Chirality is a term that describes the lack of mirror symmetry in an object. In other words, chiral objects cannot be superposed on their mirror images. For example, our feet are chiral, as the mirror image of the left foot, the right foot, cannot be superposed on the left foot.
Chiral objects exhibit a sense of handedness when they interact with another chiral object. For example, our left foot can only fit in the left shoe and not in the right shoe. Achiral objects — objects that have superposable mirror images — do not have a sense of handedness. For example, socks are achiral; as such, a sock can be worn on both feet equally well.
Chiral objects are identified by the lack of certain symmetry elements in their structure. Specifically, chiral objects lack a plane of symmetry: an imaginary plane that can divide an object into two equal halves. In addition, chiral objects also lack a center of symmetry: a point from which similar components of the object are equidistant and opposite to each other.
Chiral molecules exist as a pair of non-superposable mirror images. As a rule of thumb, molecules which have only one tetrahedral carbon atom with four different substituents attached to it are always chiral. Such a tetrahedral carbon atom is referred to as a chiral center. In general, to identify whether a molecule is chiral, the molecular geometry should be known. If the molecular geometry lacks a plane of symmetry as well as a center of symmetry, the molecule is chiral.
