- Proton number is the number of proton in the nucleus an atom.
- Nucleon number is the total number of proton and number of neutron in the nucleus an atom.
- The numbers of electron is equal to numbers of protons for the neutral atom.
- The nucleon number is also the mass of an atom.
- The mass of an atom is concentrated in the nucleus because it contains proton and neutron.
Nucleon number = number of proton + number of neutron
- Different atom, different number of protons. Each element has a specific proton number.