Do many examples, on the projector or board, from first principles. Start with partial charges and identification of the nucleophile and electrophile, then draw in arrows.
Tell them to go to Spotlight and get some toothpicks and some polystyrene balls. The problem then is you don’t have the correct angles, but usually it’s enough to get it out of their head.
We do Lewis Structures and then we do molecular orbital theory, and it's theory after theory and they say, 'Why do we have to do this theory and this theory and that theory?' You need to say 'Well, because they're all slightly different interpretations because we don't actually know how it is. This is model one and this is model two.'
A topic like this is quite theoretical and if you approach it in a very didactic way, it can be very dry. It’s undoubtedly quite abstract, and if you present it in a fairly traditional way it’s even more so. Try to engage students with it, and get them to think and discuss and use different approaches. Coming at it from different ways helps to bring it alive a bit.
An analogy in quantisation of energy states takes advantage of the fact that in many lecture theatres there are shallow steps going down to the front. Think of a ball rolling down the steps. It can't stop halfway down the steps. It seems like a really simplistic way of thinking of it, but in terms of analogy it works really well.
An analogy for talking about Hund’s rule (where the p orbitals fill up) is that it’s like parents deciding where siblings will sleep. If you have enough rooms you put each person in one room because that's peaceful for everybody and everybody prefers that. If you have an extra child you have a choice of renovating your house, which is expensive and takes a lot of energy, or you put them in the same bedroom. You are going to put them in the same bedroom because you're not going to renovate your house. They get that.
In hybridisation, we have the idea that the energy at the atomic levels are changing - they're not going to be the same as an isolated atom on its own. Think about if you were sitting next to someone on the bus. You would sit there differently than if you were sitting there alone. If you're the only person on the bus and then somebody else gets on the bus, how would you feel if they came and sat right next to you? We know instinctively they wouldn't do that. Electrons are a bit the same. They won't sit in the same spot. Once all the seats have someone in them then they’ll sit next to you.
