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AQA Chemistry 2

AQA Chemistry 2. A slideshow that covers the entire AQA 2006 Syllabus Chemistry 2 Module. W Richards. The structure of the atom. ELECTRON – negative, mass nearly nothing. NEUTRON – neutral, same mass as proton ( “ 1 ” ). PROTON – positive, same mass as neutron ( “ 1 ” ).

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AQA Chemistry 2

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  1. AQA Chemistry 2 A slideshow that covers the entire AQA 2006 Syllabus Chemistry 2 Module W Richards

  2. The structure of the atom ELECTRON – negative, mass nearly nothing NEUTRON – neutral, same mass as proton (“1”) PROTON – positive, same mass as neutron (“1”) The Ancient Greeks used to believe that everything was made up of very small particles. I did some experiments in 1808 that proved this and called these particles ATOMS: Dalton

  3. Mass and atomic number MASS NUMBER = number of protons + number of neutrons 4 He SYMBOL 2 PROTON NUMBER = number of protons (obviously)

  4. Mass and atomic number How many protons, neutrons and electrons? 1 11 16 H B O 1 5 8 23 35 238 Na Cl U 11 17 92

  5. Isotopes Notice that the mass number is different. How many neutrons does each isotope have? 16 O 17 18 O O 8 8 8 Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. An isotope is an atom with a different number of neutrons:

  6. Electron structure 39 K 19 Nucleus Consider an atom of Potassium: Potassium has 19 electrons. These electrons occupy specific energy levels “shells”… The inner shell has __ electrons The next shell has __ electrons The next shell has __ electrons The next shell has the remaining __ electron Electron structure = 2,8,8,1

  7. Periodic Table Introduction

  8. Periodic table The periodic table arranges all the elements in groups according to their properties. Vertical columns are called GROUPS Mendeleev Horizontal rows are called PERIODS

  9. The Periodic Table These elements have __ electrons in their outer shell E.g. all group 1 metals have __ electron in their outer shell These elements have __ electrons in their outer shells Fact 1: Elements in the same group have the same number of electrons in the outer shell (this corresponds to their group number)

  10. The Periodic Table E.g. Lithium has 3 electron in the configuration 2,1 Sodium has 11 electrons in the configuration 2,8,1 Potassium has 19 electrons in the configuration __,__,__,__ Fact 2: As you move down through the periods an extra electron shell is added:

  11. The Periodic Table These elements are metals This line divides metals from non-metals These elements are non-metals Fact 3: Most of the elements are metals:

  12. The Periodic Table • E.g. consider the group 1 metals. They all: • Are soft • Can be easily cut with a knife • React with water Fact 4: (Most important) All of the elements in the same group have similar PROPERTIES. This is how I thought of the periodic table in the first place. This is called PERIODICITY.

  13. Compounds Sodium chloride (salt) Methane Glucose Compounds are formed when two or more elements are chemically combined. Some examples:

  14. Some simple compounds… Methane, CH4 Key Hydrogen Oxygen Carbon Sulphur Sulphuric acid, H2SO4 Carbon dioxide, CO2 Water, H2O Ethyne, C2H2

  15. Balancing equations Sodium + water sodium hydroxide + hydrogen O Na Na H H H H H O Consider the following reaction: + + This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

  16. Balancing equations Sodium + water sodium hydroxide + hydrogen O O Na Na Na Na H H H H H H H H O O 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) We need to balance the equation: + + Now the equation is balanced, and we can write it as:

  17. Some examples Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 Ca + H2O NaOH + H2SO4 CH3OH + O2 MgO ZnCl2 + H2 FeCl3 NaCl + H2O CO2 + H2O Ca(OH)2 + H2 Na2SO4 + H2O CO2 + H2O 2 2 2 3 2 2 2 2 3 2 2 2 2 2 4

  18. Bonding Cl Cl Hi. My name’s Johnny Chlorine. I’m in Group 7, so I have 7 electrons in my outer shell I’d quite like to have a full outer shell. To do this I need to GAIN an electron. Who can help me?

  19. Bonding Cl H Cl H Here comes one of my friends, Harry Hydrogen Hey Johnny. I’ve only got one electron but it’s really close to my nucleus so I don’t want to lose it. Fancy sharing? Now we’re both really stable. We’ve formed a covalent bond.

  20. Bonding Cl + - Cl Na Na Here comes another friend, Sophie Sodium Hey Johnny. I’m in Group 1 so I have one electron in my outer shell. Unlike Harry, this electron is far away from the nucleus so I’m quite happy to get rid of it. Do you want it? Okay Now we’ve both got full outer shells and we’ve both gained a charge. We’ve formed an IONIC bond.

