Mirror Plane Symmetry Symmetry Operation Reflect sThis molecule has two mirror planes flips all points in the ci .One is horizontal, in the plane of the asymmetric unit over a paper and bisects the H-C-H bond line which is called the MOther is vertical, perpendicular to mirror and thereby the plane of the paper and bisects the changes the handedness of CkC· Cl bonds WY any figures in the asymmetric unit. The points along the mirror has reflectional symmetry if an line are all invariant lane can divide the crvstal into halves points under a reflection. hich is the mirror image of the other Rotational Symmetry Symmetry Operation Rotation turns all the points in the o Rotated about a point symmetric unit around one o Allows chirality o In crystals limited to 1,2,3,4,and6 he handedness of figures in rotations nly invariant point Symmetry Axis of Rotation Rotational Symmetry We say a crystal has a symmetry coincidence upon rotation axis of rotation when we can turn it the pattern looks exactly the same. nfold axis of rotational Think of the center of a pizza. If it the same size and have the same then the pizza could be turned and you couldn't tell the difference element for which the operation is a rotation of 3607n retry. The below has rotational symmetry of graphite 60 degrees.7 This molecule has two mirror planes: One is horizontal, in the plane of the paper and bisects the H-C-H bonds Other is vertical, perpendicular to the plane of the paper and bisects the Cl-C-Cl bonds A crystal has reflectional symmetry if an imaginary plane can divide the crystal into halves, each of which is the mirror image of the other. Mirror Plane Symmetry Symmetry Operation Reflection qflips all points in the asymmetric unit over a line, which is called the mirror and thereby changes the handedness of any figures in the asymmetric unit. The points along the mirror line are all invariant points under a reflection. Rotational Symmetry Rotated about a point Allows chirality In crystals limited to 1,2,3,4, and 6 rotations Symmetry Operation Rotation turns all the points in the asymmetric unit around one point, the center of rotation. A rotation does not change the handedness of figures in the plane. The center of rotation is the only invariant point. Symmetry Axis of Rotation We say a crystal has a symmetry axis of rotation when we can turn it by some degree about a point and the pattern looks exactly the same. Think of the center of a pizza. If it is made so that all the pieces are the same size and have the same ingredients in the same places, then the pizza could be turned and you couldn't tell the difference. This means the pizza has rotational symmetry. The pizza below has rotational symmetry of 60 degrees. Rotational Symmetry coincidence upon rotation about the axis of 360°/n Þ n-fold axis of rotational symmetry graphite O H Symbol for a symmetry element for which the operation is a rotation of 360°/n C2 = 180°, C3=120°, C4 = 90°, C5 = 72°, C6 = 60°, etc