Click the image to run the resource

What is this?

This is an Open Educational Resource designed to summarise key concepts in organic mechanism that are required for entry to an undergraduate course. The resource is designed for first year undergraduates or able A-level students in mind and it revisits ideas from A-level. It also begins to show how they are applied early in a University course. The resource was created as part of The Royal Society of Chemistry’s work under the National HE STEM Programme to help bridge the gap between the knowledge expected in a first year undergraduate course and the knowledge gained at A-level.


Learning Objectives

On completion of this activity you should be able to:

  • Use the hybridisation model to explain the bonding in alkanes and alkenes in terms of σ and π bonds.
  • Use curly arrows to represent the movement of electrons in nucleophilic substitution reactions and electrophilic addition reactions.
  • Explain the differences between the SN1 and SN2 mechanisms and where they occur.
  • Appreciate some limitations of the curly arrow model

Previous Knowledge

It is anticipated that users will have some knowledge of A-level chemistry before undertaking the activity. This resource is designed to revise A-level concepts but, even with good subject knowledge, there should also be some material here students are unfamiliar with. This resource is not designed to support any specific A-level specification but may also be used in schools to aid independent study where appropriate.


How was this resource designed?

These resources were designed to be used either by able KS5 students or students at the beginning of their undergraduate course. Some of the concepts that appear in the resources are from A-level courses, some of the concepts might be found in the first year of a university course. The resource wasn’t designed to replace teaching of either but to give students an idea of the things they ought to study themselves before starting a course that builds on these principles. I went to a lot of effort to work with a range of teaching staff at Bristol and at Bath. The idea was to come up with a resource that shows where the story has come from and where it is going to next. I couldn’t keep everyone happy but I’ve created something that hopefully sits in both the world of undergraduate chemistry and “Planet A-Level“! Special thanks on this resource goes to Ian Williams at Bath with whom I sat for at least two hours working through the activity and modelling orbitals and discussing A-level teaching approaches to higher level concepts.

This OER has been created in Articulate and is made available as an interactive learning object for your VLE. The associated PowerPoint file may also be useful for learning and teaching


Related Resources

There are currently 3 other resources and this resource builds on some of the ideas presented in the activities on dynamic equilibria and mechanism basics.


Is it perfect?

No! There are some known and some unknown errors. At some point I will republish but it’s a bit of a mission so want to build up more errors before I go in and fix them all. Some errors just can’t easily be fixed and are a result of the buggy way that Articulate interprets PowerPoint’s motion path animations.

There is a typo in the contents tree for “hybridisation”

Slide 17 has a glitch in the audio where I repeat myself. When I view the resource in Chrome, the two flash animations do not show claiming a “missing plug-in” even though I’m running an up-to-date version of Flash. They do work in Firefox.

In future I’d like to develop slide 17 some more as I found that students’ inability to identify the importance of leaving groups in mechanism was really holding them back in their first year tutorials. I Put this slide in in its current form as students doing Salters (and perhaps other courses) will have done an experiment like this but the main point (that polarity is broadly irrelevant) is not made.  It’d difficult when to know to remove the bond polarity step ladder students have climbed up in KS5! It’s arguable that a couple of the “spot the mistake” questions in the earlier exercise do not help here!

All the resources are from the same generation. The fact that not all the numbers reflect this is the result of a typo.

.. if you find other errors please let me know in the comments!


Can I run this on my own machine / VLE?

Yes you can.  Once unzipped on your VLE, the file you need to link to is “player.html” in each resource’s root folder. It will run directly from a local machine but some of the linked resources will not display correctly.

Here is the original zip file which can be unzipped to your VLE:

If you want to use / adapt the PowerPoint it’s here. Some of the animation / transparency had to be faked with layered slides .. if you delete the upper layers, the base layer should look like the one in the resource.



This resource is copyright The Royal Society of Chemistry but licensed under Creative Commons Attribution-Non Commercial-ShareAlike 2.0 (CC BY-NC-SA 2.0). Internal content licenses are referenced at the end of the resource.