Chemistry at a glance ( PDFDrive ).pdf

FROM THE AUTHORS Chemistry at a Glance has been written to cover the Chemistry content of GCSE Double Science Specifications and the core content of GCSE courses in Chemistry. It includes pages that summarise those sections of Key Stage Three Science fundamental to GCSE Chemistry. The purpose is t...

FROM THE AUTHORS Chemistry at a Glance has been written to cover the Chemistry content of GCSE Double Science Specifications and the core content of GCSE courses in Chemistry. It includes pages that summarise those sections of Key Stage Three Science fundamental to GCSE Chemistry. The purpose is to provide a text that sets out all the relevant GCSE material as easily identifiable topics. It is presented in a format designed to describe the facts and explain the concepts clearly and simply. The information on each page comprises discrete sections organised to contribute to comprehensive units of knowledge. Questions at the foot of each page reinforce the content of the topic and can be answered by reference to it. (Questions in italics require either application of that information, or reference to information elsewhere in the book, or further reading.) There are also Review Questions at the end of each section. This book can serve as a traditional text supporting the overall delivery of the Science curriculum, and is suitable for homework and revision. Its layout also allows easy access to this material for students who are supplementing their homework with independent study. The authors would like to acknowledge the advice of colleague Tad Newton and the assistance of Mark Owen. Roger Owen and Sue King The publishers would like to acknowledge the following: Cover picture shows large crystals of gypsum (CaSO4.2H2O) replacing anhydrite (CaSO4) - a hydration reaction. The sediment is a chemical precipitate (an evaporite) which has been modified since deposition. This picture is reproduced courtesy of Professor W. S. MacKenzie (formerly Emeritus Professor of Petrology, University of Manchester). Page 26, photographs of Robert Boyle, John Dalton, Dimitri Mendeleev, John Newlands, and Johan Dobereiner are reproduced courtesy of the Library and Information Centre, Royal Society of Chemistry. The photograph of Henry Moseley is reproduced courtesy of the Library and Information Centre, Royal Society of Chemistry. Reprinted from ‘Torchbearers of Chemistry’, M. M. Smith, Academic Press, 1949. Photographs of Joseph Thomson, Ernest Rutherford, Niels Bohr, James Chadwick, and Glenn Seaborg are reproduced courtesy of The Nobel Foundation, Stockholm, Sweden. Page 61, the photographs of granite, sandstone, limestone, and gneiss, and page 88, the photograph of the neon sign are reproduced courtesy of Mark Steven Owen. Page 72, the photograph of Sydney Harbour Bridge is reproduced courtesy of Susan Farley. C H E M I S T RY at a Glance Roger Owen Sue King Senior Science Teachers Akeley Wood School, Buckingham, UK Illustrations by Cathy Martin MANSON PUBLISHING CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2005 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Version Date: 20150115 International Standard Book Number-13: 978-1-84076-544-1 (eBook - PDF) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. 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Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com CONTENTS CLASSIFYING MATERIALS CHANGING MATERIALS Solids, Liquids and Gases 5 Changes 41 State of matter 5 Physical changes 41 Changes of state 6 Chemical changes 42 Particle theory 7 Oil and Hydrocarbons 43 Using particles to explain behaviour 8 Fossil fuels 43 Elements 9 Problems of fossil fuels 44 Metals or non-metals 9 Fractional distillation 45 Classifying elements 10 Crude oil 46 Atoms and atomic symbols 11 Alkanes 47 Organising the elements 12 Alkenes and cracking 48 Compounds 13 Reactions of alkanes and alkenes 49 Compounds 13 Polymers and polymerisation 50 Combination reactions 14 Metal Ores and Rocks 51 Naming chemical compounds 15 Using rocks 51 Chemical formulae 16 Reduction and methods of extraction 52 Chemical equations 17 Extracting iron 53 Mixtures 18 Extracting aluminium 54 Air 18 Uses of iron and aluminium 55 Further examples of mixtures 19 Extracting and using copper 56 Mixing and separating 20 Review Questions Changing materials I 57 Separation processes 21 The Atmosphere 58 Review Questions Classifying materials I 22 Current composition of the atmosphere 58 Atomic structure 23 Evolution of the atmosphere 59 Protons, neutrons and electrons 23 The carbon cycle 60 Atomic number and mass number 23 The Earth 61 Electron arrangements 24 Types of rock 61 Isotopes 25 The rock cycle 62 Periodic Table I 26 Weathering 63 Development of ideas 26 Evidence from sedimentary rocks 64 The first 20 elements 27 Evidence from rock layers 65 Patterns of electron arrangements 28 Evidence from igneous and metamorphic rocks 66 Plate tectonics 67 Ions and bonding 29 Limestone 68 Outer electrons 29 Review Questions Changing materials II 69 Ions I 30 Ions II 31 PATTERNS OF BEHAVIOUR Ionic bonds 32 Metals 70 Formulae and Equations I 33 Reactions with oxygen I 70 Writing formulae 33 Reactions with oxygen II 71 Covalent Bonds 34 Reactions with oxygen III Rusting 72 Covalent bonds 34 Reactions with acids 73 Structure and Properties 35 Reactions with water 74 Giant ionic structures 35 Reactions with oxides 75 Giant covalent structures 36 Oxidation and reduction 75 Simple molecular structures 37 Reactivity series 76 Conducting electricity 38 Displacement reactions 77 Ions and electrolysis 39 Review Questions Classifying materials II 40 3  Acids, Bases and Salts 78 Calculations 105 Indicators and pH 78 Formula mass and percentage composition 105 Neutralisation I – acids and alkalis 79 Reacting masses and the mole 106 Neutralisation II – acids and insoluble bases 80 Using moles 107 Acids and carbonates 81 Rates of Reaction 108 Acids and metals 82 Slow and fast reactions 108 Applications of neutralisation 83 Measuring rates 108 Acids in the environment 83 The effect of temperature 109 Review Questions Patterns of behviour I 84 The effect of concentration and pressure 110 Formulae and Equations II 85 The effect of surface area 111 Symbol equations I 85 The effect of a catalyst 112 Symbol equations II 86 Collision theory 113 Periodic Table II 87 Enzymes 114 Group trends in groups 1 and 7 87 Fermentation 114 Group trends in group 0 88 Temperature, pH and enzyme action 115 Explaining group