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25/05/2017 AQA Chemistry 2 A slideshow that covers the entire AQA 2006 Syllabus Chemistry 2 Module W Richards The structure of the atom 25/05/2017 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 NEUTRON – neutral, same mass as proton (“1”) PROTON – positive, same mass as neutron (“1”) ELECTRON – negative, mass nearly nothing Mass and atomic number 25/05/2017 Particle Relative Mass Relative Charge Proton 1 +1 Neutron 1 0 Electron Very small -1 MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously) Mass and atomic number 25/05/2017 How many protons, neutrons and electrons? Isotopes 25/05/2017 An isotope is an atom with a different number of neutrons: Notice that the mass number is different. How many neutrons does each isotope have? Each isotope has 8 protons – if it didn’t then it just wouldn’t be oxygen any more. Electron structure 25/05/2017 Consider an atom of Potassium: Potassium has 19 electrons. These electrons occupy specific energy levels “shells”… Nucleus 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 Periodic Table Introduction 25/05/2017 Periodic table 25/05/2017 The periodic table arranges all the elements in groups according to their properties. Vertical columns are called GROUPS Mendeleev Horizontal rows are called PERIODS The Periodic Table 25/05/2017 Fact 1: Elements in the same group have the same number of electrons in the outer shell (this corresponds to their group number) H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Br Kr I Xe Fe Ni Cu Zn Ag Pt E.g. all group 1 metals have __ electron in their outer shell Au Hg These elements have __ electrons in their outer shells These elements have __ electrons in their outer shell The Periodic Table 25/05/2017 Fact 2: As you move down through the periods an extra electron shell is added: Li Be Na Mg K Ca E.g. Lithium has 3 electron Hin the configuration 2,1 He Ni Sodium hasFe11 electrons in the configuration 2,8,1 Pt Cu Zn Ag Au Potassium has 19 electrons in the configuration __,__,__,__ Hg B C N O F Ne Al Si P S Cl Ar Br Kr I Xe The Periodic Table 25/05/2017 Fact 3: Most of the elements are metals: H These elements are metals He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Br Kr I Xe Fe Ni Cu Zn Ag Pt Au This line divides metals from nonmetals Hg These elements are non-metals The Periodic Table 25/05/2017 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. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Br Kr I Xe Fe Ni Cu Zn Ag Pt Au 1Hgmetals. They all: E.g. consider the group 1) Are soft 2) Can be easily cut with a knife 3) React with water Compounds Compounds are formed when two or more elements are chemically combined. Some examples: 25/05/2017 Methane Sodium chloride (salt) Glucose Some simple compounds… 25/05/2017 Methane, CH4 Water, H2O Carbon dioxide, CO2 Key Hydrogen Ethyne, C2H2 Oxygen Sulphuric acid, H2SO4 Carbon Sulphur Balancing equations 25/05/2017 Consider the following reaction: Sodium + water Na + sodium hydroxide + hydrogen Na O H H O H + H H 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”) Balancing equations 25/05/2017 We need to balance the equation: Sodium + water sodium hydroxide + hydrogen Na O H Na + Na H O O H Na H O H + H H Now the equation is balanced, and we can write it as: 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g) H Some examples 2Mg O2 2 MgO Zn + 2 HCl ZnCl2 2 Fe + 3Cl2 2 FeCl3 NaOH CH4 Ca + + HCl + 2 O2 NaCl CO2 + + 25/05/2017 H2 H 2O + 2H2O + 2 H2O Ca(OH)2 + + H2SO4 Na2SO4 + 2H2O 2 CH3OH + 3 O2 2 NaOH 2 CO2 + 4H2O H2 Bonding Cl 25/05/2017 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? Cl Bonding Cl 25/05/2017 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? Cl H Now we’re both really stable. We’ve formed a covalent bond. H Bonding Here comes another friend, Sophie Sodium Cl Na 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 + Cl 25/05/2017 Na Now we’ve both got full outer shells and we’ve both gained a charge. We’ve formed an IONIC bond. Covalent bonding 25/05/2017 Consider an atom of hydrogen: 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 Dot and Cross Diagrams 25/05/2017 Water, H2O: H O H Dot and Cross Diagrams 25/05/2017 Oxygen, O2: O O Dot and cross diagrams 25/05/2017 Water, H2O: Step 1: Draw the atoms with their outer shell: H Step 2: Put the atoms together and check they all have a full outer shell: O H O H H Oxygen, O2: O O O O Dot and cross diagrams 25/05/2017 Nitrogen, N2: Methane CH4: H N N H C H H Ammonia NH3: H Carbon dioxide, CO2: N H H O C O 25/05/2017 Other ways of drawing covalent bonds Consider ammonia (NH3): H N H H H N H H H