What is chirality?

Chiral molecules are enantiomers. A requirement for molecule to be chiral, and therefore have 2 possible enantiomers, there must be four different substituents bonded to a carbon centre. By swapping two bonds in such a molecule you can obtain the other stereoisomer. These molecules cannot be superimposed and the best way of demonstrating this is by trying to superimpose your two hands. While both hands are equivalent there is no way that they can be superimposed- they are mirror images. Since I have a molecular model kit I would quickly build any two equivalent molecules that should be expected to be chiral. I would then show that these can be superimposed. Then I would change two bonds in one of the molecules to demonstrate that now these are mirror images of one another. So why are these important? A great example would be (+) limonene and (-) limonene enantiomers. The first gives oranges their smell and the second is responsible for the smell of lemons. Such a small structural difference can have significant consequences on the function and properties of the compound. Explaining what a racemic mixture would be useful too as this could be asked for in an exam- It is a 1:1 mixture of the two different enantiomers. Such a mixture would have no effect on plane polarised light as each 50% of molecules in a mixture would rotate the light to the left while the other 50% would rotate it to the right, causing a net rotation of 0 degrees.