  21. Covalent bonding Notice that hydrogen has just __ electron in its outer shell. A full (inner) shell would have __ electrons, so two hydrogen atoms get together and “_____” their electrons: Now they both have a ____ outer shell and are more _____. The formula for this molecule is H2. When two or more atoms bond by sharing electrons we call it ____________ BONDING. This type of bonding normally occurs between _______ atoms. It causes the atoms in a molecule to be held together very strongly but there are ____ forces between individual molecules. This is why covalently-bonded molecules have low melting and boiling points (i.e. they are usually ____ or ______). Words – gas, covalent, non-metal, 1, 2, liquid, share, full, weak, stable Consider an atom of hydrogen:

  22. Dot and Cross Diagrams H H Water, H2O: O

  23. Dot and Cross Diagrams Oxygen, O2: O O

  24. Dot and cross diagrams O O H O H O H H O O Water, H2O: Step 1: Draw the atoms with their outer shell: Step 2: Put the atoms together and check they all have a full outer shell: Oxygen, O2:

  25. Dot and cross diagrams N N C O O H H H N H C H H H Nitrogen, N2: Methane CH4: Ammonia NH3: Carbon dioxide, CO2:

  26. Other ways of drawing covalent bonds H H N H H H H N N H H H Consider ammonia (NH3):

  27. Ions The electron is negatively charged - + The proton is positively charged + + An ion is formed when an atom gains or loses electrons and becomes charged: If we “take away” the electron we’re left with just a positive charge: This is called an ion (in this case, a positive hydrogen ion)

  28. Ionic bonding This is where a metal bonds with a non-metal (usually). Instead of sharing the electrons one of the atoms “_____” one or more electrons to the other. For example, consider sodium and chlorine: Sodium has 1 electron on its outer shell and chlorine has 7, so if sodium gives its electron to chlorine they both have a ___ outer shell and are ______. Cl Na + - A _______ charged sodium ion A _________ charged chloride ion Cl Na As opposed to covalent bonds, ionic bonds form strong forces of attraction between different ions due to their opposite ______, causing GIANT IONIC STRUCTURES to form (e.g sodium chloride) with ______ melting and boiling points:

  29. Some examples - 2+ 2+ Cl Cl Cl Ca Mg Mg - Cl 2- + Ca O O Magnesium chloride: + MgCl2 Calcium oxide: CaO

  30. Giant structures (“lattices”) + + + + + + + + + 1. Diamond – a giant covalent structure with a very ____ melting point due to ______ bonds between carbon atoms 3. Sodium chloride – a giant ionic lattice with _____ melting and boiling points due to ______ forces of attraction. Can conduct electricity when _______. 4. Metals – the __________ in metals are free to move around (“delocalised”), holding the _____ together and enabling it to conduct _________ 2. Graphite – carbon atoms arranged in a layered structure, with free _______ in between each layer enabling carbon to conduct _________

  31. A closer look at metals + + + - - + + + - + + - + + + + + + + + + + + - + + + + + - + - - Delocalised electrons Metals are defined as elements that readily lose electrons to form positive ions. There are a number of ways of drawing them:

  32. Nanoscience Definition: Nanoscience is a new branch of science that refers to structures built from a few hundred atoms and are 1-100nm big. They show different properties to the same materials in bulk. They also have a large surface area to volume ratio and their properties could lead to new developments in computers, building materials etc. Task: research nanoscience and find two current and/or future applications of this science.

  33. Group 1 – The alkali metals

  34. Group 1 – The alkali metals Potassium + water potassium hydroxide + hydrogen 2K(s) + 2H2O(l) 2KOH(aq) + H2(g) Some facts… 1) These metals all have ___ electron in their outer shell. 2) Density increases as you go down the group, while melting point ________ 2) Reactivity increases as you go _______ the group. This is because the electrons are further away from the _______ every time a _____ is added, so they are given up more easily. 3) They all react with water to form an alkali (hence their name) and __________, e.g: Words – down, one, shell, hydrogen, nucleus, decreases

  35. Group 0 – The Noble gases

  36. Group 0 – The Noble gases Some facts… 1) All of the noble gases have a full outer shell, so they are very ______ 2) They all have _____ melting and boiling points 3) They exist as single atoms rather then _________ molecules • Helium is ________ then air and is used in balloons and airships (as well as for talking in a silly voice) • Argon is used in light bulbs (because it is so unreactive) and argon , krypton and ____ are used in fancy lights Words – neon, stable, low, diatomic, lighter

  37. Group 7 – The halogens

  38. Group 7 – The Halogens Decreasing reactivity Cl Cl Some facts… 1) Reactivity DECREASES as you go down the group (This is because the electrons are further away from the nucleus and so any extra electrons aren’t attracted as much). 2) They exist as diatomic molecules (so that they both have a full outer shell): 3) Because of this fluorine and chlorine are liquid at room temperature and bromine is a gas

  39. The halogens – some reactions H H Cl Cl Halogen + metal ionic salt Na + - Cl Na Cl Halogen + non-metal covalent molecule 1) Halogen + metal: + 2) Halogen + non-metal: +

