AQA C4.2. Bonding, Structure and the properties of matter.

Transcription

1 AQA C4.2 Bonding, Structure and the properties of matter. Abstract [Draw your reader in with an engaging abstract. It is typically a short summary of the document. When you re ready to add your content, just click here and start typing.] Ashbee2, Ruth [ address]

2 Contents Chemical bonds, ionic, covalent and metallic Page Chemical bonds Ionic bonding Ionic compounds Covalent bonding Metallic bonding How bonding and structure are related to the properties of substances States of matter Chemical equations Structure and function of ionic compounds Structure and function of simple covalent compounds Polymers Giant covalent compounds Metals as conductors Structure and bonding of Carbon Diamond Graphite Graphene Bulk and surface properties of matter including nanoparticles (Chemistry only) Nano dimensions Applications of nanoparticles 1

3 4.2.1 Chemical bonds, ionic, covalent and metallic Chemical bonds There are three types of strong chemical bonds: ionic, covalent and metallic. For ionic bonding the particles are oppositely charged ions. For covalent bonding the particles are atoms which share pairs of electrons. For metallic bonding the particles are atoms which share delocalised electrons. Ionic Compounds Covalent Compounds 1. Crystalline solids (made of ions) 2. High melting and boiling points 3. Conduct electricity when melted 4. Many soluble in water but not in nonpolar liquid 1. Gases, liquids, or solids (made of molecules) 2. Low melting and boiling points 3. Poor electrical conductors in all phases 4. Many soluble in nonpolar liquids but not in water Ionic bonding occurs in compounds formed from metals combined with non-metals. In ionic bonding, the metal atoms lose electrons and non-metal atoms gain them in order to produce a noble gas electron configuration. Typical of ionic bonds are those in the alkali halides such as sodium chloride, NaCl. Covalent bonding occurs in most non-metallic elements. 2

4 Covalent chemical bonds involve the sharing of a pair of valence electrons by two atoms. These bonds lead to stable molecules if they share electrons because they can create a noble gas configuration for each atom. Hydrogen gas forms the simplest covalent bond in the diatomic hydrogen molecule. The halogens such as chlorine also exist as diatomic gases by forming covalent bonds. The nitrogen and oxygen which makes up the bulk of the atmosphere also exhibits covalent bonding in forming diatomic molecules. Metalic bonding occurs in metallic elements and alloys. The properties of metals suggest that their atoms possess strong bonds, yet the ease of conduction of heat and electricity suggest that electrons can move freely in all directions in a metal. The general observations give rise to a picture of "positive ions in a sea of electrons" to describe metallic bonding. Electrostatic forces of attraction. 3

5 The force of attraction between two opposing charges. Activities: 1. Define electrostatic forces of attraction. 2. Extended writing: describe why atoms bond in order to obtain a noble gas configuration/full outer level of electrons. 3. Describe/draw the structure of common atoms and suggest how they could bond to obtain a full outer level of electrons. 4. Demo the formation of sodium chloride in a fume cupboard. Questions: 1. What type of bond will form between nitrogen and oxygen? 2. An atom that has lost or gained electrons if called an? 3. Draw lines to match up the key words with their definitions and explanations: Key word Ionic bonding Definition Type of bonding where atoms share electrons with each other Explanation Usually occur between non-metal atoms. Diatomic molecules are formed by this type of bonding. Covalent bonding Metalic bonding Type of bonding where one atom loses electrons and one atom gains electrons Type of bonding where a sea of free electrons is created Occurs between metal atoms. Electrons become delocalised and more free to move. Occurs between a metal and a nonmetal. Atoms become charged and are attracted to each other. 4. Explain why elements in Group 0 (Group 8) of the periodic table do not form bonds. 5. Explain why elements in Group 1 react violently with elements in Group Write electron structures to show the ions that would be formed when the following atoms are involved in ionic bonding. For each one, state how many electrons have been lost or gained and show the charge on the ions formed. a. Aluminium b. Fluorine c. Potassium d. Oxygen Extension: Look at the exam questions. Decide which one is the hardest to answer and say why. Then answer the hardest question. Q1.This question is about magnesium. 4

6 (a) (i) The electronic structure of a magnesium atom is shown below. Use the correct answer from the box to complete each sentence. electrons neutrons protons shells The nucleus contains protons and... The particles with the smallest relative mass that move around the nucleus are called... Atoms of magnesium are neutral because they contain the same number of electrons and... (3) (ii) A magnesium atom reacts to produce a magnesium ion. Which diagram shows a magnesium ion? Tick ( ) one box. (1) (b) Magnesium and dilute hydrochloric acid react to produce magnesium chloride solution and hydrogen. 5

7 Mg(s) + 2 HCl(aq) MgCl 2(aq) + H 2(g) (i) State two observations that could be made during the reaction (2) (ii) In this question you will be assessed on using good English, organising information clearly and using specialist terms where appropriate. Describe a method for making pure crystals of magnesium chloride from magnesium and dilute hydrochloric acid. In your method you should name the apparatus you will use. You do not need to mention safety (6) (Total 12 marks) 6

8 Q2.This question is about salts. (a) Salt (sodium chloride) is added to many types of food. Sodium chloride is produced by reacting sodium with chlorine. sodium + chlorine sodium chloride The diagram shows what happens to atoms of sodium and chlorine in this reaction. The dots ( ) and crosses ( ) represent electrons. Only the outer electrons are shown. Describe, in terms of electrons, what happens when a sodium atom reacts with a chlorine atom to produce sodium chloride (3) (b)... Lack of iodine can affect the learning ability of children. One idea is that salt (sodium chloride) should have iodine added. (i) Iodine consists of simple molecules. What is a property of substances that have simple molecules? Tick ( ) one box. Have no overall electric charge Have high boiling points 7

9 Have giant covalent structures (1) (ii) Which one of the following questions cannot be answered by science alone? Tick ( ) one box. How much sodium chloride is in food? What harm does a lack of iodine do? Should iodine be added to salt in food? Give one reason why this question cannot be answered by science alone.... (2)... (c) A student produced the salt ammonium nitrate by adding an acid to ammonia solution. (i) Name the acid used. (1)... (ii) Use the correct answer from the box to complete the sentence. an acid an alkali a salt (1) Ammonia solution (ammonium hydroxide) is.... (iii) The student added a few drops of a solution which changed colour when the reaction was complete. Complete the sentence. 8

10 (1) (d) The solution added is an.... Farmers buy solid ammonium nitrate in poly(ethene) sacks. (i) How is solid ammonium nitrate made from a solution of ammonium nitrate? Tick ( ) one box. Crystallisation Decomposition Electrolysis (1) (ii) Why do farmers use ammonium nitrate on their fields?... (1)... (iii) The properties of poly(ethene) depend on the reaction conditions when it is made. State one reaction condition that can be changed when making poly(ethene) (1) (Total 12 marks) 9

11 Q3. High quality connectors are used to connect a satellite box to a television. The connectors should conduct electricity very well and should not corrode. By Alphathon (Own work) [CC-BY-SA-3.0 or GFDL], via Wikimedia Commons The connectors on this scart lead are coated with gold. (a) Gold is a typical metal. (i) Describe the structure and bonding of gold (3)... (ii) Why is gold a good conductor of electricity?... (1) (b)... The surface of some metals, such as iron, corrode when exposed to the air. Suggest why this reduces the electrical conductivity of the metal (2) (Total 6 marks) 10

12 Answers: 1. A covalent bond will form between nitrogen and oxygen. 2. If an atom has lost or gained electrons then it is an ion. 3. Draw lines to match up the key words with their definitions and explanations: Key word Ionic bonding Definition Type of bonding where atoms share electrons with each other Explanation Usually occur between non-metal atoms. Diatomic molecules are formed by this type of bonding. Covalent bonding Metalic bonding Type of bonding where one atom loses electrons and one atom gains electrons Type of bonding where a sea of free electrons is created Occurs between metal atoms. Electrons become delocalised and more free to move. Occurs between a metal and a nonmetal. Atoms become charged and are attracted to each other. 4. Group 0 (Group 8) do not form bonds and are highly unreactive because their outer most shell (Higest energy level) of electrons is already full. This means that they do not need to share electron pairs or form ions to reach their stable state and so do not form bonds. 5. Group 1 and group 7 elements react very violently with each other as they form ionic bonds. Group 7 elements need to gain 1 electron to reach their most stable state and have a complete outer shell of electrons. Group 1 elements need to lose 1 electron to reach their most stable state. Group 1 donates its electron to the group 7 element and an ionic bond is formed with both elements achieving an electronic arrangement of a noble gas. 6. a. 11

13 b. Gained 1 electron c. Potassium has lost 1 electron d. Extension: 1A this order only neutrons 1 electrons 1 protons 1 (ii) box on the left ticked (b) (i) effervescence / bubbling / fizzing / bubbles of gas do not accept just gas alone magnesium gets smaller / disappears allow magnesium dissolves allow gets hotter or steam produced ignore references to magnesium moving and floating / sinking and incorrectly named gases

14 M2.(a) (ii) Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response. Examiners should also refer to the information in the Marking Guidance and apply a best fit approach to the marking. 0 marks No relevant content Level 1 (1 2 marks) There are simple statements of some of the steps in a procedure for obtaining magnesium chloride. Level 2 (3 4 marks) There is a description of a laboratory procedure for obtaining magnesium chloride from dilute hydrochloric acid and magnesium. The answer must include a way of ensuring the hydrochloric acid is fully reacted or a method of obtaining magnesium chloride crystals. Level 3 (5 6 marks) There is a well organised description of a laboratory procedure for obtaining magnesium chloride that can be followed by another person. The answer must include a way of ensuring the hydrochloric acid is fully reacted and a method of obtaining magnesium chloride crystals. examples of the points made in the response: hydrochloric acid in beaker (or similar) add small pieces of magnesium ribbon until magnesium is in excess or until no more effervescence occurs * filter using filter paper and funnel filter excess magnesium pour solution into evaporating basin / dish heat using Bunsen burner leave to crystallise / leave for water to evaporate / boil off water decant solution pat dry (using filter paper). *Student may choose to use a named indicator until it turns a neutral colour, record the number of pieces of magnesium added then repeat without the indicator. sodium loses (electron) sharing / covalent / metallic = max 2 chlorine gains (electron) 1 or an (electron) [12] (b) (i) Have no overall electric charge (ii) Should iodine be added to salt?

