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# Summary of session 6

1. Molecules have a three-dimensional shape which plays a crucial role in the way it reacts.
2. Bulky irregularities in the shape of a molecule around a reactive site can exclude a potential reactant. Such effects are described as steric.
3. A sufficient refinement of the molecular shape in the region of the reactive site can make that site specific to just one particular reactant. Many enzymes operate in this way.
4. The shapes of simple molecules can be predicted by taking into account the repulsions between electron pairs surrounding a central atom.

5. So far you have seen there is a link between the shapes of molecules and chemical reactivity. Indeed this course concludes with a look in more detail at reactions in general. However to carry out a reaction in the laboratory it is important to mix reactants in the correct proportions, and this entails having some means of doing this on the basis of the number of atoms or molecules of the substances reacting. You will be exploring this requirement in more detail in the next session.

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OpenLearn - Discovering chemistry
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