Iodine | Chemical Properties, Uses, & Applications

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class="md-content"> <div class="md-article-container template-desktop infinite-pagination"> <div class="infinite-scroll-container article last"> <article class="article-content container-lg qa-content px-0 pt-0 pb-40 py-lg-20 content md-expanded" data-topic-id="292625"> <div class="grid gx-0"> <div class="col-auto"> <div class="topic-left-rail md-article-drawer position-relative d-flex border-right-sm border-left-sm open"> <div class="drawer d-flex flex-column open"> <div class="left-rail-section-content"> <div class="topic-left-rail-header text-truncate bg-gray-50 position-relative text-right d-flex align-items-center"> <div class="tlr-title px-20 py-15 text-left"> <em class="material-icons text-gray-400 d-lg-none" data-icon="toc"></em> <a class="font-serif font-weight-bold text-black link-blue" href="https://www.britannica.com/science/iodine">iodine</a> </div> <button aria-label="Close" class="js-sections-close-button btn-link btn-sm btn d-lg-none position-absolute top-0 p-10 right-0" > <em class="material-icons font-26" data-icon="close"></em> </button> </div> <div class="section-content pl-10 pr-20 pl-sm-50 pr-sm-60 pl-lg-5 pr-lg-10 pt-10 pt-lg-0 bg-gray-50 clear-catfish-ad"> <div class="toc mb-20"> <div class="font-serif font-14 font-weight-bold mx-15 mb-15 mt-20"> Table of Contents </div> <ul class="list-unstyled my-0" data-level="h1"><li data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/iodine">Introduction</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref280157"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/iodine#ref280157">History</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref280158"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/iodine#ref280158">Occurrence and distribution</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref280159"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/iodine/Physical-and-chemical-properties">Physical and chemical properties</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref280160"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/iodine/Production-and-use">Production and use</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref280161"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/iodine/Production-and-use#ref280161">Analysis</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li></ul> <a class="toc-extra-link link-gray-900" href="https://www.britannica.com/science/iodine/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" 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Dumas</a></dd> <dd><a href="/biography/Viktor-Meyer" topicid="379489">Viktor Meyer</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> </div> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>Related Topics: </dt> <dd><a href="/science/chemical-element" topicid="108636">chemical element</a></dd> <dd><a href="/science/halogen" topicid="252990">halogen</a></dd> <dd><a href="/science/iodine-deficiency" topicid="292674">iodine deficiency</a></dd> <dd><a href="/science/iodine-131" topicid="292668">iodine-131</a></dd> </dl> <button class="js-more-btn d-none btn btn-unstyled font-12 bg-gray-50" aria-label="Toggle more/less fact data"> <em class="js-content link-blue">(Show more)</em> </button> </div> <div class="text-center"> <a class="btn btn-sm btn-link p-0" href="/facts/iodine"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><section data-level="1" id="ref1"><span class="marker PREMOD1 mod-inline"></span><p class="topic-paragraph"><strong><span id="ref110497"></span>iodine (I)</strong>, <a href="https://www.britannica.com/science/chemical-element" class="md-crosslink autoxref " data-show-preview="true">chemical element</a>, a member of the <a href="https://www.britannica.com/science/halogen" class="md-crosslink " data-show-preview="true">halogen elements</a>, or Group 17 (Group VIIa) of the <a href="https://www.britannica.com/science/periodic-table" class="md-crosslink " data-show-preview="true">periodic table</a>.