Welcome to this demonstration interview. We're going to be talking to you during the interview using Teams and at the same time using Miro so that we can both write things ... both the interviewer and the interviewee on the same whiteboard while we talk, and it's really good idea to get some practice with using Miro and if you can practice using the Miro whiteboard in advance of the interview have a look at what you can do with the different functions it'll help you feel more relaxed when the time comes. If the technology doesn't work something goes wrong during the interview then the main message is don't panic the interviewer will know about that you can tell them if you don't hear them, you know make them aware that you don't hear them properly and we'll just go back to where we were and start again, or ... in the worst case scenario we'd talk to you again at another time when we managed to get everything sorted out so really don't panic. In order to make it ... as as likely as possible to succeed then it's a good idea to have a good talk with your supporting teacher beforehand to make sure that your internet connection is nice and stable and they have a quiet place to sit and you have everything you need at hand before the interview starts and that might include some pen and paper next to you just in case. In in terms of what we're doing really we want to get the people who are best suited to this course onto this course, and we care about giving you every opportunity to do it. The key things are it really doesn't matter what you know when you come in there but we need you to be able to apply knowledge and to apply facts that we give you, so that we can say that things are happening and we've got clear-cut evidence for what's going on around it. We're looking for how you solve problems so we're not going to give you something to which there's a straightforward answer where it's something where you immediately get where we're coming from. We might deliberately do things that contradict your knowledge of the world to see how you respond to evidence and how you deal with that, and we want to see how you put the jigsaw together, we want to see how when you're looking at a question how you connect facts together and how you apply what you're learning to the next bit of a problem, so we're not asking trick questions we're asking you stuff where we're looking for you to provide evidence for your own abilities, evidence for what you can do, and there are going to be lots of ways to do that so as you go along think about what you're talking about. We're not looking for any particular prior knowledge, we're not seeking to find those students who already know the most facts about chemistry, so how can you possibly prepare for such an interview? Well there are several things you can do that will really help you to feel ready and relaxed and in the best possible position for your interview. Firstly practice talking about chemistry and practice talking about reasons for things. Maybe you can talk to yourself in the mirror or you can find someone in your family or some of your friends who won't mind listening as you explain out loud reasoning or explanations for some of the concepts that you've come across in your chemistry until now. Since we're going to be presenting you with material that you might not have seen before it's useful to become familiar with handling different explanations or different concepts which might be somewhat at odds with what you've already seen in your schoolwork so to prepare for that maybe look up explanations for concepts or different ways of reasoning around the same sorts of material and perhaps looking in different textbooks to the ones you usually use. Having said that we don't have any particular prior knowledge and we're not looking for a person who knows the most chemistry already, it's nonetheless really useful if you do revise and understand as best you possibly can all the material you have done at school so far because these are going to be useful language and terminology that will come into the discussion, of course we don't mind telling you and explaining meanings for words when the interview comes if you haven't encountered them already, but it's always good and we're always able to go further if a candidate has revised their schoolwork until now. When you're in the mix and you're actually doing the interview time is going to pass really quickly, you've got a lot of things to think about I think the most important thing is that when you're doing stuff try and talk about what you're doing don't just draw a picture and say nothing and equally don't just say something and don't draw a picture if a picture will help you understand it. Talk through what you're doing, it helps the interviewer understand what you're thinking about, it helps you with where you're going that it's not always going to be something where you immediately get to the answer don't be surprised if you get stuck and don't panic if you get stuck, the interviewers are there to prompt you as well as to ask