Atomic
Nucleus Model 
Navigating the site:
The nuclei, is the plural of the word nucleus meaning a center or central mass.
This may be a confusing term because nucleus refers to the center of a cell, and the core of an even far smaller unit of material existence: atomic nuclei. By definition there is no one nucleus. There is a nuclei for every atom just as there are cell nuclei for every eukaryotic cell. Since there are multiple cells which are themselves comprised of even more multitudinous atoms, the abstraction of a nucleus is handy when we try to label the parts of either 1) the organic cell or 2) the inorganic atomic elements.
Atoms. 
All atoms are massive nuclei surrounded by incredibly fast moving centers of negative charge called electrons:
encircled by electron orbitals like clouds .
In the nuclei of Atoms there are protons and neutrons shielded by an electrically charged wall or shell of electrons. In the artists rendering below neutrons are blue and protons are red.
Atomic nuclei
proton is a positively charged subatomic particle
and a
neutron is an uncharged subatomic particle.
unbound neutrons decay into protons
Sub atomic particles are themselves comprised of even smaller units.
Representations of the atom from our "billiard ball" metaphor may distort our imaginations' attempts to visualize these unseen atoms and their subatomic parts.
Carbon is C
Hydrogen is H
The binding energies of nucleons, or the particles within an atomic nuclei,are in the range of millions of electron volts compared to tens of eV for the force that holds atomic electrons around the nuclei. Whereas an atomic transition might emit a photon in the range of a few electron volts, perhaps in the visible light region, nuclear transitions in the atom's nucleus can emit gamma-rays with quantum energies in the MeV (millions of electron volts) range.
The curve is a quantitative and graphical depiction of the stability of protons and neutrons held by the strong force together and tightly packed in the nuclei of atoms.
The curve graphically reveals that as the mass of the atoms increases and the ratio of neutrons to protons varies in heavier isotopes, there is less stability in those atomic elements whose mass is greater than iron.
