Periodic table - Elements, Groups, Blocks

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data-target="#ref1"><div class="pl-25"><a class="link-gray-900 w-100" href="/science/periodic-table">Introduction & Top Questions</a></div><div class="ml-40 toc-drawer sub-toc-drawer"></div></li><li data-target="#ref80826"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table#ref80826">History of the periodic law</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80827"><a class="w-100 link-gray-900" href="/science/periodic-table#ref80827">Classification of the elements</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80828"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table">The first periodic table</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80829"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80829">Other versions of the periodic table</a></li></ul></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80830"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80830">Predictive value of the periodic law</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80831"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80831">Discovery of new elements</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80832"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80832">Significance of atomic numbers</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80833"><a class="w-100 link-gray-900" href="/science/periodic-table/The-first-periodic-table#ref80833">Elucidation of the periodic law</a></li></ul></li></ul></div></li><li data-target="#ref80834"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table">The periodic table</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80835"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80835">Periods</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80836"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80836">Groups</a><ul class="list-unstyled" data-level="h3"><li data-target="#ref80837"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80837">Classification of elements into groups</a></li></ul><ul class="list-unstyled" data-level="h3"><li data-target="#ref80838"><a class="w-100 link-gray-900" href="/science/periodic-table/The-periodic-table#ref80838">Periodic trends in properties</a></li></ul></li></ul></div></li><li data-target="#ref80839"><div class="d-flex align-items-center"><button class="h1-link-drawer-button btn btn-xs btn-circle d-flex rounded" type="button" aria-label="Toggle Heading"><em class="material-icons font-18" data-icon="keyboard_arrow_right"></em></button><a class="w-100 link-gray-900" href="/science/periodic-table/The-basis-of-the-periodic-system">The basis of the periodic system</a></div><div class="ml-40 toc-drawer sub-toc-drawer"><ul class="list-unstyled" data-level="h2"><li data-target="#ref80840"><a class="w-100 link-gray-900" href="/science/periodic-table/The-basis-of-the-periodic-system#ref80840">Electronic structure</a></li></ul><ul class="list-unstyled" data-level="h2"><li data-target="#ref80841"><a class="w-100 link-gray-900" href="/science/periodic-table/Periodicity-of-properties-of-the-elements">Periodicity of properties of the elements</a></li></ul></div></li><li data-target="#ref80842"><div class="d-flex align-items-center"><div class="ml-25"></div><a class="w-100 link-gray-900" href="/science/periodic-table/Periodicity-of-properties-of-the-elements#ref80842">Other chemical and physical classifications</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/periodic-table/additional-info">References & Edit History</a> <a class="toc-extra-link link-gray-900" href="/facts/periodic-table">Quick Facts & Related Topics</a> </div> <div class="tlr-media-slider pb-10 mb-30"> <a class="section-header link-gray-900 font-serif font-14 font-weight-bold mb-10 mx-10" 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height="50" /> </a> <a href="/video/How-the-periodic-table-organizes-the-elements/246857" data-href="/media/1/451929/246857" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/57/216557-138-6420551F/How-the-periodic-table-organizes-the-elements.jpg?w=400&h=225&c=crop" alt="Understanding the organization of the periodic table" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="https://cdn.britannica.com/13/220013-050-16EC5F2F/periodic-table-atomic-weight.jpg" data-href="/media/1/451929/253085" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/13/220013-004-B8D5F089/periodic-table-atomic-weight.jpg" alt="periodic table with atomic number, symbol, and atomic weight" height="50" /> </a> <a