15 reason any one from: cannot be done by experiment accept difficult to get / not enough evidence based on opinion / view allow must be done by survey ethical or economic issue. (c) (i) nitric (acid) (ii) (iii) an alkali indicator accept any named acid base indicator (d) (i) Crystallisation (ii) (iii) fertiliser allow to help crops grow any one from: pressure allow concentration temperature ignore heat catalyst [12] M3. (a) (i) mention of molecules or any reference to incorrect bonding = max 2 giant structure / lattice or particles arranged in a regular pattern allow close packed / layers 1 (ii) sea of electrons / delocalised electrons allow free electrons positive ions and electrons attract each other ignore metallic bonds appropriately labelled diagrams can gain first two marks (sea of) electrons can move through the structure allow free / roaming / mobile electrons or delocalised electrons (b) (metal) oxide / ionic compound formed 1 14

16 ions not free to move or electrons cannot move through the structure allow no / fewer delocalised / free / roaming / mobile electrons 1 [6] Intervention Questions: 1. Why does bonding occur in elements? 2. In an ionic compound, what type of element forms a positive ion? 3. What is a covalent bond? 4. What happens to the outer electrons of metal atoms? 5. What is metallic bonding? 15

17 Intervention Answers: 1. So that the atoms get a full outer electron shell 2. Metal elements form a positive ion because they lose electrons. 3. Bonds which form between two non-metal elements by the sharing of electron pairs. 4. They form a delocalised sea of electrons 5. The attraction between delocalised electrons and positive metal ions. 16

18 Ionic bonding When a metal atom reacts with a non-metal atom, electrons in the outer shell of the metal are transferred. Metal atoms lose electrons to become positively charged ions. Non-metal atoms fain electrons to become negatively charged ions. The ions produced by metals in groups 1 and 2 and by non-metals in groups 6 and 7 have the electronic structure of a noble gas (group 0). The electron transfer during the formation of an ionic compound can be represented by a dot and cross diagram, eg for sodium chloride. The charge of the ions produced by the metals in groups 1 and 3 and by non-metals in group 6 and 7 relates to the number of the element in the periodic table. Ionic bonding occurs between positive and negative ions, which attract each other and bind together to form ionic compounds. For example, sodium chloride consists of Na + ions and Cl - ions bound together. Each ion is surrounded by oppositely charged ions held in place by electrostatic attraction and forming an ionic crystal lattice. The ions in a crystal lattice are very strongly bonded - a high temperature is required to melt the crystal. There are several ways in which atoms chemically combine together to make compounds. One of these ways is called ionic bonding. Atoms turn into ions when they lose or gain electrons. Metal ions; In some circumstances metal atoms may lose electrons. The atom then has more protons than electrons and so it will be positively charged, a positive ion. Example: A magnesium atom may lose two electrons and become a Mg 2+ ion. Non-metal ions; Non-metal atoms may gain electrons and become negatively charged. Example: An oxygen atom may gain two electrons and become an O 2- ion. Positive and negative ions attract one another and bind together forming a new substance. This is called ionic bonding. For example: Sodium chloride consists of Na + ions and Cl - ions bound together. 17

19 Magnesium oxide consists of Mg 2+ ions and O 2- ions bound together. Ionic compounds like magnesium oxide and sodium chloride have high melting points and do not conduct electricity when solid. They do conduct electricity when molten. Sodium chloride is soluble in water and the solution conducts electricity. Dot and cross model The formation of ionic compounds is often shown with dot and cross models. For example, a sodium atom loses one electron from its outer shell to become a positively charged sodium ion. It can be represented in a diagram like this: A sodium atom and a sodium ion On the other hand an oxygen atom gains two electrons in its outer shell to become a negatively charged oxygen ion: An oxygen atom and an oxide ion Notice how atoms gain or lose just the right number of electrons to produce an ion with a complete outer shell of electrons. This is sometimes called a stable octet. The positive and negative ions attract each other and form an ionic bond. We can draw this using dots for one atom and crosses for the other atom. This is called a dot and cross diagram. 18

20 Activities: 1. Tabulate common atoms and state the charges of the ions formed. 2. Grade 9: explain an example of ionic bonding including detail on electron transfer, group numbers of the atoms involved and the use of correct terms, eg cation and anion. 3. Use magnesium ribbon to produce magnesium oxide. Draw the dot and cross diagram for this reaction. Questions: 1. Copy and complete the table: Atomic number Atoms Electonic structure of the atom 9 F 2,8 3 2,1 Li + Ion 16 S S ,8,8,2 Electronic structure of ion 2. Write aown the general rules used to remember the charge on any ions formed by elements in: a. Group 1, Group 2, and Group 3. b. Group 5, Group 6, and Group What elements are required to form ionic bonds? 4. Ionic compounds are held together by strong forces in all directions between oppositely charged ions. What is the name of this force? 5. Draw a diagram to show the electronic arrangement of a fluorine ion Extension: Create an exam question based on this topic and include the mark scheme. Include a two mark question and an extended writing question. 19

21 Answers: 1. Atomic number Atoms Electonic structure of the atom 9 F 2,7 F - 2,8 3 Li 2,1 Li + 2,2 16 S 2,8,6 S Ca 2,8,8,2 Ca 2+ 2,8,8 Ion Electronic structure of ion 2. Charges a. Charge = (group number) + b. Charge = (8 group number) 3. Metal and non-metal atoms 4. Electrostatic 5. 20

22 Extension example answer Q1.(a) The diagram shows an atom of magnesium and an atom of chlorine. Magnesium Chlorine Describe, in terms of electrons, how magnesium atoms and chlorine atoms change into ions to produce magnesium chloride (MgCl 2). (4) (b) Calculate the relative formula mass (M r) of magnesium chloride (MgCl 2). Relative atomic masses (A r): magnesium = 24; chlorine = 35.5 Mark Scheme.(a) two electrons Relative formula mass (M r) =... magnesium loses electrons there are four ideas here that need to be linked in two pairs. chlorine gains electrons magnesium loses electrons and chlorine gains electrons scores 2 marks. two atoms of chlorine magnesium loses two electrons and two chlorines each gain one electron will score full marks. (2) (Total 6 marks) (b) 95 correct answer with or without working gains 2 marks if answer incorrect, allow for 1 mark 2 [6] 21

23 Intervention Questions: 1. What electronic structure is consistent throughout all ions? 2. What is the formula of the ionic compound formed by Al 3+ and O Magnesium chloride has the formula MgCl2. What are the ions in magnesium chloride? 4. What holds ionic compounds together? 22

24 Intervention Answers: 1. All ions have a full outer shell of electrons 2. Al2O3 3. Mg2 + + Cl - 4. Electrostatic forces of attraction between oppositely charged ions. 23

25 Ionic compounds An ionic compound is a giant structure of ions. Ionic compounds are held together by strong electrostatic forces of attraction between oppositely charged ions. These forces act in all directions in the lattice and this called ionic bonding. The structure of sodium chloride can be represented in the following forms: The ions in a compound such as sodium chloride are arranged in a lattice structure. This regular arrangement results in the formation of a crystal. This pattern is repeated in all directions, giving a giant three-dimensional lattice structure in sodium chloride crystals. Because of the strong electrostatic forces between them, it takes a great deal of energy to separate the positive and negative ions in a crystal lattice. This means that ionic compounds have high melting points and boiling points. Solid ionic compounds do not conduct electricity, because the ions are held firmly in place. They cannot move to conduct the electric current. But when an ionic compound melts, the charged ions are free to move. Molten ionic compounds do conduct electricity. When a crystal of an ionic compound dissolves in water, the ions separate. Again, the ions are free to move, so a solution of an ionic compound in water also conducts electricity. Activities: 1. Extended writing: describe the bonding in the sodium chloride lattice using the correct terms, eg electrostatic forces of attraction. 2. Model the sodium chloride lattice using molecular model kits. 3. Deduce that a compound is ionic from a diagram of its structure in one of the specified forms 4. Describe the limitations of using dot and cross, ball and stick, two and three dimensional diagrams to represent a giant ionic structure 5. Work out the empirical formula of an ionic compound from a given model or diagram that shows the ions in the structure. 24

