Transcript for:
Topic 1 Atomic structure and the periodic table

[Music] hello and welcome to this video on Ed XL topic one atomic structure and the periodic table my name is Chris Harris and I'm from Aller tutors.com and basically the whole point of this video is to go through um an overview of topic one um for year one um for Ed XL um now the slides that I'm using us here um you can purchase them they're great value great for revision um an alternative to books um and they summarize the the content for Ed XL as well uh if you'd like to purchase them you can click on the link in the description box and you can get a hold of them there and but like I say this is linked to the Ed XL specification and obviously the specification points are listed on here for topic one so if you're studying Ed EXL chemistry a level chemistry then this should be perfect for you okay right so we're going to start with looking at the structure of the atom so the atom is made up of a nucleus um the nucleus contains neutrons and protons it's very small not very big at all and the electrons whiz around in shells on the outside of the atom uh in terms of the structure of these the relative charge of protons is plus one the mass is one for Neutron it's neutral so has no charge relative mass is one same as a proton electrons are negatively charged they have a charge of minus one and their relative mass is 1 over 2,00 so you can't put no Mass you have to put some Mass cuz electrons do have a mass okay uh just looking at the element obviously in the periodic table the top number or the bigger number because it might be on the bottom in some periodic tables the bigger number is the mass number it tells you the number of protons and electrons in the nucleus um the smaller number tells you the number of protons it's called the atomic number um which and obviously in in atoms the number of protons equals the number of electrons as well okay so let's look at some ions and isops so ions have a different number of electrons and protons um so we've got here the negative ions uh have obviously gained two electrons in this case this is for oxygen and they've done that to gain a full shell of electrons and you can see we've got eight protons um with a charge of plus eight eight neutrons and with a charge of zero um and the number of electrons is 10 so it's gained two extra ones from the normal eight that it has and if we add all them numbers up we should get a total charge of minus 2 and obviously this is negatively charged ion and this would be attracted to a positive ion and this was what makes them stable and positive ions obviously lost an electron to form a positive charge um the number of protons in this one in this case is 11 so charge of + 11 12 neutrons in this case for sodium but they have a charge of zero it's lost an electrons so it only has 10 electrons instead of the 11 it would normally have as an atom so if we add all them numbers up we should get a total charge of plus one so obviously these would combine together to form a compound which is what makes them stable okay it's the formation of compounds that do that okay Isotopes are basically elements with the same number of protons but a different number of neutrons so you can see we've got three examples three carbon examples um these are all isotopes of each other um and you can see that we've got six protons they've all got the same number of protons but they've got a different number of neutrons and you can see that the obviously the carbon on the left here has six neutrons seven neutrons in this one eight neutrons in this one that's why the mass number is increasing at the top there okay make sure you know your definitions as well um the relative atomic mass is the weighted mean mass of an atom of an element compared to 1 12th of the mass of of an atom of carbon 12 must remember that and the relative isotopic mass is basically the mass of an atom of an isotope compared to 11 12 of the mass of an at of carbon 12 relative molecular masses down here as well um you don't need to know this one for Ed XL um but it's just useful to kind of compare it with the other two as well okay so Mass Spectra is a great way in which we can identify um a an element from its Isotopes so just um going to give you a bit two around the um uh the graph here and you can see the bottom axis is the Master charge or MZ as it's also known as this is basically the mass of an isotop divided by its charge so most have a charge of plus one so effectively this is just the same as the isotopic mass so the MZ is the same as that and someons can have a double charge in which case it obviously halves the um uh the normal value because it's mass divided by two if it's a double charge uh alongside it's percentage abundance um it's always SE shown on the left hand side of the axis it can be shown as percentage um or as a ninal value it depends you've got to be vigilant with that and have a look um but if it's a percentage abundance obviously all the all the isotope abundances must add up to 100% so in this case it does because you got 75% and 25% okay this Spectra it shows two isops of one element um so there are 75% of the Isotopes with a mass of 35 and we've got 25% of the Isotopes with a mass of 37 as you can see here so this is assuming that they have a OnePlus charge if they have a double charge this will have this amount but that most of them do have a single positive charge okay