary Chemistry vii The Chemical Earth

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Notes

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The Chemical Earth viii Dot Point Preliminary Chemistry

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1. Uses of metals and alloys 481.1 Uses of metals through history 481.2 Energy for metal extraction 481.3 Availability of metals over time 491.4 Uses and properties of alloys 491.5 Composition and uses of alloys 501.6 Bronze Age, Iron Age and 50

Modern Era of metals1.7 Applied Question Section 1 522. Reactivity of metals 53

Activity series of metals

2.2 Reactions of metals with dilute acids, 53 water and oxygen

2.4 Criteria for activity series of metals 562.5 Transfer of electrons occurs when 57

metals react with acids

transfer reactions2.7 Uses and reactivity of metals 592.8 Reactivity of metals and the Periodic Table 592.9 Reactivity of metals and 60

3. Properties of elements 61 and the Periodic Table

3.1 A model of atomic structure 613.2 Development of the Periodic Table 623.3 Trends in properties of elements and 64

their position in the Periodic Table

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3.4 Recognising patterns in properties 68 of elements

tabulate and graph

3.6 Applied Question Section 3 704. Measuring chemicals in reactions 714.1 The mole concept 71

4.3 Mass changes in combustion of metals 724.4 Empirical and molecular formulas 73

Chemical composition

4.8 Calculations of moles 764.9 Volume of gases and the mole 775. Extraction and recycling of metals 795.1 Minerals, ores and resources 795.2 Predicting yield of ore deposits 795.3 Extraction of copper from its ore 805.4 Commercial prices, cost of production 81

and abundance of metals

5.6 Recycling of metals 835.7 Recycling aluminium 845.8 Cost to extract and recycle aluminium 85Answers to Metals 191

Metals

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Dot Point Preliminary Chemistry ix Metals

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Metals x Dot Point Preliminary Chemistry

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1. Distribution of water on Earth 881.1 Solute, solvent, solution 881.2 Water as a solvent 881.3 Distribution of water on Earth 881.4 Roles of water 891.5 Calculations of density 90

1.7 Investigation: Effect of antifreeze or salt 92 on boiling point of water

2. Structure and bonding of water 932.1 Lewis electron dot structures 932.2 Structure and shape of water, 93

2.3 Polarity of water 94

2.5 Hydrogen bonding 962.6 Modelling structure and bonding of water 962.7 Water – properties and 97

intermolecular forces2.8 Boiling point of water and 98

other similar sized molecules

Properties of water3. Water as a solvent 101

substances in water

3.2 Interactions of water with chemicals 1023.3 Polarity of water and its solubility 1043.4 Modelling dissolution 104

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4. Solutions, solubility and precipitation 1054.1 Solubility rules and precipitates 1054.2 Modelling dissolution and precipitation 1054.3 Ion movement in saturated solutions 106

and precipitation

Solubility of salts

4.6 Describing molarity of solutions 1074.7 Calculating concentration of solutions 1084.8 Measures of concentration 108

Making and diluting solutions

4.10 Calculating mass and 110 concentration in precipitation reactions

5. 111

and other solvents

H = –mC T

Finding molar heat of solution

5.6 Exothermic dissolutions 1145.7 Endothermic dissolutions 1145.8 Limitations of calorimetry experiments 115

5.10 Thermal pollution 116Answers to Water 203

Water

Dot Point Preliminary Chemistry xi Water

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Water xii Dot Point Preliminary Chemistry

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1. Organic origins of energy 1181.1 Photosynthesis – raw materials 118

and energy changes1.2 Photosynthesis and solar energy 1181.3 Photosynthesis and fossil fuels 1191.4 Investigating a fossil fuel – 120 reliability, validity, accuracy2. Carbon and its compounds 1232.1 Carbon 1232.2 Allotropes of carbon 1232.3 Models of diamond, graphite 126

and fullerenes2.4 Properties and uses of diamond 126

and graphite2.5 Single, double and triple bonds 126

2.7 Carbon compounds 1283. Petroleum, alkanes and alkenes 1293.1 Modelling alkanes and alkenes 1293.2 Naming alkanes and alkenes 1313.3 Properties of alkanes and alkenes 133

distillation of a mixture

3.5 Fractional distillation of petroleum 1363.6 Properties and bonding of hydrocarbons 1373.7 Storing alkanes safely 1383.8 Safety of alkanes and bonding 1393.9 Applied Question Section 3 1424. Chemical reactions – combustion 1434.1 Indicators of chemical reactions 143

and exothermic reactions

4.3 Combustion as an exothermic 144 chemical reaction

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4.5 Combustion of a candle 146

in chemical reactions

and breaking

4.9 Activation energy 149

and exothermic reactions4.11 Ignition temperature and 151

activation energy4.12 Pollution from combustion 1515. Rates of reactions 153

of factors on reaction rates

5.2 Slow, spontaneous and 156 explosive combustion

5.3 Conditions for explosions 1575.4 Reaction rates and particle collisions 1585.5 Explosions and work environments 1595.6 Temperature and kinetic energy 160

of particles5.7 Catalysts in chemical reactions 1605.8 Catalysts, activation energy 161

and rates of reactions5.9 Modelling the role of a catalyst 1616. Chemical reactions in the 163 Preliminary course

chemical reactions

Answers to Energy 215

Energy

Dot Point Preliminary Chemistry xiii Energy

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Energy xiv Dot Point Preliminary Chemistry

Dot Point Preliminary Chemistry 1 The Chemical Earth

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DOT POINTThe Chemical Earth

The Chemical Earth 2 Dot Point Preliminary Chemistry

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1. The living and non-living components of the Earth contain mixtures.

1.1 Identify the difference between elements, compounds and mixtures in terms of particle theory.

1.1.1 State the particle theory.

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1.1.2

(a) element

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(b) compound

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(c) mixture

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1.1.3 Identify each of the following diagrams as representing an element, mixture or compound.

(a) ........................................................ (b) ....................................................... (c) ........................................................

(d) ....................................................... (e) ........................................................ (f) .........................................................


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1.2 Identify that the biosphere, lithosphere, hydrosphere and atmosphere contain examples of mixtures of elements and compounds.

1.2.1 Complete the following table to show the zones in which each of the following mixtures is

Zone Mixture present Components of mixture

Biosphere Wood Mixture of compounds such as water, carbohydrates, oils.

Copper carbonate ore

Salt water

Air

1.3 Identify and describe procedures that can be used to separate naturally occurring mixtures of:

1.3.1 Use diagrams to describe the following processes:

(a) Filtration (b) Sedimentation and decanting

(c) Evaporation and crystallisation (d) Fractional distillation of a mixture of liquids

(e) Sieving (f) Using a separating funnel to separate two liquids


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1.3.2 Complete the following table to relate some mixtures and methods of separating their

Type of mixture Example Suitable process to separate components

Solids of different sizes. A mixture of partly crushed rock particles and silt.

Sieving – particles smaller than the hole in the sieve pass through, large particles stay in the sieve.

A liquid and a solid that will not dissolve in that liquid.

A solid dissolved in a liquid.

Miscible liquids with different boiling points.

Immiscible liquids with different densities.

Gases.

1.3.3

(a) Air is a mixture. Identify the main gases present.

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(b) Identify the steps in the separation of gases such as oxygen and nitrogen from a mixture such as air.

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the components of a naturally occurring or appropriate mixture such as sand, salt and water.

1.4.1 Identify the components of the mixture that you separated in the laboratory.

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1.4.2 Describe the method you used.

(Note: You should list the steps in order and include a diagram. Your method should be so clear that anyone else could repeat your experiment exactly as you did it.)

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1.5 Assess separation techniques for their suitability in separating examples of Earth materials, identifying the differences in properties which enable these separations.

1.5.1 Assess the use of fractional distillation to separate oxygen and nitrogen from air.

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1.5.3 Use the following table to summarise the differences in properties that allow the listed mixtures to be separated.

Components of mixture Process used to separate components

Property that makes this use possible

Oil and water.

Solid wastes from sewage.

Sand and gravel.

Nitrogen and oxygen from air.

1.6 Describe situations in which gravimetric analysis supplies useful data for chemists and other scientists.

1.6.1mercury in a sample of mercury oxide.

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1.6.2 Identify three other situations in which scientists might use gravimetric analysis to provide useful data about mixtures.

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1.6.3 The label on a packet of oats contains the following information:

Contents Per 100 g Contents Per 100 g

Energy 1600 kJ Dietary fibre 6.9 g

Protein 9.4 g Sodium 20 mg

Fat 5.9 g Potassium 265 mg

Carbohydrate 68.6 g

(a) Describe how the manufacturer could have determined such information.

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(b) Describe the purpose of providing such information on food packaging.

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percentage composition.

1.7.1

(a) Identify the mixture that you analysed in the laboratory, by means of gravimetric analysis.

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(b) Assess the reliability of your results.

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(c) Discuss the need for safety precautions while carrying out this experiment.

