let's see how quickly we can cover everything you need to know for AQA GCC chemistry paper 1 this is good for higher and Foundation Tier double combined Trilogy and triple separate chemistry that's topics 1 to five atoms bonding quantitative chemistry and chemical and energy changes I'll tell you when something is just for triple and when some of the bigger concepts are just for high tier we're going to have to be moving it quite a right here you can pause the video if you need a bit more time to get your head around something you see let's go substances stuff are made of atom the different types or elements of atoms there are are represented in the periodic table by a symbol a compound is a substance that contains two or more different types of atoms chemically bonded together for example the chemical formula for water is H2O it's made up of hydrogen and oxygen atoms for every one oxygen atom there are two hydrogen atoms if there's no number after a symbol there's an invisible one there these atoms change what they're bonded to and how they're bonded through chemical reactions we can represent a reaction with a word equation and a chemical equation using symbols as atoms are not created or destroyed in any chemical reaction there must be the same number of each type of atom on both sides so sometimes we must balance equations Pro tip start balancing atoms that are only in compounds so with this one let's go with the carbons first there's one on the left one on the right so that's all good hydrogens there are four on the left only two on the right now we can't change the small numbers because that would change what the compound is so what we can do is put numbers in front of elements or compounds to multiply them up sticker two in front of the H2O we now have 2 * 2 hydrogens so that's four that's also double the oxygen in it however so now we have four oxyg on the right still only two on the left so doubling this O2 on the left takes care of that if there's an element in a reaction Like Oxygen here we always finish balancing that as there's no KnockOn effect a mixture is any combination of any different types of elements and compounds that aren't chemically bonded together for example air is a mixture of oxygen nitrogen and more solutions are mixtures to like salt water a mixture of water and sodium chloride you can separate large insoluble particles from a liquid using filtration like sand from water as sand can't dissolve crystallization can leave a solute that's the solid dissolved in a liquid behind after you evaporate the solvent from a solution like salt from water similarly distillation involves heating the solution as well but this time the gas is cooled so it condenses back into a liquid you can also do this at different temperatures to separate the different liquids of a mixture as they will have different boiling points this is called fractional distillation these are all physical processes though and not chemical reactions because no new substances are being made solid liquid and gas are the three main states of matter for example water can be ice a solid where the particles or molecules in this case vibrate around fixed positions it can also be liquid water where the molecules are still touching but are free to move past each other and it can also be a gas water vapor we call it when it's water where the particles are far apart and move randomly and they also have the most energy and so move quickly as molecules in a gas are far apart gases can be compressed while solids and liquids cannot to melt or evaporate a substance you must supply energy usually in the form of heat to overcome the electrostatic forces of attraction between the particles we don't say we're breaking Bonds in this case note that none of these make a new substance so these have to be physical changes again not chemical reactions we're not breaking any chemical bonds in chemical reaction equations we indicate what state subst es in with state symbols brackets s for solid L for liquid G for gas and also AQ for aquous that means dissolved or in solution again like salt in water the idea of what atoms are like came about gradually JJ Thompson discovered that atoms are made up of positive and negative charges he came up with the plum pudding model of the atom a positive charge with lots of little electrons dotted around it it was Ernest Rutherford who found that the positive charge must actually be incredibly small We Now call this the nucleus and the electon must orbit relatively far away from it he discovered this by finding that most alpha particles fired at a thin Leaf of gold atoms went straight through proving that atoms must be mostly empty space Neil's B later discovered that electrons exist in shells or orbitals then James Chadwick discovered that the nucleus must also contain some neutral charges he called them neutrons while the positive charges are called protons protons and electrons have equal and opposite charges so we just say they're plus one and minus one relatively speaking neutrons have a charge of zero protons and neutrons have essentially the same mass so we say they have a relative mass of one electrons are very light in comparison so we say they have a mass of zero or just very small depending on the situation the periodic table tells us everything