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Mr Daniel Worrall Mr Worrall Mr Dan IGCSE Chemistry UNIT 10: Structure and Bonding UNIT 1: Periodic Table UNIT 2: Air and Water UNIT 3: Acid, Alkalis and Salts UNIT 4: Organic Chemistry UNIT 5: Chemical Analysis Techniques UNIT 6: Amount of Substance UNIT 7: Electrochemistry UNIT 8: Periodic Table 2 UNIT 9: Organic Chemistry 2 Core curriculum Grades C to G available Extended curriculum Grades A* to G available Paper 1 (45 minutes) Compulsory A multiple-choice paper consisting of forty items of four-choice type. The questions will be based on the Core curriculum, and will be of a difficulty appropriate to grades C to G. This paper will be weighted at 30% of the final total available marks. Either: Paper 2 (1 hour 15 minutes) Core theory paper consisting of 80 marks of short-answer and structured questions. The questions will be of a difficulty appropriate to grades C to G. The questions will be based on the Core curriculum. The Paper will be weighed at 50% of the final total available marks. Or: Paper 3 (1 hour 15 minutes) Extended theory paper consisting of 80 marks of short-answer and structured questions. The questions will be of a difficulty appropriate to the higher grades. A quarter of the marks available will be based on Core material and the remainder on the Supplement. The Paper will be weighed at 50% of the final total available marks. Practical Assessment Candidates will not be required to use knowledge outside the Core curriculum. Paper 6 Alternative to Practical (1 hour). This is a written paper designed to test familiarity with laboratory based procedures. The practical assessment will be weighted at 20% of the final total available marks. Bonding and Structure Section 1:Kinetic particle theory Learning objective By the end of this period, candidates should be able to : Describe the states of matter and explain their conversion in terms of the kinetic particle theory; What is matter? Matter is defined as anything that occupies space & has mass. Examples ? States of Matter Matter can exist as a solid, liquid, gas. Task: Fill in the blanks with ‘definite’ or ‘not definite’. Physical state Volume Shape Example Solid Ice Liquid Water Gas Water vapor States of Matter Matter can exist as a solid, liquid, gas. Physical state Solid Volume Shape Example Definite Definite Ice Liquid Definite Not definite Water Gas Not definite Not definite Water vapuor Solid, Liquid, Gas Kinetic Theory of Matter 1. All matter is made of many small discrete particles (atoms, ions, & molecules) In solids, the particles are closely packed in orderly manner. In liquids, the particles are not as closely packed as solids and are arranged in disorderly manner. In gases, the particles are distributed very far apart in random manner. Kinetic Theory of Matter 2. The particles are always in constant random motion. In solids, the particles vibrate about their fixed positions. In liquids, the particles move about sliding and rolling past one other in random motion. In gases, the particles move about freely at high speeds and in random motion. Interconversion between the three states of matter Task: Use the words below to fill in the gaps… Evaporation slowly liquid cooled vibrate x 2 melting quicker expand boiling forces gas In-class activity Crossword 10min Plenary List 3 things you learnt today Homework Homework sheet Properties Solid Liquid Gas Shape Fixed Takes the shape of the container Takes the shape of the container Diagram showing the arrangement of particles Forces of attraction Very strong Strong between particles (Intermolecular forces) Very weak Motion of particles Vibrate about their fixed positions Roll and slide past each other Random motion Move about freely at high speeds Random motion Energy content Low Moderate High Physical properties of the solid, liquid and gaseous states Solid Liquid Gas Volume Fixed fixed Same as the volume of the container Density High Moderate Low Compressibility Cannot be compressed Cannot be compressed Highly compressible Fluidity Does not flow Generally flows easily Flows easily Heating curve Bonding and structure Part 2: Diffusion Starter Work with the person sitting next to you to match the definitions to the correct word. Solids, Liquids and Gases 1. Why can solids not flow? Solid particles are not free to move about. 2. Why can you squash gases more than liquids? There are more spaces in between the particles in gases than in liquids. 3. Which state of matter has a fixed shape and volume? The solid state. 4. In which state are the particles closest together? Solids. 