An aspect of student thinking about ionic bonding
At school level, the structure of ionic lattices is largely explained in terms of the interactions between charges (cations and anions are come together under mutual attraction until an equilibrium is reached where repulsions balance attractions). Even when ionic bonding is taught along those lines students commonly develop alternative understandings.
Misunderstanding the ionic bond
Students commonly develop alternative conceptions of ionic bonding (Taber, 1994). In particular they often understand ionic solid structures in terms of a 'molecular' framework that can be seen as part of a wider 'octet' alternative conceptual framework for thinking about chemistry. The molecular framework includes four related alternative conceptions:-
- The valency conjecture: each singly charged ion can only form one bond.
- The history conjecture: a bond exits between a pair of ions that have been involved in an electron transfer event
- The 'just force' conjecture: oppositely charged ions that have not shared an electron transfer event do not have proper/formal bonds between them, just attractions (cf., "The bond is understood in simple terms as due to an electrostatic interaction between counter ions")
- With the result that students commonly consider that there are Na+-Cl- ion pairs which make up sub-units of the structure, ether being molecules, or having a similar role to that played by molecules in simple covalent solids
Read about the molecular framework for thinking about ionic bonding
Evidence for student thinking about charge interactions
The original evidence that students thought in this way derived from interviews with students. This led to a research probe being developed (which was later developed in to a diagnostic instrument for classroom use by teachers). The original instrument had 30 items, but after feedback from teachers a shorter, 20 item version was produced.
How do learners conceptualise the interactions in an ionic solid?
Students were presented with a number of statements to judge as true or false. The original sample of students responding to the instrument included upper secondary students (KS4) who were meant to have studied the topic at that ('G.C.S.E.') level; A level students (who had not yet studied the topic beyond KS4 ('G.C.S.E.') level, and A level students who had studied the topic further as part of their A level course.
This work was reported in: Taber, K. S. (1997) Student understanding of ionic bonding: molecular versus electrostatic thinking?, School Science Review, 78 (285), pp.85-95. [Download a copy of the author's manuscript version of the paper]
The shorter, 20-item version of the instrument was later translated to be administered to undergraduate students in Greece and Turkey. (The Greek undergraduates were given a 'forced choice' between 'true' and 'false', without the 'I do not know' option.)
That work was reported in Taber, K. S., Tsaparlis, G., & Nakiboğlu, C. (2012). Student Conceptions of Ionic Bonding: Patterns of thinking across three European contexts. International Journal of Science Education,34 (18), 2843-2873. doi: 10.1080/09500693.2012.656150.
It was found that students often acknowledged electrostatic interactions, yet still conceptualised bonding as being something quite distinct and only occurring between some adjacent counter ions
An ionic bond is the attraction between a positive and a negative ion
True or False?
An ionic bond is the attraction between a positive and a negative ion
A positive ion will be bonded to any neighbouring negative ions
True or False?
A positive ion will be bonded to any neighbouring negative ions
A negative ion will be attracted to any positive ion
True or False?
A negative ion will be attracted to any positive ion
A negative ion can only be attracted to one positive ion
True or False?
A negative ion can only be attracted to one positive ion
The reason a bond is formed between chloride ions and sodium ions is because they have opposite charges
True or False?
The reason a bond is formed between chloride ions and sodium ions is because they have opposite charges
In the diagram each sodium ion is bonded to more than one chloride ion
True or False?
In the diagram each sodium ion is bonded to more than one chloride ion
A positive ion can only be attracted to one negative ion
True or False?
A positive ion can only be attracted to one negative ion
A negative ion will be bonded to any neighbouring positive ion
True or False?
A negative ion will be bonded to any neighbouring positive ion
Each sodium ion in the diagram is attracted to only one chloride ion
True or False?
Each sodium ion in the diagram is attracted to only one chloride ion
A positive ion will be attracted to any negative ion
True or False?
A positive ion will be attracted to any negative ion
Each chloride ion in the diagram is bonded to only one sodium ion
True or False:
Each chloride ion in the diagram is bonded to only one sodium ion
Sources:
- Taber, K. S. (1997) Student understanding of ionic bonding: molecular versus electrostatic thinking?, School Science Review, 78 (285), pp.85-95. [Download a copy of the author's manuscript versions of the paper]
- Taber, K. S., Tsaparlis, G., & Nakiboğlu, C. (2012). Student Conceptions of Ionic Bonding: Patterns of thinking across three European contexts. International Journal of Science Education,34 (18), 2843-2873. doi: 10.1080/09500693.2012.656150.