and so from this we can work out the relative atomic mass which is what we're going to look at now okay so the relative atomic mass can be calculated using the abundance of a which is the master to charge of a uh so abundance of isotope a Times by The Master charge of a plus the abundance of B Times by The M the charge of B etc etc depending on how many Isotopes we've got because we've got two of them here this is obviously sufficed divided by the total abundance in this case it's percentage abundance so it'll be out of 100 but if it's not percentage make sure you add up the total abundances that you got and add them up and divide them there okay so in this case 75 * 3 uh 75 * 35 sorry uh and we got 25% so it's 25 * 37 for this one add them two up divide them by 100 CU your total abundance is 100 and that gives us a relative atomic mass of 35.5 so in this case if you look at the periodic table the element for this spectrum here is chlorine uh we can also work it out using tables as well obviously we've used a graph there but we can use a table so we've got an isotope here the Master charge isotope of um various Isotopes here we've got five Isotopes making up this element uh and we've given the relative abundances of each isotope so again using this formula here we can work out the relative atomic mass so all we do is we do 70 * by 20.5 72 * 27 for and so on and we keep multiplying them and we add them up individually as you can see here then we divide it by 100 because it's the abundance is a percentage so it's always out of 100 and we should get the answer is 72.6 um and if you look in the periodic table this should point to geranium so um it's really good for obviously identifying these elements like I say so make sure you have your periodic table handy for this type of stuff okay so we need to know how we can calculate isop opic mass as well so let's say we got potassium it has an AR of 39.1 and we got to calculate the isotopic mass of an isotope with an abundance of 5.78 eight% and other Isotopes being um potassium 39 which is 94.2% and pottassium 40 being 0.012% so this is a bit different because actually we've been given the relative atomic mass we've got to calculate the isotopic mass so this is a bit tricky You' be all right with this if you do maths you probably look familiar with it but there's a bit of maths here so just to warn you okay so let's look at our uh formula here first so we're using the same formulas we've seen before abundance of a m z of a abundance of b m z of B abundance of c m z of C because remember we've got three Isotopes here and you can see that we've got a total abundance obviously on the bottom and total abundance is obviously going to be out of 100s because it's all percentages so what we're going to do is going to put our numbers in here so we know the relative atomic mass is 39.1 we know 94.2 * 39 and we know the 0.012 * 40 um because obviously that's the um that's the the the isotopic mass we know the percentage of this one but we don't know what its abundance is uh so we don't know what the um mass is of this IOP and that's what we want to work out which is I've represented that with a big red X there okay divided by 100 okay so this is where the massive bit comes in so what I've done is we've basically multiplied these two out and we've basically got a grand total here of 36.748373 the divide by 100 here then once we've done that we then drag this number here across over to this side um and when we go across the equal sign we subtract so it's 3910 minus 36742 equals 5. 788 x as you can see it's a bit of algebra here obviously if we do this sum we should get 235.68 ax remember this is the bit we want to work out and this is where the magic happens so uh we rearrange this we want to get X on its own um so what we need to do is divide both sides by 5.78 to get rid of this bit here so divide by that number that cancels that out divide this side by the same number because whatever you do to one side you got to do to the other so it's 235.68 ided 5.78 and that should give us X as a value of 40.7 so if we round that up to the nearest whole number that's 41 uh cuz Isotopes must have a whole number Mass that's why it's whole number so make sure you do do that so the answer to this one is 41 and there's quite a few marks available there so but if you you know if you follow the method you know how to do it you should be fine okay predicting Mass Spectra so oxygen is made from two isotopes Okay so we've got 98% abundance of Oxygen 16 and 2% abundance of oxygen 18 got to predict the mass Spectra for O2 Okay so we've got 98% is basically 0.98 and 2% is 0.92 so what we're doing is writing the percentages of decimals then what we need to do is create a table showing the isotope combinations of them in a molecule of o2 and we're going to multiply the decimal form abundances of each isotope to get the relative abundance for each molecule all right so what we're doing is we're looking at the different combinations remember O2 is two lots of oxygen but oxygen comes in two isotopes we've got Oxygen 16 and oxygen 18 so if we have two oxygen 16s bonded together then what we do is we multiply the two decimal percentages of Oxygen 16 and that gets that number if we add an oxygen 18 and an Oxygen 16 there's the bond there look so 0 1816 and we do the um the percentage of or the decimal of the um abundance of oxygen 18 times by 0.98 and we get this number