26 Questions: 1. Which elements are joined together by ionic bonding? 2. What is the name of the force that holds the ions together in an ionic bond? 3. List three properties of ionic compounds 4. Give the charges of the metal and non-metal ions in an ionic structure. 5. Give the name of the solid that is produced in a liquid via a displacement reaction 6. Calcium oxide is an ionic compound. Why do ionic compounds have high melting? Extension Come up with a role play drama to illustrate one of your answers. You may wish to work in groups so find other people who have finished. 25

27 Answers: 1. Elements that are joined together by ionic bonding are metals and nonmetals. 2. The name of the force that holds the ions together is electrostatic forces of attraction. 3. High melting and boiling points/do not conduct electricity when solid/do conduct electricity when dissolved or molten 4. The metal ions have a positive charge and the non-metal ions have a negative charge 5. The solid that is produced in a displacement reaction is a precipitate. 6. Ionic compounds are held together by strong forces of attraction. This requires a lot of energy and high temperatures to break the bonds. 26

28 Intervention Questions: 1) Why do ionic substances have high melting points? 2) Why are ionic substances brittle? 3) Why are ionic substances soluble in water? 4) Why do molten/dissolved ionic substances conduct electricity? 5) Why don t solid ionic substances conduct electricity? 27

29 Intervention Answers: 1) Ionic substances have high melting points because they are held together by strong forces of attraction between the bonds. 2) Because the lattice is of alternate positive and negative charges, if an ionic lattice receives a sharp blow, this may move the ions and produce contact between ions of like charges. These ions of like charge would be repelled from each other, resulting in the brittle property. 3) Water is a polar molecule, this means it has a slight positive charge on one side, and a negative charge on the other. The positive side of water attracts the negative ions electrostatic attraction. The negative side of water attracts the positive ions electrostatic attraction. This breaks up the ionic lattice dissolving it in the water. 4) When molten or dissolved in water, the ionic lattice has been broken. Therefore the ions are free to move and carry charge. 5) When solid, the ions are locked into the lattice and cannot move. Therefore solid ionic substances do not conduct electricity. 28

30 Covalent bonding When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong. Covalently bonded substances may consist of small molecules. Some covalently bonded substances have very large molecules, such as polymers. Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide. The covalent bonds in molecules and giant structures can be represented in the following forms: Polymers can be represented in the form: where n is a large number. 29

31 A covalent bond is formed between non-metal atoms, which combine together by sharing electrons. Covalent compounds have no free electrons and no ions so they don't conduct electricity. Non-metals combine together by sharing electrons. The shared pair of electrons holds the two atoms together. It's called a covalent bond. The group of atoms bonded together in this way is called a molecule. The types and numbers of atoms in a molecule are shown in its formula. Examples of covalent molecules Name Structure Model Hydrogen (H 2) Water (H 2O) Ammonia (NH 3) Methane (CH 4) 30

32 Activities: 1. Draw dot and cross diagrams for the molecules of hydrogen, chlorine, oxygen, nitrogen, hydrogen chloride, water, ammonia and methane 2. Represent the covalent bonds in small molecules, in the repeating units of polymers and in part of giant covalent structures, using a line to represent a single bond 3. Describe the limitations of using dot and cross, ball and stick, two and three dimensional diagrams to represent molecules or giant structures 4. Deduce the molecular formula of a substance from a given model or diagram in these forms showing the atoms and bonds in the molecule. 5. Extended writing: describe the difference between simple covalent substances and giant covalent substances. 6. Grade 9: explain an example of covalent bonding including detail on electron transfer, group numbers of the atoms involved and the use of correct terminology. Questions: 1. How many electrons are involved in each covalent bond? 2. Name a molecule of an element that are joined together by a covalent bond? 3. What type of bonding takes place between a non-metal and a non-metal? 4. How does a covalent bond form? 5. Draw a dot and cross model, of a methane CH4 molecule. Remember C is carbon a non-metal and H is hydrogen a non-metal, therefore the bond formed between them is a covalent bond (this helpful pointer would not be given in an exam). 6. Carbon dioxide and pure water are simple molecules, explain why they: a. do not conduct electricity b. have low melting points. 7. What properties will substances with simple molecular structures usually have? 31

33 Answers: 1. 1 pair of electrons 2. Oxygen 3. Covalent bonding 4. When non-metals combine together by sharing electron pairs, this is called covalent bonding Carbon dioxide and water do not conduct electricity because their molecules contain strong covalent bonds; there are no ions or free moving delocalised electrons in covalent bonds. Substances that conduct electricity must contain charged particles that can move freely when a current is applied. 7. Simple molecular substances are likely to have the following properties: a. be liquids or gas at room temperature b. have low melting points c. do not conduct electricity. 32

34 Intervention Questions: Draw dot and cross diagrams to show the bonding in the following compounds. a) hydrogen (H2) b) hydrogen chloride (HCl) c) methane (CH4) d) water (H2O) e) oxygen (O2) 2. a) Complete the table below. Name Formula Melting point ( C) Electrical conductivity Type of structure Methane CH insulator Diamond C 3550 insulator giant covalent structure Water H2O 0 simple molecular structure Sulfur S8 115 insulator Graphite C 3652 conductor Silicon dioxide SiO insulator Using the data in the table, identify the following: b) simple covalent compounds. c) elements with giant structures. d) compounds with giant structures. 33

35 3. Diamond and graphite are allotropes of carbon. By referring to their bonding and structure, explain each of the following: diamond a) why both diamond and graphite have a high melting point graphite b) why diamond is very hard and graphite is soft.. c) why diamond acts as an electrical insulator and graphite acts as a conductor of electricity Explain why carbon nanotubes are used in the manufacture of tennis rackets. Include reference to the structure of the nanotubes in your answer

36 Intervention Answers: Draw dot and cross diagrams to show the bonding in the following compounds. a) hydrogen (H2) b) hydrogen chloride (HCl) c) methane (CH4) d) water (H2O) e) oxygen (O2) 35

37 2. a) Complete the table below. Name Formula Melting point ( C) Electrical conductivity Type of structure Methane CH insulator Simple molecular structure Diamond C 3550 insulator giant covalent structure Water H2O 0 Conductor simple molecular structure Sulfur S8 115 insulator Simple molecular structure Graphite C 3652 conductor Giant covalent structure Silicon dioxide SiO insulator Giant covalent structure Using the data in the table, identify the following: b) simple covalent compounds Methane, Water, Sulfur,. c) elements with giant structures Carbon and silicon d) compounds with giant structures Diamond, Graphite, Silicon Dioxide 4. Diamond and graphite are allotropes of carbon. By referring to their bonding and structure, explain each of the following: a) why both diamond and graphite have a high melting point 36

38 Diamond and graphite both have very high melting points because they are held together by covalent bonds. These bonds are very strong and require a lot of energy to break them... b) why diamond is very hard and graphite is soft Diamond is a covalent compound which is made of carbon atoms only. These atoms are held together by 4 covalent bonds. This means that they are very strong. Graphite is carbon that is only joined by 3 covalent bonds and therefore the layers can slide over each other. c) why diamond acts as an electrical insulator and graphite acts as a conductor of electricity Graphite conducts electricity because it has free electrons in its structure. Diamond doesn t and therefore cannot conduct electricity Explain why carbon nanotubes are used in the manufacture of tennis rackets. Include reference to the structure of the nanotubes in your answer. The tube fullerenes are called nanotubes which are very strong and are conductors of electricity. Their unusual electrical properties mean that nanotubes are used as semiconductors in electronic circuits. Their strength makes them useful in reinforcing structures where exceptional lightness and strength are needed for example, the frame of a tennis racket. They are also used as a platform for industrial catalysts. 37

39 Metallic bonding Metals consist of giant structures of atoms arranged in a regular pattern. The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure. The sharing of delocalised electrons gives rise to strong metallic bonds. The bonding in metals may be represented in the following form: Giant structures with free electrons Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular structure and usually have high melting and boiling points. Metals are good conductors of electricity and heat, because the free electrons carry a charge or heat energy through the metal. The free electrons allow metal atoms to slide over each other, so metals are malleable and ductile Activities: 1. Define delocalised electrons. 2. Use copper wire and silver nitrate solution to grow silver crystals. 3. Create a model of the metallic lattce. 38

40 Questions: 1. List the physical properties of metals 2. Explain why iron is used to make cars and bridges. 3. Explain why copper is used to make electrical wiring. 1. What properties will a saucepan base need? 2. What properties will a pylon wire need? 3. Draw a labelled diagram to show metallic bonding 4. Explain, in terms of structure, why metals conduct electricity. 5. Explain, in terms of structure, why metals have high melting points and boiling points. 6. Describe what is meant by the term superconductor. 7. Describe the potential benefits of superconductors: 8. Explain some of the drawbacks of superconductors. 39