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1.7.2 Two Year 11 students, Karen and Robert, are provided with a mixture of sand and salt and asked to carry out a gravimetric analysis of this mixture to determine the percentage of salt present. The total mass of the mixture is 4.90 grams. The students add water and stir to dissolve the salt.

evaporating it to dryness. The results Karen and Robert obtain are:

Weight of evaporating basin (empty) = 23.43 g

(a) Calculate the following:

(i) the mass of the residue

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(ii) the mass of the solid in the evaporating dish

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(iii) the percentage composition of salt in the original mixture

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(iv) the total mass of chemicals recovered after separation

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improvements.

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1.8 Identify data sources, gather, process and analyse information from secondary sources to identify the industrial separation processes used on a mixture obtained from the biosphere, lithosphere, hydrosphere or atmosphere and use the evidence available to:

1.8.1 During this course you researched an industrial separation process (e.g. gravimetric analysis

Name of industrial separation process researched

Components of mixture separated by this process.

Properties of components that allow them to be separated by this process.

Uses of components when they have been separated.

Issues associated with any wastes produced during this process.

1.8.2 Explain how you assessed the reliability of the reference sources you chose.

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1.9 Applied Question Section 1

Some junior students were arguing about whether air is a mixture or a compound. You are called in, as an expert, to help settle the argument.

Identify arguments you could use to convince them that air is a mixture.

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2. Although most elements are found in combinations on Earth, some elements are found uncombined.

2.1 Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element.

2.1.1 Identify whether each of the following elements would be more likely to exist naturally as an uncombined element or as a compound

(a) magnesium (b) gold

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2.1.2 Compare the reactivity of the metals magnesium and gold.

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2.1.3 Explain the relationship between the reactivity of an element and the likelihood of its existing as an uncombined element.

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2.2.1 Distinguish between the terms physical property and chemical property.

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2.2.2 Identify the following properties as either physical or chemical.

(a) melting point ........................................................................................................................................

(b) hardness ..................................................................................................................................................

(c) malleability ...........................................................................................................................................

(d) decomposition .....................................................................................................................................

(e) reaction with acid ..............................................................................................................................

(f) density .....................................................................................................................................................


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2.2.3 Complete the following table to summarise the differences between the physical properties of

Physical property Metals Non-metals

Melting and boiling points.

Conductivity of heat.

Conductivity of electricity.

Malleability (able to be bent and hammered into shapes).

Ductility (able to be stretched into wires).

Lustre.

2.2.4the brackets.

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and they have (high/low) melting and boiling points.

than metals.

2.3 Plan and perform an investigation to examine some physical properties, including malleability, hardness and electrical conductivity, and some uses of a range of common elements to present

2.3.1 During your studies you investigated the physical properties of some elements.

(a) Identify three elements you studied.

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(c) Use a labelled diagram to show how you tested the electrical conductivity of these elements.


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2.3.2

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2.4 Analyse information from secondary sources to distinguish the physical properties of metals

2.4.1 Analyse the following information to classify each of the elements described below as a

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(b) A yellow powder which is a poor conductor of electricity.

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(c) A colourless gas at room temperature.

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2.4.2

Element Melting point (°C) Melting point (°C) Conductivity Metal or non-metal

A 1083 2600 Good

B –157 –152 Poor

C 44 280 Poor

D 1770 4530 Good

E –210 –196 Poor

2.4.33), sodium carbonate (Na2CO3) and carbon dioxide

(CO2

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2.4.4 Identify the following elements:

.........................................................................................

....................................................................................................

(c) an inert gas used in advertising signs ...........................................................................................................................

..................................................................................................


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2.5 Process information from secondary sources and use a Periodic Table to present information

2.5.1P

erio

d

7654321

II III IV V VI VII VIII

non-metals

semi-metals

metals

Group I

2.5.2 Using a key, shade the following Periodic Table to identify which elements occur as solids,

solidsliquids

Po

Ar

FOCB NClSSiAl

KrSe

XeI

BiPbTl

AsGe

Sb Te

Ga

Sn

Hg

Zn

In

AuPt

CuNi

Ag Cd

Ir

Co

PdRh

OsReW

FeMn

Tc Ru

Cr

Mo

Ta

Db

V

Nb

HfLa

Ac Ru

BaCs

Fr Ra

TiSc

Y Zr

CaK

Rb Sr

BeLi

Na Mg

He

Ne

P

H

RnAt

gases

Br

2.5.3

Element Melting point (°C) Melting point (°C) Solid/liquid/gas at room temperature

A 1490 2900

B –7 58

C 114 183

D –39 357

E –210 –196


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2.5.4

Metals Non-metals

Potassium Phosphorus

Copper Carbon

Calcium Ar

Na H

Al S

Mercury I

2.6.1 For each of the elements listed in the table below, describe one use and the physical

Element Use Properties

Gold Jewellery Shiny lustre, malleable

Carbon

Aluminium

Helium

Iron

2.6.2 Complete the table by matching the properties listed in the table with the names and uses of the elements shown below.

Names of elements described UsesNeon Building constructionSelenium Light sensitive switchesHelium JewelleryAluminium Filling balloonsCarbon (diamond) Advertising signsIron Wrapping food

Name of element Properties Use

Conductor of electricity in the light, non-conductor in the dark.

Durable, clear, shiny solid.

Gas which is inert and has a very low density.

Strong, solid, malleable metal.

Durable metal, very malleable, can be rolled into thin sheets, insoluble in water.

Unreactive gas which emits red light when electricity is passed through.


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The physical properties of a metal are usually given as:

properties mentioned above, what makes each of the following elements unusual?

(a) the metal lead

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(d) the metal mercury

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(e) the metal copper

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3. Elements in Earth materials are present mostly as compounds because of interactions at the atomic level.

3.1 Identify that matter is made of particles that are continuously moving and interacting.

3.1.1 Identify the three types of particles that make up matter.

...............................................................................................................................................................................................................................

3.1.2 Matter can occur as three states, depending on the energy of the particles. The states of matter are ........................................ , ................................................. and ................................................................ .

3.1.3 Complete the table below to summarise the properties of the three states of matter.

Property Solid Liquid Gas

Arrangement of particles. Particles are close together and moving more freely.

Diagram.

Shape. Depends on container.

Volume (space occupied). Definite volume.

Ability to be compressed (be pushed into a smaller volume).

Can be compressed.

Ability to diffuse (spread through another substance).

Cannot diffuse.

Kinetic energy of particles.

3.2 Describe atoms in terms of mass number and atomic number.

3.2.1

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3.2.2 Complete the following table to show the particles present in atoms.

Particle Where found Symbol Relative charge Relative mass

Proton Nucleus of atom +1 1

Neutron

Electron e–

3.2.3 Compare the mass number and the atomic number of an element.

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3.2.4 Complete the following table to show the particles in the atoms of some elements.

Name of element

Atomic number

Mass number

Number of protons

Number of neutrons

Number of electrons

Hydrogen 1 0

Beryllium 4 9

10 20

13 14

80 121

3.2.5 Use your Periodic Table and atomic numbers provided to identify the names and symbols for each of the following elements.

Atomic number Name of element Symbol

5

7

19

92

3.2.6 Identify which two of the following species are both the same element. ................................................

Number of neutrons Number of protons Number of electrons

A 13 12 12

B 13 13 10

C 12 12 10

D 12 11 10

3.3 Describe qualitatively the energy levels of electrons in atoms.

3.3.1each energy level.

Energy level Maximum number of electrons

K (1st shell)

8

M (3rd shell)

32

3.3.2 Which electrons have the most energy, those in level K, L, M or N? ........................................................


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3.3.3structure of its atoms:

(a) Lithium – atomic number 3, mass number 7

Diagram:

...................................................................................

(b) Calcium – atomic number 20, mass number 40

Diagram:

...................................................................................

3.4 Describe the formation of ions in terms of atoms gaining or losing electrons.

3.4.1

...............................................................................................................................................................................................................................

3.4.2 Complete the following table to show whether each of the following atoms gains or loses one or more electrons when it forms an ion.

Name of atom Gains or loses electron(s)

Number of electrons gained or lost

Symbol of ion formed

Sodium loses Na+

Chlorine 1

Magnesium loses

Oxygen 2

Neon 0

Aluminium

3.4.3 Complete the following rules for the formation of ions:

(a) Metal atoms tend to ................................................ electrons and form ........................................................ ions.

................................................... electrons and form ....................................................... ions.


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3.5.1 Write symbols for the following ions.

(a) potassium ion ........................................................... (b) calcium ion ............................................................

(c) bromide ion ............................................................... (d) silver ion .................................................................

(e) hydrogen ion ............................................................ (f) lead(II) ion .............................................................

3.5.2 Complete the summary below to show the relationship between the group of the Periodic Table to which an element belongs and the ions it can form.

Group of Periodic Table Electrons lost or gained Charge on ion formed

I 1 lost +1

II

III

VI

VII 1 gained –1

3.5.3the following polyatomic ions:

Ion Symbol Valency

Sulfate ion

Nitrate ion

Carbonate ion

Phosphate ion

Hydroxide ion

Ammonium ion

3.6.1

(a) sodium

...............................................................................................................................................................................................................................

(b) magnesium

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(c) chlorine

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3.7 Apply Lewis electron dot structures to:

3.7.1 Apply Lewis electron dot structures to the formation of:

(a) sodium ions

(b) chloride ions

3.7.2 Apply Lewis electron dot structures to electron sharing between:

(a) Two atoms of chlorine sharing electrons to form a molecule of chlorine.