N H H Ions 25/05/2017 An ion is formed when an atom gains or loses electrons and becomes charged: + - The electron is negatively charged The proton is positively 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) Ionic bonding 25/05/2017 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: Na 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 ______. + A _______ charged sodium ion Na Cl - Cl A _________ charged chloride ion 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: Some examples Magnesium chloride: Mg 25/05/2017 2+ Cl Cl Mg + - Cl Cl MgCl2 Calcium oxide: Ca + 2+ O Ca 2- O CaO Giant structures (“lattices”) 25/05/2017 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 _______. 2. Graphite – carbon atoms arranged in a layered structure, with free _______ in between each layer enabling carbon to conduct _________ + + + + + + + + + 4. Metals – the __________ in metals are free to move around (“delocalised”), holding the _____ together and enabling it to conduct _________ A closer look at metals 25/05/2017 Metals are defined as elements that readily lose electrons to form positive ions. There are a number of ways of drawing them: + - + - + + + - + + + + + - - - + + + + + + + + + + + + + + + Delocalised electrons Nanoscience 25/05/2017 Definition: Nanoscience is a new branch of science that refers to structures built from a few hundred atoms and are 1100nm 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. Group 1 – The alkali metals 25/05/2017 Li Na K Rb Cs Fr Group 1 – The alkali metals 25/05/2017 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: Potassium + water 2K(s) + 2H2O(l) potassium hydroxide + hydrogen 2KOH(aq) + H2(g) Words – down, one, shell, hydrogen, nucleus, decreases Group 0 – The Noble gases 25/05/2017 He Ne Ar Kr Xe Rn Group 0 – The Noble gases 25/05/2017 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 4) Helium is ________ then air and is used in balloons and airships (as well as for talking in a silly voice) 5) 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 Group 7 – The halogens 25/05/2017 F Cl Br I At Group 7 – The Halogens 25/05/2017 1) Reactivity DECREASES as you go down the group Decreasing reactivity Some facts… (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): Cl Cl 3) Because of this fluorine and chlorine are liquid at room temperature and bromine is a gas The halogens – some reactions 25/05/2017 1) Halogen + metal: + + Na Cl Halogen + metal Cl Na ionic salt 2) Halogen + non-metal: H + Cl Halogen + non-metal Cl H covalent molecule Atomic mass 25/05/2017 RELATIVE ATOMIC MASS, Ar (“Mass number”) = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (obviously) Relative formula mass, Mr 25/05/2017 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: Relative atomic mass of O = 16 Relative atomic mass of H = 1 Therefore Mr for water = 16 + (2x1) = 18 Work out Mr for the following compounds: 1) HCl H=1, Cl=35 so Mr = 36 2) NaOH Na=23, O=16, H=1 so Mr = 40 3) MgCl2 Mg=24, Cl=35 so Mr = 24+(2x35) = 94 4) H2SO4 H=1, S=32, O=16 so Mr = (2x1)+32+(4x16) = 98 5) K2CO3 K=39, C=12, O=16 so Mr = (2x39)+12+(3x16) = 138 A “Mole” 25/05/2017 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... Calculating percentage mass 25/05/2017 If you can work out Mr then this bit is easy… Percentage mass (%) = Mass of element Ar Relative formula mass Mr x100% 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: 1) Hydrogen in hydrochloric acid, HCl 2) Potassium in potassium chloride, KCl 3) Calcium in calcium chloride, CaCl2 4) Oxygen in water, H2O Recap questions Work out the relative formula mass of: 1) Carbon dioxide CO2 2) Calcium oxide CaO 3) Methane CH4 Work out the percentage mass of: 1) Carbon in carbon dioxide CO2 2) Calcium in calcium oxide CaO 3) Hydrogen in methane CH4 25/05/2017 25/05/2017 Calculating the mass of a product E.g. what mass of magnesium oxide is produced when 60g of magnesium is burned in air? Step 1: READ the equation: 2Mg + O2 2MgO IGNORE the oxygen in step 2 – the question doesn’t ask for it 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: 1) 48g of Mg makes 80g of MgO 2) 1g of Mg makes 80/48 = 1.66g of MgO 3) 60g of Mg makes 1.66 x 60 = 100g of MgO 1) When water is electrolysed it breaks down into hydrogen and25/05/2017 oxygen: 2H2O 2H2 + O2 What mass of hydrogen is produced by the electrolysis of 6g of water? Work out Mr: 2H2O = 2 x ((2x1)+16) = 36 2H2 = 2x2 = 4 1. 36g of water produces 4g of hydrogen 2. So 1g of water produces 4/36 = 0.11g of hydrogen 3. 6g of water will produce (4/36) x 6 = 0.66g of hydrogen 2) What mass of calcium oxide is produced when 10g of calcium burns? 