The Atom

The atom is constituted of a number of electrons orbiting around a nucleus made up of protons and neutrons. In an electrically neutral atom, the number of electrons is equal to the number of protons. Protons and neutrons are about 2000 times heavier than electrons, so that most of the atomic mass is concentrated in the nucleus. On the other hand, the size of the nucleus is about 10.000 times less than the size of the electronic orbits. Electrons, protons, and neutrons possess an intrinsic angular momentum called spin.
The Proton in the Quark Model Back to table of contents