Tag: chemical bonding

Calcium and oxygen would not need to bond, they would just combine…

Calcium and oxygen would not need to bond, they would just combine, joining on to make up full shells

Keith S. Taber 

Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonly used in chemistry teaching. Near the end of the interview, she was asked some general questions to recap on points she had made earlier. She suggested that Ca2+ and O2- would combine, but without any chemical bonding.

Could you have a double ionic bond?

(pause, c.3s)

Can you have a double bond that's ionic?

Not really sure.

If you had say, say you had calcium, two-plus (Ca2+), and oxygen two-minus (O2-),

yeah,

could that form a double bond?

(pause, c.4s)

Are you not sure?

It wouldn't need to.

It wouldn't need to?

No.

Why's that?

Because one's lacking two electrons, and one's got two, so, they would just combine without needing to sort of worry about other, other erm elements.

Right so they…

Sort of joining on to make up full shells.

So they combine, but you wouldn't call that a chemical bond?

No.

From what Annie had reported earlier in the interview, she would see Ca2+ as a calcium atom (that's "got two" electrons in its outer shell) and O2- as a oxygen atom (that was "lacking two electrons"), as she held an alternative conception of what was meant by the symbols used to indicate electrical charge plus and minus signs represent the charges on atoms)*.

Annie here suggests that the atoms with their charges (i.e., for Annie, deviations form full shells) would combine, and join up to obtain a full shell. From her perspective, there was no need for ionic bonding. Although Annie's notion of what was signified by the charge symbols would seem to be idiosyncratic, the idea that chemical processes occur to allow atoms to obtain full shells (the 'full shells explanatory principle') is one of the most common alternative conceptions in chemistry.

Atoms evolved so that they could hold on to each other

Bert Suggests Chemical Bonding Evolved 

Keith S. Taber

Bert was a participant in the Understanding Science Project. During one interview he reported that he had just completed a topic of alkanes and alkenes in his chemistry classes. He explained that a carbon atom has "to have four bonds", so if a carbon atom had "only got one two carbons on one side and one hydrogen then it'll make a double bond, to have four bonds". So I asked him what he understood a bond to be:

I: …what's a bond?

B: A bond is erm, it just, it's something to hold, hold two atoms together.

I: So what might you use to hold two atoms together?

B: Erm, So they can be kept, so that they're not too, I think it's just to make, so it can make big lines so it can erm, oh, so they, so not every, so because solids they have erm, I guess a lot of bonds, to keep it all, all together, I'm guessing. And erm like gas has a lot less bonds because it's a lot more free.

I: That makes sense [Bert], I'm just wondering what you would use to bond two atoms together. … I'm just wondering what kind of thing you use to bond two atoms together.

B: Erm • • I'm not sure. I guess, I guess they were just, when er, they're made with it I guess.

I: Yeah. Do you think it's made of adhesive? … is it made of a glue do you think?

B: No, I don't think so. I think it was like, I don't know, it could have been like evolution, like.

I: Ah.

B: Yeah, the atoms evolved so that they could hold on to each other.

I: Oh I love that. • • • The atoms evolved so that they could hold on to each other?

B: I guess so. That's how the world was made.

In this interview segment Bert seems not to have considered the nature of the bonds between atoms, but just to have accepted what he has learnt about valency. When asked about the nature of the bond he could offer no mechanism for bonding, but instead suggested that chemical bonds had evolved as "that's how the world was made". Here Bert is drawing upon a general explanation considered to be universal in the domain of living things, but applying his learning from biology to explain a physical phenomena.

This seems to be a creative association drawing upon prior learning, but the idea of evolution is being used outside is canonical range of application, leading to a potential associative learning impediment. Potentially, Bert's thinking about evolution as explaining how atoms can bond (a potential explanation about origins, though inappropriate if evolution is understood as natural selection) could stand in place of seeking a physical explanation for the nature of bonding.

Sharing the same shell and electron makes them more joined together like one

Keith S. Taber

Umar was a participant in the Understanding Chemical Bonding project. When I spoke to him in the first term of his advanced level chemistry course he identified figure 2 (below) as representing a hydrogen molecule, with covalent bonding.

