The ethane molecule can be directly superimposed upon its mirror image. Ethane is not a chiral molecule.
A monochloroethane molecule can be directly superimposed upon its mirror image. So it is not a chiral molecule either.
What is a chiral molecule?
Here we have a molecule of 1-monochloro-1-ethanol and its mirror image. The carbon atom is attached to four different groups ( -H, -Cl, -OH and -CH3).
The blue molecule cannot be directly superimposed on the red molecule. Such molecules are a special kind of stereoisomer known as enantiomers. The molecules have no axis of symmetry. They are said to be chiral molecules.
