[Music] hello and welcome to this video on periodicity um this video is particularly for AQA uh my name is Chris Harris and I'm from allert tutors.com and basically this video is for revision purposes to give you an overview of the periodicity topic um the Powerpoints that I'm going to be using here the ones that I've made uh can be uh purchased from uh for well for your use you can use it for revision you can print them off Etc so if you find uh the link in the description box below this video you can click that link and you can uh you can access them there um like I said these videos are specifically for uh the AQA specification um so you can see that we've taken the bits from the spec to make sure that it fits um with what you need so they're pretty targeted to your exam board if you're studying the AQA syllabus okay so let's make a start so periodicity is obviously to do with the periodic table we're looking at Trends there's a lot of Trends here and descriptions and some really um important key wordss really for this topic it's really important so basically we need to know how the elements arranged in the periodic table so the elements are ordered by proton number not mass number okay it's really really really important that you don't write down that the orders in terms of mass number um it's always proton number so proton number is obviously the number uh the smaller number on the period table tells you the number of protons groups are columns so these go down and the elements in the same group they have the same number of electrons in their outer shell so group one have one electron group two have two electrons Etc so that's what we're seeing there so group two elements have two electrons in the outer shell and that relates to the group number as well so elements in the same group they have similar properties so for example all the group one elements here they react violently with water you might have seen this when you put them into a big trough of water uh and they explode they produce hydrogen um yeah they're pretty reactive so um and they basically react with increasing Vigor as we go down the group so I mean I would want to know exactly what happens to francium but uh I wouldn't be standing next to it put it that way so it'll be really really violent whereas lithium doesn't react as much um periods or rows this is going across this is really important because this topic is all about periodicities so we're going to do a lot of that in here elements in the same period they have the same number of electron shells so elements for example in this period that all have four electron shells okay and this one this one will have three this will have two and that will have one so that's very important okay these ones are known as sblock elements so which are these ones in um in the red basically their highest electron or the electron furthest from the nucleus occupies the S orbital these ones are known as P block elements so this group here and there um they com in bunches of six and the purple lot are known as DB block elements they have electrons that occupy the highest electron um in the highest energy level they they occupy the D Block okay and these are known as F block elements so as long as you know the the different blocks okay let's look at Atomic radi so as we go across period 3 uh the radius decreases it gets marginally smaller as you can see there okay now you need to know um obviously this trend in terms of atomic radius you can see obviously here's the data to actually show it this is atomic radius remember OB the atoms are really small so this is measured in nanometers and you can see it generally decreases okay so there's an increased nuclear charge as we go across here in other words we've got more protons in the nucleus this pulls in the electrons um in the Shell but crucially the um that's what we're saying there so it's pulling closer towards the nucleus but very importantly you've obviously got this shielding effect that's very similar now shielding is the um basically the protection of inner electron shells from the nucleus so because the shielding is pretty similar across this period here we're not entering any new shells then the um increased nuclear charge or the increased number of protons does have an effect and it just pulls in them mouter electrons a little bit more okay so you need to be able to describe that okay so the atomic radius increases down groups so when we go down a group down here the atomic radius increases we've got extra electron shells basically as we go down this group here um so the um the atomic radius increases so therefore removal of electron becomes easier but we'll look at that later okay melting points right so the first three elements these ones here sodium magnesium and aluminium uh in Period three are metals and so they all have metallic bonding there's a an example of metallic bonding this is for sodium uh has a positive charge OB the positive metal ion in the middle and the electrons obviously surrounding it um if you look for magnesium magnesium's got a two plus charge and two electrons in here now this is going to have a much bigger attractive Force electrostatic attraction between the two plus and the negative electrons okay so basically there's a general increase in melting points as the metalin have an increased positive charge more delocalized electrons therefore um we have a stronger metallic bond increased electrostatic attraction between these so that's why magnesium's got a higher melting point um okay so if we look at um the next one which is silicon okay so silicon is uh much much higher compared to the rest of them so it must have some kind of special type of bonding um and it does to an extent it's a giant coent structure um it's macro molecular these are huge structures there's an example here this is Diamond um but silicon forms the similar structure here um many strong coant bonds look at all the coant bonds there these are the blue lines these hold in this case silicon atoms together loads of energy is required to overcome these strong coent bonds this is the type of words you need to be using when describing why silicon has a high melting point carbon for example like diamond can be um explained in the same way as well okay next one now phosphorus this is this element down here so phosphorus is the formula P4 okay bit unusual you have to know about that much lower melting point compared to Silicon not macro molecular it's called Simple moleculus it's very small molecules and the melting point is actually determined by vile's forces which are a lot weaker than these many strong coent bonds that you have in Silicon so the melting point is now determined by vandals here we're talking about breaking bonds okay here we're talking about vs so phosphorus is P4 it rises marginally for sulfur okay you need to be able to explain this sulfur is S8 as you can see here it's like in an octagon shape okay higher melting point because it's a slightly bigger molecule compared to phosphorus so because it's a slightly bigger molecule it has larger Vander vales forces and therefore it has a higher melting point so that's why it's slightly higher there chlorine dips a bit so we're going to look at the next one here's chlorine very small only two of them it's not as big as S8 there only cl2 much lower melting point simple molecular again smaller Vander Val's forces much lower and again it drops again for Argon argon is literally just on its own it doesn't bond with anything smaller again lower melting point so um therefore um it only exists on its own we call it monoatomic uh much smaller Vander vals lower melting point okay so as long as you can describe them Trends and Link it with structure that's the main thing okay ionization okay this is really important again this is where I said right at the start about the key words keywords are King in this thing especially for ionization okay 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 okay you've got to know them uh certain key words okay so here's the