so basically what we're doing is we're multiplying all of the different combinations and we're getting these numbers here then any molecules which are the same we add the abundances up so we see we've got Oxygen 16 and 18 and 18 and 16 are actually the same they're just um obviously different different way around but in terms of the the abundances they are the same so what we do is we do .01 196 plus 0.0196 so these two here um so these add them up and we get 0392 so we're taking account that then what we need to do is we need to divide all of the relative abundances worked out before by the smallest value now the smallest value here was 0.4 okay because it's quite rare this to get two of these together uh and this will give you the whole number ratio which can be used to predict your Spectra so you can see here there's the molecule Oxygen 16 and 16 okay U this gives a mass of obviously 16 + 16 is 32 um so we'll use that in a minute but you see the relative abundance is 0.604 that was for that one there divided by the smallest number which is that one and that gives us a relative abundance of 241 remember for this one 16 and 18 we're using this number here because we've got two of them we're taking this count both of them here divide that by the smallest number we get 98 and then finally the 18 and 18 one um we get uh one for this one because we're just dividing it by the smallest number okay and then what we're doing is we're using these mrss here these are your Isotopes remember the masses of your isotope uh of your molecule sorry so we've got um 13 here so um 32 sorry here which has got the relative abundance of 241 we've got one at 34 which has got a relative abundance of 98 and we've got one at 36 which has got relative abundance of one and that is basically how we predict the mass Spectra from these molecules again pretty tricky make sure you follow these methods here and you should be fine okay let's have a look at Mass Spectra of molecules so again we've got this abundance here on the left hand side shown as a percentage um so if it isn't a percentage your isops must add up to 100 just be careful it might be a nominal value uh and obviously we've got these mzs here um which is your um obviously your master charge ratio as we've shown before and the Peaks here this shows the n plus1 Peak um so this is the molecular ion Peak and this is the same as the relative molecular mass of the molecule so sometimes we get fragments that break up the molecule um and sometimes this isn't so this is an unfragmented molecule hasn't been broken up and you just get this n plus1 Peak so basically this is just the mass of the full molecule okay right electric configuration so this is quite important this bit so we need to know about the different types of shells that we've got so elect Elon shells are split into four subshells we've got an S subshell can hold two electrons a p subshell has three orbitals it can hold six electrons the D subshell has five orbitals it can hold two lots of five which is 10 electrons and the F orbital has seven orbitals uh and basically can hold 14 electrons so I've colorcoded these you can see them down here so shell number one has a 1s orbital which is there and the number of electrons is two so got two electrons sitting in there uh shell number two also has a p orbital now of these P orbitals can have two electrons each orbital can hold two electrons but we've got three of them so you do 3 * 2 so it's 2 + 3 * 2 it's eight electrons in total third shell we have a d orbital and obviously if you can get the 3D subshell involved here uh and the 3D subshell again each orbital can hold two we' got five of them in total 5 * 2 uh plus the p orbital electrons plus the S orbital 18 in total so as long as you know these different orbitals here okay we need to know about the shape of these things as well so the S has one orbital and it can hold two electrons as we've discovered before so the S orbital is spherical in shape um and the two electrons can move anywhere within this sphere uh the p orbital has three orbitals uh and each one can hold two electrons and they've got these really classy names so we've got the PX orbital the py orbital and the pz orbital and you see one's um along the horizontal one's vertical and one is kind of going away from you so it's like sticking out towards you and we combine all these together obviously all these are 90° of each other as well so in a three-dimensional shape but we can combine them all and we make the full P subshell so we've got three orbitals each holding two electrons each um and we combine them to form this shape here and this is the P subshell so there are three p orbitals in the shape of dumbbells as you can see there or figures of eight uh they can hold two electrons and they can move anywhere like say within this shape okay you do have something called spin pairing as well and so when two electrons occupy one orbital what they do is they spin in opposite directions and you'll see some of these diagrams these energy diagrams with arrows representing electrons and the arrows show which way it's spinning and but I'll show that later on Okay so we've got this electron configuration remember we got this very specific uh configuration that we write them out in so basically you write them out like this this is an example of one so the number in front of it tells you the shell number to which it belongs to the letter