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.
Heavy atoms tend to be radioactive.
A billion atoms in a row would make a line only a few centimeters long. This study is nuclear physics and quantum physics. When atoms bond together by sharing their electrons they form molecules. Water molecules each contain two hydrogen atoms and one oxygen atom. Some proteins contain thousands of atoms per molecule, largely carbon, oxygen, hydrogen, and nitrogen.