Iodine absorption spectrum7/1/2023 ![]() (The fifth and sixth halogens, the radioactive astatine and tennessine, are not well-studied due to their expense and inaccessibility in large quantities, but appear to show various unusual properties for the group due to relativistic effects.) Iodine has an electron configuration of 4d 105s 25p 5, with the seven electrons in the fifth and outermost shell being its valence electrons. Iodine is the fourth halogen, being a member of group 17 in the periodic table, below fluorine, chlorine, and bromine it is the heaviest stable member of its group. In early periodic tables, iodine was often given the symbol J, for Jod, its name in German. In 1908, he introduced tincture of iodine as a way to rapidly sterilise the human skin in the surgical field. Antonio Grossich (1849–1926), an Istrian-born surgeon, was among the first to use sterilisation of the operative field. In 1873 the French medical researcher Casimir Joseph Davaine (1812–1882) discovered the antiseptic action of iodine. Arguments erupted between Davy and Gay-Lussac over who identified iodine first, but both scientists acknowledged Courtois as the first to isolate the element. Davy sent a letter dated 10 December to the Royal Society of London stating that he had identified a new element. Ampère had given some of his sample to English chemist Humphry Davy (1778–1829), who experimented on the substance and noted its similarity to chlorine. Gay-Lussac suggested the name "iode", from the Ancient Greek ἰοειδής ( ioeidēs, "violet"), because of the colour of iodine vapor. On 6 December, Gay-Lussac announced that the new substance was either an element or a compound of oxygen. They described the substance to a meeting of the Imperial Institute of France. On 29 November 1813, Desormes and Clément made Courtois' discovery public. He also gave some of the substance to chemist Joseph Louis Gay-Lussac (1778–1850), and to physicist André-Marie Ampère (1775–1836). Ĭourtois gave samples to his friends, Charles Bernard Desormes (1777–1838) and Nicolas Clément (1779–1841), to continue research. Courtois suspected that this material was a new element but lacked funding to pursue it further. He noted that the vapour crystallised on cold surfaces, making dark crystals. Courtois once added excessive sulfuric acid and a cloud of purple vapour rose. The remaining waste was destroyed by adding sulfuric acid. To isolate the sodium carbonate, seaweed was burned and the ash washed with water. Saltpetre produced from French nitre beds required sodium carbonate, which could be isolated from seaweed collected on the coasts of Normandy and Brittany. At the time of the Napoleonic Wars, saltpetre was in great demand in France. In 1811, iodine was discovered by French chemist Bernard Courtois, who was born to a manufacturer of saltpetre (an essential component of gunpowder). It is on the World Health Organization's List of Essential Medicines. Iodine is also used as a catalyst in the industrial production of acetic acid and some polymers. Because of the specificity of its uptake by the human body, radioactive isotopes of iodine can also be used to treat thyroid cancer. Due to its high atomic number and ease of attachment to organic compounds, it has also found favour as a non-toxic radiocontrast material. The dominant producers of iodine today are Chile and Japan. Iodine deficiency affects about two billion people and is the leading preventable cause of intellectual disabilities. As the heaviest essential mineral nutrient, iodine is required for the synthesis of thyroid hormones. It is the least abundant of the stable halogens, being the sixty-first most abundant element. Iodine occurs in many oxidation states, including iodide (I −), iodate ( IO −ģ), and the various periodate anions. The element was discovered by the French chemist Bernard Courtois in 1811 and was named two years later by Joseph Louis Gay-Lussac, after the Ancient Greek Ιώδης 'violet-coloured'. The heaviest of the stable halogens, it exists as a semi-lustrous, non-metallic solid at standard conditions that melts to form a deep violet liquid at 114 ☌ (237 ☏), and boils to a violet gas at 184 ☌ (363 ☏). Iodine is a chemical element with the symbol I and atomic number 53. ![]()
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