They have covalent bonding and have equal energy. The term resonance itself means the use of two or more Lewis structures to represent a particular species. Resonance doesn t mean an equilibrium mixture of the contributing structures exists.
Resonance is a human invention.
Rotation about the C - C sigma bond is quite free. Consequently molecules containing carbon-carbon double bonds may have geometrical isomers. Optical isomers are compounds that are non-superimposable images of each other.