[Music] hello and welcome to um this video this is the a group 2 the alkaline earth metals my name is Chris Harris and I'm from Aller che.com and in this video we're basically just going to go through um the just an overview really of the group two topic um so it's like a revision video effect ly um just a a quick uh thing to say as well that I'm going to use this PowerPoint that I've made um now if you're um want a copy of this PowerPoint or if you need um if you'd like to print it off and use it for provision Etc and it can be purchased from um the link in the descriptions box underneath his video so if you just click on the link and you'll be able to get a hold of it there like I say this video is very specific to the specification this is the points from the a um specification so everything on here should be relevant if you are studying the AQA um syllabus okay so let's start with atomic radius so basically group two elements form plus two ions when they react so um yeah so basically they're all group two metals and they always have this configuration that ends in S2 um so you might see them here so you'll see that burum ends in S2 magnesium ends in S2 and so does calcium and basically when we lose two electrons from these elements we form the two plus ions as shown here and these are the electron configurations there okay so the atomic radius as we go down the group increases um so that's pretty important because we're obviously adding extra electron shells here you can see so it's getting bigger and bigger as we go down the group and there's just a graph just to prove that so extra shells added as we go down the group okay ionization energy so the first ionization energy decreases as we go down the group this is because and here's the graph here this is because we add extra shells uh as we go down the group as we've seen just earlier um and this is this basically leads to shielding and we're using this word again shielding so there's more shielding hence we get a weaker attraction between the nucleus and the outer electrons so as we go down obviously Down group two the first ionization energy gets lower because of this shielding the outra electrons are further from the nucleus and this weakens the attraction and basic basically both of these um effects make it easier to remove that electron from the outer shell as we go down the group less energies needed so really important there using the word shielding uh and further from the nucleus um Etc so bigger atom Etc as we go down the group really important there okay so we it's also important to note to suppose that as we go down the group we do get an increase in the number of protons um however the shielding effect over rides this increase uh increased positive charge in the nucleus so um it's just worth uh noting that um because they might ask a question on that but shielding always overrides it okay melting points so melting points generally decrease as we go down the group so you can see here um the main reason is because we got this obviously we know that metals are um they group two are metals so they have metallic bonding um and metallic bonding is basically where you have a positive met metal ion and delocalized electrons or negative C of electrons um now as we go down the group uh the size of this metal ion increases but the number um of delocalized electrons Remains the Same and so does the charge on the metal ion as well That Remains the Same and basically this means that because the ion gets bigger but the charge and the number of electrons remain the same then the distance between the delocalized electrons and the nucleus and the positive of Metaline uh gets bigger and so because that gets bigger that weakens the attractive force uh and this means it makes it easier to effectively break these bonds and therefore the melting point is lower and you can see here we've got this General um decrease um from brillium to Barium now there is this exception which is magnesium um but this is due to some structural um arrangement of magnesium and effectively this just gives it this exception you don't need to know um much about that really okay reactions with water these are obviously really important um they react with water and they form bases now the whole point of this topic this topic is called group two alkaline earth metals and that's because when we react them with water they form alkaline substances so let's have a look so these react with water to form metal hydroxide so here's an example This Is strontium reacting with water to form your hydroxide and hydrogen very similar to the reactions of group one Metals except group one metals are much more reactive than group two with water um but they still form hydroxides another thing to point out here is if you look here strums in group two all these obviously all these group two elements they form hydroxides but make sure that you have two hydroxides bonded per group two metal atom um it make sure it's balanced um that's quite important some people just put o and forget to put the bracket and the two there so yeah o is minus strum is two plus you need two of them to balance that out and hydrogen gas is obviously produced as well okay uh reactivity increases as we go down the group um just like with group ones group one Metals um no reaction