okay let's try and go through all of the chemistry that you need to know for GCSE chemistry paper 1 and we're going to be covering atoms bonding constitutive chemistry chemical changes and energy changes and below don't forget you can download the pdf version of this from science shorts net link in description and I genuinely think that this is the hardest paper because there is so much stuff you need to know for it not only that some of the questions you have involved quite a bit of tricky math so don't forget that it's not enough just to learn all this stuff the best way of getting good at GCSE science is actually having a go at questions ok let's start off with the basics what is an atom an atom is something that can't be broken down or split into its constituents or smaller bits by chemical means yes we do add or remove electrons to make ions but we're not changing the inner workings of the atom a compound is two or more types of atoms chemically bonded together mixture with different types of atoms or compounds not chemically bonded together there are a few ways that we can separate a mixture into its different substances first one is chromatography we have a very filter paper with a dot of the mixture about a centimeter above the water line the filter paper is just dipped in the water the water gets drawn up to paper due to what we call capillary action and that drags particles of the mixture with it and the particles that end up the highest on the paper are the lighter particles if this is something like ink then you'll see the different colors that the ink is made up of ending up at different heights on the paper it's a good idea to draw a line where the dot was because that might disappear and a align where the water ends up at on the paper as well but we need to do those in pencil because that's not going to be moved by the water better maths with this we have something called the RF value the stands for a retention factor we calculate it by doing how far the solute has gone up the paper that's the ink in our case divided by how far the solvent has gone water another one is filtration this removes insoluble particles like sand from water we just have filter paper in a funnel we put the stuff in the top and then we let the water drip through and then hopefully we should just be left with the sand in the filter paper however if this was salt water you'd still end up with salt in the water at the bottom that's because the salt is actually dissolved in the water so how do we get rid of that well what we do is distillation this a solid from a solvent like salt from water what we do is heat the mixture or the solution the water evaporates and then we re condense it using a condenser tube usually that's something that has cold water running around the outside and then the water gets collected in a beaker hopefully leaving just the salt behind in the flask okay what does an atom look like well we have bits in the middle that make up what we call the nucleus they are neutrons and protons and we have electrons orbiting around the outside protons have a charge of +1 electrons have a charge of minus 1 neutrons are neutral they don't have a charge atoms have to have the same number of protons as electrons so that means that they are neutral there's no overall charge that changes when they become ions of course if they lose electrons then they have become an ion and getting rid of a negative charge leaves you with a positive charge so ions technically are positive however at GCC we also say that if an atom gains electrons it becomes a negative ion we'll see more of that as we go on so here's the periodic table of elements there are eight main columns one two and then the gap and then three four five six seven eight or zero the column or group tells you how many electrons are in the outer shell and that's basically the most important thing that we need to know about an element how many electrons in its outer shell what road they're in is called the period and that tells you how many shells of electrons it actually has you can see hydrogen and helium at the top as well hydrogen is it a metal is it a nonmetal hmm it's a little bit iffy hydrogen is a bit special only needs two electrons in its outer shell to be full in the middle we have the transition metals we're not really concerned with those triple people you might need to know a couple of things basically transition metals that are further down the table are heavier obviously and also they have higher melting points everything to the left of the staircase there is a metal and the metal is an electron donator so metals lose electrons when they bond to something else to the right we have nonmetals we say they're electron acceptors Group one is called the alkali metals they get more reactive as you go down the group and this is because the outer electron is further from the nucleus so not as much energy is required to remove that electron from the atom these react with water to make an alkali solution that's why they call the alkali metals Group seven are what all the halogens they get less reactive as you go down the group that's because as the outer shell is further from the nucleus it's not as easy for the electron to be accepted onto it Group 8 or group 0 or what we call the noble gases now to all intents and purposes they do not react because they have a full outer shell but in practice we have to say they're very unreactive it is possible for them to react but it's very unusual here's what everything are a chemical symbol represents in my case I've drawn helium so capital H literally the bottom number is what we call the atomic number and that tells you the number of protons in the nucleus and yes for an atom we also know that's the same as the number of electrons mass number on the other hand at the top is the number of protons plus the number of neutrons so if you want to find the number of neutrons then you need to take top number away from bottom number electrons fill shells like this 2 8 8 2 now we only really care about the first 20 elements so that takes us down to calcium and that's because that's just before