</p><span class="marker MOD1 mod-inline"></span><div class="text-center pb-20"><div class="md-table-wrapper"><table class="md-element-table"><caption>Element Properties</caption><tbody><tr><th scope="row">atomic number</th><td>53</td></tr><tr><th scope="row">atomic weight</th><td>126.9044</td></tr><tr><th scope="row">melting point</th><td>113.5 °C (236 °F)</td></tr><tr><th scope="row">boiling point</th><td>184 °C (363 °F)</td></tr><tr><th scope="row">specific gravity</th><td>4.93 at 20 °C (68 °F)</td></tr><tr><th scope="row">oxidation states</th><td>−1, +1, +3, +5, +7</td></tr><tr><th scope="row">electron configuration</th><td>2-8-18-18-7 or (Kr)5<em>s</em><sup>2</sup>4<em>d</em><sup>10</sup>5<em>p</em><sup>5</sup></td></tr></tbody></table></div></div></section> <span class="marker h2"></span><section data-level="1" id="ref280157"> <h2 class="h1">History</h2> <span class="marker PREMOD2 mod-inline"></span><div class="assemblies"><div class="w-100"><figure class="md-assembly m-0 mb-md-0 card card-borderless print-false" data-assembly-id="129156" data-asm-type="image"><div class="md-assembly-wrapper card-media " data-type="image"><a href="https://cdn.britannica.com/68/132468-050-9DE736C3/Iodine.jpg" class="gtm-assembly-link position-relative d-flex align-items-center justify-content-center media-overlay-link card-media" data-href="/media/1/292625/129156"><picture><source media="(min-width: 680px)" srcset="https://cdn.britannica.com/68/132468-050-9DE736C3/Iodine.jpg?w=300"><img src="https://cdn.britannica.com/68/132468-050-9DE736C3/Iodine.jpg?w=300" alt="iodine" data-width="1600" data-height="1206" loading="eager"></picture><button class="magnifying-glass btn btn-circle position-absolute shadow btn-white top-10 right-10" aria-label="Zoom in"><em class="material-icons link-blue" data-icon="zoom_in"></em></button></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><a class="gtm-assembly-link md-assembly-title font-weight-bold d-inline font-sans-serif mr-5 media-overlay-link" href="https://cdn.britannica.com/68/132468-050-9DE736C3/Iodine.jpg" data-href="/media/1/292625/129156">iodine</a><button class="js-more-btn d-none btn btn-unstyled font-12 bg-white js-content" aria-label="Toggle more/less fact data"><span class="link-blue">(more)</span></button></span></div></figcaption></figure></div></div><p class="topic-paragraph">In 1811 the French chemist <span id="ref1062652"></span><a href="https://www.britannica.com/biography/Bernard-Courtois" class="md-crosslink " data-show-preview="true">Bernard Courtois</a> obtained a violet vapor by heating <a href="https://www.britannica.com/science/seaweed" class="md-crosslink " data-show-preview="true">seaweed</a> ashes with <a href="https://www.britannica.com/science/sulfuric-acid" class="md-crosslink " data-show-preview="true">sulfuric acid</a> as a by-product of the manufacture of <a href="https://www.britannica.com/science/saltpeter" class="md-crosslink " data-show-preview="true">saltpeter</a>. This vapor condensed to a black crystalline substance, which he called “substance X.” In 1813 British chemist <a href="https://www.britannica.com/biography/Sir-Humphry-Davy-Baronet" class="md-crosslink " data-show-preview="true">Sir Humphry Davy</a>, who was passing through Paris on his way to Italy, recognized substance X as an element <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="analogous" href="https://www.merriam-webster.com/dictionary/analogous" data-type="MW">analogous</a> to <a href="https://www.britannica.com/science/chlorine" class="md-crosslink " data-show-preview="true">chlorine</a>; he suggested the name <em>iodine</em> from the Greek word <em>ioeides</em>, “violet colored.”</p><span class="marker MOD2 mod-inline"></span> </section> <span class="marker h3"></span><section data-level="1" id="ref280158"> <h2 class="h1">Occurrence and distribution</h2> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">Iodine is never found in nature uncombined, and it is not concentrated sufficiently to form independent minerals. It is present in <a href="https://www.britannica.com/science/seawater" class="md-crosslink autoxref " data-show-preview="true">seawater</a>, but sparingly, as the iodide <a href="https://www.britannica.com/science/ion-physics" class="md-crosslink " data-show-preview="true">ion</a>, I<sup>−</sup>, to the extent of approximately 50 mg per metric ton (0.0016 ounce per ton) of seawater. It is also formed in <span id="ref110498"></span><a href="https://www.britannica.com/science/seaweed" class="md-crosslink " data-show-preview="true">seaweeds</a>, <a href="https://www.britannica.com/animal/oyster" class="md-crosslink " data-show-preview="true">oysters</a>, and <a href="https://www.britannica.com/animal/cod-fish-Gadus-species" class="md-crosslink " data-show-preview="true">cod</a> livers. Sodium iodate (NaIO<sub>3</sub>) is contained in crude <a href="https://www.britannica.com/place/Chile" class="md-crosslink autoxref " data-show-preview="true">Chile</a> <a href="https://www.britannica.com/science/saltpeter" class="md-crosslink " data-show-preview="true">saltpeter</a> (sodium nitrate, NaNO<sub>3</sub>). The <a href="https://www.britannica.com/science/human-body" class="md-crosslink autoxref " data-show-preview="true">human body</a> contains iodine in the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="compound" href="https://www.merriam-webster.com/dictionary/compound" data-type="MW">compound</a> <a href="https://www.britannica.com/science/thyroxine" class="md-crosslink " data-show-preview="true">thyroxine</a>, which is produced in the <span id="ref957508"></span><a href="https://www.britannica.com/science/thyroid-gland" class="md-crosslink " data-show-preview="true">thyroid gland</a>.