41 Answers: 1. List the physical properties of metals. Answer - The physical properties of metals are: lustrous, hard and high density high tensile strength high melting and boiling points good conductors of heat and electricity. 2. Explain why iron is used to make cars and bridges. Answer - Cars and bridges must withstand impact forces and carry large loads therefore the material they are made of should be hard and strong, iron is hard and strong. 3. Explain why copper is used to make electrical wiring. Answer - Copper is used to make electrical wiring because it is a very good electrical conductor and it is ductile. 4. What properties will a saucepan base need? Answer - A saucepan base should have the following properties good heat (thermal) conductor high melting point 5. What properties will a pylon wire need? Pylon wires should have the following properties: Good electrical conductor A low density solid (lightweight as possible) 6. Draw a labelled diagram to show metallic bonding Close packed metal positive ion Sea of delocalised electrons 7. Explain, in terms of structure, why metals conduct electricity. Answer - Metals have a sea of delocalised electrons that are able to carry charge from one place to another and this allows the metals to conduct electricity 8. Explain, in terms of structure, why metals have high melting points and boiling points. Answer - Metals have high melting points and boiling points because metallic bonding, is due to a strong attraction between the metal positive ions and the sea of delocalised electrons, a lot of energy is needed to overcome this attraction before a metal can metal or boil. 9. Describe what is meant by the term superconductor. Answer - At a critical temperature some metals will have little or no electrical resistance, they are called superconductors. 10. Describe the potential benefits of superconductors: Answer - The potential benefits of superconductors are: loss free power transmission 40

42 super-fast electronic circuits powerful electromagnets. 11. Explain some of the drawbacks of superconductors. Answer - The drawbacks of superconductors are that they only work at low temperatures, they must be kept very cold with liquid nitrogen or helium and this limits their usefulness. 41

43 Intervention Questions: 1. What happens to the outer electrons of metal atoms? 2. What is metallic bonding? 3. Why do metals have high melting points? 4. Why are metals malleable? 5. Why are metal alloys often stronger than a pure metal? 6. Why do metals conduct heat well? 42

44 Intervention Answers: 1. What happens to the outer electrons of metal atoms? a. The form a delocalised see of electrons 2. What is metallic bonding? a. The attraction between delocalised electrons and positive metal ions. 3. Why do metals have high melting points? a. The metallic bonds require a lot of energy to break apart. 4. Why are metals malleable? a. The layers of metal ions slide over each other rather than shattering 5. Why are metal alloys often stronger than a pure metal? a. They do not always have layers which can slide over each other. 6. Why do metals conduct heat well? a. The delocalised electrons transfer the kinetic energy through the metal, 43

45 4.2.2 How bonding and structure are related to the properties of substances States of matter The three states of matter are solid, liquid and gas. Melting and freezing take place at the melting point, boiling and condensing take place at the boiling point. The three states of matter can be represented by a simple model. In this model, particles are represented by small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing. The amount of energy needed to change state from solid to liquid and from liquid to gas depends on the strength of the forces between the particles of the substance. The nature of the particles involved depends on the type of bonding and the structure of the substance. The stronger the forces between the particles, the higher the melting point and boiling point of the substance. (Higher Tier only) Limitations of the simple model above include that in the model there are no forces, that all particles are represented as spheres and that the spheres are solid. Activities: 1. Extended writing: describe the properties of matter in a solid, liquid and gas. 2. Define melting point and boiling point. 3. Grade 9: explain the differences in changes of state in terms of intermolecular forces of attraction between a short molecule ie methane and a longer molecule ie pentane. 4. States of matter circus activity. 44

46 Questions: 1. Which theory describes the arrangement and movement of particles in solids, liquids and gases? 2. Which state of matter are the particles mostly touching but arranged in a random way? 3. In which state of matter do the particles have the most energy? 4. Why can liquids not be compressed easily? 5. Why do solids have a fixed shape? 6. Describe these three difference changes: a. Melting b. Boiling c. Freezing 7. Explain sublimation and give an example. Extension: Create your own model for solids, liquids and gases and evaluate it. 45

47 Answers: 1. Kinetic theory 2. Liquid 3. Gas 4. The particles in a liquid are closely packed together. 5. The particles are in a fixed place 6. Three different changes: a. When a solid turns into a liquid b. When a liquid turns into a gas c. When a liquid turns into a solid 7. Sublimation happens when a solid turns directly into a gas and doesn t change into a liquid first. An example of where this happens is solid carbon dioxide which trus back into a gas at room temperature. 46

48 Intervention Questions: 1. What change of state occurs when a solid becomes a liquid? 2. What is the name of the temperature at which evaporation takes place? 3. How are the particles represented in the particle theory? 4. Give one limitation the particle theory. 5. Give the 4 state symbols with explanations. 47

49 Intervention Answers: 1. Melting 2. Boiling point 3. Small circles 4. Limitations to the particle theory a. There are no forces acting between the particles b. The spheres are solid c. The particles are represented as spheres 5. State symbols a. S = Solid b. L = Liquid c. G = Gas d. Aq = Aqueous (Dissolved in solution) 48

50 Chemical equations In chemical equations, the three states of matter are shown as (s), (l) and (g), with (aq) for aqueous solutions. Word equations Information Word equations are a shorthand used to describe chemical reactions. Although there are many millions of possible chemical reactions you are not expected to know about them all. It helps to remember that many reactions are of similar types. 1. Metal + acid One type of reaction is that between a metal and an acid. When a metal reacts with an acid the reaction produces a salt, and hydrogen gas is released. The salt produced depends upon the metal and the acid. If magnesium reacts with hydrochloric acid, then the salt produced is magnesium chloride. metal + acid salt + hydrogen 2. Metal carbonate + acid Metal carbonates also react with acid, to give a salt. When a carbonate reacts with acid the gas carbon dioxide is given off. The salt produced depends upon which acid, and which metal carbonate react. If zinc carbonate reacts with sulfuric acid, then the salt produced is zinc sulfate. metal carbonate + acid salt + carbon dioxide + water 3. Acid + alkali When an alkali and an acid react the product is a salt solution. The particular salt produced depends upon which acid and which alkali reacted. When nitric acid reacts with potassium hydroxide the salt produced is potassium nitrate. acid + alkali salt + water 4. Metal + salt solution When a reactive metal is placed in the solution of a salt of a less reactive metal, a displacement reaction occurs. The more reactive metal is said to displace the less reactive metal from solution. For example, if zinc is added to copper nitrate solution the copper is displaced and the solution will contain zinc nitrate. 5. Element + element When two elements react together to form a compound the compound is given a name to show which elements reacted. So if calcium reacts with chlorine the compound is called calcium chloride. These examples show you the patterns that are found in five important types of reaction. If you look for patterns you should find it easier to work out how to complete word equations. Balanced symbol equations Copper and oxygen reaction: getting a balanced equation Balanced symbol equations show what happens to the different atoms in reactions. For example, copper and oxygen react together to make copper oxide. Take a look at this word equation for the reaction: copper + oxygen copper oxide Copper and oxygen are the reactants because they are on the left of the arrow. Copper oxide is the product because it is on the right of the arrow. 49

51 If we just replace the words shown above by the correct chemical formulas, we will get an unbalanced equation, as shown here: Cu + O 2 CuO Notice that there are unequal numbers of each type of atom on the left-hand side compared with the right-hand side. To make things equal, you need to adjust the number of units of some of the substances until you get equal numbers of each type of atom on both sides. Here is the balanced symbol equation: 2Cu + O 2 2CuO You can see that now there are two copper atoms and two oxygen atoms on each side. This matches what happens in the reaction. Two atoms of copper react with two atoms of oxygen to form two molecules of copper oxide Remember: never change a formula to balance an equation. 50

52 Write a word and symbol equation for the reaction when magnesium burns in air to produce a white ash of magnesium oxide. Step 1 Identify the reactants and the products in the question Use a highlighter if you want. Magnesium burns in air to produce a white ash of magnesium oxide When something burns it only reacts with the oxygen in the air. So in a combustion reaction the second reactant is always oxygen. Step 2 Write out the equation. Put the reactants on the left hand side and the reactants on the right. Use an arrow to show how the reactants change into the products. Magnesium + oxygen magnesium oxide Reactants Product Step 3 Use the periodic table to look up the symbols for the substances in the reaction. Remember only symbols for elements are found on the periodic table, so you will have to work out the chemical formula of any compounds yourself. magnesium = Mg oxygen = O Oxygen in the air exists as diatomic molecules, O2, so we use this in the equation. Magnesium forms Mg 2+ ions and oxygen forms O 2- ions. As the ions have the same charge the formula for magnesium oxide will be MgO. Step 4 Replace the words with the symbols. Mg + O2 MgO Step 5 Balance the equation. Are the numbers of atoms of each element the same on both sides of the equation? Mg + O2 MgO No? Then you can change the number of atoms/molecules by adding a large number in front of their formula. Never change the formula of compound. 2Mg + O2 2MgO Step 6 Add state symbols (s) = solid (l) = liquid (g) = gas (aq) = solution Most acids and alkalis that we use in school are solutions. 51