with Barum though um it's pretty unreactive so it doesn't react with water um and the reason why is the atom gets larger as we go down the grip the electron further away from the nucleus as we go down so that means it's easier to remove that electron more reactive more shielding as we go down the group um so that makes the uh the metals more reactive there's a little bit of an ex ction though magnesium um reacts slowly with cold water okay but it's a lot more lively when you react it with steam so it's obviously it's a higher temperature but another weird thing is that actually when we react magnesium with steam we don't produce a hydroxide we actually produce an oxide we produce magnesium oxide so just watch out for that one there and make sure that if they're talking about magnesium and steam that you actually produce an oxide and not hydroxide okay solubility obviously this is quite important because we're talking about how soluble these things are so group two hydroxides and sulfates have opposite solubility as we go down the group okay so as a general rule um if the anion the negative ion has a double charge they become less soluble as we go down the group in other words they become more insoluble so you can see here magnesium sulfate is very soluable because that's at the top of the group but as we go down the group to Barium Bari ium sulfate is very very well it's pretty much insoluble it doesn't really dissolve whatsoever so um this basically because this is a double charged anion s so42 minus it becomes less soluble if we look at the hydroxide though generally um if it has a single charge like a hydroxide they become more soluble as we go down the group and you can see here that magnesium hydroxide is pretty insoluble but barium hydroxide is very soluble so as you can see the solubility decreases you've got to know about the solubility of these that's pretty important okay uh right okay so test for sulfates using these solubilities this can be really useful okay so we test for sulfates using barium chloride okay so when we're testing for them we're going to see if a compound contains sulfur ions all we do is we do this following method so we add hydrochloric acid first basically what this does is it removes or reacts with any carbonates that may be in in there um that um could effectively precipitate out when we add the Barum chloride um and this would give a false result because we see a white precipitate thinking that actually yeah we do have a sulfate in there and actually we don't we just have a carbonate so we basically remove this to mop up any carbonates left in there it's naturally found in the water once we've done that then we just add barium chloride um and surprisingly um we get a white precipitate well not really it's a bit of a joke so effectively we do yeah we do get this white precipitate but no surprise really because uh the reaction is barium chloride reacting with let's say A sulfate zinc sulfate forms barium sulfate just in the previous slide obviously we seen that sulfates are in soluble especially um well barium sulfate sorry is insoluble so we're bound to get this white precipitate uh we get zinc clide which is obviously soluble so we observe this white precipitate if there are sulfates and this is because um you form barium sulfate which is insoluble the ionic equation is this so barium ba2 plus reacting with sulfate s so42 minus forms barium sulfate notice the state symbols acris acris solid okay we always form a precipitate so if we see a white precipitate barium chloride add that to your um compound if you get a white precipitate it contains a sulfate remember to add the HCL to remove any carbonates okay neutralization now these things are like we said um they can be used as alkalines um so group two compounds they can be used to neutralize acids so we looked at the one when we reacted it with water and you formed your group two hydroxides they're alkaline so we can use them to neutralize acids so one example is with acidic soils um so calcium hydroxide um which is caoh is basically used to neutralize these soils so we can spray this onto a soil some plants prefer to um grow in less acidic soils so if the soil is reasonbly acidic you spray some calcium hydroxide on and it just neutralizes the acidic soil H ant acids this is probably more common again we use magnesium hydroxide for ant acids M mg2 and this is used to neutralize excess stomach acid that may obviously occur particular if you've eaten things like chilies Sometimes some people get um a bit of excess acid stomach acid buildup you take magnes I hydroxide and it should satle down neutralizes the acid okay so the ionic equation dead easy this one for neutralization H+ that's produced from the acid oh minus is from the alkaline that produces your neutral compound h2o which is a liquid notice your ions are always aquous okay your water's liquid right burying meals so these are pretty useful uh these used in medicine actually so um the barium sulfate is also known as a barium me uh barium sulfate is used to help identify problems with the digestive tract in particular barium sulfate is pretty dense actually is pretty heavy pretty heavy material so how it works the patient drinks basically a suspension of H berium sulfate and what this does this lines the the soft