5. In which state are the particles furthest apart? Gases. Can you write three bullet points about each state of matter. Arrangement The particles in a solid are arranged………. Forces They have _________ interactive forces between particles. Movement Solid particles are unable to move about but can ___________ Learning objective By the end of this period, candidates should be able to : Describe and explain diffusion; Describe evidence for the movement of particles in gases and liquids Describe dependence of rate of diffusion on molecular mass. Diffusion is the random movement of particles from a place of high concentration to a place of low concentration. How Does Diffusion Work? Initially the aftershave particles and air particles are separate When allowed to, the aftershave particles begin to move through the available spaces… Eventually the aftershave particles and gas particles in the air are totally mixed. In LIQUIDS diffusion occurs a lot MORE SLOWLY because there are NOT AS MANY GAPS in between the particles. Diffusion Diffusion is the seemingly random movement of a substance from where these particles are in high concentration to where there are fewer. The diffusion stops where there is no concentration gradient existing. The diffusion of gases The lighter the particles of gas, the faster the gas will diffuse. Example: A particle of ammonia gas has about half the mass of a particle of hydrogen chloride so it will diffuse faster. This is shown in your notes. The cloud formed when the two gases meet is nearer to the hydrogen chloride than the ammonia. Bonding and structure Part 3: Atom Starter What is diffusion? Learning objective By the end of this period, candidates should be able to : State the relative charges and approximate relative masses of protons, neutrons and electrons; Define proton number and nucleon number; Calculate the proton number and mass number from given information. Element Elements are substances that cannot be chemically broken down into simpler substances. It is made of one type of atom… History of the Atom Democritus: Ancient Greek Philosopher-Scientist, ‘a tomos’ – cannot be cut. The problem: he was unable to provide the evidence needed to convince people that atoms really existed. Atom: The smallest part of an element that can exist as a stable entity. History of the Atom In 1808, an English school teacher named John Dalton proposed that atoms could not be divided and that all atoms of a given element were exactly alike. Dalton’s theory is considered the foundation for the modern atomic theory. Dalton’s theory was developed with scientific basis and was accepted by others. History of the Atom At the end of the nineteenth century, a scientist called J.J. Thomson discovered the electron. Thomson suggested that they could only have come from inside atoms. So Dalton's idea of the indestructible atom had to be revised. Thomson imagined the electrons as the bits of plum in a plum pudding History of the Atom In 1872-1937, Rutherford et al. ran experiments to determine the structure of an atom. He found a dense, positively charged central region containing most of the atomic mass and that the atom is mostly space. History of the Atom In the 1920’s deBroglie & Shrodinger showed that the “solar system” model of the atom was incorrect. Instead, electrons orbit the nucleus in orbitals. This is called quantum mechanics. We will look at this in our next lesson. Even Smaller Particles! • For some time people thought atoms were the smallest particles and that they could not be broken into anything smaller. • We now know that atoms are themselves made from even smaller and simpler particles. • These particles are • Protons • Neutrons • Electrons Structure of Atoms Neutron The protons and neutrons are found in the middle of the atom, this is called the nucleus. Proton Electron The electrons orbit around the outside of the nucleus. Lithium atom Properties of Sub-atomic Particles There are two properties of sub-atomic particles that are especially important: Mass Electrical charge Particle Charge Relative Mass Location in atom Protons +1 1 In nucleus Neutrons 0 1 In nucleus Electrons -1 negligible Outside nucleus Element atoms contain equal numbers of protons and electrons and so have no overall charge An example There are 12 electrons • There are 12 protons • There are 24 protons and neutrons in the nucleus • There are 12 neutrons Potassium 19 electrons 19 protons 39 protons and neutrons in the nucleus 20 neutrons Working out the numbers of protons and neutrons No of protons = ATOMIC NUMBER of the atom The atomic number is also given the more descriptive name of proton number. No of protons + no of neutrons = MASS NUMBER of the atom The mass