[Music] hello my name is chris harris and i'm from alley chemistry and welcome to this video on group two elements um this is the topic 10 video for the cie which is the cambridge international specification so if you're stood in the cambridge um course then this video is perfect for you obviously you're going to look at areas of group 2 elements um there is the full range of a level videos on alloy chemistry youtube channel i massively appreciate it if you hit the subscribe button just to show you support and but also any videos that you see on here with the black backgrounds these are just powerpoint slides which i'm um which i've created and they're available to purchase by my test shop if you click on the link in the description box below you can get a hold of them there they're great value for money great for supplementing your revision your notes and your books and everything like that so it's just electronic form that you can obviously take wherever you want so let's crack on with this then um so this is a a relatively short topic um you know compared to some of the other topics within the ci bit also a lot of the topics you'll probably see kind of um merge within each other um you'll see that there's a bit of a kind of cross-reference in between the two and you'll probably find some of the equations on here may also fit with topic nine um so yeah there's a little bit of some duplication but it just puts it into context i suppose so obviously this topic is purely going to look at group two elements um obviously group two elements form plus two ions when they react as you probably will have seen before so group two metals they lose two electrons to form plus two ions and all group two metals have an electron configuration that ends in s two so obviously looking at your subshells so let's have a look so there's beryllium and there's magnesium so you can see this pattern here okay it's the all end in s2 but they also do form ions as you can see on there they form the kind of plus two ions and so when you remove the electrons from the s the 2s orbital then you're left with these here so as we go down the group the atomic radius gets bigger so it increases as we go down the group and the reason for this is because we add extra shells to to the atom so obviously because we're adding extra shells then obviously the radius increases overall so relatively straightforward i think excuse me so um ionization energy so you would have seen again bits of this in the previous um previous topics but this is specifically looking at group two elements um and the first ionization energy decreases and reactivity increases as we go down group two so extra shells obviously as we've seen before are added as we go down group two um and obviously this does have an impact in terms of ionization energy and this is because as we go down the group more shells means more shielding and so therefore that attractive force between the nucleus the positive nucleus and the outer electrons is obviously weakened as we go down the group so therefore it makes it easier to remove the electron from the outer shell and obviously that's why the ionization energy decreases as we go down obviously as you can see on that graph there so both of these obviously um the the fact that the outer electrons are further away from the um um from the uh the nucleus and the fact that there's more shielding obviously this makes it easier to lose that electron as we say so um we do have obviously an increase in the number of protons as we go down the group and you might think well hang on does that not have an impact but the the shielding effect is so powerful it overrides any increase in the number of protons in the nucleus but normally that that might be something they might kind of throw in as a bit of a curveball and say look but the number of protons are actually increasing as we go down the group does this not mean that you've got an increased nuclear charge it does but that kind of attractive forces is just completely overwhelmed by the fact that you have more shielding so just kind of be aware of that okay so let's have a look at some kind of chemical reactions here so group two elements they react with water to form bases um and obviously they react with water to form metal hydroxides now there is a little bit of a quirky as you'll kind of see later on with regards to these reactions um but let's have a look at this first one first so this is strontium reacting with water and this will form strontium hydroxide and hydrogen gas you get some fizzing you'll see some fizzing with this reaction so as we go down the group so as we go down group two the reactivity increases with water so there's the the reactions are much more vigorous there isn't any reaction with beryllium which is at the top so it's effectively inert and when it reacts with water and the atom obviously gets larger as we go down the group and so that electron is further away from the nucleus and so therefore it's much easier to remove that electron when it you know when it interacts with another atom and so therefore it's more reactive and obviously there's more shielding so remember when we're looking at chemical reactions the thing which allows the reaction to occur is the fact that electrons can be removed um from an atom and if it's easier to remove an electron from an atom then it's like to be more reactive so it's that distance from the nucleus and the shielding which again has an impact here so magnesium does react with water it's really slow