we hit the transition metals it gets messy after that so if we take something like chlorine its atomic number is 17 that means it has 17 protons that means it also has 17 electrons so how will they arranged in the shells well we know it's 2 in the first shell 8 in the second shell we're up to 10 and so that means that we're gonna have 7 in the outer shell to bring us up to 17 this is how we can draw it it's very unusual for you to have to draw all of the shells around an atom generally we just draw the outer shell we can think of atoms wanting either a full or an empty outer shell but never right want in your resume so that means either having eight or a zero okay for hydrogen and helium that's just two so atoms get what they want by bonding to something else and they can do this different ways metals achieve this generally by bonding to nonmetals and we call this ionic bonding a metal will donate an electron or electrons that means we've made a positive ion where is the electron gone well it's gone to the nonmetal and that becomes a negative ion overall the charge must still be zero though let's take the example of magnesium chloride and magnesium is in group two that means it has two electrons in its outer shell so it has to lose two electrons to have an empty shell so it's ion is always mg 2 plus chlorine has to gain one electron because it's in group 7 so it's iron is always CL minus so if we make magnesium chloride that means it's not just mg CL but it's mgcl2 because we need two minuses to balance out the two plus here's how we draw a dot and cross diagram for ionic bonding the metal on the left always has an empty shell so just a circle around it and then we put the charge at the top right the nonmetal on the other hand well we draw its electrons with say crosses and then we add on the electron from the metal using a dots doesn't matter if they're the other way around cause only one electron goes to one chlorine atom but we have two of those so we put a little two down the bottom right these ions generally form lattices that has grids of ions and so we end up with crystals ionic compounds generally have high melting and boiling points they're soluble in water they can conduct electricity when they're molten or in solution that means dissolved because the ions are free to move in both cases covalent is when nonmetals bond to other non metals non-metals don't donate electrons so all they can do is share them to get a full outer shell and the number of electrons needed by a nonmetal to get a full outer shell is equal to the number of covalent bonds it forms so hydrogen only needs one electron so it always makes one covalent bond carbon is in Group four so it needs four more electrons so it makes four covalent bonds and so on usually we end up with small molecules we call this simple covalent bonding take something like methane ch4 here's the structural formula for it we draw lines representing covalent bonds between atoms and we can see that each hydrogen has one bond carbon has four bonds around it here's the dot and cross diagram for it all we do is draw the outer shell and I've drawn the one electron on each hydrogen in the bonds and then of course carbon shares one electron with each of the hydrogens as well there's a quick way of learning how to draw these though if you see a covalent bond in the structural formula then you know that that's going to be a dr. cross electron pair just make sure at the end check out all of the shells four hydrogen's have to in this case carbon have eight altogether yes it's full it just so happens that all the electrons are being used up in the bonds that's not always the case you might some electrons left over let's take co2 oxygen has to make two bonds because it's in group six carbon has to make four again so that means we have to have a double covalent bond between the carbons and the oxygens so if you see a double bond I means we're gonna have two pairs of cross in the double bonds giant covalent is basically when we have covalent bonds just carrying on and carrying on we don't make small molecules we end up making huge molecules take diamond for example here we have carbons arranged in a sort of 3d triangle the little wedge and dotted line just show that the carbons coming out towards you and away from you so we have this little pyramidal tetrahedron that repeats and repeats until we have just one giant molecule of carbons and that's what a diamond on your ring is graphite is what we call another allotrope of carbon and we have these layers of hexagonal e arranged carbons on top of each other you might see that the carbons can only be bonded to three other carbons so that means they make three covalent bonds where's the fourth well the spare electrons what we say a delocalized disorder free to move they're not actually on the atom they exist between the layers and they form a kind of bond between the layers it's a really weak bond though so that means that these layers can slide over each other one layer of this we call graphene another allotrope of carbon is fullering or buckminsterfullerene also known as of buckyball it's like a football we have sixty carbons all joined together in a sphere we know nanotubes if you can imagine a layer of graphene that's been folded over to make a tube that's what it is and these three allotropes on the right it generally used as lubricant because they can slide over each other very easily having graphite you know that's in your pencils that's because the layers can slide off onto your piece of paper easily metallic bonding not really much to say here atoms form a lattice when this happens the electrons become delocalized so actually what we have is a bunch of ions in a lattice and they're surrounded by a sea of delocalized electrons now because they're delocalized they're free to move and that's why metals can conduct electricity polymers are long chains that are formed by joining together lots of individual molecules known as monomers if we have ethene and the double bond in the middle can split so that means that it's ready to bond to another one and another one and another one and we