number is also called the nucleon number. This information can be given simply in the form: How many protons and neutrons has this atom got? The atomic number counts the number of protons (9); the mass number counts protons + neutrons (19). If there are 9 protons, there must be 10 neutrons for the total to add up to 19. Atomic number (Z)=number of protons in the nucleus, Mass number (A)=number of protons +number of neutrons. A Z X Bonding and structure Part 4:Isotopes Atom: The smallest part of an element that can exist as a stable entity. Structure of Atoms Neutron The protons and neutrons are found in the middle of the atom, this is called the nucleus. Proton Electron The electrons orbit around the outside of the nucleus. Lithium atom Learning objective By the end of this period, candidates should be able to : Define isotopes; State the two types of isotopes as being radioactive and non-radioactive; State one medical and one industrial use of radioactive isotopes; Describe radioactive isotopes, such as 235U as a source of energy. Starter Atom 24 13 X 28 13 X Number of protons Number of neutrons Number of electrons Isotopes Isotopes are atoms of the same element with different mass numbers; They have the same number of protons and electrons in each atom, but different numbers of neutrons in the nucleus. Properties of Isotopes Same chemical propertiesthe same number of electrons; Different physical properties the different masses of the atoms Relative atomic masses Ar The relative atomic mass (Ar ) is the average mass of an atom of an element, taking account of its natural isotopes and their percentage abundance. Radio-isotopes Some isotopes have unstable nuclei; they are radio-isotopes and emit various forms of radiation. Uses of isotopes: Carbon Dating Carbon has three isotopes: C-12 and C13 are stable. C-14 is unstable and emits alpha particles Used to find the age of ancient materials. Living wood has a tiny proportion of radioative carbon C-14 The Shroud of Turin Oxford University, the University of Arizona, and the Swiss Federal Institute of Technology, agreed with a dating in the 13th to 14th centuries (1260–1390). Smoke Detectors It can detect particles of smoke that are too small to be visible. It includes a tiny mass of radioactive americium-241, which is a source of alpha radiation. The radiation passes through a chamber. Any smoke that enters the chamber absorbs the alpha particles, setting off the alarm. Medical Tracers PET scan The PET scanner detects gamma rays Thickness Control in Manufacturing 235 U (Homework) Write about some of the advantages and disadvantages of using 235 U as a source of energy, possible issues for discussion include the long term nature of nuclear energy (sustainable long after coal and oil run out) and environmental considerations such as the disposal of radioactive waste (make it simple but clear, 150-200 words.) Structure and Bonding Part 5: Elements, mixtures and compounds What is… An atom? An element? A compound? A mixture? What is… An atom? The smallest part of an element. An element? Something made up of only one type of atom or something that cannot be broken down by chemical means. A compound? Two or more elements chemical joined. A mixture? Two or more elements or compounds which are NOT chemically joined. Drawing Use and An atom An element A compound A mixture to represent Drawing An atom An element A compound A mixture or What are these? Element, compound or mixture? Which might be Neon, air, oxygen, water, carbon dioxide? How many atoms are present in the molecules below? Oxygen O2 Iron oxide Fe2O3 Sodium chloride NaCl Copper sulphate CuSO4 Ammonia NH3 Copper oxide CuO Methane CH4 Water H2O Odd one out Magnesium, aluminium, lead, silicon Ca, Cu, Cl, Cs CO, Co, Ca, Cu Helium, argon, hydrogen, krypton Li, Na, K, Fe Lithium, nitrogen, oxygen, carbon Unit 10: Structure and Bonding Part 6: Metallic Bonding Describe the properties of metals and non metals Describe how metals are used according to their properties Describe the structure of metals and how the structures result in a metals properties Describe the structure of alloys The Periodic Table Non Metals H He 1 2 Li Be B C N O F Ne 3 4 5 6 7 8 9 10 Na M g Al 4 11 13 P S Cl Ar 15 16 17 18 12 K Ca Sc Ti V Cr 19 20 21 22 23 24 M n Fe Co Ni Cu Zn Ga Ge As Se Br Kr 26 27 28 29 30 31 32 33 34 35 36 Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 43 44 45 46 47 48 49 50 51 52 53 54 25 Rb Sr Y Zr Nb 37 38 39 40 41 M o 42 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Metals Al Au Ti Fe Cu Properties of Materials Ductile Can be drawn into wires. Strong Resistant to forces. Brittle Easy to break (but hard). Malleable Transparent Electrical conductor Electrical insulator Heat conductor Heat insulator Flexible Sonorous Can be hammered into shape. ‘See-through’. Lets electricity flow through it easily. Does not let electricity flow through it easily. Lets heat through it easily. Does not let heat through it easily. Can change its shape without snapping. Make a ringing sound when struck. Properties of Materials Property Metals Appearance Shiny Melting and boiling point Density Strength Malleability Ductility Heat Conductivity Electrical Conductivity Non-Metals What is the structure of metals? The atoms in a pure metal are in tightly-packed layers, which form a regular lattice structure. sea of electrons The outer electrons of the metal atoms separate from the atoms and create a ‘sea of electrons’. These electrons are delocalized and so are free to move through the whole structure. The metal atoms become positively charged ions and are attracted to the sea of electrons. This attraction is called metallic bonding. metal ions Why are metals strong? Metals are usually strong, not brittle. When a metal is hit, the layers of metal ions are able to slide over each other, and so the structure does not shatter. metal before it is hit metal after it is hit force force The metallic bonds do not break because the delocalized electrons are free to move throughout the structure. This also explains why metals are malleable (easy to shape) and ductile (can be drawn into wires). How do metals conduct heat and electricity? Delocalized electrons in metallic bonding allow metals to conduct heat and electricity. For example, when a metal is heated, the delocalized electrons gain kinetic energy. These electrons then move faster and so transfer the gained energy throughout the metal. This makes heat transfer in metals very efficient. Delocalized electrons also conduct electricity through metals in a similar way. heat Metals positive ions A metal structure is an ordered pattern of positive ions in a ‘sea’ of negative electrons. free electrons Electrical Conductors Metals are able to conduct electricity because…… (Complete this sentence) Ductility Electrons act as a type of (lubricant/bond) between the layers of (atoms/ions). This explains why it’s possible to pull metals to form wires. Melting Point The strength of metallic bonds depends on the number of outer neutrons/protons/electrons in the atoms (the more outer neutrons/protons/electrons the stronger the bonds. Metals The key to understanding a metal’s properties lies in its structure positive ions A metal structure is an ordered pattern of positive ions in a ‘sea’ of negative electrons. GCSE Additional Science Chapter 7 free electrons Ductility Electrical Conductors Connecting the sides to a battery makes the electrons move from the negative side towards the positive – this is the flow of current. Explaining the properties of METALS Electrons act as a type of lubricant between the layers of ions. This explains why it’s possible to pull metals to form wires. Melting Point The strength of metallic bonds depends on the number of outer electrons in the atoms (the more outer electrons there are , the higher the melting point). Alloys The atoms in pure iron are arranged in densely-packed layers. These layers can slide over each other. This makes pure iron a very soft material. The atoms of other elements are different sizes. When other elements are added to iron, their atoms distort the regular structure of the iron atoms. It is more difficult for the layers of iron atoms in steel to slide over each other and so this alloy is stronger than pure iron. Unit 10: Structure and Bonding Part 7: Ionic Bonding Lesson Objectives Describe the build-up of electrons in ‘shells’ and understand the significance of the noble gas electronic structures and of valency electrons. Describe the formation of ions by electrons loss or gain. Describe the formation of ionic bonds between elements from Groups I and VII. Describe the formation of ionic bonds between metallic and non-metallic elements. Describe the lattice structure of ionic compounds as a regular arrangement of alternating positive and negative ions. BONDING Ionic Structures GCSE Additional Science Chapter 7 Sodium chloride is formed when atoms of sodium bond with atoms of chlorine. Cl- Na+ +) [2.8.1] Sodium Sodiumatom ion (Na (Na) [2.8] -) [2.8.8] Chlorine Chlorideatom ion (Cl (Cl) [2.8.7] Both atoms are trying to achieve a full set of outer electrons. They can do this if the sodium atom gives its outer electron to the chlorine atom. We now have a sodium ion Na+, and a chloride ion Cl-. BONDING Ionic Structures GCSE Additional Science Chapter 7 Na+ Cl- Sodium ion (Na+) [2.8.] Sodium chloride (salt) Chloride ion (Cl-) [2.8.8] BONDING So there are two types of ion:1) Ionic Structures Positive ion (cation) – the atom has lost an electron or electrons. 