Ownership of electrons

A topic in learners' conception and thinking

An alternative conception

A common feature of student thinking in learning chemistry is that electrons are owned, so belong to, by particular atoms. Although a term like 'that atom's electrons' may be used as short-hand, meaning no more than to refer to the electrons that are part of a particular atom at some moment in time (and this may be perfectly clear to a reader/listener), learners often use the notion that an electron belongs to an atom when giving explanations of chemical phenomena. So, the problem is:

  1. Learners often think there is some permanent link between an electron and the atom it is, or was recently, part of;
  2. Learners may use this idea to build explanations (which they may use in chemistry tests and examinations);
  3. This notion is one part of a more extensive alternative conceptual framework (the 'octet framework', Taber 1998 – read about the octet framework)
  4. This notion contributes (as 'the history conjecture') to part of a common alternative conceptual framework for thinking about ionic bonding the 'molecular framework', Taber, 1994, 1997 – read about the molecular framework for ionic bonding);
  5. Such language is anthropomorphic – it implies that atoms and similar species think and act like people (read about anthropomorphism), contrary to scientific norms.
  6. Learners often think that atoms can share their electrons to form bonds, and that this 'sharing' explains what the bond is.
A challenge for chemistry teachers

Perhaps the examples I offer below might seem to reflect outliers, and you might suspect that your students are perfectly clear about the limitations of language referring to electrons owned by and shared by atoms. Perhaps, but some of my best students were not clear – so perhaps have a conversation with your students – ask them what they understand by terms like 'a carbon electron', 'a donated electron' and 'a shared pair of electrons'?

Some examples:

Electrons belong to atoms:

Paminder (c.16-17 years of age) is so used to thinking that electrons belong to atoms, that she does not seem to understand the point of my asking her what this actually means!

[The shading in the diagram] is just to signify that the dark ones are the chlorine electrons, and these clear ones are the carbon electrons.

So what's the difference between a chlorine electron and a carbon electron?

Well they're different because they belong to different atoms.

How does an electron belong to an atom?

What do you mean?

What do you mean by 'belong'? These two electrons seem to be about equal distance from the chlorine centre and the carbon centre, but you're saying that this dark one belongs to the chlorine, and the light one belongs to carbon. In what way do they belong to them?

I think it's because like, certain elements, they have a different number of electrons. And chlorine has seven electrons in its outer shell, and carbon has four electrons in its outer shell, and you can tell from those characteristics that it's chlorine [tapping the diagram] and that's carbon.



Interviewing Paminder, Advanced level chemistry student – quoted in Taber & Watts, 1996, p.56o

Of course, it was completely arbitrary which of the bonding pair of electrons was shaded as it if was form carbon, and which form chlorine. It is easy for teachers to simply expect students to simply know which features of diagrams are meant to be highly significant, and which are somewhat arbitrary!

Owned electrons can be shared

It is very common in chemistry to refer to covalent bonding as electron-sharing, but of course this is just a metaphor, and does not explain why there is a bond. Unfortunately, learners often adopt the metaphor as if it explains the bond.

In an interview-based study with college students taking advanced level chemistry,

Reference to the covalent bond as sharing of electrons were ubiquitous. In some cases this notion was viewed as a sufficient explanation of the covalent bond: it was considered to hold atoms together because it is sharing electrons. Indeed the act of sharing was described as being 'like a force'. Another colearner explained that a molecule was held together by 'the two electrons shared' which 'makes them more like joined together like one'.

Usually the sharing of electrons was related to the full shells explanatory principle, so that 'the electrons are shared to create a full outer shell', and the 'covalent bond is the sharing of electrons to complete full valency shells'. As one student wrote in a test paper,

'A covalent bond is one in which two atoms join together by the sharing of electrons. Each of the atoms achieves noble gas configuration in the process of covalent bonding'."

Taber, 1988, p.602

So, when the teacher says the electrons are being share, she probably means something like they are mostly between, and are being strongly pulled by, both nuclei; or they they occupy a bonding orbital that has high electron density between and near both atomic centres…but the student probably thinks the two atoms are behaving like good neighbours who have agreed to pool some owned property!

There are 32 electrons [in the diagram being discussed]. Are these electrons all the same?

No. Because, I think the electrons that are shaded-in belong to chlorine, and the electrons that are shown as a circle belong to the carbon atom.

You said belong to. So do they actually own them?

Er, originated from. But now they're being shared, between the carbon and the chlorine.

Interviewing Lovesh, Advanced level chemistry student – quoted in Taber & Watts, 1996, p.56o
Owned electrons can be borrowed

If an electron is owned by an atom, then it's owner cannot only share it, but lend it, as when in ionic bonding "a sodium atom 'is lending chlorine' 'one of its electrons'…" (Taber & Watts, 1996, p.560)

Because electrons are still owned by their own atoms, they retain some kind of link with that atom:

One electron is the same as any other. An electron can be characterised by its energy, by what larger structure it is part of (atom, ion, molecule, lattice) but these are accidental attributes. The only inherent, unchanging properties of electrons are properties such as mass, charge and 'spin'. Mass and charge are precisely the same for all electrons. Electrons can exist in two spin sates (±1/2) but the spin of an electron in a free state can be flipped by a magnetic field. So, one an electron has been removed form an atom, it retains no strong connection, and is no more likely to return than any other.

However, learners often have quite different intuitions.

For example, in explaining ionic bonding, learners often think bonds are limited to ions that have a history of electron transfer:

Read about the history conjecture


Work cited

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