Category: language

Covalent bonding is when atoms share electrons to combine into one whole thing

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.

UCB Figure 2 (for interview-about-instances technique)

Can you tell me what you think that's meant to represent?

Er, two hy-, a hydrogen molecule, 'cause it's like they've got one electron, in the only one shell, and they're joined together, a covalent bonding, and they're sharing it.

So what is a covalent bond exactly?

When they share electrons.

When you share electrons?

Yeah.

So when Umar thought of covalent bonding he seemed to primarily associate this with the notion of 'sharing' of electrons. The idea that atoms can 'share' anything could be considered an example of anthropomorphism, but this is a common metaphor that is widely used in discussing bonding.

The 'sharing' notion is however little more than a descriptive label, and has limited explanatory power. Acceptable explanations of the bond would draw upon scientific concepts, such as electrical forces, or atomic orbital overlaps allowing the formation of lower energy molecular orbitals. I probed Umar to see how he understood the nature of the covalent bond.

Or do you think they're stuck together?

I think they're quite strong together, covalent is quite a strong bond.

So that will hold them together will it?

Yeah.

Umar certainly saw the bond as a strong linkage of some kind, but so far my questions had not revealed how he understood the bond to hold the molecule together.

Well how does it do that?

It's like, they're joined together, 'cause first of all they just had two atoms with one electron each, and now they're sharing two electrons between them. So it's quite strong.

Oh, why's that?

Because the the the actual, when they share them they're like combined into like one sort of whole thing, instead of two separate atoms.

Right, so the, so the bond, which is the sharing of two electrons, that holds them together,

Yeah.

to make one thing, which we've called a molecule.

Yeah.

So at this point in Umar's course he seemed to conceptualise the covalent bonding as electron sharing and saw the action of sharing to inherently hold the molecule together, and seemed to be satisfied with that as an explanation for the bond. This 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 (see Sharing the same shell and electron makes them more joined together like one)*.

Gas particles like to have a lot of space, so they can expand

Keith S. Taber

Derek was a participant in the Understanding Science Project. I interviewed Derek when he was in Y7 of the English school system. We had been talking about work that Derek has been doing in his science classes on burning. As part of the conversation, Derek defined a solid in particle terms:

what's a solid then, what's a solid?

Lots of particles really close together that can't move a lot.

When I followed this up, Derek explained how a liquid or gas was different to a solid:

And you say solids are made of particles. What are liquids then, they are not made of particles then?

No they are, they are just more spread out particles. And then, you get a gas, which the particles can move a lot more than solid and liquid, they can move wherever they like.

And where do they like to move?

As far away from each other as possible.

Why do you think that is?

'cause they like to have a lot of space, so they can expand.

Why do you think particles like to have a lot of space?

(Pause, c.3s)

Don't know.

Are they unfriendly lot, unsociable?

(Pause, c.2s)

No, they just, they like to have, like be as well away from each other as possible.

The question "where do they like to move" was couched in anthropomorphic terms to reflect the anthropomorphism of Derek's statement that gas particles could "move wherever they like", to see if he would reject the notion of the particles 'liking'. However Derek did not query my use of this language, and indeed suggested that the particles "like to have a lot of space".

When he was asked why, there was a pause, apparently suggesting that for Derek the notion of the particles liking to be far apart seemed to be reasonable enough for him not to have thought about any underlying reason, and his "don't now" was said in a tone suggesting this was a rather uninteresting question. Although Derek rejected the suggestion that the particles were 'unfriendly', 'unsociable' his tone did not suggest he thought this was a silly suggestion: rather it was just that the particles "like" to be as far "away from each other as possible".

The use of anthropomorphism is very common in student talk about particles. Whether or not Derek really believed these gas particles actually had 'likes' in the way that, say, he himself did, cannot be inferred from this exchange. But, in Derek's case, as in that of many other students, the anthropomorphic metaphors seem to offer a satisfactory way of thinking about particle 'behaviour' that is likely to act as a grounded learning impediment because Derek is not open to looking for a different kind (i.e., more scientifically acceptable) type of explanation. Given the common use of his language, it seems likely that it derives from the way teachers use anthropomorphic language metaphorically to communicate abstract ideas to students ('weak anthropomorphism'), but which students accept readily because thinking about particle behaviour in terms of the 'social' models makes sense to them ('strong anthropomorphism').

An element needs a certain number of electrons

An element needs a certain amount of electrons in the outer shell

Keith S. Taber

Bert was a participant in the Understanding Science project. In Y10 Bert was talking about how he had been studying electrolysis in class. Bill had described electrolysis as "where different elements are, are taken out from a compound", but it transpired that Bert thought that "a compound is just a lot of different elements put together"*. He seemed to have a tentative understanding that electrolysis could only be used to separate elements in some compounds.

if they're positive and negative then they would be able to be separated into different ones.

So some things are, some things aren't?

Yeah, it matters how many electrons that they have.

