Until the early part of the nineteenth century it was generally thought that what we now call the atom was the smallest constituent of matter.
Quarks There are six quarks that combine to make sub-atomic particles.
Quarks are studied in high energy physics. Subatomic particles Classified as baryons, mesons, leptons, and bosons, only the proton and electron have both mass and stability. Neutrons are stable only while inside nuclei of atoms of elements up to and including those of lead. The study of these is particle physics. Atoms Atoms have nuclei containing protons and neutrons, and have electrons in the surrounding space.