Use model kits for third year pericyclic reactions: It's visual and it's used every lesson because everything uses the same rule. That's the message to get to them - that you’re not teaching four new things. It's all the same rules. They just move slightly differently. So they see the same models and they can see where the cyclic reactions close. That's very hard to demonstrate in two dimensions. The bigger models are much better as well.
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.'
Particularly for the VSEPR theory, models of any kind are great. Tell the students, 'Buy a model kit.' Because it has to be something three-dimensional. They need to bring their own models in so they can do it themselves.
3D modelling software is very good. There are some Java Applets that show 3D visualisations of orbitals. You just select whichever orbital you want and you can rotate it and view it from different angles.
Use models to illustrate shapes formed by molecules. Or use balloons to illustrate bonding pairs and electron pair repulsions leading to the determination of molecular shape You can show them a tetrahedron and an octahedron etc.
Use balloons to illustrate bonding pairs and electron pair repulsions leading to the determination of molecular shape For example, if you tie 6 balloons together, it automatically forms the octahedral shape. Then each time you pop one, they rearrange themselves to sequentially form the other shapes: trigonal bipyramidal, tetrahedral, trigonal planar and linear. It’s visually appealing, a concrete example and memorable for students. Also, popping the balloons wakes the students up!
Use Lego pieces. For example, HCl built out of Lego. Use a little blue brick and a yellow one, showing physically that on this side you’ve got one blue Lego brick and then on this side you’ve got two and so on, trying to make them see them not as chemical formulas but identities of some sort.