href="/video/Explanation-periodic-table/159065" data-href="/media/1/451929/159065" class="media-overlay-link d-inline-block mr-5"> <div class="position-relative --aspect-ratio: 16/9"> <img loading="lazy" src="https://cdn.britannica.com/63/151063-138-8D2B90F4/Explanation-periodic-table.jpg?w=400&h=225&c=crop" alt="What is the periodic law?" class="col-100" /> <div class="btn btn-sm btn-white btn-circle position-absolute shadow" style="top: 50%; left:50%; transform: translate(-50%, -50%)"> <em class="material-icons font-14" data-icon="play_arrow" > </em> </div> </div> </a> <a href="https://cdn.britannica.com/42/7442-050-B877FB08/periodic-table-system-elements-gases.jpg" data-href="/media/1/451929/89" class="media-overlay-link d-inline-block mr-5"> <img loading="lazy" src="https://cdn.britannica.com/42/7442-004-3625545B/periodic-table-system-elements-gases.jpg" alt="periodic system of elements with periods demarcated by noble gases" height="50" /> 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Pauling</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Research Professor, Linus Pauling Institute of Science and Medicine, Palo Alto, California, 1973–94. Professor of Chemistry, Stanford University, California, 1969–74. Nobel Prize for Chemistry, 1954; Nobel...</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> Linus C. Pauling</span>, <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup gtm-byline font-12 byline-contributor" href="/contributor/JJ-Lagowski/1666" > <div class="editor-title font-16 font-weight-bold">J.J. Lagowski</div> <div class="editor-description font-12 font-serif mt-5 clamp-description text-black">Professor of Chemistry, University of Texas at Austin. Author of <i>The Chemical Bond.</i></div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link gtm-byline font-12 byline-contributor text-decoration-underline"> J.J. Lagowski</span><span class="text-gray-700 mx-5">•</span><a class="see-all border-gray-700 gtm-byline" rel="nofollow" href="https://www.britannica.com/science/periodic-table/additional-info#contributors">All</a> </div> <div class="font-serif font-12 text-gray-700"> <span class="qa-fact-checked-by">Fact-checked by</span> <div class="editor-popover popover p-0"> <a class="d-block p-20 qa-editor-popup font-12" href="/editor/The-Editors-of-Encyclopaedia-Britannica/4419" > <div class="editor-title font-16 font-weight-bold">The Editors of Encyclopaedia Britannica</div> <div class="editor-description font-12 font-serif mt-5 text-black">Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.</div> </a> <div data-popper-arrow></div> </div> <span class="btn btn-link editor-link p-0 qa-byline-link font-12 "> The Editors of Encyclopaedia Britannica</span></div> <div class="last-updated font-12 font-serif"> <span class="text-gray-700"> Last Updated: <time datetime="2025-02-09T00:00:00CST" >Feb 9, 2025</time> •</span> <a class="byline-edit-history" href="https://www.britannica.com/science/periodic-table/additional-info#history" rel="nofollow">Article History</a> </div></div> </div> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button d-none d-sm-block js-sections-inline-button module-spacing btn d-lg-none"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <div class="d-flex d-sm-none flex-row"> <button class="d-flex d-lg-none btn btn-outline-blue border rounded-sm shadow-sm mobile-toc-button gtm-mobile-toc-inline-button js-sections-inline-button module-spacing"> <em class="material-icons mr-5 ml-n10 my-n5 md-icon" data-icon="toc"></em> Table of Contents </button> <button class="ai-ask-button btn btn-sm border-2 btn-outline-red-400 border-red-400 module-spacing js-inline-ai-ask-button p-10 ml-5"> Ask the Chatbot </button> </div> <div class="js-qf-module qf-module px-40 px-sm-20 py-15 mx-auto module-spacing font-14 bg-gray-50 rounded"> <div class="facts-list mt-10"> <div class=""> <div class="js-fact mb-10 line-clamp clamp-3"> <dl> <dt>In full: </dt> <dd>periodic table of the elements</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>Key People: </dt> <dd><a href="/biography/Dmitri-Mendeleev" topicid="374765">Dmitri Mendeleev</a></dd> <dd><a href="/biography/Lothar-Meyer" topicid="379472">Lothar Meyer</a></dd> <dd><a href="/biography/Paul-Emile-Lecoq-de-Boisbaudran" topicid="334399">Paul-Émile Lecoq de Boisbaudran</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/atom" topicid="41549">atom</a></dd> <dd><a href="/science/group-periodic-table" topicid="247062">group</a></dd> <dd><a href="/science/period-chemistry" topicid="451862">period</a></dd> <dd><a href="/science/periodic-law" topicid="451901">periodic