(b) An atom of oxygen sharing electrons with two atoms of hydrogen to form a molecule of water.

3.7.3

(a) Complete the following:

When elements form ........................................ , their atoms gain, lose or share ........................................ with atoms of other elements. Their ability to do this is called their combining power or .......................................... . Gaining, losing or sharing one or more electrons allows an atom to obtain a complete, .......................................... outer shell of electrons.


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(b) Complete the following table to show the name, symbol and valency of the elements listed.

Name Symbol Valency Name Symbol Valency

Strontium N

Cu 1 or 2 Carbon

Ca Bromine

Nickel Iodine

Magnesium Zn

Fe 2 or 3 Hg

(c) Should valency (combining power) be shown as a positive or negative value or simply a number?

...............................................................................................................................................................................................................................

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3.8 Describe the formation of ionic compounds in terms of the attraction of ions of opposite charge.

3.8.1

...............................................................................................................................................................................................................................

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3.8.2 To which of the following ions would magnesium ions be attracted: sodium ions, calcium ions, chloride ions, ammonium ions, zinc ions. Explain your answer.

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3.8.3 Identify the term used to describe the force between sodium ions and chloride ions in the compound sodium chloride.

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3.9 Describe molecules as particles which can move independently of each other.

3.9.1

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3.9.2 Distinguish between an atom of hydrogen and a molecule of hydrogen.

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3.10 Distinguish between molecules containing one atom (the noble gases) and molecules with more than one atom.

3.10.1 Identify the following:

(a) three elements with molecules composed of only one atom

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(b) three examples of molecules composed of two identical atoms

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(c) the term used to describe molecules composed of two atoms

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(d) three examples of compounds that exist as molecules

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3.10.2 Show symbolically the structure of:

(a) an atom of hydrogen ..................................... (b) a molecule of hydrogen .........................................

(c) an atom of chlorine ........................................ (d) a molecule of chlorine ............................................

(e) a molecule of neon ......................................... (f) a molecule of carbon dioxide .............................

(g) a molecule of water .......................................

3.11 Describe the formation of covalent molecules in terms of sharing of electrons.

3.11.1 Compounds with formula HCl(g) and HCl(l) are covalent molecular, whereas the compound

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3.11.2 Covalent molecules are ones in which electrons are shared. Use Lewis electron dot diagrams to show molecules of:

(a) water (b) methane

(c) oxygen (d) ammonia

3.12 Construct formulas for compounds formed from:

3.12.1 Write formulas for the following ionic compounds:

(a) potassium chloride ......................................... (b) sodium nitrate .............................................................

(c) magnesium carbonate ................................... (d) lithium phosphate ......................................................

(e) aluminium sulfate ............................................ (f) iron(II) hydroxide .....................................................

3.12.2 Write formulas for the following molecular compounds:

(a) ammonia .............................................................. (b) dinitrogen oxide .........................................................

(c) sulfur dioxide ..................................... (d) sulfur trioxide ..............................................................

(e) dinitrogen tetraoxide ..................................... (f) silicon dioxide .............................................................


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3.13 Analyse information by constructing or using models showing the structure of metals, ionic compounds and covalent compounds.

3.13.1

(a) Complete the following passage:

Metals are elements on the .......................................... side of the Periodic Table and they tend to give up their outer shell .......................................... to form ions with a .......................................... charge.

Metals are good .......................................... of electricity because they consist of a lattice made of positive ions surrounded by a sea of .......................................... electrons and the electrons are free to move.The random movement of the outer shell electrons provides the .......................................... or force that holds the crystal structure of the metal lattice together. This force is called a .......................................... bond. Metallic bonds are very ...........................................

3.13.2 In the following list, circle the substances which have metallic bonds.

(a) aluminium (b) aluminium oxide

(c) copper (d) copper sulfate

(e) sodium (f) sodium chloride

3.13.3

(a) Complete the following passage about ionic compounds.

An ionic compound is a compound that contains .......................................... which are held together by an .......................................... force. Most ionic compounds are crystalline solids at room .......................................... .

.........................................or network of .......................................... which are held together by

.......................................... bonds.


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3.13.4

(a) Complete the following passage using the list of words below the passage.

Covalent compounds are compounds that contain .......................................... bonds, thus they involve the .......................................... of one or more pairs of electrons between atoms. Covalent compounds are formed between elements in .......................................... IV, V, VI and VII of the Periodic .......................................... . Covalent compounds exist as .......................................... . These molecules can be small, e.g. carbon dioxide or large, e.g. silicon dioxide. Large molecules are called .......................................... .......................................... .......................................... . These giant covalent lattices can be also called macromolecules and covalent network substances.

The covalent bond within a molecule is a very .......................................... bond. In giant covalent lattices these strong .......................................... extend throughout the lattice. Small covalent molecules have weak intermolecular .......................................... holding the molecules together.

List of words: Groups, strong, molecules, covalent, bonds, forces, sharing, giant covalent lattices, Table

(b) Use a diagram to model molecules of methane, showing all bonding.

(c) Use a diagram to model a giant covalent lattice of silicon dioxide.

3.13.5 Describe the method YOU used to model:

(a) metals

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(b) ionic compounds

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(c) covalent compounds

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4. Energy is required to extract elements from their naturally occurring sources.

4.1 Identify the differences between physical and chemical change in terms of rearrangement of particles.

4.1.1 Classify each of the following as a physical change or a chemical change.

(a) boiling water ..........................................................................................................................

(b) cooking an egg ......................................................................................................................

................................................................................................................

(d) combustion of magnesium .............................................................................................

(e) decomposition of mercury oxide ................................................................................

(f) evaporation ..............................................................................................................................

(g) condensation ...........................................................................................................................

4.1.2 The main indication that a chemical change has occurred is the production of a new substance. Identify three observations that would indicate that this had occurred.

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4.1.3 Identify which of the following reactions is a physical change and which is a chemical change. Justify your choice.

(b) +

(a) + +

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4.1.4 Complete the following table to compare physical and chemical changes in terms of their particles.

Physical change Chemical change

New substance No new substance is formed.

Particles New particles are formed (atoms have been rearranged).

Reversal Easy to reverse by physical methods.

Energy Small energy changes usually involved.


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4.2 Analyse and present information to model the boiling of water and the electrolysis of water tracing the movements of and changes in arrangements of molecules.

4.2.1

(a) Describe the particles that make up water.

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(b) When you start heating water in a beaker, you can see tiny bubbles of a gas on the inside of the beaker, in the water. Does this mean that the water molecules are breaking up into hydrogen and oxygen gas? Explain.

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(c) When water is heated, what happens to the H2O particles?

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(d) When water boils and evaporates, what happens to the particles?

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(e) When water is heated and boiled, do the H2O molecules ever break up? Explain.

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4.2.2 Use diagrams to model the arrangement and movement of particles in cold water and boiling water.

Cold water Boiling water

4.2.3 changes respectively.

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analyse the information provided as evidence that water is a compound, and identify an application of the use of this reaction.

4.3.1 You carried out an experiment in which you passed an electric current through water and the water decomposed.

(a) Draw a labelled diagram to show how you did this and the results you obtained.

(b) Use a diagram to show the water molecules before and after the passage of the electric current through the water.

Water molecules before electrolysis: Molecules present after electrolysis of water:

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(d) Outline one use for electrolysis of water.

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(e) Describe the tests you used to identify the oxygen and hydrogen produced.

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4.4 Summarise the differences between the boiling and electrolysis of water as an example of the difference between physical and chemical change.

4.4.1 Complete the following table to show the differences between the boiling and electrolysis of water.

Boiling of water Electrolysis of water

Changes in water. Water changes state from liquid to gas.

Changes in particles. Particles have changed. Water particles (H2O) have disappeared and new particles (H2 and O2) have appeared.

Reversal of process. Easy to reverse – cool water vapour and it changes back to a liquid.

Physical or chemical change.

4.4.2

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(b) combustion of hydrogen

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salts and identify an application of the use of this reaction.

4.5.1

(a) Describe the changes that occur in a silver salt (e.g. silver chloride, bromide or iodide) when it is exposed to light.

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(b) Identify the type of chemical reaction that has occurred.

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4.5.2 Explain how silver salts are used in photography.

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using appropriate tests to identify carbon dioxide and the oxide as the products of the reaction.

4.6.1

(a) Use a labelled diagram to show how you carried out this experiment.

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(c) Describe how you tested the oxide and the gas produced.

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(d) Before you carry out any experiment it is essential to do a risk assessment. Outline reasons why we bother with this step.

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(e) Describe one safety concern that you anticipated when planning this experiment and outline how you prevented or overcame this potential problem.

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4.7 Identify light, heat and electricity as the common forms of energy that may be released or absorbed during the decomposition or synthesis of substances and identify examples of these changes occurring in everyday life.

4.7.1the examples complete the table to identify the type of energy released or used.

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Example Method used Energy used or released

Production of metals from their ores, e.g. copper from copper carbonate.

Heat in a furnace. Heat energy used to decompose the copper carbonate.

Production of aluminium from aluminium oxide (in bauxite).

Development of film.

