The core of Atom contains protons and neutrons. In chemistry, Proton is subatomic particles that carry a positive charge (+) while neutrons carry a negative charge (-). Neutrons and Protons are both called as Nucleons in which may be bind together to form atomic nuclei. The atomic mass unit of protons and neutrons is also called as nucleons. Atomic mass number or nucleon number is the number referred to the mass number of protons and neutrons found in the nucleus.