Discussions from the magazine, website and social media


Chemical bonding

Last issue we launched our CPD for teachers series with an article that described some common misconceptions that students acquire surrounding chemical bonding. It offered strategies for alleviating them and suggested a teaching route based on an electrostatics approach. Michael Seery followed up with a blog article where he looked at the same issue in third level education.

On the blog, Alan Crooks described a problem that we imagine many teachers face:

I have to teach a two year IGCSE course in one year so, sadly, there’s no time to ‘develop models’. I just have to teach what they need to know to pass the exam. Neither the specification nor the course-specific textbook mentions the role of electrostatic attraction between nuclei and electrons in covalent molecules – although I have mentioned it in passing.

Neil Goalby, Head of Chemistry at Bancroft’s School in London, UK, took to twitter to add his thoughts:

@NGoalby: It cannot help that both AQA and OCR at A-level define covalent bonding as a shared pair of electrons. Edexcel do define covalent bonding as an electrostatic attraction. Consistency would help.

Writing from Vietnam, Gavin M left a comment on the article’s webpage:

I find a thermodynamic approach works well with Year 12/Grade 11, often in the context of the myth of the reactivity of the group 1 elements. I don’t mean to say they’re not reactive but the group trend is often overstated. There’s a good debunking of the Brainiac item on this that gets students into the thermodynamics quite nicely but needs careful follow up in class. You can easily link it into standard electrode potentials later in the year and to illustrate why we don’t have caesium powered laptops.

Members of the Education in Chemistry group on LinkedIn also shared their opinions. Here’s a selection of their comments, starting with Rehab Farid, a chemistry teacher from the United Arab Emirates:

Unfortunately it is true that students tend to forget (or aren’t properly taught) that even covalent bonding is an electrostatic force between the shared electrons and the nuclei. We need this idea and I found difficulty when trying to explain how bond length relates to bond strength due to this attraction being weakened by the distance.

Mohammad Salleh abid, also from the United Arab Emirates, added:

It depends on which grade you teach. For lower grades the octet rule is enough to start with. However for A-levels the electrostatic concept is the right way.

Alon Eisenstein from Toronto, Canada, seemed to agree:

I find a fundamental concept missing in this intriguing discussion: the fact that we use models to explain what we observe.

The octet rule is a useful tool to explain some of the things we observe, but is lacking for others. The same is true for electrostatic attraction/repulsion.

Why stop at the electrostatic approach? Why not talk about delocalised molecular orbitals? The answer is that it has too much detail and is far too complicated for high school.

The octet rule should not be brushed off as a simpleton approach, since it has its merits for the appropriate entry level for chemistry and when we find examples for which we cannot use the octet rule. We should not feel embarrassed or dismiss the approach altogether. Rather we should use this as the perfect learning lesson that science explains reality. It does not dictate it. And when we reach the limits of one theory/rule/approach, we start looking for more comprehensive, more complicated, more inclusive explanations.

Justice Mantey Larbi, a chemistry tutor from Ghana, was able to identify with the issues raised:

I love this discussion. I had a similar problem this year when I was teaching some senior high students. But at the end I had to rely on specific examples to make the understanding clearer. The octet rule is ok, but the electrostatic approach is the best.

Take a look at this issue’s CPD article for advice on how to avoid misconceptions when teaching about energy change.

The impact of innovations

Michael Seery recently wrote on our blog about how teachers, himself included, often learn about exciting new pedagogical techniques at education conferences, but on returning home fail to convince their colleagues of their merits. Tina Overton from the University of Hull, UK, commented:

We have to ask why we want our colleagues to innovate. For me it’s about thinking about what skills, values, attitudes and capabilities we want our graduates to have. That is my only driver for trying to do things differently. Innovation for our sakes or for its own sake or to get good student evaluation won’t convince colleagues. Programme design and pedagogy design should be based on desired graduate outcomes. Long ago we talked about active learning. It sounds old fashioned now but all the ‘new’ pedagogies utilise active learning. Technology has made some of it easier but I am wary of some trends becoming as all pervasive as didactic lectures are with some people. Variety is what we and our students need.

Simon Lancaster, from the University of East Anglia, UK, said:

You’ve given me an excellent opportunity to plug a current project. I often pose the question: What would it take for your department to adopt innovative teaching practices? Experience tells me positive student evaluations are not enough. Colleagues often tell me that what they want to see is quantitative evidence. The kind of evidence that Eric Mazur, Simon Bates and Ross Galloway have been able to gather using the Force Concept Inventory (FCI). As a chemist, I’ve viewed the FCI with considerable jealousy. There is a movement to start using Chemical Concept Inventories to gain robust and reliable evidence to refute reluctant recalcitrants and you can find further details at www.chemistryvignettes.net.  [link no longer available]