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Example How it occurs Energy used or released

The rusting of iron. Iron reacts with oxygen in air, in the presence of water to form a hydrated form of iron(III) oxide.

Energy released in the form of heat.

Photosynthesis.

Formation of nitrogen oxides in the atmosphere.

Burning of coal or coke to produce electricity or to make steel.

4.7.2

Decomposition: ...............................................................................................................................................................................................................................

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Synthesis: ...............................................................................................................................................................................................................................

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4.7.3 Identify whether each of the following reactions is an example of synthesis or decomposition.

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(c) Heating mercury oxide to form mercury and oxygen. .......................................................................................

(d) CaCO3 2(g) .......................................................................................................................................

(e) + .............................................................................................................................

(f) + ........................................................................................................................................................

4.8 Explain that the amount of energy needed to separate atoms in a compound is an indication of the strength of the attraction, or bond, between them.

4.8.1 Mercury oxide (HgO) can be easily decomposed by heating whereas potassium oxide (K2O) cannot. Explain.

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4.8.2 The following table shows the decomposition by heat of some types of compounds.

Metal Chloride Carbonate Hydroxide Nitrate Oxide Sulfate

PotassiumSodium

Stable. Stable. Stable. Forms nitrite and oxygen.

Stable. Stable.

BariumCalcium

Forms metal oxide and carbon dioxide.

Forms metal oxide and water.

Forms metal oxide, nitrogen dioxide and oxygen.

MagnesiumAluminiumZincIronTinCopper

Forms metal oxide and sulfur trioxide.

Lead Stable.

Mercury Sublimes. Forms metal, oxygen and carbon dioxide.

Do not exist. Forms metal, nitrogen dioxide and oxygen.

Forms metal and oxygen.

Forms metal, sulfur trioxide and oxygen.

Silver Stable.

PlatinumGold

(a) Of the metals listed in the table, which two form the most stable compounds?

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(b) Identify the two types of compounds, from those listed in the table, that are the most stable.

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(c) Identify any products formed when:

(i) calcium carbonate decomposes

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(ii) silver chloride decomposes

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(iii) aluminium oxide is heated

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(d) Neither water nor aluminium oxide can be decomposed by heat, yet both of these compounds can be decomposed by electrolysis. Explain.

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5. The properties of elements and compounds are determined by their bonding and structure.

5.1 Identify differences between physical and chemical properties of elements, compounds and mixtures.

5.1.1 Classify each of the following as either a physical property or a chemical property.

(a) ability to burn ............................................................................................................

(b) ability to react with water ...................................................................................

(c) boiling point ...............................................................................................................

(d) colour ..............................................................................................................................

(e) high reactivity ............................................................................................................

(f) density ............................................................................................................................

(g) unreactive or inert ...................................................................................................

(h) conductivity ................................................................................................................

(i) melting point ..............................................................................................................

(j) hardness ........................................................................................................................

5.1.2physical and chemical properties of the elements listed in the tables.

(a) Physical properties:

Element Melting point (°C) Boiling point (°C) Density (g/mL at 20°C)

Calcium

Mercury

Nitrogen

(b) Chemical properties:

Element Reactivity with water Ability to burn

Hydrogen

Silver

Magnesium

5.1.3

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5.1.4(a) physical and (b) chemical properties of the compounds listed.

(a) Physical properties:

Compound Melting point (°C) Boiling point (°C) Density (g/mL at 20°C)

Calcium iodide

Mercury(I) chloride

Nitric acid


Compound Reactivity with water Decomposition

Copper sulfate

Silver chloride

Magnesium carbonate

their elemental state with the properties of the compound(s) of these elements (e.g. the elements magnesium and oxygen and the compound magnesium oxide).

5.2.1

(a) Identify the compound you studied.

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(b) Identify the elements that make up this compound, and the ratio in which they are combined.

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(c) List the physical and chemical properties you studied.

Physical properties:

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Chemical properties:

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(d) Comment on the accuracy and reliability of your results.

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5.2.2 When elements combine to form a compound, the compound has properties which are different to the properties of the elements used to make the compound.

(a) Explain why this happens, using an example.

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(b) We eat sodium chloride on our food and yet it is made from sodium, a silver metal which

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5.2.3 Complete the following table to show that the properties of water differ from those of the elements from which it is made.

Chemical properties Physical properties

Water

Hydrogen

Oxygen

5.3 Describe the physical properties used to classify compounds as ionic or covalent molecular or covalent network.

5.3.1 Classify the following compounds as ionic, covalent molecular or covalent network.

(a) sodium chloride ......................................................................................................................

(b) silicon dioxide .........................................................................................................................

(c) ammonia .....................................................................................................................................

(d) carbon dioxide .........................................................................................................................

(e) carbon tetrachloride ..............................................................................................................

5.3.2 Identify the physical properties used to classify compounds as ionic, covalent molecular or covalent network.

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5.3.3 Complete the following sentences to explain why ionic, covalent molecular and covalent network substances have different melting and boiling points.

(a) When an ionic substance such as sodium chloride is heated enough to change state, .......................................... bonds have to be broken. These are .......................................... bonds, so the melting and boiling points are ...........................................


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(b) When a covalent molecular substance such as water is heated enough to change state, the forces that break are the .......................................... forces, e.g. .......................................... forces. As these are weak forces the melting and boiling points of covalent molecular substances are .......................................... .

(c) When a macromolecular substance such as silicon dioxide is heated enough to change state, the bonds that break are the .......................................... bonds that extend throughout the lattice. These are strong bonds so the melting and boiling points of these types of substances are ...........................................

5.3.4 Complete the following sentences to explain why ionic, covalent molecular and covalent network substances have different conducting abilities.

(a) Ionic substances cannot conduct when in the .......................................... state as their ions are ........................................... They can ..........................................

when molten or in solution as their ions are free to move.

(b) All covalent substances are poor conductors of electricity because they do not have .......................................... or free .......................................... .

5.3.5 Tabulate the differences between the melting and boiling points, hardness and electrical conductivity of ionic, covalent molecular and covalent network compounds.

Property Ionic Covalent molecular Covalent network


Very high

Hardness. Hard

Electrical conductivity when solid.

Electrical conductivity when dissolved in water.

Poor

Electrical conductivity when molten.

Good Poor

5.4 Perform an investigation to examine the physical properties of a range of common substances in order to classify them as metallic, ionic or covalent molecular or covalent network substances and relate their characteristics to their uses.

5.4.1

(a) Identify the substances you investigated to determine their types of bonds.

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(b) Identify physical properties that you measured or researched for each substance.

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5.4.2 Use the following descriptions of the properties of substances to classify those substances as ionic, metallic, covalent molecular or covalent network.

Description Classification

(a) Shiny, insoluble solid which is a good conductor of electricity when solid and when molten.

(b) Gas at room temperature, soluble in water, does not conduct electricity, low melting point.

(c) Very high melting and boiling points, non-conductor of electricity when solid and when molten.

(d) Low melting and boiling points, soluble in water, non-conductor.

(e) Good conductor of electricity when molten and in aqueous solution, but not when solid.

5.4.3 Classify each of the following substances as metallic, ionic, covalent molecular or covalent network. Then for each substance determine a use that relies on properties associated with its type of bonding.

Factor Copper Sodium chloride Nitrogen Silicon dioxide

Type of substance.

Use.

Property that allows for this use.

Reason for this property.

5.5.1 Use a labelled diagram to represent the structure of a metal.


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5.5.2 of the structure of metals to explain the properties of metals shown in the following table.

Physical property of metal Explanation in terms of structure

Good conductor of electricity. Outer shell electrons are delocalised (not held tightly to the metal ion) and thus mobile so they are free to carry charge.

Good conductor of heat.

High melting and boiling points.

Malleable and ductile.

Shiny lustre.

5.6.1 Sodium chloride is an ionic compound with the formula NaCl. What does this formula represent?

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

5.6.2 Complete the following:

Ionic compounds consist of a repeating .......................................... .......................................... of positively and .......................................... charged ........................................... These ions are held together by strong forces called .......................................... bonds which extend throughout the .......................................... . Ionic lattices form crystals which can be of any size.

5.7 Explain why the formula for an ionic compound is an empirical formula.

5.7.1

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(c) Identify each of the following as an empirical or a molecular formula:

(i) C6H12O6 .................................................................. (ii) CH2O .............................................................................

(iii) CH2 ........................................................................... (iv) C3H6 ...............................................................................


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5.7.2 Explain why NaCl is an empirical formula rather than a molecular formula.

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5.8 Identify common elements that exist as molecules or as covalent lattices.

5.8.1

(a) Identify three elements that exist as molecules.

...............................................................................................................................................................................................................................

(b) Identify one element that exists as a covalent network structure.

...............................................................................................................................................................................................................................

5.8.2

(a) What is meant by an allotrope?

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(b) Identify three allotropes of carbon.

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...............................................................................................................................................................................................................................

(c) Identify two other elements that also occur as allotropes.

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................


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5.9 Explain the relationship between the properties of conductivity and hardness and the structure of ionic, covalent molecular, and covalent network structures.

5.9.1 Complete the following table to identify the physical properties of ionic compounds that are determined by the structural features shown.

Structural feature of ionic compounds Physical property determined by structure

Strong ionic bonds throughout the crystal lattice. A lot of energy is needed to break these bonds.

