Quarks

The six quarks are arranged into three generations, up and down are the lightest, then come strange and charm, and heaviest of all are bottom and top. Each generation has associated with it two light particles called leptons - from the Greek for light. The electron is one of the leptons in the lightest generation, the other is called the electron-neutrino. All of ordinary matter can be made from up-quarks, down-quarks, and electrons. The electron-neutrinos play no role in making up atoms, but they are very important nevertheless, as we will see later. Particles of the other generations are identical in every way to the lighter ones, except they are heavier. That is why they don't appear in ordinary matter, they tend to shed their excess mass as energy and transform themselves into the lightest particles - up-quarks, down-quarks, and electrons.

The latest knowledge about the fundamental constituents of matter: six different quarks and six different leptons divided into three families.

The "periodic table" of the quarks and leptons looks like this. As far as we know, these particles have nothing inside them - to all intents and purposes, they are the "atoms" dreamed of by Leucippus 2500 years ago. But who says history won't repeat itself again...

The structure of matter.