Carbon skeletons may vary in length, shape, number and location of double bonds and other elements covalently bonded to available sites.
A carbon atom contains four valence electrons thus, exhibiting a strong tendency to make covalent bonds with other atoms so as to complete its octet. Covalent bonds join carbon atoms together in long chains that create the skeletal framework for organic molecules.
A carbon atom could be linked to as many as four additional carbon atoms in an organic compound. Carbon atoms can also quickly form double bonds (where four electrons are shared among two atoms) and triple bonds (where six electrons are shared).
This variation in carbon skeletons contributes to the diversity and complexity of organic molecules.