you questions and those prompts will hopefully lead you in the right direction, so keep going keep thinking about it and try and relax and try not to take the stresses of the situation, be calm, breathe, if you don't understand something say that you don't understand, the world is full of people who claim to understand when they don't understand and it's really important to say "I don't get this" it's an important skill for life and it's an important skill for learning things so, it's legitimate not to know all the answers. We're there to help you explore what the answers might be. Good morning Charlie can you hear me okay? Yeah I can hear you, all good. Great thank you so much for joining us for this interview. I'll begin by introducing us and telling you a bit about how the interview is going to run and then we'll get started and if at any point you can't hear us or you don't understand the words we're using then just let us know and we can explain them a bit more clearly okay? Sounds good. So my name's ... Susan Perkin I'm a physical chemist and my colleague is Professor Steve Faulkner who's an inorganic chemist and we're each going to ask some questions in this interview. Okay. We're going to be using the Miro board, would you like to just check that your pen works on the Miro board? Yeah I'll give it a go. There we go. That looks great thank you very much. Now the interview is going to be about 20 minutes long and ... we're going to start with some questions ... from Steve so I'll hand over to Steve now Thanks Susan ... hi Charlie can you hear me all right? Yeah sounds good. Good okay so maybe we'll begin by thinking about something that I'm sure you've met before can you tell me a bit about water? Yeah it's a polar molecule I'll draw it out, so it's got a bent shape due to the two lone pairs with an angle a bond angle of 104.5 degrees. Okay so you have this water molecule and it exists like that what kinds of things can it do with those lone pairs? So it can form hydrogen bonds so that is an interaction where the lone pair is attracted to the delta positive hydrogen which is a strong intermolecular force due to the polarity of the o-h bond Okay and then that gives rise to lots of the properties of water sure, and you can think in terms of hydrogen bonding and you can think about it being liquid and solid in a variety of other things. Yeah. Maybe let's start just by thinking about an h2o molecule all by itself, so we've got three atoms in that molecule, and you've described it in terms of two bonds and two lone pairs. Yes. I want to think about it in terms of how we might make those bonds, so if we think about that, have you come across the concept of atomic orbitals before? Yes I have. Okay ... and you're happy with the idea that hydrogen has a 1s orbital that has an electron in it and the oxygen can do its bonding through 2s and 2p orbitals? Yes. Yeah, okay ... have you seen the shapes of those orbitals before? So the s orbital is spherical so hydrogen one s would be spherical and the oxygen p orbital should be shaped like, a normal p orbital would be shaped, shaped like that, dumbbell. Fair enough, ... let me maybe try and paste something in here ... let's see if ... okay if we can successfully, okay, so here are some pictures of some orbitals yeah so really we we've got an oxygen atom ... and we've got two hydrogen atoms and they're going to be arranged in roughly the way you've drawn ... so we can say that there are three different p orbitals on oxygen .... and an s orbital and we use this convention of saying that the orbital has different phase or different sign either side of the bit where you've got no electrons for p orbitals so there's a plane in which you don't find any electron density. So what I want to start to think about is how you might do bonding in that. Maybe if I explain a little bit first. When a bond arises in a molecule it arises because the electrons in one orbital interfere constructively with the electrons in an orbital on another atom and you end up with more electron density between the nuclei and that stabilizes the species that you've got. It could work the other way around that you could end up with less electron density between the nuclei and then you'd have what's called an antibonding orbital. I'm not going to worry about antibonding for now I'm going to focus on bonding. So if we were to think about having, just draw your oxygen and your two hydrogens without a bond between them for a second. Okay. And we have something that you can see that looks like that you've got a picture. Let's put the 2s orbital onto the oxygen. Okay ... like this? Yeah that's fine ... and if we put orbitals on the hydrogens could we make them interfere constructively with that? Well would it look like that? Try draw them around the hydrogens for now yeah because you're getting to where you you're going but you're going in the right way, yeah just draw a round 1s orbital on the hydrogens yeah. Oh yeah yeah I see I've muddled the two hang on. No no you're fine, you're doing all right. So