trends 89 Uses of enzymes and biotechnology 116 Period trends 90 Reversible Reactions 117 Noble gases 91 Examples of reversible reactions 117 Noble gases 91 The Haber Process 118 Alkali Metals 92 Uses of ammonia and nitric acid 119 Reactions with water 92 Energy Changes 120 Alkalis and neutralisation 93 Energy changes 120 Reactions with non-metals 94 Review Questions Patterns of behaviour III 121 Sodium chloride 95 Halogens 96 DEFINITIONS AND FORMULAE 122 The halogens 96 Reactions of halogens 97 APPENDIX I Uses of halogens and their compounds 98 The periodic table 124 Transition Metals 99 APPENDIX II Transition metals 99 Materials and their uses 125 Review Questions Patterns of behaviour II 100 Reactions 101 APPENDIX III Types of reaction 101 Chemical data 126 Displacement and neutralisation 102 Redox reactions and ionic equations 103 SAFETY IN THE LABORATORY 127 Precipitation reactions 104 INDEX 128 4 CLASSIFYING MATERIALS KS3 SOLIDS, LIQUIDS AND GASES States of matter Substances may be classified as solids or liquids or gases. Chemistry involves studying substances like water, The universe is believed to be steel, plastic, oxygen, and salt. made up of energy and matter. Substances may be sorted into types by looking for Light, sound, and heat are similarities and differences. examples of energy. Substances like Solid, liquid and gas are the three states of matter. rocks, air, and water – which can be touched or felt – are all examples of matter. Carbon dioxide Salt Petrol Oil SOLID LIQUID GAS Iron Chalk Water Oxygen Nitrogen The different states have different properties. Density measures how much substance SOLID Has a fixed shape. fits into a certain volume (how many Has surfaces all round. grams per cm3). Generally, gases are least dense and solids are most dense, although some solids float on water. LIQUID Changes shape to fit its container. Has one upper surface. Gas bubble floating Liquid Solid sinking GAS Spreads and changes shape to fill its container. Has no real surface. Oil, least dense In science all materials should be handled safely. Water Particular care has to be taken with some substances. Hazard warning signs are used Mercury, h Harmful to identify particular problems. very dense Questions 1. What are the three states of matter? Hydrogen, less 2. Name two gases and two liquids. dense (‘lighter’) 3. Iron is a typical metal. What is the usual state of most metals? than air 4. Name a substance which is likely to spread out to fill its container. 5. Will water change shape if it is poured from a bottle into a glass? Carbon dioxide, 6. Gold, chlorine, helium, diamond, hydrogen, ice, alcohol, and more dense diesel is a list of substances made up of two liquids, three (‘heavier’) than air solids, and three gases. Sort them according to their state. 5  SOLIDS, LIQUIDS AND GASES Changes of state KS3 Many substances can be made to change state by heating or cooling. will freeze will evaporate WATER ICE VAPOUR WATER Solid Liquid Gas Water is one of the few substances which is commonly found in all three states. Most Substances metals are solid at room which are gases can be made temperature but will become liquid if heated. liquid if cooled. Gold above 1064°C Lead above 328°C Oxygen below –183°C Butane below –1°C Melting point is that temperature at which a solid Boiling point is that temperature at which a liquid begins to melt. In order to remain solid a substance begins to boil. In order to remain liquid a substance must be kept below its melting point. This is also must be kept above its melting point but below its the temperature at which liquids begin to boiling point. A gas will condense to liquid freeze or solidify. below its boiling point. Liquid iron has to be kept above 1535°C or it becomes a solid. Liquid air has to be kept below –196°C or it becomes a gas. Melting Evaporating heat heat SOLID LIQUID GAS cool cool Freezing Condensing DRY ICE Solid carbon dioxide has to be kept below –78°C Carbon otherwise it turns back dioxide into carbon dioxide gas. gas Solid carbon dioxide Questions 1. What is meant by ‘change of state’? 7. The melting point of mercury is –39°C and its 2. What causes substances to change state? boiling point is 357°C. What will be the normal 3. What happens to iron above 1535°C? state of mercury at room temperature (25°C)? 4. What happens to liquid air at room temperature? 8. What will happen to mercury if it is cooled by 5. What happens to a gas if it condenses? liquid oxygen? 6. Is it easier to melt iron or gold? 9. What is dry ice and why is it unusual? 6 SOLIDS, LIQUIDS AND GASES Particle theory KS3 Differences between solids, liquids and gases can be explained in terms of particles. wan Gases t to A solid is reluctant spread out to change its shape. Liquids in all will follow direction s the shape of their container All substances are made of small particles such as atoms or molecules. The properties of a substance depend on how strongly these particles are held in place. Gases, liquids and solids behave differently. The particles The particles Solids do not change shape are close cannot move readily because there are together in about but strong bonds or forces a regular can vibrate. between the particles which pattern. keep them in position. SOLID The particles The particles Liquids can change shape are close are free to move because the forces between together, but about beneath the particles are not strong there is no the surface of enough to stop them moving regular pattern. the liquid. around. LIQUID The particles The particles Gases spread out because the will spread are free to forces between the particles as far apart move in all are very weak and cannot as the space directions. keep them together. allows. GAS Changes of state occur when substances are heated or cooled. Heat gives the particles more energy to move and overcome the forces between them. A solid melts when the particles have enough energy to break free from their normal positions and move around. At boiling temperature the particles of a liquid have enough energy to completely break free from each other, and a gas is formed. Cooling removes energy from the particles so they slow down. Questions 1. What are atoms and molecules? 2. Why do solids have a fixed shape? 3. In which state are the forces between particles weakest? 4. In which state are particles close but free enough to move around? 5. Why are changes of state caused by heating or cooling? 