Recent theoretical and experimental advances provide new insights into how mass is distributed within particles like protons, neutrons, and pions, offering critical guidance for future research.

It also tells us that chlorine has 18 neutrons (35 - 17) and, as the number of electrons and protons are equal in a neutral atom, chlorine also has 17 electrons. The relative mass of a nucleus is ...

Since a nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.

Nuclear and particle physics are fundamentally puzzled by the distribution of mass in protons. The three valence quarks that make up a proton's core contribute very little to the proton's mass.