end up with a long chain and we call that polythene or polythene and it always has to have a double bond in of what we say unsaturated more on this in paper 2 to make a polymer that is to do polymerization we need high pressure to force these molecules together and a catalyst and you know that catalyst reduces activation energy the periodic table didn't come out of nowhere John Sulton was the first one to put the elements in weight order yeah he called them weight instead of mass so Dalton didn't have a table it was just a long list Newlands then grouped elements together with similar properties and he found out that every eighth element had similar properties so we're starting to get there and then it was finally Mendeleev who put the elements in columns and rows to make what we basically know as the periodic table today okay moving on to chemical changes there are a bunch of different things that can react you need to know what they make a metal and oxygen makes a metal oxide we call this oxidation a metal or a metal oxide when it reacts with water makes a metal hydroxide that's an alkali and hydrogen gas an acid and a metal hydroxide makes a salt and water so here's an example of an acid and metal hydroxide let's take hydrochloric acid and sodium hydroxide that makes the salt sodium chloride that's just your table salt and water this incidentally is a neutralization reaction we're going to talk about more of that in a bit so that's how you make things but you can also break things down you can break things down with thermal decomposition heat something up and it might just break you let's take copper carbonate you heat that enough and it makes copper oxide and carbon dioxide displacement reactions this is when we have a compound with a metal in but if a more reactive metal comes along it'll muscle out the less reactive wimpy metal from the compound take potassium coming in contact with sodium chloride potassium is more reactive so it kicks it out to make potassium chloride and sodium is left out in the cold we can use this to extract metals from ores we can also use the idea of reactivity in sacrificial metals we can put bits of a reactive metal on the outside of the hull of a boat so it will react with the water first hopefully leaving the metal probably the steel in the hull intact when iron reacts with oxygen or water it makes iron oxide it's rust other metals can react with oxygen as well like aluminium to make aluminium oxide copper to make copper oxide that's green that's why the Statue of Liberty looks green it's copper underneath but we still don't call those rust rust is just for iron oxide to get iron out of iron ore we can use a blast furnace we have coke that's carbon where you react that with oxygen to make co2 and then that will go on to make carbon monoxide carbon monoxide can be reacted with the iron carbonate to leave pure iron get let's go on to some quantitative chemistry math is always considered that means that atoms are not created or destroyed in chemical reactions any chemical reaction we write down we have to make sure it's balanced so let's take sink and hydrochloric acid it makes zinc chloride and hydrogen now we only have one chlorine on the Left two on the right so it's not currently balanced and we can't change the chemical makeup of these molecules so we can't just put a little - after the HCL to make two chlorines we have to put a number before the symbols to multiply these up so it's a little puzzle but the trick is to start with the complex molecules and then end on the elements so we're going to end on the zinc or the hydrogen h2 here so we know we need two chlorines so we're going to put a 2 in front of the HCL we know how to you chlorines on the left but we also know how to hydrogens on the left as well lomi hold oh we have two hydrogens on the right as well therefore the formula is now balanced if there are more hydrogen's on the left and we would just multiply up the h2 on the right relative atomic mass or relative formula mass well we get that from the mass number of an element and its relative because we're dealing with what we call moles right we have a dozen eggs a mole is 6.02 times 10 to the 23 atoms or molecules and we get moles by doing grams thus the mass of something we have in grams divided by ramps that's the relative atomic mass of grams over Ram's moles equals grams they programs really useful equation to remember so that means actually that the mass number of an atom as she tells you how many grams a mole of that stuff weighs so a mole of carbon weighs 12 grams if we want to get the ram we should say relative formula mass actually for co2 well we just add all the numbers up so carbon is 12 plus 2 lots of 16 for the o2 that gives us 44 so one mole of carbon dioxide weighs 44 grams and this is important when we're dealing with chemical reactions because well let's take the reaction on the Left if we use 1 mole of zinc in the reaction we would need 2 moles of hydrochloric acid because we can see we have the 2 in front of it and incidentally if we had less than 2 moles of hydrochloric acid that would mean the reaction would be incomplete so the hydrochloric acid would be what we call the limiting reactant there's not enough of it for the reaction to complete solution concentration another thing that people find tricky but let's just have a think about the unit its grams per decimeter cubed or moles per decimeter cubed so it is just how much stuff do we have in a decimeter cubed now a decimeter cubed is the same as 1,000 centimeters cubed or 1,000 milliliters if you have to convert from one to the other just remember you will always end up with a more centimetres cubed than decimeter cubed because it's enemy eschewed are smaller so that means concentration is equal to grams or number of moles we had divided by the volume of the water that we're dissolving it in a couple of things for usually just triple percentage yield is how much stuff do we actually get out of a reaction compared to how much stuff could we get in a perfect world so it's the mass of the products divided by the maximum a theoretical mass we could