we need to know about an atom the bottom number is the atomic number that's the number of protons in the nucleus this is what determines what element you have every atom has an overall neutral charge so that means they must have the same number of electrons as protons if an atom gains or loses electrons it's now called an ion not an atom the top number is the mass number or relative atomic mass or RAM for short it tells you how many protons and neutrons are in the nucleus so that must mean that this carbon atom carbon 12 has six neutrons on top of its six protons to make that 12 however you can get a carbon atom with seven neutrons instead so its relative mass is 13 these are what we call Isotopes atoms of the same element but different numbers of neutrons you might see a number that isn't a whole number for the mass this is because periodic tables sometimes show the average mass for all of the Isotopes of that element found in the world for example if you have some chlorine gas it turns out that 75% of the atoms will have a mass of 35 while 25% of the atoms will be 37 these are what we call their relative abundance to find the average we just pretend that we have 100 atoms we add up the total masses of all the Isotopes then just divide by 100 that's why chlorine average relative atomic mass is 35. 5 the periodic table is incredibly useful but how was was it made before it scientists just put elements in order of their atomic weights some were then grouped together if they were seen to have similar properties but still using the atomic weight order Dimitri Mev then came along and grouped elements together based on their properties even if the order didn't follow atomic weight using this method he found there were gaps in his table he asserted that these elements were yet to be discovered in time he was proven correct showing that his table was indeed correct like we said electrons exist in shells around the nucleus the shells fill up from the inside with a Max maximum of two on the first shell eight on the second and third shells then we only go to two on the fourth shell that's 20 electrons Al together which brings us to a calcium atom after this we get into the transition metals where things get a little bit crazy so we leave that until a level chemistry so we only care about the electron configuration going up to 2882 magnesium has 12 electrons so its electron configuration for example would be 282 the modern periodic table can be split up into different sections for example everything to the left of this staircase is called a metal metal atoms always donate electrons to gain an empty outer shell of electrons again slightly weird with transition metals but we don't think about their shells to the right of the stair case nonmetals they always accept electrons to gain a full outer shell the column an atom is in is called the group it tells you how many electrons an atom has in its outer shell again the transition metals work in a really weird way so they don't get their own group if fact it turns out this is because they can donate a different number of electrons when they bond to different things the at atoms in group one are called the alkal metals they all have one electron in their outer shell which they give away donate when they bond to something so they have similar properties like when they react with water the further down the group you go though the further that outer electron is from the nucleus so the electrostatic attraction is weaker between the negative electron and the positive nucleus this means that the electron is more readily donated this means the metals get more reactive as you go down the group group seven are what we call the halogens they're essentially the opposite they have seven electrons in their outer shell so they need one more to gain a full outer shell the further down the group you go the less readily an electron is accepted onto that shell that's further away from the nucleus so they get less reactive down the group their boiling points also increase down the group too group zero sometimes referred to as group eight are called the noble gases they already have an empty or full outer shell just depends on your perspective so they don't react in reality they can react under special conditions so we just say they're very unreactive we don't really say group eight anymore though because some people thought that helium might feel a little left out as it only has two electrons in its out shell as electrons are negative themselves Metals become positively charged when they lose them they always form positive ions all of group one lose one electron when they turn into an ion so all of their ions are one plus but again we don't write the one we just put plus group two lose two electrons to get an empty outter shell so their ions are all two plus group seven gain one electron each so all their ions are minus group six is ions are all two minus the atoms in group 3 4 and 5 don't really form ions except for aluminium which is 3+ like we said transition metals can donate different numbers of electrons for example an ion ion can be fe2+ or fe3+ it can donate two or three electrons so we give them the names Ion 2 and ion 3 to distinguish between them transition metals are generally harder and less reactive than the alkaline metals