like that. Yeah okay and in that case all of those three atoms could interact with each other yeah? Yeah. And we're going to form something which is stronger than what we started with okay? Yeah. So that's what we'd call the constructive interference you're going to end up building up the electron density in the bit that you're drawing around at the moment. Yeah okay. So that combination of orbitals is giving rise to one bonding orbital .... let's think about what else we could do. So in the way that I pasted the figure in you've got p orbitals that point along x y and z yes and we're kind of defining the x z plane as been the plane of the paper and anything coming out of it yeah? Yeah. So if we were to draw your three atoms again your oxygen and your two hydrogens yeah okay so we've got those there, and we think about let's start with the px orbital. Okay. The one that points left and right can you draw that? From the oxygen? Yeah from the oxygen okay okay right so now we've got a bit of an issue, that when we did the orbital in in the picture that orbital is linear effectively it follows .... the line of the x-axis. In drawing it to make it meet the hydrogens you've made it bent yes ... so that might be where we're going, but it's, it's got a problem in the getting there, ... and it's got another little issue if you look at the picture you've got one side of it which is shaded and one side of it that isn't, yeah? Yeah. And what we really want is for a shaded bit to match a shaded bit and for an unshaded bit to match an unshaded bit ... so if we were to draw that p orbital yeah how could we arrange hydrogens so that we've got a shaded one on one side and an unshaded one on the other? Okay so I'll start again here. Yeah okay. So call that the shaded end. Yeah okay .... maybe just draw it horizontal for now just to, yeah you don't have to point it at the atoms, yeah so draw it the way it's drawn in the picture, yeah that's it, that's good, and then maybe shade one side of it. Okay. Right so what would you have to do to that right hand hydrogen to make it work? Shade that in as well. Yeah okay yeah what about on the left hand side? So if it, when it bonds to the other hydrogen it's going to be a separate p orbital. Well not necessarily just stick with this p orbital for now. Okay. Yeah so we're mixing orbitals together we're taking combinations of them so we can play games yeah. So for the other side it's going to be a non-shaded. Yeah okay ... so that's pretty close to reality apart from the fact that all of those orbitals are in a straight line ... and what we're actually going to have is the two hydrogens offset downwards a bit so it looks like h2o aren't we? Yeah. Yeah so what might be the consequence of offsetting it downwards a bit are the orbitals going to overlap just as well or are they going to overlap less well? I think they're going to overlap more. But in the case of this one it's going to be less isn't it? Because as you move them away ... as you go from having your oxygen and your two hydrogens being in a line to being, oops, offline yeah? Yeah. Then we're going to get to the point that actually they don't point at each other but those clouds fill space so you're still going to get a favourable interaction yes? Yes yes I see. If we're in the plane of those three atoms let's look just briefly at the other two orbitals, z pointing along the z axis and y pointing along the y axis, so what what could we say about the one that points along the z axis, could that help in bonding? It's going to be perpendicular to the other p orbital. Yeah. Though more in this plane if there's no overlap you're gonna have ... Hang on, try up and down again, let's keep the axes the same. Okay. So let's define the z-axis as going straight up there yeah? Yeah so you're gonna have this. Yeah okay ... and one side or the other is gonna be shaded ... so let's shade the top, yeah that's good ... so what combination of hydrogens would we have to have at the bottom? You'd have to have a shaded at the top and a ... Yeah but there's no hydrogen at the top, the hydrogens are where those h's are, ... yeah? So we'd have to have them both unshaded wouldn't we. Yes. So they're going to overlap together yeah ... and again it's not going to be perfect, it's not going to be like the spherical orbitals on the oxygen, but it's going to be that you get some overlap and something favourable yeah? Yeah. What about the last one, what about y? So pointing in that axis. Yeah have you got a problem now because I think if it's going along that axis what's going to be... The plane of the hydrogens. Yeah and the hydrogen orbitals have the same phase throughout. Yeah. So in front of it you're going to see constructive interference ... and behind it you're going to see different destructive interference ... and that's not gonna be good so overall you do nothing. Okay. So we've drawn this ... and you've got a bunch of orbitals, and in that bunch of orbitals we've said well okay s orbitals lots of bonding yeah? Yeah. P, y for the sake of