The Eightfold Way

That means that two ups and a down result in a particle with charge +1: a proton. Two downs and an up result in a particle with charge 0: a neutron.

A proton has three smaller particles called quarks inside it.

When Gell-Mann and Ne'eman classified particles according to quantities like charge and strangeness, for example, they found that they fit into tidy patterns called multiplets. In the multiplet containing protons and neutrons, there are eight particles, hence The Eightfold Way.

A "periodic table" of the proton and the neutron and some of their relatives: The Eightfold Way.

History had just repeated itself. Gell-Mann and Ne'eman had described observation perfectly, and they had provided a way to predict a new particle called the omega-minus, a negatively charged particle with three units of strangeness, corresponding to a missing particle in one of the multiplets. Sure enough, in due course the omega-minus was discovered. Its three units of strangeness simply mean that it is made up of three strange quarks, each of which has charge -1/3, leading to a total charge of -1.