they also form colored compounds bonding next metal atoms bond to each other through metallic bonding essentially a lattice or grid of ions is formed with a CA of delocalized electrons around them delocalized just means they're not exactly on the atom as these electrons are free to move Metals make good conductors of electricity and heat Metals bond to non-metals through ionic bonding like we said a group one metal needs to lose an electron while a group seven atom needs to gain one it's a match made in heaven for example a lithium atom donate or loans its outer electron to the chlorine we can draw a DOT and cross diagram to show where the electrons end up you can choose which one belongs to which we only need to draw the outer shell for each don't forget to put brackets and the charge of the ions when it comes to ionic bonding the charges of all ions in an ionic compound must add up to zero so l+ and cl minus is all good so this is the chemical formula for it same with burum oxide be2 plus and O2 minus burum chloride on the other hand well the the burum needs to lose two electrons while a chlorine only needs one so that means there must be two chlorines or chloride ions for every burum so be2 plus and two lots of Cl minus adds up to zero so that means the chemical formula is be cl2 sorted ionic compounds consist of lots of repeating units of these ions in a latice to form a crystal they have high melting points and boiling points due to the strong electrostatic forces that need to be overcome and they can conduct electricity but only in liquid form that is molten or when dissolved in Solution that's because the ions are free to move in both cases and they carry charge you can also get molecular ions for example o minus is a hydroxide ion and consists of a hydrogen atom and an oxygen atom so magnesium would need two of these to make magnesium hydroxide here are a few other examples by the way I spell sulfate with a pH instead of an F because I'm stubborn and refuse to adopt the American spelling you'll get the mark either way any ionic compound can be called a salt not only sodium chloride you table salt the name is always the metal ion positive ion or cat we can call it followed by the non-metal ion or anion annion names are different from their normal names like we've just seen it's not sodium chlorine but sodium chloride some people remember which way around cat ions and annion are by liking cats and they say cat ions are positive non-metals bond to each other with Cove valent bonding to form molecules they do this by sh sharing electrons to gain full out of shells for example chlorine gas is cl2 each chlorine atom shares an electron with the other so they're both happy never write down happy in the exam though here's the dot and cross diagram we can also draw the structural formula for molecules with just symbols and lines we could also say that every one of these represents a DOT cross electron pair each oxygen needs two extra electrons so O2 is a result of each oxygen atom sharing two electrons each as such this is a double coal Bond nitrogen N2 is one of the few molecules with a triple bond in in Cove valent bonding the number of electrons an atom knes is the same as the number of bonds it must make hydrogen can only ever make one Bond carbon makes four bonds Etc here's a few more if you're not in a rush pause the video and have a go with them and here are the answers these above are what we call Simple molecular or simple Cove valent structures individual molecules that can all mix together these have relatively low boiling points as there are only weak intermolecular forces between them that need to be overcome with heating be careful though there not calent Bonds being broken like we said and unlike ionic compounds these can't conduct electricity even as liquids giant calent bonding is similar to the ltis nature of ionic compounds atoms form coent bonds to other atoms which form bonds to other atoms and so on until what we have in effect is one giant molecule diamond is an example of this it's a crystal of carbon atoms bonded to each other that's why it's so high hard and has such a high melting point you would have to break the Cove valent Bonds in order to do that and they're incredibly strong graphite is only made of carbon as well but it's not Diamond so it's an allotrope of carbon made out of the same atoms bonded together in a different way graphite consists of layers of carbons with three bonds each in a hexagonal structure where's the fourth Bond though well the spare delocalized electrons form special weak bonds between the layers which means that it can conduct electricity because the electrons can move between the lers as well and it also means the layers can slide over each other easily which is why it's used in pencils as a side note metal alloys are stronger than pure Metals having mixtures of metals means that we have different size atoms and that disrupts the regular lattice so layers can't slide over each other as easily back to carbon allotropes graphine is just a single layer of graphite ferin are 3D structures of carbon atoms for example Buckminster ferine is a spherical football-like structure consisting of 60 carbon atoms each ferin that have a tube shape are called nanot tubes just for triple real quick surface to