law</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/periodic-table"> See all related content </a> </div> </div> </div> </div><span class="marker before-article"></span><span class="marker h3"></span><section data-level="1" id="ref80834">  <section data-level="2" id="ref80835"> <h2 class="h2">Periods</h2> <span class="marker PREMOD1 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="272672" data-asm-type="video"><div class="md-assembly-wrapper card-media" data-type="video" video-id="233763"><a data-id="233763" class="gtm-assembly-link d-flex justify-content-center" style="--aspect-ratio: 16/9" href="/video/did-you-know-periodic-table/-272672"><img src="https://cdn.britannica.com/63/233763-138-457BECB7/did-you-know-periodic-table.jpg?w=800&h=450&c=crop" alt="Who created the periodic table?" loading="lazy"><script type="application/json"> { "sources": [ { "file" : "//content.jwplatform.com/manifests/4U4BZOdG.m3u8" } ], "image": "https://cdn.britannica.com/63/233763-138-457BECB7/did-you-know-periodic-table.jpg" ,"tracks": [ { "file" : "//assets-jpcust.jwpsrv.com/tracks/96bVl2kz", "label": "English" } ] ,"adfile": "//content.jwplatform.com/manifests/A5vPPwKq.m3u8" } </script><div class="btn btn-xl btn-white btn-circle position-absolute shadow" style="top: 50%; transform: translateY(-50%)"><em class="material-icons" data-icon="play_arrow"></em></div></a></div><figcaption class="card-body"><div class="md-assembly-caption text-muted font-14 font-serif line-clamp"><span><span class="md-assembly-title font-weight-bold mr-5 d-inline font-sans-serif md-video-caption" video-control="233763">Who created the periodic table?</span><span>Learn about the history of the periodic table.</span><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><a class="font-14 mt-10 d-inline-block" href="/science/periodic-table/images-videos">See all videos for this article</a></figcaption></figure></div></div><p class="topic-paragraph">The periodic table of the elements contains all of the <span id="ref1274978"></span><a href="https://www.britannica.com/science/chemical-element" class="md-crosslink " data-show-preview="true">chemical elements</a> that have been discovered or made; they are arranged, in the order of their atomic numbers, in seven horizontal periods, with the lanthanoids (lanthanum, 57, to <a href="https://www.britannica.com/science/lutetium" class="md-crosslink autoxref " data-show-preview="true">lutetium</a>, 71) and the actinoids (actinium, 89, to <a href="https://www.britannica.com/science/lawrencium" class="md-crosslink autoxref " data-show-preview="true">lawrencium</a>, 103) indicated separately below. The periods are of varying lengths. First there is the <a href="https://www.britannica.com/science/hydrogen" class="md-crosslink autoxref " data-show-preview="true">hydrogen</a> period, consisting of the two elements hydrogen, 1, and <a href="https://www.britannica.com/science/helium-chemical-element" class="md-crosslink autoxref " data-show-preview="true">helium</a>, 2. Then there are two periods of eight elements each: the first short period, from <a href="https://www.britannica.com/science/lithium-chemical-element" class="md-crosslink autoxref " data-show-preview="true">lithium</a>, 3, to <a href="https://www.britannica.com/science/neon-chemical-element" class="md-crosslink autoxref " data-show-preview="true">neon</a>, 10; and the second short period, from <a href="https://www.britannica.com/science/sodium" class="md-crosslink autoxref " data-show-preview="true">sodium</a>, 11, to <a href="https://www.britannica.com/science/argon-chemical-element" class="md-crosslink autoxref " data-show-preview="true">argon</a>, 18. There follow two periods of 18 elements each: the first long period, from <a href="https://www.britannica.com/science/potassium" class="md-crosslink autoxref " data-show-preview="true">potassium</a> 19, to <a href="https://www.britannica.com/science/krypton-chemical-element" class="md-crosslink autoxref " data-show-preview="true">krypton</a>, 36; and the second long period, from <a href="https://www.britannica.com/science/rubidium" class="md-crosslink autoxref " data-show-preview="true">rubidium</a>, 37, to <a href="https://www.britannica.com/science/xenon" class="md-crosslink autoxref " data-show-preview="true">xenon</a>, 54. The first very long period of 32 elements, from <a href="https://www.britannica.com/science/cesium" class="md-crosslink autoxref " data-show-preview="true">cesium</a>, 55, to <a href="https://www.britannica.com/science/radon" class="md-crosslink autoxref " data-show-preview="true">radon</a>, 86, is condensed into 18 columns by the omission of the lanthanoids (which are indicated separately below), permitting the remaining 18 elements, which are closely similar in their properties to corresponding elements of the first and second long periods, to be placed directly below these elements. The second very long period, from <a href="https://www.britannica.com/science/francium" class="md-crosslink autoxref " data-show-preview="true">francium</a>, 87, to <a href="https://www.britannica.com/science/element-118" class="md-crosslink autoxref " data-show-preview="true">oganesson</a>, 118, is likewise condensed into 18 columns by the omission of the actinoids.