tells you the subshell so this is an S subshell and the little number above it h tells you the number of electrons that are in this shell okay so the electron configuration for iron is this so we've got 56 and 26 here so this is the electric this is the um element here that we're using now the electric configuration is 1 S2 2 S2 and you can see we're filling them up remember I talked about them marrows this is shown the spin pairing of electrons fit two electrons in the 1s uh and two electrons in the 2s but they're spinning in opposite directions uh 2 P6 3 S2 3 P6 4 4 S2 3d10 okay so this is the electron configuration for ION Now The crucial thing is you got to check use these small numbers on the top and they should add up to give 26 okay so you're adding up all these that's really really important this is shown how the electrons are arranged you can see lowest energy is down here this is the one closest to the nucleus and as we go further up we're getting further away from the nucleus and these are higher energy so we fill from the lowest and and we fill orbital singly first as well so you can see here these ones are all filled singly then we pair up if we have to so this is due to electron repulsion I kind of liken this to a bit like a bus I don't know if you've ever been on a bus before where you've got um where it's reasonably full and you get people sitting on the individual seats they put the bags next to them because they don't want anybody sitting next to them um you know they like their own private space which is fair enough um electrons are a little bit like that they will occupy an orbital if there's a free one they will sit on it first um and then only when all of these seats are full does then the electron start and have to sit next to somebody it's a bit reluctant to do so because it repels but it's a bit like that and buses I know it seems a bit odd but it's one of these bizarre observations I kind of make so it's a little bit like what electrons do so they fill singly first then they pair up okay so's have a look at some irons so with irons um you just add or remove electrons from the highest energy level first uh transition metals behave a little bit differently but we'll look at that on the on the next slide so the electron configuration for ca2+ what it does it loses two electrons from the 4S okay and you'll see it disappear here a little bit later on so but there they are there um it'll lose them ones and it'll basically just have a full shell in the 3p and 3s so there's the configuration okay and so what it's going to do is lose that 4s2 as you can see on there and you can check if you add up all the numbers um you got 2 2 6 2 and six they should add up to be 20 minus 2 cuz calcium had 20 electrons we've lost two so it should add to 18 so just just check and make sure that happens so we loosen the 4S there it goes okay so it disappears and that is now the energy level diagram for calcium 2+ okay let's have a look at them transition metals that we were talking about now chromium and copper behave a little bit differently so an electron from the 4S orbital moves into the 3D orbital to create a more stable T half full or full 3 3D subshell respectively okay so for example if we look at chromium the electron configuration of chromium is actually this 1 S2 2 S2 2 P6 3 S2 3 P6 3d5 4 S1 now not it's not this where you've got 4s2 3 D4 okay the electron in here would actually jump into this 3D and create a half full D subshell which is 3d5 so it's really really unusual just make sure you look out for that so the transition met lines as well they behave a little bit differently so the electron configuration for fe3+ what it does actually loses three electrons which is fine but two of them come from the 4S and one comes from the 3D so we're not actually removing them from the um all of them from the 3D orbital even though the 3D is slightly higher in energy so you can see here here's the electrc configuration okay this is for ION and then we remove the three electrons and we have 3d5 as you can see and again if we add all them numbers up we should have 26 ion did have 26 electrons take away three should be 23 so we add up all these little numbers here should get a total of 23 okay let's have a look lose them from the 4S first then the 3D lose them there and then we've got the one there okay so 4S first then the 3D that's the key thing when we're removing electrons from transition metal ions or transition metal atoms should I say to forms right okay okay so just obviously we know about these SPD blocks we know about ionization and how the electrons are removed but we need to know how that correlates to the periodic table because you could be using the periodic table quite a bit obviously so the group number relates to the number of electrons in the outer shell so for example group two elements have two electrons in their outer shell um these blocks here the ones in red um are also known as your s block elements so that includes group two for example the green ones here these elements are also known as P block elements okay because they contain their outermost electron in the P orbitals these ones are known as DB block elements so these are the ones in the middle here some of them are um transition metals not all of them but most of them uh these blue ones down here these are called f block elements so these are the ones which are really big elements so uranium's