argument, no bonding at all yeah? Yeah. P x and z a bit of bonding yeah? Yeah. So in this model all of those orbitals are going to have different energies, different degrees of bonding ... does that fit with what you said originally? When you said you've got two lone pairs and two bonds. Well there's more repulsion from the lone pairs but the bonds are equal in stability ... in my original drawing. Yeah. That doesn't match, no that doesn't match to what we've just said. Yeah and we've only really got one lone pair ... so what ... and what we've described is true for an isolated water molecule ... so why does your approximation stand up in the real world? Because does it explain the shape of molecules better? The shape's probably much the same the, shape is just the minimum energy. Okay. But what what did we talk about when we were talking about water in solution in your first figure that you drew? Oh it's polar. Polar? Yes. And it's doing hydrogen bonding yeah? Yeah. So if we introduce lots of water molecules into the mix rather than just considering one what's likely to happen? They're likely to interact how I've shown. Yeah, you're gonna get an arrangement certainly, maybe that's a good point for me to swap to Susan. Okay. Okay? Yeah. Thank you. Thank you. Thanks Steve and well done Charlie. Okay we're going to continue with the thinking about water because you've actually introduced to us that you've come across the concept of hydrogen bonding and interactions between water so let's think more about water in the condensed phases, so that's to say liquid water and ice. Okay. So at atmospheric pressure that's ... ambient pressure water forms ... liquid and it can form ice at depending on the temperature. Yeah. Do you know at what temperature ... liquid water and ice are at equilibrium? Would it be zero degrees celsius? Yeah absolutely and do you know what that is in kelvin scale? Is it 273, no negative 2, no 273. Yeah absolutely right and so I've just moved slightly to the right on the Miro board I hope you'll see me drawing now. And so if I was to draw ... the graph with pressure on this axis and temperature over here ... do you see that? Yes I can. So we could mark in 273 kelvin down here and we could mark in our atmospheric pressure let's call that one bar standard pressure here and so this is ... a point on the graph which represents the equilibrium between liquid and solid water ... and ... if I were to ... increase the pressure of the surroundings ... do you know what happened to the freezing point of water? Would it decrease? Yeah, do you want to draw that on the graph, sketch a point which illustrates that? Absolutely yeah good so in fact for liquid water although it's a very steep line, so we're going to exaggerate this curve but there is a curve like this, and on the right hand side of that we have the liquid region and over here we have the solid region ... we're just drawing a part of the phase diagram which is very close to the freezing point of water ... so from this diagram or from your knowledge do you know which is more dense, liquid water or solid ice? I think solid ice is more dense. What makes you say that? If pressure increases ... which decreases the temperature then so the molecules interacting, a higher temperature breaks the intermolecular forces, so a higher pressure, if these, if it's not solid, no, at a high pressure if it turns solid earlier You're thinking really well there, I like the way you're thinking. If we imagine having some ice at the point where I'm just, sorry, at the point where I'm marking now on the diagram ... so we've got some ice here and we're going to increase the pressure of the ice at constant temperature so we're going up here, at some point by increasing the pressure we can cause the ice to liquefy. Yeah okay. Does that help you? So we want to know which is more dense the liquid or the solid? If increasing the pressure causes it to liquefy that'll mean the liquid is more dense because you're packing it tighter together. Yeah yeah absolutely very good thinking thank you that's right, and can you think of an everyday experience actually relating to water and ice at equilibrium that helps us to remember or visualize that ice is less dense than water around the ambient freezing point? Oh ice expands so water expands when it freezes. Yeah so when you see ice and water for example on a frozen lake or ice in a cold drink the ice is at the top it floats doesn't it? Yes. So now let's get back to your sketch of water molecules and you talked about hydrogen bonding as something that it can can be acting between molecules and we've just thought that about the fact that liquid water ... around this part of the phase diagram is more dense ... than the ice, can you have a think through why that might be ... in relation to the hydrogen bonding? So have a go at sketching hydrogen bonding ... and how you think it might look in ice and how you think it might look in liquid water, and see if you can come up with a explanation for the difference in density. So that's normal