High melting and boiling points.Hard. Crystalline.

Heating makes the ions vibrate. This breaks the bonds and the ions are then free to move and carry the current.

Water moves between the ions, pushing them apart and breaking the ionic bonds. The ions are then free to move and carry the electric charge.

Ions are held in fixed positions by strong ionic bonds that extend throughout the lattice. The ions can only vibrate, they are not free to move and carry the charge.

5.9.2 Compare the following physical properties of substances with metallic, ionic and covalent bonding.

Property Metallic Ionic Covalent molecular

Covalent network


High Low

Hardness. Hard


Good Poor


Insoluble Poor


Good

5.9.3 Complete the following table to summarise the relationship between the structure and properties of covalent molecular substances.

Properties Structure

Poor conductors of electricity in all states.

Hardness.


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5.9.4 Complete the following table to summarise the relationship between the structure and properties of covalent network substances.

Properties Structure

Poor conductors of electricity in all states.

Hardness.

5.10 Distinguish between metallic, ionic and covalent bonds.

5.10.1 Complete the following passages using the words listed below:

covalent, metals, sharing, metal ions, electrons, ionic, ions, V, VI and VII, molecular (covalent), dispersion, atoms, electrostatic, electrons.

(a) Metallic bonds occur in .......................................... where they hold the positive metal ions together. The metallic bond is caused by the random motion of the delocalised outer shell .......................................... of metal atoms and their attraction to the positive .......................................... .

(b) Ionic bonds occur in .......................................... compounds where they hold positively charged .......................................... .......................................... or polyatomic ion(s). Ionic bonds are caused by the ................................................................. attraction between oppositely charged ions.

(c) Covalent bonds occur in .......................................... compounds and in elements from Groups .......................................... of the Periodic Table. Covalent bonds occur in both small covalent molecules and large covalent networks. Covalent bonds are caused by atoms .......................................... of one or more pairs of .......................................... .

(d) Covalent molecular compounds have strong .......................................... bonds within the molecule (intramolecular bonds) holding the .......................................... together and weak forces between the molecules which are called .......................................... forces.


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5.10.2the types of bonds they contain.

Elements andcompounds.

A good conductor when solid?

Yes

It is a metal.

No No

A good conductorin aqueous solution?

No

It is covalent.

M.p. and B.p. high?

No

It is covalent molecular.

Yes

It is covalent network.

Yes

It is ionic.

(a) sodium ........................................................................................................................

(b) sodium chloride .....................................................................................................

(c) sulfur ............................................................................................................................

(d) hydrogen ....................................................................................................................

(e) dilute hydrochloric acid ....................................................................................

Note:all ionic substances are soluble in water, and this is not correct. Also graphite (carbon) would


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5.11 Choose resources and process information from secondary sources to construct and discuss the limitations of models of ionic lattices, covalent molecules and covalent and metallic lattices.

5.11.1

(a) Models can take many forms. Suggest some forms in which models can occur.

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

(b) The following diagram represents a model of a metal as a lattice structure. Discuss advantages and limitations of this model.

e– e– e–

e–

e–e–

e–

e–

e–

e–

e–

e–

e–

e–e–

e–

e–

e–

e–

e–

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5.11.2 The following diagrams represent two models of an ionic substance as an ionic lattice. Discuss advantages and limitations of these two models.

(a) Na+ Cl–

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...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

(b)

Cl–

Cl–

Cl–

Cl– Cl–

Cl–

Cl–

Na+Na+

Na+

Na+

Na+

Na+

Na+

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

5.11.3

usefulness of these models.

Ammonia

H

N

H H

Hydrogen

sulfide

S

HH H

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

...............................................................................................................................................................................................................................

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Dot Point Preliminary Chemistry 169 Answers

DOT POINTAnswers

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Answers 170 Dot Point Preliminary Chemistry


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The Chemical Earth

1.1.1 All matter is made of tiny particles which are continually moving.

1.1.2 (a) An element is a pure substance containing only one type of particle, e.g. atoms of copper, molecules of hydrogen.

(b) A compound consists of two or more different types of particles, chemically combined, with the ratio of these particles always the same.

(c) A mixture contains two or more types of particles in any proportion. It is not a pure substance. The components of a mixture keep their own properties and can be separated by physical methods.

1.1.3 (a) element (b) compound (c) mixture (of element and compound) (d) mixture (of two compounds) (e) element (f) mixture (of two elements)

1.2.1 Zone Mixture present Components of mixture

Biosphere Wood Mixture of compounds such as water, carbohydrates, oils.

Lithosphere Copper carbonate ore Mixture of copper carbonate and other mineral compounds that we cannot use (called gangue).

Hydrosphere Salt water Mixture of compounds, e.g. water and salts such as sodium chloride.

Atmosphere Air Mixture of elements such as nitrogen, oxygen, argon as well as the compounds water vapour and carbon dioxide.

1.3.1(a) Filtration (b) Sedimentation and decanting (c) Evaporation and crystallisation

Filter funnel

Retortstand

Filter ring

Filter papercontains residueleft behind

Beaker

Filtrate

Liquid beingpoured off

Solid staysin container

Evaporating basin

Gauze

Bunsen burner

(d) Fractional distillation of a mixture of liquids

(e) Sieving (f) Using a separating funnel to separate liquids

Large particlesstay in sieve

Small particlesfall through sieve

Less denseliquid

More denseliquid

Separatingfunnel

Mixture

Condenser

Bunsen

Distillate

Thermometer

Fractionatingcolumn

FlaskHot water

bath

Cool water in

Water out

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1.3.2 Various, e.g.

Type of mixture Example Suitable process to separate components

Solids of different sizes. A mixture of partly crushed rock particles and silt.

Sieving – particles smaller than the hole in the sieve pass through, large particles stay in the sieve.

A liquid and a solid that will not dissolve in that liquid.

Sand and salt water. Filtering separates the sand from the salty water.

A solid dissolved in a liquid. Salt water. Distillation or evaporation and crystallisation.

Miscible liquids with different boiling points. Petroleum. Fractional distillation.

Immiscible liquids with different densities. Oil and water. Separating funnel.

Gases. Nitrogen and oxygen from air. Fractional distillation.

1.3.3 (a) Approximately 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide.

1.4.1 Various, e.g. sand and salt.

1.4.2 Various, e.g.

Place the mixture in a beaker. Add 100 mL water. Using a stirring rod, stir until all of the salt dissolves in the water. Set up the

Filter funnel

Retortstand

Filter ring

Filter paper contains mixture – residue left behind

Beaker

Filtrate

heating it in an evaporating dish (see diagram).

Evaporating basin

Gauze

Bunsen burner

1.5.1

1.5.2

be washed with lots of fresh water.

The salt crystals could then be recrystallised by evaporating the water.


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1.5.3Components of mixture Process used to separate components Property that makes this use possible

Oil and water. Fractional distillation or Using a separating funnel.

Water has a higher boiling point than oil or Oil is less dense than water.

Solid wastes from sewage. Filtration. Solid wastes are insoluble in water.

Sand and gravel. Sieving. Gravel particles are larger in size than sand.

Nitrogen and oxygen from air. Fractional distillation. Different boiling points, i.e. oxygen –183°C, nitrogen –196°C.

1.6.1 Weigh a sample of mercury oxide. Heat the mercury oxide to make it decompose, making sure that no mercury is lost. Collect the mercury produced and weigh it. Calculate the percentage of the original sample that was mercury (mass of mercury/mass of mercury oxide × 100).

1.6.2 Various, e.g. analysing the percentage of a mineral in rock, alcohol content of wine, water of crystallisation in a compound, fat in food.

1.6.3 (a) Gravimetric analysis. Weigh a sample of the oats. Separate out the components, e.g. carbohydrate, protein. Weigh the amount of each component in the sample being analysed. Calculate the amount present in 100 g of the food.

allows people to avoid those foods that contain a substance to which they are allergic.

1.7.1 (a) Various, e.g. a mixture of sand and salt or copper ore and rock.

(b) Various. If your teacher can tell you the actual composition of your original mixture you can calculate the percentage accuracy of the procedure you used. You should make a statement about how accurate this procedure was and then discuss reasons for any discrepancy between the actual values and those you obtained. You should be able to identify some ways you could have improved the accuracy of your method. Examples of the sorts of suggestions you could

(c) Various. In your answer you should discuss such things as:

1.7.2 (a) (i) the mass of the residue = 1.45 g

(ii) the mass of the solid salt in the evaporating dish = 3.25 g

(iii) the percentage composition of salt in the original mixture = 3.25/4.90 × 100 = 66.33%

(iv) the total mass of chemicals recovered after separation = 4.70 g

(b) The accuracy of the procedure used can be calculated as 4.70/4.90 × 100 = 95.92%.

Only 0.20 g (4.08%) of the original mixture has been lost which still means that the process was reasonably accurate.

Some salt may have been lost by spitting as the mixture was evaporating. This could be avoided by heating the mixture more gently and perhaps partly covering the top of the evaporating basin. Also, some sand may have been

ensure that all sand is transferred.

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1.8.1 Various, e.g.