down there and amarium Etc okay right let's look at the electromagnetic spectrum because we're going to look at about the um uh the electron shell and look for the evidence for a shell structure okay so this bit is going to be quite tricky so listen carefully right we got this electromagnetic spectrum okay and you might have seen this in physics if you do physics of course the electromagnetic spectrum shows the types of radiation at different frequencies okay um so we have have you might have remembered maybe he's Richard um not Richard of York give bat van that's the colors for just the visible light bit you might have known that bit Anyway Richard of York give batlin vein tells you the order of the visible light but you might have got a pneumonic that basically helps you to remember the order of this radio waves down here lowest energy all the way up to gamma rays which have the highest energy so yeah increase in energy and the frequency as well so the waves are much squashed here um shorter wavelength uh along here and obviously the U frequency is increased as we go along to gamma rays so atoms then what's it got to do with atoms so atoms can release energy uh named in the electromagnetic spectrum um and basically we're going to say how how that happens atoms can be very strange things at times okay we're going to look at something called an emission Spectra okay and we look at something called line Spectra and this is a way of identifying elements and is evidence for quantum shells okay so Quantum shells remember that word you're going to hear it quite a bit okay so an atom or the atom has shells okay and we know them as Quantum shells okay or energy levels we got a diagram here showing three different energy levels so this is known as ground state the one at the bottom uh and it's the shell closest to the nucleus so we call it Nal 1 so they have discrete energy values and the electrons can move from one Quantum shell to another quantum shell shell but they can't exist in between so when an electron absorbs energy there it goes okay it moves up to a higher energy Quant or higher Quantum shell okay and this electron is effectively being excited okay yes but you never heard about that electrons being excited but they yes they can get excited okay so if they absorb some of this um some energy eventually though the electron will move back down and release some of this energy so it moves back down to an energy level now it could fall back to the same one that it came from which is N2 could go back to n equals 1 okay and obviously we can we can we can actually identify where this electron might have landed where hit where it's hit uh we'll have a look at that later on okay so we get this line Spectra or we call it an emission spectrum okay which is the frequency of light given out when an electron moves down energy levels okay and we see them as colored bands which looks really really pretty looks a bit like a barod okay you can see all these different colored bands here so red ones over here and your violets and purples over here so every element has a different electron configuration and so will absorb and emit different frequency of radiation so the emission Spectra is unique to different elements now this is brilliant it is literally like a barcode if you go into the supermarket got a barcode on a product that barcode is unique to that product so when it's scanned at the checkout the right price comes out and obviously the right item comes up as well um so it is literally like a barcode for um for an element okay so is unique so the lines on an emission spectrum show the electrons moving to different energy levels okay and I'm going to show you using this energy level diagram here or Quantum shell diagram okay so emission spectas show lines in different regions of the electromagnetic spectrum okay so we call this a group of lines a series so series of lines are created when electrons move to the same energy level from different ones okay so let's have a look at some examples here so the lines get closer together as the energy and frequency increases okay so remember this is the bit where um the energy and frequency is the bit where we've got um uh UV and Gamma and x-rays they're the really high energy frequency ones remember from that diagram so let's have a look so you see we got these yellow ones here okay so basically the arrows here are showing the potential path an excited electron remember the electron already been excited could follow to different energy levels in a hydrogen atom so you can see this one's moving down here this one's moving from a level slightly lower this one's moving exactly so it's going all the way all the way down to ground state which is Nal 1 now electrons which fall into the ground state which is n equals 1 they produce a series of lines in the ultrav Viet part of the spectrum okay so I'm just going to go back and just watch how these arrows correspond to the bands in your um line Spectra okay so I'm just going to go back and then just have a look okay so you can see this one here that's traveled the shortest distance has a band that's very spaced out here it's got this very thick Band Here whereas the ones like here cuz they travel in a very similar distance the gap between them isn't as great then they Bunch up really close together and they're a little bit thinner but again these ones here you need to know that if they fall to ground state