though if you've ever seen magnesium ribbon and put it in water it doesn't really do a lot to be honest um it's incredibly slow reaction so normally um magnesium if you want a reaction from it is you heat it with steam um this produces a slightly different product though so instead of producing magnesium hydroxide you produce magnesium oxide instead so magnesium hydroxide is only formed when magnesium reacts with cold water okay so just that's the kind of slight quirk in this okay so they um group two elements also react with oxygen as well and they form bases as a result so um reaction with oxygen to form metal oxides so there's your first one so this is magnesium reacting with oxygen to form mgo now the magnesium is burned with a really bright white flame and you shouldn't look at magnesium directly when it's burning in a bunsen burner you should use your peripheral vision and kind of glance at it just through the corner of your eye because it will cause it can cause damage to your eye permanently um if you stare at it directly um new they used in fireworks actually magnesium or oxides and magnesium and it gives that kind of sparkle that bright color so looking at some oxidation states on here um remember magnesium and this is in group sorry this is topic six if you're not familiar with this when we look at oxidation states but magnesium has an oxidation state of zero because it's an element um and then when it reacts with oxygen it forms mgo now the oxidation state of magnesium in mgr is plus two um because obviously it's reacted with oxygen which is minus two so here you can see it's obviously been oxidized um now the oxygen itself has been reduced so obviously this is an example um of a redox reaction now group two oxides when you do form a group two oxides they are white solids to be honest a lot of chemistry a lot powders and chemistry are white um unless the transition metals may normally foam coloured uh coloured substances but um yeah so group two oxides are white solids again if you look at magnesium when you burn it in a bunsen burner you get this white powder that's left behind so you might you might have seen that okay so let's look at some group two oxides and what we can do with the oxides so we can react them oxides with water and we form bases with them so alkaline solutions like i say are formed so let's have a look at strontium oxide as an example so protect strontium oxide and react at with water we form strontium hydroxide which is the solution obviously that's formed um now we can obviously break that up into the ions that are formed so you get sr2 plus strontium two plus ion and the two oh and remember it's the oh minus sign that makes something um basic so that obviously that's the alkaline there that's um the iron that's responsible for that property so oxides they react readily with water they make hydroxides obviously they dissociate to form that oh minus ion and magnesium oxide reacts very slowly though um and the hydroxide barely dissolves at all so obviously this we picked strontium deliberately because obviously it's lower down in the group and it does um allow obviously just form that oh minus ion as well so they become more strongly alkaline as we go down the group and this is purely because the the hydroxides are actually more soluble in water and if they're more soluble that means they dissociate readily and you get plenty of these oh minor signs that are produced if you go towards this say the top end of the group like magnesium obviously it doesn't produce as many of these and that's obviously the main feature of an of an alkaline or basic solution okay so let's have a look at some neutralization reactions then so we've looked at oxides dissolving in water so now we're going to look at these oxides and reacting them with hydroxides so they can neutralize acids which is probably no surprise and an example of how oxides react with acids is here so this is obviously calcium oxide reacting with hydrochloric acid so hcl and that will form your salt which is calcium chloride and water is produced so this is your classic um acid plus base gives salt plus water and type of reaction so let's have a look at some hydroxides they follow a same rule obviously so calcium hydroxide reacts with hcl that'll form calcium chloride still and water so the products are still the same obviously the balancing is going to be slightly different so oxides and hydroxides act as bases when they're reacting with acids as you can see there okay so let's have a look at some decomposition reactions um so group two carbonates and nitrates they can decompose upon heating so this is effectively just heating them up you've got a carbonate a pile of carbonate and a pile of nitrate we just apply some heat to it and what happens to that so carbonates they do break down into metal oxides and carbon dioxide normally when you've got carbonates involved you will produce carbon dioxide so that's a bit of a clue and obviously this occurs by a thermal decomposition so it's basically just heating the compound up so is calcium carbonate that's going to produce calcium oxide and carbon dioxide gas and nitrates so these are group 2 nitrates these break down into metal oxides nitrogen dioxide and oxygen so you're getting three different products here but again a bit like with carbonates where you form carbon dioxide with nitrates you'll form nitrogen dioxide and again this is through thermal decomposition so here's the reaction here so you've got calcium nitrate which will form calcium