2Ca + O2 Mr: 2Ca = 2x40 = 80 2CaO 2CaO = 2 x (40+16) = 112 80g produces 112g so 10g produces (112/80) x 10 = 14g of CaO 3) What mass of aluminium is produced from 100g of aluminium oxide? 2Al2O3 4Al + 3O2 Mr: 2Al2O3 = 2x((2x27)+(3x16)) = 204 4Al = 4x27 = 108 204g produces 108g so 100g produces (108/204) x 100 = 52.9g of Al2O3 Another method 25/05/2017 Try using this equation: Mass of product IN GRAMMES Mass of reactant IN GRAMMES Mr of product Mr of reactant 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 6g 4 36 So mass of product = (4/36) x 6g = 0.66g of hydrogen Problems with this technique 25/05/2017 Calculating the amount of a product may not always give you a reliable answer... 1) The reaction may not have completely _______ 2) The reaction may have been _______ 3) Some of the product may have been ____ 4) 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 Atom Economy Percentage atom economy = 25/05/2017 Relative formula mass of useful product Total masses of products Calculate the atom economies of the following: 1) Converting ethanol into ethene (ethene is the useful bit): C2H5OH C2H4 + H20 2) Making zinc chloride from zinc and hydrochloric acid: Zn + 2HCl ZnCl2 + H2 Numbers of moles 25/05/2017 Consider two liquids: 20cm3 of 0.1mol/dm3 of hydrochloric acid 20cm3 of 0.1mol/dm3 of sodium hydroxide These two beakers contain the same number of moles Now consider two gases: 20cm3 of helium at room temperature and pressure 20cm3 of argon at room temperature and pressure These two gases contain the same number of moles 25/05/2017 Endothermic and exothermic reactions Step 1: Energy must be SUPPLIED to break bonds: Step 2: Energy is RELEASED when new bonds are made: Energy Energy A reaction is EXOTHERMIC if more energy is RELEASED then SUPPLIED. If more energy is SUPPLIED then is RELEASED then the reaction is ENDOTHERMIC Example reactions Reaction Sodium hydroxide + dilute hydrochloric acid Sodium hydrogencarbonate + citric acid Copper sulphate + magnesium powder Sulphuric acid + magnesium ribbon 25/05/2017 Temp. after mixing/OC Exothermic or endothermic? Reversible Reactions 25/05/2017 Some chemical reactions are reversible. In other words, they can go in either direction: A + B e.g. Ammonium chloride NH4Cl C + D Ammonia + hydrogen chloride NH3 + HCl If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction? For example, consider copper sulphate: Hydrated copper sulphate (blue) + Heat CuSO4.5H2O Anhydrous copper sulphate (white) CuSO4 + H2O + Water Reversible Reactions 25/05/2017 When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions: A + B Endothermic reactions Increased temperature: A + B C + D C + D Exothermic reactions Increased temperature: A + B C + D More products Less products Decreased temperature: Decreased temperature: A + B C + D Less products A + B C + D More products Making Ammonia 25/05/2017 Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I am going to tell you how to use a reversible reaction to produce ammonia, a very important chemical. This is called the Haber Process. Nitrogen + hydrogen Ammonia N2 + 3H2 2NH3 Fritz Haber, 1868-1934 To produce ammonia from nitrogen and hydrogen you have to use three conditions: Nitrogen Hydrogen •High pressure •450O C •Iron catalyst Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy. Recycled H2 and N2 Haber Process: The economics 25/05/2017 A while ago we looked at reversible reactions: Endothermic, increased temperature A + B Endothermic C + D Exothermic, increase temperature A + B Nitrogen + hydrogen Ammonia N2 + 3H2 2NH3 C + D Exothermic 1) If temperature was DECREASED the amount of ammonia formed would __________... 2) However, if temperature was INCREASED the rate of reaction in both directions would ________ causing the ammonia to form faster 3) If pressure was INCREASED the amount of ammonia formed would INCREASE because there are less molecules on the right hand side of the equation Haber Process Summary 25/05/2017 A low temperature increases the yield of ammonia but is too slow A high temperature improves the rate of reaction but decreases the yield too much A high pressure increases the yield of ammonia but costs a lot of money To compromise all of these factors, these conditions are used: Nitrogen Hydrogen •200 atm pressure •450O C •Iron catalyst Mixture of NH3, H2 and N2. This is cooled causing NH3 to liquefy. Recycled H2 and N2 Rates of Reaction 25/05/2017 Oh no! Here comes another one and it’s got more energy… Here comes another one. Look at how slow it’s going… It missed! Here comes an acid particle… No effect! It didn’t have enough energy! Hi. I’m Mike Marble. I’m about to have some acid poured