they form in the ultraviolet part of the spectrum now I'm going to show you what happens when they fall to Nal 2 and they'll form a little bit further over so watch this okay so you can see the bands correspond to these so we've got the electrons which fall in the second energy level which is the n equal two they produce a series of lines in the visible part of the spectrum and you can see them there notice we don't have as many B as we did here because we're not going down to the N equal 1 uh banding here so we've got less arrows dropping and if we go to the N equals 3 we get bands appearing in the infrared bit okay so you can see here they appear in the infrared part of the spectrum and there's the banding there okay so make sure you're able to identify depending on where the electrons are dropping to which part of the EM spectrum you will see these bands form okay so how does this linked with evidence for Quantum shells well emission Spectra is evidence to prove the existence of these shells so the radiation emitted will have a fixed frequency okay as the energy of these shells is fixed okay remember we can't have the electron hovering between these shells so they can only exist in these very specific shells they can't be in between like I say each shell has a fixed energy there's a fixed amount of energy we call this quantization or quantum chemistry sounds very Grand doesn't it okay the electromagnetic radiation is absorbed remember uh to move the electrons to higher energy shells remember we seen that in two slides ago and it's emitted when they drop to lower ones and so what we get is these defined lines very discret lines there's no blurriness to them they're very um defined crisp lines as as we go across the Spectrum okay and this proves that electrons can only exist in shells they can never exist in between them so we get this nice defined Spectrum here here okay no ambiguity nice clean lines so that's proof that we actually do have a Quantum atom and it's shell-based Theory so this is proof of that okay now we're going to look at some Trends now to do with these now we've proved this shell model we're going to um look at other bits of evidence which could look at that and the first one is ionization so ionization energy is the minimum amount of energy required to remove one mole of electrons from one mole of atoms in the gaseous State you must must remember these key things especially the bits underline there okay so this is an equation to show an ionization of sodium so notice the gaseous State okay sodium gas na+ gas the first ionization is plus 4 95.8 K per Mo this is an endothermic process energy needed to remove that electron always include your state symbols and obviously like I say it requires energy positive value all the time it's endothermic so we need to consider some things when we're talking about ionization Okay so we've got shielding and basically the more electrons uh the more electron shells between the positive nucleus and the negative electron that has been removed which will be in the outer shell and the less energy is required we've got this weaker attraction so shielding you'll see quite a lot and you're going to use this word quite a bit as well the atomic size the bigger the atom um the further away that electron is the outer electron from the nucleus so that means the attractive force between the nucleus and the outer electron is reduced and therefore it's easier to remove that electron okay so these are all factors which will determine how much energy is needed to remove that electron which we call ionization and obviously nuclear charge the more protons in the nucleus the bigger the attraction is between the nucleus and the outer electron this means that we need more energy required to remove that electron um and so therefore um it's have a higher ionization energy for atoms with a larger positive charge okay so let's look at some Trends and we'll look at groups first now this is a graph showing the first ionization energy in group two um but as we go down a group The ionization energy decreases okay and the reason why is because the atomic radius increases as we go down the group the outer electrons are further from the nucleus and the attractive forces a lot weaker so energy is required to remove an electron is actually less it decreases because the atom is getting bigger so it's about this size of the atom here increased radius and not only that I told you this word shielding is going to come up quite a bit the shielding increases as well as we go down the group we have more shells between the positive nucleus and the outer electron so shielding is increased that means energy required to remove the electron decreases less energy is needed and this actually provides strong evidence for shells and atoms just like the line Spectra so it's more evidence to prove this okay so let's look at successive ionization energies um so basically this is just the removal of one uh or more electrons from the same atom so we just keep removing electrons from the same thing and we call this successive ionization energy now you can see here on the graph we've got a the successive ionization energy for magnesium so basically we take magnesium atom we just keep removing moving all of its electrons um it's got 12 electrons in total now I'm going to use the energy level diagram you can see on the left there to basically try and explain it so here's the