10. Playing with a Full Deck:
       The Periodic Table
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       The Structures of the Elements: an aside

The connection between delocalized electrons and metallic luster can be illustrated in a simple way by looking at a series of linear conjugated molecules of the type encountered in Chapter 9 and illustrated opposite.

The maximum wavelength absorbed and the color seen in this series of molecules are given in the table for molecules with chain lengths from n = 1 to 8. As the length of the delocalized chain increases, the absorption of radiation shifts from the ultraviolet into the visible, the complement of the absorbed color is seen, and at n = 7 or 8 a metallic luster begins to appear. Compounds of longer molecules in this series are a shiny black, like graphite, because the region of absorption is so broad that it encompasses virtually the entire visible spectrum. Graphite, with its endless hexagonal-mesh sheets, can be considered as the infinite extension of aromatic molecules like benzene and naphthalene.

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