Quantum Particles: Quarks

In the core of every atom is a nucleus consisting of one or more protons, and (except for hydrogen) some neutrons as well.  Protons and neutrons are responsible for most of the mass of an atom.  The electrons “orbit” around this central nucleus, generally in equal numbers to the protons, which makes the overall atom electrically neutral.  Electrons are elementary – meaning they are not made of any smaller particles.  But protons and neutrons are composite particles; they are made of smaller particles called quarks.