6. Hydrogen is normally a gas but if it is used as a fuel it is carried as a liquid. Why is liquid hydrogen used? 7. How is hydrogen made liquid? 7  SOLIDS, LIQUIDS AND GASES Using particles to explain KS3 behaviour Particle theory explains the properties of substances in terms of particles. Individual particles like atoms and molecules are too small to be seen directly. Indirect evidence from the behaviour of substances is used to support this theory. DIFFUSION Observation The colour or smell of a gas will automatically spread throughout a container or a room. bromine Explanation liquid gas The molecules of the gas (and air) are moving in all directions. bromine DISSOLVING Observation water A coloured crystal will slowly dissolve and the colour will spread throughout the solution. solution of copper Explanation copper Molecules of water are free to move beneath the sulphate sulphate surface and they allow the crystal particles to crystal separate from each other. PRESSURE Observation A balloon filled with air stays inflated as long as the air cannot escape. gas molecules moving about Explanation Molecules of air in the balloon are constantly hitting the sides so that it remains inflated. Force (causes PRESSURE more pressure on gas) Observation If pressure is applied to a gas it will be compressed to a smaller volume. gas occupies Explanation smaller volume There is a lot of space between the gas molecules at higher pressure and pressure can force them closer together. The behaviour of solids, liquids, and gases can Questions 1. Why are atoms and molecules not observed directly? be described and explained in terms of particles, 2. Why is it possible for a gas to spread throughout a No one has seen the atoms of a gas such as helium room? What name is given to this process? or separate molecules of a liquid like water. 3. When a salt crystal dissolves, why does the taste A single atom of helium is so small that spread to all parts of the water? 10,000,000 atoms would fit across 1 mm. 4. Why do gases exert a pressure on the walls of their Each atom of helium has a diameter of container? 0.0000001 mm. 5. Why can gases be compressed more readily than solids or liquids? 8 ELEMENTS Metals or non-metals KS3 Elements can be classified as either metals or non-metals. a gold bar an iron nail sticks of sulphur argon gas in a light bulb argon gas Air contains a colourless gas called oxygen which is essential for respiration. Oxygen is a non-metal. Cooking foil is made from aluminium. Aluminium is a shiny, reflective metal which does not melt in a hot oven. By looking at their properties elements may be classified as either metals or non-metals. Physical state Is the element a solid, liquid or gas under normal conditions such as room temperature? Appearance Melting point What does the element look like? Does it have a shiny reflective At what temperature does the solid surface like polished metal? form of the element melt? Properties of elements Flexible or brittle Conductor How does the element respond Does the element allow an to attempts to bend it? Does it bend electric current to pass through (flexible) or break without it easily? bending (brittle)? solid gas, liquid or solid shiny dull high melting point low melting point conductor non-conductor flexible brittle METAL NON-METAL Questions 1. Name four elements. 5. What are the two main types of element? 2. Aluminium is used for cooking foil. What does this 6. Which type of element can be bent into a new suggest about its melting point? shape? 3. Name the gas which is used to fill filament light 7. Name one metal which is not normally found in bulbs. the solid state, 4. Why is air not used in light bulbs? 9  ELEMENTS Classifying elements KS3 Metals and non-metals have different characteristic properties. Gold bends Sulphur breaks BENDING flexible brittle high molten gold MELTING low 1064°C molten sulphur 113°C The element is placed across contacts A and B to see if CONDUCTING the bulb lights up. ELECTRICITY Element tested Bulb on or off Conductor Gold on yes A B Sulphur off no Argon is a Gold is a flexible, shiny, yellow colourless gas. Its solid which melts at 1064°C melting point is –189°C and conducts electricity. Silicon is a solid and it does not conduct which is slightly electricity. shiny and melts at 1410°C. It is a semiconductor Sulphur is a Iron is a flexible, shiny, silver but is not flexible brittle, dull, yellow solid which melts at 1535°C solid. Its melting point is and conducts electricity. 113°C and it does not conduct electricity. Properties such as melting point and conductivity are physical Questions properties. 1. Name two elements which conduct electricity. Oxides of non-metals, for example 2. Why did the light stay off when sulphur was tested in the circuit? sulphur dioxide, are mostly 3. What would happen if iron were placed in the circuit? 4. Chromium, tungsten, and nickel are all metals. What properties are acidic. they likely to have? Oxides of metals, for example 5. Phosphorus and iodine are both solid and are non-metals. Will they calcium oxide, are mostly basic. conduct electricity? Being basic or acidic is a 6. Fluorine and chlorine are gases. Are they metals or non-metals? difference in chemical properties. 7. What is meant by the term semiconductor? 8. Why is it difficult to classify silicon as a metal or a non-metal? 9. Is silicon a metal or a non-metal? 10 ELEMENTS Atoms and atomic symbols KS3 Elements are made up of small particles called atoms. Copper is an element. Water is not an element. Helium is an element. Air is not an element. Elements are the simplest chemicals and cannot be split into simpler substances. Each element is made only from itself; copper is only copper, and helium is only helium. hydrogen can be split water (a compound) by electricity oxygen oxygen 21% air (a mixture) can be separated nitrogen 78% oxygen (an element) cannot be split oxygen Copper contains Helium contains only Elements only copper atoms. are made of atoms, helium atoms. and each element He Cu Cu Cu Cu Cu He contains only one He type of atom. He Cu Cu Cu Cu Cu He Molecules of Water is not an element. water contain two Water is made of different types of hydrogen atoms bonded H H to oxygen atoms. atom. O Atoms can be represented by H hydrogen calcium Ca There are only 26 letters and chemical symbols. A single S sulphur copper Cu just over 100 elements so some capital letter is used as the C carbon chlorine Cl have a small letter as well as a atomic symbol for some elements. O oxygen helium He capital for their atomic symbol. Atoms are the particles of Atoms can join together in Molecules are made of two or which elements are made. small groups called molecules. more atoms chemically combined. He H2 H2O (H–H) helium atoms hydrogen molecules water molecules Questions 1. Can copper be split into simpler substances? 