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The Periodic Spiral is a graphical representation, illustrating the relationship between the chemical & physical properties, and the occurrence of the elements. Also known as the Helix Chemica, the diagram below is scanned from Hackh`s Chemical Dictionary, 3rd Edition, 1944. Drawn by E.C.Pozzi in 1937.

Helix Chemica, drawn 1937

In the upper half of the diagram: All elements have low density (below 4.0), simple spectra, strong e.m.f., and generally a single valence. Upper left: Elements are acid-forming and negative, i.e., attract additional electrons. Upper center: Elements are inert, i.e., have a complete octet. Upper right: Elements are base-forming or positive, i.e., give up their valence electrons.

In the lower half of the diagram: All elements have greater density (above 4.0), complex spectra, weak e.m.f., and generally many valencies; they are amphoteric and may gain or lose electrons.

The abundance of the elements is shown by the hexagons as indicated at the top of the table.

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