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 part of a lattice of ions in sodium chloride (see: Sodium and chlorine don't actually overlap or anything), but Annie identified the signified as atoms, not ions, because Annie had an idiosyncratic understanding of what was meant by charge. (Read: Na+ has an extra electron in its outer shell and Cl- is minus an electron and K-plus represents a potassium atom that has an extra electron.)
Annie was asked whether the structure made up of sodium and chlorine 'atoms' would hold together:
Do you think this thing would fall apart? Or would it hold together?
(pause, c.9s)
If you heated it, or reacted it in some way, it would hold together, and it would probably get held together by just forces.
By forces. Any idea what kind of forces would hold it together?
Probably just the attraction.
Uh hm?
The attraction from the plus to the minus because like chlorine's minus an electron and sodium is over an electron. So they could just like hold them together, but not actually combine.
Right, chlorine's, so sodium's, say that about the electrons again.
Sodium has like one extra electron, 'cause it has like an extra electron in its outer shell, and chlorine has seven electrons in its outer shell so its minus an electron so by sort of exchanging, the sodium combining with the chlorine just by force pulls they would hold together.
So Annie saw the plus (+) symbol to mean one electron over a full shell (2.8.1), and the minus (-) symbol to mean one electron short of an octet of electrons (2.8.7). For Annie these charges were not net electrical charges, but deviations from octet configurations. Yet, these 'deviation charges', for Annie, provided the basis for the attraction between the 'charged' atoms.
This was checked by asking Annie about the electron configurations.
So we looked at a sodium atom earlier, you recognised it as being a sodium atom, …
Can you tell me what the configuration is in terms of shells? How many in the first shell, how many in the second shell…
2.8.1
2.8.1?
Yeah.
So this here (indicating a cation on the figure), you are saying that this here is 2.8.1
Yes.
And this is 2.8.7 would it be?
Yeah, 2.8.7
And that is what holds them together the fact that this is one short,
yeah,
one over and one short.
One over, and that one's one short.
So the plus means one electron more than an outer, the full shell,
Yeah.
and the minus means one electron
Minus.
less than an outer shell,
Yeah.
and that's what holds them together.
Yeah.
Okay, so there is something holding them together,
right,
and it's to do with these pluses and these minuses,
Yes.
but what we don't have there is chemical bonding like we had before.
No.
Annie held an alternative conception of the nature of the charges associated with ions: that neutral atoms had 'charges' if they did not have full shells/octets of electrons. Whilst Annie's specific deviation charge conception would seem to be rather unusual, alternative conceptions relating to the significance of full shells / octets of electrons seems to be very common among chemistry students. Although Annie's thinking was idiosyncratic it reflected the common full shells explanatory principle that sees electronic configuration as a cause for chemical processes.
So Annie considered that these 'deviation' charges could actually give rise to forces between atoms (see also The force of lack of electrons pulls two hydrogen atoms together*).
Annie did not see ions, but atoms. But she thought that after a reaction, there would be attractions, 'force pulls', holding the product together, but this would not amount to chemical bonding.
Annie's notion of 'charges' on atoms (being extra or missing electrons in the outer shell), that led to her not recognising bonding in the NaCl, was an uncommon alternative conception notion. However, her notion that chemical bonding was something other than 'just forces', and that sometimes structures were held together by 'just forces' when there was no bonding, is a common alternative conception. Indeed it is part of a common 'molecular framework' for conceptualising ionic bonding, that is in turn a part of a common alternative conceptual framework for thinking about chemical bonding, stability and reactions: the octet framework.
