Protons, Neutrons and Electrons

The observation that elements contained different combinations of the same building blocks eventually brought the number of fundamental particles down from all the elements to just three particles: protons, neutrons and electrons. With these three particles physicists could explain all known matter. Protons and neutrons are about 2000 times heavier than electrons, so it's the number of them that determines an atom's mass. The number of protons, which are positively electrically charged, matches the number of electrons in an atom and determines its chemical properties.

Atoms consist of neutrons and protons, bound in a nucleus, and electrons.

In the early 20th century, however, physicists saw another explosion of complexity. By studying particles coming from space, they saw other particles beside protons, neutrons, and electrons. They asked themselves where these particles belonged. Symmetry again provided the answer. By looking at the properties of all the particles and organising them in a "periodic table", two physicists found symmetries that betrayed the presence of smaller particles inside protons, neutrons, and the new particles. This periodic table goes by the name of The Eightfold Way. It was so-named in 1964 by Murray Gell-Mann and Yuval Ne'eman, for reasons we'll soon find out. Earlier, Gell-Mann had noted a new property in some of the new particles that had been discovered. Since these new particles were strange, he called this property strangeness.

Gell-Mann and Ne'eman. Gell-Mann received the Nobel prize in 1969.

In their book, The Eightfold Way, Gell-Mann and Ne'eman suggested that protons and neutrons could be made up of two types of smaller particles. In their theory, a third kind gave rise to the property of strangeness observed in the more exotic particles. Borrowing from James Joyce's novel Finnigan's Wake, which bears the line "three quarks for muster mark", Gell-Mann called these three types of particle quarks.