[{"from": "human", "value": "Could you give me a brief overview of this molecule? [131I][131I]"}, {"from": "gpt", "value": "The molecule is a chemical element that has the symbol I and atomic number 53. Chemically, iodine is the second least reactive of the halogens, and the second most electropositive halogen; trailing behind astatine in both of these categories. However, the element does not occur in the free state in nature. As with all other halogens, when freed from its compounds iodine forms diatomic molecules. Iodine naturally occurs in the environment chiefly as a dissolved iodide in seawater, although it is also found in some minerals and soils. Iodine is an essential trace element for life, mainly as constituents of the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). Iodine-131 is used in nuclear medicine both diagnostically and therapeutically. Examples of its use in radiation therapy include the treatment of thyrotoxicosis and thyroid cancer. Diagnostic tests exploit the mechanism of absorption of iodine by the normal cells of the thyroid gland. Iodine-131 is also used as a radioactive label for radiopharmaceuticals that can be used for imaging and therapy. (L1845, L1846)"}]