</p><div class="one-good-fact-module"> </div><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">The only naturally occurring <a href="https://www.britannica.com/science/isotope" class="md-crosslink " data-show-preview="true">isotope</a> of iodine is stable <span id="ref957513"></span>iodine-127. An exceptionally useful <a href="https://www.britannica.com/science/radioactive-isotope" class="md-crosslink autoxref " data-show-preview="true">radioactive isotope</a> is <span id="ref957514"></span><a href="https://www.britannica.com/science/iodine-131" class="md-crosslink ">iodine-131</a>, which has a half-life of eight days. It is employed in medicine to monitor thyroid gland functioning, to treat <a href="https://www.britannica.com/science/goitre" class="md-crosslink autoxref " data-show-preview="true">goitre</a> and thyroid <a href="https://www.britannica.com/science/cancer-disease" class="md-crosslink " data-show-preview="true">cancer</a>, and to locate <a href="https://www.britannica.com/science/tumor" class="md-crosslink " data-show-preview="true">tumors</a> of the <a href="https://www.britannica.com/science/brain" class="md-crosslink " data-show-preview="true">brain</a> and of the <a href="https://www.britannica.com/science/liver" class="md-crosslink " data-show-preview="true">liver</a>. It is also used in investigations to trace the course of <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="compounds" href="https://www.merriam-webster.com/dictionary/compounds" data-type="MW">compounds</a> in metabolism. Several iodine compounds are used as contrast mediums in diagnostic <a href="https://www.britannica.com/science/radiology" class="md-crosslink " data-show-preview="true">radiology</a>. In aqueous solution even minute amounts of iodine in the presence of <a href="https://www.britannica.com/science/starch" class="md-crosslink " data-show-preview="true">starch</a> produce a blue-black color.</p><span class="marker MOD4 mod-inline"></span> </section> <span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-root"></div> </div> </div> </div> <div class="ai-dialog-placeholder"></div> </div> </div> <aside class="col-md-da-320"></aside> </div> </div> </div> </div> </article></div> </div></div> </div> </main> <div id="md-footer"></div> <noscript><iframe src="//www.googletagmanager.com/ns.html?id=GTM-5W6NC8" height="0" width="0" style="display:none;visibility:hidden"></iframe></noscript> <script type="text/javascript" id="_informizely_script_tag"> var IzWidget = IzWidget || {}; (function (d) { var scriptElement = d.createElement('script'); scriptElement.type = 'text/javascript'; scriptElement.async = true; scriptElement.src = "https://insitez.blob.core.windows.net/site/f780f33e-a610-4ac2-af81-3eb184037547.js"; var node = d.getElementById('_informizely_script_tag'); node.parentNode.insertBefore(scriptElement, node); } )(document); </script>  <script> window.ap3c = window.ap3c || {}; var ap3c = window.ap3c; ap3c.cmd = ap3c.cmd || []; ap3c.cmd.push(function() { ap3c.init('ZO4siT4cLwnykPnzZWJtd3Byb2Q', 'https://engage.email.britannica.com/'); ap3c.track({v: 0}); }); ap3c.activity = function(act) { ap3c.act = (ap3c.act || []); ap3c.act.push(act); }; var s, t; s = document.createElement('script'); s.type = 'text/javascript'; s.src = "https://engage.email.britannica.com/app.js"; t = document.getElementsByTagName('script')[0]; t.parentNode.insertBefore(s, t); </script> <script class="marketing-page-info" type="application/json"> {"pageType":"Topic","templateName":"DESKTOP","pageNumber":1,"pagesTotal":3,"pageId":292625,"pageLength":340,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-130/js/libs/jquery-3.5.0.min.js?v=3.130.14"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-130/dist/topic-page.js?v=3.130.14' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"C","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":1,"hasSummarizeButton":false,"hasAskButton":false} </script> <script type="text/javascript"> EBStat={accountId:-1,hostnameOverride:'webstats.eb.com',domain:'www.britannica.com', json:''}; </script> <script type="text/javascript"> ( function() { $.ajax( { dataType: 'script', cache: true, url: '//www.britannica.com/webstats/mendelstats.js?v=1' } ) .done( function() { try {writeStat(null,EBStat);} catch(err){} } ); })(); </script> <div id="bc-fixed-dialogue"></div> </body> </html>

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Iodine | Chemical Properties, Uses, & Applications | Britannica