oxide plus nitrogen dioxide plus oxygen so just be aware of these reactions um obviously they're interchangeable depending on the group two elements um but um yeah you've got to be aware of these so the carbonates and nitrates become more thermally stable as we go down group two so in other words it becomes more difficult to get them to decompose as we go down the group um and the reason why is the carbon of the carbonate nitrate ion has a large electron cloud that can be distorted when nearby positive group two metal ions are obviously bonded to it so all group two metal ions they all have that plus two charge remember um but they do become large as we go down the group obviously because you're adding that extra shell on you so the charge that that plus two iron has is actually spread out over a much larger area and so that means the charge density is lower so it's a bit like imagine if you've got um to use an example let's say you've got some toast for example and you have a fixed amount of butter on your knife now if you had a small slice of toast or small slice of bread sorry which is toasted fair enough um and you had the fixed amount of butter then you could spread that butter quite evenly and nicely across the across the the bread or the toast if the toast or the bread was much larger but you had the same amount of butter which is a bit like um i suppose the electron cloud then you could still spread it but it's spread a lot more thinly and it probably won't taste as nice um so it's the same with this so you've got group two well not quite the same but it's the same concept so you've got a group two element the bigger the element the more that charge has to be distributed across the atom and so therefore the density of charge decreases now this does have an impact so obviously magnesium two plus um of magnesium in a smaller element has a high charge density and what this means is it distorts the electron cloud in the carbonate all the nitrate ions much more than the barium one which has a much lower charge density because it's bigger and obviously the less distortion you have the more stable the carbonate is okay so for example obviously you've got a lot more distortion here so this is your carbonate iron you see the electron clouds being pulled or distorted away towards the mg2 plus because it's got a nice heavily dense high density charge in the ion whereas barium is a bit bigger spread out a little bit more and it doesn't distort the electron cloud as much in the carbonate so this is more stable because the distortion isn't as great okay so just hopefully that diagram kind of makes it a bit clearer anyway okay so let's look at some solubilities here we'll look at some various different group two compounds here um but group two hydroxides and carbonates have opposite solubility as we go down the group okay so let's have a look so as a general rule if the anion that's your negative ion if that has a double charge they become less soluble as we go down the group okay so this is because there's a decrease in the enthalpy of hydration of the metal basically entropy of hydration you'll kind of see a lot more of this in um in year two but it's effectively just where you um you have a basically water molecules can surround the metal line on that don't worry too much about that what really in year one what you're mainly focusing on is the fact that it has a double charge and as we go down the group they become less soluble okay and if we look on the other side if they have a single charge such as hydroxides for examples or group two hydroxides they actually become more soluble as we go down the group and again the lattice of dissociation enthalpy decreases and this outweighs the enthalpy change of hydration on the metal ion so again this is really something you would probably use in well you will use in year two rather than year one but again what you need to be aware of for year one chemistry s chemistry is the fact that hydroxides group two hydroxides become more soluble as we go down the group so the extra bit of info is if you're doing the full air level okay so let's look at some uses finally um so obviously group two compounds are used in everyday life as you'd probably expect and so the first one which is lime so calcium hydroxide is also known as slacked lime as well and that's used to neutralize acidic soils really important for farmers obviously some crops will grow better in certain um phs of soil and so therefore the farmer wants to try and utilize or maximize their crop yield they'll make sure that the soil ph is perfect and they can spray calcium hydroxide for example slat lime onto the soil before they grow the crop limestone um obviously calcium carbonate um is used in construction material and buildings so it can be used to make cement as you can see on there or some lovely stone cottages obviously that's a an example of limestone that's been used so it's a quite a useful and building material as well okay and that's it i thought it was a short topic um so like i said please subscribe to my channel the full range of cia level videos are are on halloween chemistry and please spread the word tell your friends etc um these slides are available to purchase as well i've grouped them up as part of the inorganics chemistry topic so it's not just this one there's other ones in there as well but you can buy the full a level content as well via the test shop the link is in the description box as you would expect um but hope that was helpful that's it bye bye