get out reactions often don't complete and that goes especially for reversible reactions like the harbor process at some economy looks similar but it's very different this would still be in play even if we had a hundred percent yield it's the mass of desired products divided by the total mass of the reactants going in so let's take our equation above if we wanted zinc chloride then we do the mass of that we can actually use the rams divining by the mass or grams of all of the stuff going in moly gas constant what's weird is that it doesn't actually matter what kind of gas you have one mole of it always fills 24 decimeters cube of volume so if we want the volume of a gas we just take the number of moles times it by 24 moles are useful for comparing how much stuff we need compared to how much stuff we get out so let's look at a typical question how many kilograms of zinc chloride can be made from three kilograms of a zinc well what we do is go from the mass we have three kilograms to number of moles so we do grams over Rams actually it doesn't have to be gram so long as you're using the same unit of mass it can stay as kilograms it can stay as tonnes whatever just as long as you're consistent in the question so find out the number of moles of reactants then use that to find out the number of moles of product made so in our case we can see that if we have one mole of zinc going in we're gonna have one mole of zinc chloride coming out it would be different if we set three kilograms of hydrochloric acid because we have that two before it and then finally you convert the number of moles of your product back into mass using the equation again similar idea is used for our neutralization reaction if you want to find out the concentration of a solution like an acid or an alkali then we can do a titration we have a burette and we always put acid in the burette not the alkali we have a fixed volume of the base or alkaline in the beaker and I should have drawn a conical flask to be perfectly honest you measure that using a bulb or glass pipette we put a couple of drops of methyl orange indicator in the bottom what we do is a rough titer or rough titration that the acid flow fairly quickly while swirling the flask at the bottom and then as soon as it turns pink then we know that it hasn't been neutralized and we've probably overshot it but that's why we do a rough Titus so once we got a rough titer then we go back and do it a little bit more slowly once we get to near what we know the value is then we slow it down by closing the tap and we let the acid just drip through drop by drop and after each drop we swirl the flask and see if it stays pink not only turns pink but it has to stay pink if it turns back to orange them it's not quite complete if the stoichiometry that just means ratio of moles is one-to-one in our case it is where there's no numbers before the hey CL or NaOH that means for each mole of base that we have in the flask that means however many moles of base we have in our beaker then we've just used the same number of moles of acid to neutralize it so then it's going to be just what we saw with our zinc chloride let's say that a concentration of our alkaline is 0.1 moles per decimeter cubed we calculate the number of moles that we actually had and say that's the same number of moles for our acid and then we can divide that by the volley I've acid used to find out the concentration speaking of pH it goes from 1 to 14 1 being acidic 14 mean alkaline 7 being neutral now an acid is something that dissociates that means separates into its H+ ions and it's negative ions but an acid will always have H+ ions in it a strong acid is one which dissociates very easily so you have a high concentration of these h+ ions swimming around or weak acid here's one where they don't dissociate very easily for an alkali it's Oh 8 - it's a logarithmic scale so that means an acid that is one lower than another acid is actually 10 times stronger but what does it actually mean well we have pH 2 and pH 1 that means that the pH 1 acid has a 10 times higher concentration of H+ ions than the pH 2 acid electrolysis we can use electrolysis to separate chemicals from solution say brine that's just salt water the sodium chloride in solution we have carbon electrodes because we don't want them to react when we have salt water we basically have a mess of na plus CL minus h plus and o h minus ions just swimming around in solution they're dissociated so they're free to move when we attach these electrodes to a battery we have a positive electrode we call that the anode and a negative electrode we call that the cathode the CL minus ions well opposites attract so they will go to the anode where they will be turned into chlorine gas however it's the H+ that goes to the cathode and this turn into hydrogen gas it's not the sodium that goes to the cathode that's because sodium is more reactive than hydrogen so sodium wants to stay in solution more than hydrogen as it were we can write an ionic or 1/2 equation for what's going on at each electrode we know that H+ is a hydrogen that's lost it's one electron so if we have the H+ going to the cathode which has lots of electrons to spare then it will give the H+ an electron and it will be turned into it just a normal atom hydrogen gas is h2 it's diatomic like pretty much most gases apart from noble gases so that means to balance it we have to have two H+ and we can put the state symbols in equi us that means it's dissolved plus two electrons that goes to h2 gas incidentally because they go towards the cathode we call these cations positive ions in solution are called cations see our - however we call an anion because it moves to the anode it has an extra electron so it loses that electron it gives it to the electrode so therefore we have two cl- aqueous goes to CL 2 gas plus 2 electrons if you wrote 2 CL - take away 2 electrons but goes to chlorine gas that's also acceptable and there are two things going on here oxidation and reduction and the mnemonic you need to remember is oil rate oxidation is loss reduction is gain that is of electrons so what's happening at the