2) Negative ion (anion) – the atom has gained electron(s). GCSE Additional Science Chapter 7 The ions attract and the attraction is ionic bonding. The oppositely charged ions attract each other. They cluster around each other (six Cl- around each Na+ and vice versa) to make an ionic giant structure. Six Chloride ions cluster around one Sodium ion Molecular structure of Sodium Chloride (Click molecule to show animation) Six Sodium ions cluster around one Chloride ion PROPERTY DUE TO High melting point Strong electrostatic forces of attraction between the ions. A lot of energy is needed to break them. Solid ionic compounds do not conduct electricity. The ions are held in fixed positions, and are not free to move. Molten ionic compounds conduct electricity. Melting has separated the ions so that they can move past each other. Unit 10: Structure and Bonding Part 8: Covalent Bonding BONDING Covalent Bonding GCSE Additional Science Chapter 7 Non-metal atoms bond with each other by sharing outer shell electrons. This is called COVALENT BONDING. Covalent bonding can produce: •Small molecules of elements, e.g. H2 •Small molecules of compounds, e.g. HCl •Giant molecules of elements, e.g. diamond and graphite •Giant molecules of compounds, e.g. SiO2 BONDING Covalent molecules GCSE Additional Science Chapter 7 Some elements form covalent compounds. This happens as atoms share electrons. H Cl Chlorine atom (Cl) [2.8.7] Hydrogen atom (H) [1] Molecule of hydrogen chloride (HCl) Hydrogen has the electron pattern of helium, and chlorine has the electron pattern of argon. This is written as H-Cl, where the ‘-’ represents a covalent bond (pair of shared electrons). Properties of molecular covalent compounds GCSE Additional Science Chapter 7 Melting points Low (attraction between molecules is weak) Physical state at room temperature Gases or liquids with low boiling points or solids with low melting points (weak forces of attraction between molecules) Electrical conductivity Do not conduct electricity (the molecules have no charge) Solubility in water Most are insoluble in water An exercise to recognise atomic or covalent bonds. (Only the outer shell is shown in the diagrams) GCSE Additional Science Chapter 7 H Ca2+ 2Fionic H O covalent H H covalent Cl Mg2+ Cl2ionic Cl covalent O H Cu N H H covalent Show the answers Cu2+ O2ionic Unit 10: Structure and Bonding Part 9: Giant Covalent Bonding Giant Covalent Structures Comparing the properties of graphite and diamond GCSE Additional Science Chapter 7 Some covalent molecules exist as giant covalent structures. These have a high melting point because all the atoms are held by strong covalent bonds. Graphite and diamond are examples of giant covalent structures made up of a collection of carbon atoms only. PROPERTY Appearance Hardness Conductivity Melting point Diamond Graphite Transparent crystals Grey/ black shiny solid Incredibly hard – used for cutting glass and in drill bits for drilling through rocks in the oil industry. Very soft – used as a lubricant. Also used to make pencils. Electrical insulator A non-metal that conducts electricity. Used for making electrodes. Very high – over 3500°C. Very high – over 3600°C. An explanation of the properties of diamond and graphite GCSE Additional Science Chapter 7 Diamond Every atom is bonded to 4 other atoms. Every outer electron has its role to play in the covalent bonding that happens here. The result is a very rigid structure. As there are no free electrons, it doesn’t conduct electricity and it’s a good conductor of heat. Graphite Graphite has layers formed from hexagonal rings – these layers can slide over each other, and this is why it is used as a lubricant. Every carbon atom bonds strongly to other carbon atoms by three covalent bonds. The fourth outer electron in each atom is free to move, and this is what makes graphite a good conductor. The future, and other forms of carbon GCSE Additional Science Chapter 7 Whilst experimenting with Fullerene C60, it was found that other structures of carbon could be formed. One of them is seen below: Fullerene C60 The carbon atoms are bonded covalently into a football shape. Carbon Nanotube The nanotube is like rolled graphite. 1) It conducts electricity 2) It’s very small – 10,000 times thinner than a human hair Nanotube 3) Crystals can be grown inside it Human hair 4) They may solve the problem of how to produce smaller circuits, where they might replace wires.