53 All metals are solids (except mercury!) All ionic substances are solid. 2Mg (s) + O2 (g) 2MgO (s) Useful information: Common acids and alkalis Gases and Others Hydrochloric acid HCl Carbon dioxide CO2 Sulphuric acid H2SO4 Sulphur dioxide SO2 Nitric acid HNO3 Oxygen O2 Sodium hydroxide NaOH Hydrogen H2 Potassium hydroxide KOH Chlorine Cl2 Ammonium hydroxide NH4OH Ammonia NH3 Complex ions Sulphate SO4 2- Nitrate NO3 - Phosphate PO4 3- Carbonate CO3 2- Hydroxide OH- Ammonium NH4 + Acid + metal salt + hydrogen Acid + alkali (or base) salt + water Acid + carbonate salt + water + carbon dioxide Salts formed when acids react with metals, alkalis and bases are named after the acid used. Hydrochloric acid produces chlorides Nitric acid produces nitrates Sulphuric acid produces sulphates When any fuel burns carbon dioxide and water are produced. Activities: 1. Write an explanation of word equation on a mini whiteboard 2. Students complete the sheets Word equations 1 and Information to try. It is important to think about the reasons behind the answers. Ideas can be shared. 3. Describe balanced symbol equations including the states of matter. 52

54 Questions: Produce word and symbol equations for the following: 1. Iron reacts with oxygen to produce iron (III) oxide. 2. Methane burns in air to produce carbon dioxide and water vapour. 3. Magnesium reacts with sulphuric acid to produce a solution of magnesium sulphate and water. 4. Hydrochloric acid reacts with calcium carbonate to produce carbon dioxide gas, calcium chloride solution and water. 5. Zinc displaces copper from a solution of copper (II) sulphate, copper metal is produced and a colourless solution. Extension: complete your own flow diagram for producing word and balanced symbol equations. 53

55 Answers: 1. Iron reacts with oxygen to produce iron (III) oxide. a. Iron (s) + Oxygen (g) Iron (III) Oxide (s) b. 4Fe + 3O2 2Fe2O3 2. Methane burns in air to produce carbon dioxide and water vapour. a. Methane (g) + Oxygen (g) Carbon dioxide (g) + Water (g) b. CH4 + 3O2 CO2 + 2H2O 3. Magnesium reacts with sulphuric acid to produce a solution of magnesium sulphate and water. a. Magnesium(s) + Sulfuric acid(aq) Magnesium sulfate(aq) + Water(l) b. Mg + H2SO4 MgSO4 + H2O 4. Hydrochloric acid reacts with calcium carbonate to produce carbon dioxide gas, calcium chloride solution and water. a. Hydrochloric acid(aq) + Calcium carbonate(s) Carbon dioxide(g) + Calcium chloride(aq) + water (l) b. 2HCl + CaCO3 CO2 + CaCl2 + H2O 5. Zinc displaces copper from a solution of copper (II) sulphate, copper metal is produced and a colourless solution. a. Zinc(s) + Copper (II) Sulfate Zinc Sulfate(aq) + Copper(s) b. Zn + CuSO4 ZnSO4 + Cu 54

56 Intervention Questions: 1. Balance the equation: Fe + Cl2 FeCl3 2. Hydrogen and oxygen molecules are formed in a reaction where water splits apart. For this reaction: a. State the word equation b. Give the balanced symbol equation 3. Define an a. Atom b. Element c. Compound 4. What are the reactants and what are the products of a reaction? 55

57 Intervention Answers: 1. 2Fe + 3Cl2 2FeCl3 2. State the word and symbol equations for the reaction. a. Water Hydrogen + Oxygen b. 2H2O 2H2 + O2 3. Definition a. The smallest part of an element that can exist b. An element is a substance consisting of atoms which all have the same number of protons - i.e. the same atomic number. c. Composed of two or more elements 4. The reactants are the two substances that undergo change in the reaction and the products are the substances that are made. 56

58 Structure and function of ionic compounds Ionic compounds have regular structures (giant ionic lattices) in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions. These compounds have high melting points and high boiling points because of the large amounts of energy needed to break the many strong bonds. When melted or dissolved in water, ionic compounds conduct electricity because the ions are free to move and so charge can flow. Ionic bonds form when a metal reacts with a non-metal. Metals form positive ions; nonmetals form negative ions. Ionic bonds are the electrostatic forces of attraction between oppositely charged ions. Ionic lattice of sodium chloride, showing positively charged sodium ions bonded to negatively charged chloride ions Positively charged Na ions and negatively charged Cl ions The oppositely charged ions are arranged in a regular way to form giant ionic lattices. Ionic compounds often form crystals as a result. The illustration shows part of a sodium chloride (NaCl) ionic lattice. Properties of ionic compounds High melting and boiling points - Ionic bonds are very strong - a lot of energy is needed to break them. So ionic compounds have high melting and boiling points. Conductive when liquid - Ions are charged particles, but ionic compounds can only conduct electricity if their ions are free to move. Ionic compounds do not conduct electricity when they are solid - only when dissolved in water or melted. Ionic compound Sodium chloride, NaCl Magnesium oxide, MgO Properties High melting point: 800ºC Non-conductive in its solid state, but when dissolved in water or molten NaCl will conduct electricity. Higher melting point than sodium chloride: around 2,800ºC. This is because its Mg 2+ and O 2- ions have a greater number of charges, so they form stronger ionic bonds than the Na + and Cl - ions in sodium chloride. Because magnesium oxide stays solid at such high temperatures, it remains non-conductive. It is used for high-temperature electrical insulation. 57

59 Activities: 1. Extended writing: describe the electrical conductivity of ionic substances. 2. Extended writing: explain why solid ionic substances do not conduct electricity but dissolved or molten ionic substances do conduct electricity. 3. Grade 9: explain how ionic substances dissolve in water. 4. Extended writing: explain why sodium chloride is difficult to melt. Questions: See page 24 58

60 Structure and function of simple covalent compounds Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points. These substances have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils. The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points. These substances do not conduct electricity because the molecules do not have an overall electric charge. Covalent bonds form between non-metal atoms. Each bond consists of a shared pair of electrons, and is very strong. Covalently bonded substances fall into two main types: 1. Simple molecules 2. Giant covalent structures Simple molecules A molecule of carbon dioxide These contain only a few atoms held together by strong covalent bonds. An example is carbon dioxide (CO 2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen. Properties of simple molecular substances Low melting and boiling points - This is because the weak intermolecular forces break down easily. Non-conductive - Substances with a simple molecular structure do not conduct electricity. This is because they do not have any free electrons or an overall electric charge. Hydrogen, ammonia, methane and water are also simple molecules with covalent bonds. All have very strong bonds between the atoms, but much weaker forces holding the molecules together. When one of these substances melts or boils, it is these weak 'intermolecular forces' that break, not the strong covalent bonds. Simple molecular substances are gases, liquids or solids with low melting and boiling points. 59

61 Activities: 1. Research some uses of covalent substances. 2. Extension: make links between the uses of covalent substances, their properties and structure. 3. Practically test the conductivity of simple covalent substances using ethanol and solid wax pieces. 4. Extended writing: describe melting points and boiling points of covalent substances. 5. Extended writing: explain why the melting point and boiling point increases as the size of the molecule does in terms of intermolecular forces. 6. Extended writing: explain why covalent substances do not conduct electricity. 7. Grade 9: explain why pure water does not conduct electricity but tap water does conduct electricity Questions: The table below shows the melting point, boiling point and relative formula mass of a number of molecules and elements. Molecule Formula Relative formula mass Melting Point ( C) Boiling Point ( C) Chlorine Cl Argon Ar White phosphorus P Octasulfur S Draw axes of temperature in C from 200 to +300 (y-axis) against relative molecular mass from 0 to 300 (x-axis). Plot a graph of the melting point for these four formulae. Draw a straight line between each successive point you plot. On the same axes, plot a graph of the boiling point for these four formulae. Using a different coloured pen, draw a straight line between each successive point. Using another different coloured pen, draw and label a horizontal line at room temperature (25 C) 1 a Which molecules, if any, are solids at room temperature? b Which molecules, if any, are liquids at room temperature? 60

62 c Which molecules, if any, are gases at room temperature? d Which molecule is liquid over the smallest temperature range? 2 White phosphorus and octasulfur consist of atoms bonded covalently in a ring-like shape. Draw a ball-and-stick diagram for each element or molecule in the table. 3 Write down any conclusions you can draw from the graph you have drawn in relation to the relative formula mass and the melting and boiling points of molecules and elements. 61

63 Answers: 1 a White phosphorus and octasulfur are solid at room temperature. b c d None Chlorine and argon. Argon 2 3 Answers could include: The larger the relative formula mass, the larger the melting point. The larger the relative formula mass, the larger the boiling point. The above two rules don t necessarily apply in every case (the boiling point of white phosphorus is higher than that of octasulfur). The boiling point is always higher than the melting point. 62

64 Intervention Questions: 1. Four elements in Group 7 of the periodic table are fluorine, chlorine, bromine, and iodine. These elements all exist in nature as diatomic molecules, that is, molecules made up of two identical atoms with a covalent bond between them. The table shows some information about these four elements. Element Relative atomic mass Formula Fluorine 19 Fl2 Chlorine 35.5 Cl2 Bromine 80 Br2 Iodine 127 I2 a Which of these elements do you expect to have the highest melting point? Explain your answer. (2) b Using the graph you plotted in the activity, predict whether each of these elements will be a solid, a liquid, or a gas at room temperature. Show clearly on the graph how you make these predictions. (4) Fluorine: Chlorine: Bromine: Iodine: 63