Name of Industrial separation process researched Froth flotation

Components of mixture separated by this process. Metal compounds (minerals such as copper carbonate) and gangue (waste rock minerals).

Properties of components that allow them to be separated by this process.

Gangue minerals have different surface properties to metal minerals. Metal minerals cling to the bubbles and gangue minerals become wet and sink to the bottom of the frothy mixture.

Uses of components when they have been separated. Metal minerals are treated further to remove the wanted metal (e.g. copper) from the compound (e.g. copper carbonate).

Gangue minerals are sent to a tailings dam where they accumulate and are eventually disposed of safely, e.g. they may be used to fill an old mining shaft.

Some tailings still contain small percentages of the metal minerals and they may be further treated at a later date when technology improves.

Issues associated with any wastes produced during this process. The tailings may contain toxic substances (e.g. arsenic in tailings from gold mines or copper salts in tailings from copper mines). Therefore care must be taken that the tailings dam is lined to prevent seepage of chemicals from the dam into the water supply. The wastes must also be kept away from birds and native animals.

1.8.2 Check that the reference used is not a manufacturer of the product being researched as they could give a biased presentation. Choose a government or university based reference rather than a company as these are more likely to be impartial. Check the date when the reference was published or the website was updated, to ensure that the information is not outdated.


Various, e.g.

carbon dioxide.

boiling points.

can be mixed in any proportion.

2.1.1 (a) a compound

(b) an uncombined element

2.1.2 Magnesium is much more active than gold.

2.1.3 Most elements are chemically active so they occur as compounds combined with other elements. The less reactive an element is, the more likely it will occur as uncombined element. For example, the inert gases (Group VIII) and unreactive metals, such as silver and gold, occur as elements.

2.2.1 Physical properties are those that can be found by studying the substance itself rather than its reactions, e.g. hardness, conductivity, malleability, density. Chemical properties describe how a substance reacts, e.g. whether it reacts with water, oxygen or acids and if it decomposes when heated.

2.2.2 (a) physical

(b) physical

(c) physical

(d) chemical

(e) chemical

(f) physical


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2.2.3Physical property Metals Non-metals

Melting and boiling points. High. Low.

Conductivity of heat. Good conductors. Poor conductors.

Conductivity of electricity. Good conductors. Poor conductors (except graphite).

Malleability (able to be bent and hammered into shapes).

Malleable. Not malleable (brittle).

Ductility (able to be stretched into wires). Ductile. Not ductile.

Lustre. Shiny lustre. No lustre – usually powders or gases at room temperature.

2.2.4 Various, e.g. silicon and germanium, high, poorer.

2.3.1 (a) Various, e.g. magnesium, sulfur, iron.

(b) Various, e.g. Magnesium is a shiny silver solid at room temperature, it is malleable, hard and is a good conductor of both heat and electricity. It has a melting point of 650ºC and a boiling point of 1110ºC.

classify magnesium as a metal you would need to show that it is a shiny solid, is malleable, has high melting and boiling points, good conductivity of electricity.

(c)

Substance being tested

ElectrodesContainer

A

Each element to be tested was placed in the container, one at a time. The ends of the element were touched with the

current, the better the ability of the element to conduct electricity.

2.3.2 It has the characteristics of a metal – shiny lustre, high melting and boiling point, a good conductor of heat and electricity and it is malleable.

2.4.1 (a) metal

2.4.2 Metals – A and D.

2.4.3

2.4.4 (a) carbon

(b) mercury

(c) neon or argon

(d) bromine

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2.5.1

Per

iod

7654321

II III IV V VI VII VIII

Non-metals

Semi-metals

Metals

Group I

2.5.2

Solids Liquids

Po

ArFOCB NClSSiAl

KrSe

XeI

BiPbTl

AsGe

Sb Te

Ga

Sn

Hg

Zn

In

AuPt

CuNi

Ag Cd

Ir

Co

PdRh

OsReW

FeMn

Tc Ru

Cr

Mo

Ta

Db

V

Nb

HfLa

Ac Ru

BaCs

Fr Ra

TiSc

Y Zr

CaK

Rb Sr

BeLi

Na Mg

He

Ne

P

H

RnAt

Gases

RnRRRRn

K

XeXXX

K

rANAANA

K

AAAN

ee

r

er

r

e

r

r

H

Ne

H

N

HHe

ee

eee

N O FN ONN ON OOO FO F

CCCCll

HHHH

HgHgHggHgHgHHgH

Br

2.5.3

2.5.4Metals Non-metals

Potassium K Phosphorus P

Copper Cu Carbon C

Calcium Ca Argon Ar

Sodium Na Hydrogen H

Aluminium Al Sulfur S

Mercury Hg Iodine I

2.6.1 Various, e.g.

Element Use Properties

Gold Jewellery. Shiny lustre; Malleable.

Carbon Jewellery (diamonds are carbon) or Drawing (graphite in ‘lead’ pencils is carbon).

Good reflector and refractor of light; hard and durable. Makes marks on paper.

Aluminium Window frames. Lightweight; malleable.

Helium Filling balloons. Low density – floats in air.

Iron Making steel for buildings. High strength.


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2.6.2 Name of element Properties Use

Selenium Conductor of electricity in the light, non-conductor in the dark.

Light sensitive switches.

Carbon (diamond) Durable, clear, shiny solid. Jewellery.

Helium Gas which is inert and has a very low density. Filling balloons.

Iron Strong, solid, malleable metal. Building construction.

Aluminium Durable metal, very malleable, can be rolled into thin sheets, insoluble in water.

Wrapping food.

Neon Unreactive gas which emits red light when electricity is passed through.

Advertising signs.


(a) Lead is soft and dull in appearance.

(b) Carbon in the form of graphite is a good conductor. Carbon in the form of diamond is a hard and strong solid at room temperature and has a high melting point (3547°C).

(c) Iodine is a shiny solid at room temperature.

3.1.1 Atoms, ions, molecules.

3.1.2

3.1.3 Property Solid Liquid Gas

Arrangement of particles Particles are close together and vibrating in fixed positions.

Particles are close together and moving more freely.

Particles are far apart and moving very freely.

Diagram

Shape Definite shape. Takes the shape of the container. Depends on container.

Volume Definite volume. Definite volume. Fills all available space.

Ability to be compressed Cannot be compressed. Cannot be compressed. Can be compressed.

Ability to diffuse Cannot diffuse. Can diffuse. Can diffuse.

Kinetic energy of particles Least. More than solids, less than liquids.

Greatest kinetic energy.

3.2.1 The smallest unit of an element that can take part in a chemical reaction.

3.2.2 Particle Where found Symbol Relative charge Relative mass

Proton Nucleus of atom p+ +1 1

Neutron Nucleus of atom n 0 1

Electron Orbit the nucleus of atom e– –1 1/1835

3.2.3 Mass number of an element is the number of protons plus the number of neutrons in the nucleus of its atom.

Atomic number of an element is the number of protons in the nucleus of its atom. (Note:electrons in the atom.)

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3.2.4Name of element Atomic number Mass number Number of protons Number of neutrons Number of electrons

Hydrogen 1 1 1 0 1

Beryllium 4 9 4 5 4

Neon 10 20 10 10 10

Aluminium 13 27 13 14 13

Mercury 80 201 80 121 80

3.2.5Atomic number Name of element Symbol

5 Boron B

7 Nitrogen N

19 Potassium K

92 Uranium U

3.2.6 A and C (same number of protons).

3.3.1Energy level Maximum number of electrons

K (1st level – closest to nucleus) 2

L – 2nd level 8

M – 3rd level 18

N – 4th level 32

3.3.2 N

3.3.3 (a)

3p+

4ne–

e–e–

Lithium atom

(b)

20p+

20ne–e–e–

e–e–e–

e–e–e–e–

e–e–

e–e–

e–e–

e–e–

e–e–

Calcium atom

3.4.1 A charged particle formed when an atom gains or loses one or more outer shell electrons.

3.4.2 Name of atom Gains or loses electron(s) Number of electrons gained or lost Symbol of ion formed

Sodium loses 1 Na+

Chlorine gains 1 Cl–

Magnesium loses 2 Mg2+

Oxygen gains 2 O2–

Neon neither 0 No ion formed

Aluminium loses 3 Al3+

3.4.3 (a) lose ... positive

(b) gain ... negative


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3.5.1 (a) K+

(b) Ca2+

(c) Br–

(d) Ag+

(e) H+

(f) Pb2+

3.5.2Group of Periodic Table Electrons lost or gained Charge on ion formed

I 1 lost +1

II 2 lost +2

III 3 lost +3

VI 2 gained –2

VII 1 gained –1

3.5.3Ion Symbol Valency

Sulfate ion SO2–

4 2

Nitrate ion NO3

–1

Carbonate ion CO2–

3 2

Phosphate ion PO3–

4 3

Hydroxide ion OH–

1

Ammonium ion NH+

4 1

3.6.1 + + e–

2+ + 2e–

(c) Cl + e– –

3.7.1 (a) sodium ions

sodium

ionsodiumatom

Na _ Na+e–

(b) chlorine ions

chloride ionchlorine atom

ClCl

_

+ e–

3.7.2 (a)

chlorine (Cl2)

Cl ClClCl or

Shared pair of electrons

(b)

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water (H2O)

orO O

H

H

H

H

Shared pairs of electrons

3.7.3 (a) compounds, electrons, valency, stable

(b) Name Symbol Valency Name Symbol Valency

Strontium Sr 2 Nitrogen N 3

Copper Cu 1 or 2 Carbon C 4

Calcium Ca 3 Bromine Br 1

Nickel Ni 2 Iodine I 1

Magnesium Mg 2 Zinc Zn 2

Iron Fe 2 or 3 Mercury Hg 2

(c) A number, not positive or negative. Valency is the combining power, the tendency to lose, gain or share one or more electrons. A valency of 1 means that atoms of that element will gain, lose or share 1 electron from the outer shell. Ions are positive (if the atom loses electrons) or negative (if the atom gains electrons), not valency.