Sharing the same shell and electron makes them more joined together like one

Umar was a participant in the Understanding Chemical Bonding Project. When I spoke to him in the first term of his advanced level chemistry course he identified figure 2 (below) as representing a hydrogen molecule, with covalent bonding.

Figure 2 (Focal image – Understanding Chemical Bonding project)

Umar suggested that covalent bonding is when atoms share electrons to combine into one whole thing. That discussion took place early in the interview, before we then discussed a whole range of other images. Near the very end of the interview I returned to ask about figure 2 again.

Interviewer: And number 2 was what kind of bond?

Umar: Covalent.

I: Now, what holds the molecule together in number 2?

U: The two electrons – shared.

I: And how does that hold them together?

U: 'cause they're sharing the same – shell and electron.

I: And why does that hold them together?

U: Makes them more, together like, makes them more like joined together like one.

After we had first discussed what this image was meant to represent early in the interview, Umar discussed a wide range of other images, and in the context of some of these he discussed bonding in terms of forces and electrical charge. As he had not mentioned such notions in the context of figure 2, even after using the ideas elsewhere, I sought to see if he recognised that forces were acting in the hydrogen molecule.

I: I see. Is there any force there holding them together?

U: It's, erm could be the charges of the electrons and the charge of the nucleus.

I: Would the nucleus have some sort of interaction with the electrons – some sort of attraction or repulsion?

U: Yeah.

I: Would it be attraction or repulsion?

U: Erm, attraction.

I: So which electron does this nucleus attract.

U: Erm, it attracts both of them, and the other one attracts both of them because they are both, like, opposite charges. So that's why they are like, around there. It might be like they move around. Around that part.

I: So they might actually move about?

U: Yeah.

I: I: But you think the two nuclei attract the two electrons?

U: Yeah.

I: Do the two electrons attract the two nuclei?

(Pause, c.3s)

U: Yeah, think so, the – yeah.

I: Yeah? Do the two electrons attract each other?

U: No, they repel.

I: Do the two nuclei attract each other?

U: No they repel.

So it seemed that Umar understood the forces acting in the covalent molecule but that these ideas were not readily cued in that context even though he readily used the idea of forces between charges to explain other kinds of chemical bonding. In the context of covalent bonding however, the notion of the bond as electron 'sharing' was cued instead. Arguably the notion of the covalent bond as sharing of electrons acted as a grounded learning impediment perhaps blocking him bringing to mind alternative ways of thinking about the bond. This could be seen as an example of weak anthropomorphism: the idea that the electrons were 'shared' stood in place of a more scientific explanation of the bonding process.

A double bond is different to a covalent bond

Keith S. Taber

Annie was a participant in the Understanding Chemical Bonding project. She was interviewed near the start of her college 'A level' course (equivalent to Y12 of the English school system). Annie was shown, and asked about, a sequence of images representing atoms, molecules and other sub-microscopic structures of the kinds commonly used in chemistry teaching. She was shown a representation of the resonance between two canonical forms of the ethanoate ion, sometimes used to imply the delocalisation of the ionic charge across the COO- grouping.

Focal figure (13) presented to Annie

Any idea what this is?

They're organic compounds. And one's an inversion of the other.

Any idea what that arrow means in the centre of the page?

Does it mean that if you turned either of the, the O-minus, or the O that's double bonded around then you'd get the other compound? And it's exactly the same for that one if you turn that around, and you'd get, so it's like a reversible (pause, c4.s) thing.

Now what did you say about double bonded, what's this about being double bonded?

The oxygen is joined on the carbon with double bonds.

So what's a double bond? Is that, is that, you talked about covalent bonds earlier. Is a double bond the same as a covalent bond, or different to a covalent bond or?

Different.

So are there any covalent bonds, – the top one for example – are there any covalent bonds there?

Yeah.

How many covalent bonds are there?

Five.

And how many double bonds?

One.

And are there any ionic, ionic bonds?

No.

So we've got five covalent and one double.

Yeah.

Annie recognised the presence of a double bond (C=O) in the canonical forms shown, but seemed to see 'double bond' as an additional category of chemical bonding, different to covalent bonding, rather than referring to a particular type of covalent bond. So for Annie, each canonical form contained five covalent bonds (3H-C, C-C, C-O) and one double bond (C=O).

As the interview proceeded, Annie also suggested that single bonds are different to covalent bonds or ionic bonds.