Chapter 3: Why Do Molecules Exist?
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A Brief Introduction to Matter & Energy
In Chapter 1 we discussed some basic ideas about chemicals and touched briefly on their pliable nature: compounds can react to form new materials. This is perhaps the central theme in the study and practice of chemistry. Biochemists study how organisms effect these changes. Synthetic chemists are constantly searching for ways to make new useful materials as well as for new useful ways to make familiar materials. Other branches of chemistry seek to understand how such reactions take place.
We take for granted the idea that molecules are real and can (sometimes) be manipulated with precision (more or less). There are many subtleties in the governing principles of these manipulations, so much so that chemists can spend entire careers unraveling small bits of them. Inevitably, such transformations involve energy – either because it is necessary to drive a particular chemical change, such as those involved in cooking, to use a very familiar example, or because the chemical change releases energy, as is the case with combustion. Yet, despite seemingly endless examples of chemical reactions, there are actually only a handful of foundational concepts that describe the interplay between matter and energy. We introduce some of these in the current chapter and expand on them throughout the rest of this book. To frame these ideas, let’s not take for granted the notion that molecules should exist. We know they do, but why do they? First things first, though.
We’ll begin by stepping back even further by examining even simpler particles – atoms themselves. What exactly are they? Atoms constitute every tangible form of matter you experience, including yourself, Dear Reader, yet we have no firsthand sensory evidence for their existence as discrete particles. They are conceptually very familiar, yet surprisingly difficult to really understand.
Figure Credit. The explosion of the Hindenburg on May 6, 1937 provided a spectacular display of the rapid release of chemical potential energy. (Public Domain)