Molecules

Abstract

“Everything is made from atoms. That is the key hypothesis. The most important hypothesis in all of biology, for example, is that everything that animals do, atoms do. In other words, there is nothing that living things do that cannot be understood from the point of view that they are made of atoms acting according to the laws of physics”

The Feynman lectures in physics, vol. 1, 1963 (pp. 1–8).

Richard Feynman’s hypothesis is the core of our goal as food chemists; we want to be able to relate all of the properties of foods to the atoms they contain. For some questions, this is fairly straightforward (“this fat is harder because it is more crystalline”) while others are so complex we struggle to even frame them in terms of chemistry (“why does this sauce taste creamier than that one?”). However, in principle if we can properly understand how the atoms are behaving, we should be able to explain any behavior of food.

A common approach to many problems in science is to divide the subject up into a hierarchy of structures and focus only on the most relevant. For example, an engineer might notice that when a building collapses individual bricks are still intact in the rubble. From that observation, it would be sensible to study the cement holding the bricks together rather than the strength of the bricks themselves. By analogy, most of the physical changes in foods involve changes in the arrangements of molecules rather than the breaking and making of bonds within molecules. Therefore, the atomic scale is far less important to most of our physical problems than the molecular scale and we can treat molecules as the building blocks of our food, reframing Feynman’s hypothesis as:

Everything that food does, molecules do.

So what do molecules do? Their behavior is governed by the laws of thermodynamics described in the last chapter but to properly relate chemical behavior to chemical structure we need to understand the nature of kinetic and potential energy at the molecular level. Molecules have kinetic energy because of their masses and velocities while potential energy results from intra- and intermolecular bonding. In this chapter we will start by considering molecular movement then look at bonding. We will finally return to Feynman’s hypothesis and look at some ways that molecular properties can be related to bulk properties of a food.