Ah. [pause, c.3s] So have you got any examples of things that you know would definitely be positive and negative?

Well I could tell you what happens.

Yeah, go on then.

Well erm, well if a, if an element gives away, electrons, then it becomes positive. But if it gains, then it becomes negative. Because the electrons are negative, so if they gain more, they just go a bit negative.

Yeah. So why would an element give away or gain some electrons? Why would it do that?

Because erm, it needs a certain amount of electrons in the outer shell. It matters on what part of the periodic table they are.

Okay, let me be really awkward. Why does it need a certain number of electrons in the outer shell?

[Pause, c.2 s]

Erm, well, I don't know. It just – 

So Bert thought that an element "needs a certain amount of electrons in the outer shell" depending upon it's position in the periodic table, but he did not seem to recall having been given any reason why this was. The use of the term 'needs' is an example of anthropomorphism, which is commonly used by students talking about atoms and molecules. Often this derives from language used by teachers to help humanise the science, and provide a way for students to make sense of the abstract ideas. If Bert comes to feel this is a sufficient explanation, then talk of what an element needs can come to stand in place of learning a more scientifically acceptable explanation, and so can act as a grounded learning impediment.

References to atoms needing a certain number of electrons is often used as an explanatory principle (the full shells explanatory principle) considered to explain why bonding occurs, why reactions occur and so forth.

Bert's final comment in the short extract above seems to reflect a sense of 'well that's just the way the world is'. It is inevitable that if we keep asking someone a sequence of 'well, why is that' question when they tell us about their understanding of the world, they eventually reach the limits of their understanding. (This tendency has been labelled 'the explanatory gestalt of essence'.) Ultimately, even science has to accept the possibility that eventually we reach answers and can not longer explain further – that's just the way the world is. Research suggests that some students seem to reach the 'it's just natural' or 'well that's just the way it is' point when teachers might hope they would be looking for further levels of explanation. This may link to when phenomena fit well with the learner's intuitive understanding of the world, or tacit knowledge.

Bert's reference to an element needing a certain amount of electrons in the outer shell also seems to confuse description at two different levels: he explicitly refer to substance (element), when he seems to mean a quanticle (atom). Element refers to the substance, at the macroscopic level of materials that can be handled in the laboratory, whilst an atom of the element (which might better be considered to gain or lose electrons) is part of the theoretical model of matter at a submicroscopic level, used by chemists as a basis for explaining much macroscopic, observed behaviour of samples of substances.


A sodium atom wants to donate its electron to another atom

Keith S. Taber

Lovesh was a participant in the Understanding Chemical Bonding Project, studying 'A level' chemistry in a further education college. He was interviewed in his second year of the two year A level course, and was presented with focal figure 1 (below). He recognised figure 1 as showing a "sodium, atom", and was asked about its stability:

Is that a stable species, do you think?

Erm (pause, c.3s) No, because it hasn't got a, a full outer – electron shell, outer electron shell hasn't got eight electrons in.

Lovesh shared the common notion that an atom without a full outer shell / octet of electrons would be unstable compared with the corresponding ion with a full outer shell / octet of electrons. When comparing isolated atoms with the corresponding ions this is seldom the case, yet this is a common alternative conception about chemical stability. A sodium ion can be considered stable in an ionic lattice, or when hydrated in solution, but does not spontaneously ionise as the outer shell electron is attracted to the atom's positive core. Ionisation only occurs when sufficient work is done to overcome this attraction.

Lovesh was demonstrating the common full shells explanatory principle alternative conception which is central to the common octet rule framework – an alternative conceptual framework reflecting very common 'misconceptions' found among learners studying chemistry.

Lovesh was asked what would happen to the atom that he considered unstable:

So if it's not stable, what would tend to happen to that, do you think?

It will wanna donate the electron to another atom.

Right, when you say 'it wants to donate' it?

Erm. (pause, c.3s) Well because that outer electron is less attracted to the nucleus, erm it is, it can easily be transferred, attracted by another atom.

Lovesh's first response here used the term 'wanna' (want to) which if take literally suggests the atom has desires and preferences. This is an example of anthropomorphism, imbuing objects with human-like traits. Using anthropomorphic explanations is a common feature of the octet rule framework which often leads to students talking as if atoms deliberately act to get full outer electron shells.

It has been suggested that such anthropomorphism may be either 'strong'- where the learner is offering an explanation they find convincing – or 'weak' if they are using language metaphorically, just as a figure of speech.

In this case, when Lovesh's use of the notion of 'wants' was queried he was able to shift to a different language register in terms of the action of physics forces – the electron being attracted elsewhere. Lovesh had clearly acquired an appropriate way of thinking about the interactions between atoms, but his spontaneous explanation was couched in anthropomorphic terms. Although in this case the anthropomorphism was of a weak form, the habitual use of this kind of language may come to stand in place of offering a scientifically acceptable account.