</p><span class="marker MOD1 mod-inline"></span> </section> <section data-level="2" id="ref80836"> <h2 class="h2"><span id="ref621303"></span><a href="https://www.britannica.com/science/group-periodic-table" class="md-crosslink " data-show-preview="true">Groups</a></h2> <section data-level="3" id="ref80837"> <h2 class="h3">Classification of elements into groups</h2> <span class="marker PREMOD2 mod-inline"></span><p class="topic-paragraph">The six noble gases—helium, neon, argon, krypton, xenon, and radon—occur at the ends of the six completed periods and <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="constitute" href="https://www.merriam-webster.com/dictionary/constitute" data-type="MW">constitute</a> the Group 18 (0) <a href="https://www.britannica.com/science/group-periodic-table" class="md-crosslink autoxref " data-show-preview="true">group</a> of the periodic system. It is customary to refer to horizontal series of elements in the table as periods and vertical series as groups. The seven elements lithium to <a href="https://www.britannica.com/science/fluorine" class="md-crosslink autoxref " data-show-preview="true">fluorine</a> and the seven corresponding elements sodium to <a href="https://www.britannica.com/science/chlorine" class="md-crosslink autoxref " data-show-preview="true">chlorine</a> are placed in the seven groups, 1 (Ia), 2 (IIa), 13 (IIIa), 14 (IVa), 15 (Va), 16 (VIa), and 17 (VIIa), respectively. The 17 elements of the fourth period, from potassium, 19, to <a href="https://www.britannica.com/science/bromine" class="md-crosslink autoxref " data-show-preview="true">bromine</a>, 35, are distinct in their properties and are considered to constitute Groups 1–17 (Ia–VIIa) of the periodic system.</p><span class="marker MOD2 mod-inline"></span> <span class="marker PREMOD3 mod-inline"></span><p class="topic-paragraph">The first group, the <span id="ref621305"></span><a href="https://www.britannica.com/science/alkali-metal" class="md-crosslink " data-show-preview="true">alkali metals</a>, thereby includes, in addition to lithium and sodium, the metals from potassium down the table to francium but not the much less similar metals of Group 11 (Ib; <a href="https://www.britannica.com/science/copper" class="md-crosslink autoxref " data-show-preview="true">copper</a>, etc.). Also the second group, the <span id="ref621306"></span><a href="https://www.britannica.com/science/alkaline-earth-metal" class="md-crosslink " data-show-preview="true">alkaline-earth metals</a>, is considered to include <a href="https://www.britannica.com/science/beryllium" class="md-crosslink autoxref " data-show-preview="true">beryllium</a>, <a href="https://www.britannica.com/science/magnesium" class="md-crosslink autoxref " data-show-preview="true">magnesium</a>, <a href="https://www.britannica.com/science/calcium" class="md-crosslink autoxref " data-show-preview="true">calcium</a>, <a href="https://www.britannica.com/science/strontium" class="md-crosslink autoxref " data-show-preview="true">strontium</a>, <a href="https://www.britannica.com/science/barium" class="md-crosslink autoxref " data-show-preview="true">barium</a>, and <a href="https://www.britannica.com/science/radium" class="md-crosslink autoxref " data-show-preview="true">radium</a> but not the elements of Group 12 (IIb). The <a href="https://www.britannica.com/science/boron-chemical-element" class="md-crosslink autoxref " data-show-preview="true">boron</a> group includes those elements in Group 13 (IIIa). The other four groups are as follows: the <a href="https://www.britannica.com/science/carbon-chemical-element" class="md-crosslink autoxref " data-show-preview="true">carbon</a> group, 14 (IVa), consists of carbon, <a href="https://www.britannica.com/science/silicon" class="md-crosslink autoxref " data-show-preview="true">silicon</a>, <a href="https://www.britannica.com/science/germanium" class="md-crosslink autoxref " data-show-preview="true">germanium</a>, <a href="https://www.britannica.com/science/tin" class="md-crosslink autoxref " data-show-preview="true">tin</a>, lead, and flerovium; the <span id="ref621307"></span><a href="https://www.britannica.com/science/nitrogen-group-element" class="md-crosslink " data-show-preview="true">nitrogen group</a>, 15 (Va), includes <a href="https://www.britannica.com/science/nitrogen" class="md-crosslink autoxref " data-show-preview="true">nitrogen</a>, <a href="https://www.britannica.com/science/phosphorus-chemical-element" class="md-crosslink autoxref " data-show-preview="true">phosphorus</a>, <a href="https://www.britannica.com/science/arsenic" class="md-crosslink autoxref " data-show-preview="true">arsenic</a>, <a href="https://www.britannica.com/science/antimony" class="md-crosslink autoxref " data-show-preview="true">antimony</a>, <a href="https://www.britannica.com/science/bismuth" class="md-crosslink autoxref " data-show-preview="true">bismuth</a>, and moscovium; the <a href="https://www.britannica.com/science/oxygen" class="md-crosslink autoxref " data-show-preview="true">oxygen</a> group, 16 (VIa), includes oxygen, <a href="https://www.britannica.com/science/sulfur" class="md-crosslink autoxref " data-show-preview="true">sulfur</a>, <a href="https://www.britannica.com/science/selenium" class="md-crosslink autoxref " data-show-preview="true">selenium</a>, <a href="https://www.britannica.com/science/tellurium" class="md-crosslink autoxref " data-show-preview="true">tellurium</a>, <a href="https://www.britannica.com/science/polonium" class="md-crosslink autoxref " data-show-preview="true">polonium</a>, and livermorium; and the <span id="ref621308"></span><a href="https://www.britannica.com/science/halogen" class="md-crosslink " data-show-preview="true">halogen</a> group, 17 (VIIa), includes fluorine, chlorine, bromine, <a href="https://www.britannica.com/science/iodine" class="md-crosslink autoxref " data-show-preview="true">iodine</a>, <a href="https://www.britannica.com/science/astatine" class="md-crosslink autoxref " data-show-preview="true">astatine</a>, and <a href="https://www.britannica.com/science/element-117" class="md-crosslink autoxref " data-show-preview="true">tennessine</a>.</p><span class="marker MOD3 mod-inline"></span> <span class="marker PREMOD4 mod-inline"></span><p class="topic-paragraph">Although hydrogen is included in Group 1 (Ia), it is not closely similar to either the alkali metals or the halogens in its chemical properties. It is, however, assigned the <a href="https://www.britannica.com/science/oxidation-number" class="md-crosslink autoxref " data-show-preview="true">oxidation number</a> +1 in <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> such as hydrogen fluoride, HF, and −1 in compounds such as lithium hydride, LiH; and it may hence be considered as being similar to a Group 1 (Ia) element and to a Group 17 (VIIa) element, respectively, in compounds of these two types, taking the place first of Li and then of F in lithium fluoride, LiF. Hydrogen is, in fact, the most individualistic of the elements: no other element resembles it in the way that sodium resembles lithium, chlorine resembles fluorine, and neon resembles helium. It is a <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="unique" href="https://www.britannica.com/dictionary/unique" data-type="EB">unique</a> element, the only element that cannot conveniently be considered a member of a group.</p><span class="marker MOD4 mod-inline"></span> <span class="marker PREMOD5 mod-inline"></span><p class="topic-paragraph">A number of the elements of each long period are called the transition metals. These are usually taken to be <a href="https://www.britannica.com/science/scandium" class="md-crosslink autoxref " data-show-preview="true">scandium</a>, 21, to <a href="https://www.britannica.com/science/zinc" class="md-crosslink autoxref " data-show-preview="true">zinc</a>, 30 (the iron-group transition metals); <a href="https://www.britannica.com/science/yttrium" class="md-crosslink autoxref " data-show-preview="true">yttrium</a>, 39, to <a href="https://www.britannica.com/science/cadmium" class="md-crosslink autoxref " data-show-preview="true">cadmium</a>, 48 (the palladium-group transition metals); and <a href="https://www.britannica.com/science/hafnium" class="md-crosslink autoxref " data-show-preview="true">hafnium</a>, 72, to <a href="https://www.britannica.com/science/mercury-chemical-element" class="md-crosslink autoxref " data-show-preview="true">mercury</a>, 80 (the platinum-group transition metals). By this definition, the transition metals include Groups 3 to 12 (IIIb to VIIIb, and Ib and IIb).