Читать книгу Solid State Chemistry and its Applications - Anthony R. West - Страница 20

A mirror plane, m, exists when two halves of, for instance, a molecule can be interconverted by carrying out the imaginary process of reflection across the mirror plane. The silicate tetrahedron possesses six mirror planes, one of which, running vertically and perpendicular to the plane of the paper, is shown in Fig. 1.7(a). The silicon and two oxygens, 1 and 2, lie on the mirror plane and are unaffected by reflection. The other two oxygens, 3 and 4, are interchanged on reflection. A second mirror plane lies in the plane of the paper; for this, Si and oxygens 3, 4 lie on the mirror but oxygen 2, in front of the mirror, is the image of oxygen 1, behind the mirror.

The photograph in Fig. 1.7(d) shows the British comedian Harry Worth creating a mirror image of half of his body by posing at the end of a high street shop window. Half of the picture is of his body and half is its mirror image. It therefore exhibits perfect mirror symmetry which is never achieved by human bodies in reality!