What is an Atom?
Metaphysics and Chemistry 1

What is chemistry?  When I am asked to define just what exactly chemistry is to my students I almost always answer that it is a way of describing the composition, structure, properties, and transformations of matter.  This is usually then quickly followed up with the question, what is matter?  Okay, well, matter is all of the stuff around us.  Our best answer now is that it is composed of atoms arranged into various structures that we call molecules or compounds.  This can lead to well what is an atom?  Well that is a collection of subatomic particles that has a certain set of properties that distinguish it as a given element.  What are subatomic particles then?  Smaller bits of matter that we term protons, neutrons, and electrons.  Pressed further, we leave the field of chemistry entirely and enter particle physics to discuss quarks and strings and what not.  We can keep going down the rabbit hole so to speak, and ultimately we are left with a metaphysical question.  Just what is a particular thing anyway?  As I began to study philosophy of science and metaphysics in particular, the more I felt the urge to think more about my definition of matter.  Let me explain my reasoning by pulling back away from atoms to something a bit more concrete and see what metaphysics tells us about things.

As I type this, I’m enjoying a nice cup of black coffee.  I’ll pose the simple question: what is this thing I call a cup?  What is a cup in general?  I know it is something because I can see it, feel it, hear the sound of it as I set it on my desk or when my wedding ring clangs against it.  It is certainly matter and not energy.  In metaphysical philosophy one would say that the cup is a particular; a concrete entity existing in time and space.   But what is the nature of its existence?  In chemistry, we often start by giving a detailed description of something and its appearance. I’ll do that for my cup.   My cup is white.  It is solid and made of ceramic.  It has the lettering of a logo on it.  It has a certain amount of mass.  But have I really explained what a cup is?  I have described the properties of my cup yes, but what is the true essence of the cup? It seems that all I have been able to do so far is describe the cup’s properties.  Is there anything more fundamental lurking underneath?

One strategy we can try is to remove all of the properties of the cup and see if something is left behind that would identify the nature of the cup. This is known as the substratum view.  The essence of the cup is what remains when we remove all of its properties.  If I remove its shape, color, mass, etc  there doesn’t seem to be much of anything left at all.  It seems that I cannot have a cup without properties.  We might assume that particularity is a fundamental part of our known reality.

Let’s try another approach.  The Scottish philosopher David Hume defined things as nothing more than collections of properties.  In the so-called bundle theory, an object consists of its properties only. An object without properties cannot even be conceived. Okay, sounds good.  Objects are collections of their properties.

But a problem ensues if we take the theory to its limits.  Bundle theory says my cup is a collection of properties.  What if there is an identical cup sitting right next to it?  It will have the exact same set of properties which would lead to the conclusion that they are the same object.  This is clearly absurd by our day to day reasoning.  Bundle theory doesn’t allow there to be change.  A change requires a different set of properties and a different set of properties would entail that I have a different object.  Bundle theory looks to have some major issues to overcome.

I’m now left to conclude that my cup is a particular with a certain set of properties but is not identical with, nor reducible to, those properties.

Now what about atoms?  We could describe the properties of my cup in terms of the atoms that make it up.  Ceramic is a specific arrangement of metal, non metal, and metalloid ions held together by a mixture of ionic and covalent interactions.  What then are atoms?  Are they also just a particular with a set of properties but also not identical, nor reducible to, those properties as well?

Some have argued that atoms are the fundamental bearers of properties.  They are were the rabbit hole reaches its bottom.  If we want to know what a cup is we use chemistry to look at the types and arrangements of atoms that each have their particular properties that they convey onto the object as a whole.  I like this idea but it seems that there must be more to it.  As we have strode into the nanoscale realm of observation we find that even atoms change their properties at a certain level.  For example, gold atoms at differing concentrations (at the nanoscale) give quite different colors.  It doesn’t look like atoms are the bottom of the rabbit hole after all.  We better keep digging.


The color of silver and gold particles is determined by their sizes.