Matter Constituents Matter Constituents Matter Constituents as Understood in 1931 Matter is made of atoms, atoms are made of a nucleus plus electrons , and electrical forces between the nucleus and the electrons explain the structure and stability of the atom. The attempt to understand and classify the many particles discovered led to the recognition that protons and neutrons are not fundamental particles but are made of smaller objects called quarks .
Observable hadrons are composite objects made from quarks and antiquarks and gluons .
These particles are called neutrinos. In the Standard Model, quarks and leptons are fundamental particles. As far as we know today there is no evidence that refutes this assumption, nor any evidence for a size or structure for any of these particles. All we can say from experiment is that any structure is at a size smaller than 10 -18 meters. Decays The notion of a constituent or building block gets a new twist here, too.