3.8.1 A compound formed by the electrostatic attraction (ionic bonds) between two or more ions, e.g. sodium chloride, magnesium oxide and sodium hydroxide.

3.8.2 Chloride ions. Magnesium ions are positive (metals lose electrons forming positive ions). Ions are attracted to other ions with the opposite charge. Chloride ions are the only ions in the list that are negative.

3.8.3 Ionic bond – an electrostatic force.

3.9.1 The smallest particles of an element or molecular compound which can move independently of each other.

3.9.2 An atom of hydrogen is the smallest unit of hydrogen that can take part in a chemical reaction. However, one atom of hydrogen cannot exist and move independently. The smallest particle that can do this is a molecule of hydrogen – which consists of two atoms.

3.10.1 Various, e.g.

(a) helium, argon, neon

(b) hydrogen, oxygen, nitrogen

(c) diatomic

(d) water, ammonia, carbon dioxide, methane, hydrogen chloride

3.10.2 (a) H

(b) H2

(c) Cl

(d) Cl2

(e) Ne

(f) CO2

(g) H2O

3.11.1 HCl(g) is hydrogen chloride gas. Atoms of hydrogen share an electron with atoms of chlorine to form this covalent molecular compound.

covalent molecular compound.

this process, hydrogen and chloride ions are formed, so the compound is ionic.


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3.11.2 (a) water (b) methane

H H

O

C H H

H

H

(c) oxygen (d) ammonia

O O N

H H H

3.12.1 (a) KCl (b) NaNO3

(c) MgCO3 (d) Li3PO4

(e) Al2(SO4)3 (f) Fe(OH)2

3.12.2 (a) NH3 (b) N2O

(c) SO2 (d) SO3

(e) N2O4 (f) SiO2

3.13.1 (a) Left, electron(s), positive, conductors, delocalised, bond, metallic, strong

(b)

e– e– e–e–

e–e–

e–

e–

e–

e–

e–

e–

e–

Positivemetal ions

e–e–

e–

e–

e–

e–

e–

Delocalisedelectrons

3.13.2 (a) aluminium, (c) copper, (e) sodium

3.13.3 (a) ions, electrostatic, temperature, lattice, ions, ionic

(b)

Cl– Cl– Na+

Cl– Cl– Na+

Cl– Cl– Na+

Cl– Na+ Na+

Cl– Na+ Na+

Cl– Na+ Na+

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3.13.4 (a) covalent, sharing, Groups, Table, molecules, giant covalent lattices, strong, bonds, forces

(b)

H

H

C H H

Weakintermolecular

dispersionforces

H

H

C H H

H

H

C H H

Strong intramolecularcovalent bonds

(c)

O

Si Si Si

Si Si

Si

Si

Si

Si

Si

Si

Si

Si O

O

O O

O O

O

O

O

O

O

O

O

O

O

O

O O

O

O

O

O

O

O

O

Strong covalent bondsextend throughout the lattice

3.13.5 (a), (b) and (c): Various – you may have used commercial sets or substances such as plasticine and matchsticks.

Describe what you used and what each substance or structure represents. It is a good idea to include diagrams in answers to

4.1.1 Physical – a, c, f, g. Chemical – b, d, e.

4.1.2 Permanent colour change, gas produced, precipitate (solid) formed, solid disappears, heat produced.

4.1.3 (a) A chemical change as new particles are produced by the rearrangement of atoms.

(b) A physical change as no new particles are produced.

4.1.4 Physical change Chemical change

New substance No new substance is formed. A new substance is formed.

Particles Particles are the same (although they may move differently).

New particles are formed (atoms have been rearranged).

Reversal Easy to reverse by physical methods. Usually difficult to reverse.

Energy Small energy changes usually involved. Energy changes are usually large.

4.2.1 (a) Molecules of H2O each consisting of atoms of hydrogen and oxygen combined in the ratio 2:1.

bubbles coming out of solution.

(c) H2O molecules gain energy and move faster. They do not break up as they are held together by strong covalent bonds.

(d) H2O molecules then have enough energy to leave the surface of the water – we say the water is changing state – from

(e) No. Heat cannot break up a water molecule. It can only give them more energy so they move fast enough to break the weak intermolecular forces and pull away from each other.


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4.2.2Cold water

Water particles moving more slowly

Bunsen burner

Boiling water

Water particles moving rapidly

Bunsen burner

Water particles escaping(changing state)

4.2.3 Boiling is a physical change because no new substance is produced. The only change is to the movement of the particles, the particles themselves do not change, they remain water (H2O) particles.

Electrolysis is a chemical change because new substances are produced – hydrogen and oxygen. The particles of oxygen and hydrogen differ from the original water particles.

4.3.1

(a)

Water

Tap to release gas

O2 gas

+ -

e–

Inert cathodeInert anode

Reservoir

H2 gas

(b)Water molecules before electrolysis

HO

H HO

H

Molecules present after electrolysis of water

HO

H H HO

2H2 2(g) + O2(g)

(d) To produce hydrogen and oxygen (from water) for use in fuel cells.

(e) Hydrogen – Place a lighted taper in the gas – if it pops, the gas is hydrogen.

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4.4.1 Boiling of water Electrolysis of water

Changes in water. Water changes state from liquid to gas (two different forms of water – liquid water and water vapour).

Water decomposes to form two new substances – hydrogen gas and oxygen gas.

Changes in particles. Particles stay the same but move faster and become further apart.

Particles have changed. Water particles (H2O) have disappeared and new particles (H2 and O2) have appeared.

Reversal of process. Easy to reverse – cool water vapour and it changes back to a liquid.

Reversal is not as easy. To convert hydrogen and oxygen back to water a chemical reaction is needed – you have to burn the hydrogen in the presence of oxygen.

Physical or chemical change. Physical. Chemical.

4.4.2

H2 2O(l)

2H2(g) + O2 2O(l)

4.5.1 (a) Silver chloride changes from white to purple and then black.

Deposit of silver metal is formed.

The mass of the silver chloride decreases.

(b) Decomposition

2(g)

4.5.2silver deposit in the shape of the image on the negative.

4.6.1 (a) Various, e.g.

Test tube

Bunsen

Green coppercarbonate

decomposing

Tubing

Test tube

Limewater(calciumhydroxidesolution)

CuCO3 2(g)

(c) CuO – I added dilute sulfuric acid to the black powder. A blue colour was produced indicating the presence of copper ions.

CO2 – the gas produced was bubbled through limewater (calcium hydroxide solution) and the limewater turned milky.

CO2(g) + Ca(OH)2 3(s) + H2O(l)

(d) To identify and address any potential hazards so we do not cause damage to the environment or to people.


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(e) Various, e.g. the risk of the test tube breaking while being heated and hot chemicals entering and burning the eye. To prevent this, wear goggles and point the test tube away from all people.

When heating is complete or the production of carbon dioxide gas slows down the cold limewater could be drawn back into the hot test tube causing it to crack and releasing the hot chemicals. This could damage the bench and/or burn students.

To prevent this, the tube must be removed from the limewater as soon as heating is complete and the production of carbon dioxide gas slows down.

4.7.1 (a) Decomposition is a chemical reaction in which a compound is broken down into simpler substances.

Example Method used Energy used or released

Production of metals from their ores, e.g. copper from copper carbonate.

Heat in a furnace. Heat energy used to decompose the copper carbonate.

Production of aluminium from aluminium oxide in bauxite.

Pass electricity through molten aluminium oxide.

Electrical energy used.

Development of film. Action of sunlight on silver bromide (on the film).

Solar energy used to decompose the silver bromide.

(b) Synthesis is a chemical reaction in which simple substances combine to form a more complex substance.

Example How it occurs Energy used or released

The rusting of iron. Iron reacts with oxygen in air, in the presence of water to form a hydrated form of iron(III) oxide.

Energy released in the form of heat.

Photosynthesis. Carbon dioxide and water combine to form glucose and oxygen.

Solar energy is used.

Formation of nitrogen oxides in the atmosphere.

Lightning causes atmospheric nitrogen to combine with oxygen to form nitrogen monoxide.

Electrical energy is used.

Burning of coal or coke to produce electricity or to make steel.

Coal is heated in industrial furnaces forming carbon dioxide.

Energy is used to start the reaction and then energy is released.

4.7.2 Various, e.g.

2Al2O3 2(g)

N2(g) + O2

4.7.3 Synthesis – a,b,e

Decompositiom – c,d,f

4.8.1 Potassium is more active than mercury so it forms stronger bonds with oxygen than mercury. Therefore more heat energy is needed to break the bond between potassium and oxygen than between mercury and oxygen.

