Why does iodine appear coloured

In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript. It is obviously not a simple electrostatic solvation, for it has little to do with the dielectric constant of the solvent; nor would such a solvation serve to account for the marked difference in chemical properties between the violet and brown solutions.

Lachmann, J. Article Google Scholar. Gillam and Morton, Proc. Gillam, Trans. Download references. Department of Chemistry, University, Manchester, You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Together, they form polyiodide ions of the type I n — , for example, I 3 — , I 5 — , or I 7 —.

The negatively charged iodide in these compounds acts as charge donor, the neutral iodine as a charge acceptor. Electrons in such charge-transfer complexes are easy to excite to a higher energy level by light.

The light is absorbed in the process and its complementary color is observed by the human eye. In the case of the aqueous solution of polyiodides, the absorptions of the different species lead to an overall brownish color.

Once amylose is added, it forms another CT complex, Here, the amylose acts as a charge donor and the polyiodide as an acceptor. This complex absorbs light of a different wavelength than polyiodide, and the color turns dark blue. The exact structure of the polyiodides inside the amyloid helix is not clear. The amylose-iodine complex is amorphous i. It has been proposed that the species inside the helix are repeated I 3 — or I 5 — units.

The team investigated a related system, a pyrroloperylene—iodine complex, to study its properties as an organic electronic conductor. Pastalan , K. The binding energies of three iodine complexes. Journal of Quantitative Spectroscopy and Radiative Transfer , 42 6 , Sension , Herbert L. Comparison of experiment and theory for the resonance Raman spectrum of I 2 in solution.

The Journal of Chemical Physics , 85 7 , Bruno , M. Caselli , M. Della Monica. A spectrophotometric study of the hexamethylphosphotriamide—iodine complex. Inorganica Chimica Acta , 10 , Photochemistry and Photobiology , 9 2 , Two new color tests for determining the presence of arylmetallics.

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Ketelaar , C.