What is matter made of?

Following on from Science Week last week, and as per our inquiring students, my question for this week is, ‘what is matter made of’? No doubt your immediate answer to that question is, atoms, and you’d be correct. However, before we think we’ve arrived at the accurate answer, I need to provide you with an understanding of how small atoms are and what is inside them, for reasons you’ll appreciate later.

Scientists have known for some time that atoms, the smallest indivisible particles of an element, are very small. Around 200 years ago Scientists decided they wanted a way to have a numerically equivalent number of atoms, regardless of the type of element in question. In 1865 Josef Loschmidt estimated this number to be 6.02 x 1023, or 600,000 million million million, and he called it the Avogadro Constant. As the atoms of each element have a unique mass, the collective mass of Avogadro’s number of one element’s atoms will differ from that of a different element. For example, Avogadro’s number of hydrogen atoms weighs approximately 1 g, whereas Avogadro’s number of carbon atoms weighs approximately 12 g. Hence, each carbon atom must be 12 times the mass of each hydrogen atom.

So, if 12 g of carbon has that many atoms in it, how big is Avogadro’s number and therefore how small are atoms? Last week in a Physical Sciences class we did a quick experiment to get our minds around just how big Avogadro’s number is. The result of that experiment, approximate as it was, is that it would take a person 4,150 million million years to count Avogadro’s number of atoms – they are incredibly small.

Atoms, small as they are, are made of even smaller particles. To simplify a rather complex model of an atom, we’ll confine ourselves to accepting that there are three sub-atomic particles: protons, neutrons (both found in a tightly packed nucleus) and electrons (orbiting the nucleus). Atoms of different elements have different radii; however, in all cases, the space between the nucleus and the electron(s) surrounding it is ‘relatively’ very large; furthermore, that space is completely empty. Roughly speaking, relative to the size of an atom, its nucleus is approximately 100,000 times smaller. To provide some perspective on this, if the atom were the size of the St Leonard’s Athletics track, the nucleus would be the size of a pea at its centre and virtually all that space in between is filled with nothing, the electron being approximately 1800 times smaller than a proton or neutron.

And so back to my original question, ‘what is matter made of’? Regardless of how small atoms are, they are the building blocks of matter, but they are almost entirely empty space. For example, a hydrogen atom, the smallest atom, is over 99.99% empty space. Hence, you would be correct to say that objects are made up almost entirely of empty space. Therefore, is ‘everything’ really nothing much at all? I think I’ll leave you to ponder that one.

Andy Müller
Principal