6. Give the names and atomic symbols of three elements. 2. Can water be split into simpler substances? 7. What is the chemical symbol for calcium and why is 3. Name two elements present in air. it not just C? 4. Which type of particle is present in helium? 8. Why is there no chemical symbol for air? 5. Why is water not an element? 11  ELEMENTS Organising the elements KS3 The Periodic Table is a useful way of organising the elements. There are just over 100 different known elements and they can be organised in many ways. Alphabetically By Density (g/cm3) By Boiling Point (°C) Actinium Osmium 22.5 Helium –269 Aluminium Iridium 22.4 Hydrogen –253 Americium Platinum 21.5 Neon –246 Elements are made up of atoms, which contain even smaller particles called protons (plus neutrons and electrons). All atoms of the same element have the same number of protons. Atoms of different elements have different numbers of protons. The atomic number of an element is the number of protons in each atom of that element. 6C 13Al 16S 79Au How did the Periodic atomic number Table develop? See page 26. The elements can be listed in order of atomic number. Elements with similar chemical properties occur at regular intervals (periodically). Elements organised using atomic number and chemical properties give a Periodic Table. The elements are listed in order of atomic number beginning with hydrogen, 1H. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Elements with similar chemical properties occur at regular intervals, e.g. Li, Na, K; He, Ne, Ar. In the Periodic Table the elements are listed in order of atomic number, and elements with similar chemical properties are put in columns called groups. This is a useful way of organising the chemical elements using atomic number and chemical properties. The bold line separates metals from non-metals. 1H 2He 3Li 4Be 5B 6C 7N 8O 9F 10Ne 11Na 12Mg 13Al 14Si 15P 16S 17Cl 18Ar 19K 20Ca 21Sc 22Ti 23V 24Cr 25Mn 26Fe 27Co 28Ni 29Cu 30Zn 31Ga 32Ge 33As 34Se 35Br 36Kr A Periodic Table for Elements 1 to 36 Lithium, sodium, and potassium Helium, neon, argon, and krypton are all very reactive metals. are all colourless, unreactive gases. Questions 5. Are there more metals or non-metals? 1. How many known elements are there? 6. In the table, oxygen is shown as 8O. What 2. Why are certain elements placed in the same does the 8 represent? column as each other? 7. Why are He and Ne in the same column? 3. What are the columns called? 8. How does the table show that Na, K, and Li have 4. What does the bold line between Al and Si indicate? similar properties? 12 COMPOUNDS Compounds KS3 New substances called compounds are formed when elements combine. Experiment Heating iron and sulphur Iron and sulphur are both elements. If iron filings and powdered sulphur are mixed together they do not change. If a mixture of iron and sulphur is heated the iron and sulphur combine. When iron and sulphur combine they form a new substance. Mix Iron filings Sulphur powder Iron sulphide Fe Fe Fe S S S Heat FeS FeS FeS Iron atoms bond to sulphur atoms to form a new substance called iron sulphide. Iron sulphide is a compound of iron and sulphur. There is a chemical reaction during which iron combines with sulphur. iron + sulphur iron sulphide When elements combine they form new substances which Fe + S FeS have different properties. Experiment Heating copper in air If a piece of copper is heated in air, a black coating forms on the outside of the copper. The black substance is a compound of copper and oxygen called copper oxide. Copper atoms combine with oxygen atoms from the air. Copper foil Black coating Heat copper + oxygen copper oxide Cu Cu + O2 CuO CuO Copper oxide and iron sulphide are both compounds. Compounds are formed when atoms of different elements form bonds to each other. Compounds contain two or more elements which are chemically combined. Questions 1. How can iron be made to combine with sulphur? 5. What keeps the atoms of copper and oxygen 2. Name the compound formed when iron combines together in copper oxide? with sulphur. 6. What are compounds? 3. If a piece of copper is heated in air, what 7. Name the compounds formed when copper reacts change is seen? with sulphur, and iron reacts with oxygen. 4. What is copper oxide and what does it look like? 8. Why do iron and copper not form a compound with each other? 13  COMPOUNDS Combination reactions KS3 Combination reactions are those in which elements combine directly to form compounds. Experiment Burning sodium in chlorine Combination reactions often happen if metals and non-metals are heated together. If a piece of burning sodium is lowered into chlorine gas, the sodium continues to burn. Sodium combines with the chlorine to form a compound called sodium chloride. combustion spoon chlorine gas gas jar sodium just burning with yellow flame sodium chlorine sodium chloride Na Cl2 NaCl Sodium is a very reactive + Chlorine is a greenish- Sodium chloride is metal and must be stored yellow poisonous gas. common table salt, a and handled very carefully. harmless white solid. Experiment Burning magnesium in air Experiment Burning sulphur in air and oxygen Air contains oxygen, which is a reactive gas. Many elements react with oxygen if they are heated in air. Sulphur burns in air. Sulphur burns in oxygen. Magnesium usually burns if heated in air. oxygen powdered sulphur It combines with oxygen to form magnesium oxide. sulphur + oxygen sulphur dioxide S + O2 SO2 Magnesium is a silver-grey metal. Sulphur is a yellow solid. For more combination Oxygen is a colourless gas. Oxygen is a colourless gas. reactions Magnesium oxide is a white powder. Sulphur dioxide is a poisonous gas. see page 70 Questions 1. Which part of the air reacts when magnesium 4. How does sulphur dioxide differ from oxygen? burns? 5, What is a common method of making elements 2. What does magnesium look like after it has burnt? combine? Name the substance formed. 