65 Intervention Answers: 1 a Iodine (1) because it has the greatest relative atomic mass. (1) b Fluorine: gas (1) Chlorine: gas (1) Bromine: liquid (1) Iodine: solid (1) 64

66 Polymers Polymers have very large molecules. The atoms in the polymer molecules are linked to other atoms by strong covalent bonds. The intermolecular forces between polymer molecules are relatively strong and so these substances are solids at room temperature. Monomers and polymers Alkenes can be used to make polymers. Polymers are very large molecules made when many smaller molecules join together, end-to-end. The smaller molecules are called monomers. In general: lots of monomer molecules a polymer molecule. Alkenes can act as monomers because they are unsaturated (they have a double bond): ethene can polymerise to form poly(ethene), also called polythene propene can polymerise to form poly(propene), also called polypropylene. Displayed formulas of polymers Polymer molecules are very large compared with most other molecules, so the idea of a repeating unit is used when drawing a displayed formula. When drawing one, starting with the monomer: change the double bond in the monomer to a single bond in the repeating unit add a bond to each end of the repeating unit. Polymers have properties which depend on the chemicals they are made from, and the conditions in which they are made. For example, poly(ethene) can be low-density or highdensity depending upon the catalyst and reaction condition used to make it. The table summarises some differences in their properties: 65

67 LDPE low-density poly(ethene) HDPE high-density poly(ethene) Branches on polymer molecules Many Few Relative strength Weak Strong Maximum useable temperature 85 C 120 C Thermosoftening polymers Polymer with no cross-links Thermosoftening polymers soften when heated and can be shaped when hot. The shape will harden when it is cooled, but can be reshaped when heated up again. Poly(ethene) is a thermosoftening polymer. Its tangled polymer chains can uncoil and slide past each other, making it a flexible material. Thermosetting polymers Polymer with cross-links Thermosetting polymers have different properties to thermosoftening polymers. Once moulded, they do not soften when heated and they cannot be reshaped. Vulcanised rubber is a thermoset used to make tyres. Its polymer chains are joined together by cross-links, so they cannot slide past each other easily. Activities: 1. Model polymers. 2. Make a polymer from cornstarch. 3. Investigate the properties of plastic bags. 4. Extended writing: explain how ethene polymerises 66

68 Questions: 1. Which two elements are found in hydrocarbons? 2. The molecular formula for ethanol is C 2H 4OH. Is ethanol a hydrocarbon, explain your answer. 3. Describe the difference between an alkane and an alkene. 4. Describe the difference between an unsaturated hydrocarbon molecule and a saturated hydrocarbon molecule 5. What is the name of the process that joins monomers together? 6. The molecular formula for ethane is C 2H 6. a. Draw the displayed formula for ethane. b. How many carbon atoms are in a molecule of ethane? c. How many hydrogen atoms are in a molecule of ethane? d. How many atoms are in a molecule of ethane? 7. The molecular formula for ethene is C 2H 4. a. Draw the displayed formula for ethene. b. How many carbon atoms are there in a molecule of ethene? c. How many hydrogen atoms are there in a molecule of ethane? 8. What is the name of the process that joins monomers together? 9. Name the monomer that is used to make the polymer called poly(ethene). 10. Name the polymer made from the monomer called propene. 11. Which types of molecules are used as monomers in addition polymerisation saturated or unsaturated molecules? 12. Which of the following types of molecules are used as monomers: alkanes or alkenes? 13. Write down the displayed formula for the following hydrocarbons: a. ethene C 2H 4 b. poly(ethene) 14. What are the conditions required for polymerisation? 15. Name three different types of polymers. 16. Describe the properties of nylon. 17. Explain the difference between Gore-Tex and nylon. 18. List the properties that Gore-Tex and nylon have in common. 19. What function does the PTFE layer in Gore-Tex have? 20. Describe a use for LDPE - low density poly(ethene). Describe a use for HDPE high density poly(ethene). 21. Describe two uses for polystyrene. 22. Explain what is meant by a non-biodegradable polymer. 23. Describe some problems with non-biodegradable polymers (most plastics). 24. Describe three ways in which waste polymers can be disposed of. Extension: Chemists are developing new types of polymers, suggest a reason for developing a polymer that can be used to wrap dishwasher detergent tablets. 67

69 Answers: 1. Which two elements are found in hydrocarbons? Answer Hydrocarbon molecules are only made of hydrogen and carbon atoms. 2. The molecular formula for ethanol is C 2H 4OH. Is ethanol a hydrocarbon, explain your answer. Answer Ethanol is not a hydrocarbon because it contains oxygen atoms and hydrocarbons only contain hydrogen and carbon atoms. 3. Describe the difference between an alkane and an alkene. Answer Alkene molecules contain a double carbon-carbon bond, whereas alkanes do not. 4. Describe the difference between an unsaturated hydrocarbon molecule and a saturated hydrocarbon molecule Answer Saturated hydrocarbon molecules contain only single carbon-carbon bonds, whereas unsaturated hydrocarbon molecules contain double carbon-carbon bonds. 5. What is the name of the process that joins monomers together? Answer Addition Polymerisation 6. The molecular formula for ethane is C 2H 6. a. Draw the displayed formula for ethane. Answer b. How many carbon atoms are in a molecule of ethane? Answer 2 c. How many hydrogen atoms are in a molecule of ethane? Answer - 6 d. How many atoms are in a molecule of ethane? Answer The molecular formula for ethene is C 2H 4. a. Draw the displayed formula for ethene. Answer b. How many carbon atoms are there in a molecule of ethene? Answer - 2 c. How many hydrogen atoms are there in a molecule of ethane? Answer What is the name of the process that joins monomers together? Answer Addition Polymerisation 9. Name the monomer that is used to make the polymer called poly(ethene). Answer Ethene 68

70 10. Name the polymer made from the monomer called propene. Answer Poly(propene) 11. Which types of molecules are used as monomers in addition polymerisation saturated or unsaturated molecules? Answer Unsaturated molecules 12. Which of the following types of molecules are used as monomers: alkanes or alkenes? Answer Alkenes 13. Write down the displayed formula for the following hydrocarbons: c. ethene C 2H 4 d. poly(ethene) 14. What are the conditions required for polymerisation? Answer High pressure and catalyst. 15. Name three different types of polymers. Answer Some common polymers are: poly(ethene); poly(propene); Polystyrene; polyvinyl chloride (PVC); nylon. 16. Describe the properties of nylon. Answer Nylon is waterproof, flexible and it has a low density. 17. Explain the difference between Gore-Tex and nylon. Answer Gore-Tex is breathable nylon is not breathable. 18. List the properties that Gore-Tex and nylon have in common. Answer Gore-Tex and Nylon are both waterproof, flexible and both have a low density. 19. What function does the PTFE layer in Gore-Tex have? Answer The PTFE layer is breathable it allows water vapour to pass through but it does not allow water droplets to pass through. 20. Describe a use for LDPE - low density poly(ethene). Describe a use for HDPE high density poly(ethene). Answer LDPE can be used to make plastic carrier bags and HDPE is used to make garden furniture. 21. Describe two uses for polystyrene. Answer Packaging and insulation. 22. Explain what is meant by a non-biodegradable polymer. Answer A polymer that will not decompose by living organism known as decomposers. 23. Describe some problems with non-biodegradable polymers (most plastics). Answer They do not decompose in landfill sites, litter the countryside. 24. Describe three ways in which waste polymers can be disposed of. Answer Landfill, incineration (burning), recycling. Extension Chemists are trying to develop more useful polymers such as those that are soluble in water.why 69

71 Intervention Questions: In GCSE Chemistry you will not have looked at many addition polymers, possibly just poly(ethene) and poly(propene). However, there are many, many more. In this worksheet you are going to research several more polymers and find out about their properties and uses. Once you have filled in the grid then answer the questions that follow. Monomer Polymer repeating unit Systemic chemical name Typical uses Poly(ethene) Poly(propene) Poly(chloroethene ) Poly(propenenitril e) Poly(tetrafluoroeth ene) Questions 1 Explain what is mean by these terms:8 a monomer (1 mark) b repeating unit. (1 mark) 2 Is poly(ethene) an alcohol, an alkane or an alkene? mark) (1 3 A sample of poly(ethene) has an average relative molecular mass of How many monomers are linked together to form the chain? (Ar values: C = 12, H = 1) 70

72 marks) (2 4 a Draw a section of the polymer formed from this monomer, showing six carbon atoms in your diagram. (2 marks) b What is the common name for the polymer? (1 mark) c What is the systematic name of the polymer? (1 mark) 71

73 Intervention Answers: Monomer Polymer repeating unit Systemic chemical name Typical uses Poly(ethene) e.g., packaging Poly(propene) e.g., packaging, textiles, polymer banknotes Poly(chloroethene) e.g., construction, food packaging Poly(propenenitrile) e.g., used to produce carbon fibre Poly(1,1,2,2- tetrafluoroethene) e.g., Teflon, nonstick cookware Answers to main questions 1 a a monomer is a small reactive molecule that joins in repeating sequences to form a very large molecule. (1 mark) b the repeating unit of a polymer is the smallest group of atoms that produce the polymer when repeated over and over. (1 mark) 2 Polyethene is an alkane (1 mark) (2 marks) a (2 marks) b PVC, polyvinylchloride (1 mark) c Poly(chloroethene) (1 mark) 72