volume ratio is just one divided by the other if the length of a side of a cube doubles that means this ratio halves as nanop particles are tiny this ratio is huge for them which means that fewer could be needed to fulfill a purpose compared to larger ones quantitative chemistry next some tricky stuff coming up total mass of all substances is conserved in a chemical reaction like we said earlier that must mean the atoms that go in must come out so we must balance equations to that end we already know about relative atomic mass but if it's a compound we can add these up to give the relative formula mass we just add up the individual Rams so CO2 is 12 plus 2 lots of 16 so that's 44 some reactions produce a gas product which if it leaves the reaction vessel will result in a seeming decrease in mass of the reactants a mole is just a specific number of atoms or molecules but we don't really need to know the number it's just a way of comparing amounts of substance Es as we can't deal in individual numbers of atoms or molecules if your foundation you don't need to deal in moles by the way if you have as many grams of a substance as its relative atomic or formula mass you have one mole so one mole of carbon has a mass of 12 G that means we calculate the number of moles of something we have like this moles equals g over Rams where Rams is short for relative atomic mass but it also could be relative formula mass this is an equation worth remembering let's take our methane combustion reaction from earlier like we said in order to balance this we'd need two oxygen molecules per one molecule of methane this is also true for moles too then we'd need double the moles of oxygen to methane so here's how a question could go how many grams of water would be made if 64 G of methane reacted completely with oxygen we need to get from the mass of one thing to the mass of another so we use moles as the middleman the process is this Mass moles moles Mass we switch from one to the other at the halfway mark So a mass of 64 G of methane how many moles is that moles equals g over R so that's 64 divided by 16 that's four moles of methane but look there's no number in front of the methane but there is a two in front of the water which means we must have double the moles of water so that's 8 moles by the way we can say that the stochiometry is 1 to2 that just means the ratio of moles of one substance to another in a reaction so what we have to do then is turn that back into Mass using our equation by rearranging it put it into a triangle if you have to and cover up Mass g equals moles time Rams so that's 8 moles * water's Ram of 18 that's 144 G of water made you could also be given the mass in kilograms or even tons the great thing is is that because this is all relative we can just put those masses into our equation instead of grams and so long as you stick with that unit for the whole question you'll still end up with the right answer of course we can also use moles to predict how much of a reactant we would need in a reaction as you can see we need two moles of oxygen to every one mole of methane if we had that one mole of methane but only one mole of oxygen that means that not all of the methane would react some would be left behind we say that the oxygen is the limiting reactant in this case it ran out first the concentration of solutions can be given in G per decim cubed where a decimeter cubed is 1,000 cm cubed but it's often useful to convert this into moles per decim cubed instead if one mole of H CL is dissolved in 1 decim cubed of water we've made hydrochloric acid at a concentration of 1 mole per decim cubed sometimes we shorten this to just one Moler triple only now until the next topic chemical changes in many reactions we want to make as much product as possible more often than not though there will be some reactants Left Behind over at the end like we know for example if a reaction is reversible like the harbor process to make amonia more about that in paper too you'll always end up with hydrogen and nitrogen at the end in this case when it's reached equilibrium percentage yield merely tells you how much product is actually made compared to how much you could have made in theory had all the reactants reacted for example if you start with 20 G of reactants here but only end up with 10 G of ammonia the percentage yield is 50% you must be given the actual masses involved in questions on this so you can't predict what the yield would be just from the equation atom economy on the other hand tells you how much of a desired product you get out of a reaction compared to the mass of the reactants that went in you use relative Atomic or formula masses to do this I like to think of atom economy as efficiency of mass we calculate it like this the ram of desired product divided by the total Ram of reactants Times by 100 back to the methane reaction sometimes this is done in green houses to make CO2 for the plants it's an incredibly important gas necessary for life to thrive you see the ram of CO2 is 44 so that goes on top of our equation now we could calculate the ram of the reactants but there's a Nifty shortcut we can take here because this is also the same as the ram of all of the products due to conservation of mass as we know so we might as well use that seeing that we've