onto me. Let’s see what happens… Rates of Reaction 25/05/2017 Chemical reactions occur when different atoms or molecules _____ with enough energy (the “________ Energy): Basically, the more collisions we get the _______ the reaction goes. The rate at which the reaction happens depends on four things: 1) The _______ of the reactants, 2) Their concentration 3) Their surface area 4) Whether or not a _______ is used Words – activation, quicker, catalyst, temperature, collide Catalysts 25/05/2017 Task Research and find out about two uses of catalysts in industry, including: 1) Why they are used 2) The disadvantages of each catalyst Catalyst Summary 25/05/2017 Catalysts are used to ____ __ a reaction to increase the rate at which a product is made or to make a process ________. They are not normally ___ __ in a reaction and they are reaction-specific (i.e. different reactions need _________ catalysts). Words – different, speed up, used up, cheaper Rate of reaction graph v1 25/05/2017 Time taken for reaction to complete Reaction takes a long time here Reaction is quicker here Temperature/ concentration Rate of reaction graph v2 25/05/2017 Amount of product formed/ amount of reactant used up Fast rate of reaction here Slower rate of reaction here due to reactants being used up Slower reaction Time Rate of reaction = amount of product formed/reactant used up time Electrolysis Positive electrode Solution containing copper and chloride ions + + + + Cu2+ Cl- Cl- Cl- Cu2+ Cu2+ 25/05/2017 - Negative electrode Electrolysis 25/05/2017 Electrolysis is used to separate a metal from its compound. When we electrolysed copper chloride the _____ chloride ions moved to the ______ electrode and the ______ copper ions moved to the ______ electrode – OPPOSITES ATTRACT!!! = chloride ion = copper ion Electrolysis equations 25/05/2017 We need to be able to write “half equations” to show what happens during electrolysis (e.g. for copper chloride): At the negative electrode the positive ions GAIN electrons to become neutral copper ATOMS. The half equation is: Cu2+ + 2 e- Cu At the positive electrode the negative ions LOSE electrons to become neutral chlorine MOLECULES. The half equation is: 2 Cl- - 2 e- Cl2 Purifying Copper Impure copper Solution containing copper ions + + Cu + Cu + Cu 2+ 2+ 2+ At the positive electrode: Cu(s) Cu2+(aq) + 2e- - 25/05/2017 Pure copper At the negative electrode: Cu2+(aq) + 2e- Cu(s) Electrolysis of brine 25/05/2017 Sodium chloride (salt) is made of an alkali metal and a halogen. When it’s dissolved we call the solution “brine”, and we can electrolyse it to produce 3 things… Chlorine gas (Cl2) Hydrogen gas (H2) Sodium chloride (brine) NaCl(aq) Positive electrode Negative electrode Sodium hydroxide (NaOH(aq)) 25/05/2017 Universal Indicator and the pH scale Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is: 1 2 3 Stomach acid 4 5 Lemon juice 6 7 8 9 10 11 12 13 14 Water Soap Baking powder Oven cleaner Strong alkali Strong acid Neutral An acid contains hydrogen ions, H+ An alkali contains hydroxide ions, OH- Neutralisation reactions 25/05/2017 When acids and alkalis react together they will NEUTRALISE each other: Sodium hydroxide Na Hydrochloric acid H OH The sodium “replaces” the hydrogen from HCl Na Cl Sodium chloride General equation: H2O Water H+(aq) + OH-(aq) H2O(l) Cl Making salts 25/05/2017 Whenever an acid and alkali neutralise each other we are left with a salt, like a chloride or a sulphate. Complete the following table: Hydrochloric acid Sodium hydroxide Potassium hydroxide Calcium hydroxide Sulphuric acid Nitric acid Sodium chloride + water Potassium sulphate + water Calcium nitrate + water Making Salts 25/05/2017 Soluble salts can be made from acids by reacting them with: 1) Metals, e.g. Zn + 2HCl ZnCl2 + H2 2) Insoluble bases, e.g. CuO + 2HCl CuCl2 + H20 3) Alkalis (alkali = a “soluble base”), e.g. NaOH + HCl NaCl + H20 Salts can be made from these solutions by crystallizing them. Ammonium salts 25/05/2017 Guten tag again. When ammonia dissolves in water it produces an alkaline solution: NH3 + H20 NH4OH This solution can be used to make fertilisers. Very useful! This slideshow has been made freely available on the TES Resources website. More Science PowerPoints like this can be found at the website www.educationusingpowerpoint.com. This site contains slideshows that cover the AQA, EdExcel, OCR Gateway and OCR 21st Century courses, including the 2011 units, and A Level Physics and KS3 material. Some slideshows are free, others require a small subscription fee to be taken out (currently only £50 for a year). Further details can be found at Education Using PowerPoint.