Chemical Education Today
Report: My Favorite Element
Iodine! by Stephen W. Wright
The sublimation of iodine.
photo by J. Maynard and D. Shaw
cessful early public health measure. The body’s need for iodine, combined with the element’s relative scarcity, is what makes the radioactive isotopes of iodine produced by nuclear fission at once both dangerous and medically useful. Supporting JCE Online Material
http://www.jce.divched.org/Journal/Issues/2009/Oct/abs1137.html Abstract and keywords Full text (PDF)
Stephen W. Wright is a chemist working at Pfizer Global Research and Development, Groton, CT 06340; stephen.w.wright@ pfizer.com.
photo: J. Maynard and J. J. Jacobsen
Iodine is my favorite element. It appeals to four of the five senses. Touch, because of its high atomic weight and therefore its density; sight, because of the many bright colors associated with its compounds, such as yellow lead iodide and bright red mercuric iodide. It appeals to the sense of smell due to the sharp odor of the element itself, and the peculiar odors of many of its organic compounds. Lastly, it can even be heard, as when highly sensitive nitrogen triiodide explodes. Iodine caught my attention early in my study of chemistry due to the beautiful violet vapor it produces when heated and its key role in colorful clock and oscillating reactions. Its reactions with metals such as zinc and aluminum make dramatic demonstrations of a simple reaction type: the combination of two elements to form a compound. As I pursued chemistry further, I recognized that iodine is unusual for its ability to assume multiple oxidation states in both inorganic salts and organic compounds. As an organic chemist, I appreciate the extra reactivity that iodides impart to so many synthetic organic transformations. Most students first learn about iodine as a disinfectant solution that stings and stains the skin, and produces a black color with starch, but its significance in biology and medicine extends far beyond that. It is a key micronutrient. Iodine is used entirely by the thyroid gland to make the key metabolic regulatory hormone thyroxine, an unusual biomolecule with four iodine atoms in its structure. Lack of dietary iodine causes goiter, and the introduction of iodized salt is an example of a suc-
The precipitation of lead(II) iodide.
Speaking of iodine… “Years ago, I had students dress up
the best came as iodine—with a black
as their favorite element and come
and shiny hat and cape on top, which
to class to explain their costume
she could remove to reveal purple
along with the element’s properties.
underneath when she was in a good
The student whom I still remember
mood.” Patricia Mason, retired high school teacher
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 10 October 2009 • Journal of Chemical Education
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