74 Giant covalent compounds Substances that consist of giant covalent structures are solids with very high melting points. All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. Diamond and graphite (forms of carbon) and silicon dioxide (silica) are examples of giant covalent structures. Giant covalent structures contain a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds. The atoms are usually arranged into giant regular lattices - extremely strong structures because of the many bonds involved. The graphic shows the molecular structure of diamond and graphite: two allotropes of carbon, and of silica (silicon dioxide). From left to right - graphite, diamond, silica Properties of giant covalent structures Very high melting points - Substances with giant covalent structures have very high melting points, because a lot of strong covalent bonds must be broken. Graphite, for example, has a melting point of more than 3,600ºC. Variable conductivity - Diamond does not conduct electricity. Graphite contains free electrons, so it does conduct electricity. Silicon is semi-conductive - that is, midway between non-conductive and conductive. Activities: 1. Extended writing: describe the structure of diamond, silicon dioxide and graphite. 2. Extended writing: explain how covalent substances boil. 3. Research some uses of covalent substances. 4. Extension: make links between the uses of covalent substances, their properties and structure. 73

75 Questions: 1. Identify the following carbon allotropes: graphite, diamond and Buckminster fullerene: 2. List the physical properties of diamond. 3. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. 4. Explain, in terms of structure and bonding, why diamond does not conduct electricity. 5. List the physical properties of graphite. Extension: Write a short article to promote the use of giant covalent compounds. (Marketing add) 74

76 Answers: 1. Identify the following carbon allotropes: graphite, diamond and Buckminster fullerene: Answer - The different carbon allotropes are: diamond graphite Bukminster fullerene 2. List the physical properties of diamond. Answer - The physical properties of diamond are: lustrous, colourless and clear (transparent) hard and has a high melting point does not conduct electricity insoluble in water 3. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. Answer - Diamond is used in cutting tools because it is hard and it has a high melting point. Diamond is used in jewellery because it is lustrous and insoluble in water. 4. Explain, in terms of structure and bonding, why diamond does not conduct electricity. Answer - Diamond does not contain delocalised electrons therefore it cannot conduct electricity. It does not contain delocalised electrons because each carbon atom is joined to four other carbon atoms. 5. List the physical properties of graphite. Answer - The physical properties of graphite are: slippery conducts electricity insoluble in water high melting point black, lustrous and opaque 75

77 Intervention Questions: 1.. a. Name two forms of the element carbon b. Find out what chemists call different forms of the same element in the same state. 2. List the general properties of a substance with a typical giant covalent structure. 3. Draw a rough sketch of the structure of graphite. Insert a plus and minus sign to represent the terminals of the battery attached to the ends of the graphite. On your sketch use arrows to indicate the movement of the electrons when an electric current flows through the graphite. 4. Graphite is sometimes used to reduce the friction between two surfaces that are rubbing together. Explain how it does this. 5. Explain why graphite can conduct electricity. 76

78 Intervention Answers: 1.. a. Diamond/Graphite b. Allotropes 2. Very high melting and boiling points, hard, insoluble in water, electrical insulators. 3. Layers of hexagonally arranged carbon atoms, arrows from negative to positive charge. 4. Weak forces between layers of graphite atoms so they slip and slide over each other to act as a lubricant. 5. Graphite: hexagons of Carbon atoms arranged in layers. Each carbon atom forms three strong covalent bonds to its nearest neighbours. Because the carbon atoms have 4 electrons in their outer shell, this leaves one free outer electron on each. The free electrons drift freely along layers, enabling graphite to conduct electricity. Diamond: All outer shell electrons are involved in covalent bonding and therefore there are no free electrons to carry the electrical charge. 77

79 Metals as conductors Metals have giant structures of atoms with strong metallic bonding. This means that most metals have high melting and boiling points. In pure metals, atoms are arranged in layers, which allows metals to be bent and shaped. Pure metals are too soft for many uses and so are mixed with other metals to make alloys which are harder. Metals are good conductors of electricity because the delocalised electrons in the metal carry electrical charge through the metal. Metals are good conductors of thermal energy because energy is transferred by the delocalised electrons. Activities: 1. Extended writing: describe melting points and boiling points of metallic substances. 2. Extended writing: explain why metallic substances conduct electricity. 3. Extended writing: explain why the melting point and boiling point of metallic substances are high. 4. Extended writing: describe the structure of metal alloys. 5. Research some uses of metallic substances. 6. Extension: make links between the uses of metal substances, their properties and structure. 7. Research some uses of metal alloys. 8. Extension: make links between the uses of metal alloys, their properties and structure. Questions: See page: 78

80 4.2.3 Structure and bonding of Carbon Diamond In diamond, each carbon atom forms four covalent bonds with other carbon atoms in a giant covalent structure, so diamond is very hard, has a very high melting point and does not conduct electricity. Diamond is one allotrope of carbon. Its properties include: Lustrous (shiny) Colourless and clear (transparent) Hard High melting point Insoluble in water (does not dissolve) Does not conduct electricity Diamond is used in jewellery because, when cut by experts, it will sparkle and reflect light in an attractive way. Lattice of connected atoms Diamond Diamond's hardness and high melting point make it useful for cutting tools, such as the diamond-tipped discs used to cut bricks and concrete. Heavy-duty drill bits, like those used to drill through rocks in the oil exploration industry, are made with diamonds so that they stay sharp for longer. Structure and bonding Diamond has a giant molecular structure. Each carbon atom is covalently bonded to four other carbon atoms. A lot of energy is needed to separate the atoms in diamond. This is because covalent bonds are strong, and diamond contains very many covalent bonds. This makes diamond's melting point and boiling point very high. There are no free electrons or ions in diamond, so it does not conduct electricity. Activities: 1. Research the properties of diamond. 2. Model the structure of diamond using model kits. 3. Extended writing: link the properties of diamond to the structure. Questions: 1. List the physical properties of diamond. 2. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. 3. Explain, in terms of structure and bonding, why diamond does not conduct electricity. 79

81 Answers: 1. List the physical properties of diamond. Answer - The physical properties of diamond are: lustrous, colourless and clear (transparent) hard and has a high melting point does not conduct electricity insoluble in water 2. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. Answer - Diamond is used in cutting tools because it is hard and it has a high melting point. Diamond is used in jewellery because it is lustrous and insoluble in water. 3. Explain, in terms of structure and bonding, why diamond does not conduct electricity. Answer - Diamond does not contain delocalised electrons therefore it cannot conduct electricity. It does not contain delocalised electrons because each carbon atom is joined to four other carbon atoms. 80

82 Graphite In graphite, each carbon atom forms three covalent bonds with three other carbon atoms, forming layers of hexagonal rings which have no covalent bonds between the layers. In graphite, one electron from each carbon atom is delocalised. Graphite is another allotrope of carbon. Like diamond, its properties include: Lustrous High melting point Insoluble in water However, unlike diamond, graphite is: Black and opaque (you cannot see through it) Slippery An electrical conductor lattice of connected atoms Graphite Graphite is used inside pencils. It slips easily off the pencil onto the paper and leaves a black mark. Graphite is also a component of many lubricants, for example bicycle chain oil, because it is slippery. Structure and bonding Like diamond, graphite has a giant molecular structure. As its covalent bonds are very strong, and there are many of them, a lot of energy would be needed to separate atoms. This makes graphite's melting point and boiling point very high. However, each carbon atom is only covalently bonded to three other carbon atoms, rather than to four as in diamond. Graphite contains layers of carbon atoms. The layers slide over each other easily because there are only weak forces between them, making graphite slippery. Graphite contains delocalised electrons (free electrons). These electrons can move through the graphite, carrying charge from place to place and allowing graphite to conduct electricity. Activities: 1. Extended writing: link the properties of graphite to the structure. 2. Extended writing: explain why graphite conducts electricity. 3. Research the properties of graphite. 4. Model the structure of graphite using model kits. 81

83 Questions: 1. List the physical properties of graphite. 2. Explain, in terms of properties, why graphite is used in pencil leads. 3. Explain, in terms of properties, why graphite is used in lubricants. 4. Explain, in terms of structure and bonding, why graphite conducts electricity. 5. Explain, in terms of structure and bonding, why graphite is slippery. 82

84 Answers: 1. List the physical properties of graphite. Answer - The physical properties of graphite are: slippery conducts electricity insoluble in water high melting point black, lustrous and opaque 2. Explain, in terms of properties, why graphite is used in pencil leads. Answer - Graphite is black and slippery, it easily wears away leaving a black mark on the paper. 3. Explain, in terms of properties, why graphite is used in lubricants. Answer - Graphite is used as a lubricant because it is slippery and has a high melting point. 4. Explain, in terms of structure and bonding, why graphite conducts electricity. Answer - Graphite conducts electricity because it contains free delocalised electron. Each carbon atom in graphite is joined to three other carbon atoms instead of the four possible bonds it could make, because of this there are free electrons that are able to move around and conduct electricity. 5. Explain, in terms of structure and bonding, why graphite is slippery. Answer - Graphite is slippery because it is made up of layers that are held together by weak forces. 83