um the ionization this is the second ionization energy for magnesium so we got mg+ will form mg2+ plus an electron now this is the ionization value of it it's endothermic so it's positive notice these jumps we've got a jump in energy as removing electrons from the shell much closer to the nucleus and you're going to see how this forms here okay so let's start removing some electrons from this thing okay we've got a general increase in energy uh because we're removing an electron from something that's increasingly more positive okay so um obviously removing an electron from an mg plus is going to need more energy than removing an electron from just mg because this is already positively charg it's going to really uh pull that electron in and it's going to get increasingly more difficult to do so okay okay so the first set of electrons are the ones which are um furthest away from the nucleus these ones require the least amount of energy um because they um they're obviously further you've got more shielding Etc so these are ones in the 3s orbital the next eight are the ones in the second shell so that includes the 2s and the 2p subshell these ones require more energy because they are much closer to the nucleus um and also you're removing it from something that's increasingly more positive so so the shielding is less and obviously it's getting increasingly more positive so we've got this increase here but that's the reason for this jump and the next jump over here is removing the last two electrons which are really close to the nucleus this is going to be incredibly difficult to do um you need so much energy to this but there is this big jump because you're removing them from a shell which is much closer to the nucleus okay so we know this is Magnesium look at the number at the bottom it's got 12 electrons so look out for these little clips okay so let's go back to this um modern periodic table again okay so the elements are ordered by proton number not mass number okay this is very important because we're talking about periodicity here this is the trend so we need to know about the periodic table so proton number not mass number okay very important uh the groups are columns and uh basically elements in the same group have the same number of electrons in the outer shell so for example in group one they would have one electron in the outer shell so the group number relates to the number of electrons like I say for group two we have two electrons in the outer shell and elements in the same group they have similar properties so for example group one elements all react with water with increase in Vigor as we go down the group so they become more reactive you might seen these when you put them in these big water troughs you Chuck them in and they really react quite vigorously produce lots of hydrogen gas and some of them Catch Fire as well so your likes of um your potassium could even catch Catch Fire periods these are rows so these go across hence the word periodic table and elements in the same period have the same number of electron shells so all these ones for example across here they all have the same number of electron shells that's that's the third shell there okay so these ones are known as s block elements as we've said before these ones are known as P block these ones are known as D and these ones are known as f as you've seen just before so as long as you're familiar with these blocks that's really important okay so we're going to look at Atomic radi okay using the periodic table that we've seen so as we go across period 3 and the atomic radius decreases as you can see look they're getting smaller and smaller and smaller and you can see here's the graph showing this trend here now this is the atomic radius in nanometers remember these things are really small but you can see there General decreases we go down the reason why is because we've got this increased nuclear charge remember as you go across the period got more protons and so what this does is this pulls the outer shell of electrons further in towards the nucleus uh and obviously hugs that a little bit just just a fraction and makes it a little bit smaller but crucially the extra electrons um elements gain across the period go into the same shell okay so you've got to make that comment you've got to say look going into the same shell the shielding effect is similar okay so we need to mention that as well there's no no good just writing oh you got more protons you need to be talking about shielding as well okay so make sure you've got both of them aspects in there when talking about it okay the atomic radius increases down groups though because we've got that extra electron shell added so it gets significantly bigger each element as we go down a group okay so let's look at the ionization um in periods this time okay so the ionization energy increases as we go across a period so generally as we across a period there's an increase in number of protons in the nucleus as we've just seen this increases that nuclear attraction okay so we generally have this increase shielding is similar like we've just seen before and the distance from the nucleus marginally decreases uh we've got more energies needed then to remove this outer electron um and the ionization energy decreases as we go across the period but we do have these little blips and you can see with aluminium and Sul first so we need to try and explain them as well