already got the RAM for one product add on two lots of 18 so that's 44 divided by the total of 80 * 100 that's 55% one mole of any gas takes up a volume of 24 decim cubed regardless of its relative mass this is true for RTP room temperature and pressure that's 20° C and a pressure of one atmosphere you must be able to convert moles to volume and back by multiplying or dividing by 24 double people wake up this is chemical changes we saw briefly earlier that Metals vary in their reactivity as some donate their electrons more readily than others here's the reactivity series for the most common Metals we consider you can see that hydrogen and carbon have also snuck in there that's because it's often necessary to compare the reactivity of metals to those in order to predict what will happen in a reaction a more reactive metal will displace a less reactive metal from a compound that is kick it out for example if you place zinc in Copper sulfate solution you'll see copper forming on the lump of zinc the zinc displaces the copper to form zinc sulfate kicking the copper out of the compound we know that alkali metals react with water the reaction happens because for example potassium is more reactive than hydrogen so in essence it displaces it from the water leaving potassium hydroxide and hydrogen gas is produced we can use this when it comes to extracting metals from their ores found in the ground any metal less reactive than carbon can be displaced by it for example ion can be displaced from ion oxide with carbon this is called smelting we can also say that the ion oxide has been reduced it's the opposite of oxidation because oxygen is lost even if oxygen is not involved in a reaction we can still say that reduction and oxidation happen depending on whether a reactant loses or gains electrons the pneumonic is oil rig oxidation is loss reduction is gain of electrons that is the ion ions in the ion oxide are positive of course because they're metals and they gain electrons to turn back into atoms they become neutral they've been reduced here's the half or ionic equation for this we should never really have a minus in any half equations so think carefully about which side the electron should go on depending on whether it's oxidation or reduction Metals more reactive than hydrogen can displace it from an acid so most metals react with hydrochloric acid and sulfuric acid for example this produces a salt alkalis they have a pH greater than seven react with acids less than seven to produce say salt and water if the quantities used are correct according to this deometry they will neutralize each other completely to leave no unused reactants here's an example sodium hydroxide and hydrochloric acid makes sodium chloride in water neutral pH of 7 if sulfuric acid is used a metal sulfate is made nitric acid metal nitrate these salts are left in solution that is disol in water when any substance dissolves its ions partially dissociate as does the water actually into H+ and O minus ions we can obtain solid crystals of a dissolved salt by warming gently so the water evaporates the pH scale is a logarithmic scale base 10 it's not linear what does that mean well an acid contains H+ ions and an acid that has a pH of three will have 10 times the concentration of these compared to an acid of ph4 ph3 would have a 100 times the concentration of H+ ions compared to an acid of ph5 and so on alkal work in a similar way but with oh minus ions instead the higher you go the greater the concentration a strong acid is one that dissociates or ionizes completely when in solution like Hydrochloric Nitric and sulfuric acids weak acids on the other hand only partially dissociate like ethanoic citric and Carbonic acids the pH of an acid depends on both its strength and concentration if hydrochloric acid and ethanoic acid have the same concentration the hydrochloric acid will have the lower pH as it's stronger titrations are only for triple this is how we deduce the concentration of an acid or an alkaline we use a glass pipet to measure out a known volume of alkal and put it in a conical flask with a few drops of an indicator like methyl orange we put the acid of unknown concentration in a buet above the flask we open the tap and let it drip into the flask slowly while we swirl it when it turns pink we close the tap and if it stays pink after we swirl it that shows that neutralization has occurred you can also Al do a rough titration to get a rough value for the volume needed to do this then do another and then add a drop at a time near the end point to get a more accurate value let's say that it's sodium hydroxide and sulfuric acid here's the balanced equation so let's say that we have 50 cm cubed of 0. 2 moles per decim Cub sodium hydroxide first we need to turn that volume into decim cubed so we divide by 1,000 so that's 0.
05 DM cubed of the alkaline multiply that by the concentration and we get 0. 01 moles from the St geometry of 1 to two for the acid and Alkali we can see that we need half the number of moles of acid to neutralize it so that's 0. 005 moles of acid needed now we can use our actual volume of acid measured finally we just calculate the concentration by doing moles divided by volume that's 0.
005 / 0. 125 DM Cub that's that's we converted it which gives us a concentration of 0.
