More recent work has shown that protons and neutrons are composed of quarks. The two most fundamental types of particles are quarks and leptons . The quarks and leptons are divided into 6 flavors corresponding to three generations of matter. Leptons have charges in units of 1 or 0. Note that for every quark or lepton there is a corresponding antiparticle.
Quarks combine to form the basic building blocks of matter, baryons and mesons.
Mesons, made of quark pairs, are usually found in cosmic rays. Thus, our current understanding of the structure of the atom is shown below, the atom contains a nucleus surrounded by a cloud of negatively charged electrons. The nucleus is composed of neutral neutrons and positively charged protons. The opposite charge of the electron and proton binds the atom together with electromagnetic forces. Quarks in baryons and mesons are bound together by the strong force in the form of the exchange of gluons.