6. Why do so many elements react if they are heated 3. What is sodium chloride? In what way is it different from its elements? in air? 14 COMPOUNDS Naming chemical compounds The chemical name given to a compound indicates the elements from which it is made. A name ending in...IDE usually indicates compounds containing two elements. Compounds containing Compounds containing Compounds containing oxygen bonded to one sulphur bonded to one chlorine bonded to one other element are other element are other element are oxides sulphides chlorides Copper oxide Silver sulphide Sodium chloride CuO Ag2S NaCl is a compound of is a compound of is a compound of copper and oxygen silver and sulphur sodium and chlorine These rules also apply to compounds which seem to have less simple names. carbon monoxide carbon + oxygen carbon dioxide CO CO2 Carbon forms two different compounds with oxygen. The names monoxide and dioxide indicate the number of oxygen atoms bonded to one carbon atom. Similarly, sulphur forms a dioxide (SO2) and a trioxide (SO3). A name ending in...ATE usually indicates compounds with three elements such as a metal, another element, and oxygen. Compounds containing Compounds containing Compounds containing a metal, carbon, and a metal, sulphur, and a metal, nitrogen, and oxygen are oxygen are oxygen are carbonates sulphates nitrates Calcium carbonate Copper sulphate Sodium nitrate CaCO3 CuSO4 NaNO3 is a compound of calcium, is a compound of copper, is a compound of sodium, carbon, and oxygen sulphur, and oxygen nitrogen, and oxygen Although some formulae look quite complex the Although some names sound unusual they endings...ide and...ate still apply. generally indicate the elements in the compound. AlCl3 is aluminium chloride. Calcium carbide contains calcium and carbon. Mg(NO3)2 is magnesium nitrate. Magnesium nitride contains magnesium and nitrogen. Al2(SO4)3 is aluminium sulphate. Sodium chlorate contains sodium, chlorine, and oxygen. Questions Note: 1. Name the elements of which the following substances are compounds: Compounds with CuO NaCl Ag2O AgCl Na2S CO2 SO2 the –OH group are 2. Name the compounds in question one. 3. Name compounds which could be formed from the following pairs of elements: called hydroxides. Silver and sulphur, sodium and oxygen, copper and chlorine, magnesium and sulphur. NaOH is sodium 4. Name the following compounds: CuS, CuSO4, CaCO3, CuCO3, MgSO4, MgCO3. hydroxide. 15  COMPOUNDS Chemical formulae Chemical formulae use atomic symbols to show which elements are present in a compound. Chemical formulae show the proportions of each element present in a compound. Atomic symbols represent single atoms of an element. If atoms are combined, small subscript numbers show how many atoms are present. The chemical formula of a substance shows the type and number of atoms present. O O2 CO2 An atom of oxygen A molecule of oxygen gas A molecule of carbon dioxide This is the atomic symbol, Two atoms are combined. Two atoms of oxygen are combined not the formula of oxygen gas. This is the formula of oxygen gas. with one atom of carbon. The name of a compound and the elements in it can be worked out from its formula. NaCl Is a compound of The formula shows one sodium atom and one sodium chloride sodium and chlorine. chlorine atom. AlCl3 Is a compound of The formula shows one aluminium atom and aluminium chloride aluminium and chlorine. three chlorine atoms. CuS Is a compound of The formula shows one copper atom and one copper sulphide copper and sulphur. sulphur atom. CuSO4 Is a compound of copper, The formula shows one copper atom, one sulphur, copper sulphate sulphur, and oxygen. and four oxygen. CaCO3 Is a compound of calcium, The formula shows one calcium atom, one carbon, calcium carbonate carbon, and oxygen. and three oxygen. NaNO3 Is a compound of sodium, The formula shows one sodium atom, one sodium nitrate nitrogen, and oxygen. nitrogen, and three oxygen. Some formulae include brackets. Using brackets does not change the name but does affect the number of atoms. The number outside a bracket multiplies the number of atoms inside. 1 × Na 1 × Mg 2×N NaNO3 1×N Mg(NO3)2 2×N (NH4)2SO4 8×H 3×O 6×O 1×S (one of NO3) (two of NO3) (two of NH4) 4×0 Questions 1. Name the elements of which the following substances are compounds: Copper sulphide, copper sulphate, calcium carbonate, sodium carbonate, sodium nitrate, silver nitrate. 2. Name the following compounds: MgO, MgS, MgSO4, MgCO3, Mg(NO3)2. 3. How many oxygen atoms are used in each of the following: CO2, NaNO3, Mg(NO3)2. 4. Name each element and give the number of atoms in NaCl, CuSO4, NaNO2, Fe2O3, Na2CO3, Ca(NO3)2, Al2(SO4)3. 16 COMPOUNDS Chemical equations Chemical equations identify the reactants and products of a chemical reaction. Chemical equations summarise what happens during a chemical reaction. They indicate the starting substances (reactants) followed by the substances produced (products). Word equations use chemical names. Symbol equations use chemical symbols and chemical formulae. for iron heated with sulphur: iron + sulphur iron sulphide Fe + S FeS for carbon burning in air: carbon + oxygen carbon dioxide C + O2 CO2 for magnesium metal reacting with chlorine gas: magnesium + chlorine magnesium chloride Mg + Cl2 MgCl2 for hydrogen reacting with oxygen: hydrogen + oxygen water 2H2 + O2 2H2O Questions 1. Write out and complete the following word equations: magnesium + oxygen ; magnesium + sulphur ; sodium + chlorine ; lead + oxygen. 2. Name the elements which would have to combine to form the following compounds: Iron oxide, carbon monoxide, silver chloride, zinc sulphide, hydrogen sulphide, water, sulphur dioxide, magnesium nitride. 3. Write out and complete the following symbol equations: Cu + S ; Cu + Cl2 ; S + O2 ; H2 + S ; Zn + S ; H2 + Cl2. 4. Suggest a chemical name for water. 17  MIXTURES Air KS3 In a mixture the components are not chemically combined. Air is a mixture of gases including oxygen (21%) A burning candle needs oxygen. nitrogen (78%) and If a gas jar of air is placed over a burning candle, it burns for a carbon dioxide (0.03%) while but finally goes out. A candle stops burning when there is not enough oxygen left. In air the candle In oxygen the candle In carbon dioxide continues to burn burns more brightly the candle goes out for a while. than in air. immediately. In air the oxygen is not combined with the other gases and is free to react. In pure oxygen substances burn more brightly and more quickly, In air there is less oxygen and other gases get in the way. In carbon dioxide the oxygen atoms are already combined with carbon and are not free to react. N2 N2 N2 O2 N2 O2 CO2 N2 N2 N2 O2 CO2 N2 N2 N2 O2 O2 CO2 CO2 N2 N2 CO2 O2 O2 CO2 CO2 O2 O2 N2 CO2 CO2 CO2 N2 O2 CO2 O2 CO2 CO2 N2 N2 Air contains 1/5 oxygen Pure oxygen No free oxygen Oxygen is needed for many reactions such as burning, respiration, and rusting. Oxygen is mixed with other gases in the air but mixing does not change its properties. The main gas in air is nitrogen, which is generally unreactive. The air we breathe out Painting iron or steel Fires can be put out by contains less oxygen protects it from oxygen smothering the flames than the air we breathe in. so that it will not rust. to keep out oxygen. Questions 1. Name the two main gases in the air. 5. Why does a candle burn more brightly in oxygen 2. Why is air described as a mixture rather than than in air? a compound? 