There are 6 quarks. However, up and down are enough to make every atom in the universe.

Particles made of quarks are called hadrons. They are held together by the strong interaction.

There are two families of hadrons, baryons and mesons. Baryons are qqq and mesons are \(q\bar{q}\).

Nucleons are baryons made of up and down quarks.

The neutron is ddu and the proton is uud.

The proton is the only stable free hadron. All other free hadrons decay.

Table of quark properties

$$\begin{array}{|c|c|c|} \hline \text{name} & \text{charge (e)} & \text{rest mass (MeV)} \\ \hline \text{Up} & + \frac{2}{3} & 2.3 \\ \hline \text{Down} & - \frac{1}{3} & 4.8 \\ \hline \text{Strange} & - \frac{1}{3} & 95 \\ \hline \text{Charm} & + \frac{2}{3} & 1275 \\ \hline \text{Bottom} & - \frac{1}{3} & 4180 \\ \hline \text{Top} & + \frac{2}{3} & 173210 \\ \hline \end{array}$$

We will concentrate on the first three quarks, up, down and strange.

$$\begin{array}{|c|c|} \hline \text{name} & \text{charge (e)} \\ \hline \text{Up} & + \frac{2}{3} \\ \hline \text{Down} & - \frac{1}{3} \\ \hline \text{Strange} & - \frac{1}{3} \\ \hline \end{array}$$