The parts of the atom

In ancient Greece, there were philosophers who speculated about what everything is made of. One idea was that some tiniest-of-all particles - atoms - were in all matter. In the early 19th century, experiments seemed to confirm this theory. Atoms do really exist! They were thought of as round solid balls that couldn't be divided into smaller parts.

Almost a hundred years later, at the end of the 19th century, a new discovery was made. Atoms can emit even smaller particles - electrons. So the atoms can't be the smallest component in all matter. They are not indivisible. Since the 1930s we know that atoms consist of three types of particle.

In the middle of the atom - in the atomic nucleus - we find protons and neutrons. And around the nucleus there are electrons. At first, it was thought that the electrons orbited around the nucleus, like planets around the sun. Now we know it's a bit more complicated than that. Instead of orbits at fixed distances, there's more like a cloud of electrons around the nucleus.

You could say that the electrons are everywhere in this electron cloud - at the same time! The electron cloud is huge compared to the nucleus - tens of thousands of times larger. If we were to draw an image of an atom to scale, the nucleus would be no more than a tiny dot. This way of drawing an atom isn't very clear, so most of the time, we depict the atom with a magnified nucleus and the electrons in orbits around it. It's a useful model to show what the atom is made of, without going into too much detail.

In a chemical reaction, it's possible for an atom to lose some of its electrons, or pick up more electrons... or share electrons with each other. The atomic nucleus is more stable. It's not affected by chemical reactions. Now that we're down to protons, neutrons and electrons, does that mean that we're done?

Are these particles the smallest units of matter? ... Or can they be divided into even smaller parts? As far as we know, an electron can't be broken down into smaller pieces. It is a fundamental particle - or elementary particle. How about neutrons and protons?

They consist of smaller particles called quarks. Three quarks are needed to build one proton, or one neutron. One special thing with quarks is that you can never isolate a single quark. They always come two by two, or three by three. We don't think they are made of smaller pieces - quarks seem to be elementary particles, just like electrons.

But science keeps discovering new things, so maybe we'll have to change our view again, about what's the most fundamental component of all matter.