6. Why does a candle not burn in carbon dioxide, even 3. What is the total % of nitrogen and oxygen in though carbon dioxide contains oxygen? the air? 7. Dry iron does not rust even if air is present. 4. Which part of the air is needed for a candle What does this suggest? to burn? 8. What do rusting, burning, and breathing have in common? 18 MIXTURES Further examples of mixtures KS3 In mixtures the proportions of components may vary. Gases mix together very easily because their molecules are moving freely. Most gases are colourless and cannot be seen. Air is the most common mixture of gases. Air. See page 58 oxygen 21% nitrogen 78% Respiration uses some oxygen so EXHALED the proportion changes to about carbon AIR dioxide 16% oxygen and 4% carbon dioxide. water vapour When the Earth’s atmosphere first formed it contained no oxygen. Oxygen was produced by photosynthesis after green plants evolved. The composition of the air does not alter much from day to day except that changes in Can add gases such as carbon humidity are caused by changes in amounts EXHAUST dioxide, carbon monoxide, and of water vapour. FUMES nitrogen dioxide to the air. Water usually contains many dissolved substances. Once dissolved they cannot be seen because the particles spread evenly throughout the solution. Carbon dioxide gas is not very soluble in carbon dioxide water so pressure is used to make it FIZZ dissolve. Bubbles form as the gas escapes bubbles give the fizz from solution and the drink may go flat. citric acid gives a ‘lemon’ taste Different brands of mineral water may contain various dissolved compounds such as sulphates, water chlorides and hydrogencarbonates of sodium, magnesium, and calcium. sugar for sweet taste Is not pure but is made fit to drink. Lemonade is mostly water with dissolved TAP Chlorine will have been added to kill substances for taste. WATER bacteria. Hard water will also contain calcium compounds. Alloys are mixtures of metals with other elements, usually metals, although steels contain iron mixed with small amounts of carbon. copper G RE BRASS Is an alloy of copper and zinc. D G TH II F D ABE nickel 24 carat gold is pure gold and is soft. 9 carat gold is harder and contains 9 parts gold Z 2 I 00 EL to 15 parts base metal. 4 The proportion of carbon in steel can ‘Silver’ coins do not contain silver. STEEL vary and this will affect its hardness. They are alloys of nickel and copper. Questions 1. Why are alloys described as mixtures? 2. Name two compounds in mineral water. 19  MIXTURES Mixing and separating KS3 Mixing and combining are not the same thing. magnet sulphur iron filings Iron filings and Particles of iron A magnet can sulphur can be and sulphur pick out the iron and mixed together. can still be seen. leave the sulphur. Iron and sulphur can be Iron and sulphur keep Iron and sulphur are mixed in any proportions. their own properties. easily separated. This is a mixture because the iron and sulphur have not combined chemically. Iron can combine with sulphur. In most cases it is easier to separate a mixture than to split up a compound. See page 13. Mixture Separation What happens Why it works iron/sulphur use a magnet Iron is picked out and sulphur Iron is attracted by a magnet but is left. sulphur is not. sand/water filter Sand stays in the filter paper Filter paper is porous but the and water passes through. holes are too small for the sand to pass through. salt/water heat Water ‘disappears’ and salt Heat causes the water to is left behind. evaporate. sand/salt add water Salt ‘disappears’ into the water Salt is soluble and dissolves in but the sand does not. the water but sand is not soluble and does not dissolve. In mixtures the components tend to keep their own properties. Separation processes make use of differences in physical properties of the components. Separation processes do not usually involve chemical reactions. A separation might be straightforward or complicated, depending on the type of mixture and which components are needed. Questions 1. What quantities of iron and sulphur are needed to make a mixture? 2. By looking at a mixture of iron and sulphur, how is it possible to tell that neither has been changed by the mixing process? 3. Why does a magnet separate iron from a mixture of iron and sulphur but not from a compound of iron and sulphur? 4. If chalk is mixed with water and the mixture filtered, what happens? 5. What happens to salt when it is mixed with water, and how can the salt be recovered? 6. What happens when a mixture of salt and sand is added to water and the mixture stirred? How can the sand be separated and collected? How can the salt be collected? 20 MIXTURES Separation processes KS3 Mixtures are usually separated by physical processes rather than chemical reactions. filter paper Process Filtration. Uses To separate solids from liquids. Example Sand and water. residue How it works Small holes in the paper let only (solid) the liquid through. filter funnel Limitations Very fine particles of solid might get through the holes or block them. It filtrate does not work if the solid is dissolved. (liquid) conical flask Process Evaporation. solution evaporating Uses To extract solids from solution. dish crystallizing Example Salt from water. dish How it works The liquid evaporates and the solid is left behind. Limitations If crystals are required the evaporation must be slow. solution left in warm room Process Chromatography. Uses To separate mixtures of coloured chromatography substances. paper Example Separating coloured inks or food coloured spots move up colourings. and separate How it works A liquid carries the different colours original colour at different speeds across the surface of the chromatography paper. solvent (liquid) Process Distillation. thermometer Uses To recover the liquid from a solution. Example Water from salt water. steam enters condenser How it works The solution is boiled so that steam is given off. water The steam is cooled flask cold water cools and condenses to central tube re-form water. drops of Limitations Works best for solution liquid solutions of collect solid in liquid. condenser water Fractional distillation. distilled water See page 45 Questions 1. Give two examples of mixtures which could be 3. How may pure water be obtained from sea water? made clear by filtering. 