Presence of single C-C bond
(unsaturated has C=C)
N the nucleus, there are protons and neutrons. That's two parts.
<span>Outside the nucleus, there are electrons. That's a total of three parts and that is all that chemists discuss. Theoretical physicists talk about other sub nuclear "parts", but if you include them, the number goes way over 5. </span>
<span>The "shells", "sub-shells", "orbits", "orbitals", "probabilities" and the like are not physical parts, but only descriptions of energy</span>