hydrogen bonding, so that would be hydrogen bonding in liquid whereas in solid they're fixed so would it be is it therefore harder for the molecules to move, to act on the hydrogen bonding if they're fixed into their position, whereas in liquid they'd be able to pack closer together because of the attraction? I think you're thinking along the right lines but let's just extend your diagram a bit, could you sketch me a few more water molecules with hydrogen bonds? You told me ... some some good information there about how the water molecules are fixed more fixed in their positions in ice than in liquid water, so sketching here which is a nice regular arrangement, ... do you think that's ... more likely to be a kind of structural motif that we would find in the ice or in the liquid water here? I think that's more likely to happen in... I mean if we could extend it even more so if we keep, if we kept drawing it in the way that you've done here or we can just imagine it carrying on in this nice symmetric way. Okay. Of course it's tetrahedral, it's three-dimensional structure yeah so it had a really uniform three-dimensional hydrogen bonding structure like that. Yeah. Do you think that would be the structure in the ice or in the liquid? Would that be the structure in the liquid? Why do you say that? Because in a solid I'd imagine it's more likely to be arranged in a more rigid ... almost ... what's the word, lattice structure. I think what you've drawn is quite a ... symmetric repeating lattice, of course we're drawing something in two dimensions which is actually three-dimensional and they're actually ... but in fact in the ice the hydrogen bonding is more ordered and it's something like what you've sketched here. So in liquid water ... in liquid water I'm just want to check you can hear me okay Charlie because I know the connection is not great at the moment? Yeah I can hear you. Great, so in liquid water ... the molecules are actually moving around all the time aren't they, they're exchanging their positions and they're changing their orientations relative to one another, and they go from one place to another, so how do you think that influences the hydrogen bonding at any instant in time, if we could take a snapshot and have a little look at the hydrogen bonding at an instant in time? So in a liquid it wouldn't be as strong because if it's constantly moving around these attractions between molecules aren't fixed. Yeah so in liquid water the hydrogen bonds are present but because the water molecules are moving all the time then on average only some of them are existing in the energetically most stable way and just to make one more step of reasoning there we talked about density and you'll remember that you correctly told me that ... that the liquid water is more dense than the ice, and now we've also had this second bit of information which is that in liquid water not all the hydrogen bonding is in place as it were so not all water molecules have got four hydrogen bonds at any instant in liquid water. So putting those two together ... can you help to rationalize why it is that liquid water is actually more dense? Because they don't have these four hydrogen bonds at one time, does that mean does that mean their arrangement, they could, you can pack molecules tighter together ... because they're not fixed. Yes so the hydrogen bonds are actually quite long yeah absolutely right, so the hydrogen bonding actually somehow forces the molecules to be very slightly further apart ... than it ... would be if they were packing more closely without so many hydrogen bonds as in liquid water, absolutely right. Steve did we have anything else we wanted to talk with Charlie about before we finish the interview? I think that's pretty much covers me, ... do you have any questions for us Charlie? Yeah you should feel free to add anything you wanted to say at this point or ask a question. I'm just looking back at what we've done ... no I don't think I have any questions Well then thank you very much for joining us Charlie for the interview. Thank you very much. Thank you. Okay so that kind of interview that we've just gone through is fairly typical of what our Miro interview might look like. It contained opportunities to talk about things it contained opportunities for the candidate to use the whiteboard and illustrate things and it contained an opportunity to talk so for my part of the question I tend to believe that I only use questions in one admission cycle, so this is a question I've used before and unlikely to use again. What I'm trying to see is how people respond to something that they haven't met before in this case we were talking about atomic and molecular orbitals and we were talking in terms of how they might overlap so Charlie began by thinking about something that he knew about he looked at water he described water well in terms of bond angle in terms of shape in terms of lone pairs and then we went on to talk about orbitals and he was a little bit familiar with the idea of atomic orbitals and we moved into looking