85 Graphene Graphene is a single layer of graphite and has properties that make it useful in electronics and composites. Fullerenes are molecules of carbon atoms with hollow shapes. The structure of fullerenes is based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms. The first fullerene to be discovered was Buckminsterfullerene (C 60) which has a spherical shape. Carbon nanotubes are cylindrical fullerenes with very high length to diameter ratios. Their properties make them useful for nanotechnology, electronics and materials. Structure of a buckminsterfullerene molecule - a large ball of 60 atoms The fullerenes are a large class of allotropes of carbon and are made of balls, cages or tubes of carbon atoms. Buckminster fullerene is one type of fullerene. Its molecules have 60 carbon atoms arranged in a hollow sphere. Nanotubes Nanotubes are fullerenes that can be used to reinforce graphite in tennis rackets because they are very strong. They are also used as semiconductors in electrical circuits. The nanotube's structure allows it to be used as a container for transporting a drug in the body. A molecule of the drug can be placed inside the nanotube cage. This keeps the drug 'wrapped up' until it reaches the site where it is needed. In this way, a dose that might be damaging to other parts of the body can be delivered safely to, for example, a tumour. Activities: 1. Extended writing: link the properties of graphene to the structure. 2. Extended writing: describe the history of fullerenes. 3. Research the properties of graphene. 4. Research uses of fullerenes. 84

86 Questions: 1. What type of structure is used to reinforce tennis racquets because it is very strong? 2. Explain why fullerenes can be used in new drug delivery systems. 3. Explain how the structure of nanotubes enables them to be used as catalysts. 85

87 Answers: 1. What type of structure is used to reinforce tennis racquets because it is very strong? Answer - Fullerene molecules joined together to make nanotubes are very strong and are used to reinforce tennis racquets. 2. Explain why fullerenes can be used in new drug delivery systems. Answer - Fullerene cages can be used to cage drug molecules, they can then be coated and injected into the body. The coating could be made to target particular areas of the body 3. Explain how the structure of nanotubes enables them to be used as catalysts. Answer - Nanotubes can be coated with other catalysts, stacked side by side they have a huge surface area increasing the frequency of collisions between reactants. 86

88 Allotropes of carbon intervention questions: 1. Identify the following carbon allotropes: graphite, diamond and Buckminster fullerene: 2. Explain why diamond, graphite and fullerenes are allotropes of carbon.. 3. List the physical properties of diamond. 4. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. 5. Explain, in terms of structure and bonding, why diamond does not conduct electricity. 6. List the physical properties of graphite. 7. Explain, in terms of properties, why graphite is used in pencil leads. 8. Explain, in terms of properties, why graphite is used in lubricants. 9. Explain, in terms of structure and bonding, why graphite conducts electricity. 10. Explain, in terms of structure and bonding, why graphite is slippery. 11. Explain, in terms of structure and bonding, why diamond and graphite has a high melting point. 12. Explain why diamond and graphite have a giant molecular structure. 13. What type of structure is used to reinforce tennis racquets because it is very strong? 14. Explain why fullerenes can be used in new drug delivery systems. 15. Explain how the structure of nanotubes enables them to be used as catalysts. 87

89 Intervention Answers: 1. Identify the following carbon allotropes: graphite, diamond and Buckminster fullerene: Answer - The different carbon allotropes are: diamond graphite Bukminster fullerene 2. Explain why diamond, graphite and fullerenes are allotropes of carbon. Answer - Allotropes are different forms of the same element in the same physical state. Diamond, graphite and Buckminster fullerenes are allotropes of carbon because they are different forms of solid carbon. 3. List the physical properties of diamond. Answer - The physical properties of diamond are: lustrous, colourless and clear (transparent) hard and has a high melting point does not conduct electricity insoluble in water 4. Explain, in terms of properties, why diamond is used in cutting tools and jewellery. Answer - Diamond is used in cutting tools because it is hard and it has a high melting point. Diamond is used in jewellery because it is lustrous and insoluble in water. 5. Explain, in terms of structure and bonding, why diamond does not conduct electricity. Answer - Diamond does not contain delocalised electrons therefore it cannot conduct electricity. It does not contain delocalised electrons because each carbon atom is joined to four other carbon atoms. 6. List the physical properties of graphite. Answer - The physical properties of graphite are: slippery conducts electricity insoluble in water high melting point black, lustrous and opaque 88

90 7. Explain, in terms of properties, why graphite is used in pencil leads. Answer - Graphite is black and slippery, it easily wears away leaving a black mark on the paper. 8. Explain, in terms of properties, why graphite is used in lubricants. Answer - Graphite is used as a lubricant because it is slippery and has a high melting point. 9. Explain, in terms of structure and bonding, why graphite conducts electricity. Answer - Graphite conducts electricity because it contains free delocalised electron. Each carbon atom in graphite is joined to three other carbon atoms instead of the four possible bonds it could make, because of this there are free electrons that are able to move around and conduct electricity. 10. Explain, in terms of structure and bonding, why graphite is slippery. Answer - Graphite is slippery because it is made up of layers that are held together by weak forces. 11. Explain, in terms of structure and bonding, why diamond and graphite has a high melting point. Answer - Diamond and graphite have high melting points because they contain large numbers of strong covalent bonds between carbon atoms, and it takes a lot of energy to break many strong covalent bonds. 12. Explain why diamond and graphite have a giant molecular structure. Answer - A giant molecule contains large numbers of atoms joined by covalent bonds, both diamond and graphite contain large numbers of carbon atoms joined by covalent bonds. 13. What type of structure is used to reinforce tennis racquets because it is very strong? Answer - Fullerene molecules joined together to make nanotubes are very strong and are used to reinforce tennis racquets. 14. Explain why fullerenes can be used in new drug delivery systems. Answer - Fullerene cages can be used to cage drug molecules, they can then be coated and injected into the body. The coating could be made to target particular areas of the body 15. Explain how the structure of nanotubes enables them to be used as catalysts. Answer - Nanotubes can be coated with other catalysts, stacked side by side they have a huge surface area increasing the frequency of collisions between reactants. 89

91 4.2.2 Bulk and surface properties of matter including nanoparticles (Chemistry only) Nano dimensions Nanoscience refers to structures that are nm in size, of the order of a few hundred atoms. Nanoparticles are smaller than fine particles (PM 2.5), which have diameters between 100 and 2500 nm (1 x 10-7 m and 2.5 x 10-6 m). Coarse particles (PM 10) have diameters between 1 x 10-5 m and 2.5 x 10-6 m. Coarse particles are often referred to as dust. As the side of cube decreases by a factor of 10 the surface area to volume ratio increases by a factor of 10. Nanoparticles may have properties different from those for the same materials in bulk because of their high surface area to volume ratio. It may also mean that smaller quantities are needed to be effective than for materials with normal particle sizes. Units used to measure length Unit name Unit symbol Meaning gigametre Gm one billion metres megametre Mm one million metres kilometre km one thousand metres metre m one metre millimetre mm one thousandth of a metre micrometre µm one millionth of a metre nanometre nm one billionth of a metre Activities: 1. Extended writing: describe the history of nanoscience 90

92 Questions: 1. State each of the units below in metres using standard form, for example, 1 cm = m. a 1 mm (1 mark) b 1 μm (1 mark) c 1 nm (1 mark) d 1 pm (1 mark) 2 a Nanoparticles are typically about 100 nm in diameter. State the size of a nanoparticle in units of metres. Give your answer in standard form. (1 mark) b A typical atom has a radius of 100 pm. State the size of the radius of an atom in units of metres. Give your answer in standard form. (1 mark) c Which is smaller, a nanoparticle or an atom? (1 mark) 91

93 3 The size of each of the objects below is given using the appropriate units. a State the size of each item in units of metres in decimal form. (5 marks) b State the size of each item in units of metres in standard form. (5 marks) c List the objects in order of size from largest to smallest. (1 mark) d Calculate how many times smaller the radius of an atom s nucleus is compared with the radius of the atom itself? (1 mark) 92

94 Answers: 1 a 1 mm = m (1 mark) b 1 μm = m (1 mark) c 1 nm = m (1 mark) d 1 pm = m (1 mark) 2 a 100 nm = m (1 mark) b 100 pm = m (1 mark) c An atom is smaller than a nanoparticle. (1 mark) 3 a and b Pin head = m = m Bucky ball = m = m Human hair = m = m Atom = m = m Nucleus = m = m (1 mark for each correct size in decimal form and 1 mark for each correct size in standard form) mark) c Largest: pin head; human hair; bucky ball; atom; nucleus: Smallest (1 d m m = , that is, the nucleus is times smaller than the atom. (1 mark) 93

95 Intervention Questions: 1. What is meant by nanoscience? 2. A nanoparticle has a diameter of 50nm. Give this diameter in: a. Meters (m) b. Micrometres ( m) 3. Look at the using maths box. Show that the pattern in the surface area to volume ratio continues for a cube of side: a. 0.1cm b. 10m 4. Explain why the properties of nanoparticles of a material may differ from the properties of the bulk material. 94