example here's one sodium going to na+ plus an electron the first ionization is plus 4 95.8 K per always include your stake symbols that's really important and the ionization requires energy you are removing an electron from an atom so you have to put energy in to do that and that's why these things are always positively charged so these are effec like endothermic processes okay now the key thing here is shielding shielding is the protective um uh the protection of uh inner electron shells from the nucleus to the outer electron so basically um the more electron shells between the positive nucleus and the outer electron um that is being removed the less energy is required because there is a weaker attraction this has more shielding compared to that okay so the atomic size is also quite important as well this is a bigger atom compared to that bigger atoms means bigger distance between positive nucleus and outer electron electrons are lost more readly with atoms that are bigger than compared with the ones which are smaller the attractive force is obviously weaker for bigger atoms and the nuclear charge the more protons in the nucleus the bigger the attraction is um this means it takes more energy to remove the electron um but however this is as we go down groups this is overridden by shielding um so shielding has a much bigger impact even though we might have more protons in the nucleus we go down the group shielding has a much bigger impact on ionization than nuclear charge this is mainly relevant when we go across a period okay so we need to look at successive ionization so the removal of more than one electron from the same atom is called successive ionization so here it is here magnesium plus to magnesium 2+ plus an electron so the second ionization energy this is the removal of the second electron is + 1450 KJ per mole okay now you see we've got these jumps here so this is the removal of the uh of an electron from the same atom so this is obviously this is going to be in magnesium so you see we've got two jumps this is because we're removing electrons from a shell that's much closer to the nucleus and that's going to take a little bit more energy than what it would if it was much nearer okay so we're going to start with um looking at the general Trend like I say it increases um generally takes more energy because we're moving electrons from something that's increasingly more positive and it's getting closer to the nucleus start with this slot first first two electrons in magnesium in the outer shell sit in the 3s orbital and you can see these two here okay relatively easy to remove then we've got this big jump this is because we're having to remove electrons from the 2p and 2s um suborbitals okay so we just going to put them in there that's them ones there much closer to the nucleus these ones are imagine the nucleus is down here closer to the nucleus so therefore requires a lot more energy to remove them then it jumps again because we're haven't remove electrons from the 1 s orbital which is very close to the nucleus so that takes a lot more energy to do okay so we know this is Magnesium because we're moving 12 electrons all right okay first ionization energy so this is um looking at groups this time so ionization energy decreases as we go down a group it's easier to remove an electron as we go down in group this one we're going to look at group two so this is because the atomic radius as we go down the group increases so the outer electrons are further from the nucleus and this means the attractive force is a lot weaker so we don't need as much energy to remove that outer electron okay also as we go down the group like I said before the shielding increases shielding is really really important more shielding more shells between the nucleus positive nucleus and the outer electron that means the attractive force is weaker and that means less energy is required to remove that outer electron to ionize it so I ization and you decreases as we go down the group uh and again um you need to obviously know about the um the uh the historical aspect of the development of the atom and Neil's B basically came up with a shell Theory and this model proves it um however it doesn't explain data shown going across a period and that's where the modern subshell or suborbital um Theory comes from so let's have a look at that so this is going across a period so this is the ionization energy increases as we go across period so you can see here there's the general increase because we've got more protons in the nucleus um it requires a little bit more energy to remove that electron um because you've got an increased nuclear traction um and the shielding crucially going across is actually pretty similar so it doesn't really have much of an impact here um the obviously increas in number of protons does okay so more energy is required to remove the outer electron so generally as we go across the um across a period uh the ionization energy increases okay now you notice there's a few exceptions here okay so we have a decrease of aluminium and this is evidence for atoms having subshells which is what we mentioned before okay so the outermost electron in aluminium actually sits in a higher energy subshell than and it's slightly further from the nucleus than for in magnesium okay so let's have a look at them here so this is for aluminium you can see that its outer electron sits in the 3p1 subshell that's slightly further away from the nucleus it's slightly shielded from the 3s okay so that's it there but if we have a look at magnesium magnesium has its outro electron in the 3s subshell so the atomic model that Neils B came up with didn't actually explain this subshell Theory um he only just looked at shells um but obviously the modern one is looking at subshells okay so that's for aluminium so slightly shielded from this one here so it requires a little bit less energy for aluminium because of the shielding effect okay uh if we look at next one along which is sulfur now sulfur is a little bit um strange in this one okay so basically we've got a decrease of sulfur is evidence for electron repulsion this time so we're not talking about distance from the the nucleus because obviously this is in the same um P subshell so we're not moving into any new subshell here so if you look at phosphorus Okay so phosphorus and sulfur both have outer electrons in the 3p orbital okay so this is an energy level diagram for sulfur but phosphorus would just have one electron there and this one wouldn't be there so the shielding is actually the same so shielding is not an issue here okay but if we're trying to remove this electron here this is the electric configuration for sulfur and we're trying to remove it from an orbital that has two electrons in already okay um now electrons repel each other because they have the same charge so if they're repelling each other it means you're not going to need that much energy to take an electron away um because it doesn't want to be there anyways repelling the other electron so less energy is needed to remove an electron from an orbital which has two in it um phosphorus only has one so therefore you're going to need a little bit more energy to remove this one because there's no electron repulsion but to remove this electron it won't take too much effort because there's repulsion there anyway and this is why there's a slight drop in Sulfur compared to with phosphorus and so that is periodicity um It's relatively straightforward a lot of Trends there the key things really are shielding nuclear charge atomic radius comment on all of them in your answers these are normally worth about three marks in the exam so make sure you're using them properly uh and again if you um want to see this PowerPoint or if you want to use the PowerPoint for your own use um you can find the link you can purchase it um you can find the link in the description box of this video if you just click on that and it will take you to the place where you can um where you can buy it um but um that's it for now bye-bye