tissues within the body uh and basically the patient stands in front of an x-ray machine uh and x-rays are absorbed by barium sulfate you can see an image here um so you can see that we've got some obviously white um dense areas this is the barium sulfate inside the digestive tract um and soft tissues problem is that if we didn't use barium sulfate all the x-rays would go straight through the soft tissue so the barium sulfate basically shows up parts of this now I'm no doctor so I don't really know what's going on here but you could basically um look for things like blockages things which aren't getting through the digestive tract for example so it's pretty um pretty useful for that thing now now barium compounds are toxic okay so you got to be really careful with this yet we can ingest them which seems a bit daff but thankfully as you know from the previous slides that barium sulfate is insoluble so it doesn't get absorbed into the blood so that's that's pretty useful they ask this question um then you need to be able to kind of refer to this and they might phrase it as toxic and you might be sitting there thinking well that's that's quite bad why why would you take it but just remember your solubility ruls okay so we're just applying them solubility rules it's a real life example okay extraction of titanium now titanium is one of these great Metals it's a lightweight metal but really tough and hard so magnesium is used to extract titanium from its all routi now magnesium is a group two metal um so Titanium or is titanium dioxide tio2 uh and it's converted to Titanium chloride titanium for chloride first all we do with that is we just heat it with carbon and chlorine gas now we've got to heat it with chlorine because what we don't want is the carbon reating with the titanium because it forms titanium carbide which is brittle and that pretty much ruins your your reaction so we reacted with chlorine so we form the ti4 then once we form the ti4 we then um basically pass it through a fractional distillation column we increase the Purity so we get rid of any other bits that might be in there like titanium dioxide and carbon Etc so we just try and get a pure sample then the pure purified titanium um Titanium chloride uh tetrachloride is reduced we use magnesium to do this uh in a 1,000° cius furnace using really high temperature but we want to remove the chlorine from from titanium uh in this compound to get pure titanium so we're using magnesium and here's the reaction ti4 reacting with magnesium we get pure titanium and magnesium chloride okay so this is why we can use it so fact reducing it remember titanium here is+ 4 titanium here is zero because it's an element so that's reduction so the Magnesium is reducing the titanium chloride uh lightweight like I say very strong commonly used in Planes you can see the fins are this jet engine uh that basically allows it to um be uh used in these kind of uses because you don't want heavy metals in a plane you want the plane to fly um so yeah okay so that's the type of thing we're looking for for extraction of titanium okay uh removal of sulfur dioxide so like I say um these things are alkalines they're really good in terms of reacting with acids okay so a particular use for this is um using calcium carbonate uh and oxide both to remove sulfur dioxide emissions so this is normally produced when you burn things like fossil fuels in power stations Etc you produce silfver dioxide as a by product isn't good you don't want that getting into the atmosphere so yeah like I said we can uh produce electricity burning fossil fuels it produces this harmful pollutant so what we use we use something called wet scrubbing uh and this is a method where effectively we um neutralize the acidic gases coming from the burning of fossil fuels uh it's an acid it's acid causes acid rain this if it gets into the atmosphere so you don't really want it in there so wet scrubbing basically what we do is we spray this um this solution of calcium carbonate or an oxide either or spray it onto the uh sulfur dioxide gas as it leaves the um chimney uh and basically what we form is these uh different substances here so we've got a carbonate and oxide I'm just showing both of the reactions here so you dissolve it in water react it with the sulfur dioxide gas and you form calcium um sulfate which is uh this stuff which is cao3 that's calcium sulfate notice not sulfate sulfate plus water and carbon dioxide both both reactions produce this calcium sulfate so as long as you can uh react that just be really careful with that product there though and calcium sulfate is really useful um because actually we can sell this so it's great we remove the acidic gases from the flu and we also get a product that we can sell so that's pretty good so uh we use plaster boards so you like board out um interior Interiors of houses Etc um and that's obviously used to make plastic board so pretty useful stuff uh and that's it that's the end of the um group two um revision PowerPoint um it as you see as you can see it's obviously just an overview of the whole of the topic it's just pretty useful for things like revision and remember if you want a copy of this PowerPoint just click on the link in the description box uh and you can get a copy of it there but that's it bye-bye