4.8.2 (a) Potassium and sodium.

(b) Chlorides and oxides.

(c) (i) Calcium oxide and carbon dioxide.

(ii) Silver and chlorine.

(iii) None – aluminium oxide is stable to heat.

(d) Electric current provides more energy than heating. These substances are stable compounds, a great deal of energy holds their atoms together in the compound. Thus a lot of energy is needed to pull them apart.

5.1.1 Physical properties: (c) boiling point, (d) colour, (f) density, (h) conductivity, (i) melting point, (j) hardness.

Chemical properties: (a) ability to burn, (b) ability to react with water, (e) high reactivity, (g) unreactive or inert.

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5.1.2 (a) Physical properties:

Element Melting point (°C) Boiling point (°C) Density (g/mL at 20°C)

Calcium 838 1440 1.55

Mercury –38 357 13.6

Nitrogen –210 –196


Element Reactivity with water Ability to burn

Hydrogen No reaction Burns explosively

Silver Does not react Does not burn

Magnesium Reacts slowly with steam Burns with a white light

5.1.3 Elements and compounds are pure substances. This means that they always have the same composition so their properties stay the same, e.g. the element magnesium is always made of magnesium atoms only. The compound magnesium oxide (MgO) is always made of magnesium atoms and oxygen atoms, chemically combined in the ratio 1:1.

Mixtures are not pure substances. This means that mixtures do not always have the same composition. Their components (parts) and the proportion of each can vary, so their properties can vary.

5.1.4 (a) Physical properties:

Compound Melting point (°C) Boiling point (°C) Density (g/mL at 20°C)

Calcium iodide 575 718 4.0

Mercury(I) chloride 302 384 7.2

Nitric acid –47 86 1.5


Compound Reactivity with water Decomposition

Copper sulfate No reaction, dissolves Decomposes to form copper oxide and sulfur trioxide.

Silver chloride No reaction Stable to heat – does not decompose.Will decompose with light.

Magnesium carbonate No reaction Decomposes to form magnesium oxide and carbon dioxide.

5.2.1 Various, e.g.

(a) magnesium oxide

(b) magnesium:oxygen = 1:1

(c) Physical – melting and boiling points, colour, malleability.

Chemical – effect of heat, reaction with water.

(d) We observed colour, malleability and reaction with water individually and then compared our observations. All agreed, so the observations were accurate.

We compared our observations with those in textbooks, and they agreed with ours, indicating that our results are reliable.

temperature. Thus we had to rely solely on results published in data books and on the Internet. Our data book was


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5.2.2 (a) When the element magnesium burns, it combines with the element oxygen to form the compound magnesium oxide.

Magnesium is a metal (shiny lustre, silver, high melting and boiling point).

Magnesium oxide is a NEW substance, so it has its own properties – they are not the same as those of magnesium or oxygen. Magnesium oxide is a white powder.

(b) When sodium and chlorine combine to form sodium chloride, a new substance (sodium chloride), with different properties, is formed. Compounds have different properties to those of the elements used to make them. Sodium chloride is soluble in water (it does not react explosively) and it is composed of white crystals which are not poisonous.

5.2.3

Chemical properties Physical properties

Water Puts out fires. Good solvent.

Colourless liquid, boils at 100°C

Hydrogen Burns explosively in air. Colourless gas, boils at –253°C

Oxygen Combines chemically with substances when they burn.

Colourless gas, boils at –183°C

5.3.1 (a) sodium chloride ionic

(b) silicon dioxide covalent network

(c) ammonia covalent molecular

(d) carbon dioxide covalent molecular

(e) carbon tetrachloride covalent molecular

5.3.2 Melting and boiling points, electrical conductivity and hardness.

5.3.3 (a) ionic, strong, high

(b) intermolecular, dispersion, low

(c) covalent, high

5.3.4 (a) solid, lattice, conduct

(b) ions, electrons

5.3.5Property Ionic Covalent molecular Covalent network

Melting and boiling points. Very high Low Extremely high

Hardness. Hard Soft Hard

Electrical conductivity when solid. Poor Poor Poor


Good Poor Poor


Good Poor Poor

5.4.1 Various, e.g.

(a) Magnesium, oxygen, water, carbon dioxide, sodium chloride, sodium hydroxide, silicon dioxide.

(b) Melting and boiling points, conductivity, lustre, state.

5.4.2 (a) metal, (b) covalent molecular, (c) covalent network, (d) covalent molecular, (e) ionic

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5.4.3 Various, e.g.

Factor Copper Sodium chloride Nitrogen Silicon dioxide

Type of substance. Metal. Ionic compound. Covalent molecular element.

Covalent network compound.

Use. Electric wires. Cooking – to flavour food. Snap-freeze vegetables. Making glass insulators.

Property that allows for this use.

Good conductor of electricity.

Soluble in water. Very low boiling point. Poor conductor of electricity.

Reason for this property. Mobile delocalised electrons.

Ions present form bonds with water.

Weak attractive forces between molecules.

No mobile electrons and no ions present.

5.5.1

e– e– e–e–

e–e–

e–

e–

e–

e–

e–

e–

e–

e–e–

Positivemetal ions

Delocalisedelectrons

e–

e–

e–

e–

e–

5.5.2

Physical property of metal Explanation in terms of structure

Good conductor of electricity. Outer shell electrons are delocalised (not held in place in the atom) and thus they are mobile and free to carry charge.

Good conductor of heat. The mobile, delocalised outer shell electrons can carry heat.

High melting and boiling points. Strong metallic bonds between the positive metal ions and the sea of negatively charged delocalised electrons. A lot of energy is needed to break these metallic bonds.

Malleable and ductile. The rows of metallic ions in the lattice can slide over each other without coming apart or disrupting the bonds.

Shiny lustre. The sea of delocalised electrons reflects light.

5.6.1

5.6.2 three, lattice, negatively, ions, ionic, lattice

5.7.1 (a) Molecular formula shows the number of atoms of the elements present in a molecule of a compound – the smallest amount that can exist independently as that compound. The atoms are bonded together by covalent bonds.

(b) Empirical formula shows the simplest, whole number ratio of atoms or ions present in a compound.

(c) (i) molecular

(ii) empirical

(iii) empirical

(iv) molecular

5.7.2dimensional lattice by electrostatic forces (ionic bonds). The formula tells us the ratio of ions present, it does not tell us the number of ions in a unit. There are no molecules in sodium chloride. Thus it is an empirical formula rather than a molecular formula.

5.8.1 Various, e.g.

(a) neon, oxygen, nitrogen

(b) carbon


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5.8.2 (a) Forms of the same element in which the atoms are identical but they are arranged differently and have different physical properties.

(b) Diamond, graphite, fullerenes.

(c) Tin, oxygen, sulfur.

5.9.1 Structural feature of ionic compounds Physical property determined by structure

Strong ionic bonds throughout the crystal lattice. A lot of energy is needed to break these bonds.

High melting and boiling points.Hard and crystalline.

Heating makes the ions vibrate. This breaks the bonds and the ions are then free to move and carry the current.

Good electrical conductors when molten.

Water moves between the ions, pushing them apart and breaking the ionic bonds. The ions are then free to move and carry the electric charge.

Good electrical conductors when in solution.

Ions are held in fixed positions by strong ionic bonds that extend throughout the lattice. The ions can only vibrate, they are not free to move and carry the charge.

Poor electrical conductors when solid.

5.9.2 Property Metallic Ionic Covalent molecular Covalent network

Melting and boiling points. High Very high Low Extremely high

Hardness. Hard Hard Soft Hard


Good Poor Poor Poor


Insoluble Good Poor Poor


Good Good Poor Poor

5.9.3 Properties Structure

Poor conductors of electricity in all states. No free electrons, no ions present.

Hardness. Weak dispersion forces between molecules result in low boiling points so usually gases at room temperature. Thus hardness does not apply.

5.9.4 Properties Structure

Poor conductors of electricity in all states. No free electrons, no ions present.

Hardness. Hard due to strong covalent bonds that extend throughout the lattice.

5.10.1 (a) metals, electrons, ions

(b) ionic, metal ions, electrostatic

(c) molecular (covalent), V, VI and VII, sharing, electrons

(d) covalent, atoms, dispersion

5.10.2 (a) metallic

(b) ionic

(c) covalent molecular

(d) covalent molecular

(e) ionic

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5.11.1

(b) This model is useful because it can account for:

outer shell electrons.

each other.

The model is limited because:

boiling points or hardness and the model does not explain this.

5.11.2 (a) This model does tell us that the substance consists of ions held closely together, but it suggests that ionic solids exist as small units. This is not correct. The formula only tells us the ratio of ions present in the crystal.

(b) This model is more useful as it accounts for the crystal structure and the shape of crystals according to how the ions are packed together. It also shows that there are many ions within a crystal.

5.11.3 These models do provide some information as to the structure of molecules. However, they can be misleading as they are

models.

The following diagram illustrates this with a model of ammonia.

H H

N

H

These 2 hydrogens are behind the plane of the paper

This hydrogen is in front of the plane

of the paper

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