Weekly Recap
This week we covered the basics of atomic structure, counting atoms & molecules in mole units, and introducing energy in the context of chemistry. We will continue exploring energy this next week and see how energy, specifically light, can be used to probe matter and elucidate more details about its structure.
A central theme to the course is that structure effects properties. You saw this when we compared the network structures of diamond and graphite in the Atoms versus Molecules video. The nanoscopic structure has a significant impact on the physical properties of materials. Another example to highlight that subtle structural changes can alter a material's chemical properties is gun cotton.
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Cotton is cellulose, which is a polymer of glucose. (Polymers contain repeating units of a common structure.) You can see that there are many -OH groups present (one reason to explain why cotton can absorb a lot of water!). If we nitrate cotton by soaking it in a mixture of sulfuric and nitric acids, we get the H atoms replaced by groups.
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If we subject ordinary cotton and gun cotton to combustion, we see a drastic difference! After observing this, you are probably not surprised to learn that nitro groups are present in other common explosives, like TNT (trinitrotoluene).
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