In 1963, Nobel Laureate Richard Feynman (1918-1988), one of the most accomplished and influential scientists of the 20th century, wrote:

“If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generation of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms—little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling on being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.” (Feynman 1963)

Most of us are quite familiar with the idea that matter is composed of atoms, we have been told that this is so since childhood. But how many of us really (and we mean really) believe it, or know the reasons that it is assumed to be true? It seems so completely and totally impossible (and improbable) - we do not experience atoms directly, and it is easy to go through life, quite successfully for the vast majority of us, without having to take atoms seriously.

It seems so completely and totally impossible (and improbable) - we do not experience atoms directly, and it is easy to go through life, quite successfully for the vast majority of us, without having to take atoms seriously.

Atomic Theory is also critical for understanding a significant number of the underlying concepts of biology and physics, not to mention geology, astronomy, ecology, and engineering. How can one sentence contain so much information? Can we really explain such a vast and diverse set of scientific observations with so little to go on? In the next two chapters we will expand on Feynman’s sentence to see just what you can do with a little “imagination and thinking”. At the same time, it is worth remembering that the fact that atoms are so unreal, from the perspective of our day to day experience, means that the atomic hypothesis poses a serious barrier to understanding modern chemistry. This is a barrier that can only be dealt with if you recognize it explicitly, and try to address and adjust to it – you will be rewiring your brain in order to take atoms, and all that they imply, seriously. We are aware that this is not an easy task. It takes effort, and much of this effort will involve self-reflection, problem-solving, and question answering. In an important sense, you do not have to believe in atoms, but you do have to understand them.

What do you think you know about atoms:

You almost certainly have heard about atoms, and very likely you have been taught about them – if asked, you might profess to "believe" in their reality. You might accept that matter, in all its forms, is made up of atoms - particles that are the smallest entity that retains the identity of an element (we will discuss elements in much greater detail in the next few chapters). It is very likely that you have been taught that atoms are made up of even smaller particles; positively charged protons, uncharged neutrons and negatively charged electrons. You may even have heard (and perhaps even believe) that protons and neutrons can be further subdivided in to quarks and gluons, while electrons are indivisible. Equally difficult to appreciate is that all atoms are organized in a very similar way, with a very tiny, but relatively heavy, positively charged nucleus surrounded by the much lighter, negatively charged electrons. Part of the difficulty in really understanding atoms is associated with the fact that the forces holding the atomic nucleus together, the so called strong and weak forces, operate at such small distances that we do not experience them directly. This is in contrast to electromagnetism and gravity, which we experience directly, because they act over longer (macroscopic) distances. A second problem is associated with the fact that to experience the world we need to use energy, at the atomic scale the energy used to observe the system also perturbs it. This is the basis of the Heisenberg uncertainty principle, which you may have encountered or at least heard of before (and which we will come back to). Finally, objects at the atomic and subatomic scales behave differently from the macroscopic objects we are used to interacting with. A particle of light (a photon), an electron, a proton, or a neutron behaves as both a particle and a wave; in terms of physics, these are neither particles or waves, they are “quantum mechanical particles.” Luckily, the weirder behaviors of atomic and subatomic entities can often, but not always, be ignored in chemical and biological systems. We will touch on these topics as necessary.

Current theory holds that atoms consist of a very (very) small, but very dense nucleus that contains protons and neutrons, which is surrounded by electrons, which are very light, relatively. The space occupied by moving electrons accounts for the vast majority of the volume of an atom. Because the number of positively charged protons and negatively charged electrons are equal, and the size of the charges are the same (but opposite), atoms are electrically neutral when taken as a whole, that is: each positively charged proton is counterbalanced by a negatively charged electron. Often the definition of an atom contains some language about how atoms have the same chemical properties of an element, but what do we mean by chemical properties?

Questions to ponder:

• Is it obvious that the material world is composed of atoms?
• If you had to explain to a non-scientist why it is that scientists accept the idea that all material things are composed of atoms, what evidence would you use.
• Does the ability to explain so much about the world scientifically influence your view about the reality of supernatural forces?