at how they might be fitted together and how they might make bonds between things so in that it involved discussing effectively spatial awareness within the molecule and he picked up very quickly on the idea of where the bond ought to be and in drawing the picture initially he was fighting a frame of reference that he was trying to bring the orbitals into line with the atoms and then we moved from that towards looking at bonding ... and we talked through each of the possible bonding interactions for each of the possible orbitals and we came to a place where we looked at the overall model and he realized it was different to what he'd started with and then very briefly at the end of that we discussed how the two models might be correlated in the real world and what might be happening. So that was my part of the question. Susan do you want to talk about yours? Yes let's talk about the ... the second part of the interview. I think Charlie did very well on this because ... he kept thinking clearly as we approached some new concepts for him he was very well able to sketch the line on the phase diagram and he did a good job of sketching hydrogen bonding as I prompted him through the question. It was clear that he hadn't encountered these concepts before and that's actually what we always hope for in the interviews, if we if we have a sense that that the candidate has actually already been through this before then we would you know try to move to something that's less familiar to them, and then once we're talking about something that's a little bit unfamiliar we give some new information and help the student to use that to deduce something or to work through a problem and Charlie did this very well. He was able to see how the repeating structure in the hydrogen bonding was eventually deduced that that caused the ice to be slightly more expanded in its structure compared to liquid water which is more compact and we thought through that from a sort of thermodynamic point of view and incorporating the observation that ice floats on water and ambient ... conditions and also all the way from the molecular viewpoint the hydrogen bonding, how those two things connect up, so he did very well in that and kept talking about what he was thinking so overall that was very representative of a typical admissions interview where we knuckle straight down to a physical problem and try to resolve something in that way. And I think in in terms of the general interview it's pretty clear that Charlie is a good candidate, he's bringing in stuff, he's talking about what's going on, ... the key thing in this is speaking about is saying that this is where we are and saying when you don't get it because sometimes because time is limited it's really important to talk about how things fit together so it's clear we both agree that this is somebody who has a grasp of chemistry, who can understand things, who can feel their way towards the issue or the problem. In terms of the rest it's probably representative of what a normal interview would look like, it's clear that this technology helps you but it's also vital that candidates need to talk about things and ask. Absolutely and if there are connection problems which we've even had some today ... then we can just repeat ourselves and ... we can check that we can hear each other so we can make sure that the technology's not getting in the way for us. The other thing that it clearly illustrates is that there is no disadvantage to not knowing something, if you can work your way towards it's important to feel your way through the facts as you understand them, and if you can articulate that out loud, that's kind of one of the things that we're looking for because the idea of the process that we're doing is it replicates aspects of small group teaching, if you want to know about the things you don't understand first of all you need to be able to actually know what you don't understand, so all of that is important as you go through to say okay I don't get this, this is what I think, if somebody corrects you how do you pick up on it, and I think that's something that Charlie did well. I absolutely agree yeah and in some cases if you have some more advanced prior knowledge it can sometimes even get mixed up with thinking during the interview so you have to be very careful to just listen to the information you're being given and talk about that alone, so for example I think Charlie actually knew something a little bit more advanced about hybridization of orbitals and he was bringing his actual prior knowledge of that into his sketches ... your part of the question ... at a sort of stage ahead of it, he was going in a slightly different direction to what you were trying to. He was, and it's interesting because in one sense it represents another of these simplifications that builds the bigger world ... but it doesn't represent the reality of what we're talking about so sometimes there's a reason why we're asking the questions in the way we're asking them and we want to see you being surprised by it.