The Wonderful World of Atoms and Molecules

In this chapter you will be introduced to the science and practice of chemistry. Chemistry is all about atoms and molecules, but chemistry is practiced by real people working in government, industry, and education. Although this book focuses on the science of chemistry. I ll also try to show you the human side of it. 

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For theoretical chemistry to succeed it must develop the power to elucidate the behaviour of chemical substances to the satisfaction of experimental chemists, known to operate at many different levels. Understanding is not promoted by the generation of numbers, however accurate or numerous, without a simple picture that tells the story. It is inevitable that the chain of reasoning must reduce the problem of understanding the behaviour of substances, to the understanding of molecules, atoms, electrons, and eventually the aether. Again, this ladder of understanding should not be obscured by complicated mathematical relationships that cannot be projected into a simple picture. Small wonder that the planetary model of the atom, inspired by Kepler, and discredited almost a hundred years ago, is still the preferred icon to represent nuclear installations and activity in the commercial world. Theoretical chemistry should also communicate with the predominantly nonscientist population of the world, but in order to tell a story it is first of all necessary to know the story. 

By the time you are old enough to read this book you will surely have heard people using words like these atom, molecule, element and compound. You may know what some of them mean, but others may seem too difficult to worry about. You may have seen some strange combinations of numbers and letters, too, like those shown here, and wondered what in the world they could mean ... 

In this chapter, we will see electrocyclic reactions in which rings open and close, cycloaddition reactions in which two partners come together to make a new cyclic compound, and sigmatropic shifts in which one part of a molecule flies about coming to rest at one specific position and no other. Specificity is the hallmark of all these reactions atoms move as if in lock step in one direction or another, or move from one place to one specific new place, but no other. The chemical world struggled mightily to understand these mysteriously stereospecific reactions, and, thanks to the work by Woodward, Hoffmann, and several others, finally figured it out in a marvelously simple way. This chapter will show you some wonderful chemistry. 

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