cathode to the hydrogen well it's gaining electrons so that is reduction chlorine is losing electrons so that's oxidation that's always the case we always get oxidation at the anode and reduction at the cathode we can also use electrolysis to purify metals like copper this time our electrodes are actually made out of copper our anodes that's a positive electrode is made up of our impure copper the copper atoms that they lose electrons to turn into Cu 2 plus ions and they go swimming around in the copper sulfate electrolyte that they're dunked in and they will then move to the cathode where they will then be reduced and turn back into normal copper so what happens the impure copper electrode will decrease in size and the cathode will increase in size but it's only the copper that can go from one to the other all of the other impurities in the copper aren't soluble so they just drop to the bottom leaving us with pure copper on the cathode let's talk about energy changes energy is required to break covalent bonds but we have the same amount being made or released when these bonds are made bonds need a very specific energy to break them like a carbon hydrogen bond needs 413 kilojoules for every mole of these bonds broken so therefore we have two main types of reactions when it comes to energy exothermic and endothermic EXO sounds like explosion so that means it gets hot but what does that mean well that means that more energy is released from the bonds being made than needed to break the bonds so that means that we get net energy being so it gets hot here's what we call the reaction profile for an exothermic reaction here's the energy level of our reactants but then we can see that the energy level of our products has gone down and that's what people find a bit confusing this energy is technically potential energy they're falling this potential energy level so that means that they actually give out energy in the form of kinetic energy or heat but we do need something to get the reaction started and that's what this hump is that's our activation energy that is from the reactants to the top of that hump that's like a spark needed to get a fire going because otherwise things would be catching fire all the time not good the difference between the two energy levels is the net resultant energy out in the form of heat endothermic on the other hand more energy is needed to break the bonds than is released from the bonds being made that means it gets cold we don't have as many of these but we do get them reactants are down the bottom the products end up at the top we have activation energy again if you wanted to do a prac on this well we need to measure the energy released from a reaction and it can be EXO or endothermic all we do is have a polystyrene cup with a lid with a thermometer through the top and the bowler thermometer in the solution that's going to react when we start the reaction all we do is see what the starting temperature is and the end temperature and we measure that change in temperature then we use a specific heat capacity equation you probably know there's more from physics energy or heat is equal to the mass times the SHC times the temperature change the mass is going to be the volume in centimeters cubed of the solution we can measure that with a measuring cylinder specific capacity of water is four point two another temperature change we calculate by doing star temperature takeaway final temperature or vice versa it doesn't really matter you can get given bond energies and then get asked to calculate how much net energy is released or taken in by a reaction so let's take say methane ch4 reacting with oxygen making carbon dioxide and water just your normal combustion equation we need to balance it first of all so that means we need to lots of o2 and to lots of h2o so like we said the bond energy of CH is 413 so we do four times 413 and then we add on to lots of well it's 409 eight kilojoules per mole 400 double bonds adding those up we can see that we have two thousand six hundred and forty eight kilojoules per mole needed to break all of the covalent bonds have a look at the products we have co2 so there's two lots of C Oh double bonds and there 805 kilojoules per mole each and then we have four lots of H o bonds because we have two h2o is made here so four times four six four you'll always be given these bond energies now you might see I have made a mistake here but that means that we have three thousand four hundred and sixty-six kilojoules per mole being released from these bonds being made so one takeaway the other four 3466 kilojoules per mole released take away the two six four eight cuz you've per mole that's gone in to break the bonds and that means we get a net energy released of 818 kilojoules per mole so that means that if we have a mole of methane burning in oxygen we will get 818 kilojoules out lastly a couple of things for probably just triple sales our batteries work because metals that are in a solution of its own ions will ionize say zinc in the zinc sulfate the difference in charge between the electrode and the solution is called the electrode potential so what we do is have two pools of these as it were zinc dunked in zinc sulfate copper dunked in copper sulfate the PD between those two electrodes well that's what will drive your car or your phone or whatever but we have to have a salt bridge in between that's so the zinc ions on the Left can go towards it and the sulfate ions on the right can go towards it as well they move to it and they get added on to the salt bridge fuel cells not much to see here basically we have two tanks one containing hydrogen one containing oxygen we let them react very slowly but when they do they produce a voltage theoretically the great thing about hydrogen fuel cells they don't produce any greenhouse gases either well technically water vapor is a greenhouse gas but we tend to forget about that it doesn't make any carbon dioxide so that's it if you think I've missed anything then put it in a comment down below also done these four different papers so check those out before your exams as well see you next time