Transcript

Dyadic Task Dialogue

Two 17-18 year old students were set the task of talking through their answers to some past examination questions

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J: (Oh my God) [see transcription conventions]

N: Mondays{?}

N: Start with sodium chloride?

J: You have to read out the question, go on.

N: Alright, “describe with the aid of diagrams the structure of and the nature of the forces present in the following solids: iodine, diamond, sodium chloride and copper.” Sodium chloride?

J: (Iodine * start with)  [see transcription conventions]

N: Mm, c’mon then.

• • • • • [see transcription conventions]

J: What d’you say? This happened yesterday and it takes us a bit of time to get into it.

I: That’s alright, no problem.

J: Okay, iodine, what is it?

N: Van der Waals.

J: Van der Waals forces?

N: Yep.

J: The forces present, structure, what’s the structure?

N: The structure of a metal. {?}

J: Simple covalent isn’t it?

N: Mm.

J: The structure of

N: diamond’s, macro isn’t it? It’s erm

J: giant

N: giant macro molecule.

J: Giant covalent

N: It’s a large lattice made up of, what’s the structure of the, diamond, I don’t remember now, it’s called (Sh*t).

J: * * * * * (laughs) Plonker. [see transcription conventions]

N: Forget about that, let’s go on to sodium chloride. > Ionic. > [see transcription conventions]

J: < * * < Diamond.

N: * diamond. * diamond?

J: Giant covalent.

N: Said that.

J: Lattice structure,

N: mm

J: very hard

N: high melting temperature

J: What’s the forces?

N: * * * . Can’t be metallic, can it?

J: No.

N: Have to be erm, van der Waals, can’t be van der Waals.

J: It’s not van der Waals - graphite’s got van der Waals between the layers, innit?

N: Yeah, * * * .

J: Okay, sodium chloride.

N: Ionic.

J: Definite lattice structure,

N: What’s it called > * * >

J: < Body centred < cubic

N: 6,6 * * > The coordination’s 6, 6. >

J: < The coordination’s 6,6. < Body centred cubic.

N: Yeah.

J: Sodium chloride structure.

N: Er:m.

• • •

J: High melting, ionic bonding so it’s got a melting point.

N: Yep.

J: > Copper. >

N: < Conducts < electricity.

J: Metallic bonding.

N: Metallic bonding.

J: Delocalised orbitals.

N: Yeah.

J: It’s got the partially filled d-orbitals.

N: Has it, oh yeah, ‘cause it’s transition metal.

J: So you’ve got the variable oxidation states.

N: You can have copper 1+, copper 2+, but that doesn’t say anything about the nature of forces. (Nature of forces? * * *) What’s diamond then? What forces are between diamond.

• • • • • • • • •

N: It’s just covalent innit? It’s covalent bonding between then.

J: What was (name of lecturer) saying? Catetonic, catenating. > Carbon. >

N: < That’s that’s < carbon ability to link, > or chain up. >

J: < That’s why you can have - < diamond, and,

N: mm

J: thinking about it. I think.

J: Okay part (b) “explain the following observations. 1 sodium is softer than copper, but both are very good electrical conductors.”

• • • • • •

J: Why is sodium softer than copper?

• • •

N: It’s less dense isn’t it?

• • • •

J: M::m?

• • • • • • • • • • • • • •

J: They’re both very good - conductors, because of the - metallic bonding and the delocalised > orbitals. >

N: < electrons <

J: Delocalised electrons.

N: And they’re high erm, co.., electropositive aren’t they sorry.

• • • •

N: Copper could be strain{?} erm, what do you call it, harder because they’re erm, because instead of like having this normal filling of elect.. erm shells you’ve got electrons going to the d-orbitals, so that could like make it a bit more - strong. Something like that.

• • • •

J: Well I think I know. Yeah you know because of erm, • • • • • • • er,

N: (laughs)

J: as you’ve got, • • even though it’s got a - higher atomic radius, no higher - nucleus charge, copper, > than >

N: < mm <

J: sodium, because you have the erm, electrons go into the d-orbitals instead of the 4s, right, you’re gonna have more - sheilding effect, innit?

N: Yeah, that’s what I was thinking > back there *>

J: < So you’re gonna have <

N: * * * *

J: so you’re gonna - so the volume

N: is gonna be more, erm it’s going to be smaller compare to the > {les}s one >

J: < no, it’s gonna < be higher

N: > no >

J: < you’re gonna < have a higher volume than usual.

N: no it wouldn’t because > * * >

J: < if you’ve got a larger < atomic radius than usual, gonna have higher volume, innit?

• • • • •

J: I think.

N: But would you have a higher volume? No you wouldn’t, you wouldn’t have a larger volume because you, they gradually > getting smaller along >

J: < no right< yeah you’re gradually getting smaller, but not as smaller as you expect it to, because of the d-orbitals, that’s why the decrease in the atomic radius as you go across - isn’t as large as you expect it to, I think.

N: (Mm.)

J: Anyway, anyway, go on to the next, part 2. “Diamond is hard and an electrical insulator, graphite is soft and an excellent electrical conductor.”

N: It’s ‘cause the lattice build-up, erm, > * * >

J: < Graphite’s got van der Waals forces < between the layer, innit? So they’re able to move over > each other. >

N: < Mm. < Mm. Diamond’s got the

J: {sharp breath}

N: hard, covalent > bonding >

J: < space <

N: Mm.

J: Structure. (tut) Why are they both excellent electical conductors?

N: Because they’ve got the delocalised electrons, ain’t they? ‘Cause erm, ah no that’s not true is it though?

• • • • • • • •

J: Is it the bonds they’re able to pass - you can pass the - electron flow through the bonds, I think.

N: Haven’t you got, • • • ‘cause they’re elec.., you can have conduction taking, when, when does conduction place when you’ve got the > electrons/energy >

J: < flow of electrons <

N: going from, passing from one to the other, isn’t it? So it’s got something to do with the electrons. * we’ve got to de.., there aren’t any declo.., delocalised electrons are there?

J: Could go through the bonds. (Come on.) ( * * )

J: Part 3 “sodium chloride and caesium chloride have different structures.”

• • • • •

J: Ceaseium chloride, ceasium’s more electropositive than

N: yeah

J: sodium.

N: Mm. It’s going to be more like, more > ionic >

J: < stronger < bonding.

N: Yeah.

J: Stronger ionic bond. S:o

N: Different structures? What structure’s ceasium > chloride? >

J: < Sodium < chloride’s body centred cubic,

N: yeah

J: ceasium chloride’s probably face-centred or something like that.

N: Dunno.

J: What are, what are the different ones face-centred > body-centred? >

N: < * cubic < and erm

J: something close packing.

N: Yeah cubic close packing. Yeah that the same as the

J: Ceasium chloride’s probably the close-packing one because if it’s more electropositive you’ve got tighter bonding, more closely packed.

N: ( * * )

• • • •

N: Yes.

J: Go on, “iodine dissolves readily in tetrachloromethane.”

N: Erm , ’cause it’s erm, ‘cause it’s co, it’s erm covalent molecule, #

J: and you’ve a - non-polar > solvent >

N: < non-polar < so it will dissolve more easily.

J: Finished.

A175

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