Hurdles and Bottlenecks (in ionic bonding)

Hurdles and bottlenecks

I’ve written a few posts now about misconceptions and tricky concepts in the Structure and Bonding topic. Ultimately, I wanted to identify threshold concepts, which can be described as “portals” to greater understanding. I’ve also seen them described as “bottlenecks”, and I think this is a helpful description. It’s a concept that holds you up, and prevents you from developing a deeper understanding.

I compiled a list of tricky concepts using a variety of misconception sources, but I would describe most of these as “hurdles” rather than bottlenecks. Hurdles need to be cleared, but they don’t hold you up in the same way that bottlenecks do. I wanted to identify the true bottlenecks via teaching/ assessment. I created this tracker to help me teach the hurdles explicitly, then test and retrieve them. In this post, I looked at the optimum spacing gap for retrieval.

Measuring difficulty

I used in-class assessment to monitor how successfully these concepts had been embedded, and this informed the direction of lessons and questioning in-situ. But I also wanted to measure how pervasive certain misconceptions were, so I used True/False questions with in-built confidence measures (see previous post).

Using simple colour coding, students could quickly see whether their answers were right or wrong, and give themselves a score.

They could also annotate work to describe why answers were incorrect (or correct), to help develop self-reliance and metacognition.

Screen Shot 2017-03-30 at 12.08.27

I also wanted to measure how difficult the concepts were, by taking into account students’ right/ wrong answers, as well as their confidence in each answer.

Concepts are listed here in order of difficulty (easiest to hardest), based on combined answers from two year 10 classes, a year 11 class and a year 12 class.

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Hurdles in ionic bonding

Ionic bonding and structure encompasses a number of concepts that students found particularly problematic.

The topic is often introduced using dot/cross diagrams. This can give students a picture of “ionic molecules” (Kind: Beyond Appearances- misconceptions report) with a charge located in the top right hand corner of the ion, and with each ion forming discrete bonds with 1-3 other ions. Students often assume from this model that each ion forms a bond with ions with which it has just transferred electrons.

Screen Shot 2017-03-30 at 12.23.45

But to understand the structure and properties of ionic compounds, students have to understand that ions:

  • form a giant 3D lattice (when solid), containing millions of ions
  • remain as ions, whatever their physical state
  • are attracted to any oppositely charged particle
  • carry a charge that is distributed throughout the ion and acts in all direction

So taking this into account, when I introduced dot/cross diagrams this year:

  • I made sure I really emphasised that ion charges arise from imbalance between positive and negative particles
  • I stressed the idea that charge is distributed throughout the ion, that the whole ion is charged, and I explained that square brackets illustrate this.
  • I underlined from outset that, although electrons transfer between individual atoms, ions will be attracted to anything with an opposite charge, and in all directions. They won’t only form a bond with a particular ion with which electrons were transferred.
  • I reminded students that reactions involve millions of ions, even though we only draw a few ions in dot/ cross diagrams to illustrate the process. I pointed to the ionic formulae representing a ratio, not the total number of ions in a unit.

I have retrieved, reviewed and re-emphasised these ideas since first introducing them.

Bottlenecks or hurdles?

There were two concepts in ionic bonding/ structure that proved to be real breakthrough ideas for students.

The first idea that I think counts as a bottleneck is that in an ionic compound, ions remain as ions, whatever the physical state. This has to be understood to move on to electrical conductivity and electrolysis at KS4. However, it’s also integral to other areas of the curriculum.

One of the demonstrations I showed pupils to illustrate the idea of ions retaining their character was a simple precipitation reaction.


I happened to have the reagents in the lab when I was teaching my year 13 group later in the day. We were reviewing ionic equations, before moving on to more complex redox equations. A few students were unconfident with how and why certain ions were “excluded” from the equations, so I showed them the precipitation reaction to illustrate how some ions simply “spectate”.

Afterwards, out of nowhere, I received this email from someone in the class:

Screen Shot 2017-03-30 at 12.41.11

What more can you ask for, as a teacher? And I think it shows how fundamental these ideas are to a range of contexts.

The second idea that I think counts as a bottleneck was an unexpected one, but it became apparent as I taught the topic. This is that millions of ions are involved in any reaction to form an ionic compound, not just the few that we draw in dot and cross diagrams. Students need to appreciate this if they are to understand giant lattice formation, and related physical properties of ionic compounds in different states.

Students were sometimes still thinking of individual atoms/ ions, as illustrated by dot and cross diagrams, when they were trying to answer questions about properties of compounds, which really inhibited their understanding. But as soon as I clarified this idea for them, I would often see visible “lightbulb moments”.

Using MCQs to identify misconceptions

I recently read a paper that describes how multiple choice questions were used to identify misconceptions. On a small-scale, this is an approach that I use when setting MCQs for homework.

I can colour-code student answers, so that they can see which answers they got right/ wrong, so that I can see which questions gave the most problems, and so I can see which incorrect answers were most common.

However, sometimes I just ask students to email me their answers in advance of a lesson, so that I can do the same thing in a slightly less high-tech way!

Screen Shot 2017-03-30 at 12.53.51

One of these MCQ homeworks highlighted that some students were still struggling to identify the type of bonding present in a substance. This is something I see even at KS5, and I think this is less an issue of conceptual understanding, and more to do with students not thinking questions through properly (forgetting the “basics”). It underlines, for me, how important it is to keep emphasising key ideas throughout the course.

What is a concept?

Various discussions (mostly on Twitter) have made me consider what exactly it is that we mean by a “concept”, as opposed to a “fact”. I’ve also started to think more about the idea that a “threshold concept” is a portal to deeper understanding. My initial understanding of this idea was that once students “got” these concepts, they would be internalised, and they wouldn’t forget them. But my experience is that you to have to keep reinforcing them, retrieving them, reminding students of them, and emphasising them.

Perhaps this is highlighting a weakness in my teaching and assessment! But I have read about misconceptions being “quashed” at first, rather than overcome or completely understood and internalised. Nick Rose talks about it here, and Guzzetti describes how students revert to their previous ideas if new ideas are not reviewed.


This is something I am still pondering, and I’d appreciate any thoughts or pointers to further reading on this…







One thought on “Hurdles and Bottlenecks (in ionic bonding)

  1. Pingback: Mastery Musings 2/6/17 – Kaye Chem Notebook

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