or look at them okay it's a similar trend for Period 2 as well okay so we see we got this decrease of aluminium uh and this is evidence for atoms having subshells so you can see here the outermost electron in aluminium sits in a higher energy subshell slightly further away from the nucleus than the outer electron in magnesium okay so let's have a look there it is there look so aluminium has got that 3p1 it's electrons in the p orbital magnesium obviously just has the 3s too so the 3p the electron in the 3p is slightly shielded from the 3s there you go so it's in the 3p subshell and the Magnesium has it in the 3s and this trend is obviously similar for period two uh because they might ask you about period two as well okay let's have a look at the uh the dip at sulfur this is a little bit trick here but a decrease of sulfur is evidence for electron repulsion in an orbital remember we're talking about electron repulsion just before in that orbital so phosphorus and sulfur they both have outer electrons in the 3p orbital okay so there's no extra shielding here so it's all the same but removing an electron from sulfur involves taking it from an orbital with two electrons in remember they've got this electron repulsion they don't want to be near each other so they're not going to put up much of a resistance when you try and remove this electron from something where it's already paired so if we look at the um electron configuration for phosphorus phosphorus doesn't have that paired electron so there's no electron repulsion to kind of make it easier to remove that electron whereas um sulfur does you've got this pairing of electrons makes it easier to remove because of electron repulsion okay and again period two make sure you you can familiarize yourself with that as well because they might ask about period to okay let's have a look at some melting points um so the first three elements uh going across the period sodium magnesium and aluminium um they all have metallic bonding and obviously the metallic structure for sodium looks like that so we've got this one plus charge for the um sodium ion and we've got one electron being delocalized and obviously there's the attractive forces there uh the metallic structure for magnesium you've got a two plus charge in the middle and two electrons which are floating around um and you can see them there but we've got this slightly uh higher attractive Force because we got a bigger negative charge and a bigger positive charge got a bigger electrostatic attraction between these so therefore the melting point increases um like I say increas in positive charge more delocalized electron smaller ionic radius means we have a stronger metallic bond make sure we can talk about all these things especially the bits that are underlined they're key points okay again look out for period two because it's the same Trend right let's have a look at silicon this is like right at the top here so silicon has the highest melting point period three it has a giant Co veent or macromolecular structure okay looks a little bit like this loads of strong coent bonds they hold all these silicon atoms together loads of energy needed to overcome these bonds um and so that's why it's got a really high melting point much higher than any of the other elements that's on that graph okay so let's have a look at the next element phosphorus is a massive crash down to phosphorus now so phosphorus has the formula P4 much lower melting point than silicon it only has weak simple it's a weaker simple molecular structure all it has is it just has weaker London forces that hold these molecules together um and it doesn't take much energy to break them forces and so that's why the um melting point of phosphorus is much much lower okay simple molecular it rises a little bit though for sulfur um sulfur still again only has London forces just like phosphorus but because the molecule of sulfur is S8 it's slightly bigger than the phosphorus molecule here and so because it's slightly bigger the size of the London forces is bigger and so this means it has a slightly higher melting point than phosphorus okay and then if we look at chlorine chlorine has the formula cl2 much um well just a slightly lower binding Point um and sulfur uh it's a simple molecular structure again just like phosphorus and sulfur but because it's only cl2 it's smaller molecule smaller London forces and a lower melting point and then poor old argon at the end there doesn't bond with anything um it's literally just an atom uh it has a much lower boiling point and melting point uh and it only exists itself London forces are weaker again we're talked about London forces hence it has a lower melting point okay and again with all of these things make sure you familiarize yourself with Period 2 as well and that's it that is the summary for topic one for atomic structure and the periodic table for Ed EXL um please support this channel by subscribing um every subscriber really does count it's brilliant we've got so many uh you just click on the circle in the middle and you get all the up-to-date videos um and anything that's updated you can see on there as well uh also just a reminder that um these videos uh sorry these slides are available to purchase great uh Great Value you can use them for revision put them on your tablet smartphone Etc um but you can purchase them just click on the link in the description box that's it now bye-bye