</p><a class="link-module shadow-sm d-block qa-quiz-module" href="/quiz/periodic-table-names-symbols-quiz" data-link-module-iframe-link=""> <img loading="lazy" src="https://cdn.britannica.com/66/215466-131-16036BD8/Concept-artwork-periodic-table-elements.jpg" alt="Concept artwork on the periodic table of elements." class="rounded-sm mr-15" width="70" /> <div class="line-clamp clamp-5"> <div class="module-title bg-green">Britannica Quiz</div> <div class="font-weight-semi-bold mt-5">118 Names and Symbols of the Periodic Table Quiz</div> </div> </a><span class="marker MOD5 mod-inline"></span> </section> <section data-level="3" id="ref80838"> <h2 class="h3">Periodic trends in properties</h2> <span class="marker PREMOD6 mod-inline"></span><p class="topic-paragraph">The periodicity in properties of the elements arranged in order of <a href="https://www.britannica.com/science/atomic-number" class="md-crosslink autoxref " data-show-preview="true">atomic number</a> is strikingly shown by the consideration of the physical state of the elementary substances and such related properties as the <a href="https://www.britannica.com/science/melting-point" class="md-crosslink autoxref " data-show-preview="true">melting point</a>, density, and hardness. The elements of Group 18 (0) are gases that are difficult to condense. The alkali metals, in Group 1 (Ia), are soft metallic solids with low melting points. The alkaline-earth metals, in Group 2 (IIa), are harder and have higher melting points than the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="adjacent" href="https://www.merriam-webster.com/dictionary/adjacent" data-type="MW">adjacent</a> alkali metals. The hardness and melting point continue to increase through Groups 13 (IIIa) and 14 (IVa) and then decrease through Groups 15 (Va), 16 (VIa), and 17 (VIIa). The elements of the long periods show a gradual increase in hardness and melting point from the beginning alkali metals to near the centre of the period and then at Group 16 (VIa) an irregular decrease to the halogens and noble gases.</p><span class="marker MOD6 mod-inline"></span> <span class="marker PREMOD7 mod-inline"></span><p class="topic-paragraph">The <a href="https://www.britannica.com/science/valence-chemistry" class="md-crosslink autoxref " data-show-preview="true">valence</a> of the elements (that is, the number of bonds formed with a standard element) is closely <a class="md-dictionary-link md-dictionary-tt-off eb" data-term="correlated" href="https://www.britannica.com/dictionary/correlated" data-type="EB">correlated</a> with position in the periodic table, the elements in the main groups having maximum positive valence, or oxidation number, equal to the group number and maximum negative valence equal to the difference between eight and the group number.</p><span class="marker MOD7 mod-inline"></span> <span class="marker PREMOD8 mod-inline"></span><p class="topic-paragraph">The general chemical properties described as <span id="ref621309"></span><a href="https://www.britannica.com/science/metal-chemistry" class="md-crosslink " data-show-preview="true">metallic</a> or base forming, <span id="ref621310"></span><a href="https://www.britannica.com/science/metalloid" class="md-crosslink " data-show-preview="true">metalloid</a> or amphoteric, and <span id="ref621311"></span><a href="https://www.britannica.com/science/nonmetal" class="md-crosslink " data-show-preview="true">nonmetallic</a> or acid forming are correlated with the periodic table in a simple way: the most metallic elements are to the left and to the bottom of the periodic table and the most nonmetallic elements are to the right and to the top (ignoring the noble gases). The metalloids are adjacent to a diagonal line from boron to polonium. A closely related property is <span id="ref621312"></span><a href="https://www.britannica.com/science/electronegativity" class="md-crosslink " data-show-preview="true">electronegativity</a>, the tendency of atoms to retain their electrons and to attract additional electrons. The degree of electronegativity of an element is shown by <a href="https://www.britannica.com/science/ionization-energy" class="md-crosslink autoxref " data-show-preview="true">ionization potential</a>, <a href="https://www.britannica.com/science/electron-affinity" class="md-crosslink autoxref " data-show-preview="true">electron affinity</a>, <span id="ref621313"></span><a href="https://www.britannica.com/science/oxidation-number" class="md-crosslink " data-show-preview="true">oxidation-reduction potential</a>, the energy of formation of chemical bonds, and other properties. It is shown to depend upon the element’s position in the periodic table in the same way that nonmetallic character does, fluorine being the most electronegative element and cesium (or francium) the least electronegative (most electropositive) element.