4. If a dish of sea water is left in a warm room, what 2. Why does filtration not separate salt from sea happens? water? 5. Why is drinking water not purified by distillation? 21  REVIEW QUESTIONS Classifying materials I KS3 1. Water was kept at –10°C and then slowly heated until it reached 110°C. Describe and name the changes of state which occur between –10°C and 110°C, and indicate the temperatures at which these changes take place. 2. Draw diagrams to show the arrangements of particles in a typical solid, liquid, and gas, and describe the movement of the particles in each state. 3. Describe the processes of dissolving and diffusion, and explain each one in terms of particles. 4. (a) List the main properties which distinguish metals from non-metals. (b) Mercury is a liquid at normal temperatures so why is it classified as a metal? 5. (a) Why is hydrogen chosen as the first element in the Periodic Table? (b) Why are sodium and potassium in the same column of the Periodic Table? (c) What name is given to the columns in the Periodic Table? (d) One column comprises colourless, unreactive gases. Name two of these gases. (e) Which type of element is most common in the Periodic Table? 6. (a) From the table of melting points and boiling points classify the elements A to F as solid, liquid or or gas at a temperature of 20°C. (b) Which, if any, would undergo a change of state if the temperature rose to 2000°C? (c) Which would not change state even if cooled to absolute zero (–273°C) from 20°C? (d) Which one is water? (e) Which one is tungsten, the metal used for making filaments in light bulbs? (f) Which one would condense first as the temperature fell from 20°C? Element A B C D E F Melting point °C –182 –117 801 –201 0 3410 Boiling point °C –164 78 1413 –196 100 5660 7. The diagrams show the particles of different substances. Sort them into elements, mixtures, and compounds. A B C D E F 8. Using iron and sulphur as examples, describe and explain the differences between elements, mixtures and compounds. 9. Describe the evidence which suggests that the oxygen in the air is mixed and not combined with the other gases. 10. With the aid of diagrams describe how a mixture of salt and sand can be separated in order to obtain samples of salt crystals and clean, dry sand. 11. Explain the difference between evaporating salt water and distilling salt water. 12. From the formulae listed state the numbers and types of atoms in each compound, and name each compound: FeS NaCl CO2 FeSO4 CaCO3 Na2CO3 Ca(OH)2 Al2(SO4)3. 22 ATOMIC STRUCTURE Protons, neutrons, and electrons Atomic number and mass number An element is a substance containing only one type of atom. Particle in Relative Relative Atoms consist of a nucleus and electrons that orbit around the atom mass charge the nucleus. proton 1 +1 All atoms of a particular element have the same number of protons. neutron 1 0 Atoms of different elements have different numbers of protons. electron negligible –1 Sodium atom Nucleus – contains two sorts of particle, protons and neutrons Protons are positively charged, Electrons orbit around the electrons are negatively charged. nucleus at different An atom of an element is neutral energy levels (shells) (it has no net electrical charge), because number of protons = number of electrons. A sodium atom has 11 protons and 11 electrons. The information about a sodium atom can be shown like this: mass number (A) Protons and neutrons make up the mass of an atom 23 chemical (electrons have negligible mass); symbol Number of neutrons = because there are 11 protons for mass number – proton number there must be 12 neutrons Na sodium (atomic number) atomic number (Z) also called the proton number 11 – a sodium atom has 11 protons Another way of showing a sodium atom Dots can be is like this used to e e represent e electrons. e e 11p and yet another way e 12n Na e e The chemical symbol can e e be used to e represent the nucleus. REMEMBER However it is shown, the information is the same. A sodium atom has 11 protons, 12 neutrons and 11 electrons. Questions 1. How many types of atom are there in an element? 5. Which particles in an atom contribute to the mass 2. Which particles are found in the nucleus? of an atom? 3. What information about an atom is given by the 6. Which particles in an atom are charged? atomic number of an element? 7. Why are atoms of elements described as being 4. What information about an atom is given by the neutral? mass number? 23  ATOMIC STRUCTURE Electron arrangements Atoms of different elements have different REMEMBER Number of protons = number of electrons, numbers of protons and, therefore, different atomic numbers. REMEMBER Number of neutrons = mass number – proton number. mass number chemical 19 symbol for fluorine Particles in a fluorine atom F atomic number = 9 so there are 9 protons and 9 electrons atomic number 9 mass number = 19 so there are 10 neutrons One way of showing × × Crosses can be used to represent electrons. a fluorine atom is × like this × × F × × × × Electron arrangements The first energy level (electron shell) Electrons orbit around the nucleus at can hold up to two electrons. different energy levels (sometimes called electron shells). The second energy level Each electron in the atom is at a (electron shell) can hold up to particular energy level (in a particular eight electrons. shell). nucleus Electrons in an atom occupy the lowest The third energy level available energy levels (innermost (electron shell) has a stable electron shells). arrangement when its holds When an energy level is full, further eight electrons, although it electrons orbit at the next level. can hold a total of 18. Questions Sodium atom 1. Atoms of elements contain protons, neutrons, Notice that there are: and electrons. How do atoms of different 2 electrons at the first energy level – it is full; elements differ from one another? 