  40. Atomic mass RELATIVE ATOMIC MASS, Ar (“Mass number”) = number of protons + number of neutrons 4 He SYMBOL 2 PROTON NUMBER = number of protons (obviously)

  41. Relative formula mass, Mr Relative atomic mass of O = 16 Relative atomic mass of H = 1 The relative formula mass of a compound is the relative atomic masses of all the elements in the compound added together. E.g. water H2O: Therefore Mr for water = 16 + (2x1) = 18 Work out Mr for the following compounds: • HCl • NaOH • MgCl2 • H2SO4 • K2CO3 H=1, Cl=35 so Mr = 36 Na=23, O=16, H=1 so Mr = 40 Mg=24, Cl=35 so Mr = 24+(2x35) = 94 H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98 K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138

  42. A “Mole” Definition: A mole of a substance is the relative formula mass of that substance in grams For example, 12g of carbon would be 1 mole of carbon... ...and 44g of carbon dioxide (CO2) would be 1 mole etc...

  43. Calculating percentage mass Mass of element Ar x100% Percentage mass (%) = Relative formula mass Mr If you can work out Mr then this bit is easy… Calculate the percentage mass of magnesium in magnesium oxide, MgO: Ar for magnesium = 24 Ar for oxygen = 16 Mr for magnesium oxide = 24 + 16 = 40 Therefore percentage mass = 24/40 x 100% = 60% • Calculate the percentage mass of the following: • Hydrogen in hydrochloric acid, HCl • Potassium in potassium chloride, KCl • Calcium in calcium chloride, CaCl2 • Oxygen in water, H2O

  44. Recap questions • Work out the relative formula mass of: • Carbon dioxide CO2 • Calcium oxide CaO • Methane CH4 • Work out the percentage mass of: • Carbon in carbon dioxide CO2 • Calcium in calcium oxide CaO • Hydrogen in methane CH4

  45. Calculating the mass of a product IGNORE the oxygen in step 2 – the question doesn’t ask for it Step 1: READ the equation: 2Mg + O2 2MgO E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air? Step 2: WORK OUT the relative formula masses (Mr): 2Mg = 2 x 24 = 48 2MgO = 2 x (24+16) = 80 • Step 3: LEARN and APPLY the following 3 points: • 48g of Mg makes 80g of MgO • 1g of Mg makes 80/48 = 1.66g of MgO • 60g of Mg makes 1.66 x 60 = 100g of MgO

  46. When water is electrolysed it breaks down into hydrogen and oxygen: • 2H2O 2H2 + O2 • What mass of hydrogen is produced by the electrolysis of 6g of water? 2) What mass of calcium oxide is produced when 10g of calcium burns? 2Ca + O2 2CaO 3) What mass of aluminium is produced from 100g of aluminium oxide? 2Al2O3 4Al + 3O2 • Work out Mr: 2H2O = 2 x ((2x1)+16) = 36 2H2 = 2x2 = 4 • 36g of water produces 4g of hydrogen • So 1g of water produces 4/36 = 0.11g of hydrogen • 6g of water will produce (4/36) x 6 = 0.66g of hydrogen • Mr: 2Ca = 2x40 = 80 2CaO = 2 x (40+16) = 112 • 80g produces 112g so 10g produces (112/80) x 10 =14g of CaO Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108 204g produces 108g so 100g produces (108/204) x 100 =52.9g of Al2O3

  47. Another method Q. When water is electrolysed it breaks down into hydrogen and oxygen: 2H2O 2H2 + O2 What mass of hydrogen is produced by the electrolysis of 6g of water? Mass of product IN GRAMMES Mr of product Mass of reactant IN GRAMMES Mr of reactant Try using this equation: Mass of product IN GRAMMES 4 6g 36 So mass of product = (4/36) x 6g = 0.66g of hydrogen

  48. Problems with this technique Calculating the amount of a product may not always give you a reliable answer... • The reaction may not have completely _______ • The reaction may have been _______ • Some of the product may have been ____ • Some of the reactants may have produced other _______ The amount of product that is made is called the “____”. This number can be compared to the maximum theoretical amount as a percentage, called the “percentage yield”. Words – lost, yield, finished, reversible, products

  49. Atom Economy Relative formula mass of useful product Percentage atom economy = Total masses of products • Converting ethanol into ethene (ethene is the useful bit): • C2H5OH C2H4 + H20 • Making zinc chloride from zinc and hydrochloric acid: • Zn + 2HCl ZnCl2 + H2 Calculate the atom economies of the following:

  50. Numbers of moles 20cm3 of 0.1mol/dm3 of hydrochloric acid 20cm3 of 0.1mol/dm3 of sodium hydroxide 20cm3 of helium at room temperature and pressure 20cm3 of argon at room temperature and pressure Consider two liquids: These two beakers contain the same number of moles Now consider two gases: These two gases contain the same number of moles

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