thumb|100px|Water molecule with symmetry axis In chemistry, there are five important symmetry operations. They are identity operation (E), rotation operation or proper rotation (Cn), reflection operation (σ), inversion (i) and rotation reflection operation or improper rotation (Sn). The identity operation (E) consists of leaving the molecule as it is. This is equivalent to any number of full rotations around any axis. This is a symmetry of all molecules, whereas the symmetry group of a chiral molecule consists of only the identity operation. An identity operation is a characteristic of every molecule even if it has no symmetry. Rotation around an axis (Cn) consists of rotating the molecule around a specific axis by a specific angle. It is rotation through the angle 360°/n, where n is an integer, about a rotation axis. For example, if a water molecule rotates 180° around the axis that passes through the oxygen atom and between the hydrogen atoms, it is in the same configuration as it started. In this case, , since applying it twice produces the identity operation. In molecules with more than one rotation axis, the Cn axis having the largest value of n is the highest order rotation axis or principal axis. For example in boron trifluoride (BF3), the highest order of rotation axis is C3, so the principal axis of rotation is C3.
thumb|100px|Water molecule with symmetry axis In chemistry there are five important symmetry operations They are identity operation (E) rotation operation or proper rotation (Cn) reflection operation (σ) inversion (i) and rotation reflection operation or improper rotation (Sn) The identity operation (E) consists of leaving the molecule as it is This is equivalent to any number of full rotations around any axis This is a symmetry of all molecules whereas the symmetry group of a chiral molecule consists of only the identity operation An identity operation is a characteristic of every molecule even if it has no symmetry Rotation around an axis (Cn) consists of rotating the molecule around a specific axis by a specific angle It is rotation through the angle 360°/n where n is an integer about a rotation axis For example if a water molecule rotates 180° around the axis that passes through the oxygen atom and between the hydrogen atoms it is in the same configuration as it started In this case  since applying it twice produces the identity operation In molecules with more than one rotation axis the Cn axis having the largest value of n is the highest order rotation axis or principal axis For example in boron trifluoride (BF3) the highest order of rotation axis is C3 so the principal axis of rotation is C3