Describe the elements of symmetry.

The elements of symmetry describe the ways in which a molecule can be transformed while remaining indistinguishable from its original state. The main elements of symmetry are:

• Plane of symmetry ($\sigma$): An imaginary plane that bisects a molecule such that one half is the mirror image of the other half.
• Center of inversion ($i$): A point within the molecule such that any atom can be moved through this point to an equivalent atom on the opposite side.
• Proper axis of rotation ($C_n$): An imaginary axis around which a molecule can be rotated by an angle of $\frac{360^\circ}{n}$ to produce an identical orientation.
• Improper axis of rotation ($S_n$): An imaginary axis around which a molecule is rotated by $\frac{360^\circ}{n}$, followed by reflection through a plane perpendicular to the axis, to produce an identical orientation.

$\boxed{The elements of symmetry are the plane of symmetry (\sigma), center of inversion (i), proper axis of rotation (C_n), and improper axis of rotation (S_n).}$