</p><span class="marker MOD8 mod-inline"></span> <span class="marker PREMOD9 mod-inline"></span><p class="topic-paragraph">The sizes of <span id="ref621314"></span><a href="https://www.britannica.com/science/atom" class="md-crosslink " data-show-preview="true">atoms</a> of elements vary regularly throughout the periodic system. Thus, the effective bonding radius (or one-half the distance between adjacent atoms) in the elementary substances in their crystalline or <span id="ref621315"></span><a href="https://www.britannica.com/science/molecule" class="md-crosslink " data-show-preview="true">molecular</a> forms decreases through the first short period from 1.52 Å for lithium to 0.73 Å for fluorine; at the beginning of the second period, the bonding radius rises abruptly to 1.86 Å for sodium and gradually decreases to 0.99 Å for chlorine. The behaviour through the long periods is more complex: the bonding radius decreases gradually from 2.31 Å for potassium to a minimum of 1.25 Å for <a href="https://www.britannica.com/science/cobalt-chemical-element" class="md-crosslink autoxref " data-show-preview="true">cobalt</a> and <a href="https://www.britannica.com/science/nickel-chemical-element" class="md-crosslink autoxref " data-show-preview="true">nickel</a>, then rises slightly, and finally falls to 1.14 Å for bromine. The sizes of atoms are of importance in the determination of <a href="https://www.britannica.com/science/coordination-number" class="md-crosslink autoxref " data-show-preview="true">coordination number</a> (that is, the number of groups attached to the central <a href="https://www.britannica.com/science/atom" class="md-crosslink autoxref " data-show-preview="true">atom</a> in a compound) and hence in the <a class="md-dictionary-link md-dictionary-tt-off mw" data-term="composition" href="https://www.merriam-webster.com/dictionary/composition" data-type="MW">composition</a> of compounds. The increase in <a href="https://www.britannica.com/science/atomic-radius" class="md-crosslink autoxref " data-show-preview="true">atomic size</a> from the upper right corner of the periodic table to the lower left corner is reflected in the formulas of the oxygen acids of the elements in their highest states of oxidation. The smallest atoms group only three oxygen atoms about themselves; the next larger atoms, which coordinate a tetrahedron of four oxygen atoms, are in a diagonal belt; and the still larger atoms, which form octahedral oxygen complexes (stannic acid, antimonic acid, telluric acid, paraperiodic acid), lie below and to the left of this belt. Only the chemical and physical properties of the elements are determined by the extranuclear electronic structure; these properties show the periodicity described in the periodic law. The properties of the atomic nuclei themselves, such as the magnitude of the packing fraction and the power of entering into nuclear reactions, are, although dependent upon the atomic number, not dependent in the same periodic way.</p><span class="marker MOD9 mod-inline"></span> </section> </section> </section> <span class="marker end-of-content"></span><span class="marker after-article"></span></div> <div id="chatbot-simplify-root"></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> 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":3,"pagesTotal":5,"pageId":451929,"pageLength":1383,"initialLoad":true,"lastPageOfScroll":false} </script> <script class="marketing-content-info" type="application/json"> [] </script> <script src="https://cdn.britannica.com/mendel-resources/3-133/js/libs/jquery-3.5.0.min.js?v=3.133.36"></script> <script type="text/javascript" data-type="Init Mendel Code Splitting"> (function() { $.ajax({ dataType: 'script', cache: true, url: 'https://cdn.britannica.com/mendel-resources/3-133/dist/topic-page.js?v=3.133.36' }); })(); </script> <script class="analytics-metadata" type="application/json"> {"leg":"D","adLeg":"C","userType":"ANONYMOUS","pageType":"Topic","pageSubtype":null,"articleTemplateType":"PAGINATED","gisted":false,"pageNumber":3,"hasSummarizeButton":false,"hasAskButton":true} </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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Periodic table - Elements, Groups, Blocks | Britannica