8 electrons at the second energy level – it is full; 2. How many electrons can orbit a nucleus at: 1 electron at the third energy level – it is not full. (a) the first energy level (b) the second energy level The electron arrangement can be written as 2.8.1 (c) the third energy level? 3. What would be the electron arrangements Fluorine atom for elements with the atomic numbers: Notice that there are: (a) 17 (b) 19 (c) 13? 2 electrons at the first energy level – it is full; 4. For each of the following elements: 7 electrons at the second energy level – it is not full. (a) give the number of each type of particle (b) give the electron arrangements The electron arrangement can be written as 2.7 (c) draw a diagram to show the structure of an atom. 31 24 Reactions of elements depend on the arrangement of electrons. Elements with the same number of P Mg electrons in the outer energy level react in a similar way. 15 12 24 ATOMIC STRUCTURE Isotopes Isotopes are atoms of the same element with the same number of protons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers. Isotopes of the same element have the same chemical properties, although there will be very small differences in their physical properties. Most elements have more than one isotope. Some isotopes are radioactive. Hydrogen Carbon Chlorine 1 1p 1e 12 6p 6n 6e 35 17p 18n 17e (a hydrogen atom Most carbon atoms 75% of chlorine H has no neutrons) C are like this. Cl atoms are like this. Most hydrogen atoms This isotope is called 1 6 17 are like this. carbon-12 2 1p 1n 1e 13 6p 7n 6e 37 17p 20n 17e A few carbon atoms H This isotope is called deuterium. C are like this. Cl 25% of chlorine atoms are like this. This istope is called 1 6 17 carbon-13 3 1p 2n 1e 14 6p 8n 6e Some carbon atoms This isotope is are like this. H called tritium. C This isotope is called carbon-14 1 6 All three isotopes of hydrogen have All three isotopes of carbon have Both isotopes of chlorine have the the same atomic number (1) – they the same atomic number (6) – all same atomic number (17) – they all have one proton, but they have have 6 protons, but they have both have 17 protons, but they different numbers of neutrons and different numbers of neutrons and have different numbers of so have different mass numbers. so have different mass numbers. neutrons and so have different mass numbers. 14 Deuterium is used as a moderator 6C is used in radiocarbon in nuclear reactors. dating. This isotope is present Sometimes a Periodic Table will in constant small quantities in the give chlorine a relative atomic Tritium has a possible use in atmosphere. Once an animal or mass of 35.5. This takes account producing energy by nuclear fusion. plant has died the only change in of the proportions of the two 14 the 6 C content is due to radioactive isotopes. decay. By knowing the rate of decay 14 (6 C has a half life of 5730 years) and the level of radioactivity in the specimen, its age can be calculated. It is one of the methods used by archaeologists to determine the age of organic remains. Questions 1. Why are 12 6 C, 13 14 6 C and 6 C all considered to be atoms of the same element? 2. Name the three isotopes of hydrogen and write symbols for them. 3. From the examples on this page give two radioactive isotopes. 4. Explain why a Periodic Table might give chlorine relative atomic mass of 35.5. 235 238 5. Two isotopes of uranium are 92 U and 92 U. For each of these isotopes give (a) the atomic number (b) the mass number (c) the number of protons (d) the number of neutrons (e) the number of electrons. 25  PERIODIC TABLE I Development of ideas Atomic structure Periodic Table Robert Boyle used the term 1661 elements for basic substances which make up matter. John Dalton suggested that elements 1803 were composed of atoms. 1817 Johan Döbereiner noticed that some elements could be grouped in threesomes because they had similar properties and the atomic weight, which we now call relative atomic mass, of one of them was halfway between the other two. He called this 'The Law of Triads'. John Newlands listed the elements in order of 1863 increasing relative atomic mass – he noticed Periodicity – that every 8th element appeared to show a repeating similar chemical behaviour. He called this pattern. 'The Law of Octaves'. Dimitri Mendeleev – a Russian scientist – drew 1869 up the first version of the Periodic Table and arranged elements in order of increasing relative atomic mass. Once the order was established, the list was arranged in rows so that elements with similar properties were Joseph Thomson 1897 grouped in the same column. To do this he discovered the electron. left gaps and he predicted the properties of some of the missing elements. Ernest Rutherford discovered the proton and suggested that atoms consist of a positive 1911 Henry Moseley nucleus and negative electrons. ordered the 1913 1913 Periodic Table by Niels Bohr – a Danish scientist – put forward the idea of atomic number. electron shells. James Chadwick 1932 1944 discovered Glenn Seaborg helped to discover the neutron. 10 new elements and organised the actinide series. Scientists are still discovering – or making in There are over 90 naturally occurring elements – nuclear facilities – new elements. others have been produced artificially. Scientists regarded the Periodic Table first as a curiosity and later as a scientific tool. Now it is regarded as an important summary of the structure of atoms. Originally the elements were arranged in order of increasing relative atomic mass. Now they are arranged in order of increasing atomic number, as evidence has become available to show that the chemical properties of elements vary according to atomic number. 40 When the Periodic Table was arranged in order of relative atomic mass argon, 18 Ar, was placed after 39 potassium, 19K. Questions 1. What contribution did each of the following 4. When Mendeleev drew up the first periodic table, scientists make to our understanding of the why did he leave gaps? structure of the atom: 5. Why do you think the elements were not arranged in (a) Joseph Thomson (b) Ernest Rutherford order of increasing atomic number until 1913? (c) Niels Bohr (d) James Chadwick? 6. How many naturally occurring elements are there? 2. What were 7. Approximately how many elements have been (a) ‘The Law of Triads’ (b) ‘The Law of Octaves’? discovered? 3. How did Mendeleev arrange the elements in his version of the periodic table? 26  PERIODIC TABLE I The first 20 elements On this page mass numbers of elements have been omitted. 0 Group H He 1 2